WEBVTT 00:00:00.000 --> 00:00:04.338 align:middle line:84% [SQUEAKING] [RUSTLING] [CLICKING] 00:00:04.338 --> 00:00:11.090 align:middle line:90% 00:00:11.090 --> 00:00:15.560 align:middle line:84% DAVID KAISER: Today we're starting 00:00:15.560 --> 00:00:17.790 align:middle line:90% this new unit for the class. 00:00:17.790 --> 00:00:20.180 align:middle line:84% So the first main unit-- we had a kind 00:00:20.180 --> 00:00:23.570 align:middle line:84% of warm-up unit of a kind of 19th-century legacy, 00:00:23.570 --> 00:00:25.010 align:middle line:90% as you probably remember. 00:00:25.010 --> 00:00:27.050 align:middle line:84% And then we spent a good chunk of time 00:00:27.050 --> 00:00:28.670 align:middle line:84% right up until the previous class 00:00:28.670 --> 00:00:33.300 align:middle line:84% session on looking at physics really during the first 20 00:00:33.300 --> 00:00:37.400 align:middle line:84% or 30 years or so of the 20th century-- the real focus 00:00:37.400 --> 00:00:42.050 align:middle line:84% on what were some of the kind of approaches 00:00:42.050 --> 00:00:45.980 align:middle line:84% conceptually and intellectually that physicists 00:00:45.980 --> 00:00:47.900 align:middle line:84% in many parts of the world were using 00:00:47.900 --> 00:00:50.450 align:middle line:90% to try to make sense of nature. 00:00:50.450 --> 00:00:53.360 align:middle line:84% And that got kind of bound up with what we now 00:00:53.360 --> 00:00:56.180 align:middle line:84% call the origins of modern physics-- relativity 00:00:56.180 --> 00:00:57.780 align:middle line:84% and quantum theory in particular. 00:00:57.780 --> 00:01:00.740 align:middle line:84% We were also looking at the kinds of institutions. 00:01:00.740 --> 00:01:05.120 align:middle line:84% What kinds of settings were many of those investigations taking 00:01:05.120 --> 00:01:06.350 align:middle line:90% place in? 00:01:06.350 --> 00:01:10.220 align:middle line:84% And so with today's class and for the next several to come, 00:01:10.220 --> 00:01:12.900 align:middle line:84% we're now looking at the next main unit, which 00:01:12.900 --> 00:01:16.200 align:middle line:84% is when physics and physicists start interacting much more 00:01:16.200 --> 00:01:20.670 align:middle line:84% directly with statecraft, with formal overt politics, 00:01:20.670 --> 00:01:24.690 align:middle line:84% with governments-- nation-state governments and even 00:01:24.690 --> 00:01:25.920 align:middle line:90% international relations. 00:01:25.920 --> 00:01:28.710 align:middle line:84% And that, as we'll see, brings up 00:01:28.710 --> 00:01:31.500 align:middle line:84% a new host of questions, intellectual challenges, 00:01:31.500 --> 00:01:33.420 align:middle line:84% institutional relationships and all that 00:01:33.420 --> 00:01:36.570 align:middle line:84% for physicists throughout-- what we'll mostly focus on-- 00:01:36.570 --> 00:01:38.130 align:middle line:84% throughout various parts of Europe 00:01:38.130 --> 00:01:39.540 align:middle line:90% and then the United States. 00:01:39.540 --> 00:01:40.530 align:middle line:84% Although, there's lots to be said 00:01:40.530 --> 00:01:41.580 align:middle line:84% about other parts of the world too, 00:01:41.580 --> 00:01:44.020 align:middle line:84% and I'd be glad to talk about that if you have questions. 00:01:44.020 --> 00:01:46.470 align:middle line:84% So today we're launching this next main unit 00:01:46.470 --> 00:01:48.820 align:middle line:84% of physics-- physicists and the state, 00:01:48.820 --> 00:01:50.260 align:middle line:90% meaning through governments. 00:01:50.260 --> 00:01:52.260 align:middle line:84% And we're going to start by looking actually 00:01:52.260 --> 00:01:54.060 align:middle line:84% at developments in Germany where so much 00:01:54.060 --> 00:01:57.450 align:middle line:84% of that work on what we now call modern physics had unfolded. 00:01:57.450 --> 00:02:00.290 align:middle line:90% So that's our job for today. 00:02:00.290 --> 00:02:02.690 align:middle line:84% We have, as usual, three main parts for the class. 00:02:02.690 --> 00:02:06.800 align:middle line:84% We're going to recap or revisit some material that we actually 00:02:06.800 --> 00:02:09.032 align:middle line:84% looked rather briefly at a few sessions ago 00:02:09.032 --> 00:02:10.490 align:middle line:84% when we were talking about Einstein 00:02:10.490 --> 00:02:12.290 align:middle line:84% and the general theory of relativity 00:02:12.290 --> 00:02:15.710 align:middle line:84% and this movement that was called Deutsche Physik, which 00:02:15.710 --> 00:02:18.650 align:middle line:84% is usually translated into English as Aryan physics. 00:02:18.650 --> 00:02:20.600 align:middle line:84% A literal translation would be German. 00:02:20.600 --> 00:02:26.300 align:middle line:84% But it really meant this kind of race or racially based notion 00:02:26.300 --> 00:02:28.860 align:middle line:84% of what a proper approach to physics would be. 00:02:28.860 --> 00:02:30.950 align:middle line:84% So we'll talk about Deutsche Physik. 00:02:30.950 --> 00:02:35.300 align:middle line:84% Then we'll pivot and talk for a good chunk of today 00:02:35.300 --> 00:02:38.210 align:middle line:84% about some developments in nuclear physics, which 00:02:38.210 --> 00:02:39.980 align:middle line:84% is quite, quite new in this period. 00:02:39.980 --> 00:02:43.400 align:middle line:84% And in particular, the ideas about nuclear fission. 00:02:43.400 --> 00:02:46.730 align:middle line:84% And as you see there, again, optional lecture notes 00:02:46.730 --> 00:02:49.520 align:middle line:84% on the course Canvas site to dig into some of that a bit more. 00:02:49.520 --> 00:02:51.020 align:middle line:84% I'll go through quickly some things, 00:02:51.020 --> 00:02:53.930 align:middle line:84% but there's some more details in the optional notes. 00:02:53.930 --> 00:02:57.110 align:middle line:84% And the last part for today is really 00:02:57.110 --> 00:03:00.640 align:middle line:84% looking at the collision or the union of these first two 00:03:00.640 --> 00:03:01.140 align:middle line:90% topics. 00:03:01.140 --> 00:03:03.990 align:middle line:84% And we'll look at how did Werner Heisenberg himself and many 00:03:03.990 --> 00:03:06.540 align:middle line:84% of his immediate colleagues who stayed 00:03:06.540 --> 00:03:09.240 align:middle line:84% within Germany after the rise of Hitler, 00:03:09.240 --> 00:03:12.185 align:middle line:84% what did nuclear physics mean for them? 00:03:12.185 --> 00:03:13.560 align:middle line:84% And what did they think they were 00:03:13.560 --> 00:03:18.240 align:middle line:84% doing as they worked very, very hard during the war years 00:03:18.240 --> 00:03:20.615 align:middle line:84% on topics related to nuclear physics and nuclear fission? 00:03:20.615 --> 00:03:22.573 align:middle line:84% So that's what we're going to talk about today. 00:03:22.573 --> 00:03:24.600 align:middle line:84% And then on Wednesday, we'll turn and look 00:03:24.600 --> 00:03:27.930 align:middle line:84% at some developments in Britain, and then 00:03:27.930 --> 00:03:31.270 align:middle line:84% especially in the United States around similar timescales. 00:03:31.270 --> 00:03:31.810 align:middle line:90% OK. 00:03:31.810 --> 00:03:33.790 align:middle line:84% So this is just a reminder-- something 00:03:33.790 --> 00:03:35.740 align:middle line:84% we talked a little bit about when we talked 00:03:35.740 --> 00:03:37.030 align:middle line:90% about general relativity. 00:03:37.030 --> 00:03:39.490 align:middle line:90% As early as the spring of 1920-- 00:03:39.490 --> 00:03:43.840 align:middle line:84% I believe the very first rally was April or so of 1920-- 00:03:43.840 --> 00:03:47.830 align:middle line:84% several political opportunists within Germany took advantage 00:03:47.830 --> 00:03:49.450 align:middle line:84% of the fact that Einstein himself, 00:03:49.450 --> 00:03:51.490 align:middle line:84% as well as his general theory of relativity, 00:03:51.490 --> 00:03:54.070 align:middle line:84% had become kind of overnight sensations. 00:03:54.070 --> 00:03:56.320 align:middle line:84% Einstein was everywhere in the news 00:03:56.320 --> 00:04:00.370 align:middle line:84% after the dramatic eclipse expedition results. 00:04:00.370 --> 00:04:05.170 align:middle line:84% He was heralded around the world as this amazing genius who had 00:04:05.170 --> 00:04:06.970 align:middle line:90% toppled Isaac Newton's physics. 00:04:06.970 --> 00:04:11.830 align:middle line:84% And so some opportunists within kind of war-ravaged Germany 00:04:11.830 --> 00:04:14.200 align:middle line:84% took advantage of Einstein's fame 00:04:14.200 --> 00:04:16.420 align:middle line:90% to get their own message out. 00:04:16.420 --> 00:04:19.040 align:middle line:84% Their message was not really about physics, 00:04:19.040 --> 00:04:20.200 align:middle line:90% so they used physics-- 00:04:20.200 --> 00:04:22.990 align:middle line:84% or the debates about some ideas in physics-- 00:04:22.990 --> 00:04:24.850 align:middle line:84% to stage what was really ultimately 00:04:24.850 --> 00:04:28.210 align:middle line:90% a kind of political movement. 00:04:28.210 --> 00:04:31.370 align:middle line:84% So they began staging anti-relativity rallies 00:04:31.370 --> 00:04:35.390 align:middle line:84% in places like sports arenas and opera houses and music halls 00:04:35.390 --> 00:04:36.830 align:middle line:90% and so on. 00:04:36.830 --> 00:04:39.230 align:middle line:90% And the kind of public face-- 00:04:39.230 --> 00:04:44.990 align:middle line:84% the faces that were most often headlining these events-- 00:04:44.990 --> 00:04:47.938 align:middle line:84% were these two German Nobel Laureates in physics, both 00:04:47.938 --> 00:04:48.980 align:middle line:90% experimental physicists-- 00:04:48.980 --> 00:04:51.110 align:middle line:84% Johannes Stark and Philipp Lenard. 00:04:51.110 --> 00:04:53.150 align:middle line:84% And again, there's all kinds of ironies here. 00:04:53.150 --> 00:04:56.750 align:middle line:84% Stark had actually invited Einstein back in 1907 00:04:56.750 --> 00:04:59.150 align:middle line:84% to write a review article on Einstein's own work 00:04:59.150 --> 00:05:00.817 align:middle line:84% because Stark thought it was interesting 00:05:00.817 --> 00:05:02.420 align:middle line:84% but not getting sufficient attention. 00:05:02.420 --> 00:05:06.710 align:middle line:84% Philipp Lenard won his own Nobel Prize in 1905 00:05:06.710 --> 00:05:09.888 align:middle line:84% for Lenard's experiments on the photoelectric effect, 00:05:09.888 --> 00:05:11.930 align:middle line:84% which of course, triggered Einstein's imagination 00:05:11.930 --> 00:05:12.590 align:middle line:90% directly. 00:05:12.590 --> 00:05:15.620 align:middle line:84% These folks had all kinds of physics interests 00:05:15.620 --> 00:05:18.560 align:middle line:84% in common in the early years of the 20th century. 00:05:18.560 --> 00:05:22.760 align:middle line:84% But by the 1920s, they had really come quite far apart. 00:05:22.760 --> 00:05:25.190 align:middle line:84% So the rhetoric of what became known as the Deutsche 00:05:25.190 --> 00:05:27.230 align:middle line:84% Physik, or Aryan physics movement, 00:05:27.230 --> 00:05:32.320 align:middle line:84% was that of the tatmensch, the man of action, in their terms, 00:05:32.320 --> 00:05:35.680 align:middle line:84% that Newton and Galileo and Michael Faraday, 00:05:35.680 --> 00:05:39.190 align:middle line:84% according to people like Philipp Lenard, had all been Aryan. 00:05:39.190 --> 00:05:42.520 align:middle line:84% They'd all been of this what Lenard and Stark considered 00:05:42.520 --> 00:05:46.210 align:middle line:84% the kind of purest kind of racial stock, 00:05:46.210 --> 00:05:49.540 align:middle line:84% that they were just like the kinds of people 00:05:49.540 --> 00:05:53.410 align:middle line:84% the Nazis wanted to further elevate, according to Lenard, 00:05:53.410 --> 00:05:55.840 align:middle line:84% even though Newton and Galileo and Faraday 00:05:55.840 --> 00:05:58.420 align:middle line:84% themselves would certainly not have recognized that as such. 00:05:58.420 --> 00:06:00.760 align:middle line:84% And Lenard argued that these people, 00:06:00.760 --> 00:06:05.320 align:middle line:84% unlike people like Einstein, these older heroes of physics 00:06:05.320 --> 00:06:08.410 align:middle line:84% had partaken in the same kind of active-- 00:06:08.410 --> 00:06:13.100 align:middle line:84% man of action kind of spirit as Adolf Hitler himself. 00:06:13.100 --> 00:06:16.250 align:middle line:84% Really quite striking to go back and read some of this material. 00:06:16.250 --> 00:06:18.250 align:middle line:84% And as I mentioned in the previous time, 00:06:18.250 --> 00:06:21.580 align:middle line:84% in one of Lenard's books from the 1940s, 00:06:21.580 --> 00:06:23.950 align:middle line:84% he would include these portraits of people 00:06:23.950 --> 00:06:26.290 align:middle line:84% like Isaac Newton shown here to try 00:06:26.290 --> 00:06:28.300 align:middle line:84% to make the point that these people did not 00:06:28.300 --> 00:06:30.635 align:middle line:84% have so-called Jewish features, that even 00:06:30.635 --> 00:06:32.510 align:middle line:84% literally the shape of their face, their nose 00:06:32.510 --> 00:06:35.900 align:middle line:84% and these things proved, according to Lenard, 00:06:35.900 --> 00:06:38.870 align:middle line:84% that they were of appropriate pure racial stock, 00:06:38.870 --> 00:06:41.720 align:middle line:84% unlike the people that Lenard now 00:06:41.720 --> 00:06:44.770 align:middle line:90% was denigrating so vehemently. 00:06:44.770 --> 00:06:46.360 align:middle line:84% And so the group began on the fringes. 00:06:46.360 --> 00:06:49.750 align:middle line:84% This was really a fringe effort starting in 1920. 00:06:49.750 --> 00:06:52.070 align:middle line:84% But just a little over a decade later, 00:06:52.070 --> 00:06:54.580 align:middle line:84% they had moved squarely into the center within Germany, 00:06:54.580 --> 00:06:57.610 align:middle line:84% especially after the Nazis achieved power 00:06:57.610 --> 00:06:59.200 align:middle line:90% in January of 1933. 00:06:59.200 --> 00:07:01.240 align:middle line:84% Again, as you may know, Adolf Hitler 00:07:01.240 --> 00:07:05.890 align:middle line:84% was elected chancellor of Germany in late January of '33. 00:07:05.890 --> 00:07:08.110 align:middle line:84% And the entire Nazi party then began 00:07:08.110 --> 00:07:13.060 align:middle line:84% to take over or be put in charge of a series 00:07:13.060 --> 00:07:18.180 align:middle line:90% of German government ministries. 00:07:18.180 --> 00:07:21.300 align:middle line:84% And so in particular, they took over things 00:07:21.300 --> 00:07:22.900 align:middle line:90% like the Education Ministry. 00:07:22.900 --> 00:07:24.840 align:middle line:84% As you may remember from early in class, 00:07:24.840 --> 00:07:27.120 align:middle line:84% in Germany in particular, especially after there 00:07:27.120 --> 00:07:29.130 align:middle line:84% was a single unified Germany, there 00:07:29.130 --> 00:07:32.970 align:middle line:84% was one federal level, government level ministry 00:07:32.970 --> 00:07:35.460 align:middle line:84% that would place professors in basically 00:07:35.460 --> 00:07:39.900 align:middle line:84% every open slot within this kind of state-run university system. 00:07:39.900 --> 00:07:43.140 align:middle line:84% So the adherence of Deutsche Physik, 00:07:43.140 --> 00:07:46.200 align:middle line:84% who had begun as early as 1920, were suddenly 00:07:46.200 --> 00:07:48.840 align:middle line:84% basically in charge of things like 00:07:48.840 --> 00:07:50.682 align:middle line:84% every single professorial appointment 00:07:50.682 --> 00:07:52.140 align:middle line:84% in all the universities in Germany. 00:07:52.140 --> 00:07:55.360 align:middle line:84% Of course, much beyond that as well. 00:07:55.360 --> 00:07:59.160 align:middle line:84% So Hitler's elected in 1930-- in January of 1933. 00:07:59.160 --> 00:08:01.920 align:middle line:84% By April of that year-- very quickly-- 00:08:01.920 --> 00:08:05.340 align:middle line:84% the Nazis had begun to implement so-called civil service laws. 00:08:05.340 --> 00:08:09.360 align:middle line:84% These were basically race-based requirements for people 00:08:09.360 --> 00:08:11.280 align:middle line:90% to hold government positions. 00:08:11.280 --> 00:08:14.500 align:middle line:84% And this included things like university faculty. 00:08:14.500 --> 00:08:16.480 align:middle line:84% There were state-run universities. 00:08:16.480 --> 00:08:18.300 align:middle line:84% So the so-called civil service laws 00:08:18.300 --> 00:08:22.560 align:middle line:84% which forbid people of non-Ayran descent, like Jews and others, 00:08:22.560 --> 00:08:25.350 align:middle line:84% from holding government jobs, this 00:08:25.350 --> 00:08:29.190 align:middle line:84% starts to trigger a very, very rapid exodus 00:08:29.190 --> 00:08:30.930 align:middle line:90% of scholars out of Germany. 00:08:30.930 --> 00:08:34.650 align:middle line:84% Either they were fired, or they were not personally fired, 00:08:34.650 --> 00:08:38.190 align:middle line:84% but were concerned about the direction things were heading, 00:08:38.190 --> 00:08:40.500 align:middle line:84% and they left in protest over the way their colleagues 00:08:40.500 --> 00:08:42.340 align:middle line:90% and students were treated. 00:08:42.340 --> 00:08:47.250 align:middle line:84% And so this triggers about 100 physicists and mathematicians 00:08:47.250 --> 00:08:52.890 align:middle line:84% who leave Germany pretty quickly starting in around 1933. 00:08:52.890 --> 00:08:55.630 align:middle line:84% And many of them head toward both Britain and the United 00:08:55.630 --> 00:08:56.770 align:middle line:90% States. 00:08:56.770 --> 00:08:57.530 align:middle line:90% They move. 00:08:57.530 --> 00:08:58.780 align:middle line:90% Some of them move permanently. 00:08:58.780 --> 00:09:00.697 align:middle line:84% Some of them move for the duration of the wall 00:09:00.697 --> 00:09:02.620 align:middle line:84% and then relocate back to Germany. 00:09:02.620 --> 00:09:04.340 align:middle line:84% But many of them never went back. 00:09:04.340 --> 00:09:07.510 align:middle line:84% So most famously, Einstein himself left Germany, 00:09:07.510 --> 00:09:11.230 align:middle line:84% renounced his position with the Prussian Academy of Sciences, 00:09:11.230 --> 00:09:14.538 align:middle line:84% and he moved to the Institute for Advanced Study 00:09:14.538 --> 00:09:15.580 align:middle line:90% in Princeton, New Jersey. 00:09:15.580 --> 00:09:17.830 align:middle line:84% In fact, he was the first faculty member hired there. 00:09:17.830 --> 00:09:20.030 align:middle line:84% The Institute itself was brand new. 00:09:20.030 --> 00:09:22.570 align:middle line:84% So Einstein moves to the United States. 00:09:22.570 --> 00:09:26.170 align:middle line:84% Erwin Schrodinger, who is not Jewish, but nonetheless 00:09:26.170 --> 00:09:29.800 align:middle line:84% was very concerned very quickly at the direction 00:09:29.800 --> 00:09:31.750 align:middle line:84% of these so-called civil service laws, 00:09:31.750 --> 00:09:33.700 align:middle line:84% he resigned his position in Berlin. 00:09:33.700 --> 00:09:36.340 align:middle line:84% He moved to Oxford and then settled in Dublin 00:09:36.340 --> 00:09:37.870 align:middle line:90% for the duration of the war. 00:09:37.870 --> 00:09:40.720 align:middle line:84% Emmy Noether, who was an immensely influential 00:09:40.720 --> 00:09:42.790 align:middle line:84% mathematical physicist from Gottingen, 00:09:42.790 --> 00:09:46.660 align:middle line:84% she left Germany and she was hired at Bryn Mawr, a women's 00:09:46.660 --> 00:09:48.220 align:middle line:90% college in Pennsylvania. 00:09:48.220 --> 00:09:50.770 align:middle line:84% Max Born also left Gottingen. He went first 00:09:50.770 --> 00:09:55.330 align:middle line:84% to Cambridge, then to Edinburgh for the duration of the war. 00:09:55.330 --> 00:09:58.000 align:middle line:84% Younger scholars, like Hans Bethe, 00:09:58.000 --> 00:10:00.200 align:middle line:90% left positions in Germany. 00:10:00.200 --> 00:10:03.700 align:middle line:84% And he moved to Cornell and had a very, very long, long, long 00:10:03.700 --> 00:10:05.140 align:middle line:90% career at Cornell. 00:10:05.140 --> 00:10:09.710 align:middle line:84% He arrived at Cornell around 1935, and he stayed there. 00:10:09.710 --> 00:10:12.500 align:middle line:84% He was a professor there for maybe 60, or even more than 60, 00:10:12.500 --> 00:10:13.000 align:middle line:90% years. 00:10:13.000 --> 00:10:14.600 align:middle line:84% He had an enormously long career. 00:10:14.600 --> 00:10:17.110 align:middle line:84% James Franck moved to the University of Chicago, Felix 00:10:17.110 --> 00:10:17.860 align:middle line:90% Bloch to Stanford. 00:10:17.860 --> 00:10:19.780 align:middle line:84% Viki Weisskopf eventually makes his way 00:10:19.780 --> 00:10:22.180 align:middle line:84% to MIT, first by way of Rochester and so on. 00:10:22.180 --> 00:10:24.070 align:middle line:84% It's literally 100 of these cases 00:10:24.070 --> 00:10:26.620 align:middle line:90% that have been well-documented. 00:10:26.620 --> 00:10:29.890 align:middle line:84% And what's really important to keep in mind 00:10:29.890 --> 00:10:32.620 align:middle line:84% is that these were by no means easy transitions. 00:10:32.620 --> 00:10:34.270 align:middle line:90% For some, they were pretty easy. 00:10:34.270 --> 00:10:36.640 align:middle line:84% Einstein was welcomed immediately 00:10:36.640 --> 00:10:38.380 align:middle line:84% at the Institute for Advanced Study. 00:10:38.380 --> 00:10:41.020 align:middle line:84% It was a great boon for that new young institute. 00:10:41.020 --> 00:10:42.760 align:middle line:84% But many of these other folks who 00:10:42.760 --> 00:10:45.130 align:middle line:84% were neither so famous as Einstein, 00:10:45.130 --> 00:10:47.860 align:middle line:84% nor entering such brand new institutions, 00:10:47.860 --> 00:10:52.720 align:middle line:84% for many of these other folks it was actually not an easy move. 00:10:52.720 --> 00:10:56.090 align:middle line:84% The United States itself, like many parts of the world, 00:10:56.090 --> 00:10:58.120 align:middle line:84% not just in Europe or North America, 00:10:58.120 --> 00:11:00.130 align:middle line:84% was deep into a Great Depression. 00:11:00.130 --> 00:11:01.970 align:middle line:84% This was already several years in. 00:11:01.970 --> 00:11:04.063 align:middle line:84% So there were many US-based scholars 00:11:04.063 --> 00:11:05.980 align:middle line:84% in this case looking for university positions, 00:11:05.980 --> 00:11:07.300 align:middle line:90% as well as all kinds of jobs. 00:11:07.300 --> 00:11:10.060 align:middle line:84% Unemployment was rampant throughout the United States. 00:11:10.060 --> 00:11:13.120 align:middle line:84% But even beyond that, there was an entrenched, and again, 00:11:13.120 --> 00:11:16.880 align:middle line:84% by now well-documented, anti-Semitism throughout many, 00:11:16.880 --> 00:11:21.460 align:middle line:84% many US universities, including sometimes most rabidly among 00:11:21.460 --> 00:11:24.670 align:middle line:84% the most elite universities-- the Ivy League and others like 00:11:24.670 --> 00:11:25.300 align:middle line:90% that-- 00:11:25.300 --> 00:11:27.610 align:middle line:84% so that sometimes it was actually 00:11:27.610 --> 00:11:30.130 align:middle line:84% hard to place these people who were 00:11:30.130 --> 00:11:34.670 align:middle line:84% extremely eminent and already decorated in their fields. 00:11:34.670 --> 00:11:39.310 align:middle line:84% But many US universities balked or dragged their feet. 00:11:39.310 --> 00:11:42.010 align:middle line:84% An example of that involves Robert Oppenheimer-- someone 00:11:42.010 --> 00:11:44.440 align:middle line:84% we'll be talking quite a lot about in the coming lectures. 00:11:44.440 --> 00:11:46.420 align:middle line:84% Oppenheimer was born in New York City. 00:11:46.420 --> 00:11:49.030 align:middle line:84% He wasn't someone who had to flee Germany. 00:11:49.030 --> 00:11:52.840 align:middle line:84% But when he was hired at Berkeley in 1929 before 00:11:52.840 --> 00:11:57.310 align:middle line:84% the rise of the Nazis, the department had had to work 00:11:57.310 --> 00:12:00.400 align:middle line:84% extra hard to get him hired in a department that already had 00:12:00.400 --> 00:12:03.910 align:middle line:84% something like 60 faculty-- it was a huge department-- 00:12:03.910 --> 00:12:05.410 align:middle line:84% because the department already had 00:12:05.410 --> 00:12:08.380 align:middle line:84% one other person of Jewish background in the department. 00:12:08.380 --> 00:12:10.240 align:middle line:84% And so the department chair had to fight 00:12:10.240 --> 00:12:12.282 align:middle line:84% against the notion of having, quote unquote, "too 00:12:12.282 --> 00:12:15.700 align:middle line:84% many Jews" in a huge department by hiring this second one in. 00:12:15.700 --> 00:12:19.450 align:middle line:84% And that was even before you have this kind of exodus 00:12:19.450 --> 00:12:21.130 align:middle line:90% with the rise of the Nazis. 00:12:21.130 --> 00:12:24.070 align:middle line:84% Likewise, at Dartmouth College-- my own alma mater, 00:12:24.070 --> 00:12:27.190 align:middle line:84% so I'm not picking on a stranger here-- 00:12:27.190 --> 00:12:30.880 align:middle line:84% again, once these outflow began in the early '30s, 00:12:30.880 --> 00:12:32.380 align:middle line:84% correspondences turned up that they 00:12:32.380 --> 00:12:35.740 align:middle line:84% were perfectly happy to bring in a refugee faculty candidate 00:12:35.740 --> 00:12:38.590 align:middle line:84% as long as the candidate, quote, "shouldn't seem too Jewish." 00:12:38.590 --> 00:12:42.490 align:middle line:84% So there was a kind of entrenched anti-Semitism 00:12:42.490 --> 00:12:45.400 align:middle line:84% among even very, very elite, or especially very elite 00:12:45.400 --> 00:12:46.540 align:middle line:90% US universities. 00:12:46.540 --> 00:12:48.265 align:middle line:84% And that compounded the difficulties 00:12:48.265 --> 00:12:50.140 align:middle line:84% of placing some of these people, many of whom 00:12:50.140 --> 00:12:53.420 align:middle line:84% had to flee under very dire circumstances. 00:12:53.420 --> 00:12:54.050 align:middle line:90% OK. 00:12:54.050 --> 00:12:57.200 align:middle line:84% That's for the people who did leave 00:12:57.200 --> 00:12:58.700 align:middle line:90% after the rise of the Nazis. 00:12:58.700 --> 00:13:00.770 align:middle line:84% What about some who stayed behind? 00:13:00.770 --> 00:13:04.820 align:middle line:84% So within Germany, especially once the Nazis had taken over, 00:13:04.820 --> 00:13:07.430 align:middle line:84% Nazi officials, which included the German Education 00:13:07.430 --> 00:13:10.430 align:middle line:84% Ministry and beyond, began criticizing physicists 00:13:10.430 --> 00:13:13.100 align:middle line:84% who were not themselves of Jewish background, 00:13:13.100 --> 00:13:15.050 align:middle line:84% but who seemed to demonstrate what 00:13:15.050 --> 00:13:18.440 align:middle line:84% at least the Nazi officials considered insufficient loyalty 00:13:18.440 --> 00:13:19.490 align:middle line:90% to the regime. 00:13:19.490 --> 00:13:22.010 align:middle line:84% And one way that these folks supposedly 00:13:22.010 --> 00:13:25.220 align:middle line:84% demonstrated insufficient loyalty was that they continued 00:13:25.220 --> 00:13:27.410 align:middle line:84% to teach what was by that time branded 00:13:27.410 --> 00:13:29.840 align:middle line:84% so-called Jewish physics, which meant physics 00:13:29.840 --> 00:13:31.940 align:middle line:84% either by people who were of Jewish background, 00:13:31.940 --> 00:13:35.240 align:middle line:84% like relativity, or physics that struck some of these Deutsche 00:13:35.240 --> 00:13:38.660 align:middle line:84% Physik acolytes, like Stark or Lenard, 00:13:38.660 --> 00:13:41.660 align:middle line:84% as being somehow too mathematical, too abstract 00:13:41.660 --> 00:13:45.260 align:middle line:84% to remove from kind of proper forms of reasoning. 00:13:45.260 --> 00:13:47.120 align:middle line:84% Often, it was actually just more crude. 00:13:47.120 --> 00:13:49.408 align:middle line:84% Was that work done by someone who was Jewish? 00:13:49.408 --> 00:13:50.450 align:middle line:90% Then it's Jewish physics. 00:13:50.450 --> 00:13:53.780 align:middle line:84% Often, it was just a simple conflation. 00:13:53.780 --> 00:13:57.560 align:middle line:84% This reached its real apogee, the real highlight, 00:13:57.560 --> 00:14:02.240 align:middle line:84% or the highest point of this kind of attack occurred 00:14:02.240 --> 00:14:05.780 align:middle line:84% in 1937, so several years into the regime, 00:14:05.780 --> 00:14:09.650 align:middle line:84% when in fact, the acolytes of Deutsche Physik, who 00:14:09.650 --> 00:14:12.800 align:middle line:84% now had the ear of the German Education Ministry, 00:14:12.800 --> 00:14:15.170 align:middle line:84% they managed to block the appointment of Werner 00:14:15.170 --> 00:14:19.520 align:middle line:84% Heisenberg, who everyone within Germany and beyond Germany 00:14:19.520 --> 00:14:22.610 align:middle line:84% had just simply assumed would be appointed, 00:14:22.610 --> 00:14:26.330 align:middle line:84% would get a big promotion when his own main mentor retired. 00:14:26.330 --> 00:14:28.190 align:middle line:84% So as you may remember from some lectures 00:14:28.190 --> 00:14:31.490 align:middle line:84% on so-called old quantum theory a few sessions ago, 00:14:31.490 --> 00:14:34.910 align:middle line:84% Arnold Sommerfeld was the kind of head professor, 00:14:34.910 --> 00:14:38.000 align:middle line:84% the ordinarius professor, in Munich for theoretical physics. 00:14:38.000 --> 00:14:41.060 align:middle line:84% He trained an enormous number of gifted disciples, 00:14:41.060 --> 00:14:43.460 align:middle line:84% including Heisenberg, Wolfgang Pauli, Hans Bethe-- 00:14:43.460 --> 00:14:44.700 align:middle line:90% just a huge list. 00:14:44.700 --> 00:14:46.910 align:middle line:84% And by this point, Heisenberg was clearly 00:14:46.910 --> 00:14:49.910 align:middle line:84% Sommerfeld's most famous, most accomplished student. 00:14:49.910 --> 00:14:52.040 align:middle line:84% Heisenberg had already received the Nobel Prize 00:14:52.040 --> 00:14:55.410 align:middle line:84% by this point for his work on quantum theory. 00:14:55.410 --> 00:14:57.510 align:middle line:84% Sommerfeld retired after a long career. 00:14:57.510 --> 00:15:00.870 align:middle line:84% And everyone just assumed, including Heisenberg himself, 00:15:00.870 --> 00:15:02.940 align:middle line:84% that the central ministry would simply appoint 00:15:02.940 --> 00:15:04.500 align:middle line:90% Heisenberg as the successor. 00:15:04.500 --> 00:15:09.990 align:middle line:84% Instead, the Deutsche Physik kind of ideologues 00:15:09.990 --> 00:15:13.860 align:middle line:84% organized a press campaign against Heisenberg labeling him 00:15:13.860 --> 00:15:15.120 align:middle line:90% what was called a white Jew. 00:15:15.120 --> 00:15:16.740 align:middle line:90% And again, that was their term. 00:15:16.740 --> 00:15:18.420 align:middle line:84% They said, we know he's not personally 00:15:18.420 --> 00:15:21.480 align:middle line:84% of Jewish background, but he behaves in too friendly 00:15:21.480 --> 00:15:23.820 align:middle line:90% a manner, in their reckoning. 00:15:23.820 --> 00:15:26.940 align:middle line:84% He was too supportive of things like Jewish physics 00:15:26.940 --> 00:15:29.260 align:middle line:84% because he kept teaching relativity, for example, 00:15:29.260 --> 00:15:30.250 align:middle line:90% in his classes. 00:15:30.250 --> 00:15:32.580 align:middle line:84% So they labeled him a white Jew and began 00:15:32.580 --> 00:15:35.070 align:middle line:84% a real kind of press smear campaign 00:15:35.070 --> 00:15:37.950 align:middle line:90% in the Gestapo-controlled press. 00:15:37.950 --> 00:15:39.695 align:middle line:84% Things could really have gotten worse. 00:15:39.695 --> 00:15:41.070 align:middle line:84% In fact, there was a real concern 00:15:41.070 --> 00:15:43.070 align:middle line:84% that Heisenberg himself might have been sent off 00:15:43.070 --> 00:15:47.340 align:middle line:84% to a concentration camp, or certainly could 00:15:47.340 --> 00:15:49.590 align:middle line:84% have faced much worse treatment than only 00:15:49.590 --> 00:15:51.390 align:middle line:90% being denied a promotion. 00:15:51.390 --> 00:15:54.060 align:middle line:84% And what finally stopped the attack 00:15:54.060 --> 00:15:56.910 align:middle line:84% was that Heisenberg's mother interceded directly 00:15:56.910 --> 00:15:58.950 align:middle line:84% with a close family friend, who happened to be 00:15:58.950 --> 00:16:00.420 align:middle line:90% the mother of Heinrich Himmler. 00:16:00.420 --> 00:16:02.268 align:middle line:84% Himmler's shown here in this circle. 00:16:02.268 --> 00:16:03.810 align:middle line:84% Himmler, by that point, was the chief 00:16:03.810 --> 00:16:07.180 align:middle line:84% of the SS, one of these paramilitary Nazi forces. 00:16:07.180 --> 00:16:10.590 align:middle line:84% Here's Himmler with Hitler and other Nazi officials 00:16:10.590 --> 00:16:12.610 align:middle line:84% just a few years before they kind of took over. 00:16:12.610 --> 00:16:16.110 align:middle line:84% So it was really kind of an accident of who knows who. 00:16:16.110 --> 00:16:18.308 align:middle line:84% Heisenberg's mother calling up the mother of Himmler 00:16:18.308 --> 00:16:20.100 align:middle line:84% because they had known each other when they 00:16:20.100 --> 00:16:22.920 align:middle line:84% were each younger and basically said, can't our boys get along? 00:16:22.920 --> 00:16:24.130 align:middle line:90% It was quite extraordinary. 00:16:24.130 --> 00:16:28.800 align:middle line:84% It took that level of backroom negotiations 00:16:28.800 --> 00:16:31.320 align:middle line:84% to make sure that not worse happened to Heisenberg 00:16:31.320 --> 00:16:35.610 align:middle line:84% than only getting passed over for a fancy promotion. 00:16:35.610 --> 00:16:36.570 align:middle line:90% OK. 00:16:36.570 --> 00:16:38.250 align:middle line:84% So that's usually seen as the kind 00:16:38.250 --> 00:16:41.490 align:middle line:84% of apogee of the power of this Deutsche Physik movement 00:16:41.490 --> 00:16:42.600 align:middle line:90% within Germany. 00:16:42.600 --> 00:16:45.900 align:middle line:84% Obviously, the Nazis weren't done in 1937. 00:16:45.900 --> 00:16:51.270 align:middle line:84% As I'm sure you know, the war dragged on until 1945. 00:16:51.270 --> 00:16:52.890 align:middle line:84% But this was really the high point 00:16:52.890 --> 00:16:56.150 align:middle line:84% of this kind of power of Deutsche Physik. 00:16:56.150 --> 00:16:59.930 align:middle line:84% So not that the Nazis went away, but this notion of having 00:16:59.930 --> 00:17:03.470 align:middle line:84% a kind of racially pure or kind of ideological tests 00:17:03.470 --> 00:17:07.220 align:middle line:84% for physics, that begins to wane very soon 00:17:07.220 --> 00:17:09.230 align:middle line:84% after this very dramatic showdown 00:17:09.230 --> 00:17:10.910 align:middle line:90% over Heisenberg's promotion. 00:17:10.910 --> 00:17:13.369 align:middle line:84% And in fact, what many historians 00:17:13.369 --> 00:17:15.650 align:middle line:84% have come to conclude is that the regime-- 00:17:15.650 --> 00:17:18.740 align:middle line:84% the Nazis in power said, we actually 00:17:18.740 --> 00:17:22.250 align:middle line:84% could have real uses for all these physicists, at least 00:17:22.250 --> 00:17:24.230 align:middle line:84% the ones who weren't of Jewish background, 00:17:24.230 --> 00:17:26.480 align:middle line:84% that physics might not be only associated 00:17:26.480 --> 00:17:28.400 align:middle line:84% with kind of philosophy or ideology 00:17:28.400 --> 00:17:30.500 align:middle line:84% or kind of political talking points. 00:17:30.500 --> 00:17:32.450 align:middle line:84% But there was something stirring which 00:17:32.450 --> 00:17:35.150 align:middle line:84% got even to the highest levels of the Nazi party 00:17:35.150 --> 00:17:38.660 align:middle line:84% by the late 1930s that maybe physics and physicists could 00:17:38.660 --> 00:17:42.890 align:middle line:84% be useful, could be manifestly useful to Nazi aims and not 00:17:42.890 --> 00:17:44.540 align:middle line:84% merely something to be kind of policed 00:17:44.540 --> 00:17:45.920 align:middle line:90% as a kind of thought police. 00:17:45.920 --> 00:17:49.220 align:middle line:84% And what had changed really was summed up in two words-- 00:17:49.220 --> 00:17:50.210 align:middle line:90% nuclear physics. 00:17:50.210 --> 00:17:51.307 align:middle line:90% So let me pause there. 00:17:51.307 --> 00:17:53.390 align:middle line:84% We're going to have some questions and discussion. 00:17:53.390 --> 00:17:56.492 align:middle line:84% And then we'll look at some of the work in nuclear physics 00:17:56.492 --> 00:17:57.700 align:middle line:90% that they were talking about. 00:17:57.700 --> 00:17:58.750 align:middle line:90% Any questions about that? 00:17:58.750 --> 00:18:06.120 align:middle line:90% 00:18:06.120 --> 00:18:07.670 align:middle line:84% Had anyone heard that story before 00:18:07.670 --> 00:18:09.980 align:middle line:84% about Heisenberg and his mother and Himmler's mother? 00:18:09.980 --> 00:18:11.797 align:middle line:90% I just find that astonishing. 00:18:11.797 --> 00:18:13.130 align:middle line:90% Talk about small world networks. 00:18:13.130 --> 00:18:16.200 align:middle line:90% 00:18:16.200 --> 00:18:16.700 align:middle line:90% No. 00:18:16.700 --> 00:18:19.550 align:middle line:90% 00:18:19.550 --> 00:18:20.600 align:middle line:90% OK. 00:18:20.600 --> 00:18:21.710 align:middle line:90% I'm happy to press on. 00:18:21.710 --> 00:18:24.680 align:middle line:84% We got a lot of juicy stuff we can talk about 00:18:24.680 --> 00:18:25.820 align:middle line:90% for nuclear physics. 00:18:25.820 --> 00:18:27.945 align:middle line:84% But if any questions come up about Deutsche Physik, 00:18:27.945 --> 00:18:30.830 align:middle line:90% of course, chime in. 00:18:30.830 --> 00:18:33.710 align:middle line:84% But if not, I think I'll press on. 00:18:33.710 --> 00:18:34.780 align:middle line:90% OK. 00:18:34.780 --> 00:18:36.030 align:middle line:90% Obie, did you have a question? 00:18:36.030 --> 00:18:38.120 align:middle line:90% Was it-- Oh, OK. 00:18:38.120 --> 00:18:39.688 align:middle line:90% OK. 00:18:39.688 --> 00:18:41.480 align:middle line:84% Yeah, if only somebody called Hitler's mom. 00:18:41.480 --> 00:18:43.640 align:middle line:90% Yeah, exactly. 00:18:43.640 --> 00:18:44.795 align:middle line:90% Can you imagine? 00:18:44.795 --> 00:18:46.670 align:middle line:84% Gary says, if all these remarkable physicists 00:18:46.670 --> 00:18:49.087 align:middle line:84% stayed in Germany, what would have been the result of war? 00:18:49.087 --> 00:18:50.150 align:middle line:90% Yeah. 00:18:50.150 --> 00:18:50.840 align:middle line:90% Gary, thank you. 00:18:50.840 --> 00:18:52.215 align:middle line:84% In fact, we'll be coming to that. 00:18:52.215 --> 00:18:56.330 align:middle line:84% That sets up much of the rest of today's class. 00:18:56.330 --> 00:18:56.870 align:middle line:90% Yeah. 00:18:56.870 --> 00:18:58.880 align:middle line:84% Seeler says if only he'd been accepted at art school-- 00:18:58.880 --> 00:19:00.230 align:middle line:90% meaning Hitler, not Heisenberg. 00:19:00.230 --> 00:19:02.120 align:middle line:84% So some of you may know, Hitler was himself 00:19:02.120 --> 00:19:06.470 align:middle line:84% a kind of aspiring painter as a young person. 00:19:06.470 --> 00:19:08.390 align:middle line:84% And he felt slights at every turn, 00:19:08.390 --> 00:19:09.890 align:middle line:84% including that he was never admitted 00:19:09.890 --> 00:19:12.560 align:middle line:90% to hoped for art school. 00:19:12.560 --> 00:19:15.457 align:middle line:84% The world was out to get him, as far as he was concerned. 00:19:15.457 --> 00:19:17.040 align:middle line:84% Alex asked a very intriguing question. 00:19:17.040 --> 00:19:18.410 align:middle line:90% Why did Heisenberg stay behind? 00:19:18.410 --> 00:19:19.040 align:middle line:90% Very good. 00:19:19.040 --> 00:19:20.788 align:middle line:84% And again, we'll talk a bit about that. 00:19:20.788 --> 00:19:23.330 align:middle line:84% But that will come up in some of the themes in the next part. 00:19:23.330 --> 00:19:26.810 align:middle line:84% But as a preview, it's important to clarify. 00:19:26.810 --> 00:19:30.020 align:middle line:84% Heisenberg never ever joined the Nazi party. 00:19:30.020 --> 00:19:33.800 align:middle line:84% He never expressed anything like a clear sympathy 00:19:33.800 --> 00:19:39.600 align:middle line:84% with the most vile parts of the Nazi worldview. 00:19:39.600 --> 00:19:41.150 align:middle line:90% So I want to be very clear. 00:19:41.150 --> 00:19:44.990 align:middle line:84% On the other hand, Heisenberg was very, very patriotic. 00:19:44.990 --> 00:19:50.420 align:middle line:84% He was someone who had a deep, deep pride and a longer 00:19:50.420 --> 00:19:52.325 align:middle line:84% view of German learning and German culture. 00:19:52.325 --> 00:19:54.650 align:middle line:84% And again, we'll come to that actually pretty soon. 00:19:54.650 --> 00:19:58.170 align:middle line:84% So he was a patriotic German and not a Nazi. 00:19:58.170 --> 00:20:00.920 align:middle line:84% And he believed, as many of his colleagues 00:20:00.920 --> 00:20:04.080 align:middle line:84% did-- many, many German scientists stayed behind. 00:20:04.080 --> 00:20:07.460 align:middle line:84% He believed that the Nazi-- he hoped, in the early years-- he 00:20:07.460 --> 00:20:10.010 align:middle line:84% believed that this would be a temporary aberration, 00:20:10.010 --> 00:20:13.707 align:middle line:84% that the Nazis were so counter to what Heisenberg himself 00:20:13.707 --> 00:20:16.040 align:middle line:84% considered the kind of highest points of German learning 00:20:16.040 --> 00:20:17.900 align:middle line:84% and German philosophy and German culture, 00:20:17.900 --> 00:20:20.600 align:middle line:84% that this would be a temporary kind of fever. 00:20:20.600 --> 00:20:22.550 align:middle line:90% The fever would break. 00:20:22.550 --> 00:20:25.220 align:middle line:84% The Nazis would be run out of town soon, 00:20:25.220 --> 00:20:27.410 align:middle line:90% he hoped or believed. 00:20:27.410 --> 00:20:29.270 align:middle line:84% And therefore, there should be some kind 00:20:29.270 --> 00:20:32.870 align:middle line:84% of intellectual leaders who stayed behind to rebuild. 00:20:32.870 --> 00:20:35.180 align:middle line:84% So he thought there would be a need 00:20:35.180 --> 00:20:40.040 align:middle line:84% for many, many smart, devoted Germans who weren't Nazis, 00:20:40.040 --> 00:20:42.500 align:middle line:84% but who were proud of the kind of longer heritage 00:20:42.500 --> 00:20:44.610 align:middle line:90% of German learning and culture. 00:20:44.610 --> 00:20:46.860 align:middle line:84% Think about all the composers and the poets, 00:20:46.860 --> 00:20:48.360 align:middle line:84% and they had this long list of which 00:20:48.360 --> 00:20:50.760 align:middle line:90% they were very, very proud. 00:20:50.760 --> 00:20:53.250 align:middle line:84% So they thought they'd have to stick around 00:20:53.250 --> 00:20:55.530 align:middle line:84% because this Nazi thing was going to go away soon, 00:20:55.530 --> 00:20:56.500 align:middle line:90% they hoped. 00:20:56.500 --> 00:20:58.810 align:middle line:84% And then Germany would have to rebuild. 00:20:58.810 --> 00:21:01.110 align:middle line:84% And that was-- and so it was a kind of patriotism 00:21:01.110 --> 00:21:04.290 align:middle line:90% rather than Nazism per se. 00:21:04.290 --> 00:21:07.308 align:middle line:84% But that became for many other people who 00:21:07.308 --> 00:21:09.600 align:middle line:84% did leave Germany, either because they felt they really 00:21:09.600 --> 00:21:12.252 align:middle line:84% had to for personal safety, or people like Schrodinger who 00:21:12.252 --> 00:21:13.710 align:middle line:84% were critics of the regime but were 00:21:13.710 --> 00:21:16.170 align:middle line:84% not in the same kind of personal danger-- 00:21:16.170 --> 00:21:18.930 align:middle line:84% that kind of argument didn't convince everyone. 00:21:18.930 --> 00:21:21.720 align:middle line:84% Obviously, not everyone thought this-- 00:21:21.720 --> 00:21:23.250 align:middle line:84% thought that-- some people thought 00:21:23.250 --> 00:21:24.875 align:middle line:84% Heisenberg was kind of fooling himself, 00:21:24.875 --> 00:21:27.390 align:middle line:84% or the people like Heisenberg who chose to stay. 00:21:27.390 --> 00:21:29.850 align:middle line:84% So it was not at all obvious that this was-- even 00:21:29.850 --> 00:21:33.600 align:middle line:84% at the time, this was the best course of action 00:21:33.600 --> 00:21:36.300 align:middle line:90% or the morally appropriate one. 00:21:36.300 --> 00:21:37.420 align:middle line:90% But it was tricky. 00:21:37.420 --> 00:21:39.503 align:middle line:84% And so the short the shorter version is Heisenberg 00:21:39.503 --> 00:21:43.450 align:middle line:84% was deeply patriotic and not a Nazi. 00:21:43.450 --> 00:21:45.450 align:middle line:84% And he hoped he could help kind of rebuild 00:21:45.450 --> 00:21:47.220 align:middle line:90% the country he loved so much. 00:21:47.220 --> 00:21:49.250 align:middle line:90% And he hoped it would come soon. 00:21:49.250 --> 00:21:50.220 align:middle line:90% That's a good question. 00:21:50.220 --> 00:21:51.920 align:middle line:90% Any other questions on that? 00:21:51.920 --> 00:21:55.580 align:middle line:84% That's actually a great segue to the next part. 00:21:55.580 --> 00:21:56.080 align:middle line:90% OK. 00:21:56.080 --> 00:21:56.990 align:middle line:90% Let's press on. 00:21:56.990 --> 00:21:59.050 align:middle line:84% Let's see what else-- what might have 00:21:59.050 --> 00:22:04.330 align:middle line:84% helped convince even the ardent Nazis that there 00:22:04.330 --> 00:22:07.100 align:middle line:84% were other reasons to think about physics in new ways? 00:22:07.100 --> 00:22:09.040 align:middle line:84% So we're going to step back a little bit 00:22:09.040 --> 00:22:12.093 align:middle line:84% and look at some of the conceptual developments 00:22:12.093 --> 00:22:13.510 align:middle line:84% and experimental developments that 00:22:13.510 --> 00:22:17.320 align:middle line:84% have been going on really just in remarkable synchrony 00:22:17.320 --> 00:22:19.780 align:middle line:84% with the Deutsche Physik movement 00:22:19.780 --> 00:22:21.430 align:middle line:90% and the rise of the Nazis. 00:22:21.430 --> 00:22:24.952 align:middle line:84% So throughout the late '20s and into the early '30s, several 00:22:24.952 --> 00:22:26.410 align:middle line:84% research groups really throughout-- 00:22:26.410 --> 00:22:28.810 align:middle line:84% certainly throughout Europe and beyond-- 00:22:28.810 --> 00:22:32.320 align:middle line:90% we're working on radioactivity. 00:22:32.320 --> 00:22:34.810 align:middle line:90% That dated back to the 1890s. 00:22:34.810 --> 00:22:39.580 align:middle line:84% But this group by this point, about 20 or almost 30 years in, 00:22:39.580 --> 00:22:41.860 align:middle line:84% began to suspect that there was more going on 00:22:41.860 --> 00:22:45.760 align:middle line:84% within atomic nuclei than only protons, 00:22:45.760 --> 00:22:49.780 align:middle line:84% that there might be actually a whole second kind of particle 00:22:49.780 --> 00:22:50.928 align:middle line:90% within these nuclei. 00:22:50.928 --> 00:22:52.720 align:middle line:84% And again, to us this sounds like, no, duh. 00:22:52.720 --> 00:22:53.678 align:middle line:90% How did they know that? 00:22:53.678 --> 00:22:55.262 align:middle line:84% Well, we know that because they worked 00:22:55.262 --> 00:22:56.420 align:middle line:90% so hard to figure this out. 00:22:56.420 --> 00:22:59.600 align:middle line:84% They thought there could be an electrically neutral particle 00:22:59.600 --> 00:23:02.870 align:middle line:84% whose mass was at least pretty close to that of the proton 00:23:02.870 --> 00:23:05.990 align:middle line:84% but would not respond to the electromagnetic-- 00:23:05.990 --> 00:23:08.930 align:middle line:84% would not respond to electric attractions or repulsions 00:23:08.930 --> 00:23:10.760 align:middle line:90% the way a proton does. 00:23:10.760 --> 00:23:12.170 align:middle line:84% And they had all kinds of reasons 00:23:12.170 --> 00:23:13.940 align:middle line:90% for thinking along these lines. 00:23:13.940 --> 00:23:17.270 align:middle line:84% Among the real kind of World leaders on that topic 00:23:17.270 --> 00:23:20.870 align:middle line:84% was a husband and wife team, or a wife and husband team, Irene 00:23:20.870 --> 00:23:22.640 align:middle line:90% and Frédéric Joliot-Curie. 00:23:22.640 --> 00:23:26.460 align:middle line:84% Irene Curie was one of the daughters of Marie and Pierre 00:23:26.460 --> 00:23:26.960 align:middle line:90% Curie. 00:23:26.960 --> 00:23:29.130 align:middle line:84% So she entered the family business. 00:23:29.130 --> 00:23:32.030 align:middle line:84% She married Frédéric, who was also a nuclear scientist. 00:23:32.030 --> 00:23:36.170 align:middle line:84% And they also set up a world-class laboratory 00:23:36.170 --> 00:23:38.840 align:middle line:84% in Paris, really kind of taking the mantle 00:23:38.840 --> 00:23:41.600 align:middle line:90% from Marie and Pierre. 00:23:41.600 --> 00:23:43.580 align:middle line:84% And one of the things that they were especially 00:23:43.580 --> 00:23:47.060 align:middle line:84% adept at studying was something called 00:23:47.060 --> 00:23:48.350 align:middle line:90% artificial radioactivity. 00:23:48.350 --> 00:23:50.330 align:middle line:84% They really meant induced radioactivity. 00:23:50.330 --> 00:23:53.810 align:middle line:84% So Marie Curie and Pierre and members 00:23:53.810 --> 00:23:56.840 align:middle line:84% of their generation, even younger folks like Rutherford, 00:23:56.840 --> 00:24:00.350 align:middle line:84% they'd been excited about natural emitters-- substances 00:24:00.350 --> 00:24:02.780 align:middle line:84% that were radioactive without you 00:24:02.780 --> 00:24:04.040 align:middle line:90% having to do anything to them. 00:24:04.040 --> 00:24:06.600 align:middle line:84% They would emit these radiations-- alpha particles, 00:24:06.600 --> 00:24:09.380 align:middle line:84% beta particles, gamma rays on their own 00:24:09.380 --> 00:24:12.200 align:middle line:84% because of some kind of natural radioactive properties. 00:24:12.200 --> 00:24:14.970 align:middle line:84% By this next generation, literally next generation, 00:24:14.970 --> 00:24:18.440 align:middle line:84% meaning the daughter Irene and Frédéric, they 00:24:18.440 --> 00:24:20.180 align:middle line:84% were wondering could they actually create 00:24:20.180 --> 00:24:23.780 align:middle line:84% radioactivity or induce it by taking materials that were not 00:24:23.780 --> 00:24:27.950 align:middle line:84% on their own radioactive, irradiating them-- having 00:24:27.950 --> 00:24:31.340 align:middle line:84% a radioactive source bombard them with radiation, 00:24:31.340 --> 00:24:33.380 align:middle line:84% alpha particles, beta particles whatever-- 00:24:33.380 --> 00:24:37.220 align:middle line:84% and have that new target that they shown this stuff onto, 00:24:37.220 --> 00:24:39.560 align:middle line:84% could that then become radioactive as well? 00:24:39.560 --> 00:24:41.120 align:middle line:90% That became known as artificial. 00:24:41.120 --> 00:24:44.060 align:middle line:84% It really means induced radioactivity. 00:24:44.060 --> 00:24:46.880 align:middle line:84% And this became the next big frontier 00:24:46.880 --> 00:24:48.800 align:middle line:84% for trying to understand radioactivity 00:24:48.800 --> 00:24:50.420 align:middle line:84% in general, and by means of that, 00:24:50.420 --> 00:24:52.940 align:middle line:84% trying to get more clarity on the structure of atoms 00:24:52.940 --> 00:24:55.850 align:middle line:90% and nuclei. 00:24:55.850 --> 00:24:58.120 align:middle line:84% And so-- and as you see, Irene and Frédéric 00:24:58.120 --> 00:25:01.640 align:middle line:84% shared the 1935 Nobel Prize in Chemistry for their work. 00:25:01.640 --> 00:25:04.090 align:middle line:84% They really had already become world leaders in that. 00:25:04.090 --> 00:25:06.340 align:middle line:84% Just a little bit before they won the prize, 00:25:06.340 --> 00:25:08.380 align:middle line:84% and they're already very clearly at the top 00:25:08.380 --> 00:25:11.030 align:middle line:84% of the game in that field, one of their colleagues, 00:25:11.030 --> 00:25:13.870 align:middle line:84% James Chadwick, who was in Britain, 00:25:13.870 --> 00:25:15.730 align:middle line:84% followed up on one of their suggestions. 00:25:15.730 --> 00:25:18.130 align:middle line:84% In fact, he basically redid an experiment 00:25:18.130 --> 00:25:21.458 align:middle line:84% that the Joliot-Curie's had done almost exactly. 00:25:21.458 --> 00:25:23.500 align:middle line:84% But he thought they weren't quite interpreting it 00:25:23.500 --> 00:25:24.000 align:middle line:90% quite right. 00:25:24.000 --> 00:25:25.510 align:middle line:90% So he wanted to zoom in on this. 00:25:25.510 --> 00:25:28.540 align:middle line:84% So Chadwick had been a student of Ernest Rutherford's 00:25:28.540 --> 00:25:31.720 align:middle line:84% at Manchester, and by this point was himself now 00:25:31.720 --> 00:25:35.410 align:middle line:84% a more senior researcher at the Cavendish back in Cambridge. 00:25:35.410 --> 00:25:38.290 align:middle line:84% So this, again, really was an experimental design 00:25:38.290 --> 00:25:40.930 align:middle line:84% almost entirely coming from Irene and Frédéric 00:25:40.930 --> 00:25:41.830 align:middle line:90% Joliot-Curie. 00:25:41.830 --> 00:25:43.670 align:middle line:84% But Chadwick gave it a little tweak 00:25:43.670 --> 00:25:44.920 align:middle line:90% to try to clarify some things. 00:25:44.920 --> 00:25:47.890 align:middle line:84% The idea was to take one of these natural radioactive 00:25:47.890 --> 00:25:49.390 align:middle line:90% sources-- in this case polonium. 00:25:49.390 --> 00:25:52.240 align:middle line:84% And that's what we called an alpha emitter. 00:25:52.240 --> 00:25:55.250 align:middle line:84% So all on its own polonium will be radioactive, 00:25:55.250 --> 00:26:00.420 align:middle line:84% and its form of emission is alpha particles. 00:26:00.420 --> 00:26:03.650 align:middle line:84% So then they would shine the alpha particles 00:26:03.650 --> 00:26:07.190 align:middle line:84% onto a target, a block of beryllium. 00:26:07.190 --> 00:26:10.160 align:middle line:84% And then some different kind of radiation would come out. 00:26:10.160 --> 00:26:11.990 align:middle line:84% They had now induced radioactivity. 00:26:11.990 --> 00:26:14.090 align:middle line:84% Beryllium on its own was not radioactive. 00:26:14.090 --> 00:26:17.360 align:middle line:84% They could induce a radioactive kind of response 00:26:17.360 --> 00:26:19.850 align:middle line:84% by irradiating it with alpha particles. 00:26:19.850 --> 00:26:23.220 align:middle line:84% Some as yet unknown stuff came out. 00:26:23.220 --> 00:26:26.630 align:middle line:84% They could then-- Chadwick's idea was to shine that onto 00:26:26.630 --> 00:26:31.010 align:middle line:84% paraffin wax, a very hydrogen-rich substance, very-- 00:26:31.010 --> 00:26:33.650 align:middle line:84% each atom of which is very, very lightweight. 00:26:33.650 --> 00:26:35.102 align:middle line:90% And then protons came out. 00:26:35.102 --> 00:26:36.560 align:middle line:84% And then he could measure basically 00:26:36.560 --> 00:26:39.320 align:middle line:84% the kind of stopping power of those protons. 00:26:39.320 --> 00:26:43.220 align:middle line:84% So what Chadwick clarified-- which one of the few times 00:26:43.220 --> 00:26:45.140 align:middle line:84% that Irene and Frédéric Joliot-Curie had not 00:26:45.140 --> 00:26:47.840 align:middle line:84% kind of just nailed it the first time, so Chadwick came in 00:26:47.840 --> 00:26:50.540 align:middle line:84% and clarified-- was this unknown radiation, 00:26:50.540 --> 00:26:54.320 align:middle line:84% the stuff that came flying out upon irradiating beryllium 00:26:54.320 --> 00:26:58.220 align:middle line:84% with alpha particles was this long suspected 00:26:58.220 --> 00:27:02.360 align:middle line:84% neutral particle, electrically neutral with a mass pretty 00:27:02.360 --> 00:27:04.290 align:middle line:90% close to that of protons. 00:27:04.290 --> 00:27:06.902 align:middle line:84% So the way that Chadwick made sense of this reaction 00:27:06.902 --> 00:27:08.360 align:middle line:84% was that there were alpha particles 00:27:08.360 --> 00:27:11.690 align:middle line:84% coming out from the polonium and countering the beryllium that 00:27:11.690 --> 00:27:15.230 align:middle line:84% would convert into a stable carbon atom 00:27:15.230 --> 00:27:17.510 align:middle line:84% and have this unknown radiation be the neutron. 00:27:17.510 --> 00:27:19.880 align:middle line:84% And again, this is probably familiar notation for you. 00:27:19.880 --> 00:27:21.830 align:middle line:84% The lower-- the subscript number here 00:27:21.830 --> 00:27:24.110 align:middle line:84% is what's called the atomic number. 00:27:24.110 --> 00:27:26.180 align:middle line:84% That just counts the number of protons. 00:27:26.180 --> 00:27:29.090 align:middle line:84% The placement of any of these items on the periodic table 00:27:29.090 --> 00:27:31.640 align:middle line:84% is determined by the number of protons in the nucleus. 00:27:31.640 --> 00:27:35.390 align:middle line:84% And the superscript, the raised number, is the atomic mass. 00:27:35.390 --> 00:27:38.060 align:middle line:84% So how many basically proton masses worth 00:27:38.060 --> 00:27:39.800 align:middle line:90% did that item weigh? 00:27:39.800 --> 00:27:43.430 align:middle line:84% So an alpha particle has two units of electric charge-- 00:27:43.430 --> 00:27:45.770 align:middle line:84% twice the charge of the proton but is four times 00:27:45.770 --> 00:27:46.842 align:middle line:90% as heavy as a proton-- 00:27:46.842 --> 00:27:48.050 align:middle line:90% beryllium carbon [INAUDIBLE]. 00:27:48.050 --> 00:27:51.080 align:middle line:84% So the neutron would have had no electric charge. 00:27:51.080 --> 00:27:53.480 align:middle line:84% It had zero times the charge of a proton 00:27:53.480 --> 00:27:55.680 align:middle line:84% but had about the same mass as a proton. 00:27:55.680 --> 00:27:57.770 align:middle line:84% And that's what Chadwick finally clarified, 00:27:57.770 --> 00:28:00.440 align:middle line:84% in part because of the paraffin here. 00:28:00.440 --> 00:28:02.225 align:middle line:90% He was able to not-- 00:28:02.225 --> 00:28:06.590 align:middle line:84% to have the particles of this unknown radiation collide-- 00:28:06.590 --> 00:28:08.450 align:middle line:84% basically have two body collisions 00:28:08.450 --> 00:28:11.630 align:middle line:84% with the very proton-rich targets in the paraffin. 00:28:11.630 --> 00:28:14.270 align:middle line:84% And then he could measure the energy with which the protons 00:28:14.270 --> 00:28:18.770 align:middle line:84% came out with a kind of stopping power, much like we saw, 00:28:18.770 --> 00:28:21.520 align:middle line:84% say, Lenard do for the photoelectric effect. 00:28:21.520 --> 00:28:24.260 align:middle line:84% So with that, he could infer that each individual particle 00:28:24.260 --> 00:28:27.020 align:middle line:84% coming out here had a mass pretty similar 00:28:27.020 --> 00:28:30.320 align:middle line:84% to that of the protons because of the recoil pattern. 00:28:30.320 --> 00:28:34.880 align:middle line:84% And that's when the first really compelling empirical evidence 00:28:34.880 --> 00:28:36.740 align:middle line:84% for this new thing in the nucleus 00:28:36.740 --> 00:28:40.490 align:middle line:84% called the neutron, that really was introduced. 00:28:40.490 --> 00:28:43.740 align:middle line:84% And so Chadwick's work was also recognized very, very quickly. 00:28:43.740 --> 00:28:46.670 align:middle line:84% So in the year that the Joliot-Curies shared the Nobel 00:28:46.670 --> 00:28:49.055 align:middle line:84% Prize in chemistry Chadwick won that same year 00:28:49.055 --> 00:28:50.180 align:middle line:90% the Nobel Prize in physics. 00:28:50.180 --> 00:28:53.263 align:middle line:84% This was capturing people's attention right away. 00:28:53.263 --> 00:28:55.430 align:middle line:84% Among those people whose attention it captured right 00:28:55.430 --> 00:28:58.070 align:middle line:84% away was Enrico Fermi, another-- at this point, 00:28:58.070 --> 00:28:59.960 align:middle line:90% still pretty young-- 00:28:59.960 --> 00:29:01.790 align:middle line:90% full professor in Rome. 00:29:01.790 --> 00:29:05.990 align:middle line:84% Fermi was very eager to get the Rome group kind of on the map. 00:29:05.990 --> 00:29:09.947 align:middle line:84% Everyone was kind of jealous of Paris and the Cavendish 00:29:09.947 --> 00:29:11.780 align:middle line:84% and some of these other centers of research. 00:29:11.780 --> 00:29:14.330 align:middle line:84% And Fermi thought it was time to get his group really up 00:29:14.330 --> 00:29:16.140 align:middle line:90% to the same kind of quality. 00:29:16.140 --> 00:29:19.940 align:middle line:84% So Fermi had just only recently been made a full professor 00:29:19.940 --> 00:29:24.410 align:middle line:84% and given a kind of research lab, well-funded group in Rome. 00:29:24.410 --> 00:29:27.050 align:middle line:84% And he realized that neutrons, unlike alpha 00:29:27.050 --> 00:29:29.990 align:middle line:84% particles because the neutrons are electrically neutral, 00:29:29.990 --> 00:29:32.600 align:middle line:84% they might be able to do even more 00:29:32.600 --> 00:29:35.325 align:middle line:84% effective induced radioactive reactions 00:29:35.325 --> 00:29:36.950 align:middle line:84% because you're not going to have a kind 00:29:36.950 --> 00:29:40.130 align:middle line:84% of electrostatic repulsion of the alpha particle 00:29:40.130 --> 00:29:44.390 align:middle line:84% with its positive charge getting repelled by the target it's 00:29:44.390 --> 00:29:48.080 align:middle line:84% trying to strike, like the positively charged nucleus 00:29:48.080 --> 00:29:49.610 align:middle line:90% of a target substance. 00:29:49.610 --> 00:29:52.220 align:middle line:84% So the neutron, since it had no electric charge, 00:29:52.220 --> 00:29:55.150 align:middle line:84% Fermi realized, could maybe be an even better inducer 00:29:55.150 --> 00:29:57.490 align:middle line:84% of these nuclear reactions because it can somehow 00:29:57.490 --> 00:30:00.860 align:middle line:84% get perhaps even closer into the action, so to speak, 00:30:00.860 --> 00:30:03.490 align:middle line:84% without suffering that Coulomb repulsion. 00:30:03.490 --> 00:30:06.250 align:middle line:84% So he and his group were very, very methodical. 00:30:06.250 --> 00:30:09.640 align:middle line:84% And they basically tried to get purified, elemental sources 00:30:09.640 --> 00:30:13.438 align:middle line:84% of almost every single element on the periodic table starting 00:30:13.438 --> 00:30:15.730 align:middle line:84% practically with hydrogen, helium-- starting very, very 00:30:15.730 --> 00:30:17.320 align:middle line:90% early on, certainly beryllium. 00:30:17.320 --> 00:30:21.790 align:middle line:84% And marching just one by one up every single known chemical 00:30:21.790 --> 00:30:23.860 align:middle line:84% element, or as many of them as could, 00:30:23.860 --> 00:30:26.260 align:middle line:84% they got to the very end of the known chart. 00:30:26.260 --> 00:30:27.980 align:middle line:84% They got up to uranium, which was, 00:30:27.980 --> 00:30:31.750 align:middle line:84% at the time, the heaviest known most massive element 00:30:31.750 --> 00:30:34.000 align:middle line:84% on the periodic table, the one with the largest number 00:30:34.000 --> 00:30:35.860 align:middle line:90% of protons in its nucleus-- 00:30:35.860 --> 00:30:37.665 align:middle line:90% atomic number 92. 00:30:37.665 --> 00:30:39.040 align:middle line:84% And they would do the same trick. 00:30:39.040 --> 00:30:41.230 align:middle line:84% They would irradiate purified samples 00:30:41.230 --> 00:30:43.240 align:middle line:84% of each of these elements, including uranium, 00:30:43.240 --> 00:30:45.700 align:middle line:90% with a source of neutrons. 00:30:45.700 --> 00:30:47.530 align:middle line:90% And they would often-- 00:30:47.530 --> 00:30:49.120 align:middle line:84% not every time-- but often, they would 00:30:49.120 --> 00:30:52.452 align:middle line:84% be able to induce radioactivity much as the Joliot-Curies had 00:30:52.452 --> 00:30:54.410 align:middle line:84% been doing, and they could measure the response 00:30:54.410 --> 00:30:56.120 align:middle line:84% with Geiger counters and all the rest. 00:30:56.120 --> 00:30:59.400 align:middle line:84% What Fermi found was they got especially strong reaction 00:30:59.400 --> 00:30:59.900 align:middle line:90% rates. 00:30:59.900 --> 00:31:01.610 align:middle line:84% They would really get this uranium start 00:31:01.610 --> 00:31:03.650 align:middle line:84% acting like a radioactive material 00:31:03.650 --> 00:31:07.940 align:middle line:84% when Fermi placed a block of paraffin, this lightweight wax, 00:31:07.940 --> 00:31:10.880 align:middle line:84% between the neutron and the uranium target. 00:31:10.880 --> 00:31:13.430 align:middle line:84% So now, with Chadwick the paraffin 00:31:13.430 --> 00:31:17.630 align:middle line:84% was to interact with the neutrons that 00:31:17.630 --> 00:31:20.660 align:middle line:84% came flying out after the neutrons had already 00:31:20.660 --> 00:31:21.920 align:middle line:90% come from a target. 00:31:21.920 --> 00:31:24.020 align:middle line:84% Now, Fermi places the paraffin wax 00:31:24.020 --> 00:31:26.600 align:middle line:84% between the source of neutrons, and in this case, 00:31:26.600 --> 00:31:28.160 align:middle line:90% say, the uranium target. 00:31:28.160 --> 00:31:30.350 align:middle line:84% So what the Rome group assumed they were measuring-- 00:31:30.350 --> 00:31:33.030 align:middle line:84% and you can see in this one of the whole series of papers 00:31:33.030 --> 00:31:35.030 align:middle line:84% that they published-- this one by Fermi himself. 00:31:35.030 --> 00:31:38.390 align:middle line:84% Others had about five or six co-authors-- 00:31:38.390 --> 00:31:41.060 align:middle line:84% they thought they actually had made new elements. 00:31:41.060 --> 00:31:43.970 align:middle line:84% They thought they had gone beyond the then highest known 00:31:43.970 --> 00:31:45.140 align:middle line:90% atomic number. 00:31:45.140 --> 00:31:48.080 align:middle line:84% As you see here, his paper in Nature 00:31:48.080 --> 00:31:51.200 align:middle line:84% was the possible production of elements of atomic number 00:31:51.200 --> 00:31:54.800 align:middle line:84% higher than 92, meaning atomic number beyond uranium. 00:31:54.800 --> 00:31:56.300 align:middle line:84% So they thought what they were doing 00:31:56.300 --> 00:31:59.210 align:middle line:90% was taking a uranium target-- 00:31:59.210 --> 00:32:03.710 align:middle line:84% so each atom which had 92 protons, a total mass of 238. 00:32:03.710 --> 00:32:06.350 align:middle line:84% They would irradiate it with neutrons. 00:32:06.350 --> 00:32:10.640 align:middle line:84% And the uranium target would do what would soon 00:32:10.640 --> 00:32:12.260 align:middle line:90% be called neutron capture. 00:32:12.260 --> 00:32:14.610 align:middle line:84% So it would absorb that incoming neutron. 00:32:14.610 --> 00:32:16.280 align:middle line:90% So what happens then? 00:32:16.280 --> 00:32:18.360 align:middle line:84% The atomic number has not changed. 00:32:18.360 --> 00:32:20.570 align:middle line:90% This has zero proton units. 00:32:20.570 --> 00:32:23.180 align:middle line:90% So the 92 plus 0 remains 92. 00:32:23.180 --> 00:32:24.960 align:middle line:90% You still have uranium there. 00:32:24.960 --> 00:32:27.710 align:middle line:84% But the actual mass has increased by one unit. 00:32:27.710 --> 00:32:31.280 align:middle line:84% So neutron capture does not change the chemical identity 00:32:31.280 --> 00:32:32.270 align:middle line:90% of the target. 00:32:32.270 --> 00:32:33.500 align:middle line:90% It's still uranium. 00:32:33.500 --> 00:32:36.060 align:middle line:84% It still has only 92 protons in the nucleus. 00:32:36.060 --> 00:32:38.990 align:middle line:84% But you change it to a different isotope-- same number 00:32:38.990 --> 00:32:41.510 align:middle line:84% of protons, different total atomic mass. 00:32:41.510 --> 00:32:43.470 align:middle line:90% In this case, one more neutron. 00:32:43.470 --> 00:32:46.910 align:middle line:84% And then after some time, the neutron that had been absorbed 00:32:46.910 --> 00:32:49.490 align:middle line:84% would itself undergo a radioactive decay, 00:32:49.490 --> 00:32:52.880 align:middle line:84% a so-called beta decay, where the neutron would transform 00:32:52.880 --> 00:32:55.260 align:middle line:90% into a proton-- 00:32:55.260 --> 00:32:56.850 align:middle line:90% sorry-- transform into a proton. 00:32:56.850 --> 00:32:58.980 align:middle line:84% And then a beta ray, an electron, 00:32:58.980 --> 00:33:00.240 align:middle line:90% would come flying out. 00:33:00.240 --> 00:33:04.020 align:middle line:84% It was actually Fermi who built upon suggestions by people 00:33:04.020 --> 00:33:06.180 align:middle line:84% like Wolfgang Pauli, saying that it actually it 00:33:06.180 --> 00:33:07.890 align:middle line:84% has to be more than just a beta decay 00:33:07.890 --> 00:33:11.010 align:middle line:84% to get the energy and momentum to balance, to work out. 00:33:11.010 --> 00:33:15.450 align:middle line:84% So an electron and some as yet unseen extra particle 00:33:15.450 --> 00:33:17.280 align:middle line:84% that they eventually called the neutrino-- 00:33:17.280 --> 00:33:20.400 align:middle line:84% now we call it an antineutrino-- stuff comes flying out. 00:33:20.400 --> 00:33:23.160 align:middle line:84% The main thing is that the neutron 00:33:23.160 --> 00:33:24.940 align:middle line:90% transformed into a proton. 00:33:24.940 --> 00:33:29.040 align:middle line:84% So now, inside that nucleus you have 92 plus 1 protons. 00:33:29.040 --> 00:33:31.560 align:middle line:84% You've actually perhaps, possibly 00:33:31.560 --> 00:33:33.420 align:middle line:84% made an element that's chemically 00:33:33.420 --> 00:33:35.220 align:middle line:90% distinct from uranium. 00:33:35.220 --> 00:33:38.550 align:middle line:84% You've actually pushed it up one place on the periodic table 00:33:38.550 --> 00:33:41.340 align:middle line:84% Because now it seems to have a total of 93 protons. 00:33:41.340 --> 00:33:43.170 align:middle line:84% And yet, since the proton and neutron 00:33:43.170 --> 00:33:47.800 align:middle line:84% have basically the same mass, the atomic mass stays the same. 00:33:47.800 --> 00:33:49.740 align:middle line:84% So the idea was Fermi and his group 00:33:49.740 --> 00:33:52.830 align:middle line:84% were convinced they had conducted neutron capture 00:33:52.830 --> 00:33:54.420 align:middle line:90% followed by beta decay. 00:33:54.420 --> 00:33:58.120 align:middle line:84% They thought they had produced the first transuranic element. 00:33:58.120 --> 00:34:00.400 align:middle line:84% This would eventually be called neptunium. 00:34:00.400 --> 00:34:02.800 align:middle line:84% Just like in the solar system the planet Neptune 00:34:02.800 --> 00:34:04.870 align:middle line:84% is the first planet beyond Uranus, 00:34:04.870 --> 00:34:09.674 align:middle line:84% this would be the first element beyond uranium. 00:34:09.674 --> 00:34:12.070 align:middle line:84% I actually got to see these materials 00:34:12.070 --> 00:34:14.929 align:middle line:84% the last trip I was able to make before the pandemic, 00:34:14.929 --> 00:34:16.585 align:middle line:84% although I didn't know it at the time. 00:34:16.585 --> 00:34:18.210 align:middle line:84% I actually was in Rome for a few days-- 00:34:18.210 --> 00:34:21.630 align:middle line:84% a glorious few days this past January, not quite a year ago. 00:34:21.630 --> 00:34:24.330 align:middle line:84% And I got to see in this brand new Fermi museum. 00:34:24.330 --> 00:34:26.370 align:middle line:84% On the very site of his laboratory, 00:34:26.370 --> 00:34:28.620 align:middle line:84% there's now a museum that in principle is 00:34:28.620 --> 00:34:31.230 align:middle line:84% open to the public, though it's sealed up now I'm sure. 00:34:31.230 --> 00:34:33.870 align:middle line:84% And this was the actual lead-lined case in which they 00:34:33.870 --> 00:34:35.440 align:middle line:90% had their radioactive sources. 00:34:35.440 --> 00:34:38.157 align:middle line:84% This is the block of paraffin that Fermi used. 00:34:38.157 --> 00:34:40.199 align:middle line:84% It's like, I couldn't believe it was right there. 00:34:40.199 --> 00:34:41.969 align:middle line:84% I've been reading about this thing since I was a kid. 00:34:41.969 --> 00:34:43.530 align:middle line:84% And here are some of the examples 00:34:43.530 --> 00:34:45.300 align:middle line:84% of these purified elements-- the targets 00:34:45.300 --> 00:34:48.719 align:middle line:84% that they would irradiate with the neutrons that had 00:34:48.719 --> 00:34:50.258 align:middle line:90% gone through the paraffin wax. 00:34:50.258 --> 00:34:52.050 align:middle line:84% And here, this is what happens if you start 00:34:52.050 --> 00:34:54.050 align:middle line:84% filming in the streets of Rome, you 00:34:54.050 --> 00:34:55.300 align:middle line:90% get pulled over by the police. 00:34:55.300 --> 00:34:56.800 align:middle line:84% So it was actually-- they're working 00:34:56.800 --> 00:34:59.940 align:middle line:84% on a documentary with NOVA about Fermi and neutrons 00:34:59.940 --> 00:35:01.723 align:middle line:84% and neutrinos, and the police didn't 00:35:01.723 --> 00:35:03.390 align:middle line:84% realize we had all the proper paperwork. 00:35:03.390 --> 00:35:06.450 align:middle line:84% Here's Rosemary Cafferty, the production assistant, 00:35:06.450 --> 00:35:08.100 align:middle line:84% saying no, no, nice police officers. 00:35:08.100 --> 00:35:09.140 align:middle line:90% We do have the permits. 00:35:09.140 --> 00:35:09.640 align:middle line:90% Anyway. 00:35:09.640 --> 00:35:11.080 align:middle line:84% So I got to see lots of things in Rome, 00:35:11.080 --> 00:35:12.640 align:middle line:84% including Fermi's actual experiments. 00:35:12.640 --> 00:35:13.420 align:middle line:90% That was pretty awesome. 00:35:13.420 --> 00:35:13.920 align:middle line:90% OK. 00:35:13.920 --> 00:35:16.330 align:middle line:84% So Fermi's work actually triggered a lot 00:35:16.330 --> 00:35:19.180 align:middle line:84% of reactions in the human realm and not only 00:35:19.180 --> 00:35:20.630 align:middle line:90% in the nuclear realm. 00:35:20.630 --> 00:35:23.287 align:middle line:84% So this work was, again, seen as just unbelievably 00:35:23.287 --> 00:35:24.370 align:middle line:90% interesting and important. 00:35:24.370 --> 00:35:26.950 align:middle line:84% He starts publishing this in 1934. 00:35:26.950 --> 00:35:30.160 align:middle line:84% The main body of work comes out throughout 1935. 00:35:30.160 --> 00:35:32.450 align:middle line:90% By 1938, he again-- 00:35:32.450 --> 00:35:35.320 align:middle line:84% this work had been recognized as worthy of a Nobel Prize. 00:35:35.320 --> 00:35:37.510 align:middle line:84% Here's Fermi getting permission-- 00:35:37.510 --> 00:35:39.040 align:middle line:84% excuse me-- winning the Nobel Prize, 00:35:39.040 --> 00:35:42.220 align:middle line:84% receiving it from the King of Sweden December of 1938, 00:35:42.220 --> 00:35:45.220 align:middle line:84% just three or four years after starting that whole series 00:35:45.220 --> 00:35:46.450 align:middle line:90% of investigations. 00:35:46.450 --> 00:35:49.750 align:middle line:84% Now, that timing is pretty remarkable. 00:35:49.750 --> 00:35:53.060 align:middle line:84% As again, many of you probably know, Italy by this point, 00:35:53.060 --> 00:35:57.000 align:middle line:84% since the '20s, had been ruled by a fascist dictator, 00:35:57.000 --> 00:36:00.430 align:middle line:84% a self-pronounced fascist dictator, Benito Mussolini. 00:36:00.430 --> 00:36:02.890 align:middle line:84% Mussolini was not in the earliest days 00:36:02.890 --> 00:36:05.960 align:middle line:84% as rabidly anti-Semitic as he would become. 00:36:05.960 --> 00:36:11.170 align:middle line:84% But after Hitler attained power in Germany, Hitler 00:36:11.170 --> 00:36:13.180 align:middle line:84% and Mussolini made a series of pacts. 00:36:13.180 --> 00:36:15.940 align:middle line:84% And Mussolini's policies began mirroring or getting 00:36:15.940 --> 00:36:19.000 align:middle line:84% much closer to those of the overt anti-Semitism 00:36:19.000 --> 00:36:21.670 align:middle line:84% and so-called racial purity of the Nazis. 00:36:21.670 --> 00:36:26.770 align:middle line:84% So by the early and mid-1930s, Mussolini's regime in Italy 00:36:26.770 --> 00:36:30.400 align:middle line:84% was becoming as dangerous for people of Jewish background 00:36:30.400 --> 00:36:32.470 align:middle line:90% as Hitler's was in Germany. 00:36:32.470 --> 00:36:34.240 align:middle line:84% That mattered a great deal to Fermi. 00:36:34.240 --> 00:36:36.640 align:middle line:84% Fermi himself was not Jewish, but his wife Laura 00:36:36.640 --> 00:36:38.420 align:middle line:90% was from a Jewish family. 00:36:38.420 --> 00:36:42.280 align:middle line:84% And even though Fermi was this big fancy professor getting 00:36:42.280 --> 00:36:44.650 align:middle line:84% lots and lots of support from the central government 00:36:44.650 --> 00:36:47.770 align:middle line:84% for his research, it was becoming more and more clear 00:36:47.770 --> 00:36:49.630 align:middle line:84% that this was no-- this was not going 00:36:49.630 --> 00:36:52.990 align:middle line:84% to remain a kind of easy existence for them 00:36:52.990 --> 00:36:54.640 align:middle line:84% with a Jewish member of the family, 00:36:54.640 --> 00:36:57.760 align:middle line:84% as Mussolini began aligning policies more and more closely 00:36:57.760 --> 00:36:59.890 align:middle line:90% with those of the Nazis. 00:36:59.890 --> 00:37:03.800 align:middle line:84% So what Fermi arranged, upon learning that he would receive 00:37:03.800 --> 00:37:06.077 align:middle line:84% the Nobel Prize, was that his entire family, 00:37:06.077 --> 00:37:08.410 align:middle line:84% his immediate family, could travel with him to Stockholm 00:37:08.410 --> 00:37:11.140 align:middle line:84% to win the prize, and they basically snuck out. 00:37:11.140 --> 00:37:15.070 align:middle line:84% So Mussolini couldn't help but let Fermi leave the country. 00:37:15.070 --> 00:37:17.200 align:middle line:84% For Italy's grandeur, it was important to let 00:37:17.200 --> 00:37:19.510 align:middle line:90% Fermi receive the Nobel Prize. 00:37:19.510 --> 00:37:22.240 align:middle line:84% And then basically behind Mussolini's back, 00:37:22.240 --> 00:37:25.960 align:middle line:84% Fermi had arranged in secret to have his immediate family skip 00:37:25.960 --> 00:37:28.690 align:middle line:84% town, to leave almost directly from Stockholm, 00:37:28.690 --> 00:37:32.350 align:middle line:84% get on a steamboat out of, I think, the UK, 00:37:32.350 --> 00:37:33.910 align:middle line:90% and sail right to New York City. 00:37:33.910 --> 00:37:37.360 align:middle line:84% It's a lot like-- if you've seen the famous movie, The Sound 00:37:37.360 --> 00:37:45.280 align:middle line:84% of Music, it's a lot [AUDIO OUT] a ceremony full of fanfare 00:37:45.280 --> 00:37:47.190 align:middle line:90% and just escaped. 00:37:47.190 --> 00:37:48.900 align:middle line:84% And so Fermi and his immediate family 00:37:48.900 --> 00:37:51.750 align:middle line:84% moved and resettled for a time in New York City. 00:37:51.750 --> 00:37:54.540 align:middle line:84% So this is a reminder of the timing. 00:37:54.540 --> 00:37:57.180 align:middle line:84% We have this exciting new work in nuclear physics, 00:37:57.180 --> 00:38:00.720 align:middle line:84% new particles found, new kinds of nuclear transformations. 00:38:00.720 --> 00:38:04.170 align:middle line:84% The world scientists are getting very, very excited about this 00:38:04.170 --> 00:38:07.260 align:middle line:84% at just the moment when fascists are 00:38:07.260 --> 00:38:11.850 align:middle line:84% taking over many, many parts within Europe. 00:38:11.850 --> 00:38:13.830 align:middle line:84% Now, it turns out other groups were actively 00:38:13.830 --> 00:38:16.500 align:middle line:84% working on exactly these kinds of nuclear transformations. 00:38:16.500 --> 00:38:18.330 align:middle line:84% After all, Fermi won the Nobel Prize 00:38:18.330 --> 00:38:20.850 align:middle line:84% partly because everyone-- many, many people in the field 00:38:20.850 --> 00:38:23.290 align:middle line:84% agreed this was really, really kind of hot stuff. 00:38:23.290 --> 00:38:24.550 align:middle line:90% This was important stuff. 00:38:24.550 --> 00:38:27.420 align:middle line:84% So many groups were working on either replicating 00:38:27.420 --> 00:38:30.120 align:middle line:84% Fermi's series of experiments with this neutron capture, 00:38:30.120 --> 00:38:33.480 align:middle line:84% or trying to irradiate other sources, 00:38:33.480 --> 00:38:36.990 align:middle line:84% find other isotopes and possibly even new elements. 00:38:36.990 --> 00:38:39.300 align:middle line:84% And one of the most active in this group 00:38:39.300 --> 00:38:40.980 align:middle line:90% was a team based in Berlin. 00:38:40.980 --> 00:38:43.380 align:middle line:84% What's really interesting about this Berlin group is 00:38:43.380 --> 00:38:46.440 align:middle line:84% that they were explicitly multidisciplinary, 00:38:46.440 --> 00:38:48.660 align:middle line:84% even more so-- certainly more so than Fermi's group. 00:38:48.660 --> 00:38:51.180 align:middle line:84% Even arguably more than the Joliot-Curies, 00:38:51.180 --> 00:38:52.510 align:middle line:90% or similar, at least, to them. 00:38:52.510 --> 00:38:55.200 align:middle line:84% So the group included a theoretical physicist, 00:38:55.200 --> 00:38:58.260 align:middle line:84% Lise Meitner, as well as two very accomplished nuclear 00:38:58.260 --> 00:39:01.530 align:middle line:84% chemists, Otto Hahn and Fritz Strassmann. 00:39:01.530 --> 00:39:06.960 align:middle line:84% And for today's readings, we have a little-- an excerpt 00:39:06.960 --> 00:39:10.230 align:middle line:84% that's drawn from this really quite amazing biography 00:39:10.230 --> 00:39:13.150 align:middle line:90% of Meitner by Ruth Lewin Sime. 00:39:13.150 --> 00:39:15.150 align:middle line:84% Again, for those of you who might be interested, 00:39:15.150 --> 00:39:16.930 align:middle line:84% I can't recommend this book highly enough. 00:39:16.930 --> 00:39:19.620 align:middle line:84% I just think this book is gripping and moving 00:39:19.620 --> 00:39:22.200 align:middle line:90% and beautifully written-- 00:39:22.200 --> 00:39:23.670 align:middle line:90% Sime's biography of Meitner. 00:39:23.670 --> 00:39:25.630 align:middle line:84% So I couldn't assign the whole book, 00:39:25.630 --> 00:39:29.820 align:middle line:84% but I do encourage you to read even more from Sime's biography 00:39:29.820 --> 00:39:30.960 align:middle line:90% if you have the time. 00:39:30.960 --> 00:39:32.460 align:middle line:84% There's a little taste of an article 00:39:32.460 --> 00:39:35.710 align:middle line:84% that Ruth wrote with some colleagues in Physics Today, 00:39:35.710 --> 00:39:38.130 align:middle line:84% and then a kind of short piece inspired by her book 00:39:38.130 --> 00:39:41.040 align:middle line:84% by the very talented science writer Maria [INAUDIBLE].. 00:39:41.040 --> 00:39:44.370 align:middle line:84% But I think there's no substitute for this biography. 00:39:44.370 --> 00:39:46.530 align:middle line:84% Meitner, I think, is just endlessly fascinating. 00:39:46.530 --> 00:39:51.330 align:middle line:84% So what do we learn from Sime's biography? 00:39:51.330 --> 00:39:56.500 align:middle line:84% Meitner-- Lise Meitner grew up in a Jewish family in Austria. 00:39:56.500 --> 00:39:58.680 align:middle line:84% And she was therefore only allowed 00:39:58.680 --> 00:40:00.900 align:middle line:84% to attend formal school until age 14. 00:40:00.900 --> 00:40:04.440 align:middle line:84% At that point, the rules in the late years of the Habsburg 00:40:04.440 --> 00:40:06.728 align:middle line:84% Empire, girls couldn't even finish high school. 00:40:06.728 --> 00:40:08.520 align:middle line:84% They weren't allowed to finish high school. 00:40:08.520 --> 00:40:11.380 align:middle line:84% They could go to school through age 14. 00:40:11.380 --> 00:40:15.460 align:middle line:84% And during Meitner's kind of later teenage years, 00:40:15.460 --> 00:40:18.550 align:middle line:90% there was a series of reforms-- 00:40:18.550 --> 00:40:21.130 align:middle line:84% nationwide reforms in Austria that 00:40:21.130 --> 00:40:22.850 align:middle line:90% actually relaxed those rules. 00:40:22.850 --> 00:40:25.540 align:middle line:84% So then Meitner rushed through all the years 00:40:25.540 --> 00:40:27.467 align:middle line:84% she'd missed of the remaining years of what 00:40:27.467 --> 00:40:29.800 align:middle line:84% would have been a standard high school curriculum mostly 00:40:29.800 --> 00:40:31.150 align:middle line:90% through self-study. 00:40:31.150 --> 00:40:34.150 align:middle line:84% She finished high school effectively in a few months. 00:40:34.150 --> 00:40:37.240 align:middle line:84% And then even more astonishing, passed the entrance exam 00:40:37.240 --> 00:40:39.940 align:middle line:84% to study physics at the very elite 00:40:39.940 --> 00:40:42.640 align:middle line:84% University of Vienna, which otherwise would never 00:40:42.640 --> 00:40:44.890 align:middle line:84% have been allowed to her until these reforms had 00:40:44.890 --> 00:40:46.040 align:middle line:90% come into place. 00:40:46.040 --> 00:40:49.600 align:middle line:84% So she then studied very hard, and she 00:40:49.600 --> 00:40:51.612 align:middle line:84% was among the first women anywhere 00:40:51.612 --> 00:40:53.320 align:middle line:84% to earn not just an undergraduate degree, 00:40:53.320 --> 00:40:55.840 align:middle line:84% but actually, a full PhD in physics. 00:40:55.840 --> 00:40:58.600 align:middle line:90% She earned her PhD in 1905. 00:40:58.600 --> 00:41:00.640 align:middle line:84% And then she very quickly began to collaborate 00:41:00.640 --> 00:41:02.080 align:middle line:90% with Otto Hahn in Berlin. 00:41:02.080 --> 00:41:04.700 align:middle line:84% She had a few short-term kind of fellowships. 00:41:04.700 --> 00:41:08.020 align:middle line:84% And then eventually was hired-- sort of hired-- 00:41:08.020 --> 00:41:09.610 align:middle line:90% in Berlin. 00:41:09.610 --> 00:41:11.830 align:middle line:84% She was allowed to work with him. 00:41:11.830 --> 00:41:13.540 align:middle line:90% Hahn was glad to work with her. 00:41:13.540 --> 00:41:15.880 align:middle line:84% But she was only allowed to go into the basement 00:41:15.880 --> 00:41:18.790 align:middle line:84% of this Institute in Berlin because women were literally 00:41:18.790 --> 00:41:20.470 align:middle line:84% not allowed into the main institute, 00:41:20.470 --> 00:41:22.460 align:middle line:84% not just that there weren't women's restrooms. 00:41:22.460 --> 00:41:25.000 align:middle line:84% They weren't allowed on the first, second, third floor. 00:41:25.000 --> 00:41:29.380 align:middle line:84% So Hahn, to accommodate this very, very brilliant 00:41:29.380 --> 00:41:32.710 align:middle line:84% collaborator, colleague, agreed to work in what was essentially 00:41:32.710 --> 00:41:35.110 align:middle line:84% a kind of shop-- a kind of woodworking shop 00:41:35.110 --> 00:41:38.320 align:middle line:84% in the basement of the otherwise very fancy institute in Berlin. 00:41:38.320 --> 00:41:40.630 align:middle line:84% And that's how their collaboration started. 00:41:40.630 --> 00:41:44.740 align:middle line:84% Meitner, as a young and upcoming theoretical physicist, 00:41:44.740 --> 00:41:47.110 align:middle line:84% and Hahn, as an accomplished chemist. 00:41:47.110 --> 00:41:50.890 align:middle line:84% And here they are many years later working in their lab 00:41:50.890 --> 00:41:53.950 align:middle line:90% together in the later '30s. 00:41:53.950 --> 00:41:59.440 align:middle line:84% So what happens is in 1933, when Hitler is elected 00:41:59.440 --> 00:42:01.270 align:middle line:84% and the so-called civil service laws go 00:42:01.270 --> 00:42:03.460 align:middle line:84% into effect by that spring, people 00:42:03.460 --> 00:42:06.550 align:middle line:84% who are of Jewish background and German citizens 00:42:06.550 --> 00:42:10.270 align:middle line:84% could no longer hold university positions or other government 00:42:10.270 --> 00:42:11.710 align:middle line:90% jobs. 00:42:11.710 --> 00:42:13.360 align:middle line:84% Lise Meitner was not a German citizen. 00:42:13.360 --> 00:42:14.800 align:middle line:90% She was an Austrian. 00:42:14.800 --> 00:42:17.470 align:middle line:84% So it's quite astonishing that she was Jewish. 00:42:17.470 --> 00:42:18.730 align:middle line:90% Everyone knew she was Jewish. 00:42:18.730 --> 00:42:21.670 align:middle line:84% And she was able to keep her job because according 00:42:21.670 --> 00:42:23.860 align:middle line:84% to these new laws they didn't apply to her. 00:42:23.860 --> 00:42:26.980 align:middle line:84% They applied to German citizens of Jewish background. 00:42:26.980 --> 00:42:29.830 align:middle line:84% That changed in the spring of 1938, 00:42:29.830 --> 00:42:32.260 align:middle line:84% or beginning in the spring of '38 00:42:32.260 --> 00:42:35.330 align:middle line:84% because, again, as some of you may know, by that point, 00:42:35.330 --> 00:42:37.960 align:middle line:84% there was what is called the Anschluss, which is when 00:42:37.960 --> 00:42:42.700 align:middle line:90% Nazi [AUDIO OUT] welcomed it. 00:42:42.700 --> 00:42:46.410 align:middle line:84% But in any case, Austria became absorbed within the German-- 00:42:46.410 --> 00:42:47.760 align:middle line:90% the Nazi Reich. 00:42:47.760 --> 00:42:50.910 align:middle line:84% So now Austria, and therefore, Austrians, 00:42:50.910 --> 00:42:54.670 align:middle line:84% were subject to the kind of German laws, 00:42:54.670 --> 00:42:56.610 align:middle line:84% including these so-called civil service 00:42:56.610 --> 00:42:58.600 align:middle line:84% laws, these anti-Jewish employment laws. 00:42:58.600 --> 00:43:01.260 align:middle line:84% So only in late spring, early summer 00:43:01.260 --> 00:43:05.040 align:middle line:84% 1938, rather than spring of 1933, 00:43:05.040 --> 00:43:10.140 align:middle line:84% was Meitner no longer entitled, according to these new laws, 00:43:10.140 --> 00:43:11.220 align:middle line:90% to keep her job. 00:43:11.220 --> 00:43:13.830 align:middle line:84% So she actually had to flee in a hurry 00:43:13.830 --> 00:43:18.390 align:middle line:84% several years after this kind of exodus had begun. 00:43:18.390 --> 00:43:20.760 align:middle line:84% So Meitner actually got a temporary position 00:43:20.760 --> 00:43:21.510 align:middle line:90% in Stockholm. 00:43:21.510 --> 00:43:24.090 align:middle line:90% She was able to flee to Sweden. 00:43:24.090 --> 00:43:25.950 align:middle line:84% And in the meantime, Hahn and Strassmann, 00:43:25.950 --> 00:43:28.380 align:middle line:84% in their Berlin laboratory, continued 00:43:28.380 --> 00:43:30.720 align:middle line:84% these neutron bombardment experiments, again, doing just 00:43:30.720 --> 00:43:33.420 align:middle line:84% like what the Fermi group had gotten so famous for. 00:43:33.420 --> 00:43:37.080 align:middle line:84% They redid Fermi's experiments multiple times, 00:43:37.080 --> 00:43:40.260 align:middle line:84% even to the day at which Fermi was literally 00:43:40.260 --> 00:43:42.790 align:middle line:84% shaking the king's hand and receiving his Nobel Prize 00:43:42.790 --> 00:43:44.980 align:middle line:84% right throughout the month of December. 00:43:44.980 --> 00:43:48.220 align:middle line:84% But unlike Fermi, and unlike the Nobel committee, 00:43:48.220 --> 00:43:51.370 align:middle line:84% Hahn and Strassmann concluded that neither Fermi nor are 00:43:51.370 --> 00:43:53.260 align:middle line:84% they in their own lab had actually 00:43:53.260 --> 00:43:55.360 align:middle line:84% produced these elements beyond uranium. 00:43:55.360 --> 00:43:58.030 align:middle line:84% So literally, while Fermi was receiving the prize 00:43:58.030 --> 00:44:00.460 align:middle line:84% for having made transuranic elements, 00:44:00.460 --> 00:44:02.950 align:middle line:84% Hahn and Strassmann convinced themselves that no, he 00:44:02.950 --> 00:44:05.420 align:middle line:90% didn't, and neither had they. 00:44:05.420 --> 00:44:10.400 align:middle line:84% So this is an example of a periodic table from 1938. 00:44:10.400 --> 00:44:12.470 align:middle line:90% You can see it ends at uranium. 00:44:12.470 --> 00:44:15.530 align:middle line:84% So whereas, Fermi and the Nobel committee 00:44:15.530 --> 00:44:17.708 align:middle line:84% and all the experts-- nearly all the experts. 00:44:17.708 --> 00:44:20.000 align:middle line:84% There were a few detractors, but nearly all the experts 00:44:20.000 --> 00:44:25.070 align:middle line:84% had assumed that Fermi had nudged these nuclei up by one 00:44:25.070 --> 00:44:27.470 align:middle line:84% or maybe two places here beyond uranium. 00:44:27.470 --> 00:44:30.170 align:middle line:84% What Hahn and Strassmann kind of grudgingly 00:44:30.170 --> 00:44:33.170 align:middle line:84% conclude using their chemist knowledge, 00:44:33.170 --> 00:44:36.000 align:middle line:84% not their not the notion as physicists, is, in fact, 00:44:36.000 --> 00:44:38.120 align:middle line:84% the uranium target had been split. 00:44:38.120 --> 00:44:41.510 align:middle line:84% It hadn't been nudged to one step larger, one step 00:44:41.510 --> 00:44:43.520 align:middle line:84% beyond uranium on the periodic table. 00:44:43.520 --> 00:44:47.810 align:middle line:84% It had actually broken into two much smaller pieces midway down 00:44:47.810 --> 00:44:50.750 align:middle line:84% the periodic table into, for example, a barium fragment 00:44:50.750 --> 00:44:54.630 align:middle line:84% and a krypton fragment, where again, the atomic number would 00:44:54.630 --> 00:44:55.130 align:middle line:90% add up. 00:44:55.130 --> 00:44:57.140 align:middle line:90% You had 92 protons to start. 00:44:57.140 --> 00:44:59.630 align:middle line:84% You have 92 protons at the end, but not 00:44:59.630 --> 00:45:03.950 align:middle line:84% by having made one slightly larger blob of, say, neptunium 00:45:03.950 --> 00:45:05.220 align:middle line:90% or some transuranic. 00:45:05.220 --> 00:45:08.400 align:middle line:84% But, in fact, by splitting that initial target 00:45:08.400 --> 00:45:12.330 align:middle line:84% nucleus into two much smaller pieces. 00:45:12.330 --> 00:45:14.700 align:middle line:84% And they wrote this up in December. 00:45:14.700 --> 00:45:16.560 align:middle line:84% It was published almost immediately 00:45:16.560 --> 00:45:19.110 align:middle line:84% in some Prussian Academy publications 00:45:19.110 --> 00:45:20.970 align:middle line:90% in January of 1939. 00:45:20.970 --> 00:45:24.450 align:middle line:84% And they conclude this with this very famous closing. 00:45:24.450 --> 00:45:26.460 align:middle line:84% They say, as chemists, we must actually 00:45:26.460 --> 00:45:28.740 align:middle line:84% say the new particles that result-- 00:45:28.740 --> 00:45:32.940 align:middle line:84% the products after this reaction-- behave like-- 00:45:32.940 --> 00:45:36.593 align:middle line:84% do not behave like radium, but in fact, like barium. 00:45:36.593 --> 00:45:38.010 align:middle line:84% It looks like they really had been 00:45:38.010 --> 00:45:42.180 align:middle line:84% knocked all the way down here, not in the vicinity of uranium. 00:45:42.180 --> 00:45:44.370 align:middle line:84% So as chemists, we say we found barium. 00:45:44.370 --> 00:45:47.020 align:middle line:84% As nuclear physicists, we cannot make this conclusion, 00:45:47.020 --> 00:45:50.100 align:middle line:84% which is in conflict with all experience in nuclear physics. 00:45:50.100 --> 00:45:52.500 align:middle line:84% There was no known nuclear transformation 00:45:52.500 --> 00:45:56.370 align:middle line:84% to date after 40 years of studying such things, 00:45:56.370 --> 00:45:57.990 align:middle line:84% in which there had been that large 00:45:57.990 --> 00:46:00.750 align:middle line:84% a leap either up or down the periodic table. 00:46:00.750 --> 00:46:02.340 align:middle line:84% And I talked a bit more about this 00:46:02.340 --> 00:46:04.680 align:middle line:90% in the optional lecture notes. 00:46:04.680 --> 00:46:07.260 align:middle line:84% All the known transformations-- alpha decay 00:46:07.260 --> 00:46:08.910 align:middle line:90% would knock you down two places. 00:46:08.910 --> 00:46:10.980 align:middle line:84% Beta decay knocked-- bring you up. 00:46:10.980 --> 00:46:12.960 align:middle line:84% You would be moving one or two places 00:46:12.960 --> 00:46:17.560 align:middle line:84% in your immediate vicinity, not halfway down the table. 00:46:17.560 --> 00:46:19.530 align:middle line:84% So while she was now on the run-- 00:46:19.530 --> 00:46:23.220 align:middle line:84% she had just arrived at a kind of temporary position 00:46:23.220 --> 00:46:24.300 align:middle line:90% in Stockholm-- 00:46:24.300 --> 00:46:27.930 align:middle line:84% Meitner received an update from Otto Hahn about these latest 00:46:27.930 --> 00:46:30.390 align:middle line:84% experiments indicating the presence of barium, 00:46:30.390 --> 00:46:33.930 align:middle line:84% which again, to emphasize, Hahn and Strassmann as chemists 00:46:33.930 --> 00:46:37.380 align:middle line:84% knew how to do proper chemical analyzes to test for barium. 00:46:37.380 --> 00:46:39.090 align:middle line:84% And they were more and more convinced 00:46:39.090 --> 00:46:40.230 align:middle line:90% that's what was there. 00:46:40.230 --> 00:46:43.500 align:middle line:84% So Meitner gets the update from Hahn. 00:46:43.500 --> 00:46:45.810 align:middle line:84% She has a little break with her nephew, 00:46:45.810 --> 00:46:48.010 align:middle line:84% another theoretical physicist, Otto Robert Frisch. 00:46:48.010 --> 00:46:50.010 align:middle line:90% He often went just by Robert. 00:46:50.010 --> 00:46:53.620 align:middle line:84% Frisch was actually at this point a postdoc in Copenhagen. 00:46:53.620 --> 00:46:55.230 align:middle line:90% So he was also in Scandinavia. 00:46:55.230 --> 00:46:57.360 align:middle line:84% He was able to come see his aunt. 00:46:57.360 --> 00:47:00.510 align:middle line:84% They had a few days together outside of Stockholm 00:47:00.510 --> 00:47:02.180 align:middle line:90% in a little ski vacation-- 00:47:02.180 --> 00:47:03.570 align:middle line:90% cross-country skiing. 00:47:03.570 --> 00:47:07.230 align:middle line:84% And it's while there that Meitner had just 00:47:07.230 --> 00:47:09.030 align:middle line:90% received his letter from Hahn. 00:47:09.030 --> 00:47:11.310 align:middle line:84% Frisch comes, and they spend the day 00:47:11.310 --> 00:47:13.680 align:middle line:84% talking about how Hahn and Strassmann's results 00:47:13.680 --> 00:47:15.520 align:middle line:90% could possibly be true. 00:47:15.520 --> 00:47:18.790 align:middle line:84% And while away from any kind of workspace, 00:47:18.790 --> 00:47:21.880 align:middle line:84% while literally spending the day out in the woods-- 00:47:21.880 --> 00:47:24.970 align:middle line:84% snow-covered woods-- they work out the first ever physical 00:47:24.970 --> 00:47:26.590 align:middle line:90% model of nuclear fission. 00:47:26.590 --> 00:47:27.970 align:middle line:90% It's quite extraordinary. 00:47:27.970 --> 00:47:30.220 align:middle line:84% And again, there's plenty more in the optional notes 00:47:30.220 --> 00:47:32.740 align:middle line:84% to spell this out in more detail. 00:47:32.740 --> 00:47:34.870 align:middle line:84% They began to argue or to convince themselves 00:47:34.870 --> 00:47:38.770 align:middle line:84% that slow neutrons were the key, that remember, 00:47:38.770 --> 00:47:40.810 align:middle line:84% Fermi was finding increased reaction rates 00:47:40.810 --> 00:47:42.790 align:middle line:84% when he put that block of paraffin, 00:47:42.790 --> 00:47:46.300 align:middle line:84% that wax between the neutrons and the target uranium. 00:47:46.300 --> 00:47:47.860 align:middle line:84% And they argue that that must have 00:47:47.860 --> 00:47:51.220 align:middle line:84% been because the paraffin was slowing down the neutrons. 00:47:51.220 --> 00:47:54.633 align:middle line:84% There'd be enough scattering and recoil that the neutrons that 00:47:54.633 --> 00:47:56.050 align:middle line:84% made it through the paraffin would 00:47:56.050 --> 00:47:58.330 align:middle line:84% have lost a significant amount of energy 00:47:58.330 --> 00:48:01.540 align:middle line:84% from having scattered off an object of comparable size. 00:48:01.540 --> 00:48:04.780 align:middle line:84% And so they should be slowed down by their travel 00:48:04.780 --> 00:48:08.080 align:middle line:84% through that moderator, through that material that would 00:48:08.080 --> 00:48:10.450 align:middle line:90% slow down their kinetic energy. 00:48:10.450 --> 00:48:12.430 align:middle line:90% And then Meitner and Frisch-- 00:48:12.430 --> 00:48:13.743 align:middle line:90% unlike Fermi at first-- 00:48:13.743 --> 00:48:15.160 align:middle line:84% Meitner and Frisch realized, well, 00:48:15.160 --> 00:48:19.780 align:middle line:84% if the momentum of these neutrons has been reduced, 00:48:19.780 --> 00:48:22.938 align:middle line:84% then the quantum-like behavior should have been exaggerated. 00:48:22.938 --> 00:48:25.230 align:middle line:84% If you go back to the de Broglie wavelength-- remember, 00:48:25.230 --> 00:48:30.600 align:middle line:84% we saw this inherent waviness associated quantum mechanically 00:48:30.600 --> 00:48:33.750 align:middle line:84% with any solid matter, it's proportional to Planck's 00:48:33.750 --> 00:48:36.700 align:middle line:84% constant, but inversely proportional to the momentum. 00:48:36.700 --> 00:48:38.850 align:middle line:84% So if the neutrons are being slowed down 00:48:38.850 --> 00:48:42.330 align:middle line:84% through, say, that paraffin wax, then the velocity 00:48:42.330 --> 00:48:43.170 align:middle line:90% would be small. 00:48:43.170 --> 00:48:46.740 align:middle line:84% The waviness, the characteristic size of this quantum wave, 00:48:46.740 --> 00:48:48.480 align:middle line:90% would be enhanced. 00:48:48.480 --> 00:48:51.210 align:middle line:84% So maybe even though this uranium nucleus 00:48:51.210 --> 00:48:54.720 align:middle line:84% is nearly 240 times bigger than-- 00:48:54.720 --> 00:48:57.780 align:middle line:84% or more massive than-- the inbound neutron, 00:48:57.780 --> 00:49:00.300 align:middle line:84% if that neutron had been slowed so that its quantum 00:49:00.300 --> 00:49:03.240 align:middle line:84% properties have been stretched-- the quantumness, so to speak-- 00:49:03.240 --> 00:49:06.060 align:middle line:84% the wavelength might be comparable in size 00:49:06.060 --> 00:49:08.490 align:middle line:84% to this entire uranium target, maybe 00:49:08.490 --> 00:49:11.790 align:middle line:84% you could set the entire target wobbling coherently 00:49:11.790 --> 00:49:14.820 align:middle line:84% to get a kind of coherent or collective response 00:49:14.820 --> 00:49:18.370 align:middle line:84% to the single bombardment by the incoming neutron. 00:49:18.370 --> 00:49:21.280 align:middle line:84% And they began, again, working out this kind of picture 00:49:21.280 --> 00:49:24.108 align:middle line:84% that this neutron might be like a kind of liquid drop-- 00:49:24.108 --> 00:49:26.650 align:middle line:84% that was a model that Niels Bohr himself had been working out 00:49:26.650 --> 00:49:27.610 align:middle line:90% for a while-- 00:49:27.610 --> 00:49:31.870 align:middle line:84% this kind of barely stable equilibrium 00:49:31.870 --> 00:49:34.690 align:middle line:84% between a kind of surface tension keeping it together 00:49:34.690 --> 00:49:39.970 align:middle line:84% and a volume pressure that would work to-- 00:49:39.970 --> 00:49:41.710 align:middle line:84% work against the surface tension. 00:49:41.710 --> 00:49:44.350 align:middle line:84% And there might be just a balancing point 00:49:44.350 --> 00:49:47.110 align:middle line:84% when you get to very large nuclei like uranium. 00:49:47.110 --> 00:49:49.930 align:middle line:84% So once this kind of stretched-out, slow neutron 00:49:49.930 --> 00:49:53.290 align:middle line:84% encounters the nucleus, it gets the whole drop wobbling. 00:49:53.290 --> 00:49:56.210 align:middle line:84% And in fact, you could actually have this thin neck appear. 00:49:56.210 --> 00:49:58.600 align:middle line:84% And then finally-- because this is now 00:49:58.600 --> 00:50:01.810 align:middle line:84% a very-- a dense pack of positively charged protons, 00:50:01.810 --> 00:50:04.450 align:middle line:84% this is a separate densely packed region 00:50:04.450 --> 00:50:06.850 align:middle line:84% of positive protons that can now repel each other, 00:50:06.850 --> 00:50:09.100 align:middle line:84% maybe this neck will rupture, and you'll actually 00:50:09.100 --> 00:50:11.110 align:middle line:90% get two smaller pieces. 00:50:11.110 --> 00:50:12.790 align:middle line:84% So maybe the one large nucleus could 00:50:12.790 --> 00:50:17.525 align:middle line:84% split into because it was hit by a slow-moving neutron. 00:50:17.525 --> 00:50:19.900 align:middle line:84% They go on-- again, this part is done in much more detail 00:50:19.900 --> 00:50:20.442 align:middle line:90% in the notes. 00:50:20.442 --> 00:50:21.640 align:middle line:90% I'll just go quickly here. 00:50:21.640 --> 00:50:24.430 align:middle line:84% Still on the ski holiday while basically on a bench, 00:50:24.430 --> 00:50:28.900 align:middle line:84% or leaning against a tree, they try to wonder, would this work? 00:50:28.900 --> 00:50:31.420 align:middle line:84% Could they get a kind of order of magnitude estimate 00:50:31.420 --> 00:50:33.760 align:middle line:90% of this kind of process? 00:50:33.760 --> 00:50:36.820 align:middle line:84% And they realize that the energy scale, 00:50:36.820 --> 00:50:40.510 align:middle line:84% the rough energies involved, if this splitting of a uranium 00:50:40.510 --> 00:50:43.420 align:middle line:84% nucleus were to hold, they could estimate 00:50:43.420 --> 00:50:46.310 align:middle line:84% by the kind of Coulomb repulsion of all the pieces-- 00:50:46.310 --> 00:50:48.400 align:middle line:84% all the protons within that nucleus. 00:50:48.400 --> 00:50:50.560 align:middle line:90% They have about 100 protons-- 00:50:50.560 --> 00:50:51.230 align:middle line:90% 92. 00:50:51.230 --> 00:50:54.410 align:middle line:84% So order of magnitude about 100 protons each with unit charge. 00:50:54.410 --> 00:50:58.000 align:middle line:84% And they're packed within a very small volume. 00:50:58.000 --> 00:51:00.910 align:middle line:84% The average nuclear radii they knew by this point 00:51:00.910 --> 00:51:05.080 align:middle line:84% was on the order of 100th of an angstrom. 00:51:05.080 --> 00:51:07.270 align:middle line:84% And so on the order of-- oh, no, excuse me-- 00:51:07.270 --> 00:51:11.220 align:middle line:84% a 10,000th of an angstroms-- around 10 to the minus 12 00:51:11.220 --> 00:51:11.980 align:middle line:90% centimeters. 00:51:11.980 --> 00:51:14.440 align:middle line:84% Meanwhile, the kind typical energy scales 00:51:14.440 --> 00:51:16.910 align:middle line:84% for chemical reactions, where you're basically 00:51:16.910 --> 00:51:19.730 align:middle line:84% moving one or two electrons across distances 00:51:19.730 --> 00:51:22.770 align:middle line:84% of an atomic size, not a nuclear size. 00:51:22.770 --> 00:51:25.400 align:middle line:84% So if you take the ratio of the kind 00:51:25.400 --> 00:51:27.710 align:middle line:84% typical energy scales that seem to be involved 00:51:27.710 --> 00:51:29.630 align:middle line:84% in these nuclear transformations, 00:51:29.630 --> 00:51:32.180 align:middle line:84% compared to typical energy scales for chemical ones, 00:51:32.180 --> 00:51:36.470 align:middle line:84% the nuclear ones should be about 100 million times 00:51:36.470 --> 00:51:40.880 align:middle line:84% larger energies just from this how many charges can 00:51:40.880 --> 00:51:43.290 align:middle line:84% you-- are you moving around and what kind of volume. 00:51:43.290 --> 00:51:45.890 align:middle line:84% It's very, very kind of order of magnitude rough estimate 00:51:45.890 --> 00:51:47.600 align:middle line:84% that they're doing literally on a bench 00:51:47.600 --> 00:51:50.030 align:middle line:84% while taking a break from skiing. 00:51:50.030 --> 00:51:52.790 align:middle line:84% Meanwhile, after splitting apart, if this really 00:51:52.790 --> 00:51:55.700 align:middle line:84% were to happen, you have two roughly equal pieces of what 00:51:55.700 --> 00:51:59.210 align:middle line:84% had once been a single nucleus, each piece 00:51:59.210 --> 00:52:00.740 align:middle line:90% will carry as they go through-- 00:52:00.740 --> 00:52:04.520 align:middle line:84% and I replicate that algebra in the notes-- 00:52:04.520 --> 00:52:08.570 align:middle line:84% each piece following splitting would carry about one third 00:52:08.570 --> 00:52:10.230 align:middle line:90% of that starting energy. 00:52:10.230 --> 00:52:14.150 align:middle line:84% So this nuclear energy of the starting blob of roughly 100 00:52:14.150 --> 00:52:17.040 align:middle line:84% charged particles, after splitting, each piece 00:52:17.040 --> 00:52:19.150 align:middle line:84% would only carry about a third of that. 00:52:19.150 --> 00:52:20.490 align:middle line:90% So you have two pieces. 00:52:20.490 --> 00:52:23.130 align:middle line:84% You have one third of that kind of raw energy 00:52:23.130 --> 00:52:24.660 align:middle line:90% still to account for. 00:52:24.660 --> 00:52:26.580 align:middle line:84% And that would be this energy released 00:52:26.580 --> 00:52:29.820 align:middle line:84% every time a single, large, unstable nucleus 00:52:29.820 --> 00:52:31.900 align:middle line:90% undergoes this splitting. 00:52:31.900 --> 00:52:35.040 align:middle line:84% So you have one third of this enormous energy scale 00:52:35.040 --> 00:52:37.530 align:middle line:84% available or released every time-- 00:52:37.530 --> 00:52:40.410 align:middle line:84% they estimate-- every time a single nucleus is 00:52:40.410 --> 00:52:43.370 align:middle line:90% split in this fashion. 00:52:43.370 --> 00:52:45.980 align:middle line:84% It turns out that estimator is consistent with-- 00:52:45.980 --> 00:52:48.350 align:middle line:84% people who then fill this in within a few months-- 00:52:48.350 --> 00:52:51.470 align:middle line:84% with a different way of estimating the energy scales 00:52:51.470 --> 00:52:54.230 align:middle line:84% not based on a kind of classical Coulomb repulsion-- 00:52:54.230 --> 00:52:57.110 align:middle line:84% how many protons over here are repelling how many protons over 00:52:57.110 --> 00:52:57.710 align:middle line:90% there-- 00:52:57.710 --> 00:53:00.950 align:middle line:84% but actually, based on E equals mc squared, 00:53:00.950 --> 00:53:04.010 align:middle line:84% that the total mass of the uranium nucleus before it 00:53:04.010 --> 00:53:06.230 align:middle line:90% splits is actually greater-- 00:53:06.230 --> 00:53:09.320 align:middle line:84% is actually-- sorry-- less than the mass 00:53:09.320 --> 00:53:10.940 align:middle line:90% of the barium and the krypton. 00:53:10.940 --> 00:53:14.120 align:middle line:84% There's a binding energy left over-- negative binding energy. 00:53:14.120 --> 00:53:16.790 align:middle line:84% And that actually is what's released 00:53:16.790 --> 00:53:20.540 align:middle line:84% when this initial thing splits, and that release 00:53:20.540 --> 00:53:22.880 align:middle line:84% times C squared gives you, again, the exact same kind 00:53:22.880 --> 00:53:25.310 align:middle line:84% of estimate as you get from this classical kind 00:53:25.310 --> 00:53:26.690 align:middle line:90% of electrostatic repulsion. 00:53:26.690 --> 00:53:29.060 align:middle line:84% That was worked out in detail by Bohr himself 00:53:29.060 --> 00:53:31.070 align:middle line:90% with another colleague. 00:53:31.070 --> 00:53:34.610 align:middle line:84% So Frisch returns to Bohr's institute in late December. 00:53:34.610 --> 00:53:35.883 align:middle line:90% He tells Bohr all about this. 00:53:35.883 --> 00:53:38.300 align:middle line:84% Bohr was very excited about nuclear physics by this point. 00:53:38.300 --> 00:53:40.070 align:middle line:90% Frisch was Bohr's postdoc. 00:53:40.070 --> 00:53:42.680 align:middle line:84% Frisch tells him all about Meitner's and Frisch's ideas, 00:53:42.680 --> 00:53:45.170 align:middle line:84% that maybe this big nucleus is just barely stable 00:53:45.170 --> 00:53:48.500 align:middle line:84% and could actually be split apart into two small pieces. 00:53:48.500 --> 00:53:50.100 align:middle line:84% He asks Bohr to keep it to himself. 00:53:50.100 --> 00:53:52.100 align:middle line:84% He and Meitner were going to keep working on it, 00:53:52.100 --> 00:53:53.870 align:middle line:84% maybe even perform some laboratory tests 00:53:53.870 --> 00:53:57.560 align:middle line:84% and so on, which in fact, Frisch did wind up doing. 00:53:57.560 --> 00:54:00.710 align:middle line:84% Meanwhile, Bohr was set to leave almost practically 00:54:00.710 --> 00:54:02.690 align:middle line:84% the next day-- very soon afterwards-- 00:54:02.690 --> 00:54:04.880 align:middle line:90% to sail to the United States. 00:54:04.880 --> 00:54:07.433 align:middle line:84% He was scheduled to spend a sabbatical at Princeton-- 00:54:07.433 --> 00:54:09.350 align:middle line:84% Princeton University, right near the Institute 00:54:09.350 --> 00:54:10.430 align:middle line:90% for Advanced Study. 00:54:10.430 --> 00:54:11.235 align:middle line:90% So he does that. 00:54:11.235 --> 00:54:12.110 align:middle line:90% He sails to New York. 00:54:12.110 --> 00:54:14.068 align:middle line:84% He's actually met at the docks in New York City 00:54:14.068 --> 00:54:16.580 align:middle line:84% by Enrico Fermi, who had just fled. 00:54:16.580 --> 00:54:20.450 align:middle line:84% He had just left by way of his Nobel Prize ceremony. 00:54:20.450 --> 00:54:23.930 align:middle line:84% Younger folks like Sam Goudsmit, whom we heard about before-- 00:54:23.930 --> 00:54:25.160 align:middle line:90% we'll hear more about soon-- 00:54:25.160 --> 00:54:27.470 align:middle line:84% Goudsmit had also fled the Netherlands 00:54:27.470 --> 00:54:30.582 align:middle line:84% and had moved to the United States some years before. 00:54:30.582 --> 00:54:32.540 align:middle line:84% Bohr basically gets off the boat and tells him, 00:54:32.540 --> 00:54:34.248 align:middle line:84% you won't believe what I've just learned. 00:54:34.248 --> 00:54:35.415 align:middle line:90% Nuclear fission is possible. 00:54:35.415 --> 00:54:37.623 align:middle line:84% So even though Frisch had asked him to keep it quiet, 00:54:37.623 --> 00:54:39.080 align:middle line:84% Bohr basically can't help himself. 00:54:39.080 --> 00:54:41.122 align:middle line:84% He's spilling the beans to his physics colleagues 00:54:41.122 --> 00:54:44.270 align:middle line:84% practically on the docks as soon as he arrives in New York City. 00:54:44.270 --> 00:54:45.530 align:middle line:90% Then he gets to Princeton. 00:54:45.530 --> 00:54:49.040 align:middle line:84% He tells other émigré physicists like Wegner, Albert Einstein, 00:54:49.040 --> 00:54:51.470 align:middle line:84% John Wheeler, who's an American physicist, 00:54:51.470 --> 00:54:54.260 align:middle line:84% but had done his own postdoc with Bohr some years earlier. 00:54:54.260 --> 00:54:55.640 align:middle line:90% They knew each other very well. 00:54:55.640 --> 00:54:58.460 align:middle line:84% Within days, several laboratories up and down 00:54:58.460 --> 00:55:01.257 align:middle line:84% the East Coast had actually verified this reaction. 00:55:01.257 --> 00:55:02.840 align:middle line:84% And for them, it was easy because they 00:55:02.840 --> 00:55:04.280 align:middle line:90% knew what to look for. 00:55:04.280 --> 00:55:06.800 align:middle line:84% The hard part was having these chemists, 00:55:06.800 --> 00:55:10.370 align:middle line:84% like Hahn and Strassmann, really do the kind of chemical assays 00:55:10.370 --> 00:55:11.510 align:middle line:90% to find barium. 00:55:11.510 --> 00:55:13.340 align:middle line:84% Once you know to look for barium, 00:55:13.340 --> 00:55:16.100 align:middle line:84% then even physicists, with some chemists' help, 00:55:16.100 --> 00:55:18.560 align:middle line:84% could verify that some of the fission products 00:55:18.560 --> 00:55:19.700 align:middle line:90% were, in fact, barium-- 00:55:19.700 --> 00:55:23.450 align:middle line:84% way down the periodic table, not things near uranium. 00:55:23.450 --> 00:55:27.950 align:middle line:84% So during that sabbatical, Bohr then kept working with Wheeler. 00:55:27.950 --> 00:55:30.830 align:middle line:84% And they worked out a more detailed quantitative analysis 00:55:30.830 --> 00:55:33.810 align:middle line:84% building very directly on Meitner's and Frisch's work. 00:55:33.810 --> 00:55:35.580 align:middle line:84% By this point, Meitner and Frisch 00:55:35.580 --> 00:55:37.620 align:middle line:84% had published a few very short letters 00:55:37.620 --> 00:55:41.250 align:middle line:84% about their work that are duly cited by Wheeler and Bohr. 00:55:41.250 --> 00:55:43.470 align:middle line:84% And they work out a kind of lengthy detailed 00:55:43.470 --> 00:55:45.900 align:middle line:84% quantitative theory of this nuclear fission. 00:55:45.900 --> 00:55:48.660 align:middle line:84% In fact, building again much on Meitner's work, 00:55:48.660 --> 00:55:51.300 align:middle line:84% it's Bohr and Wheeler who finally conclude 00:55:51.300 --> 00:55:55.650 align:middle line:84% that the fissionable, the most unstable isotope of uranium, 00:55:55.650 --> 00:55:58.590 align:middle line:84% is not the most common kind you find in the ground. 00:55:58.590 --> 00:56:00.180 align:middle line:90% That's U-238. 00:56:00.180 --> 00:56:01.650 align:middle line:84% The fissionable one, the one that's 00:56:01.650 --> 00:56:04.470 align:middle line:84% most easy to undergo this kind of splitting reaction, 00:56:04.470 --> 00:56:08.670 align:middle line:84% has a couple of fewer neutrons than the common one, U-235. 00:56:08.670 --> 00:56:11.712 align:middle line:84% What's kind of chilling or stunning to me 00:56:11.712 --> 00:56:13.920 align:middle line:84% is their article was published in the Physical Review 00:56:13.920 --> 00:56:17.520 align:middle line:84% literally on the same day that the Nazis invaded Poland, which 00:56:17.520 --> 00:56:20.370 align:middle line:84% was the final kind of trigger for the start 00:56:20.370 --> 00:56:22.710 align:middle line:84% of the overt fighting of the Second World War. 00:56:22.710 --> 00:56:25.770 align:middle line:84% Again, we see the collision of these time scales. 00:56:25.770 --> 00:56:28.500 align:middle line:84% So everyone in physics-- everyone in physics 00:56:28.500 --> 00:56:32.040 align:middle line:84% knew immediately that nuclear fission could lead to bombs. 00:56:32.040 --> 00:56:34.530 align:middle line:84% This was an enormous release of energy each time 00:56:34.530 --> 00:56:36.210 align:middle line:90% a single nucleus split. 00:56:36.210 --> 00:56:38.970 align:middle line:84% The energy scales were nothing like typical chemical scales-- 00:56:38.970 --> 00:56:40.470 align:middle line:90% chemical reaction scales. 00:56:40.470 --> 00:56:41.770 align:middle line:90% So everyone knows that. 00:56:41.770 --> 00:56:44.190 align:middle line:84% And then their second thought was, oh, the Germans 00:56:44.190 --> 00:56:45.960 align:middle line:90% must know this, too. 00:56:45.960 --> 00:56:47.640 align:middle line:84% After all, fission had been identified 00:56:47.640 --> 00:56:49.020 align:middle line:90% in a Berlin laboratory. 00:56:49.020 --> 00:56:51.330 align:middle line:84% And as we were just saying a few minutes ago, 00:56:51.330 --> 00:56:53.790 align:middle line:84% although many researchers fled Nazi Germany, 00:56:53.790 --> 00:56:57.180 align:middle line:84% it still retained some of the world's leading experts 00:56:57.180 --> 00:56:59.670 align:middle line:84% in nuclear physics, or nuclear science, more broadly. 00:56:59.670 --> 00:57:01.560 align:middle line:84% Heisenberg, as we said, had stayed behind. 00:57:01.560 --> 00:57:04.980 align:middle line:84% Otto Hahn, Hans Geiger, who invented the Geiger counter, 00:57:04.980 --> 00:57:06.870 align:middle line:84% Walther Bothe, Max Planck, Max von 00:57:06.870 --> 00:57:09.960 align:middle line:84% Laue-- a long list of these folks were still in Germany, 00:57:09.960 --> 00:57:12.810 align:middle line:84% let alone at the forefront of laboratory tests 00:57:12.810 --> 00:57:13.780 align:middle line:90% of these things. 00:57:13.780 --> 00:57:16.950 align:middle line:84% So again, just to give a sense of how rapidly these things 00:57:16.950 --> 00:57:21.480 align:middle line:84% were all kind of colliding, the conceptual work, 00:57:21.480 --> 00:57:23.250 align:middle line:84% the laboratory work around these new kinds 00:57:23.250 --> 00:57:27.150 align:middle line:84% of nuclear transformations, and the headlong rush 00:57:27.150 --> 00:57:30.030 align:middle line:90% into a world-spanning war. 00:57:30.030 --> 00:57:32.700 align:middle line:84% So I mentioned the Anschluss, who were the Nazis, 00:57:32.700 --> 00:57:35.640 align:middle line:90% basically absorb Austria. 00:57:35.640 --> 00:57:37.980 align:middle line:90% That was in March of '38. 00:57:37.980 --> 00:57:40.050 align:middle line:84% By December of '38, we have these developments 00:57:40.050 --> 00:57:42.510 align:middle line:84% of Hahn and Strassmann identifying barium, Meitner 00:57:42.510 --> 00:57:45.660 align:middle line:84% and Frisch working out the first real physical explanation. 00:57:45.660 --> 00:57:47.370 align:middle line:90% Bohr arrives in New York City. 00:57:47.370 --> 00:57:50.400 align:middle line:84% That spring, the Nazis then occupy Czechoslovakia. 00:57:50.400 --> 00:57:52.410 align:middle line:84% And Poland is what finally triggers 00:57:52.410 --> 00:57:55.020 align:middle line:84% the announcements, the declarations of war 00:57:55.020 --> 00:57:56.470 align:middle line:90% by many other countries. 00:57:56.470 --> 00:57:59.740 align:middle line:84% So within days of the invasion of Poland, Britain, France, 00:57:59.740 --> 00:58:01.320 align:middle line:84% Australia, New Zealand, and Canada-- 00:58:01.320 --> 00:58:02.790 align:middle line:90% notably, not the United States. 00:58:02.790 --> 00:58:05.400 align:middle line:84% But many of these other countries 00:58:05.400 --> 00:58:07.170 align:middle line:84% explicitly declare war against Germany. 00:58:07.170 --> 00:58:09.750 align:middle line:84% The Soviet Union invades Poland soon after that. 00:58:09.750 --> 00:58:12.240 align:middle line:84% This is all happening at essentially the same time. 00:58:12.240 --> 00:58:15.930 align:middle line:84% What's also happening is that in many, many of these countries 00:58:15.930 --> 00:58:18.240 align:middle line:84% on multiple sides, multiple fronts of what 00:58:18.240 --> 00:58:20.820 align:middle line:84% would become the actual warring parties, 00:58:20.820 --> 00:58:23.460 align:middle line:84% physicists are consulting with government officials 00:58:23.460 --> 00:58:26.820 align:middle line:84% to say there could be a vastly new type of weapon 00:58:26.820 --> 00:58:29.110 align:middle line:84% based on these nuclear transformations. 00:58:29.110 --> 00:58:31.390 align:middle line:84% So this is just a handful of these, 00:58:31.390 --> 00:58:34.180 align:middle line:84% again, happening with kind of lightning speed. 00:58:34.180 --> 00:58:38.380 align:middle line:84% As we now know, as early as April 1939, 00:58:38.380 --> 00:58:41.620 align:middle line:84% barely four months after the very first indication from Hahn 00:58:41.620 --> 00:58:44.750 align:middle line:84% and Strassmann that nuclear fission could happen, 00:58:44.750 --> 00:58:46.990 align:middle line:84% the German Reich Ministry of Education 00:58:46.990 --> 00:58:50.500 align:middle line:84% started holding secret meetings on military applications 00:58:50.500 --> 00:58:52.300 align:middle line:84% of nuclear fission, meaning weapons. 00:58:52.300 --> 00:58:53.860 align:middle line:84% They could make-- they were beginning 00:58:53.860 --> 00:58:57.130 align:middle line:84% to be briefed about the possibility of nuclear bombs. 00:58:57.130 --> 00:59:00.203 align:middle line:84% And they began banning the export of uranium. 00:59:00.203 --> 00:59:02.620 align:middle line:84% They figured they need a lot of this fissionable material. 00:59:02.620 --> 00:59:05.180 align:middle line:84% That same month-- it was much less well-known-- 00:59:05.180 --> 00:59:08.050 align:middle line:84% other historians have now by now documented it quite clearly-- 00:59:08.050 --> 00:59:11.010 align:middle line:84% the Japanese government began its own secret nuclear weapons 00:59:11.010 --> 00:59:11.510 align:middle line:90% project. 00:59:11.510 --> 00:59:12.753 align:middle line:90% It was codenamed Ni. 00:59:12.753 --> 00:59:14.170 align:middle line:84% I'm not sure what that stands for. 00:59:14.170 --> 00:59:17.350 align:middle line:84% This, unlike the German one, was really underfunded. 00:59:17.350 --> 00:59:20.050 align:middle line:84% It was not seen as a high priority for the current war. 00:59:20.050 --> 00:59:24.070 align:middle line:84% In fact, what it turned out to be mostly was a kind of wait-- 00:59:24.070 --> 00:59:26.860 align:middle line:84% for senior physicists to keep younger physicists out 00:59:26.860 --> 00:59:27.850 align:middle line:90% of direct fighting. 00:59:27.850 --> 00:59:29.875 align:middle line:84% It was kind of like instead of being drafted, 00:59:29.875 --> 00:59:32.620 align:middle line:84% you could do some research is more or less how it functioned. 00:59:32.620 --> 00:59:35.680 align:middle line:84% But there was a formal Japanese nuclear weapons project 00:59:35.680 --> 00:59:38.050 align:middle line:90% founded as early as April 1939. 00:59:38.050 --> 00:59:40.060 align:middle line:84% Very soon after that, Britain starts 00:59:40.060 --> 00:59:43.250 align:middle line:84% considering nuclear weapons, and they begin ramping up, 00:59:43.250 --> 00:59:47.560 align:middle line:84% especially after Robert Frisch, who then had moved-- 00:59:47.560 --> 00:59:50.920 align:middle line:84% once the Nazis took over Denmark he was no longer safe there. 00:59:50.920 --> 00:59:54.678 align:middle line:84% So he resettled in Britain, as did Rudolf Peierls, 00:59:54.678 --> 00:59:55.720 align:middle line:90% who had to leave Germany. 00:59:55.720 --> 00:59:59.380 align:middle line:84% They compiled a top secret memo to the British government, 00:59:59.380 --> 01:00:01.840 align:middle line:84% again saying not only are nuclear weapons possible, 01:00:01.840 --> 01:00:03.700 align:middle line:90% but you only need a little bit-- 01:00:03.700 --> 01:00:07.120 align:middle line:84% comparative little bit-- of this fissionable, this rare isotope 01:00:07.120 --> 01:00:07.630 align:middle line:90% of uranium. 01:00:07.630 --> 01:00:10.390 align:middle line:84% They actually, as we now know, underestimated 01:00:10.390 --> 01:00:14.330 align:middle line:84% how little fissionable uranium you'd need. 01:00:14.330 --> 01:00:16.330 align:middle line:84% So it looked even closer to being feasible 01:00:16.330 --> 01:00:17.830 align:middle line:84% and convinced the British government 01:00:17.830 --> 01:00:18.940 align:middle line:90% to start real efforts. 01:00:18.940 --> 01:00:20.950 align:middle line:84% And at that same time in the Soviet Union 01:00:20.950 --> 01:00:23.030 align:middle line:84% another physicist, Igor Kurchatov, 01:00:23.030 --> 01:00:25.670 align:middle line:84% starts informing the Soviet government 01:00:25.670 --> 01:00:27.500 align:middle line:90% about nuclear weapons and so on. 01:00:27.500 --> 01:00:29.720 align:middle line:84% Much like in Japan, in the Soviet Union 01:00:29.720 --> 01:00:32.690 align:middle line:84% we now know this was a low priority at first. 01:00:32.690 --> 01:00:34.760 align:middle line:84% But nonetheless, was a formal project. 01:00:34.760 --> 01:00:37.790 align:middle line:84% And then again, perhaps most famously in the United States, 01:00:37.790 --> 01:00:40.580 align:middle line:84% Einstein himself really signed a letter. 01:00:40.580 --> 01:00:42.600 align:middle line:90% He didn't compose this letter. 01:00:42.600 --> 01:00:45.140 align:middle line:84% Some of his émigré friends and colleagues in physics 01:00:45.140 --> 01:00:47.850 align:middle line:84% wrote the letter in hopes that Einstein would sign it. 01:00:47.850 --> 01:00:48.410 align:middle line:90% And he did. 01:00:48.410 --> 01:00:49.640 align:middle line:90% They convinced him to. 01:00:49.640 --> 01:00:52.610 align:middle line:84% He wrote a letter directly to President Franklin Roosevelt. 01:00:52.610 --> 01:00:55.100 align:middle line:84% By this point, Einstein was such a worldwide celebrity, 01:00:55.100 --> 01:00:57.380 align:middle line:84% they had channels to get this literally 01:00:57.380 --> 01:01:00.200 align:middle line:84% into the hands of the President of the United States. 01:01:00.200 --> 01:01:02.070 align:middle line:90% And you can see the letter here. 01:01:02.070 --> 01:01:02.890 align:middle line:90% You can Google it. 01:01:02.890 --> 01:01:05.690 align:middle line:84% You can find the text where Einstein basically says, 01:01:05.690 --> 01:01:07.880 align:middle line:84% I've recently come to learn this nuclear fission 01:01:07.880 --> 01:01:08.960 align:middle line:90% thing is possible. 01:01:08.960 --> 01:01:11.420 align:middle line:84% I've also learned that Germany is now 01:01:11.420 --> 01:01:12.860 align:middle line:90% kind of hoarding uranium. 01:01:12.860 --> 01:01:15.140 align:middle line:84% This could be a very serious development. 01:01:15.140 --> 01:01:17.570 align:middle line:84% All these folks recognized very quickly 01:01:17.570 --> 01:01:22.240 align:middle line:84% that nuclear fission could have very immediate worldly effects. 01:01:22.240 --> 01:01:24.220 align:middle line:90% So I see Obie asked do they-- 01:01:24.220 --> 01:01:26.218 align:middle line:84% how do they contain the heat of a reaction? 01:01:26.218 --> 01:01:27.760 align:middle line:84% Obie asked about the nuclear fission. 01:01:27.760 --> 01:01:28.260 align:middle line:90% Good. 01:01:28.260 --> 01:01:31.820 align:middle line:90% 01:01:31.820 --> 01:01:35.600 align:middle line:84% What's important to recognize is that these very earliest 01:01:35.600 --> 01:01:38.480 align:middle line:84% experiments were never leading to anything like what we would 01:01:38.480 --> 01:01:40.703 align:middle line:90% now call a chain reaction. 01:01:40.703 --> 01:01:42.870 align:middle line:84% We'll talk more about this action in the next class. 01:01:42.870 --> 01:01:46.130 align:middle line:84% So they were never getting unlimited numbers of nuclei 01:01:46.130 --> 01:01:47.630 align:middle line:90% to undergo fission. 01:01:47.630 --> 01:01:48.830 align:middle line:90% Thank goodness. 01:01:48.830 --> 01:01:50.750 align:middle line:84% They would have blown up the laboratory. 01:01:50.750 --> 01:01:54.680 align:middle line:84% So the heat released when one or two or three, 01:01:54.680 --> 01:01:59.600 align:middle line:84% a small number of nuclei fission, was not remarkable. 01:01:59.600 --> 01:02:04.038 align:middle line:84% If they had expected that, they could have maybe instrumented 01:02:04.038 --> 01:02:06.080 align:middle line:84% their laboratory to just barely maybe measure it. 01:02:06.080 --> 01:02:08.930 align:middle line:84% But I bet it was not even measurable, given the fission 01:02:08.930 --> 01:02:10.430 align:middle line:90% rates they were encountering. 01:02:10.430 --> 01:02:12.260 align:middle line:84% We'll see, of course, soon that no 01:02:12.260 --> 01:02:16.097 align:middle line:84% longer becomes true when these reactions get scaled up. 01:02:16.097 --> 01:02:17.930 align:middle line:84% And that's more-- we'll talk more about that 01:02:17.930 --> 01:02:19.450 align:middle line:90% in Wednesday's class. 01:02:19.450 --> 01:02:21.950 align:middle line:84% Iyabo asks, why did Chadwick win the Nobel Prize for physics 01:02:21.950 --> 01:02:22.950 align:middle line:90% as opposed to chemistry? 01:02:22.950 --> 01:02:24.290 align:middle line:90% Ah, good. 01:02:24.290 --> 01:02:26.510 align:middle line:84% In the reading by Crawford, Simon, Walker, 01:02:26.510 --> 01:02:28.160 align:middle line:84% they identified one reason it was 01:02:28.160 --> 01:02:30.667 align:middle line:84% denied the Noble Prize was that radioactive was considered 01:02:30.667 --> 01:02:31.500 align:middle line:90% a chemistry project. 01:02:31.500 --> 01:02:32.083 align:middle line:90% Iyabo, thanks. 01:02:32.083 --> 01:02:32.880 align:middle line:90% It's a great point. 01:02:32.880 --> 01:02:36.780 align:middle line:84% So I think the reason that Chadwick 01:02:36.780 --> 01:02:39.360 align:middle line:84% won the Nobel Prize in physics was because he was identifying 01:02:39.360 --> 01:02:40.740 align:middle line:90% a new physical particle. 01:02:40.740 --> 01:02:42.527 align:middle line:84% I mean, or what he was credited with. 01:02:42.527 --> 01:02:44.610 align:middle line:84% The reason they thought this work was so important 01:02:44.610 --> 01:02:46.080 align:middle line:90% was not that he-- 01:02:46.080 --> 01:02:48.450 align:middle line:84% not only that he was dealing with radioactivity, 01:02:48.450 --> 01:02:50.940 align:middle line:84% which was actually winning prizes both in physics 01:02:50.940 --> 01:02:51.660 align:middle line:90% and in chemistry. 01:02:51.660 --> 01:02:54.375 align:middle line:84% Marie Curie's first prize was actually in physics and then 01:02:54.375 --> 01:02:55.500 align:middle line:90% in chemistry or vice versa. 01:02:55.500 --> 01:02:56.940 align:middle line:90% She wound up winning in both. 01:02:56.940 --> 01:02:58.890 align:middle line:84% But for Chadwick, it was actually 01:02:58.890 --> 01:03:03.180 align:middle line:84% identifying a new physical particle, which 01:03:03.180 --> 01:03:07.110 align:middle line:84% I think was then seen as a kind of physics domain, 01:03:07.110 --> 01:03:10.350 align:middle line:84% more or less, as opposed to the kind of chemical 01:03:10.350 --> 01:03:13.110 align:middle line:84% transmutations, or the transitions 01:03:13.110 --> 01:03:15.720 align:middle line:84% in the identities of chemical elements like what 01:03:15.720 --> 01:03:17.460 align:middle line:90% the Joliot-Curies were doing. 01:03:17.460 --> 01:03:19.800 align:middle line:84% And they, indeed, won the prize in chemistry that year. 01:03:19.800 --> 01:03:21.410 align:middle line:90% But, I mean, your-- 01:03:21.410 --> 01:03:23.530 align:middle line:84% the question points to a-- is a good one. 01:03:23.530 --> 01:03:24.840 align:middle line:90% It points to a larger theme. 01:03:24.840 --> 01:03:26.970 align:middle line:84% There was an awfully fuzzy line then as now, 01:03:26.970 --> 01:03:28.140 align:middle line:90% but especially then. 01:03:28.140 --> 01:03:30.060 align:middle line:84% What would count as chemistry versus physics 01:03:30.060 --> 01:03:32.040 align:middle line:84% often could become kind of political. 01:03:32.040 --> 01:03:36.930 align:middle line:84% I mean, in the sense that the very small circle of members 01:03:36.930 --> 01:03:39.000 align:middle line:84% of the Royal Swedish Academy of Sciences 01:03:39.000 --> 01:03:41.460 align:middle line:84% that decided these things, they could frankly 01:03:41.460 --> 01:03:44.160 align:middle line:84% push one way or the other based on other motives. 01:03:44.160 --> 01:03:46.230 align:middle line:84% Did they not want to give a prize to one person, 01:03:46.230 --> 01:03:48.190 align:middle line:84% or often a representative of some country? 01:03:48.190 --> 01:03:49.770 align:middle line:90% We get very nationalistic. 01:03:49.770 --> 01:03:51.030 align:middle line:90% Don't honor this country. 01:03:51.030 --> 01:03:51.840 align:middle line:90% Do honor that. 01:03:51.840 --> 01:03:53.610 align:middle line:84% They could frankly kind of bend the rules 01:03:53.610 --> 01:03:58.240 align:middle line:84% or move that move that boundary to suit many kinds of purposes. 01:03:58.240 --> 01:04:01.113 align:middle line:84% So it's not that there were clear criteria 01:04:01.113 --> 01:04:03.030 align:middle line:84% separating, say, what would count as a physics 01:04:03.030 --> 01:04:04.020 align:middle line:90% prize versus chemistry. 01:04:04.020 --> 01:04:07.050 align:middle line:84% And there's a lot of evidence, including from the first author 01:04:07.050 --> 01:04:08.580 align:middle line:90% of that article. 01:04:08.580 --> 01:04:11.100 align:middle line:84% Elizabeth Crawford was really immersed in the Nobel Prize 01:04:11.100 --> 01:04:12.930 align:middle line:84% archives for much of her career-- 01:04:12.930 --> 01:04:15.055 align:middle line:84% much as we learn from Crawford's work. 01:04:15.055 --> 01:04:15.930 align:middle line:90% So it's a good point. 01:04:15.930 --> 01:04:17.670 align:middle line:84% But I think for Chadwick, the argument 01:04:17.670 --> 01:04:20.460 align:middle line:84% would have been he found a new kind of piece of matter, 01:04:20.460 --> 01:04:21.960 align:middle line:90% a new piece of nature. 01:04:21.960 --> 01:04:23.880 align:middle line:84% And that, I think, struck him as being more 01:04:23.880 --> 01:04:25.660 align:middle line:90% like the other physics prizes. 01:04:25.660 --> 01:04:26.160 align:middle line:90% Very good. 01:04:26.160 --> 01:04:29.110 align:middle line:90% Other questions about that-- 01:04:29.110 --> 01:04:31.630 align:middle line:84% any of the nuclear physics concepts, or again this kind 01:04:31.630 --> 01:04:34.030 align:middle line:84% of amazing, we might call it a tight coupling 01:04:34.030 --> 01:04:36.250 align:middle line:84% between events in various laboratories 01:04:36.250 --> 01:04:37.840 align:middle line:84% and kind of physicist networks-- who's 01:04:37.840 --> 01:04:40.960 align:middle line:84% writing to whom, who's taking the steamer ship to where, 01:04:40.960 --> 01:04:43.690 align:middle line:84% with these kind of worldly geopolitical shifts. 01:04:43.690 --> 01:04:45.340 align:middle line:90% Amazing conjunction. 01:04:45.340 --> 01:04:50.400 align:middle line:90% 01:04:50.400 --> 01:04:52.320 align:middle line:84% Do we know if Einstein ever spoke with FDR? 01:04:52.320 --> 01:04:53.153 align:middle line:90% He did not. 01:04:53.153 --> 01:04:53.820 align:middle line:90% Thank you, Gary. 01:04:53.820 --> 01:04:55.620 align:middle line:84% So in fact, there was a bit of a delay. 01:04:55.620 --> 01:04:58.530 align:middle line:84% FDR didn't actually receive the letter for a couple of weeks. 01:04:58.530 --> 01:04:59.640 align:middle line:90% He did read it. 01:04:59.640 --> 01:05:02.220 align:middle line:84% We know it was handed to him literally in the Oval Office, 01:05:02.220 --> 01:05:03.510 align:middle line:90% and he read it. 01:05:03.510 --> 01:05:06.660 align:middle line:84% What's important, though, is that the myth 01:05:06.660 --> 01:05:09.300 align:middle line:84% that Einstein invented the Manhattan Project 01:05:09.300 --> 01:05:13.620 align:middle line:84% with this letter, that is just crazy, crazy, dramatically 01:05:13.620 --> 01:05:14.940 align:middle line:90% overblown. 01:05:14.940 --> 01:05:16.110 align:middle line:90% Einstein signed the letter. 01:05:16.110 --> 01:05:16.450 align:middle line:90% He didn't write it. 01:05:16.450 --> 01:05:17.380 align:middle line:90% He signed it. 01:05:17.380 --> 01:05:18.850 align:middle line:90% He thought it was important. 01:05:18.850 --> 01:05:21.600 align:middle line:84% And he was glad to have some intermediary get it to FDR, 01:05:21.600 --> 01:05:24.920 align:middle line:84% where it was delayed and had almost no impact. 01:05:24.920 --> 01:05:26.670 align:middle line:84% And so we'll talk more about this actually 01:05:26.670 --> 01:05:28.260 align:middle line:90% in Wednesday's class. 01:05:28.260 --> 01:05:30.750 align:middle line:84% There was a little kind of study group 01:05:30.750 --> 01:05:33.240 align:middle line:84% that was put together a few months after Einstein's letter 01:05:33.240 --> 01:05:34.698 align:middle line:90% was received, not-- 01:05:34.698 --> 01:05:36.990 align:middle line:84% well, certainly, not only because of Einstein's letter. 01:05:36.990 --> 01:05:38.910 align:middle line:84% By that point other science advisors 01:05:38.910 --> 01:05:41.713 align:middle line:84% had the ear of Roosevelt and said, 01:05:41.713 --> 01:05:44.130 align:middle line:84% this really does look like it's worth paying attention to. 01:05:44.130 --> 01:05:46.380 align:middle line:84% The British were already now much more engaged as well 01:05:46.380 --> 01:05:47.940 align:middle line:90% after the Frisch-Peierls memo. 01:05:47.940 --> 01:05:52.390 align:middle line:84% So there were many reasons for the US federal government 01:05:52.390 --> 01:05:54.430 align:middle line:84% to begin paying a little attention. 01:05:54.430 --> 01:05:56.650 align:middle line:84% We'll see they paid actually a little attention 01:05:56.650 --> 01:05:59.650 align:middle line:84% to questions about uranium and fission 01:05:59.650 --> 01:06:03.130 align:middle line:84% and weapons around the time of Einstein's letter, 01:06:03.130 --> 01:06:05.080 align:middle line:84% but not only because of Einstein's letter. 01:06:05.080 --> 01:06:07.300 align:middle line:84% And then we'll see in some more detail on Wednesday 01:06:07.300 --> 01:06:10.000 align:middle line:84% that the real kind of ramp-up came only 01:06:10.000 --> 01:06:12.190 align:middle line:84% quite a bit-- with quite a bit more of a delay. 01:06:12.190 --> 01:06:15.370 align:middle line:84% So Einstein never spoke directly with FDR about this, 01:06:15.370 --> 01:06:16.660 align:middle line:90% and he never followed up. 01:06:16.660 --> 01:06:18.760 align:middle line:84% He wrote-- he signed the letter and then-- 01:06:18.760 --> 01:06:19.750 align:middle line:90% and that was that. 01:06:19.750 --> 01:06:22.980 align:middle line:84% So the notion that Einstein kind of jump-started 01:06:22.980 --> 01:06:24.730 align:middle line:84% the Manhattan Project, which one can still 01:06:24.730 --> 01:06:28.030 align:middle line:84% find with what I'll call lazy googling, 01:06:28.030 --> 01:06:30.690 align:middle line:84% that's really kind of totally out of proportion. 01:06:30.690 --> 01:06:31.190 align:middle line:90% Good. 01:06:31.190 --> 01:06:33.050 align:middle line:90% Any other questions on that? 01:06:33.050 --> 01:06:35.410 align:middle line:84% Now, there's one last part I want to talk about today I 01:06:35.410 --> 01:06:36.910 align:middle line:90% think is very juicy. 01:06:36.910 --> 01:06:40.870 align:middle line:84% Let's launch into that and then some more time for discussion 01:06:40.870 --> 01:06:41.620 align:middle line:90% as well. 01:06:41.620 --> 01:06:43.320 align:middle line:90% OK. 01:06:43.320 --> 01:06:44.880 align:middle line:84% So let's talk about Werner Heisenberg 01:06:44.880 --> 01:06:46.130 align:middle line:90% and what was going on within-- 01:06:46.130 --> 01:06:49.230 align:middle line:84% for those who stayed within Germany with this constellation 01:06:49.230 --> 01:06:50.520 align:middle line:90% of events. 01:06:50.520 --> 01:06:54.150 align:middle line:84% So by September of 1939, right around the start 01:06:54.150 --> 01:06:57.330 align:middle line:84% of the-- the overt start of the Second World War, 01:06:57.330 --> 01:07:02.340 align:middle line:84% the German army ordnance office took over the Kaiser Wilhelm 01:07:02.340 --> 01:07:04.680 align:middle line:84% Institut fur Physik, this really quite beautiful, 01:07:04.680 --> 01:07:07.750 align:middle line:84% funky building in Berlin, or just in the outskirts 01:07:07.750 --> 01:07:08.250 align:middle line:90% of Berlin-- 01:07:08.250 --> 01:07:11.238 align:middle line:84% Berlin-Dahlem-- exactly to coordinate research 01:07:11.238 --> 01:07:12.030 align:middle line:90% on nuclear fission. 01:07:12.030 --> 01:07:12.930 align:middle line:90% They'd been briefed. 01:07:12.930 --> 01:07:15.210 align:middle line:84% They'd had these secret briefings since that spring. 01:07:15.210 --> 01:07:16.230 align:middle line:90% Fission is a thing. 01:07:16.230 --> 01:07:17.370 align:middle line:90% It could lead to weapons. 01:07:17.370 --> 01:07:19.740 align:middle line:84% So the army took over the Physics Institute-- 01:07:19.740 --> 01:07:21.450 align:middle line:90% took over control of it. 01:07:21.450 --> 01:07:23.640 align:middle line:84% A little while later, Heisenberg was actually 01:07:23.640 --> 01:07:25.020 align:middle line:90% placed in charge of it. 01:07:25.020 --> 01:07:27.450 align:middle line:84% So Heisenberg, from the very early days, 01:07:27.450 --> 01:07:31.110 align:middle line:84% became a member of what was called the Uranverein, which 01:07:31.110 --> 01:07:34.110 align:middle line:84% is the uranium club, the little informal group 01:07:34.110 --> 01:07:36.330 align:middle line:84% of nuclear physicists and chemists 01:07:36.330 --> 01:07:39.450 align:middle line:84% who were working on fission trying to learn more. 01:07:39.450 --> 01:07:43.030 align:middle line:84% Heisenberg personally advised the military multiple times 01:07:43.030 --> 01:07:46.300 align:middle line:84% about possibilities of nuclear fission, both for weapons-- 01:07:46.300 --> 01:07:49.510 align:middle line:84% this could lead to explosive release of explosive power 01:07:49.510 --> 01:07:50.200 align:middle line:90% in a bomb-- 01:07:50.200 --> 01:07:52.420 align:middle line:84% but also for civilian power generation-- what 01:07:52.420 --> 01:07:54.100 align:middle line:90% we now call reactors. 01:07:54.100 --> 01:07:57.160 align:middle line:84% And, again, this has been shown now in a lot of detail 01:07:57.160 --> 01:08:01.240 align:middle line:84% that Heisenberg and other from the small circle of colleagues 01:08:01.240 --> 01:08:03.610 align:middle line:84% were actively advising the army ordnance 01:08:03.610 --> 01:08:05.652 align:middle line:90% from as early as '39, '40. 01:08:05.652 --> 01:08:08.110 align:middle line:84% And like I say, within a few years, then Heisenberg himself 01:08:08.110 --> 01:08:11.170 align:middle line:84% was put in charge of the entire nuclear effort. 01:08:11.170 --> 01:08:12.790 align:middle line:84% At the same time, Heisenberg was sent 01:08:12.790 --> 01:08:15.580 align:middle line:84% on these diplomatic missions throughout neutral countries, 01:08:15.580 --> 01:08:18.290 align:middle line:84% or especially occupied countries, including, 01:08:18.290 --> 01:08:20.260 align:middle line:90% for example, Denmark. 01:08:20.260 --> 01:08:22.930 align:middle line:84% And now this is right on the heels-- this is only two years 01:08:22.930 --> 01:08:25.682 align:middle line:84% or three years after he had been denied 01:08:25.682 --> 01:08:27.640 align:middle line:84% this promotion by the Deutsche Physik movement. 01:08:27.640 --> 01:08:30.189 align:middle line:84% So you can see how rapidly Heisenberg's star 01:08:30.189 --> 01:08:34.390 align:middle line:84% had risen yet again among leading German government 01:08:34.390 --> 01:08:35.170 align:middle line:90% officials. 01:08:35.170 --> 01:08:37.750 align:middle line:84% By 1939, '40, he was seen as actually 01:08:37.750 --> 01:08:41.240 align:middle line:84% quite useful in the context of nuclear fission. 01:08:41.240 --> 01:08:44.950 align:middle line:84% So what he would do is basically go on diplomatic missions 01:08:44.950 --> 01:08:47.560 align:middle line:84% to basically be one of the public faces 01:08:47.560 --> 01:08:52.779 align:middle line:84% of the German government, not to proclaim pro-Nazi slogans, 01:08:52.779 --> 01:08:55.450 align:middle line:84% but rather to show off the kind of grandness 01:08:55.450 --> 01:08:58.149 align:middle line:84% of German accomplishments in higher learning. 01:08:58.149 --> 01:09:00.790 align:middle line:84% Here's this very young Nobel Laureate 01:09:00.790 --> 01:09:03.560 align:middle line:84% who knows about the atom and these mysterious things. 01:09:03.560 --> 01:09:07.180 align:middle line:84% So he'd give these very well-attended public lectures 01:09:07.180 --> 01:09:09.490 align:middle line:84% usually in places that the Nazis had just 01:09:09.490 --> 01:09:12.819 align:middle line:84% taken over and occupied, and sometimes in neutral countries. 01:09:12.819 --> 01:09:15.399 align:middle line:84% He-- as I say, to many colleagues who heard him, 01:09:15.399 --> 01:09:18.580 align:middle line:84% colleagues who had known him for years, he sounded-- 01:09:18.580 --> 01:09:21.010 align:middle line:84% he often sounded explicitly nationalistic. 01:09:21.010 --> 01:09:25.330 align:middle line:84% He was never spouting the kind of most what I would consider 01:09:25.330 --> 01:09:28.990 align:middle line:84% grotesque or most obvious Nazi kind of speaking points, 01:09:28.990 --> 01:09:30.939 align:middle line:84% but he was certainly proudly German. 01:09:30.939 --> 01:09:32.950 align:middle line:84% And at some points, even seemed to suggest, 01:09:32.950 --> 01:09:34.450 align:middle line:84% at least to some of these colleagues 01:09:34.450 --> 01:09:36.520 align:middle line:84% heard him, that maybe it would be good thing 01:09:36.520 --> 01:09:38.770 align:middle line:84% if Germany ruled all of Europe-- not the Nazis, 01:09:38.770 --> 01:09:41.080 align:middle line:84% but if Germany really extended its rule. 01:09:41.080 --> 01:09:45.040 align:middle line:84% Because after all, this was the high point of European culture 01:09:45.040 --> 01:09:45.859 align:middle line:90% and learning. 01:09:45.859 --> 01:09:47.590 align:middle line:84% This is what inspires this play-- 01:09:47.590 --> 01:09:52.000 align:middle line:84% this amazing play, Copenhagen, which hopefully some of you 01:09:52.000 --> 01:09:53.450 align:middle line:90% are familiar with. 01:09:53.450 --> 01:09:55.390 align:middle line:84% There's a link on the Canvas site 01:09:55.390 --> 01:09:58.030 align:middle line:84% you can actually watch for free through the MIT library 01:09:58.030 --> 01:10:00.520 align:middle line:84% site, a really quite beautiful BBC 01:10:00.520 --> 01:10:04.180 align:middle line:84% production, a filmed production, of this play Copenhagen 01:10:04.180 --> 01:10:06.130 align:middle line:90% by Michael Frayn. 01:10:06.130 --> 01:10:08.758 align:middle line:84% It stars Daniel Craig who plays the young Heisenberg-- 01:10:08.758 --> 01:10:11.050 align:middle line:84% the same actor who would then go on to play James Bond. 01:10:11.050 --> 01:10:12.740 align:middle line:84% It's a really high-end production. 01:10:12.740 --> 01:10:14.690 align:middle line:84% So this play is really fascinating. 01:10:14.690 --> 01:10:17.170 align:middle line:84% I encourage you to watch the film or read the play. 01:10:17.170 --> 01:10:20.047 align:middle line:84% And it swirls around one of these real life visits 01:10:20.047 --> 01:10:22.630 align:middle line:84% where Heisenberg was sent on one of these diplomatic missions, 01:10:22.630 --> 01:10:25.840 align:middle line:84% in this case, to Copenhagen very soon after the Nazis had 01:10:25.840 --> 01:10:27.610 align:middle line:90% occupied Denmark. 01:10:27.610 --> 01:10:30.910 align:middle line:84% So while he's in Copenhagen giving these fancy lectures, 01:10:30.910 --> 01:10:33.910 align:middle line:84% he visits with his own mentor, almost kind 01:10:33.910 --> 01:10:36.370 align:middle line:90% of father figure, Niels Bohr. 01:10:36.370 --> 01:10:39.310 align:middle line:84% Now, they were afraid that by this point Bohr's house might 01:10:39.310 --> 01:10:41.830 align:middle line:84% have been bugged, might have recording devices placed 01:10:41.830 --> 01:10:42.850 align:middle line:90% in it by the Nazis. 01:10:42.850 --> 01:10:46.570 align:middle line:84% Bohr was well-known to be not at all sympathetic to the Nazis. 01:10:46.570 --> 01:10:49.330 align:middle line:84% And so Bohr and Heisenberg take these long strolls, 01:10:49.330 --> 01:10:52.600 align:middle line:84% as they always used to do, in the gardens near Bohr's house 01:10:52.600 --> 01:10:55.300 align:middle line:84% away from any inside microphones. 01:10:55.300 --> 01:10:57.820 align:middle line:84% And what the play does I think just beautifully, 01:10:57.820 --> 01:11:01.345 align:middle line:84% very evocatively, is try to reimagine scenarios 01:11:01.345 --> 01:11:03.220 align:middle line:84% of what they possibly could have talked about 01:11:03.220 --> 01:11:05.950 align:middle line:84% away from the microphones-- sometimes with Margrethe 01:11:05.950 --> 01:11:08.020 align:middle line:84% Bohr, who we know was almost always part 01:11:08.020 --> 01:11:10.910 align:middle line:84% of Bohr's kind of conversation-- scientific, political, 01:11:10.910 --> 01:11:11.720 align:middle line:90% and otherwise. 01:11:11.720 --> 01:11:14.800 align:middle line:84% So the play has these three characters-- 01:11:14.800 --> 01:11:18.010 align:middle line:84% Margrethe Bohr, Niels Bohr, and Werner Heisenberg. 01:11:18.010 --> 01:11:19.953 align:middle line:84% What do they think is going on with the world? 01:11:19.953 --> 01:11:22.120 align:middle line:84% What do they think the scientists' responsibility is 01:11:22.120 --> 01:11:22.620 align:middle line:90% and so on? 01:11:22.620 --> 01:11:24.220 align:middle line:90% It's a marvelous play. 01:11:24.220 --> 01:11:25.060 align:middle line:90% OK. 01:11:25.060 --> 01:11:27.075 align:middle line:84% So we know that Heisenberg advised 01:11:27.075 --> 01:11:29.200 align:middle line:84% the German military authorities, and multiple times 01:11:29.200 --> 01:11:32.170 align:middle line:84% actually, that nuclear bombs were possible, but probably 01:11:32.170 --> 01:11:33.910 align:middle line:90% not during the present war. 01:11:33.910 --> 01:11:36.850 align:middle line:84% And that was as much because it looked like the Germans would 01:11:36.850 --> 01:11:38.150 align:middle line:90% just win very quickly. 01:11:38.150 --> 01:11:39.733 align:middle line:84% This was the period of what was called 01:11:39.733 --> 01:11:42.740 align:middle line:84% the blitzkrieg, the lightning war, where everyone expected 01:11:42.740 --> 01:11:44.330 align:middle line:90% Germany would win right away. 01:11:44.330 --> 01:11:47.275 align:middle line:84% They invaded Poland on September 1, 1939. 01:11:47.275 --> 01:11:48.650 align:middle line:84% Everyone figured the war would be 01:11:48.650 --> 01:11:50.870 align:middle line:84% over within a year or two because it 01:11:50.870 --> 01:11:52.160 align:middle line:90% started going so well. 01:11:52.160 --> 01:11:56.510 align:middle line:84% Very few-- the Nazis suffered very few setbacks militarily 01:11:56.510 --> 01:11:59.665 align:middle line:90% once open warfare had started. 01:11:59.665 --> 01:12:01.040 align:middle line:84% But the authorities, nonetheless, 01:12:01.040 --> 01:12:03.170 align:middle line:84% saw a future promise for this kind of weapon. 01:12:03.170 --> 01:12:05.480 align:middle line:84% They were imagining, remember, a thousand-year Reich. 01:12:05.480 --> 01:12:07.040 align:middle line:90% They had a long view. 01:12:07.040 --> 01:12:09.830 align:middle line:84% And so they continued to fund Heisenberg's effort 01:12:09.830 --> 01:12:12.898 align:middle line:84% and also do things like seize the Belgian Congo-- 01:12:12.898 --> 01:12:14.690 align:middle line:84% the so-called Belgian Congo-- the territory 01:12:14.690 --> 01:12:16.700 align:middle line:84% within Central Africa that was known 01:12:16.700 --> 01:12:19.070 align:middle line:90% to be very rich in uranium ore. 01:12:19.070 --> 01:12:21.677 align:middle line:84% And so they wanted to get more raw uranium 01:12:21.677 --> 01:12:23.510 align:middle line:84% and fund Heisenberg's efforts and eventually 01:12:23.510 --> 01:12:27.140 align:middle line:84% install him to the head of the Kaiser Wilhelm Institut. 01:12:27.140 --> 01:12:29.780 align:middle line:84% Members of Heisenberg's team, then, of this group, 01:12:29.780 --> 01:12:31.490 align:middle line:84% began working on what would it take 01:12:31.490 --> 01:12:33.980 align:middle line:84% to scale up these nuclear fission reactions. 01:12:33.980 --> 01:12:37.040 align:middle line:84% One member, Walther Bothe, estimated 01:12:37.040 --> 01:12:40.200 align:middle line:84% that the moderate-- the material to slow down the neutrons, 01:12:40.200 --> 01:12:43.560 align:middle line:84% like the paraffin wax in the early experiments, that 01:12:43.560 --> 01:12:45.630 align:middle line:84% to do that with carbon or graphite, 01:12:45.630 --> 01:12:48.330 align:middle line:84% you'd need kind of ultra-pure carbon. 01:12:48.330 --> 01:12:50.820 align:middle line:84% Any impurities would absorb neutrons and not 01:12:50.820 --> 01:12:51.750 align:middle line:90% slow them down. 01:12:51.750 --> 01:12:54.240 align:middle line:84% If you absorb the neutrons, you stop the fission reactions. 01:12:54.240 --> 01:12:55.660 align:middle line:90% You stop a chain reaction. 01:12:55.660 --> 01:12:58.590 align:middle line:84% So Bothe, as we now know, overestimated 01:12:58.590 --> 01:13:01.330 align:middle line:84% how hard it would be to do this with carbon. 01:13:01.330 --> 01:13:04.110 align:middle line:84% So he advised instead that they turn to heavy water-- 01:13:04.110 --> 01:13:06.750 align:middle line:84% water that's made not with ordinary hydrogen, 01:13:06.750 --> 01:13:11.910 align:middle line:84% but with deuterium, with hydrogen atoms that have 01:13:11.910 --> 01:13:13.840 align:middle line:90% extra neutrons in the nuclei. 01:13:13.840 --> 01:13:15.810 align:middle line:84% So you have what's called heavy water. 01:13:15.810 --> 01:13:17.910 align:middle line:84% There was this kind of amazing commando raid 01:13:17.910 --> 01:13:20.537 align:middle line:84% to blow up a heavy water plant in Norway 01:13:20.537 --> 01:13:22.620 align:middle line:84% that the Nazis wanted because they wanted to steal 01:13:22.620 --> 01:13:24.150 align:middle line:90% large amounts of heavy water. 01:13:24.150 --> 01:13:26.130 align:middle line:84% Literally, like parachuting in in cover 01:13:26.130 --> 01:13:28.660 align:middle line:90% of night-- crazy, crazy stuff. 01:13:28.660 --> 01:13:31.590 align:middle line:84% Meanwhile, Heisenberg began on the theoretical side 01:13:31.590 --> 01:13:35.640 align:middle line:84% to estimate how much of this fissionable isotope U-235 01:13:35.640 --> 01:13:38.230 align:middle line:84% would then need to have a runaway explosion-- 01:13:38.230 --> 01:13:39.690 align:middle line:90% the so-called critical mass. 01:13:39.690 --> 01:13:43.210 align:middle line:84% And he actually overestimated by a factor about 10 01:13:43.210 --> 01:13:45.450 align:middle line:84% how much you'd need, at the same time, 01:13:45.450 --> 01:13:48.300 align:middle line:84% though, in ignorance of the underestimate 01:13:48.300 --> 01:13:51.220 align:middle line:84% by this Frisch-Peierls calculation. 01:13:51.220 --> 01:13:53.250 align:middle line:84% So as the war dragged on, the bomb project 01:13:53.250 --> 01:13:56.280 align:middle line:84% gets lower and lower priority within Germany, at first 01:13:56.280 --> 01:13:58.860 align:middle line:84% because they figured they'll just win by conventional means. 01:13:58.860 --> 01:14:03.090 align:middle line:84% And later, as the war begins to really bog down, 01:14:03.090 --> 01:14:06.870 align:middle line:84% and the Nazis do get turned back militarily at various points, 01:14:06.870 --> 01:14:09.900 align:middle line:84% then the Reich needs to actually direct resources 01:14:09.900 --> 01:14:12.870 align:middle line:84% to the short-term immediate military priority. 01:14:12.870 --> 01:14:14.670 align:middle line:84% So it's a low priority at first because it 01:14:14.670 --> 01:14:15.690 align:middle line:90% looks like they'll win. 01:14:15.690 --> 01:14:17.732 align:middle line:84% It remains a low priority later because they have 01:14:17.732 --> 01:14:20.350 align:middle line:90% other short-term priorities. 01:14:20.350 --> 01:14:22.530 align:middle line:84% So the physicist, Sam Goudsmit, who 01:14:22.530 --> 01:14:24.720 align:middle line:84% helped introduce the notion of quantum spin, 01:14:24.720 --> 01:14:26.640 align:middle line:84% he had emigrated from the Netherlands 01:14:26.640 --> 01:14:29.340 align:middle line:84% actually in the late '20s-- well before the rise of Nazism. 01:14:29.340 --> 01:14:30.573 align:middle line:90% His family stayed behind. 01:14:30.573 --> 01:14:32.490 align:middle line:84% And in fact, they later perished in Auschwitz, 01:14:32.490 --> 01:14:34.290 align:middle line:90% in Jewish background 01:14:34.290 --> 01:14:38.010 align:middle line:84% He led the Allied reconnaissance missions inside Germany 01:14:38.010 --> 01:14:39.630 align:middle line:90% to learn about this German-- 01:14:39.630 --> 01:14:42.600 align:middle line:84% the Nazi nuclear effort, and to literally kidnap 01:14:42.600 --> 01:14:44.310 align:middle line:84% German nuclear scientists before they 01:14:44.310 --> 01:14:47.010 align:middle line:84% could flee to either the Soviets or anywhere else. 01:14:47.010 --> 01:14:49.800 align:middle line:84% This is happening before the end of the Second World War. 01:14:49.800 --> 01:14:52.560 align:middle line:84% There's other crazy stories, that a pro baseball 01:14:52.560 --> 01:14:54.930 align:middle line:84% player named Moe Berg-- this really happened-- 01:14:54.930 --> 01:14:58.650 align:middle line:84% was basically drafted into what would become the CIA. 01:14:58.650 --> 01:15:00.660 align:middle line:84% It was the Office of Strategic Services 01:15:00.660 --> 01:15:02.700 align:middle line:84% at the time in the United States. 01:15:02.700 --> 01:15:03.630 align:middle line:90% He spoke German. 01:15:03.630 --> 01:15:07.200 align:middle line:84% He was sent to neutral countries near Germany, 01:15:07.200 --> 01:15:09.750 align:middle line:84% like Switzerland, to listen to these public lectures 01:15:09.750 --> 01:15:12.030 align:middle line:90% by Heisenberg. 01:15:12.030 --> 01:15:15.000 align:middle line:84% The baseball player was armed with a pistol. 01:15:15.000 --> 01:15:17.520 align:middle line:84% And he was basically a amateur spy. 01:15:17.520 --> 01:15:19.950 align:middle line:84% And if it sounded like the Nazi bomb project was 01:15:19.950 --> 01:15:22.320 align:middle line:84% getting too advanced, Berg was ordered 01:15:22.320 --> 01:15:23.585 align:middle line:90% to assassinate Heisenberg. 01:15:23.585 --> 01:15:24.960 align:middle line:84% He didn't because it didn't sound 01:15:24.960 --> 01:15:27.240 align:middle line:84% like they were that close, and these amazing, pretty 01:15:27.240 --> 01:15:29.400 align:middle line:90% ridiculous or crazy stories. 01:15:29.400 --> 01:15:32.670 align:middle line:84% Meanwhile, the Alsos mission is successful. 01:15:32.670 --> 01:15:34.850 align:middle line:84% They gather enormous documentation 01:15:34.850 --> 01:15:35.850 align:middle line:90% from the German efforts. 01:15:35.850 --> 01:15:39.300 align:middle line:84% And they also captured 10 German nuclear scientists 01:15:39.300 --> 01:15:42.210 align:middle line:84% in the spring even before Germany formally surrenders. 01:15:42.210 --> 01:15:45.260 align:middle line:84% They capture them as basically prisoners of war, 01:15:45.260 --> 01:15:47.810 align:middle line:84% and they ferret them out of the country to Farm Hall, 01:15:47.810 --> 01:15:49.760 align:middle line:90% this quite lovely country home-- 01:15:49.760 --> 01:15:52.970 align:middle line:84% country house in rural England not too far 01:15:52.970 --> 01:15:54.470 align:middle line:90% from Cambridge University. 01:15:54.470 --> 01:15:56.630 align:middle line:84% This was called Operation Epsilon. 01:15:56.630 --> 01:15:58.490 align:middle line:84% Once again, the house was bugged. 01:15:58.490 --> 01:16:00.860 align:middle line:84% The conversations were constantly audiotaped, 01:16:00.860 --> 01:16:02.540 align:middle line:90% transcribed, and translated. 01:16:02.540 --> 01:16:04.370 align:middle line:84% And you have an excerpt in the reader-- 01:16:04.370 --> 01:16:06.200 align:middle line:90% I'll let you read through here. 01:16:06.200 --> 01:16:08.150 align:middle line:90% Let me just say very quickly-- 01:16:08.150 --> 01:16:09.860 align:middle line:84% I know I'm running late on time-- 01:16:09.860 --> 01:16:13.490 align:middle line:84% the first reaction upon hearing that nuclear weapons had been 01:16:13.490 --> 01:16:15.770 align:middle line:84% made and had actually been used, in this case 01:16:15.770 --> 01:16:19.640 align:middle line:84% against the city of Hiroshima by the American forces, 01:16:19.640 --> 01:16:22.670 align:middle line:84% the first reaction is utter disbelief. 01:16:22.670 --> 01:16:26.060 align:middle line:84% Heisenberg couldn't believe that anyone, let alone the bumbling 01:16:26.060 --> 01:16:28.433 align:middle line:84% Americans, could possibly have gotten so far 01:16:28.433 --> 01:16:30.350 align:middle line:84% along in this project, which his own group had 01:16:30.350 --> 01:16:32.810 align:middle line:90% made only halting progress on. 01:16:32.810 --> 01:16:34.610 align:middle line:84% A little while later, as the transcript 01:16:34.610 --> 01:16:37.460 align:middle line:84% reveals, it's a different physicist, Carl Friedrich von 01:16:37.460 --> 01:16:40.280 align:middle line:84% Weizsacker, who says, well, we didn't make a bomb 01:16:40.280 --> 01:16:41.666 align:middle line:90% because we didn't want to. 01:16:41.666 --> 01:16:44.230 align:middle line:84% We didn't do it, as he says, on principle. 01:16:44.230 --> 01:16:46.030 align:middle line:84% If we'd wanted Germany to win the war, 01:16:46.030 --> 01:16:47.140 align:middle line:90% we would have succeeded. 01:16:47.140 --> 01:16:48.820 align:middle line:90% And Heisenberg then says, ah. 01:16:48.820 --> 01:16:53.260 align:middle line:84% I was convinced of the possibility of making a reactor 01:16:53.260 --> 01:16:55.960 align:middle line:90% not for power, not as a weapon. 01:16:55.960 --> 01:16:57.610 align:middle line:84% But I never thought we'd make a bomb. 01:16:57.610 --> 01:16:58.810 align:middle line:84% And at the bottom of my heart, I was 01:16:58.810 --> 01:17:00.970 align:middle line:84% really glad it would be a reactor and not a bomb. 01:17:00.970 --> 01:17:03.792 align:middle line:84% They began making-- trying to make sense of what's happening 01:17:03.792 --> 01:17:04.750 align:middle line:90% so quickly around them. 01:17:04.750 --> 01:17:06.050 align:middle line:90% Again, just to go quickly here. 01:17:06.050 --> 01:17:08.050 align:middle line:84% Sorry for the-- I'll post the slides, of course. 01:17:08.050 --> 01:17:09.100 align:middle line:90% You can see them. 01:17:09.100 --> 01:17:13.270 align:middle line:84% The idea that Heisenberg had actually purposefully resisted 01:17:13.270 --> 01:17:17.050 align:middle line:84% Hitler by dragging his feet, by slowing the project, 01:17:17.050 --> 01:17:19.150 align:middle line:84% was not a position that Heisenberg 01:17:19.150 --> 01:17:20.860 align:middle line:90% himself ever articulated. 01:17:20.860 --> 01:17:24.280 align:middle line:84% But other people began saying it on his behalf. 01:17:24.280 --> 01:17:25.780 align:middle line:84% Heisenberg said, we'd worked hard 01:17:25.780 --> 01:17:27.250 align:middle line:90% on reactors, which was true. 01:17:27.250 --> 01:17:29.230 align:middle line:84% He just chose not to emphasize they had also 01:17:29.230 --> 01:17:30.460 align:middle line:90% had ideas about weapons. 01:17:30.460 --> 01:17:32.470 align:middle line:84% But other people speaking in some sense 01:17:32.470 --> 01:17:35.320 align:middle line:84% on behalf of Heisenberg, put together a story 01:17:35.320 --> 01:17:37.720 align:middle line:84% that Heisenberg had purposefully dragged his feet so as 01:17:37.720 --> 01:17:41.330 align:middle line:90% to deny Hitler a nuclear weapon. 01:17:41.330 --> 01:17:43.160 align:middle line:84% And we have this amazing correspondence 01:17:43.160 --> 01:17:45.830 align:middle line:84% of Heisenberg writing privately to these journalists saying, 01:17:45.830 --> 01:17:47.120 align:middle line:90% you've got it all wrong. 01:17:47.120 --> 01:17:48.000 align:middle line:90% Here's an example. 01:17:48.000 --> 01:17:50.780 align:middle line:84% I would not want this remark to be misunderstood, 01:17:50.780 --> 01:17:54.200 align:middle line:84% as saying that I myself engaged in resistance to Hitler. 01:17:54.200 --> 01:17:55.520 align:middle line:90% And so I'll stop there. 01:17:55.520 --> 01:17:57.557 align:middle line:84% I apologize for running a bit long. 01:17:57.557 --> 01:17:58.890 align:middle line:90% I have time for a few questions. 01:17:58.890 --> 01:18:01.015 align:middle line:84% I'd be glad to stay on longer if people would like. 01:18:01.015 --> 01:18:04.220 align:middle line:84% Of course, feel free to head off to your other classes. 01:18:04.220 --> 01:18:06.990 align:middle line:84% And again, the slides are on the Canvas site. 01:18:06.990 --> 01:18:08.660 align:middle line:84% So anyway, here's part of, again, 01:18:08.660 --> 01:18:12.230 align:middle line:84% this kind of unsteady mixture of really cutting-edge 01:18:12.230 --> 01:18:15.590 align:middle line:84% nuclear physics unfolding in real time with this kind 01:18:15.590 --> 01:18:20.190 align:middle line:84% of really fast-changing series of political 01:18:20.190 --> 01:18:22.580 align:middle line:84% and kind of military and bureaucratic maneuvers 01:18:22.580 --> 01:18:24.663 align:middle line:90% all getting wrapped up together. 01:18:24.663 --> 01:18:25.580 align:middle line:90% Any questions on that? 01:18:25.580 --> 01:18:31.510 align:middle line:90% 01:18:31.510 --> 01:18:35.910 align:middle line:84% So I encourage you to go back to the Operation Epsilon excerpts. 01:18:35.910 --> 01:18:38.490 align:middle line:84% We do have the excerpts of the actual Farm Hall 01:18:38.490 --> 01:18:40.840 align:middle line:84% transcripts, which I put on the Canvas site, 01:18:40.840 --> 01:18:43.410 align:middle line:84% including the fateful day of August 6-- 01:18:43.410 --> 01:18:45.000 align:middle line:84% their reactions to the BBC reports 01:18:45.000 --> 01:18:47.668 align:middle line:84% of the bombing of Hiroshima and lots, 01:18:47.668 --> 01:18:49.210 align:middle line:84% lots more to talk about that as well. 01:18:49.210 --> 01:18:51.720 align:middle line:84% We'll see some hints of this in the documentary film. 01:18:51.720 --> 01:18:55.570 align:middle line:84% We can talk more in our informal discussion next week. 01:18:55.570 --> 01:18:58.680 align:middle line:84% And in the meantime, we'll pick up this story then on Wednesday 01:18:58.680 --> 01:19:01.800 align:middle line:84% with what does some of the physicists outside of Germany 01:19:01.800 --> 01:19:04.470 align:middle line:84% do with these same set of ideas about nuclear fission 01:19:04.470 --> 01:19:05.740 align:middle line:90% and weapons prospects. 01:19:05.740 --> 01:19:08.670 align:middle line:84% So we'll talk more about Allied efforts 01:19:08.670 --> 01:19:10.980 align:middle line:84% during the Second World War on Wednesday. 01:19:10.980 --> 01:19:12.570 align:middle line:90% So sorry for running long. 01:19:12.570 --> 01:19:13.410 align:middle line:90% Stay well. 01:19:13.410 --> 01:19:16.210 align:middle line:84% Good luck with paper two, and I'll see you soon. 01:19:16.210 --> 01:19:18.110 align:middle line:90% Bye, everyone. 01:19:18.110 --> 01:19:33.000 align:middle line:90%