1 00:00:00,240 --> 00:00:02,120 Speaker 1: This Day in History Class is a production of I 2 00:00:02,200 --> 00:00:07,520 Speaker 1: Heart Radio. Hi, I'm Eves and Welcome to This Day 3 00:00:07,520 --> 00:00:11,399 Speaker 1: in History Class, a show that uncovers history one day 4 00:00:11,440 --> 00:00:25,000 Speaker 1: at a time. Today is May ninth, nineteen. The day 5 00:00:25,239 --> 00:00:30,200 Speaker 1: was May twenty ninth, nineteen nineteen. A total solar eclipse 6 00:00:30,400 --> 00:00:34,320 Speaker 1: lasted for more than six minutes, casting darkness from South 7 00:00:34,320 --> 00:00:40,080 Speaker 1: America to Africa. German physicist Albert Einstein had recently published 8 00:00:40,120 --> 00:00:43,600 Speaker 1: his general theory of relativity, but it was not yet proven. 9 00:00:45,120 --> 00:00:49,040 Speaker 1: During the eclipse, British astronomer Arthur Eddington led an experiment 10 00:00:49,120 --> 00:00:52,360 Speaker 1: to test the deflection of light by a gravitational field. 11 00:00:53,040 --> 00:00:57,880 Speaker 1: Eddington's research teams found that their eclipse measurements confirmed Einstein's 12 00:00:57,880 --> 00:01:03,240 Speaker 1: predictions about general relativity. Einstein, a professor in Berlin, had 13 00:01:03,360 --> 00:01:07,119 Speaker 1: yet to achieve worldwide fame, but after the eclipse experiment, 14 00:01:07,480 --> 00:01:12,920 Speaker 1: Einstein rose to prominence. In nineteen fifteen, Einstein published four 15 00:01:12,959 --> 00:01:17,720 Speaker 1: papers describing his general theory of relativity. At the time, 16 00:01:17,840 --> 00:01:21,360 Speaker 1: Isaac Newton's model of classical mechanics and law of universal 17 00:01:21,400 --> 00:01:26,160 Speaker 1: gravitation ruled, but Einstein's work was at odds with Newton's theory. 18 00:01:27,000 --> 00:01:30,319 Speaker 1: According to Newton, space was inert and gravity was a 19 00:01:30,360 --> 00:01:35,280 Speaker 1: four step pulled objects together. But Einstein's special theory of relativity, 20 00:01:35,680 --> 00:01:39,480 Speaker 1: proposed in nineteen o five, said that space and time 21 00:01:39,600 --> 00:01:44,000 Speaker 1: were relative informed of four dimensional continuum called space time, 22 00:01:44,760 --> 00:01:47,920 Speaker 1: and his general theory of relativity posed gravity as a 23 00:01:47,960 --> 00:01:51,400 Speaker 1: distortion in the fabric of space caused by the presence 24 00:01:51,440 --> 00:01:55,960 Speaker 1: of massive objects. Einstein and Newton's views on how gravity 25 00:01:56,000 --> 00:02:00,800 Speaker 1: influences light also differed. Classical dynamics says that the gravity 26 00:02:00,800 --> 00:02:03,160 Speaker 1: of a star can deflect the path of a photon 27 00:02:03,800 --> 00:02:08,240 Speaker 1: or a quantum of electromagnetic radiation, but Einstein predicted that 28 00:02:08,320 --> 00:02:12,239 Speaker 1: light curves while traveling through spacetime near the warp induced 29 00:02:12,480 --> 00:02:17,880 Speaker 1: by an objects gravitational field. So both scientists predicted that 30 00:02:18,000 --> 00:02:21,040 Speaker 1: light would bend due to gravity, though newt end predicted 31 00:02:21,120 --> 00:02:23,440 Speaker 1: it would do so by only half as much as 32 00:02:23,480 --> 00:02:27,919 Speaker 1: Einstein's theory did, but the difference in measurements was small, 33 00:02:28,040 --> 00:02:31,640 Speaker 1: and the two theories made similar predictions for tests of 34 00:02:31,680 --> 00:02:36,079 Speaker 1: gravity and light. Figuring out which theory was more accurate 35 00:02:36,120 --> 00:02:39,120 Speaker 1: seemed pointless at a time when it seemed like science 36 00:02:39,360 --> 00:02:42,640 Speaker 1: did not have the capability to measure such a tiny curvature. 37 00:02:43,400 --> 00:02:46,679 Speaker 1: But the more massive an object is, the bigger the warp, 38 00:02:46,760 --> 00:02:51,000 Speaker 1: and the more its gravity can bend light. Einstein realized 39 00:02:51,040 --> 00:02:53,639 Speaker 1: that the Sun was massive enough to measure such a 40 00:02:53,720 --> 00:02:57,760 Speaker 1: subtle effect. As the Sun moved toward a background star, 41 00:02:58,240 --> 00:03:00,960 Speaker 1: it would bend the stars light and star would appear 42 00:03:01,000 --> 00:03:04,400 Speaker 1: to move. This kind of observation would have to be 43 00:03:04,480 --> 00:03:07,400 Speaker 1: made when the Sun was out, but its light was blocked, 44 00:03:07,680 --> 00:03:11,519 Speaker 1: so stars were visible, and eclipse was the perfect time 45 00:03:11,560 --> 00:03:16,880 Speaker 1: to carry out tests of Einstein's theory. German astronomer Erwin 46 00:03:16,960 --> 00:03:21,240 Speaker 1: Finlay Fronleech attempted to prove Einstein's theory, but war broke 47 00:03:21,280 --> 00:03:23,640 Speaker 1: out and he was arrested as a spy as he 48 00:03:23,720 --> 00:03:27,120 Speaker 1: was preparing to experiment during an eclipse in nineteen fourteen. 49 00:03:28,400 --> 00:03:33,000 Speaker 1: Astronomers from California's Lick Observatory also attempted to photograph the 50 00:03:33,000 --> 00:03:36,040 Speaker 1: eclipse from near Kiev, but clouds got in the way. 51 00:03:37,040 --> 00:03:40,839 Speaker 1: Around this time, Einstein realized his calculations about how much 52 00:03:40,880 --> 00:03:44,240 Speaker 1: the stars would move was incorrect, and he published his 53 00:03:44,320 --> 00:03:49,360 Speaker 1: completed General Theory of Relativity in nineteen fifteen. World War 54 00:03:49,440 --> 00:03:52,880 Speaker 1: One kept Einstein's work isolated, and people in the science 55 00:03:52,880 --> 00:03:57,040 Speaker 1: community pushed back against the new theory, but Sir Arthur Eddington, 56 00:03:57,280 --> 00:04:01,200 Speaker 1: director of the Cambridge Observatory support Or, did Einstein's theory 57 00:04:01,280 --> 00:04:04,600 Speaker 1: and wanted to lead an experiment to test it. The 58 00:04:04,720 --> 00:04:08,920 Speaker 1: nineteen nineteen total solar eclipse presented an opportunity to carry 59 00:04:08,960 --> 00:04:15,000 Speaker 1: out tests. Britain's astronomer, Royal Sir Frank W. Dyson, proposed 60 00:04:15,040 --> 00:04:18,560 Speaker 1: an expedition to experiment during the solar eclipse, set to 61 00:04:18,600 --> 00:04:23,239 Speaker 1: occur on May twenty ninth, nineteen nineteen. If scientists measured 62 00:04:23,240 --> 00:04:26,279 Speaker 1: the position of the stars during the eclipse and compared 63 00:04:26,360 --> 00:04:29,440 Speaker 1: them to their normal positions, the tests could confirm the 64 00:04:29,440 --> 00:04:34,800 Speaker 1: general theory of relativity. Eddington would lead the expedition. He 65 00:04:34,839 --> 00:04:37,719 Speaker 1: took measurements of the stars in the Hyades cluster in 66 00:04:37,839 --> 00:04:41,640 Speaker 1: January and February of nineteen nineteen, since the sun would 67 00:04:41,640 --> 00:04:45,240 Speaker 1: cross that cluster during the eclipse, and the Royal Society 68 00:04:45,320 --> 00:04:50,600 Speaker 1: in Royal Astronomical Society organized expeditions to Principal, An Island 69 00:04:50,640 --> 00:04:54,200 Speaker 1: off the coast of West Africa, and to sober Al, Brazil. 70 00:04:55,279 --> 00:04:57,919 Speaker 1: The May twenty nine eclipse was one of the longest 71 00:04:58,000 --> 00:05:02,039 Speaker 1: in centuries, and despite at whether in Principe for a period, 72 00:05:02,360 --> 00:05:05,640 Speaker 1: astronomers had a considerable amount of time to take photos 73 00:05:05,720 --> 00:05:08,400 Speaker 1: of the location of the stars and the Hyades cluster. 74 00:05:09,920 --> 00:05:12,919 Speaker 1: Months later, the team had measured the precise position of 75 00:05:12,920 --> 00:05:16,080 Speaker 1: the stars that were visible on the photographic plates. They 76 00:05:16,160 --> 00:05:20,680 Speaker 1: found that their measurements were consistent with Einstein's predictions. The 77 00:05:20,760 --> 00:05:25,359 Speaker 1: expedition's results became front page news in Einstein became famous 78 00:05:25,400 --> 00:05:30,640 Speaker 1: for his theory. On November six, nineteen nineteen, Eddington and 79 00:05:30,720 --> 00:05:34,000 Speaker 1: Dyson presented their findings at a joint meeting of the 80 00:05:34,080 --> 00:05:38,240 Speaker 1: Royal Society and the Royal Astronomical Society in England. Not 81 00:05:38,320 --> 00:05:44,560 Speaker 1: everyone accepted or understood Einstein's theory, and Einstein himself had detractors, 82 00:05:44,600 --> 00:05:50,000 Speaker 1: but later eclipses corroborated Einstein's predictions. By the nineteen sixties, 83 00:05:50,160 --> 00:05:53,600 Speaker 1: most physicists had accepted the validity of the general theory 84 00:05:53,640 --> 00:05:57,680 Speaker 1: of relativity. The deflection of light passing near a massive 85 00:05:57,720 --> 00:06:02,440 Speaker 1: object is now called gravitational len thing. Gravitational lensing has 86 00:06:02,480 --> 00:06:06,400 Speaker 1: been used to map out dark matter and discover distant galaxies. 87 00:06:08,080 --> 00:06:10,760 Speaker 1: I'm Eves Deacote and hopefully you know a little more 88 00:06:10,800 --> 00:06:15,080 Speaker 1: about history today than you did yesterday, and if you'd 89 00:06:15,080 --> 00:06:17,680 Speaker 1: like to follow us on social media. You can find 90 00:06:17,800 --> 00:06:23,600 Speaker 1: us at t D i h C Podcast on Twitter, Instagram, 91 00:06:23,640 --> 00:06:28,760 Speaker 1: and Facebook. Thanks for showing up. We'll meet here again tomorrow. 92 00:06:32,800 --> 00:06:35,080 Speaker 1: For more podcasts from I Heart Radio, visit the iHeart 93 00:06:35,160 --> 00:06:37,599 Speaker 1: Radio app, Apple Podcasts, or wherever you listen to your 94 00:06:37,640 --> 00:06:38,279 Speaker 1: favorite shows.