1 00:00:01,920 --> 00:00:06,480 Speaker 1: Welcome to brain Stuff production of I Heart Radio. Hey 2 00:00:06,559 --> 00:00:09,360 Speaker 1: brain Stuff Lauren Vogbaum here with another classic from the 3 00:00:09,360 --> 00:00:12,399 Speaker 1: podcast archives. In this one, we take a look at 4 00:00:12,440 --> 00:00:16,079 Speaker 1: what turned out to be theoretical physicist Stephen Hawkings final 5 00:00:16,160 --> 00:00:22,200 Speaker 1: research paper about the multiverse. Hey brain Stuff, Lauren vog 6 00:00:22,239 --> 00:00:26,800 Speaker 1: Obam here. Days before his death, on March fourteen, famed 7 00:00:26,840 --> 00:00:31,040 Speaker 1: theoretical physicist and cosmologist Stephen Hawking completed what would be 8 00:00:31,160 --> 00:00:34,479 Speaker 1: his final research paper. It has since passed peer review 9 00:00:34,520 --> 00:00:36,920 Speaker 1: and was published online in the Journal of High Energy 10 00:00:36,960 --> 00:00:41,680 Speaker 1: Physics on April. Written with co author Thomas Hertog, a 11 00:00:41,800 --> 00:00:45,640 Speaker 1: theoretical physicist at the University of louisn Belgium, the paper 12 00:00:45,720 --> 00:00:48,920 Speaker 1: adds another facet to our understanding of this universe that 13 00:00:48,960 --> 00:00:53,199 Speaker 1: we live in, and needless to say, it's complicated. Titled 14 00:00:53,400 --> 00:00:57,440 Speaker 1: a Smooth Exit from Eternal Inflation, the publication discusses an 15 00:00:57,520 --> 00:01:01,760 Speaker 1: enigmatic problem facing cosmologists. But before we delve into the 16 00:01:01,800 --> 00:01:03,960 Speaker 1: crux of the study, let's go back to when our 17 00:01:04,040 --> 00:01:07,560 Speaker 1: universe was a baby, some thirteen point eight billion years ago. 18 00:01:08,880 --> 00:01:11,960 Speaker 1: A lot of evidence suggests that our universe originated from 19 00:01:11,959 --> 00:01:15,520 Speaker 1: a singularity, an infinitely dense point from which all the 20 00:01:15,600 --> 00:01:18,440 Speaker 1: universe as we know it was born. We call that 21 00:01:18,520 --> 00:01:21,880 Speaker 1: event the Big Bang. But how the Singularity came to 22 00:01:21,920 --> 00:01:24,600 Speaker 1: be and why the Big Bang happened isn't of concern 23 00:01:24,720 --> 00:01:28,080 Speaker 1: right now. We're interested in what happened immediately after our 24 00:01:28,160 --> 00:01:32,920 Speaker 1: universe was spawned, a period known as inflation. Cosmologists predict 25 00:01:33,000 --> 00:01:36,800 Speaker 1: that inflation occurred over a vanishingly small period right after 26 00:01:36,840 --> 00:01:39,920 Speaker 1: the Big Bang, during our universe's very first ten to 27 00:01:40,000 --> 00:01:44,960 Speaker 1: thirty two seconds. During inflation, the universe expanded exponentially and 28 00:01:45,240 --> 00:01:48,280 Speaker 1: much faster than the speed of light. After only a second, 29 00:01:48,480 --> 00:01:53,000 Speaker 1: the energy from this inconceivably gargantuan explosion condensed to form 30 00:01:53,240 --> 00:01:58,760 Speaker 1: sub atomic particles that, over millions of years, created the stars, galaxies, planets, and, 31 00:01:59,040 --> 00:02:01,840 Speaker 1: after another few years, a life as we know it. 32 00:02:02,680 --> 00:02:07,000 Speaker 1: Once this inflationary period ended, the universe's rate of expansion slowed, 33 00:02:07,200 --> 00:02:10,880 Speaker 1: but it continues to expand to this day. Because inflation 34 00:02:10,919 --> 00:02:14,880 Speaker 1: powered a faster than light speed expansion, the observable universe 35 00:02:14,919 --> 00:02:18,919 Speaker 1: that we see today is not the entire universe. Rather, 36 00:02:19,080 --> 00:02:22,079 Speaker 1: we exist inside a region of the cosmos that light 37 00:02:22,120 --> 00:02:25,200 Speaker 1: has had time to reach. It's like dropping a pebble 38 00:02:25,240 --> 00:02:28,520 Speaker 1: into a calm swimming pool, The first circular ripple to 39 00:02:28,560 --> 00:02:31,760 Speaker 1: propagate from the splash travels at a fixed speed across 40 00:02:31,800 --> 00:02:34,360 Speaker 1: the surface of the pool. If we imagine that the 41 00:02:34,400 --> 00:02:38,080 Speaker 1: limit of our observable universe is that ripple traveling across 42 00:02:38,080 --> 00:02:40,320 Speaker 1: the pool at the speed of light, it's not that 43 00:02:40,360 --> 00:02:44,440 Speaker 1: nothing exists beyond that ripple. There's more pool or universe 44 00:02:44,440 --> 00:02:47,960 Speaker 1: beyond it. We just can't see it yet. So the 45 00:02:48,040 --> 00:02:50,760 Speaker 1: consequence of inflation is that there should be a lot 46 00:02:50,840 --> 00:02:53,480 Speaker 1: more universe beyond what we can see, even with our 47 00:02:53,480 --> 00:02:57,640 Speaker 1: most powerful telescopes. And cosmologists have been grappling with the 48 00:02:57,639 --> 00:03:01,480 Speaker 1: possibility that our universe is not the only universe. In fact, 49 00:03:01,800 --> 00:03:03,919 Speaker 1: we could be nothing more than a single bubble in 50 00:03:04,000 --> 00:03:08,200 Speaker 1: an infinite, frothy ocean, a concept known as the multiverse. 51 00:03:08,840 --> 00:03:12,560 Speaker 1: The idea here is that inflation didn't happen once, It's 52 00:03:12,639 --> 00:03:16,679 Speaker 1: always happening via some infinitely vast chain reaction known as 53 00:03:16,960 --> 00:03:21,480 Speaker 1: eternal inflation. One universe will appear, and inflation will take over, 54 00:03:21,560 --> 00:03:24,679 Speaker 1: expanding that universe, and that universe will have its own 55 00:03:24,760 --> 00:03:28,000 Speaker 1: quantum instabilities that will spawn more singularities that go on 56 00:03:28,120 --> 00:03:32,080 Speaker 1: to create more universes. It's like blowing up a party 57 00:03:32,120 --> 00:03:35,320 Speaker 1: balloon that itself spawns many other party balloons that are 58 00:03:35,360 --> 00:03:38,520 Speaker 1: rupped from its rubbery surface, seemingly at random. If this 59 00:03:38,600 --> 00:03:43,320 Speaker 1: situation sounds chaotic, it is. Proponents of this hypothesis think 60 00:03:43,440 --> 00:03:48,760 Speaker 1: that eternal inflation is unstoppable, vastly complex, and continually generating 61 00:03:48,800 --> 00:03:52,440 Speaker 1: new universes, and the math of this situation suggests that 62 00:03:52,520 --> 00:03:56,360 Speaker 1: the multiverse acts like a fractal, fractals being sets of 63 00:03:56,440 --> 00:04:00,800 Speaker 1: data that contain repeating patterns at every scale. Visually, this 64 00:04:00,920 --> 00:04:03,560 Speaker 1: means that complex shapes look pretty much the same at 65 00:04:03,600 --> 00:04:06,240 Speaker 1: a wide range of scales, like a small piece of 66 00:04:06,240 --> 00:04:08,800 Speaker 1: it looks pretty similar to the whole structure. Think of 67 00:04:08,800 --> 00:04:11,880 Speaker 1: a head of cauliflower. Any given segment will resemble the 68 00:04:11,880 --> 00:04:14,760 Speaker 1: whole head, and if you zoom in further, each cluster 69 00:04:14,840 --> 00:04:19,080 Speaker 1: of buds resembles the larger segments. It's worth noting that 70 00:04:19,120 --> 00:04:22,040 Speaker 1: in this theory, each success of universe and the multiverse 71 00:04:22,120 --> 00:04:25,800 Speaker 1: doesn't likely share the same physics as our universe. One 72 00:04:25,920 --> 00:04:28,919 Speaker 1: universe might not have gravity, another may not support the 73 00:04:28,960 --> 00:04:32,240 Speaker 1: forces that hold matter together. There would be a lot 74 00:04:32,279 --> 00:04:35,720 Speaker 1: of stillborn universes that just don't amount too much. We 75 00:04:35,960 --> 00:04:38,280 Speaker 1: humans are simply lucky to have a universe that has 76 00:04:38,320 --> 00:04:41,640 Speaker 1: the right environment to create what we see, a philosophical 77 00:04:41,720 --> 00:04:45,760 Speaker 1: argument known as the anthropic principle. The problem with eternal 78 00:04:45,800 --> 00:04:48,680 Speaker 1: inflation is that it's messy and infinite, and that the 79 00:04:48,760 --> 00:04:54,040 Speaker 1: hypothesis is ultimately untestable. So what does Hawking and her 80 00:04:54,120 --> 00:04:58,839 Speaker 1: Tog's research have to do with this unrelenting multiverse In 81 00:04:58,880 --> 00:05:02,039 Speaker 1: the multiverse? Are you? Niverse is merely a pocket universe 82 00:05:02,040 --> 00:05:05,919 Speaker 1: where inflation has ended, and despite the odds, it found 83 00:05:06,040 --> 00:05:08,880 Speaker 1: enough calm to create a bounty of stars and galaxies 84 00:05:08,920 --> 00:05:11,280 Speaker 1: and a bunch of humans living on some random rock 85 00:05:11,400 --> 00:05:14,680 Speaker 1: pondering the cosmos. What's going on beyond our pocket of 86 00:05:14,760 --> 00:05:19,279 Speaker 1: calm is, however, somewhat different, Hawking said in an interview. 87 00:05:19,279 --> 00:05:24,039 Speaker 1: In the usual theory of eternal inflation predicts that globally, 88 00:05:24,120 --> 00:05:27,599 Speaker 1: our universe is like an infinite fractal with a mosaic 89 00:05:27,640 --> 00:05:31,880 Speaker 1: of different pocket universes separated by an inflating ocean. The 90 00:05:31,920 --> 00:05:34,520 Speaker 1: local laws of physics and chemistry can differ from one 91 00:05:34,520 --> 00:05:38,120 Speaker 1: pocket universe to another, which together would form a multiverse. 92 00:05:38,560 --> 00:05:40,720 Speaker 1: But I have never been a fan of the multiverse. 93 00:05:41,080 --> 00:05:43,640 Speaker 1: If the scale of different universes in the multiverse is 94 00:05:43,760 --> 00:05:47,800 Speaker 1: large or infinite, then the theory can't be tested. The problem, 95 00:05:47,880 --> 00:05:51,480 Speaker 1: according to Hawking in her Dog, allies with the incompatibility 96 00:05:51,560 --> 00:05:54,960 Speaker 1: of Einstein's general relativity that governs the evolution of the 97 00:05:55,040 --> 00:05:58,760 Speaker 1: universe and quantum mechanics that seeds the creation of new 98 00:05:58,839 --> 00:06:03,760 Speaker 1: universes through quantum fluctuations. The eternal inflation model of the multiverse, 99 00:06:03,920 --> 00:06:06,760 Speaker 1: as her Tog said in a press release quote, wipes 100 00:06:06,800 --> 00:06:10,880 Speaker 1: out separation between classical and quantum physics. As a consequence, 101 00:06:11,080 --> 00:06:15,640 Speaker 1: Einstein's theory breaks down in eternal inflation. Their study doesn't 102 00:06:15,640 --> 00:06:19,440 Speaker 1: go as far as reconciling general relativity with quantum physics, 103 00:06:19,480 --> 00:06:22,720 Speaker 1: a quest that has so far been unsuccessful, but they 104 00:06:22,880 --> 00:06:25,760 Speaker 1: use the math of string theory to help simplify the 105 00:06:25,839 --> 00:06:29,800 Speaker 1: multiverse model. A quick recap. String theory predicts that all 106 00:06:29,839 --> 00:06:32,960 Speaker 1: subtomic particles in our universe are in fact composed of 107 00:06:33,040 --> 00:06:37,280 Speaker 1: one dimensional strings that propagate through space. The vibrational state 108 00:06:37,320 --> 00:06:40,120 Speaker 1: of these strings is what gives these particles their quantum 109 00:06:40,160 --> 00:06:44,479 Speaker 1: state such as charge, spin, and mass. But string theory 110 00:06:44,560 --> 00:06:48,560 Speaker 1: also predicts the existence of the hypothetical graviton, a quantum 111 00:06:48,600 --> 00:06:51,560 Speaker 1: particle that carries the force of gravity. The math that 112 00:06:51,600 --> 00:06:54,640 Speaker 1: suggests that gravitons exist is solid, but no one's been 113 00:06:54,680 --> 00:06:57,960 Speaker 1: able to point to one yet. String theory would therefore 114 00:06:58,040 --> 00:07:02,880 Speaker 1: provide an explanation of how einstein general relativity gravity jibes 115 00:07:02,960 --> 00:07:07,440 Speaker 1: with quantum physics using the mathematical framework of string theory. 116 00:07:07,760 --> 00:07:11,640 Speaker 1: This final study from Hawking simplifies the multiverse. Hawking and 117 00:07:11,720 --> 00:07:14,680 Speaker 1: her dog used the string theory concept of holography to 118 00:07:14,760 --> 00:07:17,920 Speaker 1: reduce our three dimensional universe down to a two dimensional 119 00:07:18,200 --> 00:07:21,800 Speaker 1: surface from which the universe we know and love is projected. 120 00:07:22,440 --> 00:07:25,160 Speaker 1: By doing this, they were able to describe eternal inflation 121 00:07:25,320 --> 00:07:31,120 Speaker 1: without general relativity, creating a timeless state. Her dog explained 122 00:07:31,160 --> 00:07:33,880 Speaker 1: this move in a statement. When we trace the evolution 123 00:07:33,880 --> 00:07:36,520 Speaker 1: of our universe backwards in time, at some point we 124 00:07:36,600 --> 00:07:40,080 Speaker 1: arrive at the threshold of eternal inflation, where our familiar 125 00:07:40,120 --> 00:07:44,040 Speaker 1: notion of time ceases to have any meaning. The math 126 00:07:44,120 --> 00:07:47,680 Speaker 1: is complex, but the result is interesting. The calculations have 127 00:07:47,760 --> 00:07:51,320 Speaker 1: the effect of turning the infinite and fractal multiverse into 128 00:07:51,360 --> 00:07:56,240 Speaker 1: a far simpler and finite situation that eternal inflation does predict. 129 00:07:57,000 --> 00:07:59,800 Speaker 1: Hawking said this about it. We are not down to 130 00:07:59,840 --> 00:08:03,720 Speaker 1: a single, unique universe, but our findings imply a significant 131 00:08:03,720 --> 00:08:06,840 Speaker 1: reduction of the multiverse to a much smaller range of 132 00:08:06,880 --> 00:08:11,320 Speaker 1: possible universes. To put it in perspective, Hawking's final paper 133 00:08:11,400 --> 00:08:15,200 Speaker 1: doesn't revolutionize our understanding of how the universe and indeed 134 00:08:15,200 --> 00:08:18,440 Speaker 1: the multiverse works, but it is a valuable addition to 135 00:08:18,640 --> 00:08:22,720 Speaker 1: a huge field of theoretical work. Specifically, her Tug hopes 136 00:08:22,760 --> 00:08:25,560 Speaker 1: that this study may help a search for ancient gravitational 137 00:08:25,600 --> 00:08:29,480 Speaker 1: waves that were generated by eternal inflation. These ripples in 138 00:08:29,520 --> 00:08:32,840 Speaker 1: space time are far too weak for current gravitational wave 139 00:08:32,880 --> 00:08:37,079 Speaker 1: detectors to detect. However, we need to wait until advanced 140 00:08:37,120 --> 00:08:41,240 Speaker 1: space based observatories such as the European Space Agencies planned 141 00:08:41,360 --> 00:08:45,520 Speaker 1: LIESA mission are launched. Regardless of whether the study leads 142 00:08:45,559 --> 00:08:48,360 Speaker 1: to groundbreaking discoveries about the cosmos that we live in, 143 00:08:48,720 --> 00:08:51,840 Speaker 1: it's a testament to a great scientist who worked tirelessly 144 00:08:51,960 --> 00:08:54,720 Speaker 1: his entire life to answer some of the biggest questions 145 00:08:54,720 --> 00:08:58,600 Speaker 1: that humanity has pondered, and on Hawking's shoulders, other great 146 00:08:58,640 --> 00:09:01,520 Speaker 1: minds will build on this work to hopefully decipher whether 147 00:09:01,559 --> 00:09:04,400 Speaker 1: our universe is unique or if it's just one bubble 148 00:09:04,480 --> 00:09:13,320 Speaker 1: chaotically floating in the ocean of the multiverse. Today's episode 149 00:09:13,400 --> 00:09:16,319 Speaker 1: is based on the article Stephen Hawking's Last Paper Takes 150 00:09:16,320 --> 00:09:19,560 Speaker 1: on the Multiverse on Housetofworks dot com, written by Ian O'Neill. 151 00:09:20,200 --> 00:09:22,520 Speaker 1: Brain Stuff is production of I Heart Radio in partnership 152 00:09:22,520 --> 00:09:25,000 Speaker 1: with housetfworks dot com and it's produced by Tyler clang 153 00:09:25,640 --> 00:09:28,040 Speaker 1: Or more podcasts my heart Radio, visit the I heart 154 00:09:28,120 --> 00:09:30,720 Speaker 1: Radio app, Apple Podcasts, or wherever you listen to your 155 00:09:30,760 --> 00:09:31,480 Speaker 1: favorite shows.