All language subtitles for How the Universe Works s08e07 Edge of the Universe.eng

af Afrikaans
ak Akan
sq Albanian
am Amharic
ar Arabic
hy Armenian
az Azerbaijani
eu Basque
be Belarusian
bem Bemba
bn Bengali
bh Bihari
bs Bosnian
br Breton
bg Bulgarian
km Cambodian
ca Catalan
ceb Cebuano
chr Cherokee
ny Chichewa
zh-CN Chinese (Simplified)
zh-TW Chinese (Traditional)
co Corsican
hr Croatian
cs Czech
da Danish
en English
eo Esperanto
et Estonian
ee Ewe
fo Faroese
tl Filipino
fi Finnish
fr French
fy Frisian
gaa Ga
gl Galician
ka Georgian
de German
el Greek
gn Guarani
gu Gujarati
ht Haitian Creole
ha Hausa
haw Hawaiian
iw Hebrew
hi Hindi
hmn Hmong
hu Hungarian
is Icelandic
ig Igbo
id Indonesian
ia Interlingua
ga Irish
it Italian
ja Japanese
jw Javanese
kn Kannada
kk Kazakh
rw Kinyarwanda
rn Kirundi
kg Kongo
ko Korean
kri Krio (Sierra Leone)
ku Kurdish
ckb Kurdish (Soranî)
ky Kyrgyz
lo Laothian
la Latin
lv Latvian
ln Lingala
lt Lithuanian
loz Lozi
lg Luganda
ach Luo
lb Luxembourgish
mk Macedonian
mg Malagasy
ms Malay
ml Malayalam
mt Maltese
mi Maori
mr Marathi
mfe Mauritian Creole
mo Moldavian
mn Mongolian
my Myanmar (Burmese)
sr-ME Montenegrin
ne Nepali
pcm Nigerian Pidgin
nso Northern Sotho
no Norwegian
nn Norwegian (Nynorsk)
oc Occitan
or Oriya
om Oromo
ps Pashto
fa Persian Download
pl Polish
pt-BR Portuguese (Brazil)
pt Portuguese (Portugal)
pa Punjabi
qu Quechua
ro Romanian
rm Romansh
nyn Runyakitara
ru Russian
sm Samoan
gd Scots Gaelic
sr Serbian
sh Serbo-Croatian
st Sesotho
tn Setswana
crs Seychellois Creole
sn Shona
sd Sindhi
si Sinhalese
sk Slovak
sl Slovenian
so Somali
es Spanish
es-419 Spanish (Latin American)
su Sundanese
sw Swahili
sv Swedish
tg Tajik
ta Tamil
tt Tatar
te Telugu
th Thai
ti Tigrinya
to Tonga
lua Tshiluba
tum Tumbuka
tr Turkish
tk Turkmen
tw Twi
ug Uighur
uk Ukrainian
ur Urdu
uz Uzbek
vi Vietnamese
cy Welsh
wo Wolof
xh Xhosa
yi Yiddish
yo Yoruba
zu Zulu
Would you like to inspect the original subtitles? These are the user uploaded subtitles that are being translated: 1 00:00:04,120 --> 00:00:06,390 Islands have edges. 2 00:00:08,090 --> 00:00:10,790 Planets have edges. 3 00:00:12,930 --> 00:00:16,976 Even galaxies have edges. 4 00:00:17,000 --> 00:00:20,376 But what about the universe? 5 00:00:20,400 --> 00:00:25,216 As explorers, as curious humans that we are, 6 00:00:25,240 --> 00:00:27,656 we're obsessed with boundaries and limits. 7 00:00:27,680 --> 00:00:28,956 And we want to know, 8 00:00:28,980 --> 00:00:33,896 "does the whole thing, the universe, have a limit?" 9 00:00:33,920 --> 00:00:38,866 Does the universe have an edge? Well, the answer is yes and no. 10 00:00:38,890 --> 00:00:42,006 It depends on what you mean by edge. 11 00:00:42,030 --> 00:00:44,736 The edge of what we can see? 12 00:00:44,760 --> 00:00:49,046 The edge of where we can go? 13 00:00:49,070 --> 00:00:52,070 Or the edge of reality itself? 14 00:00:54,000 --> 00:00:55,816 Looking out to the edge of the universe 15 00:00:55,840 --> 00:00:58,156 is tremendously important to understand 16 00:00:58,180 --> 00:01:00,656 our place in the universe itself. 17 00:01:00,680 --> 00:01:02,126 We're talking about our universe. 18 00:01:02,150 --> 00:01:04,526 We're talking about the thing that we exist within. 19 00:01:04,550 --> 00:01:06,156 The most fundamental thing there is, 20 00:01:06,180 --> 00:01:08,396 we're driven to understand it. 21 00:01:08,420 --> 00:01:12,436 There is always a desire to push the knowledge to the edge. 22 00:01:12,460 --> 00:01:15,736 So, can we ever find 23 00:01:15,760 --> 00:01:17,836 the edge of the universe? 24 00:01:20,530 --> 00:01:23,600 captions paid for by discovery communications 25 00:01:33,580 --> 00:01:36,286 2016, the Hubble space telescope 26 00:01:36,310 --> 00:01:39,096 turned toward a dark patch of sky 27 00:01:39,120 --> 00:01:42,050 in the constellation Ursa Major. 28 00:01:45,760 --> 00:01:51,436 It captured an image of an indistinct blob of light. 29 00:01:51,460 --> 00:01:56,700 The glow is from a distant galaxy called GN-Z11... 30 00:02:02,040 --> 00:02:05,370 ...the most distant galaxy we've ever observed. 31 00:02:08,150 --> 00:02:12,656 But is this the edge of the universe? 32 00:02:12,680 --> 00:02:16,026 The universe all around us is filled with galaxies, 33 00:02:16,050 --> 00:02:19,396 so it's kind of natural to say, "would there be a final galaxy? 34 00:02:19,420 --> 00:02:21,296 If you traveled far enough away, 35 00:02:21,320 --> 00:02:24,236 would you finally be at the very last galaxy in the universe 36 00:02:24,260 --> 00:02:25,830 looking out into empty space?" 37 00:02:28,130 --> 00:02:30,500 That's a difficult question to answer. 38 00:02:33,270 --> 00:02:36,886 Because there's a limit to how far we can see. 39 00:02:36,910 --> 00:02:40,786 It all comes down to the speed of light 40 00:02:40,810 --> 00:02:44,586 and the age of the universe. 41 00:02:44,610 --> 00:02:47,756 The key to understanding the edge of the universe 42 00:02:47,780 --> 00:02:51,396 is that light travels very, very fast, 43 00:02:51,420 --> 00:02:53,336 but not infinitely fast. 44 00:02:53,360 --> 00:02:55,636 It takes time for it to get from one place 45 00:02:55,660 --> 00:02:57,506 in the universe to the other. 46 00:02:57,530 --> 00:02:59,636 You open the curtains, light fills the room. 47 00:02:59,660 --> 00:03:01,746 It doesn't seem to travel at all. 48 00:03:01,770 --> 00:03:03,746 But over the vast distances of the universe, 49 00:03:03,770 --> 00:03:07,346 you actually notice this travel time. 50 00:03:07,370 --> 00:03:09,916 Even the sun 93 million miles away, 51 00:03:09,940 --> 00:03:12,616 the light takes eight minutes to get to us. 52 00:03:12,640 --> 00:03:15,056 When you look out at the stars, we start to think of distance 53 00:03:15,080 --> 00:03:18,196 in terms of light-years because it takes years 54 00:03:18,220 --> 00:03:20,696 for the light to get from those stars to us. 55 00:03:20,720 --> 00:03:22,996 Then when you look at galaxies, then you're talking about 56 00:03:23,020 --> 00:03:25,890 millions or billions of light-years. 57 00:03:28,090 --> 00:03:32,876 When we look at the light from galaxy GN-Z11, 58 00:03:32,900 --> 00:03:37,770 we're seeing light emitted 13.4 billion years ago. 59 00:03:42,570 --> 00:03:44,286 You can't really even find a galaxy 60 00:03:44,310 --> 00:03:45,916 too much farther away than that 61 00:03:45,940 --> 00:03:49,756 because the universe is only 13.8 billion years old, 62 00:03:49,780 --> 00:03:52,926 and it takes a certain amount of time for galaxies to even form. 63 00:03:52,950 --> 00:03:55,126 So we're not going to find too many more galaxies 64 00:03:55,150 --> 00:03:56,796 farther away than this. 65 00:03:56,820 --> 00:03:59,666 If things are far enough away, there is no way that light 66 00:03:59,690 --> 00:04:02,336 can get to us in the age of the universe. 67 00:04:02,360 --> 00:04:04,536 What this means is there's a hard limit 68 00:04:04,560 --> 00:04:07,306 to the edge of the universe that we can see, 69 00:04:07,330 --> 00:04:11,946 and this is set by the age of the universe. 70 00:04:11,970 --> 00:04:14,516 GN-Z11 sparked into life 71 00:04:14,540 --> 00:04:17,416 early in the history of the universe, 72 00:04:17,440 --> 00:04:21,626 just 400 million years after the big bang. 73 00:04:21,650 --> 00:04:26,756 Before that, there were no stars to send out light. 74 00:04:26,780 --> 00:04:28,826 If you look in any direction at all, 75 00:04:28,850 --> 00:04:31,296 you get all the way back to when there were no stars, 76 00:04:31,320 --> 00:04:34,896 no galaxies, nothing but very, very hot gas, 77 00:04:34,920 --> 00:04:39,306 and that sort of forms a shell around us. 78 00:04:39,330 --> 00:04:44,606 That outer shell is the cosmic microwave background. 79 00:04:44,630 --> 00:04:48,586 It is the oldest light in the universe, 80 00:04:48,610 --> 00:04:51,616 the echo of the birth of the universe, 81 00:04:51,640 --> 00:04:54,286 the big bang. 82 00:04:54,310 --> 00:04:55,656 The edge of our universe, 83 00:04:55,680 --> 00:04:58,296 the very furthest thing that we can see, 84 00:04:58,320 --> 00:04:59,956 is one of the earliest relics 85 00:04:59,980 --> 00:05:01,926 of the formation of the universe itself. 86 00:05:01,950 --> 00:05:05,496 That is the cosmic microwave background. 87 00:05:05,520 --> 00:05:11,366 We call this the edge of our observable universe. 88 00:05:11,390 --> 00:05:14,276 So we have an observable universe, but beyond that, 89 00:05:14,300 --> 00:05:15,476 even if there are things out there, 90 00:05:15,500 --> 00:05:17,346 there's no way we can see them 91 00:05:17,370 --> 00:05:20,600 because the light just could not have gotten to us by now. 92 00:05:25,210 --> 00:05:27,916 As the name states, the observable universe 93 00:05:27,940 --> 00:05:32,356 is simply the part of the universe we can see. 94 00:05:32,380 --> 00:05:34,096 We can think of the observable universe 95 00:05:34,120 --> 00:05:35,626 sort of like a spotlight 96 00:05:35,650 --> 00:05:38,596 centered on wherever you're standing right now 97 00:05:38,620 --> 00:05:42,020 and you can see to the edge of your spotlight and not beyond. 98 00:05:44,490 --> 00:05:46,736 But if you move a little bit to the left, 99 00:05:46,760 --> 00:05:47,976 a little bit to the right, 100 00:05:48,000 --> 00:05:50,900 your observable universe actually moves with you. 101 00:05:54,740 --> 00:05:57,346 For someone living in galaxy GN-Z11, 102 00:05:57,370 --> 00:06:02,226 a totally different part of the universe would be observable. 103 00:06:02,250 --> 00:06:07,956 So that distant galaxy is at the edge of our observable universe, 104 00:06:07,980 --> 00:06:13,396 and we are at the edge of their observable universe. 105 00:06:13,420 --> 00:06:15,206 We have different spotlights. 106 00:06:15,230 --> 00:06:16,836 One of the wonderful things to think about 107 00:06:16,860 --> 00:06:19,376 is that there are other spheres around other galaxies, 108 00:06:19,400 --> 00:06:22,206 there are other aliens looking up into the sky tonight 109 00:06:22,230 --> 00:06:25,000 wondering what the true extent of the universe is. 110 00:06:27,240 --> 00:06:29,346 The true extent of our universe 111 00:06:29,370 --> 00:06:32,670 doesn't end with galaxy GN-Z11. 112 00:06:35,810 --> 00:06:39,026 But when astronomers use the Hubble space telescope 113 00:06:39,050 --> 00:06:44,066 to accurately measure the distance to GN-Z11, 114 00:06:44,090 --> 00:06:46,520 they find something shocking. 115 00:06:48,630 --> 00:06:53,036 It's 32 billion light-years away, 116 00:06:53,060 --> 00:06:55,930 three times further than thought possible. 117 00:06:57,700 --> 00:07:00,146 So if nothing can travel faster than light 118 00:07:00,170 --> 00:07:03,346 and we measure the distance to this galaxy, 119 00:07:03,370 --> 00:07:06,370 how can it be 32 billion light-years away? 120 00:07:08,480 --> 00:07:10,756 There hasn't been enough time 121 00:07:10,780 --> 00:07:12,356 in the history of the universe 122 00:07:12,380 --> 00:07:15,566 for light from GN-Z11 to reach us. 123 00:07:15,590 --> 00:07:19,596 There must be some mistake here. Right? 124 00:07:19,620 --> 00:07:21,066 At this point, your brain 125 00:07:21,090 --> 00:07:22,666 is probably thinking of leaping out 126 00:07:22,690 --> 00:07:24,766 of your skull and running around screaming. 127 00:07:24,790 --> 00:07:27,606 Trust me, I know. I'm an astronomer. 128 00:07:27,630 --> 00:07:29,246 I've been doing this my whole life, 129 00:07:29,270 --> 00:07:32,116 and this stuff twists my imagination up. 130 00:07:32,140 --> 00:07:34,700 It's really hard to grasp this. 131 00:07:36,640 --> 00:07:40,086 How do we see a galaxy that's 32 billion light-years away 132 00:07:40,110 --> 00:07:43,280 and only 13.4 billion years old? 133 00:07:46,320 --> 00:07:51,026 GN-Z11 is further away than it should be 134 00:07:51,050 --> 00:07:55,366 because something strange is going on with our universe. 135 00:07:55,390 --> 00:07:57,236 It's expanding. 136 00:07:57,260 --> 00:07:59,836 And if the universe is expanding, 137 00:07:59,860 --> 00:08:03,376 then where does its edge lie 138 00:08:03,400 --> 00:08:06,200 and can we ever reach it? 139 00:08:24,050 --> 00:08:26,266 13.8 billion years ago, 140 00:08:26,290 --> 00:08:29,190 a speck of energy burst into life. 141 00:08:32,700 --> 00:08:35,246 We call it the big bang... 142 00:08:35,270 --> 00:08:39,246 space and time pushed out in all directions. 143 00:08:39,270 --> 00:08:42,700 Ever since, our universe has expanded. 144 00:08:44,940 --> 00:08:48,626 But the way it's expanding makes finding an edge 145 00:08:48,650 --> 00:08:51,926 a major challenge. 146 00:08:51,950 --> 00:08:53,626 The universe is expanding 147 00:08:53,650 --> 00:08:56,296 and expands according to a very simple law 148 00:08:56,320 --> 00:08:58,836 that the farther away a galaxy is from us, 149 00:08:58,860 --> 00:09:01,620 the faster it appears to be receding away from us. 150 00:09:03,990 --> 00:09:08,006 The furthest galaxies are moving at very high speeds. 151 00:09:08,030 --> 00:09:12,816 The most distant galaxy we've ever spotted, GN-Z11, 152 00:09:12,840 --> 00:09:17,846 seems to have moved 32 billion light-years away from us 153 00:09:17,870 --> 00:09:22,286 in just 13.4 billion years. 154 00:09:22,310 --> 00:09:26,026 That's faster than the speed of light. 155 00:09:26,050 --> 00:09:28,666 We can measure the speeds with which galaxies 156 00:09:28,690 --> 00:09:30,126 are moving away from us, 157 00:09:30,150 --> 00:09:32,496 and many, many galaxies are moving away from us 158 00:09:32,520 --> 00:09:35,436 at speeds faster than the speed of light. 159 00:09:35,460 --> 00:09:37,506 This sounds like it's breaking the law, right? 160 00:09:37,530 --> 00:09:39,776 There's this idea that you've all been told 161 00:09:39,800 --> 00:09:41,536 that relativity says nothing goes faster 162 00:09:41,560 --> 00:09:42,806 than the speed of light. 163 00:09:42,830 --> 00:09:46,016 Okay, you've been lied to. 164 00:09:46,040 --> 00:09:49,016 Space itself can do what it wants. 165 00:09:49,040 --> 00:09:52,616 It makes the rules, it can break the rules. 166 00:09:52,640 --> 00:09:55,586 That rule applies to matter, not to space itself. 167 00:09:55,610 --> 00:09:59,296 Space can expand at whatever rate it wants. 168 00:09:59,320 --> 00:10:02,196 Simple way to think of this expansion law is imagine 169 00:10:02,220 --> 00:10:04,666 standing on an infinite rubber sheet 170 00:10:04,690 --> 00:10:06,836 that stretches all the way out into the distance 171 00:10:06,860 --> 00:10:08,366 and you're standing on the same place. 172 00:10:08,390 --> 00:10:10,466 You can mark it with a little "X." 173 00:10:10,490 --> 00:10:14,436 Now, all the sheet expands in every direction. 174 00:10:14,460 --> 00:10:16,846 So if it expands by a factor of two, 175 00:10:16,870 --> 00:10:19,746 another galaxy that was, say, one foot away from you 176 00:10:19,770 --> 00:10:22,946 is now two feet away from you as we stretch the sheet, 177 00:10:22,970 --> 00:10:25,586 but another galaxy was 10 feet away from you. 178 00:10:25,610 --> 00:10:27,186 Expand that by a factor of 2 179 00:10:27,210 --> 00:10:29,356 and now it's 20 feet away from you. 180 00:10:29,380 --> 00:10:33,226 So in the same amount of time, one galaxy moved one foot, 181 00:10:33,250 --> 00:10:36,026 where another galaxy moved 10 feet. 182 00:10:36,050 --> 00:10:37,866 So the more stuff there is, 183 00:10:37,890 --> 00:10:40,536 the more elastic between you and another galaxy, 184 00:10:40,560 --> 00:10:43,090 the more it seems to expand away from you. 185 00:10:45,560 --> 00:10:48,476 Expansion means our observable universe 186 00:10:48,500 --> 00:10:52,946 stretches for a colossal 46 billion light-years 187 00:10:52,970 --> 00:10:57,270 in all directions, 92 billion light-years across... 188 00:10:59,780 --> 00:11:02,340 ...and getting bigger by the second. 189 00:11:06,580 --> 00:11:09,566 This number is so incomprehensibly large 190 00:11:09,590 --> 00:11:12,966 that it's difficult to wrap your brain around. 191 00:11:12,990 --> 00:11:16,666 There are trillions of galaxies within this volume. 192 00:11:16,690 --> 00:11:18,136 It's staggering. 193 00:11:18,160 --> 00:11:22,176 It's so much larger than anything we're familiar with. 194 00:11:22,200 --> 00:11:23,746 If we were to travel 195 00:11:23,770 --> 00:11:27,016 to the edge of the observable universe, 196 00:11:27,040 --> 00:11:31,586 we would enter even more unfamiliar territory. 197 00:11:31,610 --> 00:11:34,786 Imagine we're in an ultra-fast spaceship. 198 00:11:34,810 --> 00:11:37,950 We leave the solar system, then the milky way. 199 00:11:40,420 --> 00:11:43,666 As we travel deeper into intergalactic space, 200 00:11:43,690 --> 00:11:46,190 things start to get really weird. 201 00:11:49,690 --> 00:11:53,836 For every million light-years we go from the milky way, 202 00:11:53,860 --> 00:11:56,646 the galaxies move away from us 203 00:11:56,670 --> 00:12:00,530 at around 13 miles per second faster. 204 00:12:02,910 --> 00:12:05,886 We have to accelerate just to keep up. 205 00:12:05,910 --> 00:12:10,850 But the galaxies keep on moving, always beyond our reach. 206 00:12:24,790 --> 00:12:27,136 Imagine you're a sprinter on a racetrack. 207 00:12:27,160 --> 00:12:28,636 If you're running towards the finish line, 208 00:12:28,660 --> 00:12:30,876 it may take you a few seconds to cross it. 209 00:12:30,900 --> 00:12:34,446 But now imagine that that finish line is moving away from you. 210 00:12:34,470 --> 00:12:36,816 If it's moving away from you at the same speed you're running, 211 00:12:36,840 --> 00:12:38,186 you'll never reach it. 212 00:12:38,210 --> 00:12:41,286 And if it's moving faster than the runner, 213 00:12:41,310 --> 00:12:43,526 then even faster runners won't reach it. 214 00:12:43,550 --> 00:12:47,726 And that's sort of what we're seeing here with the universe. 215 00:12:47,750 --> 00:12:49,326 Beyond a certain distance, 216 00:12:49,350 --> 00:12:54,496 galaxies are racing away from us faster than the speed of light. 217 00:12:54,520 --> 00:12:58,130 It's a line called the cosmic event horizon. 218 00:13:00,360 --> 00:13:05,476 And 97% of galaxies we see in the observable universe 219 00:13:05,500 --> 00:13:08,846 are beyond this line and unreachable, 220 00:13:08,870 --> 00:13:11,570 including GN-Z11. 221 00:13:13,140 --> 00:13:14,916 They're sort of teasing us to say, "look at me, 222 00:13:14,940 --> 00:13:16,486 what a nice piece of real estate." 223 00:13:16,510 --> 00:13:19,626 But we know even if we started going there now, 224 00:13:19,650 --> 00:13:21,280 we could never reach them. 225 00:13:24,020 --> 00:13:26,736 Anything that has crossed the cosmic event horizon 226 00:13:26,760 --> 00:13:29,366 is out of our reach forever. 227 00:13:29,390 --> 00:13:31,066 But that's not the full picture 228 00:13:31,090 --> 00:13:34,560 because the expansion rate of the universe is changing. 229 00:13:36,500 --> 00:13:39,216 A little over 20 years ago, astronomers discovered 230 00:13:39,240 --> 00:13:42,316 that the current rate of the universe's expansion 231 00:13:42,340 --> 00:13:44,610 is accelerating, it's speeding up. 232 00:13:46,640 --> 00:13:51,386 Astronomers suspect a mysterious force is at work... 233 00:13:51,410 --> 00:13:54,426 dark energy. 234 00:13:54,450 --> 00:13:58,266 Dark energy is what we think is pushing the universe apart, 235 00:13:58,290 --> 00:14:01,396 causing this accelerating expansion. 236 00:14:01,420 --> 00:14:05,606 And the origin and true physical nature of dark energy 237 00:14:05,630 --> 00:14:07,260 is a big mystery. 238 00:14:09,700 --> 00:14:12,746 Thanks to dark energy, more and more galaxies 239 00:14:12,770 --> 00:14:15,116 are crossing the cosmic event horizon 240 00:14:15,140 --> 00:14:17,670 and leaving the observable universe. 241 00:14:20,440 --> 00:14:22,326 These galaxies... 242 00:14:22,350 --> 00:14:24,810 Are lost to us forever. 243 00:14:27,480 --> 00:14:30,296 There are galaxies that we can see today 244 00:14:30,320 --> 00:14:33,796 that in a few million years, say, we won't be able to see 245 00:14:33,820 --> 00:14:35,666 because the edge of the observable universe 246 00:14:35,690 --> 00:14:39,076 has basically moved in closer than that galaxy. 247 00:14:39,100 --> 00:14:40,806 That's going to happen all the time. 248 00:14:40,830 --> 00:14:43,376 And in a trillion years or something like that, 249 00:14:43,400 --> 00:14:45,446 all these galaxies that we see in our sky 250 00:14:45,470 --> 00:14:46,976 will be completely invisible 251 00:14:47,000 --> 00:14:50,070 because they'll be beyond the edge of the universe. 252 00:14:53,140 --> 00:14:55,926 So eventually, every last galaxy 253 00:14:55,950 --> 00:14:57,726 will be so far away from us 254 00:14:57,750 --> 00:15:01,326 that light cannot reach us through that expanding space. 255 00:15:01,350 --> 00:15:04,096 It's almost as if you're driving through a dark desert 256 00:15:04,120 --> 00:15:06,836 in your car and the very, very last town 257 00:15:06,860 --> 00:15:08,696 that ever exists has gone over the horizon 258 00:15:08,720 --> 00:15:10,990 and they'll never be any light again. 259 00:15:14,360 --> 00:15:16,806 We can see less and less of the universe 260 00:15:16,830 --> 00:15:18,976 as we go into the future. 261 00:15:19,000 --> 00:15:21,016 What a strange thought. 262 00:15:21,040 --> 00:15:25,210 So that means we should build all the telescopes we can now. 263 00:15:27,240 --> 00:15:29,886 There's a limit to the universe we can see, 264 00:15:29,910 --> 00:15:33,726 even with the most advanced telescopes. 265 00:15:33,750 --> 00:15:36,226 But what lies beyond 266 00:15:36,250 --> 00:15:39,150 is one of the biggest mysteries in astronomy. 267 00:15:41,260 --> 00:15:44,506 The greater universe could be stranger 268 00:15:44,530 --> 00:15:46,630 than our wildest imagination. 269 00:15:49,000 --> 00:15:50,176 When you stand on the beach 270 00:15:50,200 --> 00:15:51,406 and you look at the horizon 271 00:15:51,430 --> 00:15:53,816 and you kind of think, "oh, what beautiful lands 272 00:15:53,840 --> 00:15:55,276 are there beyond the horizon? 273 00:15:55,300 --> 00:15:58,586 Things I've never imagined before." 274 00:15:58,610 --> 00:15:59,886 It's so natural. 275 00:15:59,910 --> 00:16:03,286 It's so human to ask, "what lies beyond that? 276 00:16:03,310 --> 00:16:05,850 What is the true extent of the universe?" 277 00:16:21,160 --> 00:16:23,146 The observable universe 278 00:16:23,170 --> 00:16:25,370 contains trillions of galaxies. 279 00:16:27,940 --> 00:16:31,140 It's about 92 billion light-years across... 280 00:16:33,380 --> 00:16:34,886 ...but astronomers believe 281 00:16:34,910 --> 00:16:37,780 this isn't the full extent of the universe. 282 00:16:41,020 --> 00:16:44,266 What we don't know is how much of the universe 283 00:16:44,290 --> 00:16:46,266 is our observable universe. 284 00:16:46,290 --> 00:16:49,306 It could be a tiny, microscopic speck of this 285 00:16:49,330 --> 00:16:51,766 much more vast universe. 286 00:16:51,790 --> 00:16:53,836 We just don't know. 287 00:16:53,860 --> 00:16:56,106 We have no idea how much stuff there is 288 00:16:56,130 --> 00:16:57,576 outside the observable universe, 289 00:16:57,600 --> 00:17:01,416 but because by definition, it's outside the observable universe, 290 00:17:01,440 --> 00:17:04,216 we really don't know right now. 291 00:17:04,240 --> 00:17:06,286 So what is out there? 292 00:17:06,310 --> 00:17:10,686 One theory says that space outside the observable universe 293 00:17:10,710 --> 00:17:16,126 is pretty much the same as our own cosmic neighborhood. 294 00:17:16,150 --> 00:17:18,626 It's just more universe. It's just like here. 295 00:17:18,650 --> 00:17:21,236 It's just far enough away that we can't see it. 296 00:17:21,260 --> 00:17:24,706 So it's not like there's bizarre places where time runs backwards 297 00:17:24,730 --> 00:17:27,090 or aliens have two heads, well, yeah, maybe. 298 00:17:29,570 --> 00:17:30,946 But further out 299 00:17:30,970 --> 00:17:33,446 in the deepest parts of the greater universe, 300 00:17:33,470 --> 00:17:35,400 all bets are off. 301 00:17:37,670 --> 00:17:40,556 We expect that as you go sort of twice or three times 302 00:17:40,580 --> 00:17:42,056 beyond the observable universe, 303 00:17:42,080 --> 00:17:44,926 it's probably very similar to the universe we inhabit. 304 00:17:44,950 --> 00:17:48,426 But if you go a thousand times or a million times farther, 305 00:17:48,450 --> 00:17:50,150 who knows what you might see? 306 00:17:52,190 --> 00:17:55,220 It might be very, very different if we go far enough away. 307 00:17:57,860 --> 00:17:59,776 Strangely, it all comes back 308 00:17:59,800 --> 00:18:02,206 to the expansion of the universe 309 00:18:02,230 --> 00:18:05,400 and one crucial detail in that process. 310 00:18:08,070 --> 00:18:09,146 There was a brief moment 311 00:18:09,170 --> 00:18:11,286 in the very early history of the universe 312 00:18:11,310 --> 00:18:15,316 where its expansion accelerated hugely. 313 00:18:15,340 --> 00:18:17,386 This acceleration is called inflation, 314 00:18:17,410 --> 00:18:20,826 and in a brief moment, the universe itself expanded 315 00:18:20,850 --> 00:18:23,550 at multiple times the speed of light. 316 00:18:25,820 --> 00:18:29,436 Inflation was a formative moment 317 00:18:29,460 --> 00:18:31,006 for our universe. 318 00:18:31,030 --> 00:18:32,476 By the time it stopped, 319 00:18:32,500 --> 00:18:35,530 the universe's basic characteristics were set. 320 00:18:37,930 --> 00:18:39,846 There are these fundamental constants 321 00:18:39,870 --> 00:18:42,586 that describe the phenomena in our universe, 322 00:18:42,610 --> 00:18:46,510 the fundamentals of matter and light and space-time. 323 00:18:48,140 --> 00:18:49,786 But some scientists think 324 00:18:49,810 --> 00:18:52,386 there could be regions of the greater universe 325 00:18:52,410 --> 00:18:54,880 where inflation has never stopped. 326 00:18:57,150 --> 00:19:02,236 The idea is the greater universe is expanding at an insane speed, 327 00:19:02,260 --> 00:19:05,406 but here and there, occasionally a little region 328 00:19:05,430 --> 00:19:10,746 will stop inflating and just expand at the normal rate. 329 00:19:10,770 --> 00:19:12,746 Inflation can end somewhere 330 00:19:12,770 --> 00:19:15,016 and that gives rise to the universe we live in, 331 00:19:15,040 --> 00:19:18,946 while inflation continues somewhere else. 332 00:19:18,970 --> 00:19:21,056 Parts of the greater universe 333 00:19:21,080 --> 00:19:22,356 that continued to inflate 334 00:19:22,380 --> 00:19:25,650 would be left with different laws of physics. 335 00:19:27,280 --> 00:19:29,326 This incredibly violent inflation process 336 00:19:29,350 --> 00:19:33,366 is actually monkeyed with the very fabric of space itself, 337 00:19:33,390 --> 00:19:35,266 so that a lot of the things that we were taught 338 00:19:35,290 --> 00:19:39,976 that are laws of physics are different there. 339 00:19:40,000 --> 00:19:41,276 So in an essence, 340 00:19:41,300 --> 00:19:43,176 inflation gives us a very natural way 341 00:19:43,200 --> 00:19:46,076 to make this patchwork quilt of different parts of the universe 342 00:19:46,100 --> 00:19:48,946 where things seem different. 343 00:19:48,970 --> 00:19:52,086 So what we could imagine is a super large-scale structure 344 00:19:52,110 --> 00:19:55,656 where there's different regions of the universe, domains, 345 00:19:55,680 --> 00:19:58,980 and each domain has different local laws of physics. 346 00:20:01,950 --> 00:20:03,466 These different parts of the universe 347 00:20:03,490 --> 00:20:07,550 are separated by frontiers called domain walls. 348 00:20:11,360 --> 00:20:14,176 We have similar boundaries on earth. 349 00:20:14,200 --> 00:20:17,006 Whenever you have something that can be in many different states, 350 00:20:17,030 --> 00:20:19,876 you can end up with domain wall. 351 00:20:19,900 --> 00:20:25,516 If our fish swimming around in the arctic near an iceberg, 352 00:20:25,540 --> 00:20:27,216 there will be a domain boundary 353 00:20:27,240 --> 00:20:29,486 between the water being in the liquid state 354 00:20:29,510 --> 00:20:33,296 where I am and the solid state inside the ice. 355 00:20:33,320 --> 00:20:36,866 So a domain wall is just a wall between two domains. 356 00:20:36,890 --> 00:20:38,826 If it's water, this could be ice, 357 00:20:38,850 --> 00:20:39,896 this could be liquid. 358 00:20:39,920 --> 00:20:41,336 If you're talking about space, 359 00:20:41,360 --> 00:20:43,906 this could be a kind of space maybe you can live in. 360 00:20:43,930 --> 00:20:47,706 This could be a kind of space where you don't want to be. 361 00:20:47,730 --> 00:20:51,606 Crossing a domain wall would be very bad news 362 00:20:51,630 --> 00:20:54,376 for anyone who dared to try. 363 00:20:54,400 --> 00:20:57,016 Cross that domain wall and the laws of physics 364 00:20:57,040 --> 00:20:59,316 could change dramatically. 365 00:20:59,340 --> 00:21:01,316 The number of dimensions could change. 366 00:21:01,340 --> 00:21:03,926 If we were somehow able to travel to places in the universe 367 00:21:03,950 --> 00:21:05,326 where the laws of physics are different, 368 00:21:05,350 --> 00:21:07,696 we would die 369 00:21:07,720 --> 00:21:10,496 because all of the chemistry going on in our bodies 370 00:21:10,520 --> 00:21:15,096 depends very, very sensitively on the laws of physics. 371 00:21:15,120 --> 00:21:19,060 So you could just dissipate like Thanos snap and you're gone. 372 00:21:21,060 --> 00:21:22,746 Domain walls might be the closest 373 00:21:22,770 --> 00:21:25,400 we get to locating an edge in the universe. 374 00:21:26,970 --> 00:21:29,316 Depends on how you define the edge. 375 00:21:29,340 --> 00:21:32,686 If it is the realm where the laws of our universe operate, 376 00:21:32,710 --> 00:21:36,640 then these domain walls are in essence the age of the universe. 377 00:21:40,780 --> 00:21:42,720 But this is all just theory. 378 00:21:46,590 --> 00:21:48,396 If we ever really are to work out 379 00:21:48,420 --> 00:21:50,866 what the true size and shape of the universe is, 380 00:21:50,890 --> 00:21:54,536 we're going to have to look for clues that are close to us. 381 00:21:54,560 --> 00:21:58,046 Clues that could answer the ultimate question, 382 00:21:58,070 --> 00:22:01,946 how big is the rest of the greater universe 383 00:22:01,970 --> 00:22:04,840 and could it go on forever? 384 00:22:20,420 --> 00:22:22,806 For tens of thousands of years, 385 00:22:22,830 --> 00:22:28,136 mankind has gazed in wonder at the vastness of the cosmos, 386 00:22:28,160 --> 00:22:32,476 but just how extensive is it? 387 00:22:32,500 --> 00:22:34,176 If we could answer that question, 388 00:22:34,200 --> 00:22:39,356 it might help us to understand our place in the universe. 389 00:22:39,380 --> 00:22:41,686 One of the fundamental questions in science 390 00:22:41,710 --> 00:22:44,986 is how big is the universe? 391 00:22:45,010 --> 00:22:47,726 To answer the question, "how big is the universe?" 392 00:22:47,750 --> 00:22:51,066 We have to answer the question, "what shape is the universe?" 393 00:22:51,090 --> 00:22:52,996 And by shape, I mean geometry. 394 00:22:53,020 --> 00:22:57,766 I mean, how is the universe curved on its largest scales? 395 00:22:57,790 --> 00:23:00,176 If we are to discover that the universe 396 00:23:00,200 --> 00:23:04,206 does have some sort of geometric curvature, 397 00:23:04,230 --> 00:23:09,746 then this might imply that it wraps around in on itself 398 00:23:09,770 --> 00:23:12,386 over incredibly large distances. 399 00:23:12,410 --> 00:23:16,126 And that if you could travel in one direction long enough, 400 00:23:16,150 --> 00:23:18,126 you would end up at your starting point. 401 00:23:18,150 --> 00:23:19,796 Another version is that the universe 402 00:23:19,820 --> 00:23:22,626 is more like an infinite flat plane. 403 00:23:22,650 --> 00:23:25,126 Okay? No curvature at all. 404 00:23:25,150 --> 00:23:27,666 The further you travel, well, the further you get 405 00:23:27,690 --> 00:23:30,560 and you never get back to where you started. 406 00:23:32,800 --> 00:23:34,376 To work out the shape of something, 407 00:23:34,400 --> 00:23:37,476 we would normally just step back and take a look. 408 00:23:37,500 --> 00:23:42,746 But clearly moving outside the universe is a nonstarter. 409 00:23:42,770 --> 00:23:44,146 You can't jump on a rocket 410 00:23:44,170 --> 00:23:47,386 and fly a thousand times larger than our cosmic horizon 411 00:23:47,410 --> 00:23:49,216 and see what the shape of the universe is. 412 00:23:49,240 --> 00:23:51,126 We just can't do that. 413 00:23:51,150 --> 00:23:54,156 Our human perspective on the larger universe 414 00:23:54,180 --> 00:23:55,456 is so limited. 415 00:23:55,480 --> 00:23:57,596 So if we want to figure out what the larger shape 416 00:23:57,620 --> 00:23:59,596 and scale of the universe is, 417 00:23:59,620 --> 00:24:01,960 we're going to have to be very clever indeed. 418 00:24:04,790 --> 00:24:06,576 One way to be clever 419 00:24:06,600 --> 00:24:08,976 is to think of the geometry of the universe 420 00:24:09,000 --> 00:24:11,746 in its simplest terms. 421 00:24:11,770 --> 00:24:14,076 When we talk about the geometry of the universe, 422 00:24:14,100 --> 00:24:16,616 we really are talking about geometry. 423 00:24:16,640 --> 00:24:19,786 In order to do geometry, you have to take measures. 424 00:24:19,810 --> 00:24:21,986 You need a cosmic ruler to do this, 425 00:24:22,010 --> 00:24:24,386 and it turns out there's a great cosmic ruler 426 00:24:24,410 --> 00:24:27,250 known as baryon acoustic oscillations. 427 00:24:29,690 --> 00:24:32,426 Baryonic acoustic oscillations are ripples 428 00:24:32,450 --> 00:24:36,166 in the cosmic microwave background, 429 00:24:36,190 --> 00:24:38,660 the oldest light in the universe. 430 00:24:40,960 --> 00:24:42,676 As the universe expanded, 431 00:24:42,700 --> 00:24:47,300 these ripples were imprinted in space in a uniform way. 432 00:24:48,770 --> 00:24:50,646 They provide a cosmic ruler 433 00:24:50,670 --> 00:24:53,856 to measure vast distances over time, 434 00:24:53,880 --> 00:24:56,186 so we can gauge if the universe expands 435 00:24:56,210 --> 00:24:59,910 in curved space or over a flat plane. 436 00:25:02,820 --> 00:25:04,826 When we use these cosmic rulers 437 00:25:04,850 --> 00:25:07,096 to try to back out the shape of the universe, 438 00:25:07,120 --> 00:25:09,336 we're sure to a few percent accuracy 439 00:25:09,360 --> 00:25:12,936 that the universe is flat. 440 00:25:12,960 --> 00:25:15,076 If the universe is flat, 441 00:25:15,100 --> 00:25:17,846 we could set off traveling into the cosmos 442 00:25:17,870 --> 00:25:20,570 and continue traveling forever. 443 00:25:22,670 --> 00:25:26,356 There may be no edge to our universe 444 00:25:26,380 --> 00:25:30,926 because a flat universe can be an infinite universe. 445 00:25:30,950 --> 00:25:32,956 Now we're thinking of the universe as something 446 00:25:32,980 --> 00:25:34,826 that really does go on forever, 447 00:25:34,850 --> 00:25:38,866 that the stars and galaxies never have an end, 448 00:25:38,890 --> 00:25:42,966 and how can something truly infinite really exist? 449 00:25:42,990 --> 00:25:47,706 Infinity is weird because it's a concept of, 450 00:25:47,730 --> 00:25:50,046 because it's endless. 451 00:25:50,070 --> 00:25:52,800 What does that mean? Who knows? I don't know. 452 00:25:55,500 --> 00:25:59,046 Infinity is a concept more than anything else. 453 00:25:59,070 --> 00:26:01,016 Our brains aren't evolved for that. 454 00:26:01,040 --> 00:26:03,786 We evolved living in the plains. 455 00:26:03,810 --> 00:26:06,426 We were apes looking for food. 456 00:26:06,450 --> 00:26:09,426 We weren't evolved to think about the universe 457 00:26:09,450 --> 00:26:12,166 and all of this stuff. 458 00:26:12,190 --> 00:26:14,566 I just can't stop contemplating this stuff. 459 00:26:14,590 --> 00:26:17,466 The idea of infinity and these large numbers 460 00:26:17,490 --> 00:26:19,506 and even the tininess of everything. 461 00:26:19,530 --> 00:26:20,976 It's nuts. 462 00:26:21,000 --> 00:26:24,130 Yeah, thinking about infinity makes my head hurt a little bit. 463 00:26:28,440 --> 00:26:31,586 An infinite universe has profound implications 464 00:26:31,610 --> 00:26:34,310 for understanding our place in the cosmos. 465 00:26:36,380 --> 00:26:39,310 It guarantees we're not alone. 466 00:26:40,920 --> 00:26:42,926 But if the universe is infinite, 467 00:26:42,950 --> 00:26:44,866 then there could be an infinite number of galaxies 468 00:26:44,890 --> 00:26:49,296 that have planets with life, an infinite number without life, 469 00:26:49,320 --> 00:26:51,636 then because life did appear here on earth, 470 00:26:51,660 --> 00:26:53,076 it's physically possible, 471 00:26:53,100 --> 00:26:54,606 therefore, it will definitely happen 472 00:26:54,630 --> 00:26:57,076 elsewhere in the universe. 473 00:26:57,100 --> 00:26:58,406 In a flat universe, 474 00:26:58,430 --> 00:27:03,386 alien life could come in an infinite number of forms, 475 00:27:03,410 --> 00:27:07,616 but there is an altogether stranger guarantee. 476 00:27:07,640 --> 00:27:10,726 If the universe has no edge, this means that 477 00:27:10,750 --> 00:27:14,680 things that seem like they are impossible become possible. 478 00:27:17,390 --> 00:27:20,236 Every possible arrangement of matter, 479 00:27:20,260 --> 00:27:23,236 every possible history. 480 00:27:23,260 --> 00:27:27,706 A galaxy of a solar system of a planet like earth 481 00:27:27,730 --> 00:27:28,976 is possible 482 00:27:29,000 --> 00:27:32,576 and is happening right now in parallel to us 483 00:27:32,600 --> 00:27:35,070 somewhere over there. 484 00:27:36,610 --> 00:27:39,486 So that means that there has to be another place 485 00:27:39,510 --> 00:27:42,956 that has a galaxy just like ours 486 00:27:42,980 --> 00:27:44,856 and it would have an earth just like ours. 487 00:27:44,880 --> 00:27:49,696 It would have people who would have another version of you, 488 00:27:49,720 --> 00:27:51,166 another version of me. 489 00:27:51,190 --> 00:27:55,366 It's 100% guaranteed that there is another Max Tegmark out there 490 00:27:55,390 --> 00:27:58,790 having exactly this conversation and in fact many of them. 491 00:28:00,860 --> 00:28:03,546 An infinite universe full of Max Tegmarks 492 00:28:03,570 --> 00:28:05,606 may be a strange concept, 493 00:28:05,630 --> 00:28:08,146 but what's truly mind-bending is understanding 494 00:28:08,170 --> 00:28:11,216 the physics of a flat universe. 495 00:28:11,240 --> 00:28:14,556 If the universe is infinite and it's expanding, 496 00:28:14,580 --> 00:28:20,196 what's it expanding into and what did it expand from? 497 00:28:20,220 --> 00:28:24,626 Was there ever an edge to the universe? 498 00:28:24,650 --> 00:28:28,796 Fortunately, the answer is that it doesn't make sense 499 00:28:28,820 --> 00:28:30,766 to ask that question. 500 00:28:30,790 --> 00:28:33,076 Everything is expanding, 501 00:28:33,100 --> 00:28:36,106 including the universe that we exist within. 502 00:28:36,130 --> 00:28:39,076 So in fact, it's not expanding into anything 503 00:28:39,100 --> 00:28:40,700 because it is everything. 504 00:28:45,670 --> 00:28:47,756 To help understand what's going on 505 00:28:47,780 --> 00:28:49,356 in an infinite universe, 506 00:28:49,380 --> 00:28:51,610 we need to go back to the big bang. 507 00:28:54,280 --> 00:28:57,596 We want to think of the big bang as an explosion in space, 508 00:28:57,620 --> 00:28:59,326 like it happened some place, 509 00:28:59,350 --> 00:29:02,236 but there wasn't any place before the big bang. 510 00:29:02,260 --> 00:29:05,506 Space existed inside of the big bang itself. 511 00:29:05,530 --> 00:29:07,776 So it's not an explosion in space, 512 00:29:07,800 --> 00:29:10,276 it's an explosion of space. 513 00:29:10,300 --> 00:29:12,346 We're sometimes told that at the big bang, 514 00:29:12,370 --> 00:29:15,776 the universe started out very, very small and then got big, 515 00:29:15,800 --> 00:29:19,716 but how can a finite point become infinite? 516 00:29:19,740 --> 00:29:21,756 Well, if the universe is infinite, 517 00:29:21,780 --> 00:29:25,526 then it was also infinite at the big bang. 518 00:29:25,550 --> 00:29:27,826 This is a tough thing to think about. 519 00:29:27,850 --> 00:29:29,296 Think about it this way. 520 00:29:29,320 --> 00:29:31,896 In an infinite universe, the galaxies go on forever 521 00:29:31,920 --> 00:29:35,566 and now there's a great distance between every galaxy. 522 00:29:35,590 --> 00:29:36,606 But once upon a time, 523 00:29:36,630 --> 00:29:38,106 the galaxies were closer together, 524 00:29:38,130 --> 00:29:40,706 say half their current distance apart, 525 00:29:40,730 --> 00:29:42,076 but they still went on forever. 526 00:29:42,100 --> 00:29:45,746 The universe was still infinite. 527 00:29:45,770 --> 00:29:47,176 In a flat universe, 528 00:29:47,200 --> 00:29:51,846 space was infinite from the beginning. 529 00:29:51,870 --> 00:29:54,356 There was never a single point in space 530 00:29:54,380 --> 00:29:56,986 where the big bang happened. 531 00:29:57,010 --> 00:30:00,596 It happened everywhere. 532 00:30:00,620 --> 00:30:05,596 An infinite universe offers infinite possibilities 533 00:30:05,620 --> 00:30:08,050 but no edge to space. 534 00:30:11,190 --> 00:30:14,106 But there may be another kind of edge, 535 00:30:14,130 --> 00:30:18,670 one that will only reveal itself if the universe dies. 536 00:30:37,420 --> 00:30:42,336 We live in an infinite and expanding universe. 537 00:30:42,360 --> 00:30:46,030 Space has no edge. It goes on forever. 538 00:30:51,030 --> 00:30:55,916 But there could be a different kind of edge to our universe, 539 00:30:55,940 --> 00:30:59,046 an edge of time. 540 00:30:59,070 --> 00:31:01,186 The universe seems to have begun 541 00:31:01,210 --> 00:31:03,256 13.8 billion years ago in the past, 542 00:31:03,280 --> 00:31:06,356 so there's some inclination, some impression, 543 00:31:06,380 --> 00:31:08,156 that it's finite in time. 544 00:31:08,180 --> 00:31:12,026 What we call the big bang is, as far as we understand it, 545 00:31:12,050 --> 00:31:14,636 a beginning, a start of the universe. 546 00:31:14,660 --> 00:31:16,906 The universe has a finite age. 547 00:31:16,930 --> 00:31:20,636 Now, does it have an edge in the future? 548 00:31:20,660 --> 00:31:22,536 We used to think that time would someday 549 00:31:22,560 --> 00:31:25,146 come to a catastrophic end, 550 00:31:25,170 --> 00:31:28,516 along with the planets, galaxies, 551 00:31:28,540 --> 00:31:30,770 and all life in the universe. 552 00:31:33,440 --> 00:31:35,686 If we know there's a big bang, if we know the universe started, 553 00:31:35,710 --> 00:31:38,526 it expanded and cooled, it's very natural to wonder 554 00:31:38,550 --> 00:31:40,756 whether or not someday the expansion will stop, 555 00:31:40,780 --> 00:31:44,020 reverse, and come back, and that's a big crunch. 556 00:31:49,120 --> 00:31:50,336 In a big crunch, 557 00:31:50,360 --> 00:31:53,776 our expanding universe would begin to contract. 558 00:31:53,800 --> 00:31:56,700 Stars and planets would smash into each other. 559 00:31:58,870 --> 00:32:02,116 Galaxies would collide, 560 00:32:02,140 --> 00:32:05,386 and all of the life left in space would be compressed 561 00:32:05,410 --> 00:32:08,940 with all the other matter into a singularity. 562 00:32:17,590 --> 00:32:20,266 If this theory is true, then the universe 563 00:32:20,290 --> 00:32:25,736 would have both a beginning and an end of time. 564 00:32:25,760 --> 00:32:27,936 If we live in a universe that will expand, 565 00:32:27,960 --> 00:32:30,876 stop expanding, and then go back into a crunch, 566 00:32:30,900 --> 00:32:34,276 then it has, in effect, two edges. 567 00:32:34,300 --> 00:32:38,646 But there's a much stranger possibility. 568 00:32:38,670 --> 00:32:41,686 Perhaps the end is but a beginning, 569 00:32:41,710 --> 00:32:43,786 where the universe is a oscillating universe. 570 00:32:43,810 --> 00:32:45,686 It has a big bang like beginning, 571 00:32:45,710 --> 00:32:47,426 it expands to a maximum size, 572 00:32:47,450 --> 00:32:49,426 and then goes back into a big crunch 573 00:32:49,450 --> 00:32:51,780 and does that over and over. 574 00:32:53,520 --> 00:32:55,536 We could be residents of a universe 575 00:32:55,560 --> 00:32:58,706 created from the ashes of another, 576 00:32:58,730 --> 00:33:03,430 a single universe in a stream of bouncing universes... 577 00:33:06,570 --> 00:33:11,446 ...each full of galaxies, planets, and life. 578 00:33:11,470 --> 00:33:14,986 But our most recent observations of the universe suggest 579 00:33:15,010 --> 00:33:17,940 a big crunch isn't in the cards. 580 00:33:20,120 --> 00:33:23,580 Once again, dark energy is key. 581 00:33:26,250 --> 00:33:30,336 For a while we didn't know if the expansion of the universe 582 00:33:30,360 --> 00:33:32,666 was going to slow, stop, 583 00:33:32,690 --> 00:33:35,306 and reverse itself because of gravity. 584 00:33:35,330 --> 00:33:36,706 There are all these galaxies in the universe 585 00:33:36,730 --> 00:33:38,846 and they're pulling on each other by their gravity. 586 00:33:38,870 --> 00:33:40,516 And if the expansion isn't fast enough, 587 00:33:40,540 --> 00:33:43,146 that gravity might be strong enough to stop the expansion 588 00:33:43,170 --> 00:33:44,916 and re-collapse the universe. 589 00:33:44,940 --> 00:33:46,216 Now with dark energy, 590 00:33:46,240 --> 00:33:48,656 we know that there's no way that can happen. 591 00:33:48,680 --> 00:33:51,186 The universe is going to expand forever 592 00:33:51,210 --> 00:33:55,026 because dark energy is pumping it full of acceleration. 593 00:33:55,050 --> 00:33:57,526 In order for there to be a big crunch, 594 00:33:57,550 --> 00:34:01,136 our understanding of dark energy would have to change a lot. 595 00:34:01,160 --> 00:34:03,736 That is, dark energy would have to be extremely weird 596 00:34:03,760 --> 00:34:07,906 and turn off in some very funny way for the universe 597 00:34:07,930 --> 00:34:10,930 to suddenly stop expanding and re-collapse. 598 00:34:13,270 --> 00:34:14,876 Without a big crunch, 599 00:34:14,900 --> 00:34:19,246 there is no future edge to time. 600 00:34:19,270 --> 00:34:20,956 The universe is not only expanding, 601 00:34:20,980 --> 00:34:22,686 but it's being driven by dark energy 602 00:34:22,710 --> 00:34:26,056 to expand faster and faster and the dark energy 603 00:34:26,080 --> 00:34:28,526 doesn't dilute away, as far as we can tell. 604 00:34:28,550 --> 00:34:30,996 So the simplest idea is that the universe 605 00:34:31,020 --> 00:34:34,750 will simply continue to expand eternally toward the future. 606 00:34:36,930 --> 00:34:41,706 Just like space, time will go on forever. 607 00:34:41,730 --> 00:34:46,106 That might sound like a better fate for life and the universe, 608 00:34:46,130 --> 00:34:47,770 but it's not. 609 00:34:50,040 --> 00:34:53,046 One of the consequences of this dark energy 610 00:34:53,070 --> 00:34:56,016 that's causing the acceleration of the universe 611 00:34:56,040 --> 00:35:01,596 is that we eventually are headed towards the big chill. 612 00:35:01,620 --> 00:35:05,296 I should say, "we're eventually headed towards the big chill." 613 00:35:05,320 --> 00:35:08,436 So the universe is getting colder and colder 614 00:35:08,460 --> 00:35:11,436 and things are getting more and more spread out. 615 00:35:11,460 --> 00:35:13,736 So the accelerated and continual 616 00:35:13,760 --> 00:35:16,006 and forever expansion of our universe 617 00:35:16,030 --> 00:35:19,706 might make for a frankly depressing end to time itself. 618 00:35:19,730 --> 00:35:23,246 The ultimate entropy-based heat death of the universe 619 00:35:23,270 --> 00:35:27,856 where you would walk out and see no stars in the sky, 620 00:35:27,880 --> 00:35:29,516 see absolutely nothing. 621 00:35:29,540 --> 00:35:32,586 There will come one day when the very last star in the universe 622 00:35:32,610 --> 00:35:35,450 just fizzles out and that is it. 623 00:35:38,320 --> 00:35:40,296 In the future, 624 00:35:40,320 --> 00:35:44,066 space will be a cold, dark and infinite void, 625 00:35:44,090 --> 00:35:47,836 where time goes on forever. 626 00:35:47,860 --> 00:35:49,736 There will be nothing to do 627 00:35:49,760 --> 00:35:53,206 but suffer in the eternal expanse. 628 00:35:53,230 --> 00:35:56,886 It's our inevitable fate that there's no future edge 629 00:35:56,910 --> 00:36:00,816 of time in the universe. 630 00:36:00,840 --> 00:36:04,126 But even if there isn't an edge to the universe, 631 00:36:04,150 --> 00:36:09,856 could there be edges within the universe? 632 00:36:09,880 --> 00:36:12,396 If you wanted to visit the edge of the universe, 633 00:36:12,420 --> 00:36:15,836 then go find your nearest black hole and jump on in 634 00:36:15,860 --> 00:36:18,006 because that's a one-way trip. 635 00:36:18,030 --> 00:36:21,830 If you cross this edge, you will never return. 636 00:36:36,180 --> 00:36:38,286 April 2019, 637 00:36:38,310 --> 00:36:40,496 an international team of astronomers 638 00:36:40,520 --> 00:36:42,856 makes a special announcement. 639 00:36:42,880 --> 00:36:46,466 And we are delighted to be able to report to you today 640 00:36:46,490 --> 00:36:51,536 that we have seen and taken a picture of a black hole. 641 00:36:51,560 --> 00:36:52,830 Here it is. 642 00:36:59,000 --> 00:37:02,246 It's a picture of a supermassive black hole 643 00:37:02,270 --> 00:37:07,340 at the center of the M87 galaxy 54 million light-years away. 644 00:37:09,180 --> 00:37:14,150 It may also be the first image of an edge in the universe. 645 00:37:15,420 --> 00:37:17,996 Black holes create a really interesting scenario 646 00:37:18,020 --> 00:37:22,896 when we think about space and the universe having edges. 647 00:37:22,920 --> 00:37:27,836 The edge between space outside and inside a black hole 648 00:37:27,860 --> 00:37:31,106 is called the event horizon. 649 00:37:31,130 --> 00:37:32,576 The event horizon of a black hole 650 00:37:32,600 --> 00:37:36,146 is a region within which, once you cross inside, 651 00:37:36,170 --> 00:37:38,746 the gravitational tug is so strong 652 00:37:38,770 --> 00:37:43,386 that even light cannot escape, which means nothing can escape 653 00:37:43,410 --> 00:37:46,286 once you cross inside the event horizon. 654 00:37:46,310 --> 00:37:48,656 So that really is sort of an edge 655 00:37:48,680 --> 00:37:51,250 because it really does create a boundary. 656 00:37:56,320 --> 00:37:59,730 The event horizon is not a physical barrier in space. 657 00:38:01,930 --> 00:38:04,306 Event horizon is an edge of the part of the universe 658 00:38:04,330 --> 00:38:06,276 we can visit, but it's not an edge 659 00:38:06,300 --> 00:38:09,176 in the sense that there's anything there. 660 00:38:09,200 --> 00:38:10,546 You would just pass right through it 661 00:38:10,570 --> 00:38:12,716 if you actually got right up to that place. 662 00:38:12,740 --> 00:38:15,156 So it's sort of a conceptual boundary 663 00:38:15,180 --> 00:38:19,126 between two different parts of the universe. 664 00:38:19,150 --> 00:38:22,526 If we sent a man to probe into a black hole, 665 00:38:22,550 --> 00:38:24,320 it would be a one-way trip. 666 00:38:26,750 --> 00:38:31,536 The event horizons of black holes are a sort of edge 667 00:38:31,560 --> 00:38:34,606 because, once you pass through an event horizon, 668 00:38:34,630 --> 00:38:38,206 you are cut off from the rest of the universe. 669 00:38:38,230 --> 00:38:40,776 You can never go back out. 670 00:38:40,800 --> 00:38:45,146 You are outside of our universe. 671 00:38:45,170 --> 00:38:46,986 Once you've crossed inside that region, 672 00:38:47,010 --> 00:38:50,380 you are never coming back out, and that's an edge. 673 00:38:52,210 --> 00:38:54,196 Once inside the black hole, 674 00:38:54,220 --> 00:38:58,296 the probe would be in a separate part of space, 675 00:38:58,320 --> 00:39:02,336 cut off from the rest of the universe. 676 00:39:02,360 --> 00:39:04,366 Falling through the event horizon of a black hole 677 00:39:04,390 --> 00:39:07,636 is like jumping over the edge of a cliff. 678 00:39:07,660 --> 00:39:10,576 You can see the edge and you can see the edge go by, 679 00:39:10,600 --> 00:39:13,146 and then when you're at the bottom, you can look up 680 00:39:13,170 --> 00:39:15,616 and see what's happening at the top of the cliff, 681 00:39:15,640 --> 00:39:17,370 but you can never go back. 682 00:39:19,510 --> 00:39:21,886 At the bottom of this black-hole cliff 683 00:39:21,910 --> 00:39:24,686 sits a singularity, 684 00:39:24,710 --> 00:39:30,566 a region of space where the laws of physics go off the rails. 685 00:39:30,590 --> 00:39:33,396 Deep toward that singularity could be as surprising 686 00:39:33,420 --> 00:39:36,336 as you might imagine and yet still a possibility. 687 00:39:36,360 --> 00:39:38,806 If you map the space-time around a black hole 688 00:39:38,830 --> 00:39:40,376 in a very particular way, 689 00:39:40,400 --> 00:39:44,346 there emerges a sort of mirror universe, a parallel universe, 690 00:39:44,370 --> 00:39:46,006 on the other side of the black hole, 691 00:39:46,030 --> 00:39:50,800 identical to our own and traversable by the black hole. 692 00:39:56,080 --> 00:40:01,196 So black holes are not just edges to our universe, 693 00:40:01,220 --> 00:40:06,566 they may also be gateways to other universes. 694 00:40:06,590 --> 00:40:08,136 It's highly conjecture, 695 00:40:08,160 --> 00:40:12,366 but if there's ever going to be a space, or region, 696 00:40:12,390 --> 00:40:15,536 where you're making connections with, say, some other universe, 697 00:40:15,560 --> 00:40:18,330 a black hole, in principle, could be a portal to that. 698 00:40:22,370 --> 00:40:23,746 But it's highly unlikely 699 00:40:23,770 --> 00:40:24,946 that anyone will ever want 700 00:40:24,970 --> 00:40:29,586 to venture beyond an event horizon to find out, 701 00:40:29,610 --> 00:40:33,026 and our pursuits of the other edges in the cosmos 702 00:40:33,050 --> 00:40:35,956 offer little hope either. 703 00:40:35,980 --> 00:40:41,136 We can never travel beyond the cosmic event horizon. 704 00:40:41,160 --> 00:40:44,336 We will never be able to see beyond the edge 705 00:40:44,360 --> 00:40:47,736 of our observable universe. 706 00:40:47,760 --> 00:40:51,906 So can we ever hope to discover the true edge 707 00:40:51,930 --> 00:40:56,200 of the greater universe or find out if it even has one? 708 00:40:58,040 --> 00:41:00,416 My feeling is that probably we should not think 709 00:41:00,440 --> 00:41:03,216 about edges for the universe. 710 00:41:03,240 --> 00:41:05,926 Everything you've ever seen in your life is finite, 711 00:41:05,950 --> 00:41:10,096 it has an inside and the outside, it has an edge. 712 00:41:10,120 --> 00:41:11,896 The universe might not be like that. 713 00:41:11,920 --> 00:41:13,366 It's probably not like that. 714 00:41:13,390 --> 00:41:16,520 There's probably no sense in which the universe has an edge. 715 00:41:19,560 --> 00:41:22,106 We used to think that the ultimate limits 716 00:41:22,130 --> 00:41:24,946 on the future life were set by nature, 717 00:41:24,970 --> 00:41:26,246 we couldn't get off the planet, 718 00:41:26,270 --> 00:41:29,446 or there was nothing beyond our solar system. 719 00:41:29,470 --> 00:41:31,916 Now we realized we have this vast, 720 00:41:31,940 --> 00:41:35,256 vast cosmos out there and that the ultimate limits 721 00:41:35,280 --> 00:41:38,456 are actually simply our own imagination 722 00:41:38,480 --> 00:41:41,226 and our ability to do great things with it 723 00:41:41,250 --> 00:41:42,926 rather than self-destruct. 724 00:41:42,950 --> 00:41:46,066 Our future destiny is in our own hands 725 00:41:46,090 --> 00:41:49,866 and I find that very empowering. 726 00:41:49,890 --> 00:41:52,206 It is beautifully frustrating 727 00:41:52,230 --> 00:41:53,936 to realize how limited we are, 728 00:41:53,960 --> 00:41:56,606 to realize that we're probably never going to get a true view 729 00:41:56,630 --> 00:41:58,506 of the real extent of the universe. 730 00:41:58,530 --> 00:42:00,576 We should keep an open mind, we should be humble, 731 00:42:00,600 --> 00:42:02,446 but I think that we should give up on the idea 732 00:42:02,470 --> 00:42:03,886 that things should have edges 733 00:42:03,910 --> 00:42:05,346 because that's what we're familiar with. 734 00:42:05,370 --> 00:42:08,116 The universe is something special. 735 00:42:08,140 --> 00:42:12,886 What matters to us, and will only ever matter to us, 736 00:42:12,910 --> 00:42:15,296 is the observable universe 737 00:42:15,320 --> 00:42:17,996 because that's the limit of what we can see 738 00:42:18,020 --> 00:42:19,896 and that is the limit of what we can know. 739 00:42:19,920 --> 00:42:22,166 So there is an edge to the universe, 740 00:42:22,190 --> 00:42:24,190 there's an edge to what we can know. 741 00:42:24,240 --> 00:42:28,790 Repair and Synchronization by Easy Subtitles Synchronizer 1.0.0.0 59789

Can't find what you're looking for?
Get subtitles in any language from opensubtitles.com, and translate them here.