1 00:00:01,793 --> 00:00:03,249 Lying just beneath everyday reality 2 00:00:03,337 --> 00:00:06,124 is a breathtaking world, 3 00:00:06,256 --> 00:00:10,249 where much of what we perceive about the universe is wrong. 4 00:00:10,344 --> 00:00:14,212 physicist and best-selling author Brian Greene takes you 5 00:00:14,306 --> 00:00:17,514 on a journey that bends the rules of human experience. 6 00:00:17,601 --> 00:00:20,559 BRIAN GBEENE:Why don't we ever see events unfold in reverse order? 7 00:00:20,646 --> 00:00:24,355 According to the laws of physics, this can happen. 8 00:00:26,109 --> 00:00:28,441 It's a world hat comes to light 9 00:00:28,529 --> 00:00:31,942 as we probe the most extreme realms of fhe cosmos, 10 00:00:32,074 --> 00:00:35,032 from black holes to the Big Bang 11 00:00:35,118 --> 00:00:36,983 to the very heart of matter itself. 12 00:00:37,120 --> 00:00:38,860 I'm going to have what he's having. 13 00:00:38,956 --> 00:00:42,995 Here, empty space teems with ferocious activity. 14 00:00:43,126 --> 00:00:45,367 Our universe may be one of many, 15 00:00:45,462 --> 00:00:49,501 and the three-dimensional world merely a mirage. 16 00:00:51,510 --> 00:00:53,922 GREENE: But how could this be? 17 00:00:54,012 --> 00:00:57,800 How could we be so wrong about something so familiar? 18 00:00:57,891 --> 00:00:58,676 Does it bother us? 19 00:00:58,809 --> 00:00:59,639 Absolutely. 20 00:00:59,726 --> 00:01:01,011 There's no principe 21 00:01:01,144 --> 00:01:03,135 built into the laws of nature 22 00:01:03,230 --> 00:01:07,098 that say that theoretical physicists have to be happy. 23 00:01:07,192 --> 00:01:09,729 Its a game-changing perspective 24 00:01:09,820 --> 00:01:13,438 that opens up a whole new world of possibilities 25 00:01:13,532 --> 00:01:14,612 Coming up... 26 00:01:14,700 --> 00:01:17,567 GREENE: Look around any train station, 27 00:01:17,661 --> 00:01:20,448 and you can see how time rules our lives. 28 00:01:20,539 --> 00:01:23,121 But time is not what it seems. 29 00:01:23,208 --> 00:01:25,244 There may be no distinction 30 00:01:25,335 --> 00:01:27,667 between past, present and future. 31 00:01:27,796 --> 00:01:29,536 GREENE: If time isn't what we all think it is. 32 00:01:29,673 --> 00:01:31,083 then what is it? 33 00:01:31,174 --> 00:01:32,004 did it have a beginning? 34 00:01:32,134 --> 00:01:33,249 will it have an end? 35 00:01:33,343 --> 00:01:35,004 Where did it come from? 36 00:01:35,095 --> 00:01:37,427 The "Illusion of Time" 37 00:01:37,514 --> 00:01:40,881 on The Fabric of the Cosmos, right now on NOVA. 38 00:01:56,033 --> 00:01:59,150 Major funding for NOVA is provided by the following: 39 00:02:05,626 --> 00:02:07,287 And... 40 00:02:18,013 --> 00:02:22,097 And by the corporation for Public Broadcasting 41 00:02:22,225 --> 00:02:25,183 and by contributions to your PBS station from, 42 00:02:32,319 --> 00:02:34,935 Major funding for the Fabric of the Cosmos 43 00:02:35,072 --> 00:02:37,859 is provided by the National Science Foundation. 44 00:02:45,499 --> 00:02:47,660 And... 45 00:02:50,420 --> 00:02:53,082 Supporting original research and public understanding 46 00:02:53,173 --> 00:02:59,260 of science, technology, engineering and mathematics. 47 00:02:59,388 --> 00:03:01,379 additional funding is provided by... 48 00:03:12,984 --> 00:03:15,100 And the George D. Smith Fund. 49 00:03:38,427 --> 00:03:40,884 BRIAN GBEENE: "Once upon a time." 50 00:03:40,971 --> 00:03:44,964 That magical phrase at the beginning at every good story. 51 00:03:45,058 --> 00:03:49,347 But what is the story of the time? 52 00:03:49,479 --> 00:03:54,599 people say that time flies that time is money 53 00:03:54,693 --> 00:03:59,858 we waste time we kill time we try to save time. 54 00:03:59,990 --> 00:04:03,323 But what do we really know about time? 55 00:04:03,452 --> 00:04:08,742 well, like this river, time seems to flow endless 56 00:04:08,832 --> 00:04:13,826 from one moment to the next. 57 00:04:13,920 --> 00:04:18,254 And the flow of time seems to always be in one direction: 58 00:04:18,341 --> 00:04:19,672 toward the future. 59 00:04:19,801 --> 00:04:23,794 But that may not be right. 60 00:04:23,889 --> 00:04:25,675 Discoveries over the last century 61 00:04:25,807 --> 00:04:28,799 have shown that much of what we think about time 62 00:04:28,894 --> 00:04:32,933 may be nothing more than an illusion. 63 00:04:33,023 --> 00:04:38,859 Contrary to everyday experience,time may not flow at all. 64 00:04:38,945 --> 00:04:42,358 our past may not be gone. 65 00:04:42,491 --> 00:04:47,485 Our future may already exist. 66 00:04:47,579 --> 00:04:54,496 It turns out time itself can speed up or slow down. 67 00:04:54,586 --> 00:04:58,955 And events that we think can unfold in only one direction 68 00:04:59,049 --> 00:05:02,382 can also unfold in reverse. 69 00:05:02,511 --> 00:05:05,173 But how could this be? 70 00:05:05,263 --> 00:05:09,176 How could we be so wrong about something so familiar? 71 00:05:09,267 --> 00:05:12,509 And if time isn't what we all think it is, then what is it? 72 00:05:12,604 --> 00:05:13,719 did it have a beginning? 73 00:05:13,855 --> 00:05:14,765 will it have an end? 74 00:05:14,898 --> 00:05:15,853 Where did it come from? 75 00:05:18,443 --> 00:05:21,651 JAN NA JEVIN: we'd like to corner time as a thing, 76 00:05:21,738 --> 00:05:25,777 but it defines that completely by being momentary, 77 00:05:25,909 --> 00:05:29,276 by only having definitions that hearken back to the notion 78 00:05:29,412 --> 00:05:30,777 of time itself. 79 00:05:30,914 --> 00:05:36,079 time is the thing that everyone knows intimately 80 00:05:36,169 --> 00:05:41,209 until you ask them to tell you about it. 81 00:05:41,299 --> 00:05:42,755 ALAN GUTH: "What's time?" is really 82 00:05:42,884 --> 00:05:45,045 the$64,000 question to physics. 83 00:05:45,136 --> 00:05:47,127 There's basically no aspect of time 84 00:05:47,264 --> 00:05:50,131 which I feel we really fully understand. 85 00:05:55,355 --> 00:05:58,597 GREENE: So how do you begin to unlock a mystery 86 00:05:58,692 --> 00:06:03,311 as deep and elusive as time? 87 00:06:03,446 --> 00:06:06,062 Well, one way is to measure it. 88 00:06:06,157 --> 00:06:10,571 And using clocks of all different shapes, sizes 89 00:06:10,662 --> 00:06:12,653 and kinds, we've been measuring time 90 00:06:12,789 --> 00:06:16,702 with ever-greater accuracy for thousands of years. 91 00:06:16,793 --> 00:06:22,663 The first clock was one that you could say ticks just once a day: 92 00:06:22,799 --> 00:06:25,461 the rotating Earth. 93 00:06:25,552 --> 00:06:28,089 From the repetition of our planet's daily rotation 94 00:06:28,179 --> 00:06:29,294 on its axis 95 00:06:29,389 --> 00:06:32,347 to its yearly orbit around the sun, 96 00:06:32,475 --> 00:06:35,467 we have always used the predictable, 97 00:06:35,604 --> 00:06:39,313 consistent motion of the Earth to measure time. 98 00:06:39,399 --> 00:06:42,311 we're always looking for things that repeat over and over again, 99 00:06:42,444 --> 00:06:47,438 and that repetition, that cycle of things forms a clock. 100 00:06:47,532 --> 00:06:52,902 That's all time becomes is some repetitive process. 101 00:06:52,996 --> 00:06:54,861 GREENE: Measuring the Earth's motion with a sundial 102 00:06:54,998 --> 00:06:57,330 we divided the day into hours. 103 00:06:57,459 --> 00:06:59,040 WILLIAM PHILLIPS: The Earth rotates once a day, 104 00:06:59,169 --> 00:07:00,579 and we tick off the days 105 00:07:00,670 --> 00:07:02,911 by looking at the rising and the setting of the snn. 106 00:07:03,006 --> 00:07:05,418 GREENE: with the swing of a pendulum, 107 00:07:05,508 --> 00:07:11,219 we divided hours into minutes and seconds. 108 00:07:11,348 --> 00:07:12,884 With the vibration of a quartz crystal 109 00:07:13,016 --> 00:07:17,225 we improved accuracy to the thousandths of a second. 110 00:07:17,354 --> 00:07:19,891 But the National Institute of Standards and Technology 111 00:07:20,023 --> 00:07:21,354 in Colorado is the place to go 112 00:07:21,441 --> 00:07:23,978 if we really want to know what time it is. 113 00:07:24,069 --> 00:07:26,230 STEVE JEEEEETS: This is U.S. official time. 114 00:07:26,363 --> 00:07:29,855 It doesn't get any more accurate than this. 115 00:07:29,991 --> 00:07:33,700 GREENE: Here they measure time with mind-boggling accuracy 116 00:07:33,828 --> 00:07:36,410 using one of the smallest objects in the universe: 117 00:07:36,539 --> 00:07:39,702 an atom of a rare metal called cesium. 118 00:07:39,834 --> 00:07:43,201 PHILLIPS: Atoms have a natural frequency. 119 00:07:43,338 --> 00:07:45,078 And anything that vibrates, 120 00:07:45,215 --> 00:07:51,336 that is giving you repetitive motion, can be a clock. 121 00:07:51,429 --> 00:07:55,843 The frequency at which the cesium atom ticks 122 00:07:55,934 --> 00:08:00,428 is the official timekeeper for the world. 123 00:08:00,563 --> 00:08:03,771 GREENE: When a cesium atom is bombarded with energy, 124 00:08:03,900 --> 00:08:07,609 it vibrates, or ticks, giving off pulses of light 125 00:08:07,737 --> 00:08:10,854 over nine billion times a second. 126 00:08:10,949 --> 00:08:13,110 over nine billion times a second. 127 00:08:13,243 --> 00:08:14,528 And the cesium atom ticks 128 00:08:14,619 --> 00:08:21,286 at this 9,192,631,770 ticks in a second. 129 00:08:21,418 --> 00:08:24,876 And so every time you count up to that number, 130 00:08:24,963 --> 00:08:26,419 one second has gone by. 131 00:08:26,548 --> 00:08:28,630 And you get one second after one second, 132 00:08:28,758 --> 00:08:30,419 after one second after one second. 133 00:08:32,262 --> 00:08:34,753 PHILLIPS This is just astounding. 134 00:08:34,889 --> 00:08:37,756 My watch gains or loses a second every couple of months. 135 00:08:37,892 --> 00:08:40,725 We're talking about clocks that would only gain or lose a second 136 00:08:40,812 --> 00:08:43,770 in 100 million years. 137 00:08:43,898 --> 00:08:47,732 And that kind of story, where we take one measure of time 138 00:08:47,819 --> 00:08:50,606 and replace it with something that we decide is more accurate, 139 00:08:50,739 --> 00:08:54,323 has been the constant reform process of physics 140 00:08:54,451 --> 00:08:56,533 over hundreds of years. 141 00:08:56,619 --> 00:09:01,113 GREENE: But no matter how accurate our clocks have become, 142 00:09:01,249 --> 00:09:04,116 time remains a mystery. 143 00:09:04,210 --> 00:09:06,826 Clocks can tell us what time it is, 144 00:09:06,963 --> 00:09:11,297 but they haven't been able to tell us what time itself is. 145 00:09:11,426 --> 00:09:15,465 What is it we're actually measuring? 146 00:09:28,860 --> 00:09:30,646 we may not know what time is 147 00:09:30,779 --> 00:09:33,816 but the experience of the passage of time 148 00:09:33,948 --> 00:09:36,485 is a fundamental part of our lives. 149 00:09:44,125 --> 00:09:48,334 we're always thinking about time, remembering the past, 150 00:09:48,463 --> 00:09:50,624 making plans for the future, 151 00:09:50,715 --> 00:09:56,130 living our lives within time's constant tick,tick, ticck. 152 00:10:01,017 --> 00:10:02,928 I mean, look around any train station 153 00:10:03,019 --> 00:10:07,012 and you can see how time rules our lives. 154 00:10:07,107 --> 00:10:08,938 What may not be so obvious 155 00:10:09,025 --> 00:10:12,563 is that the rise of train travel playad a key role 156 00:10:12,695 --> 00:10:16,608 in one of the most startling discoveries about time. 157 00:10:46,563 --> 00:10:47,973 Tickets, please, sir. 158 00:10:48,064 --> 00:10:51,227 Train running on time? 159 00:10:51,317 --> 00:10:53,649 Yes, sir. 160 00:10:53,736 --> 00:10:55,067 Thank you. 161 00:10:55,155 --> 00:10:58,022 GREENE: In the early days of train travel, 162 00:10:58,116 --> 00:11:00,482 time posed a unique problem. 163 00:11:02,954 --> 00:11:07,744 Back then, each town set their own particular time. 164 00:11:07,834 --> 00:11:10,621 Noon was when the sun was directly overhead, 165 00:11:10,753 --> 00:11:12,744 you know, more or less. 166 00:11:12,839 --> 00:11:14,375 And what time it was in another city, 167 00:11:14,465 --> 00:11:15,875 well, you know, that hardly mattered. 168 00:11:17,927 --> 00:11:19,963 And to complicate things even further, 169 00:11:20,096 --> 00:11:23,839 trains would carry the time of the city 170 00:11:23,933 --> 00:11:25,514 where they began their journey. 171 00:11:25,602 --> 00:11:27,467 so, if I was going from Paris to Geneva, 172 00:11:27,604 --> 00:11:30,095 I would be on Paris time the whole way, 173 00:11:30,190 --> 00:11:32,101 since that's where I started. 174 00:11:32,192 --> 00:11:37,277 But were I going the other direction, from Geneva to Paris, 175 00:11:37,363 --> 00:11:39,194 I'd be on Geneva time. 176 00:11:39,282 --> 00:11:45,027 PETER GATISON: And as you began to have more and more train lines crossing, 177 00:11:45,121 --> 00:11:47,032 and more and more different times 178 00:11:47,123 --> 00:11:49,739 located at that interchange, 179 00:11:49,834 --> 00:11:52,416 it became a nightmare of confusion. 180 00:11:56,090 --> 00:11:59,298 GREENE: The need to coordinate clocks over great distances 181 00:11:59,427 --> 00:12:01,713 became a huge issue, 182 00:12:01,804 --> 00:12:06,138 especially when the cities were connected by a single track. 183 00:12:14,567 --> 00:12:18,651 And here's where the modern story of time begins. 184 00:12:18,780 --> 00:12:20,987 As the need for synchronized clocks 185 00:12:21,074 --> 00:12:23,190 become ever more critical, 186 00:12:23,326 --> 00:12:26,284 a young physicist named Albert Einstein 187 00:12:26,371 --> 00:12:29,863 took a job at the patent office in Bern, Switzerland. 188 00:12:29,999 --> 00:12:32,331 GALISON: It was a ringside seat 189 00:12:32,460 --> 00:12:36,328 to all of the great inventions at the time. 190 00:12:36,422 --> 00:12:38,458 The patents showed how new and exciting ways 191 00:12:38,549 --> 00:12:41,131 to synchronize clocks with the exchange of telegraph signals,, 192 00:12:41,219 --> 00:12:45,963 clocks that were synchronized by radio waves, 193 00:12:46,057 --> 00:12:51,518 all made the synchronization of time and what time was, 194 00:12:51,604 --> 00:12:53,265 and how it was measured, 195 00:12:53,356 --> 00:12:56,473 something immediately important and exciting for Einstein. 196 00:12:56,567 --> 00:12:59,525 GkEENE Einstein would soon shake up the world 197 00:12:59,612 --> 00:13:03,321 with a radical insight into the nature of time. 198 00:13:03,408 --> 00:13:09,028 And these mechanical devices provided unexpected inspiration. 199 00:13:09,122 --> 00:13:12,865 Einstein realized that these attempts to synchronize clocks- 200 00:13:13,001 --> 00:13:16,459 they were much more than merely creative inventions. 201 00:13:16,546 --> 00:13:20,209 Instead, he realized that they were revealing a deep crack 202 00:13:20,300 --> 00:13:23,588 in our understanding of time itself. 203 00:13:28,057 --> 00:13:30,389 Most people view time 204 00:13:30,518 --> 00:13:33,055 in a pretty simple, straightforward way. 205 00:13:33,146 --> 00:13:38,231 Time ticks the same for everyone everywhere. 206 00:13:38,318 --> 00:13:40,900 It's a common-sense picture 207 00:13:41,029 --> 00:13:46,740 established by the father of modern science, Isaac Newton. 208 00:13:46,826 --> 00:13:50,569 JIM MATES : Time for Isaac Newton is something that is 209 00:13:50,705 --> 00:13:53,242 an immutable property of the universe. 210 00:13:53,374 --> 00:13:56,332 Time always changes at the same rate. 211 00:13:56,419 --> 00:13:58,125 Time just goes along, 212 00:13:58,254 --> 00:14:00,540 and there's really nothing we can do about it. 213 00:14:00,631 --> 00:14:05,091 GREENE: Sensible as Newton's picture of time may seem. 214 00:14:05,219 --> 00:14:09,337 Einstein realized it wasn't right. 215 00:14:09,432 --> 00:14:12,924 He discovered that time could run at different rates. 216 00:14:13,061 --> 00:14:14,722 As strange as it sounds, 217 00:14:14,812 --> 00:14:18,475 this means that time for me may not be the same 218 00:14:18,608 --> 00:14:21,441 as time for you. 219 00:14:21,569 --> 00:14:27,280 Einstein's discovery smashed Newton's conception of reality. 220 00:14:27,408 --> 00:14:29,649 Einstein says that time is not just a label 221 00:14:29,786 --> 00:14:31,117 on the whole universe; 222 00:14:31,204 --> 00:14:33,741 time is experienced individually. 223 00:14:33,831 --> 00:14:37,198 what Einstein gave us is a much, much richer picture 224 00:14:37,293 --> 00:14:39,500 where everybody has their own private time, 225 00:14:39,629 --> 00:14:41,620 which runs at their own private rates. 226 00:14:41,714 --> 00:14:46,083 There isn't time in a sense of a universal tick-tock; 227 00:14:46,177 --> 00:14:47,667 there were times. 228 00:14:47,804 --> 00:14:51,843 GkEENE Einstein came to this shocking revelation 229 00:14:51,974 --> 00:14:54,761 by uncovering a hibben connection 230 00:14:54,852 --> 00:14:59,346 between space and time. 231 00:14:59,482 --> 00:15:04,772 What Einstein figured out is that there's a profound link 232 00:15:04,862 --> 00:15:09,777 between motion through space and the passage of time. 233 00:15:09,867 --> 00:15:11,653 roughly speaking, 234 00:15:11,744 --> 00:15:14,861 the more you have of one, the less you have of the other. 235 00:15:14,997 --> 00:15:18,615 To see how this works, let's take a little ride. 236 00:15:21,879 --> 00:15:25,838 Right now,I'm heading due north at 60 miles an hour. 237 00:15:25,925 --> 00:15:31,386 And that means all my motion is in the northward direction. 238 00:15:31,514 --> 00:15:35,223 But let's now turn onto a different road 239 00:15:35,351 --> 00:15:36,932 and head northwest. 240 00:15:42,275 --> 00:15:44,186 I'm still going 60 miles on hour, 241 00:15:44,277 --> 00:15:46,768 but I'm not making as much progress toward the north 242 00:15:46,863 --> 00:15:49,024 as I was a minute ago. 243 00:15:49,157 --> 00:15:51,694 And that's because some at my northward motion 244 00:15:51,826 --> 00:15:57,537 has been diverted, or shared with, my westward motion.. 245 00:15:57,623 --> 00:16:01,866 Einstein realized that time and space are linked 246 00:16:01,961 --> 00:16:07,126 in much the same way that north and west are. 247 00:16:07,216 --> 00:16:10,754 And with this surprising insight, 248 00:16:10,887 --> 00:16:14,880 Einstein would overthrow the common-sense idea 249 00:16:14,974 --> 00:16:17,181 that time ticks the same for everyone. 250 00:16:20,229 --> 00:16:22,060 Here's what I mean. 251 00:16:22,190 --> 00:16:26,650 That guy over there would say that I'm not moving at all. 252 00:16:26,736 --> 00:16:28,192 But I am. 253 00:16:28,279 --> 00:16:30,395 I may not be moving through space, 254 00:16:30,531 --> 00:16:32,897 but I am moving through time. 255 00:16:33,034 --> 00:16:36,401 I mean, after all, my watch just keeps on ticking 256 00:16:36,537 --> 00:16:39,620 and ticking. 257 00:16:39,749 --> 00:16:42,536 And as long as I'm standing still- 258 00:16:42,627 --> 00:16:44,868 that is, not moving through space- 259 00:16:44,962 --> 00:16:48,420 Einstein said that all of my motion is through time. 260 00:16:48,508 --> 00:16:52,467 But look what happens if I walk toward that guy. 261 00:16:57,725 --> 00:17:02,139 We've exaggerated it, but because l'm now in motion, 262 00:17:02,271 --> 00:17:05,434 he'll perceive my watch ticking slower. 263 00:17:05,566 --> 00:17:08,808 That's because from his perspective, 264 00:17:08,945 --> 00:17:12,529 some of my previous motion throngh time is being diverted 265 00:17:12,615 --> 00:17:15,231 into my motion throngh space. 266 00:17:15,326 --> 00:17:18,113 And it's not just my watch. 267 00:17:18,246 --> 00:17:20,828 It we really exaggerate the effect, 268 00:17:20,957 --> 00:17:23,915 he'd perceive all my movement my voice, 269 00:17:24,001 --> 00:17:27,084 everything about me slowing down. 270 00:17:29,674 --> 00:17:31,960 And now that I've stopped moving, 271 00:17:32,093 --> 00:17:35,631 the passage of time on our watches once again agrees. 272 00:17:35,763 --> 00:17:38,345 This was Einstein's key insight: 273 00:17:38,474 --> 00:17:43,468 that motion through space affects the passage of time. 274 00:17:45,606 --> 00:17:48,313 DAVID KAISER: It's mind-blowing that you and I will not agree 275 00:17:48,401 --> 00:17:50,107 on measurements of time. 276 00:17:50,194 --> 00:17:51,980 Isn't time separate from us, right? 277 00:17:52,113 --> 00:17:54,525 Why shonld my measurement of time depend on how I am moving, 278 00:17:54,657 --> 00:17:55,567 or how you're moving? 279 00:17:55,658 --> 00:17:56,647 That doesn't make any sense. 280 00:17:56,784 --> 00:17:59,696 Time itself is runnning more slowly 281 00:17:59,829 --> 00:18:01,865 for the person who's moving. 282 00:18:01,998 --> 00:18:03,704 That's amazing. 283 00:18:03,833 --> 00:18:06,996 No one before Einstein ever imagined 284 00:18:07,128 --> 00:18:09,961 that that sort of thing would happen. 285 00:18:10,047 --> 00:18:13,790 That was uniquely Einstein. 286 00:18:15,886 --> 00:18:20,846 GREENE: So why don't we ever see this in everydey life? 287 00:18:20,975 --> 00:18:23,512 Well, at the slow speeds we move here on Earth, 288 00:18:23,644 --> 00:18:30,391 motion's impact on time is so tiny we don't experience it. 289 00:18:30,526 --> 00:18:33,689 But the effect is real and can be measured. 290 00:18:33,779 --> 00:18:39,240 To do this, all you need are a couple of atomic clocks 291 00:18:39,368 --> 00:18:40,949 and a jet airplane. 292 00:18:44,540 --> 00:18:48,374 And this experiment was carried out in 1971 293 00:18:48,461 --> 00:18:52,545 when scientists flew an atomic clock around the world 294 00:18:52,632 --> 00:18:55,294 and then compared it to one on the ground. 295 00:18:55,384 --> 00:19:00,094 As EInstein predicted, the two clocks no longer agreed. 296 00:19:00,222 --> 00:19:04,682 They differed by only a few hundred billionths of a second, 297 00:19:04,769 --> 00:19:07,055 but that was very real proot 298 00:19:07,146 --> 00:19:10,559 of motion's effect on the passage of time. 299 00:19:10,691 --> 00:19:13,728 PHILLIPS: Einstein's theory has been tested again 300 00:19:13,861 --> 00:19:15,226 and again and again. 301 00:19:15,363 --> 00:19:17,570 And it all hangs together. 302 00:19:17,698 --> 00:19:19,108 It really forms the basis 303 00:19:19,241 --> 00:19:23,359 for the way we understand much of the way nature works. 304 00:19:23,454 --> 00:19:24,910 These effcts, which used to be considered 305 00:19:25,039 --> 00:19:26,700 sort of obscure and very small, 306 00:19:26,791 --> 00:19:29,624 are very in-your-face with today's technology. 307 00:19:29,752 --> 00:19:34,291 GREENE: With the discovery of this unexpected link 308 00:19:34,423 --> 00:19:38,132 between space and time, Einstein realized that the two 309 00:19:38,260 --> 00:19:41,423 could no longer be thought of as separate things. 310 00:19:41,514 --> 00:19:45,553 Instead, space and time are fused together 311 00:19:45,643 --> 00:19:49,932 in what came to be called "spacetime." 312 00:19:50,022 --> 00:19:54,436 Einstein unified the idea of space with the idea of time 313 00:19:54,527 --> 00:19:58,395 into this four-dimensional structure called "spacetime." 314 00:19:58,489 --> 00:20:02,778 GREENE:And this fusion of space and time would lead Einsein 315 00:20:02,910 --> 00:20:06,573 to perhaps the most mind-bending realization of all: 316 00:20:06,664 --> 00:20:09,701 The sharp difference we see between past, 317 00:20:09,792 --> 00:20:14,912 present and future may only be an illusion. 318 00:20:18,634 --> 00:20:20,590 In our day-to-day lives, 319 00:20:20,678 --> 00:20:25,138 we experience time as a continuous flow. 320 00:20:25,224 --> 00:20:28,716 But it can also be useful to think of time 321 00:20:28,811 --> 00:20:32,975 as a series of snapshots or moments, 322 00:20:33,065 --> 00:20:34,680 and everything that happens 323 00:20:34,817 --> 00:20:37,604 can be thought of as the unfolding of moment 324 00:20:37,695 --> 00:20:41,608 after moment 325 00:20:41,699 --> 00:20:43,690 after moment. 326 00:20:46,579 --> 00:20:52,540 And if we picture all moments, or snapshots, lined up- 327 00:20:52,668 --> 00:20:54,750 every moment here on Earth, 328 00:20:54,837 --> 00:20:59,126 every moment at Earth orbiting the snn, 329 00:20:59,216 --> 00:21:03,004 and every moment throughout the entire universe- 330 00:21:03,095 --> 00:21:06,883 we would see every event that has ever happened 331 00:21:07,016 --> 00:21:08,631 or will ever happen. 332 00:21:08,726 --> 00:21:15,097 Every location in space, and each and every moment in time, 333 00:21:15,191 --> 00:21:20,106 from the birth of our universe at the big Bang 334 00:21:20,196 --> 00:21:22,687 some 14 billon years ago 335 00:21:22,823 --> 00:21:27,533 to the formation of stars in the Milky Way galaxy, 336 00:21:27,620 --> 00:21:31,989 to the creation of Earth 4 1/2 billion years ago, 337 00:21:32,082 --> 00:21:35,245 to the time of the dinosaurs, 338 00:21:35,377 --> 00:21:38,585 to events happening on Earth today, 339 00:21:38,714 --> 00:21:41,877 like me working in my office. 340 00:21:42,009 --> 00:21:44,295 Thinking about spacetime like this 341 00:21:44,386 --> 00:21:47,549 lead Einstein to overturn our everyday's picture 342 00:21:47,640 --> 00:21:51,132 of past, present and future. 343 00:21:53,979 --> 00:21:57,722 To get a feel for this, you have to think 344 00:21:57,817 --> 00:21:59,808 about the seemingly simple concept of"now." 345 00:22:02,696 --> 00:22:04,106 For me, a list of things 346 00:22:04,240 --> 00:22:07,983 that I consider to be happening right now might include 347 00:22:08,077 --> 00:22:12,366 the tick of noon on my office clock, 348 00:22:12,456 --> 00:22:17,541 my cat just now jumping from the windowsill, 349 00:22:17,628 --> 00:22:20,711 things happening far away 350 00:22:20,798 --> 00:22:26,088 like a pigeon in Venice taking flight at this very moment, 351 00:22:26,220 --> 00:22:29,257 a meteor just now hitting the moom... 352 00:22:32,309 --> 00:22:38,771 and the explosion of a star at the tar reaches of the universe. 353 00:22:38,858 --> 00:22:42,726 These and all other events that I think are happenning 354 00:22:42,820 --> 00:22:45,106 at the same moment in time, 355 00:22:45,239 --> 00:22:48,481 but in different regions of our universe, 356 00:22:48,617 --> 00:22:52,405 make up what I intuitively think of as"now." 357 00:22:52,496 --> 00:22:57,160 you can picture them as lying on a single slice of spacetime. 358 00:22:57,293 --> 00:23:00,456 Let's call it a" now slice." 359 00:23:00,462 --> 00:23:04,455 Common sense would say that you and I and everyone else 360 00:23:04,592 --> 00:23:09,177 will agree on what's happening, or what exists, right now, 361 00:23:09,305 --> 00:23:13,469 moment after moment after moment. 362 00:23:13,601 --> 00:23:15,137 That is, we would all agree 363 00:23:15,269 --> 00:23:19,729 on what lies on a given "now slice." 364 00:23:19,815 --> 00:23:21,430 But Einstein showed that, 365 00:23:21,525 --> 00:23:24,642 strangely, when you take motion ino account, 366 00:23:24,778 --> 00:23:30,648 this common-sense picture of time goes out the window. 367 00:23:30,743 --> 00:23:36,739 To see What I mean, think of spacetime as a loaf of bread. 368 00:23:36,832 --> 00:23:39,164 Einstein realized that just as there are different ways 369 00:23:39,293 --> 00:23:42,706 to cut a loat of bread into individual slices, 370 00:23:42,838 --> 00:23:45,705 there are different ways to cut spacetime 371 00:23:45,841 --> 00:23:49,254 into individual now slices. 372 00:23:49,345 --> 00:23:53,179 That is, because motion affects the passage of time, 373 00:23:53,265 --> 00:23:55,847 someone who is moving will have a different conception 374 00:23:55,976 --> 00:23:58,763 of what's happening right now, 375 00:23:58,854 --> 00:24:02,517 and so they'll cut the loat into different now slices. 376 00:24:02,650 --> 00:24:06,563 Their slices will be at a different angle. 377 00:24:06,695 --> 00:24:09,357 That person who's moving will... will tilt the knife, 378 00:24:09,490 --> 00:24:11,572 will be carving out these slices at a different angle. 379 00:24:11,700 --> 00:24:14,737 They won't be parallel to my slices of time. 380 00:24:14,870 --> 00:24:18,237 To get a feel for the bizarre effect this can have, 381 00:24:18,374 --> 00:24:21,207 imagine an alien, here, 382 00:24:21,335 --> 00:24:23,917 in a galaxy ten billion light-years from Earth. 383 00:24:24,046 --> 00:24:29,040 And way over there on Earth, the guy at the gas station. 384 00:24:29,134 --> 00:24:32,217 Now, if the two are sitting still- 385 00:24:32,346 --> 00:24:34,553 not moving in relation to one other- 386 00:24:34,640 --> 00:24:37,347 their clocks tick off time at the same rate 387 00:24:37,434 --> 00:24:41,302 and so they share the same now slices, 388 00:24:41,397 --> 00:24:44,855 which cut straght across the loaf. 389 00:24:44,942 --> 00:24:49,026 But watch what happens if the alien hops on his bike 390 00:24:49,113 --> 00:24:51,855 and rides directly away from Earth. 391 00:24:51,949 --> 00:24:54,691 Since motion slows the passage of time, 392 00:24:54,785 --> 00:24:59,199 their clocks will no longer tick off time at the same rate. 393 00:24:59,289 --> 00:25:02,076 And if their clocks no longer agree, 394 00:25:02,167 --> 00:25:06,285 their now slices will no longer agree either. 395 00:25:06,422 --> 00:25:10,916 The alien's now slice cuts through the loaf differently. 396 00:25:11,010 --> 00:25:14,502 It's angled towards the past. 397 00:25:14,596 --> 00:25:18,589 GREENE: Since the alien is biking at a leisurely pace, 398 00:25:18,684 --> 00:25:22,927 his slice is angled to the past by only a miniscule amount. 399 00:25:23,022 --> 00:25:25,934 But across ten billion light years, 400 00:25:26,066 --> 00:25:31,151 that tiny angle results in a huge difference in time. 401 00:25:31,280 --> 00:25:35,114 So what the alien would find on his angled now slice-- 402 00:25:35,200 --> 00:25:38,488 what he considers as happening right now an Earth-- 403 00:25:38,620 --> 00:25:41,703 no longer includes our friend at the gas statian 404 00:25:41,790 --> 00:25:47,001 or even 40 years earlier, when our friend was a baby. 405 00:25:47,129 --> 00:25:50,462 Amazingly, the alien's now slice has swept back 406 00:25:50,591 --> 00:25:53,458 through 200 years at Earth history 407 00:25:53,594 --> 00:25:55,334 and now includes events 408 00:25:55,471 --> 00:25:58,304 that we consider part of the distant past, like... 409 00:26:00,893 --> 00:26:04,306 Beethoven finishing the fifth symphony. 410 00:26:04,396 --> 00:26:06,762 KAISER: Even at a relatively slow speed, 411 00:26:06,857 --> 00:26:08,597 we can have actually tremendous disagreements 412 00:26:08,692 --> 00:26:10,853 on our labeling of now, what happens at the same time, 413 00:26:10,986 --> 00:26:15,320 if we're spread out far enough in space. 414 00:26:15,407 --> 00:26:17,614 And if that's not strange enough, 415 00:26:17,701 --> 00:26:21,319 the direction you move makes a difference, too. 416 00:26:21,413 --> 00:26:24,075 Watch what happens when the alien turns around 417 00:26:24,166 --> 00:26:27,829 and bikes toward Earth. 418 00:26:27,920 --> 00:26:33,586 The alien's new now slice is angled to toward the future, 419 00:26:33,675 --> 00:26:37,088 and so it includes events that won't happen on Earth 420 00:26:37,179 --> 00:26:39,886 for 200 years, 421 00:26:40,015 --> 00:26:43,132 perhaps our friend's great-great-greet granddaughter 422 00:26:43,227 --> 00:26:48,688 teleporting from Paris to New York. 423 00:26:48,774 --> 00:26:51,811 Once we know that your now can be what I consider the past, 424 00:26:51,902 --> 00:26:54,609 or your now can be what I consider the future, 425 00:26:54,696 --> 00:26:58,188 and your now is every bit as valid as my now, 426 00:26:58,283 --> 00:27:00,945 then we learn that the past must be real 427 00:27:01,036 --> 00:27:02,776 The future must be real 428 00:27:02,871 --> 00:27:04,532 They could be your now. 429 00:27:04,623 --> 00:27:08,207 That means past, present, future:all equally real 430 00:27:08,335 --> 00:27:11,168 They all exist. 431 00:27:11,255 --> 00:27:15,624 SEAN CARROLL: If you believe the laws of physics, 432 00:27:15,717 --> 00:27:18,709 there's just as much reality to the future and the past 433 00:27:18,804 --> 00:27:20,385 as there is to the present moment. 434 00:27:20,472 --> 00:27:22,679 The past is not gone, 435 00:27:22,766 --> 00:27:25,758 and the future isn't non-existent. 436 00:27:25,894 --> 00:27:28,761 The past, the future, and the present are all existing 437 00:27:28,897 --> 00:27:30,387 in exactly the same way. 438 00:27:30,482 --> 00:27:35,226 Just as we think of all of space as being "out there," 439 00:27:35,320 --> 00:27:39,939 we should think of all of time as being "out there," too. 440 00:27:40,075 --> 00:27:43,567 Everything that has ever happened,or will happen. 441 00:27:43,662 --> 00:27:45,402 It all exists. 442 00:27:49,251 --> 00:27:50,707 GREENE: From Leonardo da Vinci 443 00:27:50,794 --> 00:27:53,080 laying the final brushstroke on the Mona Lisa 444 00:27:55,215 --> 00:27:57,957 to the signing of the Declaration of Independence, 445 00:28:00,220 --> 00:28:02,211 to your first day at school 446 00:28:04,600 --> 00:28:08,343 to events that from our perspective are yet to happen, 447 00:28:08,437 --> 00:28:10,849 like the first humans landing on Mars. 448 00:28:13,275 --> 00:28:14,856 With this bold insight, 449 00:28:14,943 --> 00:28:18,276 Einstein shattered one of the most basic concepts 450 00:28:18,363 --> 00:28:20,604 of how we experience time. 451 00:28:20,741 --> 00:28:24,654 "The distinction between past, present, and future," 452 00:28:24,786 --> 00:28:28,950 he once said,"is only an illusion, however persistent." 453 00:28:36,340 --> 00:28:39,457 But if every moment in time already exists, 454 00:28:39,551 --> 00:28:44,045 then how do me explain the very real feeling that time, 455 00:28:44,139 --> 00:28:49,350 like this river, seems to endlessly rush forward? 456 00:28:49,478 --> 00:28:53,812 Well, maybe we've been deceived, and time does not flow. 457 00:28:53,941 --> 00:28:58,184 Perhaps the river of time is more ike a frozen river 458 00:29:01,782 --> 00:29:05,491 with every moment forever locked in place. 459 00:29:05,619 --> 00:29:10,909 ALBERT: The most vivid example about the way the world is 460 00:29:10,999 --> 00:29:14,457 has to do with this flow of time. 461 00:29:14,544 --> 00:29:17,411 Physics does radical violence 462 00:29:17,506 --> 00:29:20,293 to this everyday experience of time. 463 00:29:20,384 --> 00:29:25,174 LEVIN:Our entire experience of time is constantly in the present. 464 00:29:25,305 --> 00:29:27,671 And all we ever grasp is that instant moment. 465 00:29:27,766 --> 00:29:30,473 TEGMARK: There is nothing in the laws of physics 466 00:29:30,560 --> 00:29:34,144 that picks out one now over any other now. 467 00:29:34,231 --> 00:29:36,938 And it's just from our subjective viewpoints 468 00:29:37,025 --> 00:29:39,311 that it feels like things are changing. 469 00:29:39,403 --> 00:29:44,022 GREENE: Just the way an entire movie exists on celluloid, 470 00:29:44,157 --> 00:29:47,900 all of time may already exist. 471 00:29:48,036 --> 00:29:50,118 The difference is that in the movies, 472 00:29:50,205 --> 00:29:55,120 a projector lights up or selects each frame as it goes by. 473 00:29:55,210 --> 00:29:56,871 But in the laws of physics, 474 00:29:57,004 --> 00:30:00,212 there is no evidence of something like a projector light 475 00:30:00,340 --> 00:30:03,207 that selects one moment over another. 476 00:30:03,343 --> 00:30:07,382 Our brains may create this impression, bnt in reality, 477 00:30:07,472 --> 00:30:10,885 what we all experience as the flow of time 478 00:30:10,976 --> 00:30:16,061 may be nothing more than an illusion. 479 00:30:16,148 --> 00:30:21,108 But if time, like this frozen river, does not flow, 480 00:30:21,236 --> 00:30:24,148 and all of time is "out there," 481 00:30:24,239 --> 00:30:32,578 Is it possible to travel to the future or the paste? 482 00:30:32,706 --> 00:30:36,415 BOARDING ANNOUNCEMENT Now departing for year 2060, Flight 24. 483 00:30:36,501 --> 00:30:38,913 GREENE: And if we could time travel, 484 00:30:39,004 --> 00:30:40,790 would it be anything like what we all imagine? 485 00:30:40,922 --> 00:30:44,255 "Catapult you through time into a world that has yet to beand" 486 00:30:44,384 --> 00:30:47,592 "The Time Travelers!" 487 00:30:47,721 --> 00:30:50,212 "Suppose something goes wrong with the time machine again?" 488 00:30:50,307 --> 00:30:51,638 "Throw the switch, Jed!" 489 00:30:51,767 --> 00:30:54,383 "Cound we go anywhere we want at any time?" 490 00:30:54,478 --> 00:30:56,560 "We're going to attempt time travel." 491 00:30:56,646 --> 00:30:58,261 GREENE: No one outside Hollywood 492 00:30:58,357 --> 00:31:01,770 has made a working time machine just yet. 493 00:31:01,860 --> 00:31:06,604 But surprisingly, time travel might be possible. 494 00:31:06,698 --> 00:31:09,610 BOARDING ANNOUNCEMENT Now boarding, flight 24 to Black Hole A Star. 495 00:31:09,701 --> 00:31:12,693 One way to travel through time 496 00:31:12,788 --> 00:31:15,951 is to make use of a strange feature of gravity. 497 00:31:16,041 --> 00:31:19,659 The familiar force that keeps our feet planted to the ground 498 00:31:19,795 --> 00:31:23,128 can have e profound impact on time. 499 00:31:23,215 --> 00:31:24,455 Hello. 500 00:31:27,969 --> 00:31:30,335 See you later, sir. 501 00:31:30,472 --> 00:31:32,337 Right, much later. 502 00:31:39,773 --> 00:31:45,143 GREENE:So how can gravity be used to make a time machivne? 503 00:31:45,278 --> 00:31:50,272 Well Einstein's theories show that gravity, like motion, 504 00:31:50,367 --> 00:31:52,232 can affect time. 505 00:31:52,327 --> 00:31:56,320 It's as if gravity can pull on time, slowing its passage. 506 00:31:59,668 --> 00:32:03,001 And the stronger the gravitational pull, 507 00:32:03,088 --> 00:32:05,921 the more time slows. 508 00:32:06,007 --> 00:32:09,591 Here on Earth, the effect is too small to notice, 509 00:32:09,678 --> 00:32:13,262 but still very real. 510 00:32:13,348 --> 00:32:17,512 Compared to someone living on the top floor of a skyscraper, 511 00:32:17,644 --> 00:32:19,726 someone living on the bottom 512 00:32:19,855 --> 00:32:23,018 experiences time elapsing a little slower 513 00:32:23,108 --> 00:32:26,191 because gravity is just a tiny bit stranger 514 00:32:26,278 --> 00:32:29,361 closer to the ground. 515 00:32:29,448 --> 00:32:33,066 But if you could trave to a back hole, 516 00:32:33,201 --> 00:32:37,695 the effect of gravity on time would be huge. 517 00:32:37,831 --> 00:32:41,870 Formed when large stars collapse in on themselves, 518 00:32:41,960 --> 00:32:45,202 black holes have immense gravitational pull, 519 00:32:45,338 --> 00:32:50,708 millions and even billions of times stronger than the Earth's. 520 00:32:50,802 --> 00:32:55,341 And if someone watched you travel close to a black hole, 521 00:32:55,432 --> 00:33:00,392 they'd see time for you slow down dramatically. 522 00:33:00,520 --> 00:33:04,559 LEVIN: You near that black hole will appear to your friend far away 523 00:33:04,649 --> 00:33:08,892 to be moving slowly, talkng slowy, 524 00:33:08,987 --> 00:33:11,478 biologically aging slowy. 525 00:33:11,573 --> 00:33:14,861 To them years are passing, while for you it might be minutes. 526 00:33:14,951 --> 00:33:19,741 GREENE: So depending on the black hole's size and how close I get, 527 00:33:19,831 --> 00:33:22,914 if I spend an hour or two in orbit... 528 00:33:26,713 --> 00:33:31,457 something like 50 years will have passed back on Earth. 529 00:33:31,593 --> 00:33:34,801 I will have traveled to Earth's future. 530 00:33:34,930 --> 00:33:35,794 Hello, sir. 531 00:33:35,931 --> 00:33:36,966 Hi. 532 00:33:37,098 --> 00:33:38,087 Long time, no see. 533 00:33:38,225 --> 00:33:39,931 Time travel becomes you. 534 00:33:40,060 --> 00:33:41,391 Thank you. 535 00:33:41,478 --> 00:33:43,764 Kind of like a fountain of youth. 536 00:33:43,897 --> 00:33:48,732 So when I return, I'll find myself in the future. 537 00:33:48,818 --> 00:33:52,185 Everyone else will have aged 50 years, 538 00:33:52,280 --> 00:33:57,445 but me, l'll have aged only a couple of hours. 539 00:33:57,536 --> 00:34:01,154 Now, time travel to the future is one thing. 540 00:34:01,289 --> 00:34:05,578 But what about time travel to the past? 541 00:34:05,669 --> 00:34:08,911 Well, that might be possible too, 542 00:34:09,005 --> 00:34:12,338 using something predicted by Einstein's equations 543 00:34:12,467 --> 00:34:14,458 known as a wormhole. 544 00:34:18,014 --> 00:34:20,426 If wormholes exist, 545 00:34:20,517 --> 00:34:23,725 they would be kind of like shortcuts through spacetime, 546 00:34:23,812 --> 00:34:27,145 tunnels that would link not just one place with another, 547 00:34:27,274 --> 00:34:30,516 but also one moment with another. 548 00:34:30,652 --> 00:34:31,937 A wormhole would connect 549 00:34:32,028 --> 00:34:35,987 one part in spacetime to another part in spacetime 550 00:34:36,116 --> 00:34:37,447 which is at on earlier time, 551 00:34:37,534 --> 00:34:43,120 like a sort of subway system through time. 552 00:34:43,206 --> 00:34:46,949 So let's say I wanted to go back in time 553 00:34:47,043 --> 00:34:50,160 and meet myself at the beginning of this program. 554 00:34:50,297 --> 00:34:52,879 If a wormhole connected here and there, 555 00:34:53,008 --> 00:34:55,249 all I'd need to do is step through. 556 00:35:03,768 --> 00:35:06,009 Hey, good to see you again. 557 00:35:06,146 --> 00:35:07,477 Thanks, good to be back. 558 00:35:09,482 --> 00:35:12,974 Well, that would be kind of weird, 559 00:35:13,069 --> 00:35:16,061 but the real problem with time travel to the best 560 00:35:16,197 --> 00:35:19,234 is that things would get pretty confusing pretty quickly. 561 00:35:19,367 --> 00:35:22,655 I mean, imagine I were to change something about my past, 562 00:35:22,746 --> 00:35:25,032 like preventing my parents from meeting. 563 00:35:25,165 --> 00:35:28,123 Would that mean I'd never be born? 564 00:35:28,209 --> 00:35:31,292 If you do travel to the past, you can't change things 565 00:35:31,379 --> 00:35:32,960 that we know are true about the best 566 00:35:33,048 --> 00:35:34,128 because they already happened. 567 00:35:34,215 --> 00:35:35,876 So if you go back 568 00:35:35,967 --> 00:35:37,958 and kill who you thought was your grandpa, 569 00:35:38,053 --> 00:35:39,418 that must have been some other guy 570 00:35:39,554 --> 00:35:40,714 you thought was your grandfather, 571 00:35:40,805 --> 00:35:42,466 and everything must somehow become 572 00:35:42,557 --> 00:35:44,047 beautifully self-consistent, 573 00:35:44,142 --> 00:35:46,053 even if it's in a twisted way. 574 00:35:46,186 --> 00:35:50,054 GREENE: And if you can travel to the past, 575 00:35:50,190 --> 00:35:54,524 why haven't we been overrun by tourists from the future? 576 00:35:54,611 --> 00:35:56,397 I mean, think about it. 577 00:35:56,488 --> 00:35:58,729 We haven't seen any intrepid time travelers 578 00:35:58,865 --> 00:36:01,356 popping into and out of our world-- 579 00:36:01,451 --> 00:36:04,238 at least, most peope don't think we have-- 580 00:36:04,329 --> 00:36:06,911 so it's probably safe to assume that time travel to the past 581 00:36:07,040 --> 00:36:11,909 just isn't possible, at least not yet. 582 00:36:12,003 --> 00:36:15,086 But since the math hasn't yet ruled it out, 583 00:36:15,173 --> 00:36:19,257 we can't dismiss time travel to the past entirely. 584 00:36:19,344 --> 00:36:21,801 PhILLIPS: So it's not at all clear 585 00:36:21,930 --> 00:36:24,512 that it could ever be a practical reality, 586 00:36:24,599 --> 00:36:28,638 but at least in principle, it doesn't seem te be forbidden. 587 00:36:28,770 --> 00:36:30,726 My guess is that it's impossible, 588 00:36:30,814 --> 00:36:34,147 but it's striking that we still haven't been able 589 00:36:34,275 --> 00:36:35,765 to rigorously prove that. 590 00:36:37,779 --> 00:36:40,316 GREENE: While it seems likey that traveling to the past 591 00:36:40,448 --> 00:36:41,779 is out of reach, 592 00:36:41,908 --> 00:36:45,867 what about the fact, so common to our everyday experience, 593 00:36:45,954 --> 00:36:48,787 that time itself seems to move in only one direction... 594 00:36:49,999 --> 00:36:52,832 toward the future? 595 00:36:52,961 --> 00:36:55,953 We call this the arrow of time. 596 00:36:56,047 --> 00:36:58,254 CARROLL: The arrow of tiwe 597 00:36:58,341 --> 00:37:01,003 is probaby the most blatant fact 598 00:37:01,136 --> 00:37:02,421 about the universe we live in 599 00:37:02,512 --> 00:37:06,300 that we don't completely understand. 600 00:37:06,433 --> 00:37:10,142 Why we live in a universe that has a directionality to time 601 00:37:10,228 --> 00:37:11,934 is a mystery. 602 00:37:12,021 --> 00:37:13,932 JOSEPH LYKKEN: This is not true of space. 603 00:37:14,023 --> 00:37:16,309 In space, I can go from New York to Chicago 604 00:37:16,443 --> 00:37:19,651 and then I can change my mind and go from Chicago to New York. 605 00:37:19,779 --> 00:37:22,441 So there is a one-way aspect to time 606 00:37:22,532 --> 00:37:25,148 that we don't understand at a fundamental level. 607 00:37:25,243 --> 00:37:26,653 PHILLIPS: Why doesn't it go backwards? 608 00:37:26,745 --> 00:37:29,953 What does it even mean 609 00:37:30,039 --> 00:37:32,280 that time goes forward from the past into the future? 610 00:37:34,169 --> 00:37:37,502 GREENE:So what can we say about where the arrow of time comes from? 611 00:37:37,630 --> 00:37:41,839 Why do we only see events unfold in one direction? 612 00:37:41,968 --> 00:37:45,005 Why don't we ever see them happen in reverse order? 613 00:37:45,096 --> 00:37:47,462 Well,it must be the laws of physics. 614 00:37:47,557 --> 00:37:50,799 I mean, surely they don't allom something like this to happen. 615 00:37:56,733 --> 00:37:58,974 Well, actually they do. 616 00:37:59,068 --> 00:38:00,524 The laws of physics 617 00:38:00,653 --> 00:38:04,521 are the mathematical equations we use to describe everything 618 00:38:04,657 --> 00:38:08,741 from the behavior of atoms to the swirl of galaxies. 619 00:38:08,870 --> 00:38:11,031 They've been devised and confirmed 620 00:38:11,164 --> 00:38:15,658 through centuries of observation and experiment. 621 00:38:15,752 --> 00:38:17,993 But surprisingly, there's nothing in the laws of physics 622 00:38:18,087 --> 00:38:21,705 that says events have to unfold through the familiar sequence 623 00:38:21,800 --> 00:38:24,712 "we call "forward in time." 624 00:38:24,844 --> 00:38:26,425 According to these equations, 625 00:38:26,554 --> 00:38:30,888 events could just as well unfold in reverse order. 626 00:38:30,975 --> 00:38:32,511 GATES: Most of the equations we use 627 00:38:32,602 --> 00:38:34,593 to describe what we see in the universe around us 628 00:38:34,729 --> 00:38:37,892 don't have an arrow of time attached to them. 629 00:38:38,024 --> 00:38:40,106 They're equations that work equally well 630 00:38:40,235 --> 00:38:43,318 moving forward in time or moving backwards in time. 631 00:38:43,404 --> 00:38:45,486 There's this contradiction between the physics, 632 00:38:45,573 --> 00:38:48,064 which seems fundamentally reversible, 633 00:38:48,159 --> 00:38:51,617 and so much of our life that seems irreversible. 634 00:38:56,584 --> 00:39:00,076 GREENE: Though it files in the face of everyday experience, 635 00:39:00,213 --> 00:39:03,125 the laws of physics actually say 636 00:39:03,258 --> 00:39:05,749 bizarre thngs like these are possible 637 00:39:05,844 --> 00:39:08,551 But how could this be? 638 00:39:08,638 --> 00:39:14,474 Well, the answer is not as far-fetched as you might think. 639 00:39:14,602 --> 00:39:16,263 Here's why. 640 00:39:16,396 --> 00:39:19,559 We all know what will happen if I drop this glass of wine. 641 00:39:30,451 --> 00:39:34,114 Now, the idea that this mess could somehow reverse itself 642 00:39:34,247 --> 00:39:38,286 and form back into a solid glass filled with wine seems absurd. 643 00:39:38,376 --> 00:39:42,210 But according to the laws of physics, this can happen. 644 00:39:42,297 --> 00:39:45,664 All I need to do is reverse the velocities of everything. 645 00:39:45,800 --> 00:39:50,590 Every piece of glass, every drop of wine, 646 00:39:50,680 --> 00:39:53,467 every moleculevve and atom in the liquid, glass, table and air. 647 00:39:53,600 --> 00:39:58,765 Just reverse at their velocities 648 00:39:58,855 --> 00:40:01,267 and...voilà! 649 00:40:09,824 --> 00:40:11,655 So if the laws of physics 650 00:40:11,784 --> 00:40:14,571 don't care about whether glasses shatter or unshatter, 651 00:40:14,662 --> 00:40:17,904 why don't we ever see them unshatter? 652 00:40:17,999 --> 00:40:19,864 How can we square the laws of physics 653 00:40:20,001 --> 00:40:21,491 with our everyday experience? 654 00:40:21,586 --> 00:40:24,328 Something must be missing in our understanding. 655 00:40:24,422 --> 00:40:25,662 But what? 656 00:40:25,757 --> 00:40:28,294 What's responsible for the arrow of time? 657 00:40:28,384 --> 00:40:30,966 (wolf howling) 658 00:40:36,684 --> 00:40:39,016 Like many good mysteries, 659 00:40:39,103 --> 00:40:44,393 this one leads us to a graveyard in our search for clues. 660 00:40:44,525 --> 00:40:47,688 In Vienna, near the final resting places 661 00:40:47,779 --> 00:40:51,738 of Beethoven, Brahms, Schubert and Strauss, 662 00:40:51,866 --> 00:40:54,107 is 19th-century Austrian physicist 663 00:40:54,202 --> 00:40:56,238 Ludwig Boltzmann's tombstone. 664 00:40:56,371 --> 00:41:02,867 Etched on top is an elegant equation:S=klogW. 665 00:41:02,961 --> 00:41:05,452 It's the mathematical formulation 666 00:41:05,546 --> 00:41:09,585 of a powerful concept known as entropy. 667 00:41:09,717 --> 00:41:13,301 Entropy is a measure of something 668 00:41:13,388 --> 00:41:17,347 that we're all familiar with: disorder, or randomness. 669 00:41:17,433 --> 00:41:20,846 And it's an important idea because there's a tendency 670 00:41:20,937 --> 00:41:24,555 of everything in the universe to move from order to disorder. 671 00:41:24,649 --> 00:41:26,731 Here's a way to get a feel for the idea. 672 00:41:26,859 --> 00:41:28,065 Take my book. 673 00:41:28,152 --> 00:41:31,690 All 569 pages of it. 674 00:41:31,781 --> 00:41:33,396 It's very ordered, 675 00:41:33,491 --> 00:41:35,573 with the first page followed by the second, 676 00:41:35,702 --> 00:41:37,909 followed by the third and so on. 677 00:41:38,037 --> 00:41:43,122 But now let's tear the pages out and let entropy go to work. 678 00:41:47,880 --> 00:41:51,543 As you can see, the pages become very disordered. 679 00:41:51,634 --> 00:41:54,797 And the reason is simpe: 680 00:41:54,929 --> 00:41:57,636 There is only one way for them to land in order, 681 00:41:57,765 --> 00:42:04,352 but a huge number of ways for them to land out of order, 682 00:42:04,439 --> 00:42:05,929 and so it's much more likely 683 00:42:06,024 --> 00:42:08,185 that they'll land in a total mess. 684 00:42:08,276 --> 00:42:11,518 And this is what we experience in our daily lives: 685 00:42:11,612 --> 00:42:14,945 things move from order to disorder. 686 00:42:15,074 --> 00:42:17,281 In this case, from e neat, ordered book 687 00:42:17,368 --> 00:42:20,701 to pages that are randomly scattered. 688 00:42:20,788 --> 00:42:22,198 Everywhere we look, 689 00:42:22,290 --> 00:42:25,782 we see examples of entropy, or disorder, 690 00:42:25,918 --> 00:42:28,705 Increasing with the passage of time. 691 00:42:28,796 --> 00:42:32,630 An egg breaks and splatters. 692 00:42:32,759 --> 00:42:38,220 Ice cubes lose their orderly shape as tkey melt into water. 693 00:42:38,306 --> 00:42:41,798 Billowing smoke becomes increasingly disordered. 694 00:42:41,893 --> 00:42:45,852 GATES: Ordered states become disordered states, 695 00:42:45,980 --> 00:42:48,096 and that appears to be, perhaps, 696 00:42:48,191 --> 00:42:50,682 the direction of an arrow of time. 697 00:42:50,818 --> 00:42:53,605 We see sort of degrees of messiness. 698 00:42:53,696 --> 00:42:56,403 A measure of disorder tends to increase 699 00:42:56,491 --> 00:42:57,981 in one direction of time. 700 00:42:58,076 --> 00:43:02,445 And so that, for Boltzmann, begins to create an arc of time. 701 00:43:02,538 --> 00:43:06,577 GREENE: So maybe this is the answer. 702 00:43:06,667 --> 00:43:10,376 Maybe the arrow of time comes from the tendency of nature 703 00:43:10,505 --> 00:43:15,169 to evolve toward ever greater disorder. 704 00:43:15,259 --> 00:43:17,591 This sure seems like progress, 705 00:43:17,678 --> 00:43:21,421 but there's just one small problem whth this reasoning: 706 00:43:21,516 --> 00:43:23,472 because the laws of physics 707 00:43:23,559 --> 00:43:26,517 don't distinguish between the future and the past, 708 00:43:26,604 --> 00:43:29,061 entropy should increase not only toward the future 709 00:43:29,190 --> 00:43:31,055 but also toward the past. 710 00:43:31,192 --> 00:43:33,683 And that makes no sense. 711 00:43:33,778 --> 00:43:35,689 KAISER: That's like saying that entropy should increase 712 00:43:35,780 --> 00:43:39,147 in either direction that we look. 713 00:43:39,242 --> 00:43:41,699 We could look backwards in time and it should increase, 714 00:43:41,828 --> 00:43:43,364 we could look forwards in time and it should increase. 715 00:43:43,496 --> 00:43:46,704 GREENE: That would mean the pages of my book in the past 716 00:43:46,791 --> 00:43:49,954 would be disordered and then come together 717 00:43:50,044 --> 00:43:53,286 to form the neat, ordered book in my hands. 718 00:43:53,381 --> 00:43:58,125 And when's the last time you saw something like that happen? 719 00:43:58,219 --> 00:44:01,552 How could our everyday experience be so at odds 720 00:44:01,681 --> 00:44:03,672 with the laws of physics? 721 00:44:03,766 --> 00:44:06,348 There must be a piece of the puzzle that's missing. 722 00:44:06,435 --> 00:44:10,724 If we're sure the past had to be more ordered 723 00:44:10,857 --> 00:44:13,269 and that everything tends toward disorder 724 00:44:13,401 --> 00:44:16,313 as the equations of entropy tell us, 725 00:44:16,404 --> 00:44:19,862 is there something else besides the laws of physics 726 00:44:19,949 --> 00:44:23,157 that might explain this? 727 00:44:23,244 --> 00:44:26,736 Well, think of hitting a baseball. 728 00:44:26,831 --> 00:44:31,074 The laws of physics can help you predict where it will land. 729 00:44:31,210 --> 00:44:36,580 But those laws are not the only things you need. 730 00:44:36,674 --> 00:44:38,255 Run the film backward 731 00:44:38,342 --> 00:44:42,802 and you can see that you also need the initial conditions, 732 00:44:42,930 --> 00:44:46,764 like how hard the ball was hit. 733 00:44:46,893 --> 00:44:48,758 Similarly, if the law of physics 734 00:44:48,853 --> 00:44:50,809 can't give us an explanation for the arrow of time, 735 00:44:50,938 --> 00:44:52,428 maybe we need to look further 736 00:44:52,523 --> 00:44:55,265 to the initial conditions of the universe. 737 00:44:55,359 --> 00:44:58,442 That brings our attention back to the Big Bang. 738 00:45:00,781 --> 00:45:04,615 If the history of the universe were like a movie 739 00:45:04,702 --> 00:45:06,658 and you ran it backwards, 740 00:45:06,787 --> 00:45:11,326 you'd see an increase in order the further back in time you go. 741 00:45:11,459 --> 00:45:14,075 Gradually, today's universe, 742 00:45:14,170 --> 00:45:17,128 with billions of galaxies clumped here and there, 743 00:45:17,256 --> 00:45:20,589 would turn back into clouds of gas and dust 744 00:45:20,676 --> 00:45:23,292 as everything contracts. 745 00:45:23,387 --> 00:45:25,548 CARROLL: So these clouds of gas and dust 746 00:45:25,640 --> 00:45:27,301 move closer and closer to each other 747 00:45:27,433 --> 00:45:29,970 so that if you get far enough into the past, 748 00:45:30,102 --> 00:45:32,844 they're squeezed into a smaller and smaller volume. 749 00:45:32,980 --> 00:45:37,519 We have now come to the place where the buck finally stops. 750 00:45:37,652 --> 00:45:41,986 If this represents all of space at each moment of time, 751 00:45:42,114 --> 00:45:45,481 then we can see there simply isn't any more space and time 752 00:45:45,576 --> 00:45:49,194 before this single moment. 753 00:45:49,330 --> 00:45:53,369 So the ultimate source of order, of low entropy, 754 00:45:53,501 --> 00:45:59,167 must be the very beginning of the universe: the Big Bang. 755 00:45:59,298 --> 00:46:03,382 GATES: The Big Bang is a highly ordered state. 756 00:46:03,511 --> 00:46:05,672 It's probably the most ordered event 757 00:46:05,763 --> 00:46:08,254 in all of physics. 758 00:46:11,143 --> 00:46:13,384 And so, everything that has come after that 759 00:46:13,521 --> 00:46:15,853 has been an increase in disorder. 760 00:46:15,940 --> 00:46:18,727 KAISER:What the Big Band gives us 761 00:46:18,859 --> 00:46:20,520 is a reason why the universe might look different 762 00:46:20,611 --> 00:46:23,068 when we look backwards in time versus forward. 763 00:46:23,197 --> 00:46:26,155 Moreover, when we go back to early times, 764 00:46:26,242 --> 00:46:28,528 the universe should have looked not just different from today 765 00:46:28,619 --> 00:46:30,450 but highy ordered. 766 00:46:30,538 --> 00:46:31,948 CARROLL: Why was the entropy low? 767 00:46:32,039 --> 00:46:33,529 We don't know. 768 00:46:33,666 --> 00:46:35,372 But at least we know that there was a point 769 00:46:35,501 --> 00:46:37,617 that the universe began in when the entropy was low 770 00:46:37,712 --> 00:46:42,001 GREENE:So our best understanding is that the Big Bang 771 00:46:42,091 --> 00:46:46,630 is what set the arrow of time on its path. 772 00:46:46,721 --> 00:46:49,804 you can picture this as something like a wind-up clock. 773 00:46:49,890 --> 00:46:53,223 Just as the stored energy of a tightly wound clock 774 00:46:53,352 --> 00:46:54,967 is released as it unwinds, 775 00:46:55,062 --> 00:46:59,226 the universe has been unwinding since the Big Bang, 776 00:46:59,358 --> 00:47:02,441 becoming ever more disordered. 777 00:47:02,570 --> 00:47:08,065 TEGMARK:Our universe started out in a very unusually orderly state, 778 00:47:08,159 --> 00:47:11,196 and that's ultimately responsible 779 00:47:11,287 --> 00:47:13,278 for the fact that time seems to have a directien. 780 00:47:13,414 --> 00:47:16,781 GREENE: We don't yet know why our universe began 781 00:47:16,917 --> 00:47:19,078 in a highly ordered state, 782 00:47:19,170 --> 00:47:20,876 but the fact that it did 783 00:47:20,963 --> 00:47:23,295 means that every time a glass shatters, 784 00:47:23,424 --> 00:47:26,916 it's actually carrying forward something set in motion 785 00:47:27,053 --> 00:47:29,135 billions of years ago. 786 00:47:29,263 --> 00:47:31,800 The glass breaks but doesn't unbreak 787 00:47:31,932 --> 00:47:34,469 because it's following the natural drive 788 00:47:34,602 --> 00:47:38,720 from order to disorder that began with the Big Bang. 789 00:47:38,814 --> 00:47:42,272 CARROLL: We only ever move from the past to the future. 790 00:47:42,401 --> 00:47:44,983 And everything we see around us, all the changes, 791 00:47:45,112 --> 00:47:47,649 from the formation of stars to our lives, 792 00:47:47,782 --> 00:47:51,616 is all little epiphenomena, surfers riding the wave 793 00:47:51,744 --> 00:47:54,281 of increasing disorganization in the universe 794 00:47:54,413 --> 00:47:57,120 that defines the difference between the past and the future. 795 00:47:57,208 --> 00:47:59,870 So the Big Bang may have stamped 796 00:47:59,960 --> 00:48:02,292 the arrow of time on our universe, 797 00:48:02,380 --> 00:48:05,543 and everything that has happened since may simply be the drive 798 00:48:05,633 --> 00:48:09,717 toward ever greater disorder that began with that event 799 00:48:09,804 --> 00:48:13,296 13.7 billion years ago. 800 00:48:13,432 --> 00:48:15,889 But if time had a beginning 801 00:48:15,976 --> 00:48:17,932 and disorder is always increasing, 802 00:48:18,020 --> 00:48:21,308 does that mean that time will have an end? 803 00:48:21,399 --> 00:48:27,360 What will the universe be like in the far, far future? 804 00:48:27,488 --> 00:48:31,822 Recent discoveries are shedding new light on this question. 805 00:48:36,997 --> 00:48:39,329 The explosive force of the Big Bang 806 00:48:39,417 --> 00:48:41,999 sent space hurtling outward. 807 00:48:42,086 --> 00:48:46,500 And as a result, the universe is still expanding today. 808 00:48:46,632 --> 00:48:48,293 Until recently, 809 00:48:48,384 --> 00:48:52,878 most people thought that expansion must be slowing down. 810 00:48:53,013 --> 00:48:57,507 That is, we thought of space, filled with galaxies, 811 00:48:57,601 --> 00:49:00,843 as kind of like a car traveling down a highway. 812 00:49:00,938 --> 00:49:06,979 RADIO ANNOUNCER:You're listening to WUNI, the stellar sounds of the cosmos. 813 00:49:07,069 --> 00:49:09,151 GREENE:If the driver takes his foot off the gas, 814 00:49:09,238 --> 00:49:11,354 the car gradually slows down. 815 00:49:11,490 --> 00:49:14,732 Similarly, we thought the universe was expanding, 816 00:49:14,869 --> 00:49:17,406 but at a slower and slower rate. 817 00:49:17,538 --> 00:49:19,870 But surprisingly, astronomers found 818 00:49:19,957 --> 00:49:24,121 the expansion of the universe is not slowing down. 819 00:49:24,211 --> 00:49:25,747 It's accelerating. 820 00:49:25,880 --> 00:49:29,418 It's as if someone's not taking their foot off the gas pwdal, 821 00:49:29,550 --> 00:49:34,385 but stepping on it, causing a turbo booster to kick in. 822 00:49:34,513 --> 00:49:37,004 And that's making the expansion of the universe 823 00:49:37,099 --> 00:49:38,589 speed up more and more. 824 00:49:40,603 --> 00:49:43,720 KAISER:Our expansion will keep accelerating in the future, 825 00:49:43,814 --> 00:49:45,054 not slow down. 826 00:49:45,149 --> 00:49:46,605 It goes against everything 827 00:49:46,734 --> 00:49:48,941 we had kind of gotten used to thinking about. 828 00:49:49,069 --> 00:49:53,813 GREENE: This has some very strange implications for the future. 829 00:49:53,908 --> 00:49:58,197 Because the expansion of our universe is accelerating, 830 00:49:58,287 --> 00:50:02,621 in the far future, after 100 billion years or so, 831 00:50:02,750 --> 00:50:05,583 all of the other distant galaxies 832 00:50:05,669 --> 00:50:07,250 will have hurtled out of sight from us. 833 00:50:07,379 --> 00:50:16,674 It will appear as if our galaxy were in the middle of nothing. 834 00:50:16,764 --> 00:50:19,597 A surprising outcome is that our descendants 835 00:50:19,683 --> 00:50:22,595 will be at a terrible loss. 836 00:50:22,728 --> 00:50:27,939 Light from distant galaxies has to travel so far to reach us 837 00:50:28,025 --> 00:50:29,890 that when we look out at them, 838 00:50:29,985 --> 00:50:32,226 we're actually looking bach in time. 839 00:50:34,365 --> 00:50:36,105 So in the far future, 840 00:50:36,200 --> 00:50:38,942 when those distant galaxies are no longer visible, 841 00:50:39,036 --> 00:50:42,528 astronomers will find that the past, in cosmic terms, 842 00:50:42,623 --> 00:50:43,954 is out of reach. 843 00:50:47,419 --> 00:50:50,661 And as far the end of time, 844 00:50:50,798 --> 00:50:53,289 one theory suggests that eventually, 845 00:50:53,425 --> 00:50:55,632 black holes will dominate the cosmos. 846 00:50:58,305 --> 00:51:02,264 Then, they too will evaporate, 847 00:51:02,351 --> 00:51:05,218 leaving nothing but random particles 848 00:51:05,312 --> 00:51:08,145 drifting throngh space. 849 00:51:08,274 --> 00:51:11,482 LEVIN: In a far distant future where everything has decayed 850 00:51:11,610 --> 00:51:14,602 and everything's just sort of smoothed out, 851 00:51:14,697 --> 00:51:15,937 there's no change. 852 00:51:16,031 --> 00:51:18,443 And without change, we don't really have a clear notion 853 00:51:18,534 --> 00:51:19,569 of the passage at time. 854 00:51:19,660 --> 00:51:22,117 If you don't have events happening, 855 00:51:22,204 --> 00:51:26,743 then it's hard to see how you would even imagine 856 00:51:26,834 --> 00:51:28,324 that there was time. 857 00:51:28,460 --> 00:51:31,668 You can't even tell which direction of time is forward 858 00:51:31,797 --> 00:51:32,912 and which is backward. 859 00:51:33,007 --> 00:51:34,622 In a very real sense, 860 00:51:34,717 --> 00:51:37,629 time itself will one day lose its meaning. 861 00:51:44,476 --> 00:51:47,218 GREENE: About 350 years ago, 862 00:51:47,354 --> 00:51:50,221 Isaac Newton, who was one of the first 863 00:51:50,357 --> 00:51:52,564 to think about time scientifically, 864 00:51:52,693 --> 00:51:55,150 wrote that he did not need to define time 865 00:51:55,237 --> 00:51:58,445 because it is something "well-known to all." 866 00:51:58,532 --> 00:52:00,693 But in trying to square 867 00:52:00,784 --> 00:52:05,699 our experience of time with the true nature of time, 868 00:52:05,789 --> 00:52:07,620 we've been forced to challenge 869 00:52:07,708 --> 00:52:10,791 some of our most deeply held beliefs. 870 00:52:13,005 --> 00:52:15,291 We now know that in every event 871 00:52:15,382 --> 00:52:18,670 that goes from order to disorder, 872 00:52:18,761 --> 00:52:21,719 there's a link to the Big Bang itself, 873 00:52:21,847 --> 00:52:24,133 giving us the arrow of time. 874 00:52:24,224 --> 00:52:28,718 The common-sense notion that one true time governs the universe 875 00:52:28,812 --> 00:52:32,054 has given way to a picture in which time is different 876 00:52:32,191 --> 00:52:34,557 for each and every one of us. 877 00:52:34,693 --> 00:52:36,649 And the flow of time, 878 00:52:36,737 --> 00:52:40,821 which seems to us as real as the flow of a river, 879 00:52:40,908 --> 00:52:43,399 may be nothing more than an illusion. 880 00:52:43,535 --> 00:52:49,656 Past, present and future may all exist on equal footing. 881 00:52:49,750 --> 00:52:52,457 Our everyday experience of time 882 00:52:52,586 --> 00:52:55,703 will always exert a powerful influence. 883 00:52:55,798 --> 00:52:59,256 We will continue to imagine that time is universal, 884 00:52:59,343 --> 00:53:02,710 that the past is gone, that the future is yet to be. 885 00:53:02,805 --> 00:53:05,592 But because of our scientific discoveries, 886 00:53:05,683 --> 00:53:08,675 we can also look beyond experience 887 00:53:08,769 --> 00:53:12,136 and recognize that we are part of a far richer 888 00:53:12,272 --> 00:53:15,264 and far stranger reality. 889 00:53:26,370 --> 00:53:28,861 Major funding for NOVA is provided by: 890 00:53:31,291 --> 00:53:32,656 And... 891 00:53:43,470 --> 00:53:46,837 And by the Corporation for Public Broadcasting 892 00:53:46,974 --> 00:53:51,138 and by contributions to your PBS station from: 893 00:53:57,776 --> 00:54:00,358 Major funding for "The Fabric of the Cosmos" 894 00:54:00,487 --> 00:54:03,149 is provided by the National Science Foundation. 895 00:54:10,914 --> 00:54:12,450 And... 896 00:54:15,502 --> 00:54:18,335 Supporting original research and public understanding 897 00:54:18,422 --> 00:54:24,292 of science, technology, engineering and mathematics. 898 00:54:24,386 --> 00:54:26,297 Additional funding is provided by... 899 00:54:38,192 --> 00:54:40,183 And the George D.Smith Fund. 900 00:54:43,155 --> 00:54:45,862 Captioned by Media Access Group at WGBH access.wgdh.org