1 00:00:06,080 --> 00:00:09,920 For more than a decade, I've made programmes about the universe. 2 00:00:13,800 --> 00:00:16,040 And our place within it. 3 00:00:19,200 --> 00:00:21,120 There it is! There it is! 4 00:00:21,120 --> 00:00:22,960 I can see the parachutes. 5 00:00:24,080 --> 00:00:26,400 I've had some remarkable encounters... 6 00:00:28,200 --> 00:00:31,880 I can't believe you can just stand next to a spacecraft. 7 00:00:31,880 --> 00:00:33,480 Release. 8 00:00:33,480 --> 00:00:35,560 ..memorable experiences... 9 00:00:37,360 --> 00:00:39,760 They came down exactly the same. Wow. 10 00:00:42,800 --> 00:00:46,640 ..and explained some beautiful science about how our planet works. 11 00:00:48,800 --> 00:00:52,440 That really is the thin blue line that protects us. 12 00:00:52,440 --> 00:00:54,160 Look at that! 13 00:00:57,360 --> 00:01:01,120 Now, I'm taking a new look at those past programmes. 14 00:01:01,120 --> 00:01:04,280 It's surely as close as I'm going to get to being in space. 15 00:01:05,640 --> 00:01:09,840 I think our knowledge really has moved on since we made these films. 16 00:01:09,840 --> 00:01:12,880 So it's really interesting to revisit 17 00:01:12,880 --> 00:01:15,000 some fundamental questions again. 18 00:01:18,400 --> 00:01:20,880 Are we alone in the universe? 19 00:01:23,720 --> 00:01:25,800 What really is gravity? 20 00:01:29,320 --> 00:01:32,000 Where will the exploration of space take us? 21 00:01:32,000 --> 00:01:35,000 CLOCK TICKS 22 00:01:32,000 --> 00:01:35,000 And what is time? 23 00:01:36,560 --> 00:01:39,240 HIGH-PITCHED BEEPING 24 00:01:39,240 --> 00:01:40,960 Beeping's never good. 25 00:02:02,560 --> 00:02:07,120 I'm back at the Royal Institution to re-watch some of my old films. 26 00:02:11,560 --> 00:02:15,200 And to explore the thing by which we measure our lives. 27 00:02:20,040 --> 00:02:21,360 Time. 28 00:02:26,080 --> 00:02:28,920 It's a concept which is so familiar, 29 00:02:28,920 --> 00:02:32,880 and yet recent discoveries have revealed it to be far stranger 30 00:02:32,880 --> 00:02:34,960 than we could have possibly imagined. 31 00:02:36,480 --> 00:02:40,120 I think the question, "What is time?" 32 00:02:40,120 --> 00:02:44,920 is one of the most fascinating and evocative scientific questions. 33 00:02:47,520 --> 00:02:51,040 Because it's so fundamental to human experience. 34 00:02:53,200 --> 00:02:57,600 Our experience of the world is that the past is written, 35 00:02:57,600 --> 00:03:01,400 it has happened, and the future is yet to be written. 36 00:03:01,400 --> 00:03:03,920 It's open. 37 00:03:01,400 --> 00:03:03,920 CLOCK TICKS 38 00:03:03,920 --> 00:03:06,640 But what is this thing ultimately that the clock is doing, 39 00:03:06,640 --> 00:03:08,360 the ticking of the clock? 40 00:03:10,880 --> 00:03:13,960 It's one of the most baffling questions in science. 41 00:03:18,680 --> 00:03:20,840 JAUNTY WHISTLING 42 00:03:20,840 --> 00:03:23,880 Ah, excellent, there you are. Where am I? A bit complicated. 43 00:03:23,880 --> 00:03:26,640 Sort of a spaceship/time machine/slash/swimming pool. 44 00:03:26,640 --> 00:03:29,320 Optional hat stand. I need five minutes of your time and obviously 45 00:03:29,320 --> 00:03:32,960 when I say five minutes, I'm lying. No, no, I'm just going to go give a lecture. 46 00:03:32,960 --> 00:03:35,680 I know, I've just seen it. It's great. But I haven't given it yet. 47 00:03:35,680 --> 00:03:37,960 Tricky to explain. Seen it anyway. 48 00:03:37,960 --> 00:03:40,960 Right, hold on to something, probably your sanity. 49 00:03:40,960 --> 00:03:42,680 Ready? 50 00:03:42,680 --> 00:03:44,640 LOUD CRACKLING 51 00:03:46,280 --> 00:03:48,280 Usually it just twirls around. 52 00:03:48,280 --> 00:03:50,720 It's probably this. Shut up, Brian! 53 00:03:50,720 --> 00:03:52,680 I'm often asked about time travel, 54 00:03:52,680 --> 00:03:55,440 and, yeah, some of it comes from Doctor Who. 55 00:03:55,440 --> 00:03:57,920 It would be great, wouldn't it, to have a TARDIS and to be able 56 00:03:57,920 --> 00:04:01,240 to go back and see some of the great moments in history. 57 00:04:01,240 --> 00:04:03,880 DOCTOR WHO THEME TUNE 58 00:04:06,160 --> 00:04:08,040 It's a tantalising prospect. 59 00:04:09,600 --> 00:04:13,720 But before we can even begin to consider time travel, 60 00:04:13,720 --> 00:04:16,360 we should explore how we experience time. 61 00:04:18,560 --> 00:04:21,320 METALLIC THRUMMING 62 00:04:21,320 --> 00:04:24,480 The way that we experience time and talk about it, 63 00:04:24,480 --> 00:04:27,680 is actually, if you think about it, quite strange. 64 00:04:27,680 --> 00:04:31,240 Because, you know, there are 60 seconds in a minute, 60 minutes 65 00:04:31,240 --> 00:04:33,240 in an hour and 24 of those in a day, 66 00:04:33,240 --> 00:04:35,680 and then there are 365 days in a year. 67 00:04:35,680 --> 00:04:38,600 It's interesting, I think, that most of us have become completely 68 00:04:38,600 --> 00:04:41,480 disconnected from what that's actually telling us. 69 00:04:41,480 --> 00:04:43,920 Which is that we live on a ball of rock, 70 00:04:43,920 --> 00:04:46,560 that is spinning around on its axis 71 00:04:46,560 --> 00:04:50,680 once roughly every 24 hours or so. 72 00:04:50,680 --> 00:04:54,200 And in a plane that can go that fast, 73 00:04:54,200 --> 00:04:56,400 you can really illustrate that. 74 00:05:00,120 --> 00:05:02,400 Because we live on a spinning sphere, 75 00:05:02,400 --> 00:05:06,080 if we turn on the after-burners and chase the setting sun, 76 00:05:06,080 --> 00:05:08,920 something really interesting happens. 77 00:05:10,840 --> 00:05:12,720 This is a Eurofighter Typhoon. 78 00:05:14,200 --> 00:05:18,680 It flies at, at least Mach 1.85, twice the speed of sound. 79 00:05:18,680 --> 00:05:21,320 I can't tell you exactly how fast, because it's classified. 80 00:05:21,320 --> 00:05:23,480 They go up to at least 55,000 feet 81 00:05:23,480 --> 00:05:26,000 but again, I can't tell you, it's classified. 82 00:05:26,000 --> 00:05:28,600 And you can't film down those air intakes 83 00:05:28,600 --> 00:05:30,640 because they're classified as well. 84 00:05:30,640 --> 00:05:33,440 This one is BAE Systems' development aircraft. 85 00:05:33,440 --> 00:05:35,560 I'm going to get in it in a minute, 86 00:05:35,560 --> 00:05:38,960 and it's got all the test software in and the pilot told me that, 87 00:05:38,960 --> 00:05:42,880 you know, it's a bit ropey so press control, alt, delete occasionally 88 00:05:42,880 --> 00:05:45,600 if it all goes funny, and usually it comes back on. 89 00:05:45,600 --> 00:05:47,360 Which is good. 90 00:05:53,280 --> 00:05:56,960 Get in. Feet-wise, comfy? Good. That's it. 91 00:05:58,480 --> 00:06:01,400 That's for, if you need to control it at any point. 92 00:06:01,400 --> 00:06:03,360 It's unlikely. Unlikely. 93 00:06:04,720 --> 00:06:06,280 Have you got a sick bag? 94 00:06:07,680 --> 00:06:08,720 No. 95 00:06:10,200 --> 00:06:12,920 Worst comes to the worst, do it in your glove. 96 00:06:14,800 --> 00:06:17,600 CONTROL TOWER: Charlie 69, runway 07, clear take off. 97 00:06:17,600 --> 00:06:20,640 Surface wind 350 degrees, seven knots over. 98 00:06:28,240 --> 00:06:31,040 PILOT: So, ready? Yeah. Going to go for it. 99 00:06:41,200 --> 00:06:43,520 ENGINES ROAR 100 00:06:47,000 --> 00:06:48,840 There we go. Wahee. 101 00:06:54,960 --> 00:06:58,200 It's every bit as good as you can imagine. 102 00:06:58,200 --> 00:07:01,080 It's beautiful. What a plane. 103 00:07:08,920 --> 00:07:11,280 On the east side, everything's darkening up quite nicely 104 00:07:11,280 --> 00:07:12,960 as the sun starts to set. 105 00:07:12,960 --> 00:07:15,960 And on the ground it's already, it's dark on the ground now, 106 00:07:15,960 --> 00:07:18,080 as far as the sun is concerned. 107 00:07:18,080 --> 00:07:19,360 So, accelerating. 108 00:07:21,400 --> 00:07:24,280 So that's Mach 0.78. Yeah. 109 00:07:25,440 --> 00:07:27,600 And the G-suit is in play here. Yeah. 110 00:07:30,080 --> 00:07:32,720 Turning directly towards the setting sun, 111 00:07:32,720 --> 00:07:36,640 the Typhoon accelerates to catch up with the Earth's spin. 112 00:07:45,480 --> 00:07:50,000 Beneath us, a 6,000 billion, billion-tonne rock 113 00:07:50,000 --> 00:07:52,840 is spinning at 650mph. 114 00:08:00,480 --> 00:08:03,080 But travel faster than the planet's surface 115 00:08:03,080 --> 00:08:06,200 and the normal passage of the day is reversed. 116 00:08:09,560 --> 00:08:12,360 Right, accelerating. Accelerating. 117 00:08:12,360 --> 00:08:16,120 Oh, there we go, that's acceleration. Mach 1. 118 00:08:17,360 --> 00:08:19,320 Through the sound barrier. 119 00:08:23,280 --> 00:08:25,880 As the jet accelerates, 120 00:08:25,880 --> 00:08:28,680 it starts to overtake the spin of the Earth. 121 00:08:34,600 --> 00:08:37,320 Causing the setting sun to rise again. 122 00:08:38,480 --> 00:08:41,600 Starting to grow a little. It is. I can see it. 123 00:08:41,600 --> 00:08:43,560 We're beating the Earth. 124 00:08:45,880 --> 00:08:47,440 Absolutely terrific. 125 00:08:50,040 --> 00:08:53,040 Starting to climb again, you can see it coming up. Yeah. 126 00:08:53,040 --> 00:08:54,560 That's Mach 1.4. 127 00:08:57,240 --> 00:08:58,880 So, that's a thousand miles an hour. 128 00:08:58,880 --> 00:09:00,840 Yeah, almost a thousand miles an hour. 129 00:09:03,920 --> 00:09:06,960 And now the sun, it's almost the full disc over the clouds. 130 00:09:09,960 --> 00:09:12,360 The sunrise. It is. 131 00:09:12,360 --> 00:09:14,480 Two sunrises in one day. 132 00:09:15,760 --> 00:09:18,960 And all you need is the world's most advanced fighter aircraft. 133 00:09:18,960 --> 00:09:20,240 There we go. 134 00:09:21,880 --> 00:09:22,960 Beautiful. 135 00:09:26,200 --> 00:09:28,800 We've done it, we've outrun the Earth. 136 00:09:28,800 --> 00:09:30,360 BRIAN CHUCKLES 137 00:09:31,760 --> 00:09:33,440 Goodbye, sun! Good. 138 00:09:33,440 --> 00:09:35,800 Right, let's get ourselves on our way home. 139 00:09:39,520 --> 00:09:43,960 I was told that we caused a bit of an incident in the Isle of Man 140 00:09:43,960 --> 00:09:48,040 because the sonic boom did rattle, rattle a few windows. 141 00:09:48,040 --> 00:09:51,880 So, I apologise to all residents of the Isle of Man! 142 00:09:51,880 --> 00:09:54,120 RADIO CHATTER 143 00:09:59,600 --> 00:10:04,320 This hidden celestial dynamics, the Earth's spin and its orbit 144 00:10:04,320 --> 00:10:08,920 around the sun, delivers our daily and yearly experience of time. 145 00:10:10,560 --> 00:10:14,080 Spring goes into summer, and summer into autumn, and autumn into winter. 146 00:10:14,080 --> 00:10:16,880 And we experience another season and another year. 147 00:10:16,880 --> 00:10:19,080 But, of course, they're not always the same, 148 00:10:19,080 --> 00:10:21,840 because every year that passes, we get older. 149 00:10:21,840 --> 00:10:27,800 And so in that sense, I think time connects with the central tragedy 150 00:10:27,800 --> 00:10:29,920 of human experience, 151 00:10:29,920 --> 00:10:34,120 the fact that inexorably and unavoidably 152 00:10:34,120 --> 00:10:37,720 we get older and ultimately we die. 153 00:10:38,960 --> 00:10:41,200 So we're born and we die. 154 00:10:41,200 --> 00:10:45,440 And that's a consequence of time passing, 155 00:10:45,440 --> 00:10:48,800 at least from our point of view, as fragile human beings. 156 00:10:48,800 --> 00:10:51,760 CLOCK TICKS 157 00:10:51,760 --> 00:10:55,000 If you want to understand something, you've got to be able to measure it 158 00:10:55,000 --> 00:10:57,240 and observe it, and look at it and quantify it. 159 00:10:59,920 --> 00:11:02,680 And if you look back at many ancient civilisations, 160 00:11:02,680 --> 00:11:07,000 the attempts to measure the passage of time are rarely small. 161 00:11:07,000 --> 00:11:09,240 Often, they're massive. 162 00:11:09,240 --> 00:11:12,360 They're huge temples that people built. 163 00:11:12,360 --> 00:11:16,880 So, clearly, there's not only the practical need to measure 164 00:11:16,880 --> 00:11:19,920 the passage of time, but there's some ritual attached to it. 165 00:11:23,000 --> 00:11:25,960 This is Chankillo on the northwestern coast of Peru 166 00:11:25,960 --> 00:11:30,280 and it's one of South America's lesser known archaeological sites. 167 00:11:30,280 --> 00:11:33,960 But, for me, it is surely one of the most fascinating. 168 00:11:43,400 --> 00:11:46,640 Around 2,500 years ago, a civilisation 169 00:11:46,640 --> 00:11:48,520 we know almost nothing about 170 00:11:48,520 --> 00:11:51,360 built this fortified temple in the desert. 171 00:11:56,200 --> 00:12:01,280 Its walls were once brilliant white and covered with painted figures. 172 00:12:05,000 --> 00:12:08,280 Today, all but the smallest fragments of the decorations 173 00:12:08,280 --> 00:12:09,920 are gone. 174 00:12:09,920 --> 00:12:14,360 The details of this culture and all traces of its language are lost. 175 00:12:19,360 --> 00:12:22,160 And yet, if you stand in the right place, 176 00:12:22,160 --> 00:12:26,040 you can still experience the true purpose of Chankillo 177 00:12:26,040 --> 00:12:29,360 in just the same way as you could the day it was built. 178 00:12:34,400 --> 00:12:38,000 But to do that, you have to be here before the sun rises. 179 00:12:38,000 --> 00:12:40,760 WIND WHISTLES AND HOWLS 180 00:12:52,960 --> 00:12:55,480 These towers form an ancient solar calendar. 181 00:12:56,920 --> 00:12:58,400 Now, at different times of year, 182 00:12:58,400 --> 00:13:02,320 the sunrise point is at a different place on the horizon. 183 00:13:02,320 --> 00:13:05,600 Actually, December 21st, which here in the southern hemisphere 184 00:13:05,600 --> 00:13:08,480 is the Summer Solstice, the longest day, 185 00:13:08,480 --> 00:13:13,160 when the sun rises just to the right of the rightmost tower. 186 00:13:13,160 --> 00:13:18,360 Then, as the year passes, the sun moves through the towers 187 00:13:18,360 --> 00:13:22,840 until on June 21st, which is the Winter Solstice, the shortest day, 188 00:13:22,840 --> 00:13:26,360 it rises just to the left of the leftmost tower. 189 00:13:26,360 --> 00:13:29,840 Actually, just in between that mountain you can see in the distance 190 00:13:29,840 --> 00:13:32,080 and the leftmost tower. 191 00:13:32,080 --> 00:13:35,640 So, at any time of year, if you watch the sun rise, 192 00:13:35,640 --> 00:13:40,120 you can measure its position and you can tell within an accuracy 193 00:13:40,120 --> 00:13:42,280 of two or three days, the date. 194 00:13:43,920 --> 00:13:46,320 Today's date is September 15th. 195 00:13:46,320 --> 00:13:49,320 And so that means that the sun will rise 196 00:13:49,320 --> 00:13:52,080 between the fifth and the sixth towers. 197 00:14:03,960 --> 00:14:08,240 Chankillo still works as a calendar because the sun still rises in 198 00:14:08,240 --> 00:14:12,440 the same place today as it did when these stones were first laid down. 199 00:14:18,120 --> 00:14:22,680 That is a magnificent sight as the sun burns through the towers. 200 00:14:30,240 --> 00:14:33,360 You can almost feel the presence of the past here. 201 00:14:33,360 --> 00:14:37,200 Imagine what it must have been like, thousands of citizens stood here 202 00:14:37,200 --> 00:14:40,280 to greet the sun, which was almost certainly a deity, 203 00:14:40,280 --> 00:14:42,720 almost certainly their god. 204 00:14:42,720 --> 00:14:44,920 What a magnificent achievement. 205 00:14:44,920 --> 00:14:48,680 It's probably one of our earliest attempts to begin to measure 206 00:14:48,680 --> 00:14:50,120 the heavens. 207 00:15:01,040 --> 00:15:06,000 Time has played a central role in the drama of human experience 208 00:15:06,000 --> 00:15:08,280 for thousands of years. 209 00:15:08,280 --> 00:15:11,800 But it's only when we try to measure it accurately that we start 210 00:15:11,800 --> 00:15:13,640 to appreciate its mystery. 211 00:15:16,080 --> 00:15:19,920 So the way that traditionally we measure the passage of time 212 00:15:19,920 --> 00:15:23,520 is to look to the heavens and look to when the sun 213 00:15:23,520 --> 00:15:26,880 reaches its highest point in the sky, and we call that noon. 214 00:15:26,880 --> 00:15:32,120 That turns out not to be sufficient because it's not accurate enough. 215 00:15:32,120 --> 00:15:35,840 The Earth doesn't spin on its axis at a constant rate. 216 00:15:35,840 --> 00:15:39,520 The Earth wobbles around by quite a bit, actually. 217 00:15:39,520 --> 00:15:42,960 The Earth's orbit is not entirely precise. 218 00:15:42,960 --> 00:15:44,680 Things change. 219 00:15:44,680 --> 00:15:48,240 So if we want to measure increasingly small time intervals 220 00:15:48,240 --> 00:15:51,440 accurately, then the heavens are not the way to do it. 221 00:15:53,160 --> 00:15:55,920 And so we can build mechanical watches, 222 00:15:55,920 --> 00:15:58,440 and that's what we did initially when we had to measure time 223 00:15:58,440 --> 00:16:00,680 more accurately for navigational purposes. 224 00:16:00,680 --> 00:16:04,920 But even bits of, you know, cogs and gears and springs, 225 00:16:04,920 --> 00:16:07,960 that's not particularly accurate either. 226 00:16:07,960 --> 00:16:11,320 And so if you really want to start dividing time up into very 227 00:16:11,320 --> 00:16:15,760 small intervals, which we have to do today for so many reasons, 228 00:16:15,760 --> 00:16:18,760 then you need to look to the subatomic world 229 00:16:18,760 --> 00:16:23,680 and you find that in the world of atoms and subatomic particles, 230 00:16:23,680 --> 00:16:28,080 you can identify exquisitely accurate natural clocks. 231 00:16:29,560 --> 00:16:31,840 MILITARY BAND PLAYS 232 00:16:31,840 --> 00:16:33,400 I'm going to try and answer 233 00:16:33,400 --> 00:16:36,120 one of the simplest questions 234 00:16:36,120 --> 00:16:38,960 you could ask - what time is it? 235 00:16:38,960 --> 00:16:41,080 These are the early days, right. 236 00:16:41,080 --> 00:16:44,800 This is one of the first television programmes that I made. 237 00:16:46,880 --> 00:16:50,120 If there's one place on Earth where you can come to find the time, 238 00:16:50,120 --> 00:16:51,920 it's here in Washington DC. 239 00:16:54,800 --> 00:16:57,640 This is the home of the US Naval Observatory, 240 00:16:57,640 --> 00:17:01,200 one of a select bunch of time lords dotted across the planet 241 00:17:01,200 --> 00:17:03,800 who are the keepers of time on Earth. 242 00:17:03,800 --> 00:17:07,840 COMPUTERISED VOICE: Universal Time, 19 hours, 54 minutes exactly. 243 00:17:09,680 --> 00:17:12,760 A time now derived from atomic clocks. 244 00:17:14,080 --> 00:17:16,840 Dennis McCarthy, Director of Time. 245 00:17:16,840 --> 00:17:21,800 We defined a time in the 1950s based on the position of the moon 246 00:17:21,800 --> 00:17:23,680 with respect to the stars. 247 00:17:23,680 --> 00:17:26,640 We needed a more accurate kind of time. 248 00:17:26,640 --> 00:17:30,840 Not only is it... does it have to be more accurate 249 00:17:30,840 --> 00:17:33,080 but it has to be more accessible. 250 00:17:34,160 --> 00:17:37,920 That accessible kind of time is provided by atomic clocks. 251 00:17:37,920 --> 00:17:41,560 What we need to tell time is something which repeats 252 00:17:41,560 --> 00:17:44,920 with great regularity that you can count on. 253 00:17:44,920 --> 00:17:50,520 How well we can tell time depends on which atom you're using. 254 00:17:50,520 --> 00:17:55,680 So we choose certain ones to... to use for keeping atomic time. 255 00:17:57,520 --> 00:18:01,400 Inside the clocks are the atoms of a rare metal called caesium. 256 00:18:02,920 --> 00:18:06,320 The electrons in the caesium atoms are made to jump up. 257 00:18:07,560 --> 00:18:10,840 Then as they fall back down, they give out light. 258 00:18:12,560 --> 00:18:17,440 These light waves peak over nine billion times every second 259 00:18:17,440 --> 00:18:20,400 and it's this light that drives the clock, 260 00:18:20,400 --> 00:18:25,000 effectively producing nine billion ticks for each atomic second. 261 00:18:26,560 --> 00:18:29,160 This number never changes, never alters 262 00:18:29,160 --> 00:18:30,960 and that's why it's so accurate. 263 00:18:32,760 --> 00:18:35,560 So the atomic clock is actually putting out an electronic signal 264 00:18:35,560 --> 00:18:40,000 which is essentially analogous to the ticking of a pendulum clock. 265 00:18:40,000 --> 00:18:42,960 You know, a pendulum clock which might tick once every second 266 00:18:42,960 --> 00:18:44,760 or once every couple of seconds. 267 00:18:44,760 --> 00:18:46,800 This thing is providing us something 268 00:18:46,800 --> 00:18:49,440 which is going nine billion times per second. 269 00:18:49,440 --> 00:18:53,840 So it provides us with a very fine definition of time. 270 00:18:53,840 --> 00:18:57,160 We actually have a number of clocks at the Naval Observatory 271 00:18:57,160 --> 00:18:59,400 located all over the grounds. 272 00:18:59,400 --> 00:19:01,560 Here's... here's one of them. 273 00:19:01,560 --> 00:19:04,120 This is the master clock system one. Oh, yeah. 274 00:19:05,680 --> 00:19:08,640 This is the master clock system two. 275 00:19:09,800 --> 00:19:13,240 So if I want an answer to the question - what time is it? 276 00:19:14,880 --> 00:19:16,600 There it is? That's it. 277 00:19:16,600 --> 00:19:20,120 COMPUTERISED VOICE: Universal Time 20 hours, zero minutes exactly. 278 00:19:21,160 --> 00:19:24,040 Why do I need a clock that accurate? 279 00:19:24,040 --> 00:19:26,400 Well, we do. 280 00:19:26,400 --> 00:19:30,720 If you're using time to measure distance, which is how the GPS 281 00:19:30,720 --> 00:19:34,040 satellite navigation system works, then it matters. 282 00:19:34,040 --> 00:19:37,320 If your clock drifts by one nanosecond, 283 00:19:37,320 --> 00:19:41,360 then your position measurement is drifting by something like a foot. 284 00:19:43,960 --> 00:19:47,520 Atomic clocks can measure and divide time into intervals 285 00:19:47,520 --> 00:19:51,040 that are so minuscule that they are beyond human perception. 286 00:19:52,520 --> 00:19:55,680 But this precision means little when we begin to consider 287 00:19:55,680 --> 00:19:59,960 the timescales that determine our ultimate fate - cosmic time. 288 00:20:05,960 --> 00:20:10,360 Timescales in the cosmos seems so unimaginably vast, 289 00:20:10,360 --> 00:20:12,800 it's almost impossible to relate to them. 290 00:20:14,720 --> 00:20:18,000 Yet there are places on Earth where we can begin to encounter 291 00:20:18,000 --> 00:20:20,160 time on these universal scales. 292 00:20:29,000 --> 00:20:32,920 This is Ostional on the northern Pacific coast of Costa Rica, 293 00:20:32,920 --> 00:20:38,000 and I've come here to witness a natural event that's been 294 00:20:38,000 --> 00:20:41,000 happening long before there were any humans here to see it. 295 00:20:42,480 --> 00:20:46,480 And I suppose it really is a window into the distant past 296 00:20:46,480 --> 00:20:48,120 of life on our planet. 297 00:20:52,320 --> 00:20:54,720 PEOPLE CHAT AND LAUGH 298 00:21:11,400 --> 00:21:13,920 Once the sun has dipped below the horizon 299 00:21:13,920 --> 00:21:17,840 and the moon conspired to make the tides just right, 300 00:21:17,840 --> 00:21:21,320 this beach is visited by prehistoric creatures. 301 00:21:32,560 --> 00:21:35,720 Under the cover of darkness, they emerge from the ocean. 302 00:21:45,000 --> 00:21:47,920 Playa Ostional is one of the few beaches in the world 303 00:21:47,920 --> 00:21:51,040 where large numbers of sea turtles make their nests. 304 00:22:01,640 --> 00:22:05,720 But what makes this truly remarkable is the sheer length of time 305 00:22:05,720 --> 00:22:08,200 scenes like this have been playing out. 306 00:22:14,120 --> 00:22:18,400 Well, this is part one of the oldest life cycles on Earth. 307 00:22:20,000 --> 00:22:24,120 On nights like these for the last 100 million years, 308 00:22:24,120 --> 00:22:27,560 turtles like this have been hauling themselves out of the ocean 309 00:22:27,560 --> 00:22:29,440 to lay their eggs. 310 00:22:31,760 --> 00:22:34,360 It's an almost incomprehensible time span. 311 00:22:34,360 --> 00:22:37,560 I mean, 100 million years ago, there were dinosaurs roaming 312 00:22:37,560 --> 00:22:41,280 the Earth, but the Earth itself looked very different. 313 00:22:41,280 --> 00:22:45,360 I mean, South America was not connected to North America. 314 00:22:45,360 --> 00:22:49,400 North America was somewhere over close to Europe. 315 00:22:49,400 --> 00:22:51,720 Australia was connected to Antarctica. 316 00:22:56,560 --> 00:22:58,840 THUNDER RUMBLES 317 00:22:58,840 --> 00:23:01,560 It really is quite wonderful to be so close 318 00:23:01,560 --> 00:23:05,600 to such an ancient cycle of life. 319 00:23:07,640 --> 00:23:09,920 You can hear her breathing, actually. 320 00:23:11,440 --> 00:23:13,760 TURTLE EXHALES 321 00:23:21,640 --> 00:23:25,080 So, a remarkable experience. 322 00:23:25,080 --> 00:23:29,760 I mean, it really is beautiful to see that on the one night 323 00:23:29,760 --> 00:23:32,760 of many hundreds of millions of nights 324 00:23:32,760 --> 00:23:34,640 stretching back into the past. 325 00:23:42,280 --> 00:23:43,960 And she's gone. 326 00:23:56,440 --> 00:23:59,680 To witness a moment like this is to open up a connection 327 00:23:59,680 --> 00:24:01,520 to the deep past. 328 00:24:03,960 --> 00:24:08,480 To experience timespans far longer than the history of our own species. 329 00:24:11,320 --> 00:24:15,160 Yet, even the 100 million year story of the turtles 330 00:24:15,160 --> 00:24:20,560 only begins to connect us with the vast sweep of cosmic time. 331 00:24:26,880 --> 00:24:29,760 Our entire solar system is travelling 332 00:24:29,760 --> 00:24:32,400 on an unimaginably vast orbit, 333 00:24:32,400 --> 00:24:34,960 spinning around the centre of our galaxy. 334 00:24:42,200 --> 00:24:47,560 It takes 250 million years to make just one circuit of the Milky Way. 335 00:24:55,560 --> 00:24:58,280 In the entire history of the human race, 336 00:24:58,280 --> 00:25:02,600 we've travelled less than a tenth of 1% of that orbit. 337 00:25:15,760 --> 00:25:19,840 The timescales of our galaxy are almost beyond human comprehension. 338 00:25:22,400 --> 00:25:25,360 But when we extend our gaze beyond the Milky Way 339 00:25:25,360 --> 00:25:28,520 and out into the universe, 340 00:25:28,520 --> 00:25:32,360 we come face-to-face with truly deep time. 341 00:25:36,040 --> 00:25:39,480 The time that ticks on your watch is the time now, 342 00:25:39,480 --> 00:25:41,120 the time of the present. 343 00:25:42,760 --> 00:25:46,160 But the feeling we experience as the present time 344 00:25:46,160 --> 00:25:48,840 is something we shouldn't take for granted. 345 00:25:48,840 --> 00:25:53,560 Much of what we believe is in the present is drawn from the past. 346 00:25:55,160 --> 00:25:58,360 What we feel is happening now happened a little while ago. 347 00:26:00,800 --> 00:26:03,720 We feel that we experience a now around us. 348 00:26:03,720 --> 00:26:06,320 Everything we see happened now. 349 00:26:06,320 --> 00:26:10,440 But actually the light coming from distant things into your eye 350 00:26:10,440 --> 00:26:13,080 takes time to get there. 351 00:26:13,080 --> 00:26:16,320 So...you look at the sun. 352 00:26:16,320 --> 00:26:20,920 The sun is 93 million miles away. 353 00:26:20,920 --> 00:26:25,520 That means light takes over eight minutes to get from it 354 00:26:25,520 --> 00:26:30,360 into my eyes. So I'm seeing the sun as it was eight minutes in the past. 355 00:26:30,360 --> 00:26:34,640 It could explode and I wouldn't notice for eight minutes. 356 00:26:34,640 --> 00:26:37,320 I'd just see that beautiful image of the setting sun. 357 00:26:40,200 --> 00:26:43,240 The fact that light travels at a finite speed 358 00:26:43,240 --> 00:26:45,480 offers us a unique opportunity. 359 00:26:46,800 --> 00:26:51,040 It allows us to look back, not just eight minutes but millions, 360 00:26:51,040 --> 00:26:53,320 even billions of years. 361 00:26:58,680 --> 00:27:02,360 I've come to Baltimore to look back in time. 362 00:27:04,840 --> 00:27:09,040 Former director of the Hubble Space Telescope Steve Beckwith 363 00:27:09,040 --> 00:27:12,120 was responsible for taking an extraordinary photograph. 364 00:27:13,560 --> 00:27:17,080 As a director, I had at my discretion 10% of the telescope time 365 00:27:17,080 --> 00:27:19,400 per year, that I could use for anything. 366 00:27:19,400 --> 00:27:22,920 One year I took all of my time, in fact I took a little bit more 367 00:27:22,920 --> 00:27:25,440 than all of my time, and decided that we would devote it 368 00:27:25,440 --> 00:27:28,000 to the deepest picture ever taken of the universe. 369 00:27:29,720 --> 00:27:34,880 In 2004, Steve pointed the Hubble Telescope at a tiny piece 370 00:27:34,880 --> 00:27:39,280 of the night sky and took a picture called the Ultra-Deep Field. 371 00:27:41,600 --> 00:27:44,040 It took a million seconds of exposure 372 00:27:44,040 --> 00:27:48,000 on the Hubble Space Telescope, the world's most powerful telescope, 373 00:27:48,000 --> 00:27:52,680 and in this image we can look back in time 13 billion years. 374 00:27:52,680 --> 00:27:55,880 It's a difficult picture almost to comprehend, isn't it? 375 00:27:55,880 --> 00:27:59,240 Because in some sense, it's... 3D is the wrong word. 376 00:27:59,240 --> 00:28:02,280 But it's, it's some sense... Oh, no, it is the right word. 377 00:28:02,280 --> 00:28:04,800 It is 3D. We are looking back in time. 378 00:28:07,120 --> 00:28:10,520 Every single galaxy in this image can be dated. 379 00:28:12,280 --> 00:28:13,960 This galaxy emitted its light 380 00:28:13,960 --> 00:28:16,560 when the universe was 8.8 billion years old. 381 00:28:16,560 --> 00:28:19,960 Then, as you go back in time, this is a galaxy that emitted its light 382 00:28:19,960 --> 00:28:22,280 when the universe was 3.3 billion years old. 383 00:28:22,280 --> 00:28:24,320 You can see it looks completely different. 384 00:28:24,320 --> 00:28:26,160 It's really very chaotic. 385 00:28:26,160 --> 00:28:28,880 And this is one billion years after the Big Bang. 386 00:28:28,880 --> 00:28:31,240 Very red, a little tail, very small. 387 00:28:33,320 --> 00:28:37,520 The most distant galaxy in the Ultra-Deep Field 388 00:28:37,520 --> 00:28:40,080 is a red one that's right over here. This one here? 389 00:28:40,080 --> 00:28:42,720 The light from that was emitted when the universe 390 00:28:42,720 --> 00:28:44,760 was 700-800 million years old. 391 00:28:45,840 --> 00:28:49,760 So, really, this is one of the first structures 392 00:28:49,760 --> 00:28:51,800 that formed in the universe? 393 00:28:51,800 --> 00:28:54,040 This is one of the first structures that formed 394 00:28:54,040 --> 00:28:56,520 and it's one of the first structures we've been able to see. 395 00:28:56,520 --> 00:28:58,800 In a sense you see this... 396 00:29:00,440 --> 00:29:03,840 ..almost, I was going to say paradoxical, 397 00:29:03,840 --> 00:29:08,880 but strange behaviour of the universe as revealed by astronomy. 398 00:29:08,880 --> 00:29:14,040 Because I'm trying to say, well, what does that look like now? 399 00:29:14,040 --> 00:29:16,320 You know, what would that look like now? 400 00:29:16,320 --> 00:29:20,160 In a sense, it's the wrong language to use, isn't it? 401 00:29:20,160 --> 00:29:22,520 That's what it looks like now. That's right. 402 00:29:24,960 --> 00:29:29,960 Steve has turned his photo into a movie to journey back in time. 403 00:29:31,640 --> 00:29:35,360 You see these little pieces coming at us? We're going back in time, 404 00:29:35,360 --> 00:29:37,720 and you can see the three-dimensional effect. 405 00:29:37,720 --> 00:29:40,360 Some of these others are a little farther back 406 00:29:40,360 --> 00:29:42,760 but here we're going back, we're probably back now 407 00:29:42,760 --> 00:29:45,520 about three billion years from the present. 408 00:29:45,520 --> 00:29:48,320 As we keep going and you get to the smaller ones, 409 00:29:48,320 --> 00:29:51,400 you get back to about eight or nine billion years. 410 00:29:53,040 --> 00:29:56,280 And then, when we get to the very tiny most distant ones, 411 00:29:56,280 --> 00:30:00,600 we'll be back probably ten or 11 billion years in time. 412 00:30:00,600 --> 00:30:03,000 And we're deep into the universe and we're just looking 413 00:30:03,000 --> 00:30:07,160 at the smallest structures back in time to about 13 billion years, 414 00:30:07,160 --> 00:30:09,200 and suddenly we run out. 415 00:30:26,560 --> 00:30:29,320 The Hubble Space Telescope can see galaxies 416 00:30:29,320 --> 00:30:33,160 that are as they were about 500 million years after the Big Bang. 417 00:30:34,800 --> 00:30:37,400 But it can't see further back than that. 418 00:30:38,520 --> 00:30:41,560 The reason is that the universe is expanding. 419 00:30:43,520 --> 00:30:46,760 And, so, as the light travels through the expanding universe, 420 00:30:46,760 --> 00:30:48,800 it gets stretched. 421 00:30:48,800 --> 00:30:51,600 And that means that it gets redder and redder and redder 422 00:30:51,600 --> 00:30:54,800 until it gets so red that the Hubble Space Telescope 423 00:30:54,800 --> 00:30:56,600 isn't sensitive to it. 424 00:30:56,600 --> 00:30:59,600 So it can't see any further away than that. 425 00:31:03,000 --> 00:31:06,480 But a new telescope with that capability 426 00:31:06,480 --> 00:31:08,800 is due to be launched later this year. 427 00:31:11,240 --> 00:31:14,800 The James Webb Telescope is going to be much more sensitive 428 00:31:14,800 --> 00:31:17,200 to those, what we call, the infrared light, 429 00:31:17,200 --> 00:31:19,160 so the very long wavelengths. 430 00:31:19,160 --> 00:31:23,400 And that means it will be able to see back past those galaxies 431 00:31:23,400 --> 00:31:26,760 that Hubble can see to the very early history of the universe. 432 00:31:28,160 --> 00:31:32,760 We'll be able to watch the formation of the first stars and galaxies. 433 00:31:40,200 --> 00:31:43,400 We're able to look very far back into the past, 434 00:31:43,400 --> 00:31:45,280 but we can't see into the future. 435 00:31:46,400 --> 00:31:48,240 Which raises the question, 436 00:31:48,240 --> 00:31:50,960 what is the difference between the two? 437 00:31:50,960 --> 00:31:54,640 Why does time appear to flow only in one direction? 438 00:31:56,240 --> 00:31:59,800 This question has puzzled many of science's greatest minds. 439 00:32:02,080 --> 00:32:05,320 All the laws of nature that we have today that we consider 440 00:32:05,320 --> 00:32:10,480 to be fundamental, so Einstein's equations or Newton's laws 441 00:32:10,480 --> 00:32:13,920 for that matter, all of them make no distinction 442 00:32:13,920 --> 00:32:18,480 in the direction of the flow of time, if you like. 443 00:32:18,480 --> 00:32:24,360 There's only one law of physics that has an explicit direction of time 444 00:32:24,360 --> 00:32:29,160 in it, and that law is concerned with something called entropy. 445 00:32:38,720 --> 00:32:42,440 Entropy explains why, left to the mercy of the elements, 446 00:32:42,440 --> 00:32:47,000 mortar crumbles, glass shatters and buildings collapse. 447 00:32:50,200 --> 00:32:54,120 And a good way to understand how is to think of objects 448 00:32:54,120 --> 00:32:58,520 not as single things but as being made up of many constituent parts, 449 00:32:58,520 --> 00:33:03,160 like the individual grains that make up this pile of sand. 450 00:33:05,960 --> 00:33:08,880 Now, entropy is a measure of how many ways 451 00:33:08,880 --> 00:33:13,640 I can rearrange those grains and still keep the sand pile the same. 452 00:33:13,640 --> 00:33:16,600 And there are trillions and trillions and trillions 453 00:33:16,600 --> 00:33:18,560 of ways of doing that. 454 00:33:18,560 --> 00:33:21,280 I mean, pretty much anything I do to this sand pile, 455 00:33:21,280 --> 00:33:23,920 if I mess the sand around and move it around, 456 00:33:23,920 --> 00:33:27,000 then it doesn't change the shape or the structure at all. 457 00:33:27,000 --> 00:33:29,960 So, in the language of entropy, 458 00:33:29,960 --> 00:33:32,440 this sand pile has high entropy 459 00:33:32,440 --> 00:33:35,320 because there are many, many ways that I can rearrange 460 00:33:35,320 --> 00:33:37,600 its constituents and not change it. 461 00:33:38,880 --> 00:33:42,320 But now let me create some order in the universe. 462 00:33:49,960 --> 00:33:54,400 Now, there are approximately as many sand grains in this sand castle 463 00:33:54,400 --> 00:33:55,880 as there are in the sand pile. 464 00:33:57,680 --> 00:34:01,120 But now, virtually anything I do to it will mess it up, 465 00:34:01,120 --> 00:34:05,080 will remove the beautiful order from this structure. 466 00:34:05,080 --> 00:34:08,920 And because of that, the sand castle has a low entropy. 467 00:34:08,920 --> 00:34:11,280 It's a much more ordered state. 468 00:34:11,280 --> 00:34:14,720 So, many ways of rearranging the sand grains 469 00:34:14,720 --> 00:34:18,760 without changing the structure - high entropy. 470 00:34:18,760 --> 00:34:22,640 Very few ways of rearranging the sand grains without changing 471 00:34:22,640 --> 00:34:26,520 the structure, without disordering it - low entropy. 472 00:34:35,480 --> 00:34:38,680 Now, imagine I was to leave this castle in the desert all day - 473 00:34:38,680 --> 00:34:41,840 then, it's obvious what's going to happen. 474 00:34:41,840 --> 00:34:44,680 The desert winds are going to blow the sand around 475 00:34:44,680 --> 00:34:47,560 and this castle is going to disintegrate. 476 00:34:47,560 --> 00:34:50,440 It's going to become less ordered. 477 00:34:50,440 --> 00:34:52,120 It's going to fall to bits. 478 00:34:55,920 --> 00:35:00,040 But think about what's happening on the fundamental level. 479 00:35:00,040 --> 00:35:02,720 The wind is taking the sand off the castle 480 00:35:02,720 --> 00:35:07,240 and blowing it over there somewhere and making a sand pile. 481 00:35:07,240 --> 00:35:11,360 There's nothing fundamental in the laws of physics that says 482 00:35:11,360 --> 00:35:15,000 that the wind couldn't pick up some sand from over here, 483 00:35:15,000 --> 00:35:19,160 deposit it here, and deposit it in precisely 484 00:35:19,160 --> 00:35:21,240 the shape of a sand castle. 485 00:35:21,240 --> 00:35:25,840 In principle, the wind could spontaneously build a sand castle 486 00:35:25,840 --> 00:35:27,640 out of a pile of sand. 487 00:35:39,000 --> 00:35:42,360 There's no reason why that couldn't happen, it's just extremely, 488 00:35:42,360 --> 00:35:46,760 extremely unlikely because there are very few ways of organising this 489 00:35:46,760 --> 00:35:49,160 sand so that it looks like a castle. 490 00:35:55,960 --> 00:35:58,400 It's overwhelmingly more likely 491 00:35:58,400 --> 00:36:01,520 that when the wind blows the sand around, it will take 492 00:36:01,520 --> 00:36:03,600 the low entropy structure, the castle, 493 00:36:03,600 --> 00:36:08,240 and turn it into a high entropy structure, the sand pile. 494 00:36:15,400 --> 00:36:18,840 So, entropy always increases. 495 00:36:18,840 --> 00:36:20,760 Why is that? 496 00:36:20,760 --> 00:36:24,640 Because it's overwhelmingly more likely that it will. 497 00:36:34,200 --> 00:36:38,920 There was a tremendous sandstorm and we all hid, 498 00:36:38,920 --> 00:36:40,760 and it was just vicious. 499 00:36:45,000 --> 00:36:47,360 And when we came out, 500 00:36:47,360 --> 00:36:49,920 we had cameras and we were opening, taking the lenses off 501 00:36:49,920 --> 00:36:52,160 and just pouring sand out of them! 502 00:37:08,400 --> 00:37:11,880 The Second Law of Thermodynamics, for me, demonstrates everything 503 00:37:11,880 --> 00:37:16,200 that is powerful and beautiful and profound about physics. 504 00:37:16,200 --> 00:37:20,360 Here's a law that entered science as a way of talking about how heat 505 00:37:20,360 --> 00:37:23,760 moves around and the efficiency of steam engines. 506 00:37:23,760 --> 00:37:29,160 But it ended up being able to explain one of THE great mysteries 507 00:37:29,160 --> 00:37:31,200 in the history of science. 508 00:37:31,200 --> 00:37:34,880 Why is there a difference between the past and the future? 509 00:37:34,880 --> 00:37:39,800 You see, the Second Law says that everything tends from order 510 00:37:39,800 --> 00:37:41,640 to disorder. 511 00:37:41,640 --> 00:37:44,000 That means that there is a difference 512 00:37:44,000 --> 00:37:45,960 between the past and the future. 513 00:37:45,960 --> 00:37:48,480 In the past, the universe was more ordered 514 00:37:48,480 --> 00:37:52,480 and in the future, the universe will be less ordered. 515 00:37:52,480 --> 00:37:56,000 And that means that there's a direction to the passage of time. 516 00:37:56,000 --> 00:38:00,520 So, the Second Law of Thermodynamics has introduced the concept 517 00:38:00,520 --> 00:38:03,760 of an arrow of time into science. 518 00:38:05,480 --> 00:38:08,560 The so-called thermodynamic arrow of time, 519 00:38:08,560 --> 00:38:11,880 this idea that entropy always increases, 520 00:38:11,880 --> 00:38:18,320 is well understood, but actually its origin at a deep level 521 00:38:18,320 --> 00:38:20,440 is not so clear. 522 00:38:22,560 --> 00:38:26,720 The reason seems to be something to do with 523 00:38:26,720 --> 00:38:30,080 the origin of the universe itself and the presence of this 524 00:38:30,080 --> 00:38:34,240 strange thing called the Big Bang way back in our past. 525 00:38:34,240 --> 00:38:38,920 Why were things in the past so beautifully ordered, 526 00:38:38,920 --> 00:38:44,440 that the universe can fall to bits gently and in the process, 527 00:38:44,440 --> 00:38:47,360 in the transition from order to disorder, 528 00:38:47,360 --> 00:38:49,120 these tremendous structures, 529 00:38:49,120 --> 00:38:52,480 of which we are the most magnificent example, 530 00:38:52,480 --> 00:38:55,240 can exist for a brief time in the universe? 531 00:38:57,120 --> 00:39:00,800 There are almost more opinions than there are theoretical physicists 532 00:39:00,800 --> 00:39:02,840 on this question! 533 00:39:04,240 --> 00:39:08,720 The Second Law of Thermodynamics is an explanation for the arrow 534 00:39:08,720 --> 00:39:12,920 of time, and what makes the past different from the future. 535 00:39:14,880 --> 00:39:18,880 But it is silent on a question that excites science fiction writers 536 00:39:18,880 --> 00:39:21,160 and physicists alike. 537 00:39:23,280 --> 00:39:26,160 If I'm in a big audience of people and someone says, 538 00:39:26,160 --> 00:39:29,040 "Is time travel possible?" there might be someone who thinks 539 00:39:29,040 --> 00:39:32,800 they know it just adds a bit of a laugh and chuckles. 540 00:39:32,800 --> 00:39:34,720 It is a very good question. 541 00:39:34,720 --> 00:39:36,920 The answer is, we don't know for sure. 542 00:39:43,120 --> 00:39:46,360 I think that, ultimately, 543 00:39:46,360 --> 00:39:49,400 the desire to go back in time 544 00:39:49,400 --> 00:39:53,640 is tied in to the tragedy of human experience. 545 00:39:53,640 --> 00:39:55,440 We've all... 546 00:39:55,440 --> 00:39:58,200 There are not only moments that we wish we could relive, 547 00:39:58,200 --> 00:40:01,320 there are people that we wish we could see again. 548 00:40:01,320 --> 00:40:03,800 People who are no longer with us. 549 00:40:03,800 --> 00:40:08,200 So, the idea that somehow the past might be accessible is extremely 550 00:40:08,200 --> 00:40:10,320 enticing and powerful, emotionally. 551 00:40:13,680 --> 00:40:17,560 But that's impossible if the past only exists in our memories. 552 00:40:18,960 --> 00:40:21,520 That was the accepted view. 553 00:40:21,520 --> 00:40:23,480 But Einstein changed that. 554 00:40:25,040 --> 00:40:28,400 If we take his Theory of Relativity at face value, 555 00:40:28,400 --> 00:40:32,200 then every moment of our past still exists. 556 00:40:37,600 --> 00:40:41,880 We feel as if we move through space as time ticks by. 557 00:40:43,000 --> 00:40:44,640 But that's an illusion. 558 00:40:44,640 --> 00:40:48,360 The separation of space and time is false. 559 00:40:48,360 --> 00:40:51,480 The first person to realise that was Albert Einstein. 560 00:40:51,480 --> 00:40:55,880 He thought deeply about motion, about the idea that we can't tell 561 00:40:55,880 --> 00:40:57,640 whether we're moving or not. 562 00:40:57,640 --> 00:41:02,200 And he tried to reconcile that with our picture of the universal laws 563 00:41:02,200 --> 00:41:05,760 of nature, and he found that he could do, 564 00:41:05,760 --> 00:41:10,880 at the expensive of jettisoning space and time as separate entities 565 00:41:10,880 --> 00:41:15,880 and merging them together into a unified whole, 566 00:41:15,880 --> 00:41:19,320 the fabric of the universe called Spacetime. 567 00:41:22,480 --> 00:41:25,320 As the Earth moves through Spacetime, 568 00:41:25,320 --> 00:41:29,120 its orbit traces out a spiral as it circles the sun 569 00:41:29,120 --> 00:41:31,600 and races into the future. 570 00:41:35,840 --> 00:41:38,840 It never returns to the same place 571 00:41:38,840 --> 00:41:41,880 because each moment is a different location 572 00:41:41,880 --> 00:41:44,120 in the fabric of the universe. 573 00:41:48,480 --> 00:41:51,640 And just as the Earth travels relentlessly onwards 574 00:41:51,640 --> 00:41:53,920 on its path through Spacetime, 575 00:41:53,920 --> 00:41:55,840 so must we. 576 00:42:11,360 --> 00:42:16,440 So this is how Einstein asks us to picture the sweep of our lives, 577 00:42:16,440 --> 00:42:19,160 the experience of living. 578 00:42:19,160 --> 00:42:21,920 Our lives are a series of moments 579 00:42:21,920 --> 00:42:25,280 and they're laid out like places on a map. 580 00:42:28,000 --> 00:42:30,120 There's me as a little baby. 581 00:42:30,120 --> 00:42:32,040 My dad with my grandad. 582 00:42:34,680 --> 00:42:38,200 That idyllic summer some time in the early '70s in a paddling pool 583 00:42:38,200 --> 00:42:39,880 with my sister. 584 00:42:42,840 --> 00:42:46,040 When I was about four years old. 585 00:42:46,040 --> 00:42:48,840 And the perfect Christmas with my grandparents 586 00:42:48,840 --> 00:42:51,160 sometime back in the 1970s. 587 00:42:51,160 --> 00:42:56,040 There's me when I was 20 years old with a ridiculous haircut 588 00:42:56,040 --> 00:42:59,360 playing a gig somewhere in the middle of Europe. 589 00:42:59,360 --> 00:43:01,000 In Budapest, I think. 590 00:43:04,280 --> 00:43:05,720 Wedding day. 591 00:43:08,640 --> 00:43:11,800 And me in Oldham, where I grew up, 592 00:43:11,800 --> 00:43:14,240 with my little boy, George. 593 00:43:19,280 --> 00:43:21,640 That was a very personal scene. 594 00:43:22,760 --> 00:43:25,680 It was really personal because, actually, it wasn't long 595 00:43:25,680 --> 00:43:27,160 after my dad had died. 596 00:43:27,160 --> 00:43:31,080 So in my mind, there was, obviously, as with everyone 597 00:43:31,080 --> 00:43:33,600 who goes through those experiences as we all do, 598 00:43:33,600 --> 00:43:36,920 there's a, you know, 599 00:43:36,920 --> 00:43:41,160 a reconsideration or a rethinking of the past. 600 00:43:41,160 --> 00:43:45,000 You find your mind wandering back into the past and past events. 601 00:43:46,640 --> 00:43:49,480 This isn't exactly like a map. 602 00:43:49,480 --> 00:43:54,080 See, I can return to these places in space, to Oldham, 603 00:43:54,080 --> 00:43:57,560 to central Europe, to Duluth, Minnesota where I got married, 604 00:43:57,560 --> 00:43:59,320 back to Oldham again. 605 00:44:00,680 --> 00:44:05,280 But I can't return to these moments, to these events in Spacetime. 606 00:44:05,280 --> 00:44:09,240 Because of the geometry of Spacetime itself, 607 00:44:09,240 --> 00:44:13,440 we are compelled to move inexorably into the future. 608 00:44:18,400 --> 00:44:22,600 What's interesting is that in Einstein's Theory of Relativity, 609 00:44:22,600 --> 00:44:26,240 the past is not accessible 610 00:44:26,240 --> 00:44:30,520 but it's still there in a very real sense. 611 00:44:30,520 --> 00:44:35,600 I think the bottom line is, no, you can't travel into the past. 612 00:44:36,680 --> 00:44:38,400 Probably! 613 00:44:38,400 --> 00:44:43,360 But the explanation for that is anything but trivial. 614 00:44:46,760 --> 00:44:49,960 But time travel into the future is a different matter. 615 00:44:49,960 --> 00:44:53,520 We are all travelling into the future all the time. 616 00:44:53,520 --> 00:44:57,600 But Einstein's Theory of Relativity tells us that we are each 617 00:44:57,600 --> 00:44:59,600 doing it at different rates. 618 00:45:02,920 --> 00:45:06,520 We experience time passing because we are all travelling 619 00:45:06,520 --> 00:45:08,920 along the time dimension. 620 00:45:10,480 --> 00:45:12,760 But, strangely, Einstein also said 621 00:45:12,760 --> 00:45:16,160 we don't all experience the same time. 622 00:45:20,600 --> 00:45:23,840 Spacetime can be pictured as a sort of fabric 623 00:45:23,840 --> 00:45:27,760 where time and space are inextricably woven together. 624 00:45:29,280 --> 00:45:33,840 As a result, the dimensions of space and time can get mixed up. 625 00:45:35,880 --> 00:45:38,280 Although we are all travelling through Spacetime 626 00:45:38,280 --> 00:45:42,680 at the speed of light, it's the mixing of time and space 627 00:45:42,680 --> 00:45:47,040 that Einstein said causes time to tick differently for each of us. 628 00:45:50,440 --> 00:45:55,880 For Einstein, time wasn't like a metronome 629 00:45:55,880 --> 00:45:59,960 that just ticks the same for everybody. 630 00:45:59,960 --> 00:46:02,400 It's different for you and me, 631 00:46:02,400 --> 00:46:07,360 and everywhere in the universe, the metronomes tick at different rates. 632 00:46:11,240 --> 00:46:14,720 Einstein said that two people will only ever agree 633 00:46:14,720 --> 00:46:19,120 on the speed time ticks if they're standing next to each other. 634 00:46:23,440 --> 00:46:26,760 If I was to fly past you incredibly fast, 635 00:46:26,760 --> 00:46:30,920 I would see your time tick much slower than mine. 636 00:46:33,120 --> 00:46:37,120 This idea lies at the heart of Einstein's Theory of Relativity. 637 00:46:38,680 --> 00:46:43,320 No-one has a right to the... to claim that their time is THE time, 638 00:46:43,320 --> 00:46:45,520 the absolute time. 639 00:46:45,520 --> 00:46:48,200 It just depends on who's moving relative to who. 640 00:46:50,200 --> 00:46:53,760 Because of the mixing of space and time, 641 00:46:53,760 --> 00:46:58,000 time ticks differently for you relative to other people, 642 00:46:58,000 --> 00:47:01,680 depending on how fast everyone is moving. 643 00:47:01,680 --> 00:47:03,320 When someone moves relative to me, 644 00:47:03,320 --> 00:47:07,520 they use some of their speed of light through Spacetime 645 00:47:07,520 --> 00:47:09,280 to move through space. 646 00:47:09,280 --> 00:47:11,880 So they haven't got as much left to move through time, 647 00:47:11,880 --> 00:47:16,600 and that means that their speed through time is a bit slower. 648 00:47:16,600 --> 00:47:19,880 They've sort of, in a very real sense, used a bit of it up. 649 00:47:19,880 --> 00:47:23,520 It's a really profound way of understanding 650 00:47:23,520 --> 00:47:25,680 Einstein's theory of Spacetime. 651 00:47:27,960 --> 00:47:31,120 And the strange nature of time doesn't stop there. 652 00:47:32,160 --> 00:47:34,560 It's not just how fast you're moving 653 00:47:34,560 --> 00:47:38,200 but what you're next to that also affects time. 654 00:47:41,000 --> 00:47:44,800 According to Einstein, you should see the time tick slower 655 00:47:44,800 --> 00:47:48,840 at my feet than at the top of my head. 656 00:47:48,840 --> 00:47:53,240 This is because the nearer you are to a big object like the Earth, 657 00:47:53,240 --> 00:47:57,160 the more bent and warped is the Spacetime, 658 00:47:57,160 --> 00:47:59,480 and the slower time ticks. 659 00:48:00,760 --> 00:48:03,280 On our planet the effect is minuscule 660 00:48:03,280 --> 00:48:07,680 but out there in the universe, the vast mass of the stars and galaxies 661 00:48:07,680 --> 00:48:13,680 bend and warp the Spacetime so much that time ticks all over the place. 662 00:48:16,000 --> 00:48:19,880 There's a very famous experiment in 1971 by Hafele and Keating 663 00:48:19,880 --> 00:48:23,040 in which they decided to, 664 00:48:23,040 --> 00:48:26,600 let's say, put Einstein to the test. 665 00:48:26,600 --> 00:48:29,560 They got atomic clocks and they flew them 666 00:48:29,560 --> 00:48:33,640 around the world on civil airliners one way, and around the world 667 00:48:33,640 --> 00:48:36,640 on civil airliners the other way, synchronised them all 668 00:48:36,640 --> 00:48:39,720 before they left and compared them when they came back. 669 00:48:40,960 --> 00:48:43,360 And the clocks that went eastward around the world 670 00:48:43,360 --> 00:48:46,400 lost 59 nanoseconds, 671 00:48:46,400 --> 00:48:49,160 59 thousand-millionths of a second. 672 00:48:49,160 --> 00:48:55,120 And the one that went westward gained 273 nanoseconds. 673 00:48:56,960 --> 00:49:01,200 The people on those planes aged at different rates, 674 00:49:01,200 --> 00:49:04,840 the same amount as the shift in the time difference 675 00:49:04,840 --> 00:49:06,640 is measured by the clocks. 676 00:49:08,000 --> 00:49:11,360 And so we can travel into the future, 677 00:49:11,360 --> 00:49:14,560 but actually, we can travel into the future at different rates. 678 00:49:16,200 --> 00:49:20,040 Let's say I get into spacecraft now and fly off to Alpha Centauri 679 00:49:20,040 --> 00:49:23,200 and come back again. I can arrange that journey, 680 00:49:23,200 --> 00:49:26,800 and if I can travel fast enough, such that I come back 1,000 years 681 00:49:26,800 --> 00:49:29,680 in the future or 10,000 years in the future. 682 00:49:29,680 --> 00:49:32,680 Actually, the closer I can make it to the speed of light, 683 00:49:32,680 --> 00:49:34,920 the further into the future I can get. 684 00:49:43,560 --> 00:49:47,400 I think the more that you know about time, 685 00:49:47,400 --> 00:49:53,360 the more you consider the fundamental nature of reality itself 686 00:49:53,360 --> 00:49:58,240 and discover that it's nothing like our experience of the world, 687 00:49:58,240 --> 00:50:01,320 then the more astonished you become! 688 00:50:01,320 --> 00:50:04,040 And at some point, I'll probably become so astonished 689 00:50:04,040 --> 00:50:06,600 that I'll no longer be able to speak about it! 690 00:50:09,800 --> 00:50:13,400 Even though physicists are still grappling with the fundamental 691 00:50:13,400 --> 00:50:18,080 nature of time, we do know with reasonable certainty 692 00:50:18,080 --> 00:50:20,960 how time will ultimately end. 693 00:50:37,480 --> 00:50:40,960 There are few places on Earth where you can get an inkling 694 00:50:40,960 --> 00:50:43,960 of what the far future has in store. 695 00:50:43,960 --> 00:50:45,880 HELICOPTER ROTORS WHIR 696 00:50:57,240 --> 00:51:00,560 This is Namibia's Skeleton Coast, where the cold waters 697 00:51:00,560 --> 00:51:03,440 of the South Atlantic meet the Namib Desert. 698 00:51:03,440 --> 00:51:07,040 And it is one of the most inhospitable places on Earth. 699 00:51:07,040 --> 00:51:10,960 Back in the 17th century, Portuguese sailors used to call this place 700 00:51:10,960 --> 00:51:15,080 The Gates to Hell because this dense fog that you see 701 00:51:15,080 --> 00:51:20,080 pretty much every morning along this coast, coupled with the constantly 702 00:51:20,080 --> 00:51:24,520 shifting shape of the sandbanks, meant that over the years 703 00:51:24,520 --> 00:51:27,840 literally thousands of ships were wrecked along this coastline. 704 00:51:34,040 --> 00:51:37,480 And even if you made it to shore, that wasn't the end of your problems 705 00:51:37,480 --> 00:51:39,880 because the currents are so strong here 706 00:51:39,880 --> 00:51:43,440 that there is no way of rowing back out to sea. 707 00:51:43,440 --> 00:51:46,360 If you look that way, there's just hundreds of miles 708 00:51:46,360 --> 00:51:48,080 of inhospitable desert. 709 00:51:51,040 --> 00:51:55,400 So, it genuinely was a place of no return. 710 00:51:55,400 --> 00:51:59,280 If you were shipwrecked here, this was the end of your universe. 711 00:52:11,200 --> 00:52:13,200 This is the Edward Bohlen. 712 00:52:13,200 --> 00:52:17,120 She was once an ocean-going steamer ferrying passengers and cargo 713 00:52:17,120 --> 00:52:18,880 between here and Europe. 714 00:52:24,400 --> 00:52:27,840 On 5th September 1909, she ran aground in thick fog. 715 00:52:34,520 --> 00:52:38,560 Yet, like all the vessels wrecked along this shoreline, the time it 716 00:52:38,560 --> 00:52:43,520 takes her to decay to nothing will be far longer than her time at sea. 717 00:52:48,320 --> 00:52:53,000 And in the far future, long after our own sun has run out of fuel, 718 00:52:53,000 --> 00:52:57,120 a similar destiny awaits the universe's last stars. 719 00:53:01,160 --> 00:53:05,400 A black dwarf will be the final fate of those last stars - 720 00:53:05,400 --> 00:53:08,680 white dwarfs that have become so cold that they barely emit 721 00:53:08,680 --> 00:53:11,080 any more heat or light. 722 00:53:15,240 --> 00:53:20,760 Black dwarves are dark, dense, decaying bowls of degenerate matter, 723 00:53:20,760 --> 00:53:23,800 little more than the ashes of stars. 724 00:53:26,040 --> 00:53:29,520 Their constituent atoms are so severely crushed 725 00:53:29,520 --> 00:53:33,440 that black dwarves are a million times denser than our sun. 726 00:53:35,520 --> 00:53:38,200 Stars takes so long to reach this point 727 00:53:38,200 --> 00:53:40,440 that after nearly 14 billion years, 728 00:53:40,440 --> 00:53:44,680 we believe there are currently no black dwarves in the universe. 729 00:53:46,200 --> 00:53:48,920 But despite never seeing one, we can still predict 730 00:53:48,920 --> 00:53:50,960 how they will end their days. 731 00:53:52,320 --> 00:53:55,880 Just as the iron that makes up this ship will eventually rust 732 00:53:55,880 --> 00:53:59,280 and be carried away by the desert winds, 733 00:53:59,280 --> 00:54:04,000 so we think that the matter inside black dwarves, the last matter 734 00:54:04,000 --> 00:54:09,720 in the universe, will eventually evaporate away and be carried off 735 00:54:09,720 --> 00:54:12,320 into the void as radiation, 736 00:54:12,320 --> 00:54:15,840 leaving absolutely nothing behind. 737 00:54:21,160 --> 00:54:26,120 There were wild dogs everywhere, actually, when we were filming that. 738 00:54:26,120 --> 00:54:31,680 And so they... Standing there on my own and they're all gone, 739 00:54:31,680 --> 00:54:34,960 they're all in the helicopter, and I thought, 740 00:54:34,960 --> 00:54:37,560 I really hope they come back 741 00:54:37,560 --> 00:54:41,760 because the dogs are circling, you know. 742 00:54:45,960 --> 00:54:48,160 With the black dwarves gone, 743 00:54:48,160 --> 00:54:50,840 there won't be a single atom of matter left. 744 00:54:53,640 --> 00:54:56,720 All that will remain of our once-rich cosmos 745 00:54:56,720 --> 00:54:59,960 will be particles of light and black holes. 746 00:55:07,160 --> 00:55:10,200 After an unimaginable length of time, 747 00:55:10,200 --> 00:55:14,040 even the black holes will have evaporated and the universe 748 00:55:14,040 --> 00:55:18,080 will be nothing but a sea of photons 749 00:55:18,080 --> 00:55:21,360 gradually tending towards the same temperature, 750 00:55:21,360 --> 00:55:25,960 as the expansion of the universe cools them towards absolute zero. 751 00:55:34,920 --> 00:55:38,320 And when I say unimaginable period of time, I really mean it. 752 00:55:38,320 --> 00:55:41,960 It's 10,000 trillion, trillion, trillion, trillion, trillion, 753 00:55:41,960 --> 00:55:44,880 trillion, trillion, trillion years. 754 00:55:44,880 --> 00:55:47,440 How big is that number? 755 00:55:47,440 --> 00:55:51,800 Well, if I were to start counting with a single atom representing 756 00:55:51,800 --> 00:55:56,960 one year, then there wouldn't be enough atoms in the entire universe 757 00:55:56,960 --> 00:56:00,200 to get anywhere near that number. 758 00:56:00,200 --> 00:56:02,960 CLOCK TICKS SOFTLY 759 00:56:05,960 --> 00:56:10,520 Once the very last remnants of the very last stars have finally 760 00:56:10,520 --> 00:56:14,640 decayed away to nothing, and everything reaches the same 761 00:56:14,640 --> 00:56:19,120 temperature, the story of the universe finally comes to an end. 762 00:56:23,560 --> 00:56:25,840 For the first time in its life, 763 00:56:25,840 --> 00:56:28,360 the universe will be permanent and unchanging. 764 00:56:30,920 --> 00:56:32,920 Nothing happens, 765 00:56:32,920 --> 00:56:36,040 and it keeps not happening forever. 766 00:56:47,080 --> 00:56:50,440 People always ask me, actually, why do you smile when you talk about 767 00:56:50,440 --> 00:56:55,040 the inevitable decay of the universe and the dissolving of everything 768 00:56:55,040 --> 00:56:59,120 that we hold most dear into a bath of radiation 769 00:56:59,120 --> 00:57:01,840 that will... will fade? 770 00:57:01,840 --> 00:57:05,400 So even the afterglow of our presence in the universe 771 00:57:05,400 --> 00:57:09,360 will become undetectable and there will be no memory at all... 772 00:57:09,360 --> 00:57:12,480 of everything or anything that we've created. 773 00:57:12,480 --> 00:57:16,400 There will be no imprint left of us at all in the far future. 774 00:57:16,400 --> 00:57:18,120 Why do you smile? 775 00:57:18,120 --> 00:57:20,320 And I just think it's quite funny. 776 00:57:20,320 --> 00:57:22,600 That's why I smile, I think! 777 00:57:22,600 --> 00:57:26,240 It certainly does take us down a peg or two, doesn't it? 778 00:57:26,240 --> 00:57:32,040 You know, I want to build a statue of myself, a grand celebration, 779 00:57:32,040 --> 00:57:34,920 a permanent monument of my achievements. 780 00:57:34,920 --> 00:57:38,200 There will be no such permanent monument of your achievements. 781 00:57:38,200 --> 00:57:40,960 Don't worry about the statues. Don't worry about them. 782 00:57:40,960 --> 00:57:44,640 They're all going to dissolve into a bath of photons!