WEBVTT 00:00:00.000 --> 00:00:13.000 (Music) 00:00:18.000 --> 00:00:20.000 Sometimes when I'm on a long plane flight, 00:00:20.000 --> 00:00:23.000 I gaze out at all those mountains and deserts 00:00:23.000 --> 00:00:26.000 and try to get my head around how vast our Earth is. 00:00:26.585 --> 00:00:29.000 And then I remember that there's an object we see every day 00:00:29.000 --> 00:00:32.692 that would literally fit one million Earths inside it. 00:00:32.815 --> 00:00:35.000 The sun seems impossibly big, 00:00:35.000 --> 00:00:39.077 but in the great scheme of things, it's a pinprick, 00:00:39.077 --> 00:00:43.000 one of about 400 billion stars in the Milky Way galaxy, 00:00:43.000 --> 00:00:45.123 which you can see on a clear night 00:00:45.123 --> 00:00:48.123 as a pale, white mist stretched across the sky. 00:00:48.123 --> 00:00:49.023 And it gets worse. 00:00:49.023 --> 00:00:52.985 There are maybe 100 billion galaxies detectable by our telescopes, 00:00:53.723 --> 00:00:58.000 so if each star was the size of a single grain of sand, 00:00:58.000 --> 00:01:01.000 just the Milky Way has enough stars to fill 00:01:01.000 --> 00:01:05.000 a 30 foot by 30 foot stretch of beach three feet deep with sand. 00:01:05.877 --> 00:01:08.615 And the entire Earth doesn't have enough beaches 00:01:08.615 --> 00:01:11.000 to represent the stars in the overall universe. 00:01:11.000 --> 00:01:15.000 Such a beach would continue for literally hundreds of millions of miles. 00:01:15.600 --> 00:01:19.000 Holy Stephen Hawking, that is a lot of stars. 00:01:19.862 --> 00:01:22.000 But he and other physicists now believe in 00:01:22.000 --> 00:01:25.000 a reality that is unimaginably bigger still. 00:01:26.138 --> 00:01:29.000 I mean, first of all, the 100 billion galaxies within range of our telescopes 00:01:29.000 --> 00:01:32.000 are probably a minuscule fraction of the total. 00:01:32.000 --> 00:01:35.000 Space itself is expanding 00:01:35.000 --> 00:01:38.000 at an accelerating pace. The vast majority of the galaxies 00:01:38.000 --> 00:01:41.000 are separating from us so fast 00:01:41.000 --> 00:01:43.000 that light from them may never reach us. 00:01:43.000 --> 00:01:46.000 Still, our physical reality here on Earth 00:01:46.000 --> 00:01:49.400 is intimately connected to those distant, invisible galaxies. 00:01:49.908 --> 00:01:52.000 We can think of them as part of our universe. 00:01:52.846 --> 00:01:55.000 They make up a single, giant edifice, 00:01:55.000 --> 00:01:58.000 obeying the same physical laws and all made from the same types of atoms, electrons, 00:01:58.000 --> 00:02:02.000 protons, quarks, neutrinos that make up you and me. 00:02:02.000 --> 00:02:05.000 However, recent theories in physics, 00:02:05.000 --> 00:02:07.000 including one called string theory, 00:02:07.000 --> 00:02:10.000 are now telling us there could be countless other universes, 00:02:10.000 --> 00:02:12.000 built on different types of particles, 00:02:12.000 --> 00:02:14.000 with different properties, obeying different laws. 00:02:14.831 --> 00:02:17.000 Most of these universes could never support life, 00:02:17.000 --> 00:02:20.000 and might flash in and out of existence in a nanosecond, 00:02:20.000 --> 00:02:22.446 but nonetheless, combined 00:02:22.446 --> 00:02:26.000 they make up a vast multiverse of possible universes. 00:02:26.000 --> 00:02:31.000 in up to 11 dimensions, featuring wonders beyond our wildest imagination. 00:02:31.000 --> 00:02:33.000 And the leading version of string theory 00:02:33.000 --> 00:02:36.000 predicts a multiverse made of up to 10 to the 500 universes. 00:02:37.031 --> 00:02:40.000 That's a one followed by 500 zeroes, 00:02:40.000 --> 00:02:44.000 a number so vast that if every atom in our observable universe 00:02:44.000 --> 00:02:46.000 had its own universe 00:02:46.985 --> 00:02:49.000 and all of the atoms in all of those universes 00:02:49.000 --> 00:02:51.000 each had their own universe, 00:02:52.000 --> 00:02:54.000 and you repeated that for two more cycles, 00:02:54.000 --> 00:02:57.000 you'd still be at a tiny fraction of the total -- 00:02:57.000 --> 00:03:05.985 namely, one trillion trillion trillion trillion trillion trillion trillion trillion trillion trillion trillion trillion trillion trillion trillionth. 00:03:07.585 --> 00:03:10.000 But even that number is minuscule compared to 00:03:10.000 --> 00:03:13.000 another number: infinity. 00:03:14.415 --> 00:03:16.000 Some physicists think the space-time continuum 00:03:16.000 --> 00:03:19.000 is literally infinite, and that it contains an infinite number 00:03:19.431 --> 00:03:22.000 of so-called pocket universes with varying properties. 00:03:22.231 --> 00:03:24.000 How's your brain doing? 00:03:24.862 --> 00:03:27.000 But quantum theory adds a whole new wrinkle. 00:03:27.000 --> 00:03:29.000 I mean, the theory's been proven true beyond all doubt, 00:03:29.000 --> 00:03:31.000 but interpreting it is baffling. 00:03:31.000 --> 00:03:34.000 And some physicists think you can only un-baffle it 00:03:34.000 --> 00:03:37.000 if you imagine that huge numbers of parallel universes 00:03:37.000 --> 00:03:39.000 are being spawned every moment, 00:03:39.000 --> 00:03:43.000 and many of these universes would actually be very like the world we're in, 00:03:43.000 --> 00:03:46.000 would include multiple copies of you. 00:03:46.000 --> 00:03:50.000 In one such universe, you'd graduate with honors and marry the person of your dreams. 00:03:50.000 --> 00:03:53.000 In another, not so much. 00:03:53.000 --> 00:03:55.000 There are still some scientists who would say, hogwash. 00:03:55.000 --> 00:03:59.000 The only meaningful answer to the question of how many universes there are is one, 00:03:59.000 --> 00:04:02.000 only one universe. 00:04:02.538 --> 00:04:05.000 And a few philosophers and mystics 00:04:05.000 --> 00:04:08.000 might argue that even our own universe is an illusion. 00:04:08.000 --> 00:04:10.000 So, as you can see, 00:04:10.000 --> 00:04:13.000 right now there is no agreement on this question, 00:04:13.000 --> 00:04:14.000 not even close. 00:04:14.000 --> 00:04:18.000 All we know is, the answer is somewhere between zero and infinity. 00:04:18.769 --> 00:04:21.000 Well, I guess we know one other thing: 00:04:21.000 --> 00:04:24.000 This is a pretty cool time to be studying physics. 00:04:25.200 --> 00:04:27.000 We just might be undergoing 00:04:27.000 --> 00:04:31.000 the biggest paradigm shift in knowledge that humanity has ever seen.