WEBVTT

00:00:00.000 --> 00:00:11.192 align:middle line:84%
[SQUEAKING]
[RUSTLING] [CLICKING]

00:00:11.192 --> 00:00:11.900 align:middle line:90%
DAVID KAISER: OK.

00:00:11.900 --> 00:00:12.720 align:middle line:90%
Welcome everyone.

00:00:12.720 --> 00:00:17.960 align:middle line:84%
Welcome back to 8225,
which is also STS 042,

00:00:17.960 --> 00:00:20.137 align:middle line:90%
Physics in the 20th Century.

00:00:20.137 --> 00:00:21.970 align:middle line:84%
Let me start by asking
just quickly if there

00:00:21.970 --> 00:00:24.657 align:middle line:84%
are any logistical
questions, any kind

00:00:24.657 --> 00:00:26.240 align:middle line:84%
of course structure
or other questions

00:00:26.240 --> 00:00:28.350 align:middle line:84%
like that we can try
to clear up quickly.

00:00:28.350 --> 00:00:31.160 align:middle line:84%
And then we'll jump into
the first main lecture.

00:00:31.160 --> 00:00:33.110 align:middle line:84%
In general, it's good
to do the readings,

00:00:33.110 --> 00:00:34.970 align:middle line:84%
at least to skim the
more technical readings

00:00:34.970 --> 00:00:38.760 align:middle line:90%
before the assigned class.

00:00:38.760 --> 00:00:40.472 align:middle line:84%
So for today, that
was a brief excerpt

00:00:40.472 --> 00:00:42.680 align:middle line:84%
from Maxwell's treatise on
electricity and magnetism,

00:00:42.680 --> 00:00:44.780 align:middle line:84%
for example, and a
chapter from Bruce Hunt's

00:00:44.780 --> 00:00:46.040 align:middle line:90%
book on the Maxwellians.

00:00:46.040 --> 00:00:48.290 align:middle line:84%
So in general, it'll be
helpful if you keep up--

00:00:48.290 --> 00:00:50.300 align:middle line:84%
if students keep up
with the readings

00:00:50.300 --> 00:00:51.800 align:middle line:84%
because it's just
going to snowball.

00:00:51.800 --> 00:00:54.710 align:middle line:84%
Otherwise, some of the
readings, as you probably

00:00:54.710 --> 00:00:58.700 align:middle line:84%
have noted with the Maxwell
in particular, are pretty--

00:00:58.700 --> 00:01:01.070 align:middle line:84%
they're not exactly a
page turning novel, right?

00:01:01.070 --> 00:01:02.460 align:middle line:90%
What's going on with that.

00:01:02.460 --> 00:01:04.790 align:middle line:84%
So I'm going to be talking
about what Maxwell thought

00:01:04.790 --> 00:01:06.290 align:middle line:84%
he was doing, what
some of Maxwell's

00:01:06.290 --> 00:01:10.620 align:middle line:84%
contemporaries-- how they read
that book in today's lecture.

00:01:10.620 --> 00:01:14.370 align:middle line:84%
So today hopefully will
exemplify the kind of use

00:01:14.370 --> 00:01:15.930 align:middle line:84%
to make of readings
like that, as we

00:01:15.930 --> 00:01:19.950 align:middle line:84%
go through the first worked
example with Maxwell today.

00:01:19.950 --> 00:01:22.470 align:middle line:84%
Other readings, as you'll
see, like the chapter

00:01:22.470 --> 00:01:25.950 align:middle line:84%
from Bruce Hunt for this
week, are by physicists,

00:01:25.950 --> 00:01:29.340 align:middle line:84%
or historians, or sociologists,
or other more recent scholars

00:01:29.340 --> 00:01:32.010 align:middle line:84%
trying to help us make
sense of that older work.

00:01:32.010 --> 00:01:34.320 align:middle line:84%
And for those, I think
it does make sense

00:01:34.320 --> 00:01:36.750 align:middle line:90%
to read them a bit more closely.

00:01:36.750 --> 00:01:38.910 align:middle line:84%
What's the actual argument
the author is making?

00:01:38.910 --> 00:01:41.562 align:middle line:84%
What are the kinds of evidence
that the author brings to bear?

00:01:41.562 --> 00:01:43.020 align:middle line:84%
Because what we'll
work on together

00:01:43.020 --> 00:01:45.420 align:middle line:84%
over the course of the
semester is actually

00:01:45.420 --> 00:01:47.490 align:middle line:84%
working on your
own written essays,

00:01:47.490 --> 00:01:49.530 align:middle line:84%
your own analyses,
where you will--

00:01:49.530 --> 00:01:51.460 align:middle line:84%
we'll help you
build up toward it.

00:01:51.460 --> 00:01:54.750 align:middle line:84%
But you'll be working on
articulating an argument,

00:01:54.750 --> 00:01:56.380 align:middle line:84%
defending that
argument with evidence

00:01:56.380 --> 00:01:59.370 align:middle line:84%
and examples from
various sources.

00:01:59.370 --> 00:02:02.250 align:middle line:84%
The readings that we would call
a secondary source, readings

00:02:02.250 --> 00:02:06.090 align:middle line:84%
by historians, or more recent
physicists, or philosophers,

00:02:06.090 --> 00:02:08.820 align:middle line:84%
or sociologists, or
journalists, or whomever, those

00:02:08.820 --> 00:02:10.470 align:middle line:84%
are more like the
kinds of writings

00:02:10.470 --> 00:02:12.300 align:middle line:84%
we're going to try
to do ourselves

00:02:12.300 --> 00:02:13.778 align:middle line:90%
over the course of the term.

00:02:13.778 --> 00:02:15.820 align:middle line:84%
And plus, I think, hopefully
they're interesting.

00:02:15.820 --> 00:02:18.310 align:middle line:90%
I chose them very carefully.

00:02:18.310 --> 00:02:21.130 align:middle line:84%
So I do recommend you try to
read those a bit differently,

00:02:21.130 --> 00:02:22.920 align:middle line:84%
let's say, than
something like skimming

00:02:22.920 --> 00:02:24.960 align:middle line:84%
over Maxwell's treatise,
which might look

00:02:24.960 --> 00:02:28.260 align:middle line:84%
both pretty bland, and
weird, and a little unusual,

00:02:28.260 --> 00:02:29.730 align:middle line:90%
given how we do things today.

00:02:29.730 --> 00:02:31.500 align:middle line:84%
So there are
different ways to read

00:02:31.500 --> 00:02:32.877 align:middle line:90%
the different kinds of sources.

00:02:32.877 --> 00:02:34.710 align:middle line:84%
And I guess, hopefully,
today we'll actually

00:02:34.710 --> 00:02:36.085 align:middle line:84%
give a bit of an
example of that,

00:02:36.085 --> 00:02:39.870 align:middle line:84%
as we talk a little bit
about that Maxwell reading

00:02:39.870 --> 00:02:41.260 align:middle line:90%
throughout today.

00:02:41.260 --> 00:02:42.660 align:middle line:90%
So that's the plan.

00:02:42.660 --> 00:02:44.410 align:middle line:84%
And if there's no
other questions,

00:02:44.410 --> 00:02:46.040 align:middle line:84%
I think we'll just
jump right in.

00:02:46.040 --> 00:02:47.790 align:middle line:84%
So I'm going to go
ahead and share screen.

00:02:47.790 --> 00:02:51.740 align:middle line:90%


00:02:51.740 --> 00:02:57.270 align:middle line:84%
And hopefully, you can
see that first slide.

00:02:57.270 --> 00:03:00.530 align:middle line:84%
So today, we're going to
start our journey in earnest.

00:03:00.530 --> 00:03:04.460 align:middle line:84%
We're going to turn the
clock back about 200 years

00:03:04.460 --> 00:03:10.250 align:middle line:84%
and talk about some of the
leading natural philosophers,

00:03:10.250 --> 00:03:13.940 align:middle line:84%
some of the leading people
who are trying to understand

00:03:13.940 --> 00:03:15.560 align:middle line:90%
the physical world.

00:03:15.560 --> 00:03:17.237 align:middle line:84%
And what do they
think their job was?

00:03:17.237 --> 00:03:19.070 align:middle line:84%
What were the settings
in which they did it?

00:03:19.070 --> 00:03:21.458 align:middle line:84%
What were the conceptual
tools they brought to bear?

00:03:21.458 --> 00:03:23.000 align:middle line:84%
And we'll always be
asking ourselves,

00:03:23.000 --> 00:03:24.458 align:middle line:84%
what looks kind of
similar and what

00:03:24.458 --> 00:03:28.400 align:middle line:84%
looks really, really unfamiliar
from our vantage point today?

00:03:28.400 --> 00:03:32.190 align:middle line:90%


00:03:32.190 --> 00:03:35.470 align:middle line:84%
So the discussion today
has three main sections.

00:03:35.470 --> 00:03:38.360 align:middle line:84%
We have a brief
warm-up on physics

00:03:38.360 --> 00:03:41.990 align:middle line:84%
then and now, just to try to
prep us to put our minds back

00:03:41.990 --> 00:03:44.900 align:middle line:84%
into the world of the
early 19th century.

00:03:44.900 --> 00:03:46.880 align:middle line:84%
Then we'll spend a
bit of time talking

00:03:46.880 --> 00:03:50.390 align:middle line:84%
about Michael Faraday, who
was one of the most widely

00:03:50.390 --> 00:03:53.823 align:middle line:84%
celebrated scientists or
natural philosophers of his day.

00:03:53.823 --> 00:03:55.490 align:middle line:84%
And we'll see some
of the things that he

00:03:55.490 --> 00:03:59.220 align:middle line:84%
introduced during his
rather unusual career.

00:03:59.220 --> 00:04:00.997 align:middle line:84%
And then the last main
section for today,

00:04:00.997 --> 00:04:02.580 align:middle line:84%
we'll talk about
some of the folks who

00:04:02.580 --> 00:04:04.830 align:middle line:84%
are a bit younger
than Faraday, who

00:04:04.830 --> 00:04:08.020 align:middle line:84%
took up his mantle who tried
to continue his line of work,

00:04:08.020 --> 00:04:11.340 align:middle line:84%
but, again, using some different
kinds of techniques and tools,

00:04:11.340 --> 00:04:14.310 align:middle line:84%
in this case William Thompson
and James Clerk Maxwell.

00:04:14.310 --> 00:04:17.560 align:middle line:90%
So that's our goal for today.

00:04:17.560 --> 00:04:19.920 align:middle line:84%
So let's just pause
and remember that we

00:04:19.920 --> 00:04:23.820 align:middle line:84%
are entering a kind of
imaginary time capsule

00:04:23.820 --> 00:04:27.090 align:middle line:84%
and going back about
200 years to start.

00:04:27.090 --> 00:04:31.080 align:middle line:84%
So the assumptions that we might
bring in as physics students,

00:04:31.080 --> 00:04:34.500 align:middle line:84%
as MIT students more generally
about how the world works,

00:04:34.500 --> 00:04:36.120 align:middle line:84%
about what the
job of a physicist

00:04:36.120 --> 00:04:40.080 align:middle line:84%
is, and so on, those won't
map on perfectly well

00:04:40.080 --> 00:04:42.700 align:middle line:84%
to some of these earlier folks
when we start talking about.

00:04:42.700 --> 00:04:44.242 align:middle line:84%
And I find that
that's part of what's

00:04:44.242 --> 00:04:46.492 align:middle line:84%
so fun for me about working
in the history of science,

00:04:46.492 --> 00:04:49.050 align:middle line:84%
is exactly those moments where
things don't look so familiar,

00:04:49.050 --> 00:04:51.863 align:middle line:84%
as well as the continuity
we can trace over time.

00:04:51.863 --> 00:04:53.280 align:middle line:84%
So one of the
biggest questions we

00:04:53.280 --> 00:04:57.330 align:middle line:84%
might ask about physics today
is, what's the world made of?

00:04:57.330 --> 00:05:00.030 align:middle line:84%
What do we think, as
modern day scientists,

00:05:00.030 --> 00:05:04.230 align:middle line:84%
are the basic building blocks
out of which the world is made?

00:05:04.230 --> 00:05:08.850 align:middle line:84%
If we were to conduct a survey
of most working physicists

00:05:08.850 --> 00:05:11.770 align:middle line:84%
at MIT or really anywhere
around the world at this point,

00:05:11.770 --> 00:05:13.830 align:middle line:84%
we'd get an answer
along these lines.

00:05:13.830 --> 00:05:15.330 align:middle line:84%
We would hear about
something called

00:05:15.330 --> 00:05:18.510 align:middle line:84%
the standard model of particle
physics, which is amazing.

00:05:18.510 --> 00:05:20.760 align:middle line:84%
And we'll actually talk a
bit about the standard model

00:05:20.760 --> 00:05:22.410 align:middle line:90%
later in the semester.

00:05:22.410 --> 00:05:24.090 align:middle line:84%
It describes the
world as made up

00:05:24.090 --> 00:05:27.330 align:middle line:84%
of a very small number
of fundamental entities,

00:05:27.330 --> 00:05:29.970 align:middle line:84%
elementary particles like
the quarks, and electrons,

00:05:29.970 --> 00:05:34.260 align:middle line:84%
and tau mesons, and neutrinos,
and even the long elusive Higgs

00:05:34.260 --> 00:05:34.830 align:middle line:90%
boson.

00:05:34.830 --> 00:05:37.170 align:middle line:84%
There's a collection, not
a very big collection,

00:05:37.170 --> 00:05:39.810 align:middle line:84%
of stuff out of which we
think literally everything

00:05:39.810 --> 00:05:41.010 align:middle line:90%
else is made.

00:05:41.010 --> 00:05:43.770 align:middle line:84%
We hear the physicists today
talk about the tools that

00:05:43.770 --> 00:05:45.600 align:middle line:84%
have been developed
to try to study

00:05:45.600 --> 00:05:48.222 align:middle line:84%
the interactions of those
elementary bits of matter,

00:05:48.222 --> 00:05:50.430 align:middle line:84%
how different particles can
interact with each other,

00:05:50.430 --> 00:05:53.790 align:middle line:84%
can scatter off each other, can
transmit the fundamental forces

00:05:53.790 --> 00:05:57.780 align:middle line:84%
of nature by exchanging certain
kinds of particles in a vacuum.

00:05:57.780 --> 00:06:00.990 align:middle line:84%
Depending on which physicist,
we ask, we might get an earful,

00:06:00.990 --> 00:06:03.480 align:middle line:84%
maybe more than we invited,
saying that actually all

00:06:03.480 --> 00:06:05.640 align:middle line:84%
those particles are
themselves really only

00:06:05.640 --> 00:06:09.660 align:middle line:84%
the efflorescence of
more fundamental entities

00:06:09.660 --> 00:06:11.903 align:middle line:84%
called strings that live
in some abstract space.

00:06:11.903 --> 00:06:14.070 align:middle line:84%
The point is, we're going
to get an answer like this

00:06:14.070 --> 00:06:16.470 align:middle line:84%
about, basically,
particles exchanging

00:06:16.470 --> 00:06:18.080 align:middle line:90%
particles in a vacuum.

00:06:18.080 --> 00:06:20.580 align:middle line:84%
Now, if we were to build our
time machine, which I sincerely

00:06:20.580 --> 00:06:24.510 align:middle line:84%
hope we can complete
soon, and we go back 100,

00:06:24.510 --> 00:06:28.440 align:middle line:84%
let alone 200 years to,
say, talk with leading

00:06:28.440 --> 00:06:31.825 align:middle line:84%
natural researchers in Britain,
and we told them this answer,

00:06:31.825 --> 00:06:34.200 align:middle line:84%
that physicists today said
the world is made of particles

00:06:34.200 --> 00:06:36.040 align:middle line:84%
exchanging particles
in a vacuum,

00:06:36.040 --> 00:06:38.930 align:middle line:84%
they would have thought we
were really not with it.

00:06:38.930 --> 00:06:41.430 align:middle line:84%
I like to think they would have
shouted bollocks or at least

00:06:41.430 --> 00:06:42.750 align:middle line:90%
something maybe more colorful.

00:06:42.750 --> 00:06:44.580 align:middle line:84%
Every single part of
this modern answer

00:06:44.580 --> 00:06:46.110 align:middle line:84%
would have looked
extraordinarily

00:06:46.110 --> 00:06:48.360 align:middle line:84%
wrongheaded to the
people that we're

00:06:48.360 --> 00:06:50.580 align:middle line:84%
going to spend some time
reading about and talking

00:06:50.580 --> 00:06:52.260 align:middle line:90%
about at the start of this term.

00:06:52.260 --> 00:06:54.000 align:middle line:90%
And why is that important?

00:06:54.000 --> 00:06:57.330 align:middle line:84%
I mean, if we did this exercise
with the ancient Mayans,

00:06:57.330 --> 00:07:01.110 align:middle line:84%
or the medieval Turks, or
the Renaissance French,

00:07:01.110 --> 00:07:02.820 align:middle line:84%
we'd also expect
some disagreement.

00:07:02.820 --> 00:07:04.620 align:middle line:84%
What I like about
this is that we're

00:07:04.620 --> 00:07:07.440 align:middle line:84%
turning the clock
back not so far,

00:07:07.440 --> 00:07:09.330 align:middle line:90%
compared to the present day.

00:07:09.330 --> 00:07:12.810 align:middle line:84%
And yet, we already see a huge
divergence in the answers.

00:07:12.810 --> 00:07:14.640 align:middle line:84%
As we'll see throughout
today and actually

00:07:14.640 --> 00:07:17.310 align:middle line:84%
the first several class
sessions for the term,

00:07:17.310 --> 00:07:19.080 align:middle line:90%
we use their equations.

00:07:19.080 --> 00:07:22.170 align:middle line:84%
We still use Maxwell's
equations, for example,

00:07:22.170 --> 00:07:25.650 align:middle line:84%
and a lot of the ideas that
Michael Faraday introduced.

00:07:25.650 --> 00:07:28.200 align:middle line:84%
And yet, what they thought
those equations meant,

00:07:28.200 --> 00:07:30.360 align:middle line:84%
what they thought they
were describing about how

00:07:30.360 --> 00:07:33.960 align:middle line:84%
the world is made up
are almost 180 degrees

00:07:33.960 --> 00:07:36.850 align:middle line:84%
opposite from how we start
our investigations today.

00:07:36.850 --> 00:07:39.540 align:middle line:84%
So even though some parts
have remained the same going

00:07:39.540 --> 00:07:44.670 align:middle line:84%
over these 150 or 200 years
to the past, how we make sense

00:07:44.670 --> 00:07:46.800 align:middle line:84%
of those ideas or
those techniques

00:07:46.800 --> 00:07:49.082 align:middle line:84%
have gone through a really
quite amazing change.

00:07:49.082 --> 00:07:50.790 align:middle line:84%
So what do we think
the world is made of?

00:07:50.790 --> 00:07:53.670 align:middle line:84%
That's not a static
set of answers.

00:07:53.670 --> 00:07:55.560 align:middle line:84%
And we see pretty
dramatic change,

00:07:55.560 --> 00:07:59.448 align:middle line:84%
even over a relatively
short span of history.

00:07:59.448 --> 00:08:00.990 align:middle line:84%
There's another kind
of shift that we

00:08:00.990 --> 00:08:04.260 align:middle line:84%
want to get our heads into,
attune ourselves to as well.

00:08:04.260 --> 00:08:06.900 align:middle line:84%
And that concerns who
pursues the study of physics

00:08:06.900 --> 00:08:09.660 align:middle line:84%
and in what kinds of
settings, what institutions.

00:08:09.660 --> 00:08:12.630 align:middle line:84%
So during the first half
of the 19th century, when

00:08:12.630 --> 00:08:14.850 align:middle line:84%
we'll start this class,
people who worked

00:08:14.850 --> 00:08:16.410 align:middle line:90%
on what we would call physics--

00:08:16.410 --> 00:08:20.460 align:middle line:84%
electricity, magnetism,
optics, other phenomena, heat--

00:08:20.460 --> 00:08:23.580 align:middle line:84%
they also worked on things
that we would call not physics,

00:08:23.580 --> 00:08:27.540 align:middle line:84%
like chemistry, or mathematics,
or astronomy, physiology, even

00:08:27.540 --> 00:08:28.500 align:middle line:90%
beyond that.

00:08:28.500 --> 00:08:32.260 align:middle line:84%
For them, this was all
one field of study.

00:08:32.260 --> 00:08:35.400 align:middle line:84%
It was often grouped under the
term natural philosophy rather

00:08:35.400 --> 00:08:38.460 align:middle line:84%
than physics, or chemistry,
or mathematics, per se.

00:08:38.460 --> 00:08:42.179 align:middle line:84%
In fact, the term for a person
who studied these things--

00:08:42.179 --> 00:08:45.510 align:middle line:84%
in English, the term we
would call a scientist

00:08:45.510 --> 00:08:48.600 align:middle line:84%
was actually only
invented in 1834.

00:08:48.600 --> 00:08:51.570 align:middle line:84%
It's remarkably new, as far
as the English language goes.

00:08:51.570 --> 00:08:53.850 align:middle line:84%
It was invented after
some of the developments

00:08:53.850 --> 00:08:55.630 align:middle line:84%
we'll actually start
talking about today.

00:08:55.630 --> 00:08:58.300 align:middle line:84%
So even having the job
description scientist

00:08:58.300 --> 00:09:01.180 align:middle line:84%
or the title is
actually relatively new.

00:09:01.180 --> 00:09:04.060 align:middle line:84%
And what these particular kinds
of scientists that we would now

00:09:04.060 --> 00:09:06.770 align:middle line:84%
call physicists-- what they
thought they should do-- again,

00:09:06.770 --> 00:09:09.130 align:middle line:84%
some pretty broad
changes compared

00:09:09.130 --> 00:09:11.870 align:middle line:90%
to what we're used to today.

00:09:11.870 --> 00:09:13.870 align:middle line:84%
Not only do they think
their job description was

00:09:13.870 --> 00:09:15.995 align:middle line:84%
different than what we
might imagine for ourselves,

00:09:15.995 --> 00:09:17.740 align:middle line:84%
but where they did
the work and what

00:09:17.740 --> 00:09:19.480 align:middle line:84%
kinds of settings
or institutions,

00:09:19.480 --> 00:09:22.850 align:middle line:84%
that was also pretty different
merely 200 years ago,

00:09:22.850 --> 00:09:25.460 align:middle line:84%
let alone much further
back in human history.

00:09:25.460 --> 00:09:27.970 align:middle line:84%
So a lot of stuff we'll
start by talking about today

00:09:27.970 --> 00:09:31.030 align:middle line:84%
was not done in schools
or universities.

00:09:31.030 --> 00:09:33.550 align:middle line:84%
They were done in separate
institutes or academies.

00:09:33.550 --> 00:09:36.700 align:middle line:84%
And the key thing is these
were not places where students

00:09:36.700 --> 00:09:38.710 align:middle line:90%
took classes to get degrees.

00:09:38.710 --> 00:09:42.220 align:middle line:84%
There was a separation
between learning

00:09:42.220 --> 00:09:43.862 align:middle line:84%
institutions--
universities existed

00:09:43.862 --> 00:09:45.320 align:middle line:84%
throughout many
parts of the world,

00:09:45.320 --> 00:09:47.620 align:middle line:84%
including Western Europe
and the United States.

00:09:47.620 --> 00:09:48.610 align:middle line:90%
Universities existed.

00:09:48.610 --> 00:09:51.070 align:middle line:84%
But that was not where
people were doing what we

00:09:51.070 --> 00:09:53.170 align:middle line:90%
would call scientific research.

00:09:53.170 --> 00:09:56.170 align:middle line:84%
In fact, some of the most
prominent natural philosophers

00:09:56.170 --> 00:09:58.690 align:middle line:84%
or leading physicists were
not only not professors

00:09:58.690 --> 00:10:01.180 align:middle line:84%
at universities, some of
them had never even attended

00:10:01.180 --> 00:10:02.380 align:middle line:90%
university themselves.

00:10:02.380 --> 00:10:04.088 align:middle line:84%
And that's true of
the first figure we'll

00:10:04.088 --> 00:10:06.340 align:middle line:90%
look at today, Michael Faraday.

00:10:06.340 --> 00:10:11.180 align:middle line:84%
So there's a big shift toward a
placement of this research that

00:10:11.180 --> 00:10:13.180 align:middle line:84%
would look more familiar--
things more like what

00:10:13.180 --> 00:10:14.890 align:middle line:90%
we'd expect to see ourselves.

00:10:14.890 --> 00:10:18.400 align:middle line:84%
That shift begins in the middle
of the 19th century, so more

00:10:18.400 --> 00:10:22.480 align:middle line:84%
like 150 or 170 years
ago, rather than 200 years

00:10:22.480 --> 00:10:24.130 align:middle line:90%
ago or more.

00:10:24.130 --> 00:10:28.240 align:middle line:84%
There's a shift to where
research in fields like physics

00:10:28.240 --> 00:10:30.190 align:middle line:84%
gets done more often
than not by people

00:10:30.190 --> 00:10:32.530 align:middle line:84%
who are professors in
universities who also spend

00:10:32.530 --> 00:10:34.120 align:middle line:84%
some of their time
teaching students,

00:10:34.120 --> 00:10:36.130 align:middle line:84%
like what we are
more used to today.

00:10:36.130 --> 00:10:38.060 align:middle line:90%
That has a history.

00:10:38.060 --> 00:10:39.550 align:middle line:90%
It's actually relatively recent.

00:10:39.550 --> 00:10:42.610 align:middle line:84%
And it emerges really
in the middle part

00:10:42.610 --> 00:10:44.330 align:middle line:90%
of the 19th century.

00:10:44.330 --> 00:10:47.170 align:middle line:84%
So the overall theme of
this very first warm-up

00:10:47.170 --> 00:10:50.620 align:middle line:84%
for the class is to
put ourselves on guard.

00:10:50.620 --> 00:10:53.680 align:middle line:84%
We shouldn't assume that
our current sense of what's

00:10:53.680 --> 00:10:57.730 align:middle line:84%
expected, or normal, or familiar
either about how we choose

00:10:57.730 --> 00:11:01.120 align:middle line:84%
to study the natural world,
what concepts we use,

00:11:01.120 --> 00:11:04.040 align:middle line:84%
let alone how we think we
should be pursuing that,

00:11:04.040 --> 00:11:06.580 align:middle line:84%
and what kinds of institutions
or job descriptions--

00:11:06.580 --> 00:11:09.340 align:middle line:84%
We shouldn't expect that
what's familiar to us today

00:11:09.340 --> 00:11:11.800 align:middle line:84%
is just how people did
things in the past.

00:11:11.800 --> 00:11:14.260 align:middle line:84%
And in fact, we'll see some
pretty dramatic changes

00:11:14.260 --> 00:11:16.725 align:middle line:84%
over a relatively
short span of time.

00:11:16.725 --> 00:11:18.850 align:middle line:84%
So let me pause there and
ask if any questions just

00:11:18.850 --> 00:11:21.580 align:middle line:90%
on that early warm-up.

00:11:21.580 --> 00:11:23.710 align:middle line:84%
Anyone have any thoughts
or questions about that?

00:11:23.710 --> 00:11:33.940 align:middle line:90%


00:11:33.940 --> 00:11:36.000 align:middle line:84%
If not, then I'm
going to press on.

00:11:36.000 --> 00:11:40.450 align:middle line:84%
Again, feel free to jump in
on the chat if things come up.

00:11:40.450 --> 00:11:43.110 align:middle line:84%
Let's talk about this first
figure I already mentioned,

00:11:43.110 --> 00:11:43.777 align:middle line:90%
Michael Faraday.

00:11:43.777 --> 00:11:46.152 align:middle line:84%
We're going to spend a little
time talking about Faraday.

00:11:46.152 --> 00:11:47.220 align:middle line:90%
I think he's fascinating.

00:11:47.220 --> 00:11:49.553 align:middle line:84%
So he became one of the most
successful and actually one

00:11:49.553 --> 00:11:52.210 align:middle line:84%
of the most famous natural
philosophers in his lifetime--

00:11:52.210 --> 00:11:54.790 align:middle line:84%
in fact, really of the
entire 19th century.

00:11:54.790 --> 00:11:57.480 align:middle line:84%
He had a pretty
remarkable personal story.

00:11:57.480 --> 00:12:00.450 align:middle line:84%
And I think we'll also see
he helps make clear some

00:12:00.450 --> 00:12:03.810 align:middle line:84%
of the larger social and
institutional changes going on

00:12:03.810 --> 00:12:04.320 align:middle line:90%
as well.

00:12:04.320 --> 00:12:08.400 align:middle line:84%
He helps us understand his
own larger time period.

00:12:08.400 --> 00:12:12.780 align:middle line:84%
Personally, he had this really
inspiring rags to riches story.

00:12:12.780 --> 00:12:14.910 align:middle line:84%
He was born into a
rather poor family.

00:12:14.910 --> 00:12:16.680 align:middle line:84%
He never attended
high school, let alone

00:12:16.680 --> 00:12:20.620 align:middle line:90%
college or university.

00:12:20.620 --> 00:12:23.530 align:middle line:84%
He was apprenticed to
a bookbinder at age 13.

00:12:23.530 --> 00:12:25.420 align:middle line:84%
That means he literally
left his family,

00:12:25.420 --> 00:12:30.280 align:middle line:84%
moved in with his
main tutor, and was

00:12:30.280 --> 00:12:33.250 align:middle line:90%
apprenticed in a kind of trade.

00:12:33.250 --> 00:12:36.220 align:middle line:84%
So in that sense,
his career path

00:12:36.220 --> 00:12:38.260 align:middle line:84%
started out closer to
what we might expect

00:12:38.260 --> 00:12:40.450 align:middle line:84%
of the Renaissance or
even the Middle Ages

00:12:40.450 --> 00:12:42.070 align:middle line:90%
than to the modern period.

00:12:42.070 --> 00:12:45.670 align:middle line:84%
It was a time still of guilds
and of trades associations.

00:12:45.670 --> 00:12:48.130 align:middle line:84%
And his role, his
way to make a living,

00:12:48.130 --> 00:12:50.830 align:middle line:84%
was to learn the kind
of manual dexterity

00:12:50.830 --> 00:12:54.880 align:middle line:84%
skills of being a bookbinder,
starting early on.

00:12:54.880 --> 00:12:58.060 align:middle line:84%
He met the very famous chemist
or natural philosopher Humphry

00:12:58.060 --> 00:13:00.910 align:middle line:84%
Davy when Davy gave a
series of public lectures

00:13:00.910 --> 00:13:03.820 align:middle line:84%
on natural philosophy at the
Royal Institution in London.

00:13:03.820 --> 00:13:06.940 align:middle line:84%
And we'll talk a bit about
the Royal Institution.

00:13:06.940 --> 00:13:08.260 align:middle line:90%
It was not a university.

00:13:08.260 --> 00:13:09.970 align:middle line:84%
It was a place where
research was done

00:13:09.970 --> 00:13:11.680 align:middle line:90%
and public lectures were given.

00:13:11.680 --> 00:13:14.590 align:middle line:84%
So Faraday was just
mesmerized by Davy's lectures.

00:13:14.590 --> 00:13:18.250 align:middle line:84%
He actually took very careful
notes on these public lectures.

00:13:18.250 --> 00:13:21.440 align:middle line:84%
Faraday then bound them into
a beautiful, very fancy book.

00:13:21.440 --> 00:13:23.150 align:middle line:84%
And here's how we
know he was so smart.

00:13:23.150 --> 00:13:25.843 align:middle line:84%
He then gave that fancy
book to Davy as a gift.

00:13:25.843 --> 00:13:27.260 align:middle line:84%
And I have a hint
here of what you

00:13:27.260 --> 00:13:29.000 align:middle line:90%
can do with that information.

00:13:29.000 --> 00:13:32.060 align:middle line:84%
He basically bribed his way into
a new kind of apprenticeship.

00:13:32.060 --> 00:13:34.040 align:middle line:84%
Davy was very
flattered and impressed

00:13:34.040 --> 00:13:36.830 align:middle line:84%
by the kind of manual
skills, by the dexterity

00:13:36.830 --> 00:13:38.360 align:middle line:90%
that Faraday had shown.

00:13:38.360 --> 00:13:41.300 align:middle line:84%
So Davy hired Faraday
for basically a new kind

00:13:41.300 --> 00:13:42.770 align:middle line:90%
of apprenticeship.

00:13:42.770 --> 00:13:44.990 align:middle line:84%
Faraday had never attended
high school or college.

00:13:44.990 --> 00:13:47.510 align:middle line:84%
It wasn't that he was trained
in mathematical physics,

00:13:47.510 --> 00:13:48.560 align:middle line:90%
quite the contrary.

00:13:48.560 --> 00:13:50.450 align:middle line:84%
But Davy figured
Faraday could do

00:13:50.450 --> 00:13:53.390 align:middle line:84%
some new kinds of
manual dexterity skills

00:13:53.390 --> 00:13:55.250 align:middle line:84%
in the laboratory
as a laboratory

00:13:55.250 --> 00:13:59.900 align:middle line:84%
assistant, a continuation of
his bookbinder apprenticeship.

00:13:59.900 --> 00:14:02.150 align:middle line:84%
So that's how
Faraday enters what

00:14:02.150 --> 00:14:04.670 align:middle line:84%
we would now call the world
of natural philosophy.

00:14:04.670 --> 00:14:05.960 align:middle line:90%
So years and years go by.

00:14:05.960 --> 00:14:07.760 align:middle line:84%
They worked very
closely for a long time.

00:14:07.760 --> 00:14:09.440 align:middle line:90%
Davy eventually steps down.

00:14:09.440 --> 00:14:10.400 align:middle line:90%
He retires.

00:14:10.400 --> 00:14:12.780 align:middle line:84%
And Faraday, in fact,
became his successor,

00:14:12.780 --> 00:14:15.800 align:middle line:84%
now the director of this
Royal Institution in London.

00:14:15.800 --> 00:14:18.170 align:middle line:84%
So much like I mentioned
a few moments ago,

00:14:18.170 --> 00:14:22.310 align:middle line:84%
Faraday worked on really a kind
mind-boggling array of topics,

00:14:22.310 --> 00:14:26.960 align:middle line:84%
mind-boggling from our modern
point of view, quite familiar

00:14:26.960 --> 00:14:28.560 align:middle line:90%
to his own contemporaries.

00:14:28.560 --> 00:14:30.500 align:middle line:84%
So he worked on what
we would separately

00:14:30.500 --> 00:14:33.440 align:middle line:84%
classify as chemistry, optics,
electromagnetism, electrolysis,

00:14:33.440 --> 00:14:35.000 align:middle line:90%
and more.

00:14:35.000 --> 00:14:36.650 align:middle line:84%
To Faraday, these
were all elements

00:14:36.650 --> 00:14:39.170 align:middle line:84%
of a single, unified
approach to nature.

00:14:39.170 --> 00:14:42.350 align:middle line:84%
And he was particularly
fascinated, even more so

00:14:42.350 --> 00:14:45.830 align:middle line:84%
than some of his contemporaries,
with this interconvertibility

00:14:45.830 --> 00:14:46.730 align:middle line:90%
of forces.

00:14:46.730 --> 00:14:50.840 align:middle line:84%
How could electrical effects
make physiological effects

00:14:50.840 --> 00:14:53.090 align:middle line:84%
happen, like using
electric shocks

00:14:53.090 --> 00:14:54.680 align:middle line:90%
to make a frog's leg jump?

00:14:54.680 --> 00:14:59.630 align:middle line:84%
How could chemical effects be
catalyzed by electric currents?

00:14:59.630 --> 00:15:02.540 align:middle line:84%
So the way that one kind
of phenomenon or force

00:15:02.540 --> 00:15:05.010 align:middle line:84%
could have effects
in some other domain.

00:15:05.010 --> 00:15:07.440 align:middle line:84%
Now, Faraday was
partly inspired in

00:15:07.440 --> 00:15:10.955 align:middle line:84%
this interconvertibility view
by his own religious background.

00:15:10.955 --> 00:15:12.330 align:middle line:84%
Some really very
interesting work

00:15:12.330 --> 00:15:14.850 align:middle line:84%
by a number of historians
and biographers of Faraday

00:15:14.850 --> 00:15:18.510 align:middle line:84%
who have tried to understand why
Faraday took this notion even

00:15:18.510 --> 00:15:20.640 align:middle line:84%
further, even more
fervently than many

00:15:20.640 --> 00:15:22.080 align:middle line:90%
of his own contemporaries.

00:15:22.080 --> 00:15:25.110 align:middle line:84%
And these other historians
make a pretty compelling case.

00:15:25.110 --> 00:15:28.680 align:middle line:84%
Faraday belonged to a rather
small religious minority

00:15:28.680 --> 00:15:29.610 align:middle line:90%
in England.

00:15:29.610 --> 00:15:32.670 align:middle line:84%
He was a Protestant, but
he was not an Anglican.

00:15:32.670 --> 00:15:35.620 align:middle line:84%
He was not a member of the
official church of England.

00:15:35.620 --> 00:15:39.360 align:middle line:84%
He belonged to this small
sect called the Sandemanians,

00:15:39.360 --> 00:15:41.370 align:middle line:90%
Protestant but not Anglican.

00:15:41.370 --> 00:15:44.370 align:middle line:84%
And the Sandemanians, even
more than the standard church

00:15:44.370 --> 00:15:48.060 align:middle line:84%
of England at the time,
emphasized an underlying unity

00:15:48.060 --> 00:15:51.600 align:middle line:84%
to all of nature-- we're all
part of one natural world--

00:15:51.600 --> 00:15:53.270 align:middle line:84%
and that people and
things are somehow

00:15:53.270 --> 00:15:54.270 align:middle line:90%
connected to each other.

00:15:54.270 --> 00:15:56.430 align:middle line:84%
And that was part of what
the Sandemanians themselves

00:15:56.430 --> 00:15:56.930 align:middle line:90%
believed.

00:15:56.930 --> 00:15:59.740 align:middle line:84%
And it had a theological
import for them.

00:15:59.740 --> 00:16:02.353 align:middle line:84%
And there's a really interesting
parallel, at the very least,

00:16:02.353 --> 00:16:05.020 align:middle line:84%
in some of the ways that Faraday
then explored the natural world

00:16:05.020 --> 00:16:05.690 align:middle line:90%
as well.

00:16:05.690 --> 00:16:08.710 align:middle line:84%
He became a beloved, very
successful public lecturer.

00:16:08.710 --> 00:16:11.110 align:middle line:84%
He continued the tradition
that Humphry Davy

00:16:11.110 --> 00:16:13.030 align:middle line:84%
had done at the
Royal Institution,

00:16:13.030 --> 00:16:15.280 align:middle line:84%
giving these very,
very well-attended

00:16:15.280 --> 00:16:16.900 align:middle line:90%
so-called Christmas lectures.

00:16:16.900 --> 00:16:19.810 align:middle line:84%
These still continue from the
Royal Institution to this day.

00:16:19.810 --> 00:16:21.760 align:middle line:84%
Faraday would really
fill the lecture hall

00:16:21.760 --> 00:16:24.820 align:middle line:84%
and give these dazzling,
spectacular demonstrations

00:16:24.820 --> 00:16:27.040 align:middle line:84%
of electrical effects, and
chemical change, and all

00:16:27.040 --> 00:16:27.910 align:middle line:90%
the rest.

00:16:27.910 --> 00:16:30.700 align:middle line:84%
That's partly why he became
so beloved and well-known

00:16:30.700 --> 00:16:31.960 align:middle line:90%
in his lifetime.

00:16:31.960 --> 00:16:33.970 align:middle line:84%
You can't quite see
it in this engraving.

00:16:33.970 --> 00:16:35.980 align:middle line:90%
It's hard to tell.

00:16:35.980 --> 00:16:38.110 align:middle line:84%
This really was the
definition of popular.

00:16:38.110 --> 00:16:40.120 align:middle line:84%
The tickets were
not too expensive.

00:16:40.120 --> 00:16:42.580 align:middle line:84%
That's partly how very
young and poor Faraday

00:16:42.580 --> 00:16:44.900 align:middle line:84%
himself was able to
attend as a child.

00:16:44.900 --> 00:16:48.730 align:middle line:84%
It wasn't like attending the
fanciest opera performance

00:16:48.730 --> 00:16:52.512 align:middle line:90%
in high elite London.

00:16:52.512 --> 00:16:53.470 align:middle line:90%
There'd be cheap seats.

00:16:53.470 --> 00:16:54.928 align:middle line:84%
You can see how
large the hall was.

00:16:54.928 --> 00:16:58.660 align:middle line:84%
So the very nice, fancy seats,
then as now, were expensive.

00:16:58.660 --> 00:17:03.610 align:middle line:84%
And tickets would go to the
affluent and well-to-do.

00:17:03.610 --> 00:17:05.410 align:middle line:84%
But there really
was what we today

00:17:05.410 --> 00:17:06.670 align:middle line:90%
would call a kind of outreach.

00:17:06.670 --> 00:17:09.220 align:middle line:84%
There was a real
effort to reach across

00:17:09.220 --> 00:17:12.880 align:middle line:84%
several social and economic
classes-- not all the way,

00:17:12.880 --> 00:17:15.130 align:middle line:84%
but broader than
only the very elite.

00:17:15.130 --> 00:17:19.510 align:middle line:84%
And they became a really beloved
city institution within London.

00:17:19.510 --> 00:17:22.599 align:middle line:84%
People would come in from
out of town to attend them.

00:17:22.599 --> 00:17:24.640 align:middle line:90%
It became an annual tradition.

00:17:24.640 --> 00:17:27.430 align:middle line:84%
And Faraday became especially
beloved as a presenter

00:17:27.430 --> 00:17:28.550 align:middle line:90%
in that tradition.

00:17:28.550 --> 00:17:30.460 align:middle line:84%
So they really were
reaching not only people

00:17:30.460 --> 00:17:33.610 align:middle line:84%
who had any interest
in natural philosophy.

00:17:33.610 --> 00:17:38.200 align:middle line:84%
It was really a way of showing
a kind of sophistication

00:17:38.200 --> 00:17:42.700 align:middle line:84%
and a way for members of the
so-called aspiring classes,

00:17:42.700 --> 00:17:44.380 align:middle line:84%
meaning those who
weren't so well-to-do,

00:17:44.380 --> 00:17:45.670 align:middle line:84%
to be able to
participate in things

00:17:45.670 --> 00:17:47.170 align:middle line:84%
that they saw the
real elites doing.

00:17:47.170 --> 00:17:50.217 align:middle line:84%
So it really had an interesting
social cross-section to them.

00:17:50.217 --> 00:17:52.300 align:middle line:84%
Historians have written a
lot of interesting stuff

00:17:52.300 --> 00:17:53.467 align:middle line:90%
about these public lectures.

00:17:53.467 --> 00:17:55.330 align:middle line:84%
They really were
talked about broadly,

00:17:55.330 --> 00:17:57.820 align:middle line:84%
covered in the broadsheet
newspapers and all that.

00:17:57.820 --> 00:18:02.800 align:middle line:84%
In this time period, the main
mechanisms were largely books.

00:18:02.800 --> 00:18:06.630 align:middle line:84%
So even scientists, whom
we would call physicists,

00:18:06.630 --> 00:18:10.050 align:middle line:84%
were mostly writing monographs
and sometimes writing

00:18:10.050 --> 00:18:11.760 align:middle line:84%
short articles for
fellow specialists.

00:18:11.760 --> 00:18:13.920 align:middle line:84%
There were scientific
journals, including

00:18:13.920 --> 00:18:16.462 align:middle line:84%
some of the earliest that have
been founded in England, going

00:18:16.462 --> 00:18:20.760 align:middle line:84%
back to the 1660s, similar
ones in other parts of Europe.

00:18:20.760 --> 00:18:25.067 align:middle line:84%
But the real transfer mechanisms
were often through monographs.

00:18:25.067 --> 00:18:27.150 align:middle line:84%
And it's partly why Maxwell's
treatise, that we'll

00:18:27.150 --> 00:18:30.570 align:middle line:84%
talk about later
today, became so widely

00:18:30.570 --> 00:18:31.980 align:middle line:90%
known and so influential.

00:18:31.980 --> 00:18:33.930 align:middle line:90%
There were then these lectures.

00:18:33.930 --> 00:18:36.480 align:middle line:84%
There were also so-called
itinerant lecturers,

00:18:36.480 --> 00:18:39.030 align:middle line:84%
people who made their
whole living just giving

00:18:39.030 --> 00:18:42.960 align:middle line:84%
popular lectures on topics
like electricity town to town--

00:18:42.960 --> 00:18:45.600 align:middle line:84%
so not just in London,
but to the outskirts

00:18:45.600 --> 00:18:47.550 align:middle line:84%
and likewise
throughout provincial

00:18:47.550 --> 00:18:48.760 align:middle line:90%
France and other places.

00:18:48.760 --> 00:18:50.610 align:middle line:90%
So there were popular lectures.

00:18:50.610 --> 00:18:53.640 align:middle line:84%
In that sense, you can think of
it almost like PBS television

00:18:53.640 --> 00:18:55.590 align:middle line:90%
today, like Nova specials.

00:18:55.590 --> 00:18:57.840 align:middle line:84%
But for fellow
specialists, there

00:18:57.840 --> 00:19:00.960 align:middle line:84%
were just the start of
professional meetings.

00:19:00.960 --> 00:19:03.210 align:middle line:84%
The British Association for
the Advancement of Science

00:19:03.210 --> 00:19:05.130 align:middle line:84%
were having annual
meetings of the sort that

00:19:05.130 --> 00:19:07.870 align:middle line:84%
would become so familiar
for fellow specialists.

00:19:07.870 --> 00:19:09.400 align:middle line:84%
Sometimes, those
would be covered

00:19:09.400 --> 00:19:11.027 align:middle line:90%
in the national newspapers.

00:19:11.027 --> 00:19:11.860 align:middle line:90%
It was a hodgepodge.

00:19:11.860 --> 00:19:13.870 align:middle line:84%
Some things would
look familiar to us.

00:19:13.870 --> 00:19:16.780 align:middle line:84%
Some things might seem
a little more unusual.

00:19:16.780 --> 00:19:19.610 align:middle line:84%
But Faraday wrote books and
books and some articles,

00:19:19.610 --> 00:19:21.375 align:middle line:90%
for example.

00:19:21.375 --> 00:19:22.750 align:middle line:84%
And certainly,
some of this would

00:19:22.750 --> 00:19:24.697 align:middle line:84%
get into the curriculum
for universities.

00:19:24.697 --> 00:19:27.280 align:middle line:84%
And we'll talk more about that
actually especially later today

00:19:27.280 --> 00:19:28.820 align:middle line:90%
and in the next class session.

00:19:28.820 --> 00:19:31.095 align:middle line:84%
But the way that kind
of fellow researchers

00:19:31.095 --> 00:19:32.470 align:middle line:84%
interact with
fellow researchers,

00:19:32.470 --> 00:19:35.203 align:middle line:84%
it was largely through books,
sometimes through journals,

00:19:35.203 --> 00:19:37.120 align:middle line:84%
and through these different
kinds of lectures.

00:19:37.120 --> 00:19:39.720 align:middle line:90%
Great, great questions.

00:19:39.720 --> 00:19:41.100 align:middle line:90%
I'm going to move on.

00:19:41.100 --> 00:19:42.530 align:middle line:90%
These are great questions.

00:19:42.530 --> 00:19:46.010 align:middle line:84%
I'll try to answer more that I
don't get to as we go further.

00:19:46.010 --> 00:19:48.890 align:middle line:84%
But I want to get to one of the
topics that was really, really

00:19:48.890 --> 00:19:52.100 align:middle line:84%
high on Faraday's list of most
important because it's really

00:19:52.100 --> 00:19:55.970 align:middle line:84%
going to set our agenda for
several classes to come.

00:19:55.970 --> 00:19:58.700 align:middle line:84%
And that's what was
called the aether,

00:19:58.700 --> 00:20:02.720 align:middle line:84%
a presumptive hypothetical
medium that pretty

00:20:02.720 --> 00:20:04.700 align:middle line:84%
much everyone that we're
going to talk about,

00:20:04.700 --> 00:20:06.800 align:middle line:90%
Faraday included, just assumed.

00:20:06.800 --> 00:20:07.790 align:middle line:90%
They knew.

00:20:07.790 --> 00:20:10.250 align:middle line:84%
They had an extremely
strong confidence

00:20:10.250 --> 00:20:12.860 align:middle line:84%
that this medium was
filling all of space,

00:20:12.860 --> 00:20:15.440 align:middle line:84%
filled every nook and
cranny of the universe.

00:20:15.440 --> 00:20:18.170 align:middle line:84%
And it was this
medium that filled

00:20:18.170 --> 00:20:21.520 align:middle line:84%
everything that enabled
various processes to affect

00:20:21.520 --> 00:20:22.020 align:middle line:90%
one another.

00:20:22.020 --> 00:20:24.380 align:middle line:84%
That was the
interconvertibility of forces.

00:20:24.380 --> 00:20:27.020 align:middle line:84%
Why did electrical effects
lead to magnetic effects?

00:20:27.020 --> 00:20:30.290 align:middle line:84%
Because they're both ultimately
effects of this aether

00:20:30.290 --> 00:20:31.520 align:middle line:90%
that connects everything.

00:20:31.520 --> 00:20:34.010 align:middle line:90%
So what's the aether?

00:20:34.010 --> 00:20:37.040 align:middle line:84%
Just during Faraday's
own childhood,

00:20:37.040 --> 00:20:39.480 align:middle line:84%
another amateur
British naturalist

00:20:39.480 --> 00:20:42.990 align:middle line:84%
named Thomas Young, building
on some work by French scholars

00:20:42.990 --> 00:20:45.780 align:middle line:84%
from around the same time,
right around the year 1800,

00:20:45.780 --> 00:20:47.798 align:middle line:84%
had advanced a wave
theory of light.

00:20:47.798 --> 00:20:50.340 align:middle line:84%
This was opposite actually to
Isaac Newton's theory of light,

00:20:50.340 --> 00:20:53.020 align:middle line:84%
who had a particle or
corpuscular theory.

00:20:53.020 --> 00:20:55.920 align:middle line:84%
So Thomas Young, like some of
the French scholars as well,

00:20:55.920 --> 00:20:58.380 align:middle line:84%
suggested that a whole
bunch of optical phenomena,

00:20:58.380 --> 00:21:01.800 align:middle line:84%
like interference, like
reflection, and refraction

00:21:01.800 --> 00:21:04.560 align:middle line:84%
could really only be
made sense of if light

00:21:04.560 --> 00:21:06.040 align:middle line:90%
was a series of waves.

00:21:06.040 --> 00:21:07.370 align:middle line:90%
And I'm sure you've seen this.

00:21:07.370 --> 00:21:09.120 align:middle line:84%
There's a very
simple illustration.

00:21:09.120 --> 00:21:12.000 align:middle line:84%
If two waves are perfectly
in sync with each other--

00:21:12.000 --> 00:21:13.300 align:middle line:90%
we'd say in phase--

00:21:13.300 --> 00:21:14.993 align:middle line:84%
you can get constructive
interference.

00:21:14.993 --> 00:21:17.160 align:middle line:84%
The peaks will become larger
than either wave alone.

00:21:17.160 --> 00:21:18.870 align:middle line:90%
The troughs become deeper.

00:21:18.870 --> 00:21:20.925 align:middle line:84%
Of course, if those
two waves are exactly

00:21:20.925 --> 00:21:23.550 align:middle line:84%
out of sync with each other, if
they're perfectly out of phase,

00:21:23.550 --> 00:21:25.150 align:middle line:84%
you can get destructive
interference.

00:21:25.150 --> 00:21:27.025 align:middle line:84%
And the resultant wave
will vanish altogether

00:21:27.025 --> 00:21:28.840 align:middle line:90%
and anything in between.

00:21:28.840 --> 00:21:30.360 align:middle line:84%
So Young and others
were convinced

00:21:30.360 --> 00:21:32.700 align:middle line:84%
that these
interference phenomena

00:21:32.700 --> 00:21:36.150 align:middle line:84%
were natural indications that
light is a wave phenomenon.

00:21:36.150 --> 00:21:38.850 align:middle line:84%
But then the next question
is, well, waves of what?

00:21:38.850 --> 00:21:40.410 align:middle line:90%
Waves in what?

00:21:40.410 --> 00:21:42.840 align:middle line:84%
Ocean waves are
clearly waves of water.

00:21:42.840 --> 00:21:46.020 align:middle line:84%
Sound waves or compressions
are waves in the atmosphere,

00:21:46.020 --> 00:21:46.900 align:middle line:90%
in the air.

00:21:46.900 --> 00:21:48.840 align:middle line:90%
What are waves of?

00:21:48.840 --> 00:21:50.400 align:middle line:84%
So they said, well,
any wave we know

00:21:50.400 --> 00:21:52.440 align:middle line:90%
about is a wave in some medium.

00:21:52.440 --> 00:21:55.320 align:middle line:84%
There must be a medium that
carries these light waves.

00:21:55.320 --> 00:21:57.180 align:middle line:84%
It was called the
luminiferous aether,

00:21:57.180 --> 00:21:58.800 align:middle line:90%
which is a very fancy word.

00:21:58.800 --> 00:22:00.540 align:middle line:84%
You can see how
to parse it here.

00:22:00.540 --> 00:22:03.240 align:middle line:84%
If you remember either
Latin or Harry Potter,

00:22:03.240 --> 00:22:04.630 align:middle line:90%
I find them equally helpful.

00:22:04.630 --> 00:22:08.400 align:middle line:84%
Think about the Lumos
spell in Harry Potter.

00:22:08.400 --> 00:22:12.360 align:middle line:84%
The lumini- part just means
light, referring to light.

00:22:12.360 --> 00:22:13.890 align:middle line:90%
-ferous means carrying.

00:22:13.890 --> 00:22:15.390 align:middle line:90%
Think of like a Ferris wheel.

00:22:15.390 --> 00:22:17.760 align:middle line:84%
So the formal name of
luminiferous aether

00:22:17.760 --> 00:22:19.560 align:middle line:84%
really just means
the light-carrying

00:22:19.560 --> 00:22:21.180 align:middle line:90%
or the light-bearing aether.

00:22:21.180 --> 00:22:23.970 align:middle line:84%
This was the medium in
which light traveled,

00:22:23.970 --> 00:22:26.910 align:middle line:84%
in which everything, all
of the physical phenomena,

00:22:26.910 --> 00:22:29.970 align:middle line:84%
were immersed, which is
why these folks would never

00:22:29.970 --> 00:22:33.300 align:middle line:84%
have said the stuff of the
world is elementary particles

00:22:33.300 --> 00:22:34.320 align:middle line:90%
traveling in a vacuum.

00:22:34.320 --> 00:22:35.670 align:middle line:90%
There is no vacuum.

00:22:35.670 --> 00:22:37.890 align:middle line:84%
Everything at root is
filled with aether.

00:22:37.890 --> 00:22:39.860 align:middle line:84%
That's where they
were starting from.

00:22:39.860 --> 00:22:42.980 align:middle line:84%
So why would you need
a medium for light?

00:22:42.980 --> 00:22:44.810 align:middle line:84%
Again, even before,
around the same time

00:22:44.810 --> 00:22:47.720 align:middle line:84%
as Thomas Young in England,
a number of French scholars

00:22:47.720 --> 00:22:50.000 align:middle line:84%
had found that the speed of
light-- the speed at which

00:22:50.000 --> 00:22:53.360 align:middle line:84%
light waves travel depends on
the medium in which they're

00:22:53.360 --> 00:22:54.020 align:middle line:90%
traveling.

00:22:54.020 --> 00:22:56.247 align:middle line:84%
In fact, they're slower
in water than in air.

00:22:56.247 --> 00:22:58.580 align:middle line:84%
That's opposite, by the way,
to sound waves sound waves.

00:22:58.580 --> 00:23:00.680 align:middle line:84%
They always travel more
quickly in a dense medium.

00:23:00.680 --> 00:23:03.020 align:middle line:84%
And that led to things
like Snell's law,

00:23:03.020 --> 00:23:07.340 align:middle line:84%
the whole set of
knowledge about refraction

00:23:07.340 --> 00:23:10.040 align:middle line:84%
and how light behaves when it
crosses from one type of medium

00:23:10.040 --> 00:23:10.790 align:middle line:90%
to another.

00:23:10.790 --> 00:23:12.530 align:middle line:84%
You can characterize
these media in terms

00:23:12.530 --> 00:23:15.050 align:middle line:84%
of what became known as
an index of refraction.

00:23:15.050 --> 00:23:17.720 align:middle line:84%
And so everything about
the behavior of these waves

00:23:17.720 --> 00:23:19.820 align:middle line:84%
seemed to depend on the
medium through which they

00:23:19.820 --> 00:23:20.810 align:middle line:90%
were traveling.

00:23:20.810 --> 00:23:23.840 align:middle line:84%
So there must be some kind
of baseline or reference

00:23:23.840 --> 00:23:26.120 align:middle line:84%
medium, the aether,
with respect to which

00:23:26.120 --> 00:23:28.740 align:middle line:84%
any of these deviations
would then be measured.

00:23:28.740 --> 00:23:31.730 align:middle line:90%
So water is one type of medium.

00:23:31.730 --> 00:23:33.890 align:middle line:84%
But even if you take all
the water away and have

00:23:33.890 --> 00:23:37.130 align:middle line:84%
a vacuated chamber, you still
have light waves traveling

00:23:37.130 --> 00:23:38.780 align:middle line:90%
in the remaining aether.

00:23:38.780 --> 00:23:40.815 align:middle line:84%
That was how they
organized these studies.

00:23:40.815 --> 00:23:42.270 align:middle line:90%
All right, so much for light.

00:23:42.270 --> 00:23:45.510 align:middle line:84%
What about other things like
electricity and magnetism?

00:23:45.510 --> 00:23:48.900 align:middle line:84%
So again, during Faraday's
early career-- by this point,

00:23:48.900 --> 00:23:52.440 align:middle line:84%
he was already ensconced
at the Royal Institution,

00:23:52.440 --> 00:23:55.860 align:middle line:84%
still working closely with
people like Humphry Davy--

00:23:55.860 --> 00:23:59.970 align:middle line:84%
there was a headline-grabbing
event not found in Britain,

00:23:59.970 --> 00:24:02.320 align:middle line:90%
but actually nearby in Denmark.

00:24:02.320 --> 00:24:04.560 align:middle line:84%
So when another natural
philosopher, Hans Christian

00:24:04.560 --> 00:24:06.553 align:middle line:84%
Oersted was giving
a public lecture

00:24:06.553 --> 00:24:08.220 align:middle line:84%
very much like at the
Royal Institution,

00:24:08.220 --> 00:24:11.430 align:middle line:84%
same kind of format-- these
were popular throughout Europe.

00:24:11.430 --> 00:24:12.930 align:middle line:84%
Oersted was giving
a public lecture.

00:24:12.930 --> 00:24:15.720 align:middle line:84%
And he accidentally discovered,
in the midst of his talk,

00:24:15.720 --> 00:24:17.560 align:middle line:84%
something that he
really didn't expect.

00:24:17.560 --> 00:24:19.920 align:middle line:84%
He had an apparatus that
looked a lot like this,

00:24:19.920 --> 00:24:21.720 align:middle line:90%
a kind of conducting coil.

00:24:21.720 --> 00:24:25.080 align:middle line:90%
So this is a conducting wire.

00:24:25.080 --> 00:24:29.310 align:middle line:84%
And he had nearby a compass,
so a magnetic needle.

00:24:29.310 --> 00:24:32.310 align:middle line:84%
And he found that when current
was flowing through the wire,

00:24:32.310 --> 00:24:34.660 align:middle line:90%
the needle would be deflected.

00:24:34.660 --> 00:24:35.910 align:middle line:90%
He did not expect that at all.

00:24:35.910 --> 00:24:37.368 align:middle line:84%
None of his audience
expected that.

00:24:37.368 --> 00:24:38.860 align:middle line:90%
No one else expected that.

00:24:38.860 --> 00:24:42.460 align:middle line:84%
Somehow the electric current,
the flow of electricity,

00:24:42.460 --> 00:24:44.260 align:middle line:90%
could affect--

00:24:44.260 --> 00:24:45.760 align:middle line:90%
could induce magnetic effects.

00:24:45.760 --> 00:24:48.400 align:middle line:84%
It could change the behavior
of that magnetic needle

00:24:48.400 --> 00:24:50.110 align:middle line:90%
of the compass.

00:24:50.110 --> 00:24:51.755 align:middle line:90%
This became headline news.

00:24:51.755 --> 00:24:53.380 align:middle line:84%
If there had been
19th century Twitter,

00:24:53.380 --> 00:24:55.932 align:middle line:84%
this would have broken
Twitter, #theneedlemoved.

00:24:55.932 --> 00:24:57.640 align:middle line:84%
I'm sure this was
literally what everyone

00:24:57.640 --> 00:24:59.080 align:middle line:84%
was super excited
about, including

00:24:59.080 --> 00:25:00.790 align:middle line:90%
people like Michael Faraday.

00:25:00.790 --> 00:25:02.860 align:middle line:84%
This was, for Faraday,
exactly this kind

00:25:02.860 --> 00:25:05.290 align:middle line:84%
of interconversion of forces
that he was so interested in,

00:25:05.290 --> 00:25:07.210 align:middle line:84%
partly from his
Sandemanian faith,

00:25:07.210 --> 00:25:09.820 align:middle line:84%
partly because he was a natural
philosopher of his time.

00:25:09.820 --> 00:25:12.910 align:middle line:84%
So not only does he quickly
replicate Oersted's finding--

00:25:12.910 --> 00:25:16.750 align:middle line:84%
he separately finds that he can
get electric current to move

00:25:16.750 --> 00:25:18.130 align:middle line:90%
a compass needle--

00:25:18.130 --> 00:25:20.980 align:middle line:90%
he then finds the inverse.

00:25:20.980 --> 00:25:23.560 align:middle line:84%
As shown here, he
takes a bar magnet

00:25:23.560 --> 00:25:27.422 align:middle line:84%
and starts moving it in a
pattern near a conducting coil

00:25:27.422 --> 00:25:29.005 align:middle line:84%
from which he can
measure the current.

00:25:29.005 --> 00:25:30.670 align:middle line:90%
He has an ammeter attached.

00:25:30.670 --> 00:25:32.470 align:middle line:84%
And he finds the
inverse can happen

00:25:32.470 --> 00:25:36.820 align:middle line:84%
as well, that a moving magnet,
a changing magnetic effect

00:25:36.820 --> 00:25:40.190 align:middle line:90%
can induce an electric current.

00:25:40.190 --> 00:25:44.110 align:middle line:84%
So he's investigating induction,
both electric currents inducing

00:25:44.110 --> 00:25:46.750 align:middle line:84%
magnetic effects, magnetic
fields or magnetic effects

00:25:46.750 --> 00:25:48.340 align:middle line:90%
inducing electric effects.

00:25:48.340 --> 00:25:50.620 align:middle line:84%
And he wants to keep
track of this stuff.

00:25:50.620 --> 00:25:52.750 align:middle line:84%
So he starts sketching
these helpful doodles

00:25:52.750 --> 00:25:54.970 align:middle line:90%
that he calls lines of force.

00:25:54.970 --> 00:25:56.620 align:middle line:84%
As far as Faraday
was concerned, these

00:25:56.620 --> 00:25:59.320 align:middle line:84%
were lines of force to
depict the underlying

00:25:59.320 --> 00:26:00.310 align:middle line:90%
state of the aether.

00:26:00.310 --> 00:26:02.590 align:middle line:84%
Remember, everything, as
far as he's concerned,

00:26:02.590 --> 00:26:04.750 align:middle line:84%
is what's going on with
the underlying aether.

00:26:04.750 --> 00:26:06.970 align:middle line:84%
So it must be, he
begins to reason

00:26:06.970 --> 00:26:10.690 align:middle line:84%
with these pictorial aids,
that the aether could

00:26:10.690 --> 00:26:13.270 align:middle line:84%
be put under states
of strain or tension.

00:26:13.270 --> 00:26:16.990 align:middle line:84%
If I have an electric charge
that I place within the aether,

00:26:16.990 --> 00:26:20.140 align:middle line:84%
it's going to have an effect
and put a strain on the aether

00:26:20.140 --> 00:26:21.250 align:middle line:90%
immediately around it.

00:26:21.250 --> 00:26:23.170 align:middle line:84%
So he draws these
lines of force,

00:26:23.170 --> 00:26:26.410 align:middle line:84%
emanating outward from
positive electric charge

00:26:26.410 --> 00:26:29.740 align:middle line:84%
or collapsing in toward a
negative electric charge.

00:26:29.740 --> 00:26:33.730 align:middle line:84%
And then he begins using
his middle school level

00:26:33.730 --> 00:26:34.330 align:middle line:90%
mathematics.

00:26:34.330 --> 00:26:36.880 align:middle line:84%
He'd had a little bit of
geometry before leaving

00:26:36.880 --> 00:26:37.960 align:middle line:90%
formal schooling.

00:26:37.960 --> 00:26:39.950 align:middle line:90%
And he puts that to work.

00:26:39.950 --> 00:26:45.080 align:middle line:84%
He supposes, what if the number
of lines that come outward

00:26:45.080 --> 00:26:47.060 align:middle line:84%
from a positive
charge is fixed and is

00:26:47.060 --> 00:26:49.610 align:middle line:84%
proportional to the amount
of that electric charge?

00:26:49.610 --> 00:26:53.390 align:middle line:84%
So a charge of, say, seven units
would have seven of these lines

00:26:53.390 --> 00:26:56.450 align:middle line:84%
radiating outward, affecting
the surrounding aether.

00:26:56.450 --> 00:26:58.400 align:middle line:84%
A charge of 10 units
would have 10 lines

00:26:58.400 --> 00:27:00.440 align:middle line:90%
radiating outward and so on.

00:27:00.440 --> 00:27:03.170 align:middle line:84%
Then you can imagine what
would happen if you surrounded

00:27:03.170 --> 00:27:06.350 align:middle line:84%
that positive charge with
a kind of imaginary sphere

00:27:06.350 --> 00:27:08.240 align:middle line:90%
at some distant radius.

00:27:08.240 --> 00:27:11.960 align:middle line:84%
Then you can ask, how
many lines per unit area

00:27:11.960 --> 00:27:14.540 align:middle line:84%
will cross through
that imagined sphere?

00:27:14.540 --> 00:27:16.640 align:middle line:84%
The density of field
lines will fall out.

00:27:16.640 --> 00:27:19.250 align:middle line:84%
The lines are dispersing as you
get further and further away

00:27:19.250 --> 00:27:20.510 align:middle line:90%
from the electric charge.

00:27:20.510 --> 00:27:23.150 align:middle line:84%
So the density of field
lines, how many of those lines

00:27:23.150 --> 00:27:26.570 align:middle line:84%
will intersect a
unit of that sphere,

00:27:26.570 --> 00:27:28.550 align:middle line:84%
will fall off like
1 over r squared?

00:27:28.550 --> 00:27:30.440 align:middle line:84%
You take the fixed
number of lines,

00:27:30.440 --> 00:27:32.540 align:middle line:84%
divide by the surface
area that you've

00:27:32.540 --> 00:27:34.430 align:middle line:90%
surrounded that charge by.

00:27:34.430 --> 00:27:37.442 align:middle line:84%
The area goes by
like 4 pi r squared.

00:27:37.442 --> 00:27:39.650 align:middle line:84%
So the density should fall
off like 1 over r squared.

00:27:39.650 --> 00:27:42.130 align:middle line:84%
That was really
exciting to Faraday

00:27:42.130 --> 00:27:44.260 align:middle line:84%
because he had learned,
again, from French scholars

00:27:44.260 --> 00:27:46.510 align:middle line:84%
like Coulomb, not too
long before really,

00:27:46.510 --> 00:27:50.350 align:middle line:84%
just in Faraday's own
childhood, that there

00:27:50.350 --> 00:27:54.340 align:middle line:84%
was this Newton-like force
of attraction or repulsion

00:27:54.340 --> 00:27:55.840 align:middle line:90%
among electric charges.

00:27:55.840 --> 00:27:58.270 align:middle line:90%
We now call it Coulomb's law.

00:27:58.270 --> 00:28:01.510 align:middle line:84%
The magnitude of the force
between two electric charges

00:28:01.510 --> 00:28:04.030 align:middle line:84%
falls off like 1 over the
square of the distance,

00:28:04.030 --> 00:28:08.500 align:middle line:84%
exactly as Faraday had reasoned
toward by thinking about states

00:28:08.500 --> 00:28:12.760 align:middle line:84%
of tension in the aether and how
that strain would be dissipated

00:28:12.760 --> 00:28:15.460 align:middle line:90%
at more and more distance.

00:28:15.460 --> 00:28:16.252 align:middle line:90%
So Faraday went on.

00:28:16.252 --> 00:28:17.752 align:middle line:84%
Remember, he was
so excited not only

00:28:17.752 --> 00:28:19.300 align:middle line:84%
about one topic
like electricity,

00:28:19.300 --> 00:28:20.640 align:middle line:90%
but also about magnetism.

00:28:20.640 --> 00:28:24.060 align:middle line:84%
What if you plop a bar
magnet down in the aether?

00:28:24.060 --> 00:28:27.420 align:middle line:84%
Then he could do that with
these things like iron filings

00:28:27.420 --> 00:28:29.580 align:middle line:84%
and trace out the kind
of lines of influence

00:28:29.580 --> 00:28:31.497 align:middle line:84%
around the magnets--
something you've probably

00:28:31.497 --> 00:28:32.580 align:middle line:90%
done even as a child.

00:28:32.580 --> 00:28:34.710 align:middle line:84%
And he realized that he
could make sense of this

00:28:34.710 --> 00:28:38.070 align:middle line:84%
also in terms of lines of force,
that these iron filings were

00:28:38.070 --> 00:28:41.940 align:middle line:84%
helping him map out the
magnetic effects, the strain

00:28:41.940 --> 00:28:45.330 align:middle line:84%
that the bar magnet, with its
north and south magnetic poles,

00:28:45.330 --> 00:28:47.790 align:middle line:84%
could do for the
surrounding aether.

00:28:47.790 --> 00:28:49.830 align:middle line:84%
What's really
interesting here is

00:28:49.830 --> 00:28:52.380 align:middle line:84%
that Faraday starts to say
that sometimes forces might not

00:28:52.380 --> 00:28:55.770 align:middle line:84%
be transmitted only along
the straight line shortest

00:28:55.770 --> 00:29:00.120 align:middle line:84%
path between A and
B. That was the rule

00:29:00.120 --> 00:29:02.040 align:middle line:90%
for all Newton-like forces.

00:29:02.040 --> 00:29:04.470 align:middle line:84%
The magnetic lines
of force would bend.

00:29:04.470 --> 00:29:05.220 align:middle line:90%
They'd curve.

00:29:05.220 --> 00:29:08.100 align:middle line:84%
They would have
these looping paths.

00:29:08.100 --> 00:29:10.110 align:middle line:84%
And so maybe the magnetic
force did not always

00:29:10.110 --> 00:29:12.300 align:middle line:90%
go on shortest distance paths.

00:29:12.300 --> 00:29:14.340 align:middle line:84%
And more generally,
Faraday starts saying,

00:29:14.340 --> 00:29:16.570 align:middle line:84%
let's keep track of all
these states of tension

00:29:16.570 --> 00:29:17.440 align:middle line:90%
in the aether.

00:29:17.440 --> 00:29:19.990 align:middle line:84%
He introduces this notion
of the field, something

00:29:19.990 --> 00:29:23.110 align:middle line:84%
that physicists to this
day use every single day

00:29:23.110 --> 00:29:24.100 align:middle line:90%
of our careers.

00:29:24.100 --> 00:29:26.350 align:middle line:90%
We now call it field theory.

00:29:26.350 --> 00:29:28.930 align:middle line:84%
It largely comes as being
introduced by Faraday,

00:29:28.930 --> 00:29:32.500 align:middle line:84%
as he tries to make sense
of, with convenient mnemonic

00:29:32.500 --> 00:29:36.520 align:middle line:84%
devices, these states
of strain in the aether.

00:29:36.520 --> 00:29:38.530 align:middle line:84%
So the electric and
magnetic fields,

00:29:38.530 --> 00:29:40.720 align:middle line:84%
as far as Faraday was
concerned, were simply

00:29:40.720 --> 00:29:42.820 align:middle line:84%
ways of characterizing
the local state

00:29:42.820 --> 00:29:46.480 align:middle line:84%
of the aether as represented
by these lines of force.

00:29:46.480 --> 00:29:48.010 align:middle line:84%
What were the
stresses and strains

00:29:48.010 --> 00:29:49.720 align:middle line:90%
at that spot in the aether?

00:29:49.720 --> 00:29:51.460 align:middle line:84%
How do they change
if I go to this spot?

00:29:51.460 --> 00:29:53.740 align:middle line:84%
How do they change at
that one spot over time?

00:29:53.740 --> 00:29:55.990 align:middle line:84%
This is what he says is
the notion of a field.

00:29:55.990 --> 00:30:00.470 align:middle line:84%
It's just shorthand for the
state of the underlying aether.

00:30:00.470 --> 00:30:01.640 align:middle line:90%
But is that real?

00:30:01.640 --> 00:30:05.575 align:middle line:84%
You might still wonder, is the
aether just a helpful thing

00:30:05.575 --> 00:30:06.200 align:middle line:90%
to think about?

00:30:06.200 --> 00:30:07.575 align:middle line:84%
Or did Faraday
and his colleagues

00:30:07.575 --> 00:30:09.320 align:middle line:84%
think it was really
part of the world?

00:30:09.320 --> 00:30:11.742 align:middle line:84%
And it was
unambiguously, for them,

00:30:11.742 --> 00:30:13.700 align:middle line:84%
part of the world, not
just convenient to think

00:30:13.700 --> 00:30:17.000 align:middle line:84%
about, but really the stuff
from which the world was made.

00:30:17.000 --> 00:30:19.880 align:middle line:84%
And we'll talk about this in
some more detail over coming

00:30:19.880 --> 00:30:21.020 align:middle line:90%
class sessions.

00:30:21.020 --> 00:30:24.110 align:middle line:84%
Faraday thought he found
the golden proof in 1845.

00:30:24.110 --> 00:30:27.140 align:middle line:84%
And now he's a much
more senior researcher.

00:30:27.140 --> 00:30:29.210 align:middle line:84%
How could you demonstrate
the aether was real?

00:30:29.210 --> 00:30:31.610 align:middle line:84%
Well, let's study
the interaction

00:30:31.610 --> 00:30:34.580 align:middle line:84%
between magnetic fields
and the behavior of light,

00:30:34.580 --> 00:30:36.980 align:middle line:90%
in particular polarized light.

00:30:36.980 --> 00:30:39.950 align:middle line:84%
This is now known as the Faraday
effect or the Faraday rotation.

00:30:39.950 --> 00:30:41.420 align:middle line:84%
It's one of these things
that's literally still

00:30:41.420 --> 00:30:42.128 align:middle line:90%
in our textbooks.

00:30:42.128 --> 00:30:43.500 align:middle line:90%
We use it all the time.

00:30:43.500 --> 00:30:45.830 align:middle line:84%
It comes from Faraday's
efforts to prove

00:30:45.830 --> 00:30:48.170 align:middle line:84%
to himself and his
colleagues that we are all

00:30:48.170 --> 00:30:52.570 align:middle line:84%
immersed in this
elastic, bendable aether.

00:30:52.570 --> 00:30:54.560 align:middle line:84%
So Faraday and his
peers-- the idea

00:30:54.560 --> 00:30:57.200 align:middle line:84%
was the following, that
if you put the aether

00:30:57.200 --> 00:31:02.600 align:middle line:84%
under local strain by putting
a local magnetic field

00:31:02.600 --> 00:31:05.120 align:middle line:84%
in some region of space,
that magnetic field

00:31:05.120 --> 00:31:07.760 align:middle line:84%
would have a twisting
or curling effect,

00:31:07.760 --> 00:31:10.760 align:middle line:84%
a kind of torsion on
the underlying aether.

00:31:10.760 --> 00:31:12.470 align:middle line:84%
And then this light
wave is traveling

00:31:12.470 --> 00:31:14.930 align:middle line:84%
through this deformed
local bit of the aether.

00:31:14.930 --> 00:31:16.280 align:middle line:90%
So its behavior will change.

00:31:16.280 --> 00:31:20.360 align:middle line:84%
And in particular, what's called
the plane of polarization,

00:31:20.360 --> 00:31:25.310 align:middle line:84%
the direction in which its
wave is waving, will rotate.

00:31:25.310 --> 00:31:28.340 align:middle line:84%
There'll be some angle,
shown here as the angle beta.

00:31:28.340 --> 00:31:30.200 align:middle line:84%
So if the field
starts out, the wave

00:31:30.200 --> 00:31:32.000 align:middle line:84%
starts out waving
in one direction,

00:31:32.000 --> 00:31:34.432 align:middle line:84%
it will literally be
rotated by some angle.

00:31:34.432 --> 00:31:36.890 align:middle line:84%
The amount of rotation depends
on the strength of the field

00:31:36.890 --> 00:31:41.160 align:middle line:84%
and the distance through which
this aether is under tension.

00:31:41.160 --> 00:31:43.580 align:middle line:84%
This is not just a
good idea for 1845.

00:31:43.580 --> 00:31:47.340 align:middle line:84%
It's how we make sense of the
world today, minus the aether

00:31:47.340 --> 00:31:47.840 align:middle line:90%
part.

00:31:47.840 --> 00:31:50.257 align:middle line:84%
But it comes from trying to
figure out is the aether real.

00:31:50.257 --> 00:31:52.250 align:middle line:84%
Just last year, I had
fun working with a really

00:31:52.250 --> 00:31:53.300 align:middle line:90%
terrific UROP student.

00:31:53.300 --> 00:31:55.670 align:middle line:84%
Some of you might
know Max Daschner.

00:31:55.670 --> 00:31:58.190 align:middle line:84%
He and my friend Joe
Formaggio in physics,

00:31:58.190 --> 00:32:00.690 align:middle line:84%
we used this exact
same phenomenon,

00:32:00.690 --> 00:32:03.180 align:middle line:84%
that an external
magnetic field will

00:32:03.180 --> 00:32:06.180 align:middle line:84%
rotate the plane of
polarization of light,

00:32:06.180 --> 00:32:09.330 align:middle line:84%
not to talk about the aether,
but as a way to jam quantum

00:32:09.330 --> 00:32:10.660 align:middle line:90%
encryption indefinitely.

00:32:10.660 --> 00:32:13.270 align:middle line:84%
So in this hyper-modern
physics of the moment,

00:32:13.270 --> 00:32:15.355 align:middle line:84%
we're still going back
to Faraday rotation.

00:32:15.355 --> 00:32:16.980 align:middle line:84%
And yet, Faraday
thought this was a way

00:32:16.980 --> 00:32:18.188 align:middle line:90%
of characterizing the aether.

00:32:18.188 --> 00:32:19.470 align:middle line:90%
I just love that.

00:32:19.470 --> 00:32:22.350 align:middle line:84%
We're going to see many examples
of that throughout the class.

00:32:22.350 --> 00:32:23.772 align:middle line:90%
Let me wrap up the Faraday part.

00:32:23.772 --> 00:32:25.480 align:middle line:84%
I'll pause again for
some more questions.

00:32:25.480 --> 00:32:26.910 align:middle line:84%
So Faraday, as
we've seen, worked

00:32:26.910 --> 00:32:30.120 align:middle line:84%
on a variety of phenomena,
what we would call separately

00:32:30.120 --> 00:32:33.570 align:middle line:84%
chemistry, and optics,
electrolysis, even physiology,

00:32:33.570 --> 00:32:35.280 align:middle line:90%
let alone electromagnetism.

00:32:35.280 --> 00:32:38.370 align:middle line:84%
He was especially interested
in the interconvertibility

00:32:38.370 --> 00:32:39.960 align:middle line:90%
of forces partly.

00:32:39.960 --> 00:32:41.490 align:middle line:90%
A compelling case had been made.

00:32:41.490 --> 00:32:43.440 align:middle line:84%
This resonated
especially closely

00:32:43.440 --> 00:32:49.410 align:middle line:84%
with his religious minority
views, his Sandemanian views

00:32:49.410 --> 00:32:53.820 align:middle line:84%
and that there was this kind
of underlying unity of nature.

00:32:53.820 --> 00:32:55.980 align:middle line:84%
Faraday was never trained
in advanced mathematics.

00:32:55.980 --> 00:32:59.400 align:middle line:84%
He had really just the rudiments
of this pictorial geometry,

00:32:59.400 --> 00:33:01.980 align:middle line:84%
like we saw with
the lines of force.

00:33:01.980 --> 00:33:03.660 align:middle line:90%
He was an apprenticed tinkerer.

00:33:03.660 --> 00:33:06.840 align:middle line:84%
He had tremendous manual
dexterity skills and also

00:33:06.840 --> 00:33:07.980 align:middle line:90%
great cleverness.

00:33:07.980 --> 00:33:10.230 align:middle line:84%
He became this leading
experimentalist

00:33:10.230 --> 00:33:13.290 align:middle line:84%
based on not formal
training at a university,

00:33:13.290 --> 00:33:15.840 align:middle line:84%
but being apprenticed
as a bookbinder,

00:33:15.840 --> 00:33:18.390 align:middle line:84%
and then essentially
apprenticed as Humphry Davy's

00:33:18.390 --> 00:33:20.190 align:middle line:84%
assistant at the
Royal Institution,

00:33:20.190 --> 00:33:22.020 align:middle line:90%
not at a university.

00:33:22.020 --> 00:33:23.760 align:middle line:84%
He introduces these
things which we still

00:33:23.760 --> 00:33:27.000 align:middle line:84%
use to this day, like lines
of force, and then fields.

00:33:27.000 --> 00:33:29.700 align:middle line:84%
For Faraday, these were ways
of characterizing the one

00:33:29.700 --> 00:33:31.800 align:middle line:84%
big prize of natural
studies, meaning

00:33:31.800 --> 00:33:33.960 align:middle line:84%
the aether, the
medium within which

00:33:33.960 --> 00:33:36.595 align:middle line:84%
all these things unfolded, and
the reason as far as Faraday

00:33:36.595 --> 00:33:38.970 align:middle line:84%
was concerned why there could
be this interconvertibility

00:33:38.970 --> 00:33:40.900 align:middle line:90%
and unity.

00:33:40.900 --> 00:33:44.070 align:middle line:84%
So in place of Newtonian action
at a distance that somehow

00:33:44.070 --> 00:33:46.530 align:middle line:84%
one object could
instantaneously affect or exert

00:33:46.530 --> 00:33:49.710 align:middle line:84%
a force on another one,
Faraday starts explaining

00:33:49.710 --> 00:33:51.490 align:middle line:90%
all physical phenomena--

00:33:51.490 --> 00:33:53.430 align:middle line:84%
He has the ambition
to explain everything

00:33:53.430 --> 00:33:55.050 align:middle line:84%
in terms of these
local fields there's

00:33:55.050 --> 00:33:58.470 align:middle line:84%
a local disturbance here
at position x equals 1

00:33:58.470 --> 00:34:01.770 align:middle line:84%
and it could convey effects
to its nearest neighbors

00:34:01.770 --> 00:34:03.070 align:middle line:90%
point by point.

00:34:03.070 --> 00:34:05.722 align:middle line:84%
So you have to study how
these fields change over time

00:34:05.722 --> 00:34:06.930 align:middle line:90%
and spread out through space.

00:34:06.930 --> 00:34:09.540 align:middle line:84%
Everything is now meant
to be local fields, not

00:34:09.540 --> 00:34:10.770 align:middle line:90%
action at a distance.

00:34:10.770 --> 00:34:12.728 align:middle line:84%
Let me pause there again
and ask any questions.

00:34:12.728 --> 00:34:15.301 align:middle line:84%
I see at least one
more item in the chat.

00:34:15.301 --> 00:34:16.884 align:middle line:84%
Any questions on the
Faraday material?

00:34:16.884 --> 00:34:22.320 align:middle line:90%


00:34:22.320 --> 00:34:22.978 align:middle line:90%
Very good.

00:34:22.978 --> 00:34:25.270 align:middle line:84%
So it was common to attend
the public science lectures.

00:34:25.270 --> 00:34:27.906 align:middle line:84%
And in fact, it was seen
as a way of being elegant.

00:34:27.906 --> 00:34:29.489 align:middle line:84%
Again, this is really
fascinating work

00:34:29.489 --> 00:34:33.239 align:middle line:84%
on the social class emulation
going on, especially

00:34:33.239 --> 00:34:36.340 align:middle line:84%
heightened, as you might know,
in Britain in this time period.

00:34:36.340 --> 00:34:39.570 align:middle line:84%
So to be considered
a fashionable lady

00:34:39.570 --> 00:34:41.699 align:middle line:84%
in the terminology
of the day, one

00:34:41.699 --> 00:34:43.770 align:middle line:84%
had to show or at
least feign interest

00:34:43.770 --> 00:34:45.510 align:middle line:84%
in a range of
topics, one of which

00:34:45.510 --> 00:34:50.492 align:middle line:84%
was these elegant demonstrations
of the glories of the world.

00:34:50.492 --> 00:34:51.909 align:middle line:84%
For many people,
this, by the way,

00:34:51.909 --> 00:34:54.330 align:middle line:84%
had a kind of overt
religious significance,

00:34:54.330 --> 00:34:56.133 align:middle line:90%
a kind of natural theology.

00:34:56.133 --> 00:34:58.050 align:middle line:84%
Not for everyone, but
for many in this period,

00:34:58.050 --> 00:35:01.260 align:middle line:84%
the idea was that learning
about how electric shocks make

00:35:01.260 --> 00:35:05.730 align:middle line:84%
frogs' legs twitch
or how a magnetic bar

00:35:05.730 --> 00:35:06.840 align:middle line:90%
magnet can change--

00:35:06.840 --> 00:35:08.520 align:middle line:84%
can induce electric
current, these

00:35:08.520 --> 00:35:12.630 align:middle line:84%
are ways of revealing the
glory of God's creation,

00:35:12.630 --> 00:35:14.130 align:middle line:84%
as many people
argued at the time.

00:35:14.130 --> 00:35:16.380 align:middle line:84%
So It was seen as
actually a function

00:35:16.380 --> 00:35:19.380 align:middle line:90%
of moral or spiritual uplift.

00:35:19.380 --> 00:35:22.900 align:middle line:84%
And therefore, again, according
to the assumptions that--

00:35:22.900 --> 00:35:24.590 align:middle line:84%
we might say prejudices
at the time--

00:35:24.590 --> 00:35:26.860 align:middle line:84%
therefore, all the more
important for young women

00:35:26.860 --> 00:35:29.200 align:middle line:84%
to be exposed to this, was
the thinking of the time,

00:35:29.200 --> 00:35:31.240 align:middle line:84%
with their tender,
moral souls that

00:35:31.240 --> 00:35:34.390 align:middle line:84%
needed special care, again
to speak in their idiom,

00:35:34.390 --> 00:35:35.538 align:middle line:90%
not my own.

00:35:35.538 --> 00:35:37.330 align:middle line:84%
So there actually was
a great encouragement

00:35:37.330 --> 00:35:39.910 align:middle line:84%
for women to attend these
public lectures, not,

00:35:39.910 --> 00:35:42.460 align:middle line:84%
as you might expect, to
move into the laboratory,

00:35:42.460 --> 00:35:43.600 align:middle line:90%
not to do the work.

00:35:43.600 --> 00:35:47.050 align:middle line:84%
That was an almost uniquely
male enclave in this period,

00:35:47.050 --> 00:35:48.700 align:middle line:84%
certainly in the
Royal Institution.

00:35:48.700 --> 00:35:52.420 align:middle line:84%
But to be exposed, to
be part of the broader,

00:35:52.420 --> 00:35:56.230 align:middle line:84%
polite discussions, it was one
way of showing that you were--

00:35:56.230 --> 00:35:58.000 align:middle line:84%
you had an appropriate
upbringing.

00:35:58.000 --> 00:35:59.170 align:middle line:84%
And again, there's
lots of cool stuff

00:35:59.170 --> 00:36:00.250 align:middle line:84%
I'd be glad to talk
more about that

00:36:00.250 --> 00:36:02.000 align:middle line:84%
or send some references
for more readings.

00:36:02.000 --> 00:36:04.675 align:middle line:84%
The short answer was, yes, to
attend the Christmas Lectures

00:36:04.675 --> 00:36:06.550 align:middle line:84%
at Royal Institute, that
was an awesome thing

00:36:06.550 --> 00:36:08.800 align:middle line:90%
to bring your daughter to.

00:36:08.800 --> 00:36:09.980 align:middle line:90%
But at the time--

00:36:09.980 --> 00:36:12.580 align:middle line:84%
and that's something we'll
see change rather slowly,

00:36:12.580 --> 00:36:14.650 align:middle line:84%
but change over time
throughout the semester--

00:36:14.650 --> 00:36:16.330 align:middle line:84%
At that time, it
was not something

00:36:16.330 --> 00:36:20.200 align:middle line:84%
that was seen as a kind of
acceptable or appropriate day

00:36:20.200 --> 00:36:21.910 align:middle line:90%
job or a career path.

00:36:21.910 --> 00:36:24.370 align:middle line:84%
So that was a very, very
clear gender disparity,

00:36:24.370 --> 00:36:26.710 align:middle line:84%
but a great openness
to have women

00:36:26.710 --> 00:36:30.083 align:middle line:84%
participate in that limited
way in the public lectures.

00:36:30.083 --> 00:36:31.000 align:middle line:90%
So very good question.

00:36:31.000 --> 00:36:35.260 align:middle line:84%
We'll come back to
that theme quite a lot.

00:36:35.260 --> 00:36:36.190 align:middle line:90%
Great questions.

00:36:36.190 --> 00:36:37.100 align:middle line:90%
Oh, that's so good.

00:36:37.100 --> 00:36:40.390 align:middle line:84%
So we'll actually come to some
of that in this very next unit

00:36:40.390 --> 00:36:41.290 align:middle line:90%
right now.

00:36:41.290 --> 00:36:42.610 align:middle line:90%
So partly, I'll just punt.

00:36:42.610 --> 00:36:45.730 align:middle line:84%
But the short answer is there
was a growing recognition

00:36:45.730 --> 00:36:48.730 align:middle line:84%
in just this time period among
many influential government

00:36:48.730 --> 00:36:49.390 align:middle line:90%
leaders--

00:36:49.390 --> 00:36:51.710 align:middle line:84%
not only in Britain, in
many parts of Europe,

00:36:51.710 --> 00:36:53.170 align:middle line:84%
in fact, many parts
of the world--

00:36:53.170 --> 00:36:58.060 align:middle line:84%
China and Japan, certainly North
America, a growing recognition

00:36:58.060 --> 00:37:00.430 align:middle line:84%
this during this
exact time period

00:37:00.430 --> 00:37:02.920 align:middle line:84%
that many nation
states would benefit

00:37:02.920 --> 00:37:05.170 align:middle line:84%
from investing in what
we would now call science

00:37:05.170 --> 00:37:06.940 align:middle line:84%
and technology or
science and engineering.

00:37:06.940 --> 00:37:10.660 align:middle line:84%
So there certainly were hot
button issues, then as now.

00:37:10.660 --> 00:37:13.402 align:middle line:84%
Natural evolution,
Darwin's theory

00:37:13.402 --> 00:37:15.610 align:middle line:84%
of evolution, which comes
just around this time first

00:37:15.610 --> 00:37:19.450 align:middle line:84%
published in 1859, that
becomes yet another flashpoint

00:37:19.450 --> 00:37:21.932 align:middle line:90%
for tension and controversy.

00:37:21.932 --> 00:37:23.890 align:middle line:84%
But for a lot of this
work in what we would now

00:37:23.890 --> 00:37:26.020 align:middle line:84%
call the physical
sciences, as we'll see,

00:37:26.020 --> 00:37:28.690 align:middle line:84%
there was actually a
kind of investment,

00:37:28.690 --> 00:37:31.993 align:middle line:84%
a new kind of priority
in a lot of this work not

00:37:31.993 --> 00:37:33.910 align:middle line:84%
across the board, not
without its own hiccups.

00:37:33.910 --> 00:37:34.940 align:middle line:90%
We'll come to that.

00:37:34.940 --> 00:37:37.340 align:middle line:84%
But it was actually
a turning point

00:37:37.340 --> 00:37:39.350 align:middle line:84%
in a new kind of
investment, partly

00:37:39.350 --> 00:37:41.420 align:middle line:84%
because many of
these places were

00:37:41.420 --> 00:37:44.850 align:middle line:84%
undergoing their own
nation-based industrial

00:37:44.850 --> 00:37:45.350 align:middle line:90%
development.

00:37:45.350 --> 00:37:46.790 align:middle line:84%
And we'll see that actually
even more explicitly

00:37:46.790 --> 00:37:49.042 align:middle line:84%
in the next class, some
of it today with Maxwell

00:37:49.042 --> 00:37:50.000 align:middle line:90%
and in the next lesson.

00:37:50.000 --> 00:37:51.300 align:middle line:90%
It was a great question.

00:37:51.300 --> 00:37:53.430 align:middle line:84%
It's a theme we'll trace
throughout the semester.

00:37:53.430 --> 00:37:56.120 align:middle line:84%
But even in Faraday's
own lifetime,

00:37:56.120 --> 00:37:59.960 align:middle line:84%
that was beginning to
change into a more--

00:37:59.960 --> 00:38:03.030 align:middle line:84%
a higher priority in investment
in exactly these topics.

00:38:03.030 --> 00:38:04.790 align:middle line:90%
Great question.

00:38:04.790 --> 00:38:05.290 align:middle line:90%
Any others?

00:38:05.290 --> 00:38:08.770 align:middle line:90%
Should we press on?

00:38:08.770 --> 00:38:09.590 align:middle line:90%
These are great.

00:38:09.590 --> 00:38:10.510 align:middle line:90%
So keep them coming.

00:38:10.510 --> 00:38:12.220 align:middle line:84%
These are great
historical questions

00:38:12.220 --> 00:38:14.830 align:middle line:84%
to help us think about what
was different back then, what

00:38:14.830 --> 00:38:15.830 align:middle line:90%
might have been similar.

00:38:15.830 --> 00:38:18.130 align:middle line:84%
So we're going to keep
that kind of back and forth

00:38:18.130 --> 00:38:21.170 align:middle line:84%
in mind as we enter now just
the last part for today's class.

00:38:21.170 --> 00:38:23.950 align:middle line:84%
I'm going to talk about William
Thompson and James Clerk

00:38:23.950 --> 00:38:25.330 align:middle line:90%
Maxwell.

00:38:25.330 --> 00:38:28.990 align:middle line:84%
So as we saw at least
briefly, Faraday

00:38:28.990 --> 00:38:31.690 align:middle line:84%
had very little formal
training in mathematics.

00:38:31.690 --> 00:38:34.030 align:middle line:84%
And he used very little in
his own studies, his very

00:38:34.030 --> 00:38:35.068 align:middle line:90%
voluminous studies.

00:38:35.068 --> 00:38:36.610 align:middle line:84%
And that's not
surprising, given what

00:38:36.610 --> 00:38:39.850 align:middle line:84%
we know about his own early
childhood and education.

00:38:39.850 --> 00:38:42.040 align:middle line:84%
There's a really
remarkable shift,

00:38:42.040 --> 00:38:44.130 align:middle line:84%
one that I still find
unbelievably fascinating.

00:38:44.130 --> 00:38:46.630 align:middle line:84%
So we're going to spend quite
a bit of time talking about it

00:38:46.630 --> 00:38:48.130 align:middle line:90%
today and next class as well--

00:38:48.130 --> 00:38:51.130 align:middle line:84%
this amazing shift
that begins really

00:38:51.130 --> 00:38:54.310 align:middle line:84%
late in Faraday's own
lifetime, in the middle decades

00:38:54.310 --> 00:38:55.780 align:middle line:90%
of the 19th century.

00:38:55.780 --> 00:38:57.310 align:middle line:84%
It doesn't only
happen in Britain.

00:38:57.310 --> 00:38:58.893 align:middle line:84%
We're going to look
at it because it's

00:38:58.893 --> 00:39:02.840 align:middle line:84%
especially dramatic or
blown out of proportion,

00:39:02.840 --> 00:39:04.690 align:middle line:84%
we might say, in
Britain at places

00:39:04.690 --> 00:39:05.800 align:middle line:90%
like Cambridge University.

00:39:05.800 --> 00:39:07.720 align:middle line:84%
It's happening also
in places like France

00:39:07.720 --> 00:39:10.550 align:middle line:84%
and other parts of the
world, even beyond Europe.

00:39:10.550 --> 00:39:12.280 align:middle line:84%
But Cambridge in
Britain gives us

00:39:12.280 --> 00:39:15.910 align:middle line:84%
the capstone picture of that
in its almost pure essence.

00:39:15.910 --> 00:39:17.980 align:middle line:84%
So there's a real
sea change going on

00:39:17.980 --> 00:39:20.860 align:middle line:84%
between Faraday's early life
and even the later years

00:39:20.860 --> 00:39:24.370 align:middle line:84%
of his own career in
the way that people

00:39:24.370 --> 00:39:27.200 align:middle line:84%
would try to approach natural
phenomena like electricity

00:39:27.200 --> 00:39:28.820 align:middle line:90%
and magnetism.

00:39:28.820 --> 00:39:33.560 align:middle line:84%
Two exemplars, two examples of
that shift are names that might

00:39:33.560 --> 00:39:36.320 align:middle line:84%
be familiar to many of you-- and
we'll spend a little time today

00:39:36.320 --> 00:39:37.910 align:middle line:84%
talking about some
of their work--

00:39:37.910 --> 00:39:41.780 align:middle line:84%
William Thompson, who was
later known as Lord Kelvin.

00:39:41.780 --> 00:39:45.350 align:middle line:84%
That's the same Kelvin from
the Kelvin temperature scale,

00:39:45.350 --> 00:39:48.630 align:middle line:84%
absolute temperature familiar
to you, and many other things.

00:39:48.630 --> 00:39:51.470 align:middle line:84%
So Thompson on one hand
and James Clerk Maxwell

00:39:51.470 --> 00:39:52.230 align:middle line:90%
on the other.

00:39:52.230 --> 00:39:54.500 align:middle line:84%
Again, I'm sure Maxwell's
a familiar name, things

00:39:54.500 --> 00:39:56.550 align:middle line:84%
like Maxwell's equations
and all the rest.

00:39:56.550 --> 00:39:59.570 align:middle line:84%
So these two folks were
about two generations

00:39:59.570 --> 00:40:00.710 align:middle line:90%
younger than Faraday.

00:40:00.710 --> 00:40:03.800 align:middle line:84%
They were coming of age
when Faraday was already

00:40:03.800 --> 00:40:06.380 align:middle line:84%
a well-known
natural philosopher.

00:40:06.380 --> 00:40:08.630 align:middle line:90%
They pick up on Faraday's work.

00:40:08.630 --> 00:40:11.510 align:middle line:84%
They were avid readers
of Faraday's books, often

00:40:11.510 --> 00:40:13.310 align:middle line:84%
monographs, not
just his articles.

00:40:13.310 --> 00:40:16.580 align:middle line:84%
And they begin to translate
it into a very powerful

00:40:16.580 --> 00:40:18.170 align:middle line:84%
mathematical
formalism of the sort

00:40:18.170 --> 00:40:21.710 align:middle line:84%
that Faraday had had no
inkling of whatsoever.

00:40:21.710 --> 00:40:24.980 align:middle line:84%
It turns out both Thompson and
Maxwell were born in Scotland.

00:40:24.980 --> 00:40:28.130 align:middle line:84%
They were not from London or the
immediate English surroundings.

00:40:28.130 --> 00:40:29.480 align:middle line:90%
They were both Scottish-born.

00:40:29.480 --> 00:40:33.410 align:middle line:84%
They both moved to Cambridge
for their formal university

00:40:33.410 --> 00:40:37.800 align:middle line:84%
training in the middle
decades of the 19th century.

00:40:37.800 --> 00:40:40.345 align:middle line:84%
So both Thompson and Maxwell
became deeply involved

00:40:40.345 --> 00:40:42.470 align:middle line:84%
coming exactly to the
question that was raised just

00:40:42.470 --> 00:40:44.330 align:middle line:90%
in that last question period.

00:40:44.330 --> 00:40:45.890 align:middle line:84%
They became deeply
involved with what

00:40:45.890 --> 00:40:49.790 align:middle line:84%
we might call engineering
aspects or applications

00:40:49.790 --> 00:40:52.520 align:middle line:84%
of natural philosophy,
all around the physics

00:40:52.520 --> 00:40:53.210 align:middle line:90%
of the aether.

00:40:53.210 --> 00:40:55.280 align:middle line:84%
They had both had
very long, illustrious

00:40:55.280 --> 00:40:58.520 align:middle line:84%
careers, not only when they
were university students.

00:40:58.520 --> 00:41:01.280 align:middle line:84%
They were pursuing these
very fancy, sophisticated

00:41:01.280 --> 00:41:03.740 align:middle line:84%
mathematical, formal
mathematical approaches

00:41:03.740 --> 00:41:06.560 align:middle line:84%
to electricity, magnetism,
and the physics of the aether

00:41:06.560 --> 00:41:08.870 align:middle line:84%
not only for the sake
of pure mathematics.

00:41:08.870 --> 00:41:10.850 align:middle line:84%
As we'll see, they
were deeply involved

00:41:10.850 --> 00:41:13.580 align:middle line:84%
in very practical
ways with things

00:41:13.580 --> 00:41:15.080 align:middle line:84%
that governments
wanted to pay for,

00:41:15.080 --> 00:41:18.380 align:middle line:84%
like telegraphy and other
practical electro-technical

00:41:18.380 --> 00:41:19.250 align:middle line:90%
devices.

00:41:19.250 --> 00:41:21.320 align:middle line:84%
So among the most
important in their own

00:41:21.320 --> 00:41:23.060 align:middle line:90%
careers was indeed telegraphy.

00:41:23.060 --> 00:41:25.760 align:middle line:84%
So as you know, Britain,
then as now, was an island.

00:41:25.760 --> 00:41:26.720 align:middle line:90%
It's still an island.

00:41:26.720 --> 00:41:28.730 align:middle line:84%
Back then, it had lots
and lots of colonies.

00:41:28.730 --> 00:41:29.780 align:middle line:90%
That's what's changed.

00:41:29.780 --> 00:41:34.490 align:middle line:84%
It was a period of
still rapid acceleration

00:41:34.490 --> 00:41:36.900 align:middle line:84%
of the British
colonial adventure.

00:41:36.900 --> 00:41:40.080 align:middle line:84%
So distant outposts or
so-called possessions,

00:41:40.080 --> 00:41:42.750 align:middle line:84%
territorial possessions,
really all around the world.

00:41:42.750 --> 00:41:44.940 align:middle line:84%
Again, many of you might
recall the old quip,

00:41:44.940 --> 00:41:47.400 align:middle line:84%
that the sun never sets
on the British empire.

00:41:47.400 --> 00:41:50.820 align:middle line:84%
In that time period, there
were colonial holdings

00:41:50.820 --> 00:41:54.460 align:middle line:84%
or territories that spanned
really the entire globe.

00:41:54.460 --> 00:41:56.400 align:middle line:84%
So at any given
time of day, the sun

00:41:56.400 --> 00:41:59.292 align:middle line:84%
was shining on some
British outpost.

00:41:59.292 --> 00:42:00.750 align:middle line:84%
So what do you need
if you're going

00:42:00.750 --> 00:42:04.320 align:middle line:84%
to try to administer a
world-spanning empire?

00:42:04.320 --> 00:42:07.140 align:middle line:84%
You need ways to have
efficient communication.

00:42:07.140 --> 00:42:10.680 align:middle line:84%
And that was an enormous impetus
for things like telegraphy.

00:42:10.680 --> 00:42:12.960 align:middle line:84%
Even with some of
the former colonies,

00:42:12.960 --> 00:42:14.820 align:middle line:84%
like the United
States or Canada,

00:42:14.820 --> 00:42:18.270 align:middle line:84%
some kind of formal
colonial holdings,

00:42:18.270 --> 00:42:20.280 align:middle line:84%
there was still an effort
in this same period,

00:42:20.280 --> 00:42:22.135 align:middle line:84%
the middle decades
of the 19th century,

00:42:22.135 --> 00:42:24.510 align:middle line:84%
to have efficient, long distance
communication for things

00:42:24.510 --> 00:42:26.460 align:middle line:90%
like commerce and diplomacy.

00:42:26.460 --> 00:42:28.020 align:middle line:84%
So there were all
kinds of reasons

00:42:28.020 --> 00:42:32.250 align:middle line:84%
why electromechanical
investigations were

00:42:32.250 --> 00:42:36.890 align:middle line:84%
given a very high priority in
Britain in this time period.

00:42:36.890 --> 00:42:37.840 align:middle line:90%
So we get a taste.

00:42:37.840 --> 00:42:41.470 align:middle line:84%
Here's our first quotation from
that little bit of the Maxwell

00:42:41.470 --> 00:42:42.640 align:middle line:90%
that I assigned.

00:42:42.640 --> 00:42:46.210 align:middle line:84%
Maxwell published this
voluminous treatise,

00:42:46.210 --> 00:42:49.180 align:middle line:90%
a two-volume treatise in 1873.

00:42:49.180 --> 00:42:51.850 align:middle line:84%
The two volumes together
run to about 900 pages.

00:42:51.850 --> 00:42:53.410 align:middle line:90%
It makes for fun beach reading.

00:42:53.410 --> 00:42:55.338 align:middle line:84%
But in the very
opening of the preface,

00:42:55.338 --> 00:42:57.130 align:middle line:84%
we get this really
interesting observation.

00:42:57.130 --> 00:43:00.230 align:middle line:84%
He tells us partly why
anyone should read this book.

00:43:00.230 --> 00:43:02.260 align:middle line:84%
And he says here, the
important applications

00:43:02.260 --> 00:43:05.890 align:middle line:84%
of electromagnetism to
telegraphy have reacted on pure

00:43:05.890 --> 00:43:08.590 align:middle line:84%
science by giving a
commercial value-- and indeed,

00:43:08.590 --> 00:43:11.590 align:middle line:84%
a governmental,
diplomatic value--

00:43:11.590 --> 00:43:13.760 align:middle line:84%
to accurate electrical
measurements

00:43:13.760 --> 00:43:15.460 align:middle line:84%
and by affording
to electricians,

00:43:15.460 --> 00:43:18.550 align:middle line:84%
as say experts in the
field, the use of apparatus

00:43:18.550 --> 00:43:20.560 align:middle line:84%
on a scale which
greatly transcends that

00:43:20.560 --> 00:43:22.390 align:middle line:90%
of any ordinary laboratory.

00:43:22.390 --> 00:43:24.940 align:middle line:84%
They're getting huge
investment to conduct

00:43:24.940 --> 00:43:28.540 align:middle line:84%
very large investigations
with very elaborate apparatus.

00:43:28.540 --> 00:43:31.840 align:middle line:84%
The consequences of this
demand, this government

00:43:31.840 --> 00:43:35.895 align:middle line:84%
and commercial private interest
demand for electrical knowledge

00:43:35.895 --> 00:43:37.520 align:middle line:84%
and of these experimental
opportunities

00:43:37.520 --> 00:43:39.950 align:middle line:84%
for acquiring that
knowledge have already

00:43:39.950 --> 00:43:42.560 align:middle line:84%
been very great,
both in stimulating

00:43:42.560 --> 00:43:44.450 align:middle line:84%
the energies of
advanced electricians

00:43:44.450 --> 00:43:47.180 align:middle line:84%
and in diffusing
among practical men

00:43:47.180 --> 00:43:49.610 align:middle line:84%
a degree of accurate knowledge
which is likely to conduce

00:43:49.610 --> 00:43:51.080 align:middle line:84%
to the general
scientific progress

00:43:51.080 --> 00:43:52.760 align:middle line:84%
of the whole
engineering profession.

00:43:52.760 --> 00:43:54.708 align:middle line:90%
PS, buy my 900-page book.

00:43:54.708 --> 00:43:56.000 align:middle line:90%
It's literally worth something.

00:43:56.000 --> 00:43:57.750 align:middle line:84%
That's what he's
announcing in the opening

00:43:57.750 --> 00:44:00.620 align:middle line:90%
pages of his treatise.

00:44:00.620 --> 00:44:03.890 align:middle line:84%
So let's go a
little bit into some

00:44:03.890 --> 00:44:06.530 align:middle line:84%
of how William Thompson
and James Clerk Maxwell

00:44:06.530 --> 00:44:10.160 align:middle line:84%
start treating Faraday's
intellectual legacy.

00:44:10.160 --> 00:44:12.740 align:middle line:84%
So Thompson began reading
Faraday's books, as well

00:44:12.740 --> 00:44:14.810 align:middle line:84%
as some articles,
as an undergraduate.

00:44:14.810 --> 00:44:19.340 align:middle line:84%
Thompson was still basically 18
and 19 years old at Cambridge

00:44:19.340 --> 00:44:21.590 align:middle line:84%
when he starts
devouring Faraday's work

00:44:21.590 --> 00:44:23.000 align:middle line:90%
or continues to do so.

00:44:23.000 --> 00:44:25.790 align:middle line:84%
He began to realize that he
could put Faraday's work-- he

00:44:25.790 --> 00:44:28.190 align:middle line:84%
could translate it,
on the one hand,

00:44:28.190 --> 00:44:30.680 align:middle line:84%
and also Newton's
work on mechanics

00:44:30.680 --> 00:44:32.850 align:middle line:84%
within the same
mathematical structure.

00:44:32.850 --> 00:44:35.670 align:middle line:84%
This was the stuff that
only in the middle decades

00:44:35.670 --> 00:44:38.850 align:middle line:84%
of the 19th century was
what university students

00:44:38.850 --> 00:44:41.010 align:middle line:84%
at Cambridge, like
William Thompson,

00:44:41.010 --> 00:44:42.390 align:middle line:90%
began to really be immersed in.

00:44:42.390 --> 00:44:45.130 align:middle line:84%
We'll talk much more about
that in the next lecture.

00:44:45.130 --> 00:44:47.370 align:middle line:84%
So he realized that
could make this bridge.

00:44:47.370 --> 00:44:49.650 align:middle line:84%
You could treat all these
disparate phenomena within

00:44:49.650 --> 00:44:52.800 align:middle line:84%
electricity and separately
all these disparate phenomena

00:44:52.800 --> 00:44:55.410 align:middle line:84%
within Newton's mechanics--
blocks sliding down planes,

00:44:55.410 --> 00:44:56.910 align:middle line:90%
the attraction of gravity--

00:44:56.910 --> 00:45:00.840 align:middle line:84%
introduce one similar
mathematical construct,

00:45:00.840 --> 00:45:03.280 align:middle line:84%
the potential, a
scalar potential,

00:45:03.280 --> 00:45:06.450 align:middle line:84%
which is often just labeled
by the Greek letter phi.

00:45:06.450 --> 00:45:08.280 align:middle line:84%
If this is brand new
to you, don't worry.

00:45:08.280 --> 00:45:11.010 align:middle line:84%
If it's very familiar
to you, great.

00:45:11.010 --> 00:45:13.530 align:middle line:84%
The idea is that a
scalar function, a scalar

00:45:13.530 --> 00:45:15.900 align:middle line:84%
field like this
potential, it has

00:45:15.900 --> 00:45:18.300 align:middle line:90%
values at every point in space.

00:45:18.300 --> 00:45:20.140 align:middle line:84%
Those values can
change over time.

00:45:20.140 --> 00:45:22.890 align:middle line:90%
But it doesn't have direction.

00:45:22.890 --> 00:45:24.750 align:middle line:90%
It only has magnitudes.

00:45:24.750 --> 00:45:28.980 align:middle line:84%
You can think of making
representing the temperature

00:45:28.980 --> 00:45:32.190 align:middle line:84%
in the room at every
location in space,

00:45:32.190 --> 00:45:34.830 align:middle line:84%
and then tracking how those
temperature readings change

00:45:34.830 --> 00:45:36.340 align:middle line:84%
over time at each
location in space.

00:45:36.340 --> 00:45:37.830 align:middle line:90%
That's a scalar function.

00:45:37.830 --> 00:45:38.820 align:middle line:90%
Temperature is scalar.

00:45:38.820 --> 00:45:41.310 align:middle line:84%
It has magnitude,
but not direction.

00:45:41.310 --> 00:45:43.080 align:middle line:90%
That's hopefully review.

00:45:43.080 --> 00:45:46.560 align:middle line:84%
Other things, like these fields
that Faraday had introduced

00:45:46.560 --> 00:45:50.270 align:middle line:84%
for electricity magnetism,
those have direction as well as

00:45:50.270 --> 00:45:50.770 align:middle line:90%
magnitude.

00:45:50.770 --> 00:45:52.420 align:middle line:90%
Those are vector quantities.

00:45:52.420 --> 00:45:54.690 align:middle line:84%
Well, as Thompson was
learning to just devour

00:45:54.690 --> 00:45:56.760 align:middle line:84%
in his undergraduate
studies, you

00:45:56.760 --> 00:46:00.330 align:middle line:84%
could create a vector
quantity by taking

00:46:00.330 --> 00:46:02.970 align:middle line:84%
rates of change of a scalar
quantity, what we now

00:46:02.970 --> 00:46:04.240 align:middle line:90%
call the gradient.

00:46:04.240 --> 00:46:08.250 align:middle line:84%
So the gradient, often with this
upside down triangle or nabla

00:46:08.250 --> 00:46:10.980 align:middle line:84%
symbol, the gradient
of a scalar function

00:46:10.980 --> 00:46:12.100 align:middle line:90%
gives a vector function.

00:46:12.100 --> 00:46:14.400 align:middle line:84%
And in particular,
one could represent

00:46:14.400 --> 00:46:16.650 align:middle line:84%
these vector
field-like quantities

00:46:16.650 --> 00:46:19.470 align:middle line:84%
of either electricity
or gravitation

00:46:19.470 --> 00:46:22.740 align:middle line:84%
by first writing down a simpler
mathematical object, the scalar

00:46:22.740 --> 00:46:25.150 align:middle line:90%
function, scalar potential.

00:46:25.150 --> 00:46:27.660 align:middle line:84%
So he first reviews
what had already

00:46:27.660 --> 00:46:30.690 align:middle line:84%
been worked out by a bunch
of 18th century savants

00:46:30.690 --> 00:46:35.100 align:middle line:84%
throughout France, so French
scholars throughout the 1700s

00:46:35.100 --> 00:46:37.050 align:middle line:90%
downstream from Newton himself.

00:46:37.050 --> 00:46:39.120 align:middle line:84%
They had really translated
Newton's own work

00:46:39.120 --> 00:46:42.600 align:middle line:84%
into this language of
directional quantities,

00:46:42.600 --> 00:46:46.090 align:middle line:84%
like fields, like forces
in the gravitational field,

00:46:46.090 --> 00:46:48.900 align:middle line:84%
and then introduced this
simplifying mathematical

00:46:48.900 --> 00:46:50.760 align:middle line:90%
structure of a scalar potential.

00:46:50.760 --> 00:46:52.260 align:middle line:84%
And then you could
study not just

00:46:52.260 --> 00:46:56.310 align:middle line:84%
how the field is related
to changes in that scalar

00:46:56.310 --> 00:46:57.870 align:middle line:90%
function, the gradient.

00:46:57.870 --> 00:47:00.540 align:middle line:84%
You could see how the
field would diverge,

00:47:00.540 --> 00:47:03.240 align:middle line:84%
the divergence of
that field related

00:47:03.240 --> 00:47:06.210 align:middle line:84%
to where the stuff is,
the density of sources

00:47:06.210 --> 00:47:07.920 align:middle line:84%
of gravitation, like
the mass density.

00:47:07.920 --> 00:47:10.560 align:middle line:84%
This was basically a
translation or retranslation

00:47:10.560 --> 00:47:15.030 align:middle line:84%
of Newton's work from
the 1680s, translated

00:47:15.030 --> 00:47:18.240 align:middle line:84%
into this more modern
language throughout the 1700s

00:47:18.240 --> 00:47:22.050 align:middle line:84%
by the French scholars of
directional vector quantities

00:47:22.050 --> 00:47:24.850 align:middle line:84%
being related to derivatives,
to rates of change

00:47:24.850 --> 00:47:26.110 align:middle line:90%
of simpler scalar quantities.

00:47:26.110 --> 00:47:27.527 align:middle line:84%
That was literally
textbook stuff.

00:47:27.527 --> 00:47:30.070 align:middle line:84%
That's what Thompson is
learning as an undergraduate.

00:47:30.070 --> 00:47:34.210 align:middle line:84%
It's now Thompson, not those
French folks in this case,

00:47:34.210 --> 00:47:36.670 align:middle line:84%
who says, can we make
a one-for-one map?

00:47:36.670 --> 00:47:38.950 align:middle line:84%
He's absorbing this
cool Faraday stuff.

00:47:38.950 --> 00:47:42.100 align:middle line:84%
He says, what if we
represent an electric field

00:47:42.100 --> 00:47:44.050 align:middle line:84%
as a state of strain
in the aether,

00:47:44.050 --> 00:47:47.800 align:middle line:84%
exactly as Faraday had begun
groping toward pictorially?

00:47:47.800 --> 00:47:50.380 align:middle line:84%
Those electrical
forces can be forces

00:47:50.380 --> 00:47:52.887 align:middle line:84%
related to an electrical
field, the state of disturbance

00:47:52.887 --> 00:47:53.470 align:middle line:90%
of the aether.

00:47:53.470 --> 00:47:54.670 align:middle line:90%
Sorry, how did that happen?

00:47:54.670 --> 00:47:57.290 align:middle line:90%


00:47:57.290 --> 00:47:58.730 align:middle line:90%
Sorry, gang.

00:47:58.730 --> 00:47:59.870 align:middle line:90%
OK.

00:47:59.870 --> 00:48:02.300 align:middle line:84%
You can then relate the
electric field again

00:48:02.300 --> 00:48:05.570 align:middle line:84%
to rates of change of a simpler
quantity, a scalar potential,

00:48:05.570 --> 00:48:08.340 align:middle line:84%
exactly analogous to
the gravitational case.

00:48:08.340 --> 00:48:12.943 align:middle line:84%
You can then ask how the
electric field is diverging

00:48:12.943 --> 00:48:15.110 align:middle line:84%
throughout space and time,
like those lines of force

00:48:15.110 --> 00:48:17.180 align:middle line:84%
getting more and more spread
out from each other in Faraday's

00:48:17.180 --> 00:48:18.140 align:middle line:90%
simple pictures.

00:48:18.140 --> 00:48:19.910 align:middle line:84%
And that's related to
where the stuff is,

00:48:19.910 --> 00:48:22.490 align:middle line:84%
to the sources of this
electrical disturbance--

00:48:22.490 --> 00:48:25.790 align:middle line:84%
the charge density, how
many electrical charged

00:48:25.790 --> 00:48:28.340 align:middle line:84%
objects are distributed
throughout space

00:48:28.340 --> 00:48:29.810 align:middle line:90%
per unit volume, say.

00:48:29.810 --> 00:48:31.760 align:middle line:90%
So he makes a one-to-one map.

00:48:31.760 --> 00:48:34.760 align:middle line:84%
And he says there's really a
precise mathematical analogy

00:48:34.760 --> 00:48:38.330 align:middle line:84%
between electrical phenomena and
mechanics, like Newton's laws.

00:48:38.330 --> 00:48:41.060 align:middle line:84%
And the mapping is done by
this a little bit more formal,

00:48:41.060 --> 00:48:42.590 align:middle line:90%
more fancy mathematics.

00:48:42.590 --> 00:48:45.170 align:middle line:90%
So far, that's not so shocking.

00:48:45.170 --> 00:48:48.200 align:middle line:84%
Thompson was among the first
to take this textbook side

00:48:48.200 --> 00:48:53.310 align:middle line:84%
and start doing new things with
the Faraday cool E&M stuff.

00:48:53.310 --> 00:48:56.700 align:middle line:84%
Within one year of when Faraday
introduced what we now call

00:48:56.700 --> 00:48:59.430 align:middle line:84%
Faraday rotation-- remember
that thing about the external

00:48:59.430 --> 00:49:01.800 align:middle line:84%
magnetic field rotating
the plane of polarization

00:49:01.800 --> 00:49:02.670 align:middle line:90%
for light--

00:49:02.670 --> 00:49:04.450 align:middle line:90%
Thompson does the same thing.

00:49:04.450 --> 00:49:06.540 align:middle line:84%
He says, oh good, Faraday
has some new cool stuff.

00:49:06.540 --> 00:49:10.830 align:middle line:84%
Let me put that through my very
fancy universe of mathematics.

00:49:10.830 --> 00:49:13.080 align:middle line:84%
So now, he's still
an undergraduate.

00:49:13.080 --> 00:49:15.660 align:middle line:84%
Thompson is now making
brand new stuff--

00:49:15.660 --> 00:49:18.300 align:middle line:84%
not just rewriting
the known regularities

00:49:18.300 --> 00:49:20.580 align:middle line:84%
among electrical
phenomena, but in fact

00:49:20.580 --> 00:49:24.120 align:middle line:84%
formalizing the brand new
stuff, like Faraday rotation.

00:49:24.120 --> 00:49:27.660 align:middle line:84%
He introduces a new kind of
mathematical object, the vector

00:49:27.660 --> 00:49:28.230 align:middle line:90%
potential.

00:49:28.230 --> 00:49:30.780 align:middle line:84%
That was not known even
to the French savant.

00:49:30.780 --> 00:49:32.640 align:middle line:84%
We still call it the
vector potential A.

00:49:32.640 --> 00:49:35.220 align:middle line:84%
And he introduces
a new operator,

00:49:35.220 --> 00:49:37.680 align:middle line:84%
a new way of manipulating
that quantity, which

00:49:37.680 --> 00:49:38.580 align:middle line:90%
we call the curl.

00:49:38.580 --> 00:49:40.920 align:middle line:84%
Thompson invents curl
as an undergraduate.

00:49:40.920 --> 00:49:43.740 align:middle line:84%
Just let that sink
in for a second.

00:49:43.740 --> 00:49:45.182 align:middle line:90%
So the new semester is early.

00:49:45.182 --> 00:49:47.640 align:middle line:84%
You all can invent all kinds
of new math before, let's say,

00:49:47.640 --> 00:49:48.300 align:middle line:90%
November.

00:49:48.300 --> 00:49:50.760 align:middle line:84%
Thompson is literally doing
this for fun on the weekends

00:49:50.760 --> 00:49:53.257 align:middle line:84%
because he can't
get enough math.

00:49:53.257 --> 00:49:55.090 align:middle line:84%
So he introduces a
vector potential and this

00:49:55.090 --> 00:49:58.000 align:middle line:84%
curl because, as
Faraday had intuited,

00:49:58.000 --> 00:50:01.900 align:middle line:84%
the effect of a magnetic field
on the surrounding aether

00:50:01.900 --> 00:50:04.990 align:middle line:84%
was a turning or
twisting strain,

00:50:04.990 --> 00:50:08.300 align:middle line:84%
unlike the straight line
strain of an electric field.

00:50:08.300 --> 00:50:10.600 align:middle line:84%
And so Thompson
wanted to formalize

00:50:10.600 --> 00:50:13.720 align:middle line:84%
what that curl, what that
twisting torsion would

00:50:13.720 --> 00:50:16.510 align:middle line:84%
be like as a different kind
of strain in the aether.

00:50:16.510 --> 00:50:18.440 align:middle line:84%
And he formalizes
this new operator,

00:50:18.440 --> 00:50:21.670 align:middle line:84%
which we now know, and love,
and use every single day.

00:50:21.670 --> 00:50:24.910 align:middle line:84%
It comes out of Thompson
trying to treat mathematically

00:50:24.910 --> 00:50:27.340 align:middle line:84%
formally what he was still
learning very actively

00:50:27.340 --> 00:50:31.010 align:middle line:84%
from people like
Faraday, pretty amazing.

00:50:31.010 --> 00:50:33.800 align:middle line:84%
So far, following
Faraday's lead,

00:50:33.800 --> 00:50:37.220 align:middle line:84%
Thompson begins to interpret
this mathematical result

00:50:37.220 --> 00:50:38.240 align:middle line:90%
mechanically.

00:50:38.240 --> 00:50:39.920 align:middle line:84%
Remember, we saw that
one to one bridge

00:50:39.920 --> 00:50:42.410 align:middle line:84%
between the Newton mechanics
stuff and the electricity

00:50:42.410 --> 00:50:43.250 align:middle line:90%
stuff.

00:50:43.250 --> 00:50:45.140 align:middle line:84%
He says, if the same
mathematics applies,

00:50:45.140 --> 00:50:47.750 align:middle line:84%
maybe it's the same
physical explanation

00:50:47.750 --> 00:50:50.900 align:middle line:90%
undergirding all of it.

00:50:50.900 --> 00:50:53.720 align:middle line:84%
He had learned from people like
Michael Faraday and others,

00:50:53.720 --> 00:50:56.570 align:middle line:84%
the aether seemed to be this
inelastic, physical medium.

00:50:56.570 --> 00:51:00.380 align:middle line:84%
It was literally a kind of
stuff spread out everywhere.

00:51:00.380 --> 00:51:03.890 align:middle line:84%
And that medium could be put
under local states of tension

00:51:03.890 --> 00:51:06.770 align:middle line:84%
or strain with twists,
with directional properties

00:51:06.770 --> 00:51:08.550 align:middle line:90%
described by these vectors.

00:51:08.550 --> 00:51:10.580 align:middle line:84%
So these new mathematical
techniques like curl

00:51:10.580 --> 00:51:14.810 align:middle line:84%
could quantify this physical,
mechanical medium's response

00:51:14.810 --> 00:51:17.990 align:middle line:84%
to pressures like electric
and magnetic fields.

00:51:17.990 --> 00:51:19.280 align:middle line:90%
He really took that to heart.

00:51:19.280 --> 00:51:20.930 align:middle line:84%
In a famous set of
public lectures,

00:51:20.930 --> 00:51:22.610 align:middle line:84%
much like these London
ones, he actually

00:51:22.610 --> 00:51:25.500 align:middle line:84%
came to Baltimore in the
United States and gave very,

00:51:25.500 --> 00:51:29.025 align:middle line:84%
very well attended popular
lectures in Baltimore.

00:51:29.025 --> 00:51:30.900 align:middle line:84%
Thompson basically tried
to give his audience

00:51:30.900 --> 00:51:33.660 align:middle line:84%
a feel for what these kind
of experts were doing.

00:51:33.660 --> 00:51:35.380 align:middle line:90%
This is a direct quotation.

00:51:35.380 --> 00:51:37.500 align:middle line:84%
So again, people in
their fancy opera gloves,

00:51:37.500 --> 00:51:39.090 align:middle line:84%
like out for a
night on the town,

00:51:39.090 --> 00:51:41.520 align:middle line:84%
hear the great Lord Kelvin
by this point, the great,

00:51:41.520 --> 00:51:46.020 align:middle line:84%
ennobled Lord Kelvin describe
about the latest advances.

00:51:46.020 --> 00:51:48.090 align:middle line:84%
And he tells his fancy
audience, stick your hand

00:51:48.090 --> 00:51:51.682 align:middle line:84%
in a bowl of jelly, OK, and
see how it wiggles and vibrates

00:51:51.682 --> 00:51:52.890 align:middle line:90%
as you move your hand around.

00:51:52.890 --> 00:51:56.550 align:middle line:84%
That's what it was to do physics
because the jelly is just

00:51:56.550 --> 00:51:57.960 align:middle line:90%
like this elastic aether.

00:51:57.960 --> 00:51:59.310 align:middle line:90%
It's everywhere.

00:51:59.310 --> 00:52:01.680 align:middle line:84%
And the job of super
smart, ambitious people

00:52:01.680 --> 00:52:04.950 align:middle line:84%
like William Thompson was
to quantify the wiggles

00:52:04.950 --> 00:52:07.680 align:middle line:84%
and vibrations of that aether,
much as you would if you

00:52:07.680 --> 00:52:09.980 align:middle line:90%
disturbed this pot of jelly.

00:52:09.980 --> 00:52:12.060 align:middle line:90%
I love that.

00:52:12.060 --> 00:52:14.610 align:middle line:84%
This becomes known as
a mechanical worldview.

00:52:14.610 --> 00:52:16.500 align:middle line:84%
If the mathematics
was the same, make

00:52:16.500 --> 00:52:18.960 align:middle line:84%
this one-to-one
mathematical map,

00:52:18.960 --> 00:52:21.990 align:middle line:84%
then maybe you could model
electromagnetism literally

00:52:21.990 --> 00:52:23.130 align:middle line:90%
on mechanical models.

00:52:23.130 --> 00:52:25.560 align:middle line:84%
You have an elastic stuff
under states of strain

00:52:25.560 --> 00:52:27.420 align:middle line:90%
with directional properties.

00:52:27.420 --> 00:52:30.510 align:middle line:84%
And if the models reproduce
all the relevant phenomena,

00:52:30.510 --> 00:52:32.550 align:middle line:84%
like Coulomb's law
and all the rest, all

00:52:32.550 --> 00:52:35.280 align:middle line:84%
the electromagnetic
phenomena, then

00:52:35.280 --> 00:52:38.130 align:middle line:84%
maybe these aren't only
analogies or models.

00:52:38.130 --> 00:52:41.790 align:middle line:84%
Maybe the aether really was
merely a mechanical system just

00:52:41.790 --> 00:52:43.740 align:middle line:90%
like that jar of jam.

00:52:43.740 --> 00:52:45.840 align:middle line:84%
So it becomes a
mechanical worldview.

00:52:45.840 --> 00:52:48.330 align:middle line:84%
All of the things
of the world are

00:52:48.330 --> 00:52:51.870 align:middle line:84%
to be understood on mechanical
vibrations or responses

00:52:51.870 --> 00:52:54.090 align:middle line:90%
of this space-filling aether.

00:52:54.090 --> 00:52:56.640 align:middle line:84%
The last part, then I'll pause
for more questions, almost

00:52:56.640 --> 00:52:57.940 align:middle line:90%
done--

00:52:57.940 --> 00:53:00.850 align:middle line:84%
we're going to turn to
Thompson's slightly younger

00:53:00.850 --> 00:53:02.530 align:middle line:90%
colleague, James Clerk Maxwell.

00:53:02.530 --> 00:53:05.340 align:middle line:90%


00:53:05.340 --> 00:53:08.190 align:middle line:84%
I mentioned they had a similar
upbringing a couple of years

00:53:08.190 --> 00:53:08.800 align:middle line:90%
apart--

00:53:08.800 --> 00:53:10.410 align:middle line:84%
both Scottish, both
come to Cambridge

00:53:10.410 --> 00:53:11.838 align:middle line:90%
for their undergraduate studies.

00:53:11.838 --> 00:53:13.380 align:middle line:84%
Maxwell is a couple
of years younger.

00:53:13.380 --> 00:53:15.547 align:middle line:84%
I don't think they actually
overlapped in Cambridge.

00:53:15.547 --> 00:53:17.468 align:middle line:84%
They came to know
each other later.

00:53:17.468 --> 00:53:20.010 align:middle line:84%
Maxwell, like Thompson, becomes
steeped in this new Cambridge

00:53:20.010 --> 00:53:21.000 align:middle line:90%
mathematical training.

00:53:21.000 --> 00:53:22.708 align:middle line:84%
We'll talk a lot more
about the Cambridge

00:53:22.708 --> 00:53:25.080 align:middle line:90%
training in the next class.

00:53:25.080 --> 00:53:27.240 align:middle line:84%
And Maxwell develops
further analogies

00:53:27.240 --> 00:53:29.910 align:middle line:84%
between these electromagnetic
aether-based systems

00:53:29.910 --> 00:53:31.010 align:middle line:90%
and mechanical systems.

00:53:31.010 --> 00:53:32.010 align:middle line:90%
Here's a famous example.

00:53:32.010 --> 00:53:34.200 align:middle line:84%
In this, by the way, you
get some more description

00:53:34.200 --> 00:53:38.500 align:middle line:84%
of this in that chapter by Bruce
Hunt in the reading for today.

00:53:38.500 --> 00:53:41.430 align:middle line:84%
So to model the effects of a
magnetic field on the aether,

00:53:41.430 --> 00:53:43.590 align:middle line:84%
Maxwell imagines this
elaborate system.

00:53:43.590 --> 00:53:46.470 align:middle line:84%
Basically, it's like a
contraption of pulleys,

00:53:46.470 --> 00:53:48.178 align:middle line:90%
and conveyor belts, and gears.

00:53:48.178 --> 00:53:50.220 align:middle line:84%
We don't have to worry
about the details so much.

00:53:50.220 --> 00:53:52.410 align:middle line:84%
The ambition is what
I want to convey,

00:53:52.410 --> 00:53:55.230 align:middle line:84%
that there's a physical
model of an actual system,

00:53:55.230 --> 00:53:58.380 align:middle line:84%
a mechanical system of
gears, levers, and straps

00:53:58.380 --> 00:54:01.950 align:middle line:84%
that he thinks is what's
really going on in the aether

00:54:01.950 --> 00:54:04.350 align:middle line:84%
when we do things like put
a little patch of aether

00:54:04.350 --> 00:54:07.570 align:middle line:84%
under local strain
from a magnetic field.

00:54:07.570 --> 00:54:10.560 align:middle line:84%
So between these vortices,
as depicted here,

00:54:10.560 --> 00:54:11.780 align:middle line:90%
are these idle wheels.

00:54:11.780 --> 00:54:13.650 align:middle line:84%
They stay in place,
but can change

00:54:13.650 --> 00:54:15.810 align:middle line:90%
the rate at which they turn.

00:54:15.810 --> 00:54:17.700 align:middle line:84%
It really is like
these conveyor belts.

00:54:17.700 --> 00:54:22.530 align:middle line:84%
If an external force changed
the rate at which one of these

00:54:22.530 --> 00:54:25.860 align:middle line:84%
vortices was spinning-- you
could change it by imposing one

00:54:25.860 --> 00:54:27.930 align:middle line:84%
of these external fields
like a magnetic field--

00:54:27.930 --> 00:54:31.170 align:middle line:84%
you change the rate at which
this unit cell is spinning.

00:54:31.170 --> 00:54:33.900 align:middle line:84%
That changes the rate at
which the immediately nearest

00:54:33.900 --> 00:54:36.700 align:middle line:84%
neighbors are going
to be behaving.

00:54:36.700 --> 00:54:40.030 align:middle line:84%
It's all this Faraday field
idea of local neighbor

00:54:40.030 --> 00:54:42.920 align:middle line:84%
to local neighbor, not
action at a distance.

00:54:42.920 --> 00:54:45.717 align:middle line:84%
So this unit cell starts to
change its rate of rotation.

00:54:45.717 --> 00:54:47.800 align:middle line:84%
That changes the speed at
which these intervening,

00:54:47.800 --> 00:54:49.720 align:middle line:84%
these so-called
idle wheels spin.

00:54:49.720 --> 00:54:51.430 align:middle line:84%
That then changes
the rate at which

00:54:51.430 --> 00:54:53.410 align:middle line:84%
their nearest neighbors spin
because they're literally

00:54:53.410 --> 00:54:53.920 align:middle line:90%
connected.

00:54:53.920 --> 00:54:55.550 align:middle line:90%
So it's all local effects.

00:54:55.550 --> 00:54:57.880 align:middle line:90%
So all effects are local.

00:54:57.880 --> 00:55:00.550 align:middle line:84%
And the way that a magnetic
disturbance affects something

00:55:00.550 --> 00:55:03.970 align:middle line:84%
over there is by these
local effects propagating

00:55:03.970 --> 00:55:07.510 align:middle line:84%
through the medium in this
gears and straps conveyor

00:55:07.510 --> 00:55:08.710 align:middle line:90%
belt sort of way.

00:55:08.710 --> 00:55:11.050 align:middle line:84%
And again, he gives
us hints about this

00:55:11.050 --> 00:55:13.630 align:middle line:84%
even in the brief excerpt
from Maxwell's treatise

00:55:13.630 --> 00:55:15.395 align:middle line:90%
that I assigned for today.

00:55:15.395 --> 00:55:17.770 align:middle line:84%
So he talks about how the
action of one electrical system

00:55:17.770 --> 00:55:21.760 align:middle line:84%
on another is affected not by
direct action at a distance,

00:55:21.760 --> 00:55:24.190 align:middle line:84%
not the way Newton
had said, but rather

00:55:24.190 --> 00:55:26.020 align:middle line:84%
by means of a
distribution of stress

00:55:26.020 --> 00:55:29.050 align:middle line:84%
in this medium, this elastic
medium, or the aether

00:55:29.050 --> 00:55:31.390 align:middle line:84%
extending continuously
throughout space.

00:55:31.390 --> 00:55:34.090 align:middle line:84%
Likewise, he says a few
pages later in the excerpt,

00:55:34.090 --> 00:55:37.000 align:middle line:84%
the distribution of stress
in this medium, this aether,

00:55:37.000 --> 00:55:39.490 align:middle line:84%
is precisely that
to which Faraday

00:55:39.490 --> 00:55:42.010 align:middle line:84%
was led in his investigation
of induction, of the fact

00:55:42.010 --> 00:55:44.050 align:middle line:84%
that a moving magnetic--
moving magnet can

00:55:44.050 --> 00:55:47.410 align:middle line:84%
induce electrical effects,
like an electric current.

00:55:47.410 --> 00:55:50.050 align:middle line:84%
At every point of the medium,
there's a state of stress.

00:55:50.050 --> 00:55:52.490 align:middle line:84%
Every part of the aether is
under some kind of stress,

00:55:52.490 --> 00:55:55.150 align:middle line:84%
such that there's tension along
the lines of force, pressure

00:55:55.150 --> 00:55:55.870 align:middle line:90%
at right angles.

00:55:55.870 --> 00:55:57.940 align:middle line:84%
He's really building
a mechanical model,

00:55:57.940 --> 00:56:00.040 align:middle line:84%
almost sometimes a
kind of hydrostatic one

00:56:00.040 --> 00:56:02.950 align:middle line:84%
and other ones more like
the gears of a factory.

00:56:02.950 --> 00:56:05.680 align:middle line:84%
This became how the
Maxwellians-- not just Maxwell,

00:56:05.680 --> 00:56:08.950 align:middle line:84%
but even his nearest followers,
and students, and proteges--

00:56:08.950 --> 00:56:12.310 align:middle line:84%
that's what they thought it
was to study the natural world,

00:56:12.310 --> 00:56:14.860 align:middle line:84%
to build more and
more articulated

00:56:14.860 --> 00:56:18.310 align:middle line:84%
mechanical models of the aether
with which they could model

00:56:18.310 --> 00:56:21.220 align:middle line:84%
and even predict more and more
features of the natural world,

00:56:21.220 --> 00:56:23.030 align:middle line:90%
like electromagnetic effects.

00:56:23.030 --> 00:56:25.600 align:middle line:84%
So one of his
acolytes, Oliver Lodge,

00:56:25.600 --> 00:56:28.000 align:middle line:84%
who himself went on to a very,
very distinguished career

00:56:28.000 --> 00:56:31.810 align:middle line:84%
in physics himself, he wrote
a book a few years later

00:56:31.810 --> 00:56:34.060 align:middle line:84%
than Maxwell's treatise
called The Modern Views

00:56:34.060 --> 00:56:35.080 align:middle line:90%
of Electricity.

00:56:35.080 --> 00:56:37.600 align:middle line:84%
And it was all about
this Maxwellian approach

00:56:37.600 --> 00:56:41.260 align:middle line:84%
within this mechanical worldview
to account for states of strain

00:56:41.260 --> 00:56:45.340 align:middle line:84%
in the aether using this much
more articulated mapping,

00:56:45.340 --> 00:56:48.580 align:middle line:84%
the fancy math that people like
Thompson, Maxwell, and soon

00:56:48.580 --> 00:56:50.890 align:middle line:84%
the whole Cambridge
group would articulate.

00:56:50.890 --> 00:56:52.490 align:middle line:84%
Well, this didn't
impress everyone.

00:56:52.490 --> 00:56:53.590 align:middle line:90%
I love this book review.

00:56:53.590 --> 00:56:57.680 align:middle line:84%
This is the nastiest book of
view for a long, long time.

00:56:57.680 --> 00:56:59.980 align:middle line:84%
Here's a review by the
French mathematical physicist

00:56:59.980 --> 00:57:03.610 align:middle line:84%
Pierre Duhem, reviewing
Oliver Lodge's book,

00:57:03.610 --> 00:57:05.890 align:middle line:90%
this Maxwellian book.

00:57:05.890 --> 00:57:07.130 align:middle line:90%
Duhem hoped he would like it.

00:57:07.130 --> 00:57:09.130 align:middle line:84%
He also was very interested
in electromagnetism.

00:57:09.130 --> 00:57:12.760 align:middle line:84%
But he just sniffs in this
wonderful sneering, French way.

00:57:12.760 --> 00:57:14.290 align:middle line:90%
It's worth quoting.

00:57:14.290 --> 00:57:16.210 align:middle line:84%
Duhem says, here
is a book intended

00:57:16.210 --> 00:57:18.760 align:middle line:84%
to expound the modern
theories of electricity.

00:57:18.760 --> 00:57:20.560 align:middle line:84%
And there are
nothing but strings

00:57:20.560 --> 00:57:23.380 align:middle line:84%
which move around pulleys,
which roll around drums, which

00:57:23.380 --> 00:57:25.840 align:middle line:84%
go through pearl beads,
which carry weights,

00:57:25.840 --> 00:57:28.960 align:middle line:84%
and tubes which pump water
while others swell and contract.

00:57:28.960 --> 00:57:31.790 align:middle line:84%
Toothed wheels are geared to
one another and gauge hooks.

00:57:31.790 --> 00:57:32.800 align:middle line:90%
This is the real kicker.

00:57:32.800 --> 00:57:34.720 align:middle line:84%
We thought we were
entering the tranquil

00:57:34.720 --> 00:57:37.390 align:middle line:84%
and neatly ordered
abode of reason.

00:57:37.390 --> 00:57:39.370 align:middle line:84%
But we find ourselves
in a factory.

00:57:39.370 --> 00:57:40.458 align:middle line:90%
This was not high praise.

00:57:40.458 --> 00:57:42.250 align:middle line:84%
He was like, I thought
I was going to learn

00:57:42.250 --> 00:57:44.410 align:middle line:90%
something edifying for my soul.

00:57:44.410 --> 00:57:47.060 align:middle line:84%
Instead, this is
literally low class stuff.

00:57:47.060 --> 00:57:50.372 align:middle line:84%
This is the most
obnoxious takedown book

00:57:50.372 --> 00:57:51.580 align:middle line:90%
review that I could think of.

00:57:51.580 --> 00:57:53.890 align:middle line:84%
So this Maxwellian
British approach

00:57:53.890 --> 00:57:55.360 align:middle line:90%
doesn't please everyone.

00:57:55.360 --> 00:57:57.328 align:middle line:84%
And yet, as we'll see
in the last little bit,

00:57:57.328 --> 00:57:59.620 align:middle line:84%
they're starting to make some
pretty remarkable strides

00:57:59.620 --> 00:58:00.750 align:middle line:90%
nonetheless.

00:58:00.750 --> 00:58:02.750 align:middle line:84%
Last little bit, then
we'll pause for questions,

00:58:02.750 --> 00:58:03.833 align:middle line:90%
the last part for Maxwell.

00:58:03.833 --> 00:58:06.020 align:middle line:90%


00:58:06.020 --> 00:58:08.570 align:middle line:84%
So while working out
this mechanical model,

00:58:08.570 --> 00:58:11.300 align:middle line:84%
how would local
disturbances propagate

00:58:11.300 --> 00:58:15.530 align:middle line:84%
through this elastic medium
of the aether, Maxwell starts

00:58:15.530 --> 00:58:19.040 align:middle line:84%
putting in some quantitative
values for the way

00:58:19.040 --> 00:58:21.050 align:middle line:84%
to characterize the
response of the aether.

00:58:21.050 --> 00:58:22.880 align:middle line:84%
These are really like
spring constants.

00:58:22.880 --> 00:58:25.040 align:middle line:90%
How stretchy is the aether?

00:58:25.040 --> 00:58:26.900 align:middle line:84%
Or how much
stretchiness or tension

00:58:26.900 --> 00:58:30.020 align:middle line:84%
do you get per unit
applied external field?

00:58:30.020 --> 00:58:32.000 align:middle line:84%
When we apply an
external electric field

00:58:32.000 --> 00:58:34.220 align:middle line:84%
to this part of the
aether, how much

00:58:34.220 --> 00:58:36.680 align:middle line:84%
does the tension change or
likewise the magnetic fields?

00:58:36.680 --> 00:58:39.398 align:middle line:84%
So really, like spring
concerts, analogous.

00:58:39.398 --> 00:58:40.940 align:middle line:84%
And that's what he
and his colleagues

00:58:40.940 --> 00:58:43.250 align:middle line:84%
are measuring in their local
laboratories and studying.

00:58:43.250 --> 00:58:45.620 align:middle line:84%
Then he goes back to
these mechanical models

00:58:45.620 --> 00:58:49.190 align:middle line:84%
to ask how quickly would a
mechanical disturbance begin

00:58:49.190 --> 00:58:52.640 align:middle line:84%
to propagate within
this mechanical aether.

00:58:52.640 --> 00:58:54.665 align:middle line:84%
And he finds, really
to his surprise--

00:58:54.665 --> 00:58:55.790 align:middle line:90%
he didn't see that coming--

00:58:55.790 --> 00:58:57.470 align:middle line:84%
these disturbances
in the aether,

00:58:57.470 --> 00:58:59.570 align:middle line:84%
the moment by
moment local effects

00:58:59.570 --> 00:59:01.400 align:middle line:84%
would move at a
speed he already knew

00:59:01.400 --> 00:59:03.203 align:middle line:90%
very well, the speed of light.

00:59:03.203 --> 00:59:05.370 align:middle line:84%
Here's a direct quotation
from his very famous paper

00:59:05.370 --> 00:59:07.500 align:middle line:90%
from 1865.

00:59:07.500 --> 00:59:10.680 align:middle line:84%
And he says, the velocity
of transverse undulations

00:59:10.680 --> 00:59:12.000 align:middle line:90%
in our hypothetical medium--

00:59:12.000 --> 00:59:14.737 align:middle line:84%
I just love that phrase,
transverse undulations

00:59:14.737 --> 00:59:16.320 align:middle line:84%
in our hypothetical,
meaning the speed

00:59:16.320 --> 00:59:19.230 align:middle line:84%
at which these waves of
aether are traveling.

00:59:19.230 --> 00:59:21.883 align:middle line:84%
That speed agrees so exactly
with the velocity of light

00:59:21.883 --> 00:59:24.300 align:middle line:84%
that's calculated from optical
experiments-- and actually,

00:59:24.300 --> 00:59:26.250 align:middle line:90%
most of the astronomical tests--

00:59:26.250 --> 00:59:28.860 align:middle line:84%
that we can scarcely
avoid the inference

00:59:28.860 --> 00:59:32.280 align:middle line:84%
that light consists of
the transverse undulations

00:59:32.280 --> 00:59:35.010 align:middle line:84%
of the same medium,
the aether, which

00:59:35.010 --> 00:59:37.650 align:middle line:84%
is the cause of electric
and magnetic phenomena.

00:59:37.650 --> 00:59:39.780 align:middle line:84%
Translated into how
we might say today,

00:59:39.780 --> 00:59:42.210 align:middle line:84%
light waves were
literally nothing,

00:59:42.210 --> 00:59:45.480 align:middle line:84%
but traveling disturbances of
electric and magnetic fields

00:59:45.480 --> 00:59:48.660 align:middle line:84%
within this light-bearing,
all pervasive aether.

00:59:48.660 --> 00:59:51.900 align:middle line:84%
He gets that-- he gets this
unification of electricity

00:59:51.900 --> 00:59:55.290 align:middle line:84%
magnetism and optics by
thinking very, very hard

00:59:55.290 --> 00:59:58.440 align:middle line:84%
and very quantitatively
about the mechanical response

00:59:58.440 --> 01:00:00.120 align:middle line:90%
of this all pervasive aether.

01:00:00.120 --> 01:00:01.660 align:middle line:84%
So let me wrap up,
and I'll pause.

01:00:01.660 --> 01:00:03.660 align:middle line:84%
I see a bunch of comments
coming up in the chat.

01:00:03.660 --> 01:00:05.010 align:middle line:84%
So I want to make sure
we have time to chat.

01:00:05.010 --> 01:00:06.390 align:middle line:90%
So let me just wrap up.

01:00:06.390 --> 01:00:09.030 align:middle line:84%
And then we'll
get to discussion.

01:00:09.030 --> 01:00:12.990 align:middle line:84%
Leading natural philosophers
of the 19th century were really

01:00:12.990 --> 01:00:15.750 align:middle line:84%
quite convinced-- and they
had very good reasons--

01:00:15.750 --> 01:00:18.630 align:middle line:84%
that the world is made up of
just different kinds of stuff

01:00:18.630 --> 01:00:22.020 align:middle line:84%
than how our contemporaries
would answer that question.

01:00:22.020 --> 01:00:24.180 align:middle line:84%
That opening question,
what's the world made of?

01:00:24.180 --> 01:00:26.640 align:middle line:84%
The folks back
then, world-leading,

01:00:26.640 --> 01:00:28.650 align:middle line:90%
rightly celebrated scholars--

01:00:28.650 --> 01:00:31.470 align:middle line:84%
Faraday, Thompson, Maxwell,
and for that matter

01:00:31.470 --> 01:00:34.370 align:middle line:84%
people like Pierre Duhem and
his contemporaries as well--

01:00:34.370 --> 01:00:36.120 align:middle line:84%
they were convinced
that the world was not

01:00:36.120 --> 01:00:38.580 align:middle line:84%
made of elementary particles
that skitter around

01:00:38.580 --> 01:00:39.700 align:middle line:90%
in a vacuum.

01:00:39.700 --> 01:00:41.670 align:middle line:90%
But rather, there was no vacuum.

01:00:41.670 --> 01:00:43.525 align:middle line:84%
And particles were a
kind of afterthought--

01:00:43.525 --> 01:00:45.150 align:middle line:84%
we'll Come back to
that in next class--

01:00:45.150 --> 01:00:48.630 align:middle line:84%
that the world is filled with
elastic, physical medium,

01:00:48.630 --> 01:00:49.410 align:middle line:90%
the aether.

01:00:49.410 --> 01:00:51.932 align:middle line:84%
And everything that
matters is a response

01:00:51.932 --> 01:00:54.390 align:middle line:84%
to that aether to various kinds
of mechanical disturbances.

01:00:54.390 --> 01:00:58.140 align:middle line:84%
As Lord Kelvin says, stick
your hand in a bowl of jelly.

01:00:58.140 --> 01:00:59.130 align:middle line:90%
See how it wiggles.

01:00:59.130 --> 01:01:02.280 align:middle line:84%
That's what the
world is made of.

01:01:02.280 --> 01:01:05.320 align:middle line:84%
Up until the middle decades
of the 19th century,

01:01:05.320 --> 01:01:07.200 align:middle line:84%
many leading,
highly accomplished,

01:01:07.200 --> 01:01:09.300 align:middle line:84%
and very influential
natural philosophers,

01:01:09.300 --> 01:01:12.510 align:middle line:84%
like Michael Faraday, could
enter research careers

01:01:12.510 --> 01:01:14.130 align:middle line:84%
based on this
apprenticeship model

01:01:14.130 --> 01:01:17.850 align:middle line:84%
closer to the Middle Ages or
the Renaissance than to today.

01:01:17.850 --> 01:01:22.240 align:middle line:84%
They often worked in institutes,
which had no formal teaching

01:01:22.240 --> 01:01:22.740 align:middle line:90%
function.

01:01:22.740 --> 01:01:25.440 align:middle line:84%
They were not, for the most
part, based at universities.

01:01:25.440 --> 01:01:27.780 align:middle line:84%
That's what begins to
change in the middle decades

01:01:27.780 --> 01:01:29.740 align:middle line:90%
of the 19th century.

01:01:29.740 --> 01:01:31.440 align:middle line:84%
So Faraday, Thompson,
and Maxwell,

01:01:31.440 --> 01:01:34.710 align:middle line:84%
in their own different ways,
pursued these analogies between

01:01:34.710 --> 01:01:37.230 align:middle line:84%
this light-bearing or
luminiferous aether

01:01:37.230 --> 01:01:38.790 align:middle line:90%
and mechanical systems--

01:01:38.790 --> 01:01:40.710 align:middle line:84%
Faraday with his
rather rudimentary

01:01:40.710 --> 01:01:44.250 align:middle line:84%
geometrical arguments and his
very clever pictorial aids,

01:01:44.250 --> 01:01:46.650 align:middle line:84%
Thompson and Maxwell with this
increasingly sophisticated

01:01:46.650 --> 01:01:47.300 align:middle line:90%
mathematics.

01:01:47.300 --> 01:01:49.800 align:middle line:84%
We'll look at that
some more next time.

01:01:49.800 --> 01:01:51.570 align:middle line:84%
They all became
convinced of what became

01:01:51.570 --> 01:01:53.700 align:middle line:90%
called a mechanical worldview.

01:01:53.700 --> 01:01:55.950 align:middle line:84%
The electromagnetic
effects were literally

01:01:55.950 --> 01:01:58.680 align:middle line:84%
nothing but mechanical
effects, mechanical effects

01:01:58.680 --> 01:01:59.950 align:middle line:90%
on this all pervasive aether.

01:01:59.950 --> 01:02:03.690 align:middle line:84%
Moreover, this is the birth of
what we now call field physics.

01:02:03.690 --> 01:02:06.090 align:middle line:84%
Local causes yield
local effects.

01:02:06.090 --> 01:02:09.240 align:middle line:84%
There's no action at a distance,
unlike Maxwell's description--

01:02:09.240 --> 01:02:11.970 align:middle line:84%
excuse me, Newton's
description of gravity.

01:02:11.970 --> 01:02:14.910 align:middle line:84%
A can affect B But it'll take
some time for the effects

01:02:14.910 --> 01:02:15.780 align:middle line:90%
to propagate.

01:02:15.780 --> 01:02:17.730 align:middle line:84%
And certain kinds of
propagating effects,

01:02:17.730 --> 01:02:21.090 align:middle line:84%
like these electric and
magnetic transverse undulations,

01:02:21.090 --> 01:02:23.910 align:middle line:84%
they'll show up as nothing
other than what we call light.

01:02:23.910 --> 01:02:26.790 align:middle line:84%
Let me stop sharing
the screen there,

01:02:26.790 --> 01:02:28.830 align:middle line:90%
open it up for questions.

01:02:28.830 --> 01:02:31.510 align:middle line:90%
There's a huge set in the chat.

01:02:31.510 --> 01:02:33.870 align:middle line:84%
I think I won't get
to them all today.

01:02:33.870 --> 01:02:43.483 align:middle line:90%


01:02:43.483 --> 01:02:44.400 align:middle line:90%
Great, great question.

01:02:44.400 --> 01:02:44.640 align:middle line:90%
Thank you.

01:02:44.640 --> 01:02:44.910 align:middle line:90%
So you're right.

01:02:44.910 --> 01:02:47.005 align:middle line:84%
So there was a spectrum,
even among what we now

01:02:47.005 --> 01:02:47.880 align:middle line:90%
call the Maxwellians.

01:02:47.880 --> 01:02:49.890 align:middle line:84%
They didn't all have
exactly the same ideas,

01:02:49.890 --> 01:02:51.120 align:middle line:90%
but they shared a lot.

01:02:51.120 --> 01:02:52.770 align:middle line:84%
And so indeed, some
of them wondered,

01:02:52.770 --> 01:02:53.937 align:middle line:90%
is this a useful analogy?

01:02:53.937 --> 01:02:56.520 align:middle line:84%
And if so, should we nonetheless
keep pursuing it and see what

01:02:56.520 --> 01:02:57.570 align:middle line:90%
we get out of it?

01:02:57.570 --> 01:02:59.550 align:middle line:84%
Others were convinced
that it's more than that.

01:02:59.550 --> 01:03:00.990 align:middle line:90%
It's not merely an analogy.

01:03:00.990 --> 01:03:03.660 align:middle line:84%
It's a helpful analogy
precisely because of some deeper

01:03:03.660 --> 01:03:04.410 align:middle line:90%
similarity.

01:03:04.410 --> 01:03:06.720 align:middle line:84%
And individuals views
changed over time.

01:03:06.720 --> 01:03:09.180 align:middle line:84%
And the whole group
would have a, let's say,

01:03:09.180 --> 01:03:10.830 align:middle line:90%
evolving center of gravity.

01:03:10.830 --> 01:03:13.830 align:middle line:84%
They were more like each
other in the Cambridge

01:03:13.830 --> 01:03:16.890 align:middle line:84%
scene than like, say, the
French, or the Germans,

01:03:16.890 --> 01:03:19.810 align:middle line:84%
or indeed communities further
afield, as we'll look at.

01:03:19.810 --> 01:03:23.250 align:middle line:84%
So I don't want to make it
sound like they all exactly had

01:03:23.250 --> 01:03:24.300 align:middle line:90%
the same notion.

01:03:24.300 --> 01:03:27.810 align:middle line:84%
They were pretty
similar, compared to--

01:03:27.810 --> 01:03:29.860 align:middle line:84%
actually, we'll see a
really interesting contrast

01:03:29.860 --> 01:03:30.450 align:middle line:90%
next class--

01:03:30.450 --> 01:03:32.610 align:middle line:84%
I think interesting--
with some leading scholars

01:03:32.610 --> 01:03:34.110 align:middle line:90%
within the German states.

01:03:34.110 --> 01:03:36.960 align:middle line:84%
So there was maybe the
strongest contrast.

01:03:36.960 --> 01:03:38.460 align:middle line:84%
But you're right
that some of these,

01:03:38.460 --> 01:03:42.030 align:middle line:84%
even within Cambridge or the
close Maxwellian colleagues,

01:03:42.030 --> 01:03:43.615 align:middle line:84%
they were all
delighted to pursue

01:03:43.615 --> 01:03:44.740 align:middle line:90%
the mathematical analogies.

01:03:44.740 --> 01:03:47.320 align:middle line:84%
And they were getting
trained in these very, very

01:03:47.320 --> 01:03:48.862 align:middle line:84%
elaborate mathematical
machinery,

01:03:48.862 --> 01:03:50.320 align:middle line:84%
as we'll talk more
about next time.

01:03:50.320 --> 01:03:51.760 align:middle line:90%
They shared that.

01:03:51.760 --> 01:03:52.300 align:middle line:90%
And They.

01:03:52.300 --> 01:03:54.580 align:middle line:84%
Were impressed by what the
analogies would bring them,

01:03:54.580 --> 01:03:56.617 align:middle line:84%
either to explain
something or to prompt

01:03:56.617 --> 01:03:59.200 align:middle line:84%
new questions to then try to go
investigate in the laboratory.

01:03:59.200 --> 01:04:01.240 align:middle line:84%
It was a productive
set of analogies.

01:04:01.240 --> 01:04:03.430 align:middle line:84%
That was already
what they agreed on.

01:04:03.430 --> 01:04:05.560 align:middle line:84%
Some then said, it's
not just analogy.

01:04:05.560 --> 01:04:08.140 align:middle line:84%
The world is filled
with jelly, effectively.

01:04:08.140 --> 01:04:09.920 align:middle line:90%
It's a great question.

01:04:09.920 --> 01:04:12.190 align:middle line:84%
It looks like Julia has
very kindly compiled

01:04:12.190 --> 01:04:14.320 align:middle line:90%
a bunch of questions for me.

01:04:14.320 --> 01:04:17.590 align:middle line:84%
Let me answer some that Julia
has private chatted to me.

01:04:17.590 --> 01:04:20.470 align:middle line:84%
And if I miss some others,
we'll have time for some more.

01:04:20.470 --> 01:04:22.750 align:middle line:84%
So someone asks,
by way of Julia,

01:04:22.750 --> 01:04:24.460 align:middle line:84%
if university and
research institutions

01:04:24.460 --> 01:04:25.810 align:middle line:84%
were separated at
the time, who used

01:04:25.810 --> 01:04:27.018 align:middle line:90%
to teach at the universities?

01:04:27.018 --> 01:04:28.180 align:middle line:90%
Oh, very good.

01:04:28.180 --> 01:04:29.905 align:middle line:84%
People would teach
at the universities

01:04:29.905 --> 01:04:31.030 align:middle line:90%
who had gone to university.

01:04:31.030 --> 01:04:32.470 align:middle line:90%
So it was self-replicating.

01:04:32.470 --> 01:04:34.400 align:middle line:90%
Now, that's still true today.

01:04:34.400 --> 01:04:37.150 align:middle line:84%
But we've achieved
a kind of monopoly,

01:04:37.150 --> 01:04:39.340 align:middle line:84%
whereas back then it
wasn't such a monopoly.

01:04:39.340 --> 01:04:42.700 align:middle line:84%
That is to say, people who
would teach at universities

01:04:42.700 --> 01:04:46.240 align:middle line:84%
had indeed been trained like
William Thompson, or James

01:04:46.240 --> 01:04:47.980 align:middle line:84%
Clerk Maxwell, or
their own students.

01:04:47.980 --> 01:04:49.780 align:middle line:84%
And in fact, we'll
talk quite a bit

01:04:49.780 --> 01:04:51.970 align:middle line:84%
about this in the next
class and something

01:04:51.970 --> 01:04:53.920 align:middle line:90%
that I find really interesting.

01:04:53.920 --> 01:04:56.200 align:middle line:84%
And that was still
separated from people

01:04:56.200 --> 01:04:58.390 align:middle line:84%
who could enter
really elaborately,

01:04:58.390 --> 01:05:00.970 align:middle line:84%
amazingly prestigious
careers, like Michael Faraday

01:05:00.970 --> 01:05:03.760 align:middle line:84%
or even Thomas Young before
him, or Hans Christian Oersted,

01:05:03.760 --> 01:05:05.920 align:middle line:84%
or many other names
we encountered today,

01:05:05.920 --> 01:05:08.990 align:middle line:84%
without going through that kind
of formal university setting.

01:05:08.990 --> 01:05:11.890 align:middle line:84%
So the apprenticeship
model-- get your hands dirty

01:05:11.890 --> 01:05:15.250 align:middle line:84%
on effectively an elaborate
internship and just like never

01:05:15.250 --> 01:05:15.970 align:middle line:90%
leave--

01:05:15.970 --> 01:05:19.900 align:middle line:84%
that was still a viable path
in to conduct really world

01:05:19.900 --> 01:05:21.580 align:middle line:90%
class, cutting-edge research.

01:05:21.580 --> 01:05:23.710 align:middle line:84%
Then you'd often
write your monograph,

01:05:23.710 --> 01:05:26.770 align:middle line:84%
your whole book about it, maybe
deliver some fancy lectures.

01:05:26.770 --> 01:05:28.960 align:middle line:84%
Maybe some of the
scholars at the university

01:05:28.960 --> 01:05:30.490 align:middle line:84%
would be interested, and
maybe write a textbook,

01:05:30.490 --> 01:05:32.230 align:middle line:84%
and maybe lecture on
it in their classes.

01:05:32.230 --> 01:05:34.120 align:middle line:90%
But they were separated.

01:05:34.120 --> 01:05:37.150 align:middle line:84%
The separation
begins to be reduced,

01:05:37.150 --> 01:05:40.060 align:middle line:90%
starting in the roughly 1850s--

01:05:40.060 --> 01:05:41.410 align:middle line:90%
1840s, 1850s.

01:05:41.410 --> 01:05:44.470 align:middle line:84%
And they become much,
much closer associated--

01:05:44.470 --> 01:05:49.570 align:middle line:84%
not automatically, not without
some switches back and forth.

01:05:49.570 --> 01:05:51.370 align:middle line:84%
But the trend really
sets in, starting

01:05:51.370 --> 01:05:52.310 align:middle line:90%
in the middle of 19th century.

01:05:52.310 --> 01:05:54.810 align:middle line:84%
And again, we'll look at that
a bit more directly next time.

01:05:54.810 --> 01:05:55.665 align:middle line:90%
Very good question.

01:05:55.665 --> 01:05:57.040 align:middle line:84%
So another question
is, why do we

01:05:57.040 --> 01:05:59.170 align:middle line:84%
go from the convention
used in Maxwell

01:05:59.170 --> 01:06:01.917 align:middle line:84%
of denoting a potential
as psi to now using a phi?

01:06:01.917 --> 01:06:02.500 align:middle line:90%
Oh, very good.

01:06:02.500 --> 01:06:03.010 align:middle line:90%
Are they different?

01:06:03.010 --> 01:06:04.093 align:middle line:90%
No, they're not different.

01:06:04.093 --> 01:06:06.670 align:middle line:84%
So I guess I skipped
ahead to the modern--

01:06:06.670 --> 01:06:08.710 align:middle line:84%
I showed my prejudices
in my slides

01:06:08.710 --> 01:06:12.478 align:middle line:84%
here, just using the Greek
letter phi for potential.

01:06:12.478 --> 01:06:14.020 align:middle line:84%
The short answer is
I don't know what

01:06:14.020 --> 01:06:15.550 align:middle line:90%
that particular letter changed.

01:06:15.550 --> 01:06:19.330 align:middle line:84%
What I do know-- and we'll
talk about, , again next time--

01:06:19.330 --> 01:06:22.360 align:middle line:84%
is that as you got a taste of
it again in the reader today,

01:06:22.360 --> 01:06:25.240 align:middle line:84%
Maxwell was not using any
of this fancy pants vector

01:06:25.240 --> 01:06:26.710 align:middle line:90%
stuff, right?

01:06:26.710 --> 01:06:29.020 align:middle line:84%
Maxwell was writing
everything out

01:06:29.020 --> 01:06:32.020 align:middle line:84%
in explicit Cartesian
coordinates.

01:06:32.020 --> 01:06:34.480 align:middle line:84%
That's probably why-- I joke--
why his book was 900 pages.

01:06:34.480 --> 01:06:36.188 align:middle line:84%
If he just used vectors,
I think it would

01:06:36.188 --> 01:06:38.020 align:middle line:90%
have been a 20-page pamphlet.

01:06:38.020 --> 01:06:39.530 align:middle line:90%
We'd be done.

01:06:39.530 --> 01:06:42.650 align:middle line:84%
And so I talk a lot about that,
actually, in the coming class.

01:06:42.650 --> 01:06:44.890 align:middle line:84%
So the particular question,
how did psi become phi,

01:06:44.890 --> 01:06:45.598 align:middle line:90%
it's interesting.

01:06:45.598 --> 01:06:47.920 align:middle line:90%
And I actually don't know.

01:06:47.920 --> 01:06:51.020 align:middle line:84%
But the larger question
about Maxwell's notation--

01:06:51.020 --> 01:06:53.950 align:middle line:84%
and in particular, how it could
become so valuable for people

01:06:53.950 --> 01:06:57.442 align:middle line:84%
like us when he writes these
incredibly clunky, pain

01:06:57.442 --> 01:06:58.900 align:middle line:84%
in the butt kinds
of things, partly

01:06:58.900 --> 01:07:00.817 align:middle line:84%
why I gave you those
excerpts from his reader,

01:07:00.817 --> 01:07:02.950 align:middle line:84%
from his treatise--
it doesn't look just

01:07:02.950 --> 01:07:06.220 align:middle line:84%
like our favorite textbooks
today, even when we're using,

01:07:06.220 --> 01:07:07.728 align:middle line:90%
quote unquote, "his equationss."

01:07:07.728 --> 01:07:08.770 align:middle line:90%
So it's a great question.

01:07:08.770 --> 01:07:10.450 align:middle line:84%
The conventions
actually show a lot

01:07:10.450 --> 01:07:12.533 align:middle line:84%
of interesting stuff, even
the particular question

01:07:12.533 --> 01:07:14.080 align:middle line:90%
about psi and phi.

01:07:14.080 --> 01:07:15.760 align:middle line:90%
I admit I don't know.

01:07:15.760 --> 01:07:18.760 align:middle line:84%
Regarding the wheels pulleys as
analogies to physical reality,

01:07:18.760 --> 01:07:21.020 align:middle line:84%
how is continuous rotational
symmetry of the physics

01:07:21.020 --> 01:07:21.520 align:middle line:90%
explained?

01:07:21.520 --> 01:07:23.390 align:middle line:90%
Oh, that's interesting.

01:07:23.390 --> 01:07:25.270 align:middle line:84%
I think the idea--
oh, that's good.

01:07:25.270 --> 01:07:26.060 align:middle line:90%
Yeah, that's good.

01:07:26.060 --> 01:07:30.100 align:middle line:84%
So I think they gestured toward
it by those molecular vortices.

01:07:30.100 --> 01:07:33.340 align:middle line:84%
That's the
two-dimensional slice.

01:07:33.340 --> 01:07:35.750 align:middle line:84%
And they certainly were
aware of things like spheres.

01:07:35.750 --> 01:07:38.020 align:middle line:84%
So a lot of it, they
talked about ball bearings.

01:07:38.020 --> 01:07:40.610 align:middle line:84%
So you actually have
spherical symmetry.

01:07:40.610 --> 01:07:42.400 align:middle line:84%
And so they
constructed even more

01:07:42.400 --> 01:07:45.130 align:middle line:90%
elaborate of pulleys and gears.

01:07:45.130 --> 01:07:47.320 align:middle line:84%
So they were certainly
very attuned, especially

01:07:47.320 --> 01:07:50.770 align:middle line:84%
thinking about these
mathematical, fancy

01:07:50.770 --> 01:07:52.955 align:middle line:84%
mathematicians, like
Thompson and Maxwell.

01:07:52.955 --> 01:07:55.330 align:middle line:84%
They were very attuned to what
we would now call symmetry

01:07:55.330 --> 01:07:56.900 align:middle line:90%
arguments in real space.

01:07:56.900 --> 01:08:00.430 align:middle line:84%
Could I rotate the
system around x, y, or z?

01:08:00.430 --> 01:08:03.100 align:middle line:84%
And so a lot of their
models were actually,

01:08:03.100 --> 01:08:12.370 align:middle line:84%
frankly, spherical, like
billiard balls or ball

01:08:12.370 --> 01:08:15.760 align:middle line:84%
bearings, as opposed
to only circles.

01:08:15.760 --> 01:08:17.510 align:middle line:84%
So we'll come we'll
come to that as well.

01:08:17.510 --> 01:08:18.850 align:middle line:90%
These are all good questions.

01:08:18.850 --> 01:08:20.575 align:middle line:84%
Other questions
here from the chat?

01:08:20.575 --> 01:08:23.185 align:middle line:90%


01:08:23.185 --> 01:08:24.560 align:middle line:84%
Or from not the
chat, anyone else

01:08:24.560 --> 01:08:27.603 align:middle line:84%
have any questions that they
want to pose for the group?

01:08:27.603 --> 01:08:29.770 align:middle line:84%
Feel free to just raise
your hand at this point too,

01:08:29.770 --> 01:08:31.062 align:middle line:90%
now that we can see each other.

01:08:31.062 --> 01:08:54.573 align:middle line:90%


01:08:54.573 --> 01:08:56.740 align:middle line:84%
I like the comment about
putting your hand in jelly,

01:08:56.740 --> 01:08:57.907 align:middle line:90%
now your keyboard is sticky.

01:08:57.907 --> 01:09:00.910 align:middle line:90%
My apologies for your keyboard.

01:09:00.910 --> 01:09:02.800 align:middle line:84%
I'm just trying to catch
up on the chat here.

01:09:02.800 --> 01:09:05.571 align:middle line:90%


01:09:05.571 --> 01:09:08.029 align:middle line:84%
Ah, there's a really interesting
comment here from Sabrina.

01:09:08.029 --> 01:09:08.529 align:middle line:90%
I like this.

01:09:08.529 --> 01:09:12.160 align:middle line:84%
So Sabrina writes that I
don't know what a GUT is

01:09:12.160 --> 01:09:13.240 align:middle line:90%
or grand unified theory.

01:09:13.240 --> 01:09:15.490 align:middle line:84%
But it seems like we're
moving back towards everything

01:09:15.490 --> 01:09:18.490 align:middle line:84%
being the same thing
again with a smile emoji.

01:09:18.490 --> 01:09:22.652 align:middle line:84%
So one of the things that
maybe it comes back to

01:09:22.652 --> 01:09:23.569 align:middle line:90%
[? Iabo's ?] question.

01:09:23.569 --> 01:09:27.760 align:middle line:84%
So for some of these folks, the
aether was a word for something

01:09:27.760 --> 01:09:29.529 align:middle line:84%
that you didn't really
know what it was--

01:09:29.529 --> 01:09:32.950 align:middle line:84%
a subject, a topic
they figured had

01:09:32.950 --> 01:09:36.732 align:middle line:84%
to be everywhere because
they could infer its effects.

01:09:36.732 --> 01:09:38.899 align:middle line:84%
If I wiggle something here,
something happens there.

01:09:38.899 --> 01:09:40.740 align:middle line:84%
There must be some
medium that transmitted

01:09:40.740 --> 01:09:44.140 align:middle line:90%
the influence from A to B.

01:09:44.140 --> 01:09:46.457 align:middle line:84%
How could a moving bar
magnet possibly affect

01:09:46.457 --> 01:09:47.290 align:middle line:90%
an electric current?

01:09:47.290 --> 01:09:49.899 align:middle line:84%
Because they're both immersed
in the shared medium,

01:09:49.899 --> 01:09:52.069 align:middle line:90%
this all-pervasive medium.

01:09:52.069 --> 01:09:53.200 align:middle line:90%
And so they gave it a name.

01:09:53.200 --> 01:09:54.700 align:middle line:84%
They gave it a name
long before they

01:09:54.700 --> 01:09:57.610 align:middle line:84%
had any articulated
descriptions or analogies of it.

01:09:57.610 --> 01:10:00.880 align:middle line:84%
They called it the light-bearing
aether, luminiferous aether

01:10:00.880 --> 01:10:05.372 align:middle line:84%
decades before they had any
more specific ideas about it.

01:10:05.372 --> 01:10:06.830 align:middle line:84%
And so in that
sense, I think it is

01:10:06.830 --> 01:10:09.438 align:middle line:84%
kind of like we're in a
similar situation today--

01:10:09.438 --> 01:10:11.480 align:middle line:84%
and we'll talk a bit about
this near the very end

01:10:11.480 --> 01:10:13.970 align:middle line:84%
of this semester--
with our quest

01:10:13.970 --> 01:10:15.780 align:middle line:84%
to understand what's
the world made of.

01:10:15.780 --> 01:10:18.890 align:middle line:84%
And we have some other-- we have
very finely articulated models,

01:10:18.890 --> 01:10:21.290 align:middle line:84%
like the standard model,
and this kind of neutrino,

01:10:21.290 --> 01:10:23.810 align:middle line:84%
and that kind of electron,
and up quarks and down quarks,

01:10:23.810 --> 01:10:26.610 align:middle line:84%
and gluons, and Higgs boson,
all this very specific stuff.

01:10:26.610 --> 01:10:31.520 align:middle line:84%
And that amounts, as you may
know, for not more than 5%

01:10:31.520 --> 01:10:34.400 align:middle line:84%
of the kind of mass
balance of the universe.

01:10:34.400 --> 01:10:36.560 align:middle line:84%
We've explained
5% of the universe

01:10:36.560 --> 01:10:40.610 align:middle line:84%
with unbelievable precision,
out to 12 decimal places.

01:10:40.610 --> 01:10:42.210 align:middle line:90%
Thank you very much.

01:10:42.210 --> 01:10:44.600 align:middle line:84%
And we know Nothing
with a capital N,

01:10:44.600 --> 01:10:49.040 align:middle line:84%
Nothing about the other
95% of the energy balance.

01:10:49.040 --> 01:10:50.340 align:middle line:90%
So we give it names.

01:10:50.340 --> 01:10:52.280 align:middle line:84%
We call it dark matter
and dark energy,

01:10:52.280 --> 01:10:54.500 align:middle line:84%
again as we'll come
to near the end

01:10:54.500 --> 01:10:56.190 align:middle line:90%
the very, very end of the term.

01:10:56.190 --> 01:10:58.795 align:middle line:84%
And I think, in some
sense, I have some sympathy

01:10:58.795 --> 01:11:00.170 align:middle line:84%
with either my
present colleagues

01:11:00.170 --> 01:11:02.570 align:middle line:84%
and myself and/or
with the people

01:11:02.570 --> 01:11:04.100 align:middle line:90%
of Faraday's and Maxwell age.

01:11:04.100 --> 01:11:06.050 align:middle line:84%
They didn't know
what the aether was,

01:11:06.050 --> 01:11:07.442 align:middle line:84%
but they knew it
had to be there.

01:11:07.442 --> 01:11:08.900 align:middle line:84%
It was conveying
all these effects.

01:11:08.900 --> 01:11:11.240 align:middle line:84%
They could measure the effects
of disturbing the aether,

01:11:11.240 --> 01:11:13.080 align:middle line:90%
as far as they were concerned.

01:11:13.080 --> 01:11:15.710 align:middle line:84%
So they gave it a name, a
kind of placeholder name,

01:11:15.710 --> 01:11:17.448 align:middle line:84%
partly to help
organize their studies.

01:11:17.448 --> 01:11:19.490 align:middle line:84%
Oh, I'm studying the
luminiferous aether as well.

01:11:19.490 --> 01:11:22.440 align:middle line:84%
That helps get scholars
on the same page.

01:11:22.440 --> 01:11:24.800 align:middle line:84%
They would give
their best estimates

01:11:24.800 --> 01:11:26.630 align:middle line:84%
of what they thought
the thing was like

01:11:26.630 --> 01:11:27.650 align:middle line:90%
and how it would behave.

01:11:27.650 --> 01:11:28.880 align:middle line:90%
But they didn't know, right?

01:11:28.880 --> 01:11:33.930 align:middle line:84%
They had better or less
well compelling responses.

01:11:33.930 --> 01:11:36.680 align:middle line:84%
And I think we're in a very
similar situation today--

01:11:36.680 --> 01:11:39.230 align:middle line:84%
not by design, not by our
hopes-- because we have been

01:11:39.230 --> 01:11:44.540 align:middle line:84%
stymied now for decades
to get any more carefully

01:11:44.540 --> 01:11:47.930 align:middle line:84%
articulated knowledge
about what specifically

01:11:47.930 --> 01:11:51.350 align:middle line:84%
is dark matter that seems to be
filling every galaxy much, much

01:11:51.350 --> 01:11:53.283 align:middle line:90%
more so than ordinary matter.

01:11:53.283 --> 01:11:55.700 align:middle line:84%
And what particularly is this
other separate kind of stuff

01:11:55.700 --> 01:11:57.690 align:middle line:90%
that we now call dark energy?

01:11:57.690 --> 01:12:00.890 align:middle line:84%
So I think, again, I don't want
to say we've learned nothing

01:12:00.890 --> 01:12:02.330 align:middle line:90%
since 1820.

01:12:02.330 --> 01:12:05.810 align:middle line:84%
But we can see some
maybe humbling,

01:12:05.810 --> 01:12:09.650 align:middle line:84%
humility-inducing parallels
between our best efforts

01:12:09.650 --> 01:12:13.040 align:middle line:84%
today and the efforts of very,
very earnest, talented folks

01:12:13.040 --> 01:12:14.580 align:middle line:90%
from long ago.

01:12:14.580 --> 01:12:16.640 align:middle line:84%
That's a great-- again,
we'll keep that in mind

01:12:16.640 --> 01:12:19.550 align:middle line:84%
as we march forward
throughout the term.

01:12:19.550 --> 01:12:21.200 align:middle line:84%
Julian asks, why were
they so reluctant

01:12:21.200 --> 01:12:22.735 align:middle line:90%
to accept action at a distance?

01:12:22.735 --> 01:12:24.110 align:middle line:84%
And how did we
come to accept it?

01:12:24.110 --> 01:12:24.830 align:middle line:90%
Oh, good.

01:12:24.830 --> 01:12:26.300 align:middle line:84%
Let me take the
first part first.

01:12:26.300 --> 01:12:30.230 align:middle line:84%
Action at a distance,
that's a great topic.

01:12:30.230 --> 01:12:32.660 align:middle line:84%
Newton famously
says, when it comes

01:12:32.660 --> 01:12:37.130 align:middle line:84%
to the phenomena of gravity,
I feign no hypotheses.

01:12:37.130 --> 01:12:39.860 align:middle line:84%
Hypotheses non
fingo was the Latin.

01:12:39.860 --> 01:12:43.340 align:middle line:84%
He says, I think that
quantitatively the effect

01:12:43.340 --> 01:12:45.380 align:middle line:84%
of one mass exerting
a force on the other

01:12:45.380 --> 01:12:47.170 align:middle line:84%
goes as the product
of the masses divided

01:12:47.170 --> 01:12:48.920 align:middle line:84%
by the square of their
distance is the law

01:12:48.920 --> 01:12:50.210 align:middle line:90%
of universal gravitation.

01:12:50.210 --> 01:12:52.320 align:middle line:84%
What's the underlying
reason for that?

01:12:52.320 --> 01:12:55.340 align:middle line:84%
He says, for that, I
feign no hypotheses.

01:12:55.340 --> 01:12:56.990 align:middle line:84%
He actually had a
lot of hypotheses.

01:12:56.990 --> 01:12:59.090 align:middle line:84%
He just knew not
to write them down.

01:12:59.090 --> 01:13:01.970 align:middle line:84%
A lot of scholars have argued
that he was actually convinced,

01:13:01.970 --> 01:13:04.070 align:middle line:84%
at least by analogy,
that gravity

01:13:04.070 --> 01:13:06.590 align:middle line:84%
was a kind of alchemical
effect, even at a time when

01:13:06.590 --> 01:13:08.900 align:middle line:90%
alchemy was in poor repute.

01:13:08.900 --> 01:13:11.570 align:middle line:84%
So he said outwardly
and publicly, I

01:13:11.570 --> 01:13:12.778 align:middle line:90%
don't know what it is.

01:13:12.778 --> 01:13:14.570 align:middle line:84%
But he seems to have
at least been inspired

01:13:14.570 --> 01:13:16.640 align:middle line:90%
in part by these very--

01:13:16.640 --> 01:13:18.970 align:middle line:84%
what we would now call occult
forces, where something

01:13:18.970 --> 01:13:20.720 align:middle line:84%
can somehow have an
influence on something

01:13:20.720 --> 01:13:24.230 align:middle line:84%
else instantly across
time and space.

01:13:24.230 --> 01:13:27.920 align:middle line:84%
So Newton was comfortable
with the notion of action

01:13:27.920 --> 01:13:30.200 align:middle line:84%
at a distance, that somehow
the Earth could instantly

01:13:30.200 --> 01:13:32.075 align:middle line:84%
tug on the moon and vice
versa without having

01:13:32.075 --> 01:13:35.780 align:middle line:84%
to wait for some influence to
travel between here and there.

01:13:35.780 --> 01:13:38.240 align:middle line:84%
That, even in its
day, was criticized

01:13:38.240 --> 01:13:40.640 align:middle line:84%
by a number of scholars,
even in Newton's own day

01:13:40.640 --> 01:13:42.500 align:middle line:84%
because they thought
it did sound occult.

01:13:42.500 --> 01:13:44.685 align:middle line:90%
It sounds like witchcraft.

01:13:44.685 --> 01:13:47.060 align:middle line:84%
How could this thing possibly
affect something over there

01:13:47.060 --> 01:13:48.320 align:middle line:90%
if everything else I see--

01:13:48.320 --> 01:13:50.330 align:middle line:90%
I throw a pond--

01:13:50.330 --> 01:13:52.100 align:middle line:90%
excuse me, a rock into the pond.

01:13:52.100 --> 01:13:53.780 align:middle line:90%
I see ripples spread out.

01:13:53.780 --> 01:13:56.540 align:middle line:84%
The distant edges of the pond
aren't affected by my rock

01:13:56.540 --> 01:13:57.830 align:middle line:90%
until the ripples get there.

01:13:57.830 --> 01:14:00.830 align:middle line:84%
There were all kinds of
common sense observations

01:14:00.830 --> 01:14:02.600 align:middle line:84%
that suggested to
people like Leibniz--

01:14:02.600 --> 01:14:05.450 align:middle line:84%
I mean, like Newton's very
smart contemporaries--

01:14:05.450 --> 01:14:08.570 align:middle line:84%
that the physical world
seemed to convey influences

01:14:08.570 --> 01:14:10.520 align:middle line:84%
by requiring some
time for influence

01:14:10.520 --> 01:14:12.080 align:middle line:90%
to travel from A to B.

01:14:12.080 --> 01:14:15.110 align:middle line:84%
So Newton's action at a
distance already at least

01:14:15.110 --> 01:14:21.650 align:middle line:84%
had a curious reputation
among the savants who cared.

01:14:21.650 --> 01:14:25.940 align:middle line:84%
And then you get to someone
like Faraday, and Oersted,

01:14:25.940 --> 01:14:27.050 align:middle line:90%
and Thomas Young.

01:14:27.050 --> 01:14:30.320 align:middle line:84%
And now, they figure they have
a reason to finally give up

01:14:30.320 --> 01:14:32.990 align:middle line:84%
or to finally reject
that action at a distance

01:14:32.990 --> 01:14:35.360 align:middle line:84%
because they have
separate reasons based

01:14:35.360 --> 01:14:38.840 align:middle line:84%
on this wave theory of light
saying, oh, there's a seat.

01:14:38.840 --> 01:14:41.600 align:middle line:84%
There's a physical
explanation available to us

01:14:41.600 --> 01:14:43.970 align:middle line:84%
for how all these physical
phenomena are transmitted

01:14:43.970 --> 01:14:45.620 align:middle line:90%
from A to B across space.

01:14:45.620 --> 01:14:48.530 align:middle line:84%
They're all sitting in this
elastic medium, this aether.

01:14:48.530 --> 01:14:51.320 align:middle line:84%
And that can have a local
disturbance that propagates.

01:14:51.320 --> 01:14:54.710 align:middle line:84%
So there was, so to speak,
an added reason to pile on

01:14:54.710 --> 01:14:57.890 align:middle line:84%
and say, not only did people
wonder about Newton's action

01:14:57.890 --> 01:14:59.570 align:middle line:84%
at a distance in
Newton's own day.

01:14:59.570 --> 01:15:03.890 align:middle line:84%
Now, roughly 100, 110 years
later, we have new inputs.

01:15:03.890 --> 01:15:06.750 align:middle line:84%
We have new evidence
from our investigations

01:15:06.750 --> 01:15:09.030 align:middle line:84%
that suggest that Newton
hadn't known about it

01:15:09.030 --> 01:15:11.970 align:middle line:84%
or hadn't taken into account
at all, all the more reason

01:15:11.970 --> 01:15:15.760 align:middle line:84%
to try to find
out a local causes

01:15:15.760 --> 01:15:18.250 align:middle line:84%
yield local effects
kind of response.

01:15:18.250 --> 01:15:20.640 align:middle line:84%
So that starts
getting more and more

01:15:20.640 --> 01:15:23.310 align:middle line:84%
compelling to this
next generation.

01:15:23.310 --> 01:15:26.730 align:middle line:84%
Now, Julian asks, because
he knows what's coming,

01:15:26.730 --> 01:15:28.500 align:middle line:84%
why do we now accept
action at a distance?

01:15:28.500 --> 01:15:29.502 align:middle line:90%
We do and don't.

01:15:29.502 --> 01:15:31.210 align:middle line:84%
We have a love/hate
relationship with it.

01:15:31.210 --> 01:15:33.090 align:middle line:84%
I assume, Julian,
that you're referring

01:15:33.090 --> 01:15:36.433 align:middle line:84%
to quantum entanglement or
so-called quantum nonlocality.

01:15:36.433 --> 01:15:38.850 align:middle line:84%
If you're not referring to
that, I'm going to hijack this.

01:15:38.850 --> 01:15:40.810 align:middle line:84%
And I'm going to talk about
it because I just love it.

01:15:40.810 --> 01:15:42.690 align:middle line:84%
So we're going to talk about
that actually in a few classes,

01:15:42.690 --> 01:15:44.140 align:middle line:90%
a little bit later this term.

01:15:44.140 --> 01:15:47.130 align:middle line:84%
So how have we made
our awkward peace

01:15:47.130 --> 01:15:49.710 align:middle line:84%
with a very certain kind
of action at a distance,

01:15:49.710 --> 01:15:51.720 align:middle line:84%
not easily, not right
away, and thanks

01:15:51.720 --> 01:15:54.450 align:middle line:84%
to a lot of hard and
contested thinking?

01:15:54.450 --> 01:15:58.050 align:middle line:84%
That's a preview for
lecture 12, I think.

01:15:58.050 --> 01:16:00.878 align:middle line:84%
So we're going to talk
about quantum nonlocality

01:16:00.878 --> 01:16:03.170 align:middle line:84%
because it's one of my favorite
topics in the universe.

01:16:03.170 --> 01:16:04.740 align:middle line:90%
So we'll get to that, too.

01:16:04.740 --> 01:16:08.700 align:middle line:84%
But for a long, long time,
between let's say 1800

01:16:08.700 --> 01:16:12.150 align:middle line:84%
and the 1960s or
'70s, people were

01:16:12.150 --> 01:16:14.370 align:middle line:84%
quite content to say
that action of distance

01:16:14.370 --> 01:16:15.810 align:middle line:90%
is always, always bad.

01:16:15.810 --> 01:16:16.680 align:middle line:90%
We never want it.

01:16:16.680 --> 01:16:18.090 align:middle line:90%
We never want it in our physics.

01:16:18.090 --> 01:16:19.890 align:middle line:84%
And they had a
range of reasons why

01:16:19.890 --> 01:16:23.910 align:middle line:84%
they thought that was going
to be an acceptable approach.

01:16:23.910 --> 01:16:26.490 align:middle line:84%
Aiden and asks,
how accessible were

01:16:26.490 --> 01:16:28.690 align:middle line:84%
the lectures and later
universities' research?

01:16:28.690 --> 01:16:30.690 align:middle line:84%
I mentioned that Faraday
did not have much money

01:16:30.690 --> 01:16:31.590 align:middle line:90%
when he was younger.

01:16:31.590 --> 01:16:33.510 align:middle line:84%
But was he the
exception to the rule?

01:16:33.510 --> 01:16:35.920 align:middle line:84%
Or did class discrimination
prevent-- oh yeah, very good.

01:16:35.920 --> 01:16:39.060 align:middle line:84%
So in Britain, in
British history, I mean,

01:16:39.060 --> 01:16:40.740 align:middle line:84%
the rough shorthand
is we're always

01:16:40.740 --> 01:16:42.210 align:middle line:84%
talking about class
discrimination,

01:16:42.210 --> 01:16:43.650 align:middle line:90%
so including in Faraday's time.

01:16:43.650 --> 01:16:46.410 align:middle line:84%
Faraday was absolutely the
exception who proved the rule.

01:16:46.410 --> 01:16:49.170 align:middle line:84%
It was, as I say, this
rags to riches story.

01:16:49.170 --> 01:16:51.780 align:middle line:84%
It wasn't that there
was no social mobility.

01:16:51.780 --> 01:16:54.060 align:middle line:84%
And you can read any
Charles Dickens novel

01:16:54.060 --> 01:16:55.980 align:middle line:84%
to see some characters
who have a breakthrough

01:16:55.980 --> 01:16:59.070 align:middle line:84%
and rise above their station
in the language of the time.

01:16:59.070 --> 01:17:01.530 align:middle line:84%
But in natural
philosophy, Faraday

01:17:01.530 --> 01:17:04.450 align:middle line:84%
stands out as a
pretty unusual case.

01:17:04.450 --> 01:17:09.590 align:middle line:84%
And the universities as well,
there were scholarship students

01:17:09.590 --> 01:17:12.350 align:middle line:84%
at places like
Cambridge, then as now.

01:17:12.350 --> 01:17:15.048 align:middle line:84%
So it wasn't only very,
very rich children

01:17:15.048 --> 01:17:17.090 align:middle line:84%
of very rich families who
could go to university.

01:17:17.090 --> 01:17:19.650 align:middle line:84%
But it was tilted very
strongly that way.

01:17:19.650 --> 01:17:22.490 align:middle line:84%
And in fact, it's only in
Britain in the middle decades

01:17:22.490 --> 01:17:24.590 align:middle line:84%
of the 20th century,
like 100 years

01:17:24.590 --> 01:17:27.140 align:middle line:84%
after the days of
Thompson and Maxwell,

01:17:27.140 --> 01:17:28.910 align:middle line:84%
when there's a very
large university

01:17:28.910 --> 01:17:30.710 align:middle line:84%
reform throughout
Britain to make

01:17:30.710 --> 01:17:34.740 align:middle line:84%
much more accessible colleges,
universities for many,

01:17:34.740 --> 01:17:37.190 align:middle line:84%
many more for people from
many more backgrounds.

01:17:37.190 --> 01:17:40.730 align:middle line:84%
That large scale national
university reform comes really,

01:17:40.730 --> 01:17:42.810 align:middle line:84%
in earnest, like
100 years later.

01:17:42.810 --> 01:17:44.540 align:middle line:84%
So there were students
on fellowship.

01:17:44.540 --> 01:17:46.580 align:middle line:84%
In fact, Isaac Newton
was a scholarship student

01:17:46.580 --> 01:17:51.620 align:middle line:84%
when he went to Cambridge in
his own lifetime in the 1600s.

01:17:51.620 --> 01:17:53.420 align:middle line:84%
Often, they would
have to be basically

01:17:53.420 --> 01:17:57.530 align:middle line:84%
like a butler or a maid
for their roommates.

01:17:57.530 --> 01:17:59.120 align:middle line:90%
Not an ideal situation, right?

01:17:59.120 --> 01:18:00.890 align:middle line:90%
This was not like work study.

01:18:00.890 --> 01:18:02.420 align:middle line:84%
It was like, you
have to go clean up

01:18:02.420 --> 01:18:05.210 align:middle line:84%
for your rich roommate,
not what I recommend today.

01:18:05.210 --> 01:18:07.752 align:middle line:84%
So there were ways to
be a student at some

01:18:07.752 --> 01:18:09.210 align:middle line:84%
of these elite
British universities

01:18:09.210 --> 01:18:12.030 align:middle line:84%
from more humble
backgrounds, not great.

01:18:12.030 --> 01:18:14.400 align:middle line:84%
This was well outside the
reach of someone like Faraday.

01:18:14.400 --> 01:18:18.120 align:middle line:84%
So again, the latter didn't
extend arbitrarily low.

01:18:18.120 --> 01:18:21.180 align:middle line:84%
But there was a range of
social classes in universities

01:18:21.180 --> 01:18:24.130 align:middle line:90%
in this time, not a full range.

01:18:24.130 --> 01:18:26.568 align:middle line:84%
And that begins to
change pretty slowly all

01:18:26.568 --> 01:18:28.110 align:middle line:84%
over the world,
including in Britain,

01:18:28.110 --> 01:18:29.760 align:middle line:84%
including, frankly,
in the United States.

01:18:29.760 --> 01:18:31.845 align:middle line:84%
And of course, we still
have challenges even here.

01:18:31.845 --> 01:18:32.970 align:middle line:90%
So that's a great question.

01:18:32.970 --> 01:18:34.440 align:middle line:84%
Faraday was, indeed,
the exception

01:18:34.440 --> 01:18:38.610 align:middle line:84%
who proves the rule
within natural philosophy.

01:18:38.610 --> 01:18:39.727 align:middle line:90%
Yeah, great question.

01:18:39.727 --> 01:18:40.810 align:middle line:90%
Any other questions there?

01:18:40.810 --> 01:18:44.677 align:middle line:84%
If not, I realize we're
pretty much at the hour.

01:18:44.677 --> 01:18:45.760 align:middle line:90%
Those are great questions.

01:18:45.760 --> 01:18:46.510 align:middle line:90%
Thank you so much.

01:18:46.510 --> 01:18:48.170 align:middle line:90%
I hope it's not too clunky.

01:18:48.170 --> 01:18:50.120 align:middle line:84%
I'll try to get
better at flowing

01:18:50.120 --> 01:18:53.158 align:middle line:84%
in the questions and discussion
throughout these Zoom lectures.

01:18:53.158 --> 01:18:54.200 align:middle line:90%
Anyway, thanks, everyone.

01:18:54.200 --> 01:18:55.183 align:middle line:90%
Great, great questions.

01:18:55.183 --> 01:18:57.350 align:middle line:84%
I'll post the video as soon
as it's done processing.

01:18:57.350 --> 01:18:58.640 align:middle line:90%
It'll go to the Canvas site.

01:18:58.640 --> 01:19:00.560 align:middle line:84%
And we'll pick it up
there for next week.

01:19:00.560 --> 01:19:01.760 align:middle line:90%
Everyone stay well.

01:19:01.760 --> 01:19:03.640 align:middle line:90%
See you soon.

01:19:03.640 --> 01:19:19.000 align:middle line:90%