0 00:00:11,511 --> 00:00:17,677 Imagine somewhere in our universe an utterly strange world. 1 00:00:19,853 --> 00:00:24,017 A place where time could both speed up and slow down. 2 00:00:25,458 --> 00:00:29,224 From where we could journey into the past, and the future. 3 00:00:30,764 --> 00:00:34,165 Somewhere time could even split in two. 4 00:00:39,139 --> 00:00:42,540 Incredibly, this is no alien world. 5 00:00:42,842 --> 00:00:44,503 It's our world. 6 00:00:45,011 --> 00:00:46,774 And it's all around us. 7 00:00:48,481 --> 00:00:50,244 Now, for the first time, 8 00:00:50,316 --> 00:00:54,446 science is enabling us to see what for thousands of years 9 00:00:54,521 --> 00:00:55,749 has remained hidden. 10 00:00:57,223 --> 00:01:00,021 The true nature of time. 11 00:01:31,257 --> 00:01:33,953 We live in a world governed by time. 12 00:01:34,994 --> 00:01:38,760 From the tiniest of cells to the most distant of stars 13 00:01:38,898 --> 00:01:43,528 our entire universe is subject to the beat of a constant clock. 14 00:01:47,607 --> 00:01:50,701 And because time is everywhere, we think we know it. 15 00:01:51,978 --> 00:01:55,175 We know that it's regular and it moves in one direction. 16 00:01:56,349 --> 00:01:59,113 We know that it's universal and eternal. 17 00:02:00,487 --> 00:02:04,082 And we know that it never ever stands still. 18 00:02:06,826 --> 00:02:09,226 But how can we be so sure? 19 00:02:10,063 --> 00:02:14,557 How much of what we think we know about time is really true? 20 00:02:18,371 --> 00:02:19,565 In this programme 21 00:02:19,639 --> 00:02:22,904 I want to get to the bottom of what time really is. 22 00:02:23,243 --> 00:02:27,907 And in doing so I'll be challenging some of our most cherished beliefs. 23 00:02:30,483 --> 00:02:32,348 As a theoretical physicist 24 00:02:32,485 --> 00:02:34,282 it's this hidden time 25 00:02:34,387 --> 00:02:35,945 that has always fascinated me 26 00:02:36,022 --> 00:02:38,286 throughout most of my professional career. 27 00:02:39,125 --> 00:02:42,424 I'm going to explore the very limits of our universe 28 00:02:42,695 --> 00:02:46,187 in order to uncover just what time really is. 29 00:02:46,633 --> 00:02:48,123 And in the process 30 00:02:48,201 --> 00:02:50,692 I'll be revealing an astonishing secret. 31 00:02:51,137 --> 00:02:54,300 Nothing less than our ultimate destiny. 32 00:02:54,541 --> 00:02:58,568 The future of the universe and the fate of time itself. 33 00:03:16,629 --> 00:03:19,029 Of all our assumptions about time 34 00:03:19,098 --> 00:03:22,295 one of the most obvious is that time is regular. 35 00:03:24,671 --> 00:03:27,538 That a minute will always be a minute. 36 00:03:28,575 --> 00:03:31,009 For everyone, everywhere. 37 00:03:32,178 --> 00:03:33,509 Here in the Swiss Alps 38 00:03:33,580 --> 00:03:37,311 I'm searching for a something that challenges this assumption. 39 00:03:37,450 --> 00:03:41,409 Something that if time was as regular as we think it is, 40 00:03:41,487 --> 00:03:42,977 shouldn't exist at all. 41 00:04:10,083 --> 00:04:14,816 Well, I'm now eleven thousand feet above sea level 42 00:04:14,887 --> 00:04:18,618 and I'm out of breath and actually feeling a little bit dizzy. 43 00:04:19,425 --> 00:04:21,017 Now the bad news is 44 00:04:21,394 --> 00:04:24,727 I till have a ways to go to reach the top of the Alps 45 00:04:25,365 --> 00:04:28,391 because what I'm looking for is something 46 00:04:28,468 --> 00:04:31,494 that becomes more plentiful the higher you go. 47 00:04:50,923 --> 00:04:53,448 And this is what I've come to see. 48 00:04:53,793 --> 00:04:55,556 It's a particle counter 49 00:04:55,695 --> 00:05:01,258 telling me that the air around me is full of tiny particles called muons. 50 00:05:03,303 --> 00:05:06,170 They come from all the way out there. 51 00:05:12,278 --> 00:05:14,872 Muons are short lived particles, 52 00:05:15,915 --> 00:05:20,511 formed when cosmic rays from space collide with the upper atmosphere. 53 00:05:26,025 --> 00:05:31,053 But the big mystery is how they come to be down here on Earth. 54 00:05:33,466 --> 00:05:37,368 Because with a lifespan ofjust two millionths of a second, 55 00:05:37,637 --> 00:05:42,597 muons should only live long enough to travel a few hundred metres. 56 00:05:43,676 --> 00:05:48,238 And yet, here they are, after ajourney of several miles. 57 00:05:48,348 --> 00:05:51,078 Something that shouldn't be possible. 58 00:05:52,785 --> 00:05:55,652 So what exactly is going on? 59 00:05:56,689 --> 00:05:58,156 The answer to this mystery, 60 00:05:58,224 --> 00:06:00,954 the reason why muons can reach us at all 61 00:06:01,127 --> 00:06:02,924 is so extraordinary 62 00:06:02,995 --> 00:06:05,429 that from the moment it was first proposed 63 00:06:05,498 --> 00:06:08,194 it literally rewrote the rule book of time. 64 00:06:26,886 --> 00:06:32,017 Less than a hundred miles from the Alps lies the affluent city of Berne. 65 00:06:35,061 --> 00:06:36,961 In the early 1900s 66 00:06:37,029 --> 00:06:39,691 this was home to a young German physicist 67 00:06:39,766 --> 00:06:44,066 who would change the way we looked at time for ever. 68 00:06:45,972 --> 00:06:48,099 His name was Albert Einstein 69 00:06:48,274 --> 00:06:51,209 and he's been my hero for the past fifty years. 70 00:06:55,181 --> 00:06:56,749 In 1905 71 00:06:56,749 --> 00:06:59,377 in this, his first floor apartment, 72 00:06:59,452 --> 00:07:03,513 Albert Einstein put the finishing touches to his radical new theory. 73 00:07:05,658 --> 00:07:07,250 Special Relativity. 74 00:07:10,530 --> 00:07:14,762 One of five papers published by Einstein in 1905, 75 00:07:14,834 --> 00:07:16,301 Special Relativity 76 00:07:16,369 --> 00:07:20,703 would make us think about time in a completely new way. 77 00:07:33,619 --> 00:07:38,249 Einstein's astonishing claim was that time was not regular at all. 78 00:07:39,959 --> 00:07:42,052 It could beat at different rates. 79 00:07:42,728 --> 00:07:47,028 Time changes depending on relative speed. 80 00:07:53,840 --> 00:07:55,364 Imagine for a minute 81 00:07:55,441 --> 00:07:59,468 that my tram is capable of travelling at phenomenal speed. 82 00:08:00,279 --> 00:08:03,407 Just a fraction less than the speed of light. 83 00:08:06,319 --> 00:08:08,150 According to Special Relativity, 84 00:08:08,221 --> 00:08:11,349 the rate at which time flowed on this speeding tram 85 00:08:11,424 --> 00:08:13,984 would depend on whether you were onboard. 86 00:08:15,094 --> 00:08:17,119 Or looking in from the outside. 87 00:08:19,699 --> 00:08:21,166 So while for me 88 00:08:21,234 --> 00:08:24,067 it would seem as though time was passing perfectly normally. 89 00:08:26,939 --> 00:08:29,169 For me, sitting on the pavement, 90 00:08:29,242 --> 00:08:32,211 assuming I could somehow peer inside the tram, 91 00:08:32,278 --> 00:08:35,338 time would assume a totally different quality. 92 00:08:40,253 --> 00:08:42,118 Looking in from the outside 93 00:08:42,188 --> 00:08:46,249 I'd sense that time onboard the tram was passing much more slowly. 94 00:08:48,160 --> 00:08:50,651 That's because, according to Einstein, 95 00:08:50,763 --> 00:08:52,754 the faster an object moves 96 00:08:52,832 --> 00:08:54,493 the slower its time will run 97 00:08:54,567 --> 00:08:57,263 to someone observing from the sidelines. 98 00:08:58,638 --> 00:09:01,436 In other words, time can vary. 99 00:09:01,874 --> 00:09:04,138 It's all a matter of speed. 100 00:09:06,312 --> 00:09:11,648 And that explains the mystery of how our muons reached the Earth. 101 00:09:16,556 --> 00:09:20,993 Because muons travel near the speed of light relative to the Earth, 102 00:09:21,060 --> 00:09:22,618 their clocks have slowed down. 103 00:09:22,929 --> 00:09:27,832 So much so that they exist long enough to reach the Earth and be detected. 104 00:09:29,969 --> 00:09:32,733 Time for our muons has stretched. 105 00:09:33,039 --> 00:09:36,497 It beats very differently to the way it does for us. 106 00:09:48,287 --> 00:09:51,347 Now the effects of Special Relativity are so small 107 00:09:51,424 --> 00:09:54,120 that they have no impact on our daily lives, 108 00:09:54,360 --> 00:09:58,194 but the fact that they are there at all has changed everything. 109 00:09:58,664 --> 00:10:00,427 Because if time is relative, 110 00:10:00,666 --> 00:10:02,133 if time is flexible, 111 00:10:02,602 --> 00:10:06,504 then our belief in the immutability of time is wrong. 112 00:10:07,340 --> 00:10:10,002 And if we can be wrong about something as basic 113 00:10:10,076 --> 00:10:12,306 and as fundamental as this, 114 00:10:12,411 --> 00:10:15,710 then in what other ways might we be mistaken? 115 00:10:26,392 --> 00:10:27,723 Do either of you play cards? 116 00:10:28,461 --> 00:10:29,553 I play a little poker. 117 00:10:29,629 --> 00:10:30,527 You play poker? 118 00:10:30,596 --> 00:10:31,790 So you can shuffle cards, can you? 119 00:10:31,864 --> 00:10:32,990 - Oh no, no. - No? 120 00:10:33,065 --> 00:10:34,862 - I let someone else shuffle. - So do you shuffle like this? 121 00:10:35,001 --> 00:10:35,695 - Yeah. - Yeah? 122 00:10:35,768 --> 00:10:37,201 - That's called the overhand shuffle. - Okay. 123 00:10:37,269 --> 00:10:38,827 'Cause if you don't shuffle cards that well, 124 00:10:39,238 --> 00:10:40,933 you can try - try this one. This one's pretty good. 125 00:10:41,073 --> 00:10:42,700 It makes a complete mess of the deck of cards. 126 00:10:42,775 --> 00:10:45,369 Some cards go back to face and some of them are like back to back. 127 00:10:45,878 --> 00:10:48,745 Our complete trust in temporal orderis 128 00:10:48,814 --> 00:10:50,509 the reason why we delight 129 00:10:50,583 --> 00:10:53,484 in the obvious impossibility of magic tricks. 130 00:10:53,753 --> 00:10:55,220 Back to face, the face to back. 131 00:10:55,488 --> 00:10:57,115 As I said it makes a total mess. 132 00:10:57,657 --> 00:10:58,453 I'll just show you. 133 00:10:58,758 --> 00:11:00,749 Some of the cards there like face to back 134 00:11:00,826 --> 00:11:02,851 not very good for playing poker or blackjack 135 00:11:03,162 --> 00:11:04,322 but if you press the button here. 136 00:11:04,397 --> 00:11:05,694 Press the button. 137 00:11:05,765 --> 00:11:06,663 Oh... fingers, 138 00:11:07,033 --> 00:11:08,898 they call come out the right way which is rather handy. 139 00:11:08,968 --> 00:11:11,095 - Oh, that's so good. - That's pretty cool, isn't it? 140 00:11:11,170 --> 00:11:11,932 Pretty good. 141 00:11:13,005 --> 00:11:14,165 My job as a magician 142 00:11:14,407 --> 00:11:16,068 is to manipulate people's faith. 143 00:11:16,976 --> 00:11:18,443 Hi, how you doing? 144 00:11:18,811 --> 00:11:19,641 Can I stop you for a moment? 145 00:11:19,712 --> 00:11:22,408 People realise that things can't disappear and reappear. 146 00:11:22,481 --> 00:11:25,541 I'm going to run through the cards and you say stop wherever you like. 147 00:11:25,618 --> 00:11:26,516 If you do yourjob properly 148 00:11:26,686 --> 00:11:29,416 you can make it look as though two things can be in the same place 149 00:11:29,488 --> 00:11:30,420 at the same time. 150 00:11:32,558 --> 00:11:33,718 And to that end essentially 151 00:11:33,793 --> 00:11:36,261 you can make it look as though you're manipulating space and time. 152 00:11:37,630 --> 00:11:38,995 You ever seen magicians use these before? 153 00:11:39,065 --> 00:11:40,089 Yeah, I've seen them. 154 00:11:40,766 --> 00:11:42,324 I'll show you a trick with two of them, okay. 155 00:11:42,401 --> 00:11:43,629 - So can you hold your hand out for me? - Yeah, sure. 156 00:11:44,670 --> 00:11:47,503 A classic way of demonstrating the manipulation of space and time 157 00:11:47,573 --> 00:11:49,666 can be done using the sponge ball trick. 158 00:11:49,909 --> 00:11:51,968 It's a hundred years old, but it's great. 159 00:11:53,045 --> 00:11:55,775 But essentially you take a ball in your own hand 160 00:11:56,015 --> 00:11:58,347 and the spectator holds a ball 161 00:11:58,417 --> 00:11:59,611 and you can do it in such a way 162 00:11:59,685 --> 00:12:02,085 that you can - it looks as though you can manipulate space of time 163 00:12:02,154 --> 00:12:04,349 and it looks as though the ball has disappeared from your hand, 164 00:12:04,623 --> 00:12:07,421 so when the spectator opens their hand suddenly they have two. 165 00:12:07,493 --> 00:12:10,553 That ball has vanished from your hand and it's reappeared in theirs. 166 00:12:13,299 --> 00:12:14,960 But, believe it or not, 167 00:12:15,034 --> 00:12:18,197 this sort of behaviour isn't always an illusion. 168 00:12:18,671 --> 00:12:21,640 Beneath the surface of our on sense world 169 00:12:21,707 --> 00:12:23,732 lies another world 170 00:12:24,176 --> 00:12:26,667 where magical things really do happen. 171 00:12:27,279 --> 00:12:29,804 Where the impossible can be made real. 172 00:12:30,249 --> 00:12:34,310 And where time can perform the most incredible tricks. 173 00:12:37,990 --> 00:12:41,221 That place is inside the atom. 174 00:12:43,929 --> 00:12:44,759 For years 175 00:12:44,830 --> 00:12:47,162 scientists had assumed that in our universe 176 00:12:47,233 --> 00:12:49,565 there was nothing smaller than an atom. 177 00:12:50,069 --> 00:12:54,335 The very word atom in fact comes from the Greek word for indivisible. 178 00:12:54,774 --> 00:12:56,867 Then in 1897, 179 00:12:56,942 --> 00:13:01,276 an Englishman named J. J. Thompson made an astounding discovery, 180 00:13:01,347 --> 00:13:03,178 that inside the atom 181 00:13:03,249 --> 00:13:06,685 there were even smaller particles called electrons. 182 00:13:07,253 --> 00:13:12,213 Thompson's discovery opened the door to the amazing world inside the atom. 183 00:13:12,591 --> 00:13:14,320 A world where everything, 184 00:13:14,393 --> 00:13:15,655 including time, 185 00:13:15,728 --> 00:13:18,595 behaves in a truly alien fashion. 186 00:13:29,074 --> 00:13:30,803 Physicist lan Walmsley 187 00:13:30,876 --> 00:13:35,506 has been studying this microscopic world for almost thirty years. 188 00:13:37,283 --> 00:13:41,720 When we get inside the atom to this world of subatomic particles 189 00:13:42,254 --> 00:13:44,518 the ideas that we have about the way the world 190 00:13:44,590 --> 00:13:46,455 works completely have to change. 191 00:13:46,525 --> 00:13:48,584 We can't think in the same sorts of 192 00:13:48,661 --> 00:13:51,858 come on sense terms that we think of in everyday experience. 193 00:13:56,435 --> 00:14:00,428 In fact, this subatomic universe is so strange 194 00:14:00,506 --> 00:14:02,667 that time becomes chaotic. 195 00:14:04,210 --> 00:14:08,340 A startling discovery that emerged from the study of light. 196 00:14:12,952 --> 00:14:17,685 Light consists of individual particles called photons, 197 00:14:18,057 --> 00:14:20,582 known for their wave-like properties. 198 00:14:22,828 --> 00:14:25,262 Waves have a very interesting sort of phenomenon. 199 00:14:25,331 --> 00:14:26,798 It's called 'interference.' 200 00:14:29,668 --> 00:14:31,602 When two waves come together 201 00:14:31,704 --> 00:14:34,104 they can add together and reinforce one another, 202 00:14:34,173 --> 00:14:37,006 or they can cancel one another out. 203 00:14:37,209 --> 00:14:40,701 And this interference is a ubiquitous property of all waves, 204 00:14:40,779 --> 00:14:42,041 notjust water waves 205 00:14:42,114 --> 00:14:43,081 but also light waves. 206 00:14:45,251 --> 00:14:47,310 But in the early 1900s, 207 00:14:47,453 --> 00:14:51,184 scientists noticed something very odd about these light waves. 208 00:14:51,857 --> 00:14:55,486 Something that proves that time isn't always ordered. 209 00:14:59,965 --> 00:15:02,900 In this reworking of a classic experiment, 210 00:15:02,968 --> 00:15:06,267 once described as 'the most beautiful in physics,' 211 00:15:06,572 --> 00:15:09,769 single photons or particles of light 212 00:15:09,842 --> 00:15:13,073 are fired down a darkened tube towards a camera, 213 00:15:13,379 --> 00:15:14,869 one at a time. 214 00:15:16,115 --> 00:15:18,140 So we have here a very simple apparatus. 215 00:15:18,350 --> 00:15:21,410 It consists of a light bulb at this end 216 00:15:21,553 --> 00:15:25,216 and a camera at the other end that can register the light 217 00:15:25,291 --> 00:15:26,315 and in between 218 00:15:26,625 --> 00:15:32,393 the light encounters a pair of slits etched onto this piece of glass 219 00:15:32,765 --> 00:15:35,632 through which the photons can pass 220 00:15:35,901 --> 00:15:39,268 on their way from the source to the camera. 221 00:15:41,040 --> 00:15:42,871 The purpose of the experiment 222 00:15:42,942 --> 00:15:45,172 is to study the behaviour of photons 223 00:15:45,244 --> 00:15:48,236 as they travel from one end of the tube to the other. 224 00:15:49,214 --> 00:15:50,238 To begin with, 225 00:15:50,316 --> 00:15:53,945 the individual photons are sent through just one of the slits. 226 00:15:55,120 --> 00:15:57,054 Each of these dots 227 00:15:57,122 --> 00:16:00,649 arriving represents a single photon 228 00:16:01,293 --> 00:16:03,386 so most of them are coming along this point, 229 00:16:03,796 --> 00:16:06,287 some of them lie above or below that point, 230 00:16:06,398 --> 00:16:08,298 but the distribution is nice and smooth. 231 00:16:09,335 --> 00:16:13,999 Now the second slit is opened up and the experiment repeated. 232 00:16:14,373 --> 00:16:19,242 Each single photon must still pass through one of the two slits, 233 00:16:19,645 --> 00:16:22,011 so the results should still be the same. 234 00:16:22,514 --> 00:16:24,106 Classical logic would say 235 00:16:24,183 --> 00:16:26,174 that what we would get when we open both slits 236 00:16:26,251 --> 00:16:28,981 is just the sum of these two detection patterns. 237 00:16:30,856 --> 00:16:33,347 But what we actually find is this. 238 00:16:34,860 --> 00:16:36,623 An interference pattern. 239 00:16:37,329 --> 00:16:39,889 Something that should be impossible. 240 00:16:41,200 --> 00:16:45,694 What that implies is that the single photon 241 00:16:45,771 --> 00:16:48,672 is somehow going through both slits at the same time. 242 00:16:48,741 --> 00:16:51,403 It's not making a choice as to go through one or the other, 243 00:16:51,477 --> 00:16:53,638 but is going through both simultaneously. 244 00:16:54,813 --> 00:16:56,212 In other words, 245 00:16:56,281 --> 00:16:59,717 each photon exists notjust in two places, 246 00:16:59,785 --> 00:17:02,345 but also in two times. 247 00:17:02,654 --> 00:17:04,918 So we have this very strange notion 248 00:17:05,591 --> 00:17:07,752 that this single photon can be 249 00:17:07,826 --> 00:17:10,727 in two different places at once. It could be delocalised. 250 00:17:11,930 --> 00:17:17,630 But we can think also of a single photon being in two different times. 251 00:17:17,936 --> 00:17:22,202 So both space and time have become delocalised and fragmented. 252 00:17:27,346 --> 00:17:30,679 On the surface, we feel time is ordered. 253 00:17:31,150 --> 00:17:33,948 But that belies a different reality. 254 00:17:35,087 --> 00:17:37,453 We are totally unaware of the chaos 255 00:17:37,523 --> 00:17:41,186 and unpredictability that lies deep within the atom. 256 00:17:41,493 --> 00:17:42,755 Not surprisingly, 257 00:17:42,828 --> 00:17:46,924 our understanding of time comes from our everyday experience. 258 00:17:48,801 --> 00:17:50,132 And it's for this reason 259 00:17:50,202 --> 00:17:54,161 that we cling to yet another of our assumptions about time. 260 00:17:54,873 --> 00:17:56,670 That it never stands still. 261 00:17:58,343 --> 00:18:01,972 In fact one thing that sets us apart as humans 262 00:18:02,047 --> 00:18:05,278 is the knowledge that time waits for no man. 263 00:18:05,684 --> 00:18:09,552 That time doesn't merely exist but is constantly flowing. 264 00:18:11,223 --> 00:18:15,387 But one discovery proved that this isn't always the case. 265 00:18:25,370 --> 00:18:27,895 TV Doctor Tom Bolton of the University of Toronto 266 00:18:27,973 --> 00:18:31,272 made more than forty observations of Cygnus X One. 267 00:18:33,545 --> 00:18:35,342 In 1971 268 00:18:35,414 --> 00:18:38,611 astronomer Tom Bolton embarked on a project 269 00:18:38,684 --> 00:18:43,451 to observe a mysterious x-ray source called Cygnus X One. 270 00:18:45,090 --> 00:18:49,049 An object assumed to be a distant neutron star. 271 00:18:51,029 --> 00:18:52,519 I started to look at Cygnus X One 272 00:18:52,598 --> 00:18:54,498 because I thought it would be a 273 00:18:54,566 --> 00:18:58,502 good opportunity to determine the mass of a neutron star 274 00:18:59,638 --> 00:19:02,072 and nobody had done that yet. 275 00:19:03,142 --> 00:19:04,541 Cygnus X One, 276 00:19:04,610 --> 00:19:07,272 some eight thousand light years away, 277 00:19:07,346 --> 00:19:10,372 is one half of what's called our binary system. 278 00:19:11,783 --> 00:19:16,083 The binary system is a pair of stars 279 00:19:16,155 --> 00:19:18,623 that are gravitationally bound to each other, 280 00:19:18,757 --> 00:19:21,453 er, just like the Earth is bound to the sun 281 00:19:21,527 --> 00:19:27,397 and they orbit er, about their mutual centre of mass. 282 00:19:28,667 --> 00:19:32,933 By measuring the speed and orbit of X One's binary partner, 283 00:19:33,038 --> 00:19:36,701 Tom was able to work out the mass of his neutron star. 284 00:19:37,743 --> 00:19:40,541 But the figure he arrived at was far, 285 00:19:40,612 --> 00:19:43,513 far bigger than the one he'd been expecting. 286 00:19:44,883 --> 00:19:48,819 That turned out to be about ten solar masses, 287 00:19:48,887 --> 00:19:50,912 with a significant error, 288 00:19:51,123 --> 00:19:54,650 but still way too big to be a neutron star. 289 00:19:56,295 --> 00:19:58,820 So I had to start thinking about 290 00:19:58,897 --> 00:20:01,832 what are the alternatives if it's not a neutron star. 291 00:20:03,702 --> 00:20:07,160 There was only one possibility that fitted the data. 292 00:20:08,207 --> 00:20:12,234 But it was something that few people believed actually existed. 293 00:20:13,178 --> 00:20:14,668 As far as I knew 294 00:20:14,813 --> 00:20:18,214 the only object that would fit that description 295 00:20:18,283 --> 00:20:20,513 and produce x-rays was a black hole. 296 00:20:21,453 --> 00:20:23,421 So I said so. 297 00:20:25,591 --> 00:20:28,788 Tom's discovery caused a sensation. 298 00:20:30,162 --> 00:20:32,858 The first incontrovertible proof 299 00:20:32,931 --> 00:20:36,230 that far from being a figment of people's imagination, 300 00:20:36,301 --> 00:20:40,260 black holes were in fact very real indeed. 301 00:20:46,178 --> 00:20:48,373 Since their discovery twenty-five years ago 302 00:20:48,580 --> 00:20:51,140 we now know that the universe is teeming with them. 303 00:20:51,516 --> 00:20:55,976 But it's how black holes affect time that make them so unusual. 304 00:21:00,926 --> 00:21:03,451 Black holes are so massive 305 00:21:03,528 --> 00:21:07,123 that their gravitational pull approaches infinity. 306 00:21:12,604 --> 00:21:15,004 And according to Einstein's second theory, 307 00:21:15,540 --> 00:21:17,633 that of general relativity, 308 00:21:18,477 --> 00:21:21,503 very intense gravity slows time 309 00:21:21,580 --> 00:21:25,038 in a similar way to moving at very high speed. 310 00:21:30,088 --> 00:21:33,717 But if you were to watch someone fall into a black hole 311 00:21:34,092 --> 00:21:37,152 you'd notice that their time was beginning to slow down. 312 00:21:37,729 --> 00:21:40,391 So much so that at the very centre 313 00:21:40,499 --> 00:21:43,229 where the gravitational pull is infinite, 314 00:21:43,302 --> 00:21:45,236 time would stop altogether. 315 00:21:46,371 --> 00:21:48,931 Time would cease to exist. 316 00:22:07,592 --> 00:22:11,688 That there are places where time can come to a grinding halt 317 00:22:11,763 --> 00:22:13,993 seems frankly incredible. 318 00:22:15,967 --> 00:22:20,597 But that's only because we live in such a uniform corner of the galaxy. 319 00:22:23,241 --> 00:22:28,372 Warmed by a benevolent sun, far from any extremes of gravity. 320 00:22:32,184 --> 00:22:36,518 Beyond our everyday environment, time is very different. 321 00:22:37,089 --> 00:22:40,923 Not only is it irregular, it's also chaotic. 322 00:22:41,293 --> 00:22:43,818 It can even stand still. 323 00:22:44,896 --> 00:22:46,158 But for all its vagaries 324 00:22:46,231 --> 00:22:49,667 there's one thing that time never seems to do. 325 00:22:50,001 --> 00:22:53,164 And that's turn back on itself. 326 00:22:59,745 --> 00:23:02,737 Which, when you think about it, is a little odd. 327 00:23:03,048 --> 00:23:08,008 After all my physical environment offers me enormous freedom. 328 00:23:12,491 --> 00:23:15,619 The thing is the laws of physics don't have any problems 329 00:23:15,694 --> 00:23:17,389 with time running backwards. 330 00:23:18,196 --> 00:23:21,654 So we physicists believe that itjust might be possible 331 00:23:21,733 --> 00:23:23,496 to build a time machine. 332 00:23:24,069 --> 00:23:27,300 The only obstacle we face is one of engineering. 333 00:23:30,542 --> 00:23:32,772 That's because the theoretical blueprint 334 00:23:32,844 --> 00:23:35,938 for our time machine already exists. 335 00:23:39,151 --> 00:23:44,248 A machine that's secret lies deep within our microscopic universe. 336 00:24:00,906 --> 00:24:03,542 At the tiniest sub-atomic level, 337 00:24:03,542 --> 00:24:07,740 the fabric of space and time becomes so unstable 338 00:24:07,813 --> 00:24:10,111 that it starts to behave like a foam. 339 00:24:10,615 --> 00:24:13,311 Its surface alive with tiny bubbles 340 00:24:13,385 --> 00:24:16,479 momentarily popping in and out of existence. 341 00:24:17,422 --> 00:24:21,688 We call this quantum state, 'the space time foam.' 342 00:24:24,696 --> 00:24:26,129 It's thought that contained 343 00:24:26,198 --> 00:24:30,032 within this foam are objects called wormholes. 344 00:24:30,502 --> 00:24:34,666 Tiny passageways between two points in space and time. 345 00:24:36,842 --> 00:24:39,208 The secret to building a time machine 346 00:24:39,277 --> 00:24:42,644 is to stabilise the space time foam long enough 347 00:24:42,714 --> 00:24:45,581 to make one of these wormholes permanent. 348 00:24:46,251 --> 00:24:47,684 And the way we do that 349 00:24:47,819 --> 00:24:52,654 is by subjecting it to enormous amounts of energy. 350 00:24:57,195 --> 00:24:59,493 I'm standing one hundred metres above 351 00:24:59,564 --> 00:25:01,327 what will be, when it's finished, 352 00:25:01,399 --> 00:25:04,232 the world's most powerful particle accelerator. 353 00:25:04,636 --> 00:25:06,797 This machine, scientists hope, 354 00:25:06,972 --> 00:25:08,940 will help to unlock some of the secrets 355 00:25:09,007 --> 00:25:11,908 of the mysterious world of sub-atomic particles, 356 00:25:12,010 --> 00:25:14,740 the building blocks of our universe. 357 00:25:25,957 --> 00:25:29,154 This tunnel is twenty-seven kilometres 358 00:25:29,227 --> 00:25:31,627 in circumference and it houses the accelerator. 359 00:25:32,197 --> 00:25:33,687 Inside this chamber 360 00:25:33,932 --> 00:25:38,198 two beams of sub-atomic particles will be travelling in opposite directions, 361 00:25:38,270 --> 00:25:40,602 boosted to near the speed of light. 362 00:25:47,779 --> 00:25:50,646 As the protons within the beams collide, 363 00:25:50,715 --> 00:25:53,479 they shatter into even smaller particles, 364 00:25:53,952 --> 00:25:58,286 releasing bursts of energy roughly half a million times greater 365 00:25:58,356 --> 00:26:01,689 than those inside a nuclear explosion. 366 00:26:04,095 --> 00:26:07,531 But even the most powerful accelerator on this planet 367 00:26:07,599 --> 00:26:11,592 can't produce enough energy to stabilise a space time foam. 368 00:26:12,237 --> 00:26:13,101 To do that, 369 00:26:13,171 --> 00:26:16,538 our particles would have to be moving even faster 370 00:26:16,608 --> 00:26:21,307 and that would require an accelerator of truly enormous proportions. 371 00:26:33,425 --> 00:26:38,021 So big in fact we would need to build it in space. 372 00:26:56,748 --> 00:26:58,215 Now we know 373 00:26:58,283 --> 00:27:02,276 that if you smash particles together at extremely high velocities, 374 00:27:02,554 --> 00:27:06,081 eventually you create something called a 'quark gluon plasma.' 375 00:27:08,727 --> 00:27:09,716 An extremely hot 376 00:27:09,794 --> 00:27:12,160 high energy cauldron of matter 377 00:27:12,230 --> 00:27:15,222 with a temperature exceeding ten trillion degrees. 378 00:27:17,302 --> 00:27:19,600 By adding even more energy, 379 00:27:21,673 --> 00:27:24,164 blasting the plasma with lasers 380 00:27:24,242 --> 00:27:27,234 we can finally stabilise space time foam 381 00:27:27,746 --> 00:27:31,341 long enough to pluck out a miniscule wormhole. 382 00:27:33,151 --> 00:27:35,312 The next task is to enlarge it 383 00:27:35,387 --> 00:27:38,447 and even that is scientifically possible. 384 00:27:39,357 --> 00:27:40,984 In 1948 385 00:27:41,059 --> 00:27:43,994 a Dutch physicist named Hendrick Casimir 386 00:27:44,062 --> 00:27:48,999 introduced us to a mysterious new force called 'negative energy.' 387 00:27:49,267 --> 00:27:52,168 Complete with anti-gravitational properties. 388 00:27:55,340 --> 00:27:55,931 So far 389 00:27:56,007 --> 00:28:00,000 we can only create minute quantities of this in the laboratory, 390 00:28:00,078 --> 00:28:01,409 but one day 391 00:28:01,479 --> 00:28:03,913 if we can create enough negative energy, 392 00:28:03,982 --> 00:28:07,611 we might be able to increase the size of a wormhole. 393 00:28:08,687 --> 00:28:11,679 And this is how we think our wormhole would look. 394 00:28:12,157 --> 00:28:16,890 Each end a sphere held in place by an electric field 395 00:28:16,961 --> 00:28:20,590 invisibly connecting two points in space and time. 396 00:28:22,467 --> 00:28:27,769 By subjecting one end of the wormhole to a huge gravitational field, 397 00:28:27,839 --> 00:28:30,364 we could bring its clock almost to a stop. 398 00:28:33,878 --> 00:28:37,336 This turns our wormhole into a time machine. 399 00:28:39,150 --> 00:28:43,849 Both ends existing in the same place, but at different times. 400 00:28:47,759 --> 00:28:51,923 Our ability to build such a machine is still some way off. 401 00:28:56,267 --> 00:28:59,100 Butjust knowing that time travel is possible 402 00:28:59,170 --> 00:29:03,470 is enough to turn yet another of our assumptions on its head. 403 00:29:05,844 --> 00:29:07,937 So far we've seen how time, 404 00:29:08,012 --> 00:29:09,707 which appears to be so regular, 405 00:29:09,781 --> 00:29:11,476 can in fact be quite flexible. 406 00:29:12,050 --> 00:29:15,850 We've seen how time can behave in such unpredictable ways. 407 00:29:17,155 --> 00:29:20,124 And as we understand more about time 408 00:29:20,291 --> 00:29:21,815 it's even becoming possible 409 00:29:21,893 --> 00:29:25,556 to solve perhaps the greatest mystery of them all. 410 00:29:27,232 --> 00:29:29,757 Whether time is eternal. 411 00:29:30,969 --> 00:29:32,664 Over the last hundred years 412 00:29:32,737 --> 00:29:35,535 it's becoming increasingly clear that our universe, 413 00:29:35,607 --> 00:29:37,666 and hence time itself, had a beginning. 414 00:29:38,143 --> 00:29:39,770 But that raises another question. 415 00:29:40,178 --> 00:29:43,670 If time had a beginning will it also have an end? 416 00:30:09,007 --> 00:30:14,206 Humanity has long pondered the origins of time and the universe. 417 00:30:17,749 --> 00:30:21,378 Almost every religion that has ever existed 418 00:30:21,452 --> 00:30:23,477 has had its own creation myth. 419 00:30:25,056 --> 00:30:26,353 When I was a child 420 00:30:26,424 --> 00:30:29,416 I remember being so confused about how we got here 421 00:30:29,727 --> 00:30:32,753 and that's because I was brought up in between two faiths 422 00:30:32,831 --> 00:30:35,629 with two very different views on creation. 423 00:30:46,277 --> 00:30:48,837 On the one hand there was Christianity. 424 00:30:49,147 --> 00:30:52,878 At Sunday school I learnt all the Old Testament stories. 425 00:30:54,619 --> 00:30:57,110 Among them the Book of Genesis, 426 00:30:57,188 --> 00:30:59,986 describing how the universe came into being 427 00:31:00,058 --> 00:31:03,050 in a single moment of divine creation. 428 00:31:05,630 --> 00:31:08,724 On the other hand, my parents were both Buddhists. 429 00:31:09,234 --> 00:31:10,132 From then 430 00:31:10,201 --> 00:31:13,830 I discovered that Buddhists believe the universe is timeless, 431 00:31:14,806 --> 00:31:17,036 without either beginning or end. 432 00:31:23,815 --> 00:31:24,474 For some time 433 00:31:24,549 --> 00:31:29,077 I continued to struggle with these two seemingly incompatible doctrines. 434 00:31:32,857 --> 00:31:35,621 Either the universe had a beginning or it didn't. 435 00:31:36,227 --> 00:31:39,253 Either time is eternal or it isn't. 436 00:31:42,300 --> 00:31:45,069 It's only in the last forty years or so 437 00:31:45,069 --> 00:31:47,367 that we think we've found the answer. 438 00:31:48,473 --> 00:31:52,534 An answer that comes from the furthest reaches of space. 439 00:31:58,016 --> 00:32:01,747 The amazing thing about looking up into the night sky 440 00:32:01,819 --> 00:32:04,811 is that it's like gazing at a cosmic map of the past. 441 00:32:05,089 --> 00:32:08,456 Every planet, every star is like a snapshot 442 00:32:08,526 --> 00:32:10,494 taken when their light first left them. 443 00:32:11,029 --> 00:32:14,590 The further the star, the more ancient its origins. 444 00:32:15,166 --> 00:32:16,394 But for centuries 445 00:32:16,467 --> 00:32:19,493 the limits of the universe were a total mystery 446 00:32:19,570 --> 00:32:24,598 until one man peered further into the heavens than ever before. 447 00:32:25,743 --> 00:32:26,675 In doing so 448 00:32:26,744 --> 00:32:30,305 he gave us a better understanding notjust of our universe, 449 00:32:30,481 --> 00:32:32,210 but of time as well. 450 00:32:58,009 --> 00:33:02,446 Perched high in the hills above Los Angeles in southern California, 451 00:33:02,513 --> 00:33:04,811 is the Mount Wilson Observatory. 452 00:33:06,751 --> 00:33:08,309 In 1919 453 00:33:08,386 --> 00:33:12,982 it saw the arrival of an ambitious new astronomer named Edwin Hubble. 454 00:33:15,393 --> 00:33:18,328 Don Nicholson remembers Hubble from regular visits 455 00:33:18,396 --> 00:33:20,557 to Mount Wilson as a young boy. 456 00:33:22,834 --> 00:33:29,569 Hubble, certainly as an astronomer was a very skilled, 457 00:33:29,640 --> 00:33:34,600 a very dedicated, very effective astronomer. 458 00:33:35,279 --> 00:33:39,375 He was highly respected er, for his professionalism. 459 00:33:41,786 --> 00:33:42,946 Hubble's arrival 460 00:33:43,021 --> 00:33:46,149 more or less coincided with completion of the world's 461 00:33:46,224 --> 00:33:48,351 then most powerful telescope. 462 00:33:50,294 --> 00:33:52,762 Capable of looking further into space 463 00:33:52,830 --> 00:33:56,459 and hence further back in time than ever before. 464 00:34:03,641 --> 00:34:08,442 Most astronomers felt that our galaxy was the universe 465 00:34:08,513 --> 00:34:09,707 and for many 466 00:34:09,781 --> 00:34:14,115 that even the solar system was at the centre of that universe. 467 00:34:15,620 --> 00:34:20,114 But on the evening of October 4th 1923, 468 00:34:20,191 --> 00:34:25,185 Edwin Hubble noticed a tiny speck deep within the Andromeda nebula. 469 00:34:29,634 --> 00:34:30,999 Before that time 470 00:34:31,069 --> 00:34:32,798 there was no telescope in the world, 471 00:34:32,870 --> 00:34:36,499 for example, that could resolve individual stars 472 00:34:36,574 --> 00:34:39,236 in these spiral nebula. 473 00:34:39,744 --> 00:34:44,477 And so there was belief that they were simply gaseous objects 474 00:34:44,549 --> 00:34:46,073 in our own galaxy. 475 00:34:47,552 --> 00:34:52,546 But Hubble was able to prove that his speck was indeed a star 476 00:34:52,623 --> 00:34:57,219 and incredibly that it was more than a million light years away, 477 00:34:57,662 --> 00:35:00,825 much too far to be part of our own galaxy. 478 00:35:01,866 --> 00:35:03,197 In one stroke 479 00:35:03,267 --> 00:35:06,464 Edwin Hubble had destroyed the notion that our milky way 480 00:35:06,537 --> 00:35:08,869 was the sum total of the universe. 481 00:35:09,774 --> 00:35:12,038 And if the universe was much bigger, 482 00:35:12,944 --> 00:35:16,380 then it also had to be far, far older. 483 00:35:56,154 --> 00:35:57,246 Every Thursday 484 00:35:57,321 --> 00:36:00,051 a whole bunch of fans congregate at this drag strip 485 00:36:00,124 --> 00:36:01,489 to enjoy the sights, 486 00:36:01,559 --> 00:36:04,995 the smells, the sounds of these muscle cars. 487 00:36:09,467 --> 00:36:13,369 These unmistakeable sounds are created by the same phenomenon 488 00:36:13,437 --> 00:36:17,396 that enabled Edwin Hubble to make his second great discovery. 489 00:36:22,580 --> 00:36:27,210 The sound of a car will always depend on the direction it's travelling. 490 00:36:29,253 --> 00:36:31,983 A car moving towards me sounds high pitched. 491 00:36:35,760 --> 00:36:39,161 But a car moving away from me sounds lower pitched. 492 00:36:40,765 --> 00:36:42,357 This shift in pitch, 493 00:36:42,433 --> 00:36:44,333 known as 'the Doppler Effect' 494 00:36:44,402 --> 00:36:47,667 is due to the fact that at the front of a moving car 495 00:36:47,738 --> 00:36:49,330 sound waves are compressed. 496 00:36:51,175 --> 00:36:53,473 While at the back they're stretched out. 497 00:36:59,217 --> 00:37:02,277 And what's true of sound is also true of light. 498 00:37:03,554 --> 00:37:07,888 As light moves away from us its waves too become stretched. 499 00:37:10,061 --> 00:37:13,428 By measuring this effect called 'the red shift' 500 00:37:13,497 --> 00:37:15,829 in one galaxy after another, 501 00:37:15,967 --> 00:37:19,903 Edwin Hubble realised that not only were they all incredibly distant 502 00:37:20,204 --> 00:37:23,071 they were all moving away from us. 503 00:37:25,343 --> 00:37:29,404 In other words the universe was expanding. 504 00:37:31,749 --> 00:37:33,341 If the universe was expanding, 505 00:37:33,551 --> 00:37:36,042 then it had to be expanding from something. 506 00:37:38,389 --> 00:37:42,519 From an event whose soundtrack is still with us today. 507 00:38:09,020 --> 00:38:12,046 What I'm listening to now are some of the sweetest sounds ever. 508 00:38:12,523 --> 00:38:14,047 The sounds of creation. 509 00:38:14,625 --> 00:38:17,753 Waves of light from the beginning of time have been stretched so much 510 00:38:17,828 --> 00:38:19,659 that we can't really see them anymore. 511 00:38:20,097 --> 00:38:24,500 Instead we can pick some of them up on the radio in the form of static. 512 00:38:27,271 --> 00:38:28,966 Although he didn't know it at the time 513 00:38:29,040 --> 00:38:31,338 Hubble's discovery that the universe was expanding 514 00:38:31,409 --> 00:38:35,539 led to one of the most important breakthroughs ever made about time. 515 00:38:36,147 --> 00:38:37,205 The Big Bang. 516 00:38:40,184 --> 00:38:42,448 Once there was nothing. 517 00:38:43,020 --> 00:38:44,351 Not even time. 518 00:38:45,623 --> 00:38:48,387 But 13.7 billion years ago 519 00:38:48,759 --> 00:38:52,627 it seems that this nothing became everything. 520 00:38:53,964 --> 00:38:59,129 When a tiny dot of infinite density spontaneously expanded 521 00:38:59,470 --> 00:39:01,529 at a phenomenal rate. 522 00:39:03,741 --> 00:39:07,233 Giving birth to the universe and everything within it, 523 00:39:08,079 --> 00:39:10,047 including time. 524 00:39:14,051 --> 00:39:15,484 But if time had a beginning 525 00:39:16,187 --> 00:39:18,849 does that also mean that time will have an end? 526 00:39:33,571 --> 00:39:36,870 Just as many cultures have their own creation myth, 527 00:39:36,941 --> 00:39:41,469 so most also have their own take on how the universe will end. 528 00:39:44,215 --> 00:39:45,876 In the 11th century, 529 00:39:45,950 --> 00:39:48,418 the ancient Norse myth of Ragnarok 530 00:39:48,486 --> 00:39:51,978 predicted that the universe and time along with it, 531 00:39:52,356 --> 00:39:57,794 would end in a desperate battle between the forces of good and evil. 532 00:40:02,133 --> 00:40:05,068 It was believed that this apocalypse 533 00:40:05,136 --> 00:40:09,038 would be preceded by something called, 'the winter of winters.' 534 00:40:11,442 --> 00:40:13,535 An epic ice age, 535 00:40:15,012 --> 00:40:19,779 during which all the stars would gradually vanish from the sky. 536 00:40:23,187 --> 00:40:24,848 How the universe will end 537 00:40:24,922 --> 00:40:28,653 continues to preoccupy us over a thousand years later. 538 00:40:37,001 --> 00:40:38,696 In 1988, 539 00:40:38,769 --> 00:40:42,102 physicist Saul Perlmutter joined this quest 540 00:40:42,173 --> 00:40:45,267 to discover the fate of the cosmos. 541 00:40:48,612 --> 00:40:50,603 It seems like a really philosophical question 542 00:40:50,681 --> 00:40:52,808 er, is the universe going to last for ever 543 00:40:52,883 --> 00:40:54,612 or is it some day going to come to an end? 544 00:40:54,985 --> 00:40:57,818 But in just the last - last few decades 545 00:40:57,888 --> 00:40:59,287 we finally have the - 546 00:40:59,356 --> 00:41:01,756 both the intellectual tools that Einstein gave us 547 00:41:01,826 --> 00:41:04,420 and the practical measurement tools. 548 00:41:12,903 --> 00:41:15,929 Saul believed that the destiny of our universe 549 00:41:16,006 --> 00:41:18,998 was linked to the rate at which it was expanding. 550 00:41:20,277 --> 00:41:24,407 Since the 1930s we've known that the universe is expanding 551 00:41:24,482 --> 00:41:28,316 and everybody's understanding was that it would be slowing down 552 00:41:28,385 --> 00:41:29,113 in that expansion 553 00:41:29,186 --> 00:41:31,211 because all of the stuff in the universe 554 00:41:31,288 --> 00:41:33,449 would gravitationally attract all the other stuff 555 00:41:33,524 --> 00:41:35,788 and so would slow the expansion down little by little. 556 00:41:37,895 --> 00:41:41,888 This would result in the universe collapsing back in on itself 557 00:41:41,966 --> 00:41:44,662 in something called, 'the Big Crunch.' 558 00:41:45,569 --> 00:41:49,130 Bringing time to an abrupt and violent halt. 559 00:41:54,879 --> 00:41:55,675 Are there any decisions coming up? 560 00:41:55,746 --> 00:41:56,872 Are there any other ones that 561 00:41:56,947 --> 00:41:59,074 we're actually going to have to decide something about? 562 00:41:59,149 --> 00:42:03,142 To discoverjust when the universe and time would end, 563 00:42:03,420 --> 00:42:07,948 Saul and his team began to hunt for extremely rare objects known as 564 00:42:08,025 --> 00:42:09,049 'supernovae.' 565 00:42:10,227 --> 00:42:13,128 The aftermath of exploded stars. 566 00:42:13,831 --> 00:42:15,560 There are two things you need to know 567 00:42:15,633 --> 00:42:16,998 about a given supernova when - once - 568 00:42:17,067 --> 00:42:17,965 - you've discovered one. 569 00:42:18,068 --> 00:42:19,660 First its peak brightness. 570 00:42:19,737 --> 00:42:21,466 That tells you how far away it is 571 00:42:21,539 --> 00:42:23,632 and hence how far back in time the explosion occurred. 572 00:42:24,375 --> 00:42:25,137 The other thing 573 00:42:25,209 --> 00:42:28,076 is you want to look at its colour through its spectrum 574 00:42:28,145 --> 00:42:32,013 and the more it's been shifted to the red - it's called Red Shift, 575 00:42:32,483 --> 00:42:36,044 the more the universe has stretched since the time of that explosion. 576 00:42:38,455 --> 00:42:39,683 Painstakingly, 577 00:42:39,757 --> 00:42:44,217 Saul and his team begin to discover one supernova after another. 578 00:42:45,429 --> 00:42:48,330 After several years of the - of the supernova hunting 579 00:42:48,399 --> 00:42:51,562 we had built up a sample of some forty two supernova 580 00:42:51,635 --> 00:42:53,193 and we were finally ready to go back - 581 00:42:53,270 --> 00:42:55,568 - to ask that question that we began the project with. 582 00:42:55,639 --> 00:42:56,936 What is the fate of the universe? 583 00:42:58,409 --> 00:43:03,278 But the answer they came up with came as something of a shock. 584 00:43:03,981 --> 00:43:09,681 When we finally graphed the results we found a very surprising result. 585 00:43:09,753 --> 00:43:11,550 Apparently the universe is not slowing down. 586 00:43:11,722 --> 00:43:14,987 It was actually speeding up and that was the big surprise. 587 00:43:20,764 --> 00:43:21,822 In other words 588 00:43:21,899 --> 00:43:24,993 the universe wasn't headed for a big crunch at all. 589 00:43:25,703 --> 00:43:28,001 So what will its fate be? 590 00:43:31,942 --> 00:43:34,103 Saul's discovery has helped scientists 591 00:43:34,178 --> 00:43:37,545 to map out how time and the universe will evolve. 592 00:43:38,248 --> 00:43:44,312 An incredible space epic separated into five long ages. 593 00:43:47,925 --> 00:43:50,655 The first of these was the Primordial Age, 594 00:43:50,728 --> 00:43:54,027 starting with the Big Bang and the birth of time. 595 00:43:55,799 --> 00:44:00,736 Lasting only 350 thousand years, that's long gone. 596 00:44:01,538 --> 00:44:06,407 We're now 13.7 billion years into the second age 597 00:44:07,111 --> 00:44:09,602 and it's only just beginning. 598 00:44:10,581 --> 00:44:13,675 We live in something called the Stelliferous Era. 599 00:44:13,951 --> 00:44:14,918 An epoch 600 00:44:14,985 --> 00:44:18,079 that has brought us notjust the stars and the planets, 601 00:44:18,155 --> 00:44:21,124 but also every speck of matter in the universe. 602 00:44:21,759 --> 00:44:22,691 One day, 603 00:44:22,760 --> 00:44:25,558 a hundred million, million years from now, 604 00:44:25,629 --> 00:44:28,530 a mere finger click in the life of the universe, 605 00:44:28,599 --> 00:44:31,227 this golden age will come to an end. 606 00:44:33,704 --> 00:44:37,071 In its place will come the Degenerate Age. 607 00:44:38,375 --> 00:44:41,742 When the last stars burn out and die. 608 00:44:42,813 --> 00:44:45,407 When the planets fall from their orbits 609 00:44:45,482 --> 00:44:49,851 and in the darkness of space matter begins to decay. 610 00:44:56,994 --> 00:45:02,557 After a truly unimaginable length of time only black holes remain. 611 00:45:03,400 --> 00:45:09,270 A fourth age that far exceeds all the time that has ever gone before. 612 00:45:11,241 --> 00:45:14,005 But even black holes don't last for ever. 613 00:45:14,645 --> 00:45:18,445 Little by little their thermal energy will leak away. 614 00:45:19,416 --> 00:45:23,375 Until ultimately they too disappear. 615 00:45:27,124 --> 00:45:29,524 So what does this mean for the future of time? 616 00:45:30,127 --> 00:45:31,788 Does the death of our universe 617 00:45:31,862 --> 00:45:34,695 mean that time is destined to run out, 618 00:45:34,765 --> 00:45:38,667 or is time really eternal, without end? 619 00:45:41,572 --> 00:45:44,939 Even as the last black hole evaporates, 620 00:45:45,008 --> 00:45:48,444 a fifth and final age is beginning. 621 00:45:49,680 --> 00:45:51,910 The age of the photon 622 00:45:52,516 --> 00:45:57,613 in which time finally fragments into total disorder. 623 00:45:59,623 --> 00:46:01,750 When all that remains of our cosmos 624 00:46:01,825 --> 00:46:03,258 are invisible, 625 00:46:03,327 --> 00:46:07,229 indestructible, low energy light particles. 626 00:46:12,836 --> 00:46:14,531 For Saul Perlmutter, 627 00:46:14,605 --> 00:46:19,406 this cold chaos represents the ultimate destiny for time. 628 00:46:20,978 --> 00:46:24,209 This particular picture of the - of the future of the universe, 629 00:46:24,281 --> 00:46:26,841 and we don't know if this will be the final answer, 630 00:46:27,451 --> 00:46:29,078 would have time lasting for ever. 631 00:46:29,153 --> 00:46:32,145 There'll be no end to the universe in this particular scenario. 632 00:46:48,338 --> 00:46:51,171 So it seems as if both religious traditions 633 00:46:51,241 --> 00:46:53,505 that I grew up with are in some sense correct. 634 00:46:54,278 --> 00:46:57,213 Time is eternal as the Buddhists believe, 635 00:46:57,414 --> 00:47:01,043 but time also came into being at a precise moment, 636 00:47:01,285 --> 00:47:04,550 and that fits well with the story of Genesis. 637 00:47:10,761 --> 00:47:14,128 As we look out to the vastness of time that lies ahead 638 00:47:14,198 --> 00:47:16,325 we begin to notice something truly incredible. 639 00:47:16,834 --> 00:47:20,600 As we move from one age of the universe to the next 640 00:47:20,671 --> 00:47:24,698 we see that the nature of time itself begins to change. 641 00:47:24,775 --> 00:47:26,333 Time evolves. 642 00:47:27,544 --> 00:47:28,272 Ultimately 643 00:47:28,345 --> 00:47:33,180 the strange and chaotic behaviour that we can only glimpse inside the atom 644 00:47:33,250 --> 00:47:37,914 may in general become the nature of time throughout the entire cosmos 645 00:47:38,188 --> 00:47:41,487 and if we could somehow hang around to experience it 646 00:47:41,625 --> 00:47:44,822 we might not even recognise it as time at all. 647 00:47:47,130 --> 00:47:50,930 Because just as particles can be in many places at once, 648 00:47:51,001 --> 00:47:53,765 so in our quantum cosmos 649 00:47:53,837 --> 00:47:56,362 we might uncover many universes, 650 00:47:56,440 --> 00:47:59,307 each one with a time of its own. 651 00:48:01,578 --> 00:48:03,773 So this new perspective of time 652 00:48:03,847 --> 00:48:06,145 over the whole life of the cosmos, 653 00:48:06,216 --> 00:48:09,674 makes us look at our time from a new point of view. 654 00:48:09,820 --> 00:48:12,380 The time that we feel passing, 655 00:48:12,456 --> 00:48:14,651 the time that we know and trust, 656 00:48:14,725 --> 00:48:16,625 may be something of an illusion. 657 00:48:16,727 --> 00:48:19,958 An illusion that allows us to make sense of our place 658 00:48:20,030 --> 00:48:22,999 in this tiny corner of the cosmos.