1 00:00:05,670 --> 00:00:10,430 In the past two decades, astronomers have made a truly revolutionary discovery: 2 00:00:10,430 --> 00:00:16,149 that the cosmos is not only expanding, but is doing so at an ever-faster rate. 3 00:00:16,149 --> 00:00:19,410 The discovery of the accelerated expansion of the Universe 4 00:00:19,410 --> 00:00:24,500 was awarded the 2011 Nobel Prize in Physics. 5 00:00:29,070 --> 00:00:30,700 This is the ESOcast! 6 00:00:30,700 --> 00:00:33,630 Cutting-edge science and life behind the scenes of ESO, 7 00:00:33,630 --> 00:00:35,620 the European Southern Observatory, 8 00:00:35,620 --> 00:00:42,640 exploring the ultimate frontier with our host Dr J, a.k.a. Dr Joe Liske. 9 00:00:46,500 --> 00:00:47,920 Hello and welcome to the ESOcast. 10 00:00:47,920 --> 00:00:49,510 In this episode, 11 00:00:49,510 --> 00:00:51,500 we’re going to find out how astronomers learned 12 00:00:51,640 --> 00:00:54,920 that the expansion of the Universe is speeding up 13 00:00:55,260 --> 00:01:00,090 and why this finding is so important not only for our understanding of the Cosmos, 14 00:01:00,090 --> 00:01:02,360 but in fact, for all of Physics. 15 00:01:02,360 --> 00:01:07,690 Now this discovery was awarded the 2011 Nobel Prize in Physics, 16 00:01:07,690 --> 00:01:09,890 and observations from ESO’s telescopes in Chile 17 00:01:09,890 --> 00:01:13,310 played a significant role in this breakthrough. 18 00:01:19,650 --> 00:01:24,940 The Universe we live in was created in the Big Bang some 13.7 billion years ago. 19 00:01:26,000 --> 00:01:28,840 Ever since then, the Universe has been expanding. 20 00:01:28,840 --> 00:01:30,190 And for decades, 21 00:01:30,190 --> 00:01:34,130 astronomers have wanted to learn more about the nature of this expansion. 22 00:01:34,130 --> 00:01:37,430 For a long time, there were two main ideas: 23 00:01:37,430 --> 00:01:42,400 Either the expansion would gradually slow down and would ultimately come to a halt 24 00:01:42,400 --> 00:01:46,770 — after which the Universe would start to contract towards a “Big Crunch”. 25 00:01:47,770 --> 00:01:50,680 Or that the Cosmos would continue to expand forever. 26 00:01:53,380 --> 00:01:54,850 But how could astronomers find out 27 00:01:54,850 --> 00:01:58,250 which of these models of the Universe is the correct one? 28 00:01:58,250 --> 00:02:00,950 Well, one of the simplest ways of doing this 29 00:02:00,950 --> 00:02:04,920 is to accurately measure distances to very faraway galaxies, 30 00:02:04,920 --> 00:02:09,130 and then to compare these measurements with the predictions from these models 31 00:02:09,130 --> 00:02:11,000 for these particular galaxies. 32 00:02:11,000 --> 00:02:15,000 The comparison between the measurements and the predictions tells us 33 00:02:15,000 --> 00:02:17,250 which of the models is the right one. 34 00:02:17,250 --> 00:02:18,930 But how does this work? 35 00:02:18,930 --> 00:02:24,200 How can astronomers precisely determine these huge distances across the Cosmos? 36 00:02:24,200 --> 00:02:29,320 Well, stellar explosions, or supernovae, play a key role here. 37 00:02:34,250 --> 00:02:38,760 Supernovae are rare cosmic events: They are exploding stars. 38 00:02:39,330 --> 00:02:43,300 There is a certain type of explosion, known as a Type Ia Supernova, 39 00:02:43,300 --> 00:02:47,130 which is ideal for measuring distances in the cosmos. 40 00:02:49,160 --> 00:02:50,800 These supernovae are very bright, 41 00:02:50,800 --> 00:02:54,540 which means they can be seen even in distant galaxies. 42 00:02:54,540 --> 00:02:58,210 And what’s more their intrinsic brightnesses are always the same, 43 00:02:58,610 --> 00:03:00,500 meaning that their distances can be inferred 44 00:03:00,540 --> 00:03:02,970 from how bright they appear to us from Earth. 45 00:03:05,690 --> 00:03:08,800 By the 1990s two separate research teams 46 00:03:08,800 --> 00:03:12,230 had begun to carefully observe these exploding stars. 47 00:03:12,230 --> 00:03:13,350 For their studies, 48 00:03:13,350 --> 00:03:18,480 astronomers partly used telescopes at ESO’s La Silla observatory in Chile. 49 00:03:20,040 --> 00:03:23,270 Observing extremely distant supernovae in the mid 1990s 50 00:03:23,270 --> 00:03:26,290 was extremely challenging and exciting. 51 00:03:26,290 --> 00:03:30,810 We at ESO used the 3.6-metre, the NTT and the 1.5-metre telescopes 52 00:03:30,810 --> 00:03:33,600 to observe these high-redshift supernovae 53 00:03:33,600 --> 00:03:36,530 discovered at the nearby Tololo Observatory. 54 00:03:36,670 --> 00:03:39,100 In those days, 15 years ago, 55 00:03:39,100 --> 00:03:42,000 we were actually counting literally every single photon, 56 00:03:42,000 --> 00:03:45,770 which is a beautiful experiment to be part of, because it was extremely challenging. 57 00:03:46,300 --> 00:03:49,660 The critical component of all of this is of course to realise 58 00:03:49,660 --> 00:03:52,430 that we did not set out to find the accelerating Universe, 59 00:03:52,430 --> 00:03:56,050 so watching a new paradigm in physics establish itself 60 00:03:56,050 --> 00:03:59,790 has of course been very interesting and it’s been great fun. 61 00:04:01,700 --> 00:04:04,460 Once we had established that the distant supernovae were too far away 62 00:04:04,460 --> 00:04:07,970 for a Universe that was dominated by gravity 63 00:04:07,970 --> 00:04:10,170 we had to go back and measure this again. 64 00:04:10,170 --> 00:04:13,770 So the accelerated expansion that we measured with the first set of supernovae 65 00:04:13,770 --> 00:04:18,500 was then translated very quickly into a new component for cosmology: 66 00:04:18,500 --> 00:04:19,649 dark energy, 67 00:04:19,649 --> 00:04:21,430 we had to confirm that result. 68 00:04:21,430 --> 00:04:26,750 What we did is we asked for VLT time like other groups as well 69 00:04:29,000 --> 00:04:33,020 to confirm what we had measured to get better data with a bigger telescope 70 00:04:33,020 --> 00:04:36,780 and to get a better sampling of the supernovae themselves. 71 00:04:38,620 --> 00:04:41,350 The discovery of the accelerating expansion of the Universe 72 00:04:41,350 --> 00:04:45,450 was one of the most unexpected and important of the last decades. 73 00:04:45,450 --> 00:04:49,210 It was so unexpected because up until that point, 74 00:04:49,210 --> 00:04:53,940 everyone believed that the expansion of the Universe should be slowed down 75 00:04:53,940 --> 00:04:58,500 by the attractive force of gravity exerted by all of the matter in the Universe. 76 00:04:59,000 --> 00:05:03,530 But, as it turns out, the Universe is in fact much more interesting than that. 77 00:05:03,530 --> 00:05:06,880 But why is this acceleration so important? 78 00:05:06,880 --> 00:05:12,450 Well, as far as we know, there are two possible explanations for the acceleration: 79 00:05:12,450 --> 00:05:14,820 The number one explanation is 80 00:05:14,820 --> 00:05:20,890 that nearly ¾ of the Universe consist of some form of this mysterious dark energy. 81 00:05:20,890 --> 00:05:25,500 Dark energy is so mysterious because it exerts negative pressure. 82 00:05:25,700 --> 00:05:27,960 That’s pretty exotic stuff. 83 00:05:27,960 --> 00:05:30,500 The number two explanation is 84 00:05:30,500 --> 00:05:33,320 that there is something wrong with our understanding of gravity. 85 00:05:33,320 --> 00:05:38,940 In other words, that Einstein’s theory of general relativity is not quite correct. 86 00:05:38,940 --> 00:05:40,820 In either of these cases, 87 00:05:40,820 --> 00:05:43,800 we are confronted with completely new physics, 88 00:05:43,800 --> 00:05:46,800 and that’s why this is so important 89 00:05:46,800 --> 00:05:51,710 and why this discovery was awarded the 2011 Nobel Prize in Physics. 90 00:05:51,710 --> 00:05:55,130 This is Dr J signing off for the ESOcast. 91 00:05:55,130 --> 00:05:58,610 Join me again next time for another cosmic adventure. 92 00:06:00,790 --> 00:06:04,000 ESOcast is produced by ESO, the European Southern Observatory. 93 00:06:04,530 --> 00:06:05,500 ESO, the European Southern Observatory, 94 00:06:05,500 --> 00:06:08,000 is the pre-eminent intergovernmental science and technology organisation in astronomy 95 00:06:08,000 --> 00:06:10,500 designing, constructing and operating the world’s most advanced ground-based telescopes. 96 00:06:13,000 --> 00:06:18,140 Transcription by ESO; translation by — 97 00:06:29,700 --> 00:06:32,500 Now that you've caught up with ESO, 98 00:06:34,000 --> 00:06:38,000 head 'out of this world' with Hubble. 99 00:06:40,780 --> 00:06:42,660 The Hubblecast highlights the latest discoveries 100 00:06:42,660 --> 00:06:46,860 of the world´s most recognized and prized space observatory, 101 00:06:49,640 --> 00:06:53,050 The NASA/ESA Hubble Space Telescope.