1 00:00:00,000 --> 00:00:13,000 (Music) 2 00:00:18,000 --> 00:00:20,000 Sometimes when I'm on a long plane flight, 3 00:00:20,000 --> 00:00:23,000 I gaze out at all those mountains and deserts 4 00:00:23,000 --> 00:00:26,000 and try to get my head around how vast our Earth is. 5 00:00:26,585 --> 00:00:29,000 And then I remember that there's an object we see every day 6 00:00:29,000 --> 00:00:32,692 that would literally fit one million Earths inside it. 7 00:00:32,815 --> 00:00:35,000 The sun seems impossibly big, 8 00:00:35,000 --> 00:00:39,077 but in the great scheme of things, it's a pinprick, 9 00:00:39,077 --> 00:00:43,000 one of about 400 billion stars in the Milky Way galaxy, 10 00:00:43,000 --> 00:00:45,123 which you can see on a clear night 11 00:00:45,123 --> 00:00:48,123 as a pale, white mist stretched across the sky. 12 00:00:48,123 --> 00:00:49,023 And it gets worse. 13 00:00:49,023 --> 00:00:52,985 There are maybe 100 billion galaxies detectable by our telescopes, 14 00:00:53,723 --> 00:00:58,000 so if each star was the size of a single grain of sand, 15 00:00:58,000 --> 00:01:01,000 just the Milky Way has enough stars to fill 16 00:01:01,000 --> 00:01:05,000 a 30 foot by 30 foot stretch of beach three feet deep with sand. 17 00:01:05,877 --> 00:01:08,615 And the entire Earth doesn't have enough beaches 18 00:01:08,615 --> 00:01:11,000 to represent the stars in the overall universe. 19 00:01:11,000 --> 00:01:15,000 Such a beach would continue for literally hundreds of millions of miles. 20 00:01:15,600 --> 00:01:19,000 Holy Stephen Hawking, that is a lot of stars. 21 00:01:19,862 --> 00:01:22,000 But he and other physicists now believe in 22 00:01:22,000 --> 00:01:25,000 a reality that is unimaginably bigger still. 23 00:01:26,138 --> 00:01:29,000 I mean, first of all, the 100 billion galaxies within range of our telescopes 24 00:01:29,000 --> 00:01:32,000 are probably a minuscule fraction of the total. 25 00:01:32,000 --> 00:01:35,000 Space itself is expanding 26 00:01:35,000 --> 00:01:38,000 at an accelerating pace. The vast majority of the galaxies 27 00:01:38,000 --> 00:01:41,000 are separating from us so fast 28 00:01:41,000 --> 00:01:43,000 that light from them may never reach us. 29 00:01:43,000 --> 00:01:46,000 Still, our physical reality here on Earth 30 00:01:46,000 --> 00:01:49,400 is intimately connected to those distant, invisible galaxies. 31 00:01:49,908 --> 00:01:52,000 We can think of them as part of our universe. 32 00:01:52,846 --> 00:01:55,000 They make up a single, giant edifice, 33 00:01:55,000 --> 00:01:58,000 obeying the same physical laws and all made from the same types of atoms, electrons, 34 00:01:58,000 --> 00:02:02,000 protons, quarks, neutrinos that make up you and me. 35 00:02:02,000 --> 00:02:05,000 However, recent theories in physics, 36 00:02:05,000 --> 00:02:07,000 including one called string theory, 37 00:02:07,000 --> 00:02:10,000 are now telling us there could be countless other universes, 38 00:02:10,000 --> 00:02:12,000 built on different types of particles, 39 00:02:12,000 --> 00:02:14,000 with different properties, obeying different laws. 40 00:02:14,831 --> 00:02:17,000 Most of these universes could never support life, 41 00:02:17,000 --> 00:02:20,000 and might flash in and out of existence in a nanosecond, 42 00:02:20,000 --> 00:02:22,446 but nonetheless, combined 43 00:02:22,446 --> 00:02:26,000 they make up a vast multiverse of possible universes. 44 00:02:26,000 --> 00:02:31,000 in up to 11 dimensions, featuring wonders beyond our wildest imagination. 45 00:02:31,000 --> 00:02:33,000 And the leading version of string theory 46 00:02:33,000 --> 00:02:36,000 predicts a multiverse made of up to 10 to the 500 universes. 47 00:02:37,031 --> 00:02:40,000 That's a one followed by 500 zeroes, 48 00:02:40,000 --> 00:02:44,000 a number so vast that if every atom in our observable universe 49 00:02:44,000 --> 00:02:46,000 had its own universe 50 00:02:46,985 --> 00:02:49,000 and all of the atoms in all of those universes 51 00:02:49,000 --> 00:02:51,000 each had their own universe, 52 00:02:52,000 --> 00:02:54,000 and you repeated that for two more cycles, 53 00:02:54,000 --> 00:02:57,000 you'd still be at a tiny fraction of the total -- 54 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. 55 00:03:07,585 --> 00:03:10,000 But even that number is minuscule compared to 56 00:03:10,000 --> 00:03:13,000 another number: infinity. 57 00:03:14,415 --> 00:03:16,000 Some physicists think the space-time continuum 58 00:03:16,000 --> 00:03:19,000 is literally infinite, and that it contains an infinite number 59 00:03:19,431 --> 00:03:22,000 of so-called pocket universes with varying properties. 60 00:03:22,231 --> 00:03:24,000 How's your brain doing? 61 00:03:24,862 --> 00:03:27,000 But quantum theory adds a whole new wrinkle. 62 00:03:27,000 --> 00:03:29,000 I mean, the theory's been proven true beyond all doubt, 63 00:03:29,000 --> 00:03:31,000 but interpreting it is baffling. 64 00:03:31,000 --> 00:03:34,000 And some physicists think you can only un-baffle it 65 00:03:34,000 --> 00:03:37,000 if you imagine that huge numbers of parallel universes 66 00:03:37,000 --> 00:03:39,000 are being spawned every moment, 67 00:03:39,000 --> 00:03:43,000 and many of these universes would actually be very like the world we're in, 68 00:03:43,000 --> 00:03:46,000 would include multiple copies of you. 69 00:03:46,000 --> 00:03:50,000 In one such universe, you'd graduate with honors and marry the person of your dreams. 70 00:03:50,000 --> 00:03:53,000 In another, not so much. 71 00:03:53,000 --> 00:03:55,000 There are still some scientists who would say, hogwash. 72 00:03:55,000 --> 00:03:59,000 The only meaningful answer to the question of how many universes there are is one, 73 00:03:59,000 --> 00:04:02,000 only one universe. 74 00:04:02,538 --> 00:04:05,000 And a few philosophers and mystics 75 00:04:05,000 --> 00:04:08,000 might argue that even our own universe is an illusion. 76 00:04:08,000 --> 00:04:10,000 So, as you can see, 77 00:04:10,000 --> 00:04:13,000 right now there is no agreement on this question, 78 00:04:13,000 --> 00:04:14,000 not even close. 79 00:04:14,000 --> 00:04:18,000 All we know is, the answer is somewhere between zero and infinity. 80 00:04:18,769 --> 00:04:21,000 Well, I guess we know one other thing: 81 00:04:21,000 --> 00:04:24,000 This is a pretty cool time to be studying physics. 82 00:04:25,200 --> 00:04:27,000 We just might be undergoing 83 00:04:27,000 --> 00:04:31,000 the biggest paradigm shift in knowledge that humanity has ever seen.