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TEDxCaltech

Sean Carroll: Distant time and the hint of a multiverse

Sean Carroll: Fjern tid og antydningen af et multivers

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Ved TEDxCaltech angriber kosmolog Sean Carroll -- i en underholdende og tankeprovokerende tur gennem tidens og universets natur -- et vildledende simpelt spørgsmål: Hvorfor eksisterer tid overhovedet? De potentielle svar peger på et overraskende syn på universets natur og vores plads i det.

- Physicist, cosmologist
A physicist, cosmologist and gifted science communicator, Sean Carroll is asking himself -- and asking us to consider -- questions that get at the fundamental nature of the universe. Full bio

The universe
Universet
00:15
is really big.
er virkelig stort.
00:17
We live in a galaxy, the Milky Way Galaxy.
Vi lever i en galakse, Mælkevejen.
00:19
There are about a hundred billion stars in the Milky Way Galaxy.
Der er omkring et hundrede milliarder stjerner i Mælkevejen.
00:22
And if you take a camera
Og hvis man tager et kamera,
00:25
and you point it at a random part of the sky,
og man peger det på en tilfældig del af himlen,
00:27
and you just keep the shutter open,
og man bare holder blænderen åben,
00:29
as long as your camera is attached to the Hubble Space Telescope,
så længe ens kamera er fæstnet til Hubble-rumteleskopet
00:31
it will see something like this.
vil det se noget som dette.
00:34
Every one of these little blobs
Hver eneste af disse små klatter
00:36
is a galaxy roughly the size of our Milky Way --
er en galakse nogenlunde på størrelse med vores Mælkevej --
00:39
a hundred billion stars in each of those blobs.
et hundrede milliarder stjerner i hver af de klatter.
00:41
There are approximately a hundred billion galaxies
Der er omkring et hundrede milliarder galakser
00:44
in the observable universe.
i det observerbare univers.
00:47
100 billion is the only number you need to know.
100 milliarder er det eneste tal, man behøver at kende.
00:49
The age of the universe, between now and the Big Bang,
Universets alder, mellem nu og Big Bang,
00:51
is a hundred billion in dog years.
er et hundrede milliarder i hundeår.
00:54
(Laughter)
(Latter)
00:56
Which tells you something about our place in the universe.
Hvilket fortæller jer noget om vores plads i universet.
00:58
One thing you can do with a picture like this is simply admire it.
En ting, man kan gøre med et billede som dette, er simpelthen at beundre det.
01:01
It's extremely beautiful.
Det er ekstremt smukt.
01:03
I've often wondered, what is the evolutionary pressure
Jeg har ofte undret mig over hvilke evolutionspres,
01:05
that made our ancestors in the Veldt adapt and evolve
der fik vores forfædre i Velden tilpasse og udvikle sig
01:08
to really enjoy pictures of galaxies
til virkelig at nyde billeder af galakser,
01:11
when they didn't have any.
når de ikke havde nogen.
01:13
But we would also like to understand it.
Men vi kunne også tænke os at forstå det.
01:15
As a cosmologist, I want to ask, why is the universe like this?
Som kosmolog vil jeg gerne spørge, hvorfor er universet sådan her?
01:17
One big clue we have is that the universe is changing with time.
Et stort spor, vi har, er, at universet forandrer sig med tiden.
01:21
If you looked at one of these galaxies and measured its velocity,
Hvis man så på en af disse galakser og målte dens hastighed,
01:24
it would be moving away from you.
ville den bevæge sig væk fra en.
01:27
And if you look at a galaxy even farther away,
Og hvis man ser på en galakse endnu længere væk,
01:29
it would be moving away faster.
ville den bevæge sig endnu hurtigere væk.
01:31
So we say the universe is expanding.
Så vi siger, universet udvider sig.
01:33
What that means, of course, is that, in the past,
Hvad det betyder er selvfølgelig, at før i tiden
01:35
things were closer together.
var ting tættere på hinanden.
01:37
In the past, the universe was more dense,
Før i tiden var universet tættere,
01:39
and it was also hotter.
og det var også varmere.
01:41
If you squeeze things together, the temperature goes up.
Hvis man presser ting sammen, går temperaturen op.
01:43
That kind of makes sense to us.
Det giver på en måde mening for os.
01:45
The thing that doesn't make sense to us as much
Det, der ikke giver så meget mening for os,
01:47
is that the universe, at early times, near the Big Bang,
er, at universet i tidlige tider nær Big Bang
01:49
was also very, very smooth.
også var meget, meget glat.
01:52
You might think that that's not a surprise.
Man kunne tro, at det ikke er en overraskelse.
01:54
The air in this room is very smooth.
Luften i dette rum er meget glat.
01:56
You might say, "Well, maybe things just smoothed themselves out."
Man kunne sige, "Jamen, måske glattede ting bare sig selv ud."
01:58
But the conditions near the Big Bang are very, very different
Men vilkårene nær Big Bang er meget, meget forskellige
02:01
than the conditions of the air in this room.
fra vilkårene for luften i dette rum.
02:04
In particular, things were a lot denser.
Især var ting meget tættere.
02:06
The gravitational pull of things
Tingenes gravitationelle træk
02:08
was a lot stronger near the Big Bang.
var meget stærkere nær Big Bang.
02:10
What you have to think about
Det, man er nødt til at tænke på,
02:12
is we have a universe with a hundred billion galaxies,
er, vi har et univers med et hundrede milliarder galakser,
02:14
a hundred billion stars each.
et hundrede milliarder stjerner hver.
02:16
At early times, those hundred billion galaxies
I tidlige tider var de hundrede milliarder galakser
02:18
were squeezed into a region about this big --
presset ind på et område nogenlunde så stort her --
02:21
literally -- at early times.
bogstaveligt talt -- i tidlige tider.
02:24
And you have to imagine doing that squeezing
Og I skal forestille jer, at presse på den måde
02:26
without any imperfections,
uden nogen ujævnheder,
02:28
without any little spots
uden nogen små steder,
02:30
where there were a few more atoms than somewhere else.
hvor der var få flere atomer end nogen andre steder.
02:32
Because if there had been, they would have collapsed under the gravitational pull
For hvis der havde været det, ville de have kollapset under det gravitationelle træk
02:34
into a huge black hole.
ind i et stort sort hul.
02:37
Keeping the universe very, very smooth at early times
At holde universet meget, meget glat i tidlige tider
02:39
is not easy; it's a delicate arrangement.
er ikke let; det er et skrøbeligt arrangement.
02:42
It's a clue
Det er et spor om,
02:44
that the early universe is not chosen randomly.
at det tidlige univers ikke blev valgt tilfældigt.
02:46
There is something that made it that way.
Der er noget, der lavede det på den måde.
02:48
We would like to know what.
Vi kunne godt tænke os at vide hvad.
02:50
So part of our understanding of this was given to us by Ludwig Boltzmann,
Så en del af vores forståelse af dette blev givet til os af Ludwig Boltzmann,
02:52
an Austrian physicist in the 19th century.
en østrigsk fysiker i det 19. århundrede.
02:55
And Boltzmann's contribution was that he helped us understand entropy.
Og Boltzmanns bidrag var, at han hjalp os med at forstå entropi.
02:58
You've heard of entropy.
I har hørt om entropi.
03:01
It's the randomness, the disorder, the chaoticness of some systems.
Det er tilfældigheden, urodenen, kaosheden i nogle systemer.
03:03
Boltzmann gave us a formula --
Boltzmann gav os en formel --
03:06
engraved on his tombstone now --
indgraveret på hans gravsten nu --
03:08
that really quantifies what entropy is.
som virkelig kvantificerer, hvad entropi er.
03:10
And it's basically just saying
Og den siger basalt set bare,
03:12
that entropy is the number of ways
at entropi er antallet af måder,
03:14
we can rearrange the constituents of a system so that you don't notice,
man kan omarrangere et systems bestanddele, så at man ikke ikke kan se det,
03:16
so that macroscopically it looks the same.
så at makroskopisk ser ligner det sig selv.
03:19
If you have the air in this room,
Hvis man tager luften i dette rum,
03:21
you don't notice each individual atom.
lægger man ikke mærke til hvert enkelt atom.
03:23
A low entropy configuration
En konfiguration med lav entropi
03:26
is one in which there's only a few arrangements that look that way.
er en, i hvilken der kun er få arrangementer, der ser ens ud.
03:28
A high entropy arrangement
Et arrangement med høj entropi
03:30
is one that there are many arrangements that look that way.
er et, som der er mange arrangementer, der ser ens ud.
03:32
This is a crucially important insight
Dette er et afgørende vigtigt indblik,
03:34
because it helps us explain
for det hjælper os med at forklare
03:36
the second law of thermodynamics --
termodynamikkens anden lov --
03:38
the law that says that entropy increases in the universe,
den lov, der siger, at entropi stiger i universet
03:40
or in some isolated bit of the universe.
eller i en isoleret lille del af universet.
03:43
The reason why entropy increases
Grunden til, at entropi stiger,
03:45
is simply because there are many more ways
er simpelthen fordi, der er mange flere måder
03:47
to be high entropy than to be low entropy.
at have høj entropi end at have lav entropi på.
03:50
That's a wonderful insight,
Det er et vidunderligt indblik,
03:52
but it leaves something out.
men det udelader noget.
03:54
This insight that entropy increases, by the way,
Dette indblik, at entropi stiger er forresten
03:56
is what's behind what we call the arrow of time,
det, der er bag det, vi kalder tidens pil,
03:58
the difference between the past and the future.
forskellen mellem fortiden og fremtiden.
04:01
Every difference that there is
Hver forskel, som der er
04:03
between the past and the future
mellem fortiden og fremtiden,
04:05
is because entropy is increasing --
er, fordi entropi stiger --
04:07
the fact that you can remember the past, but not the future.
det faktum, at man kan huske fortiden, men ikke fremtiden.
04:09
The fact that you are born, and then you live, and then you die,
Det faktum, at man bliver født, og så lever man, og så dør man,
04:12
always in that order,
altid i den rækkefølge,
04:15
that's because entropy is increasing.
det er fordi, entropi stiger.
04:17
Boltzmann explained that if you start with low entropy,
Boltzmann forklarede, at hvis man starter med lav entropi,
04:19
it's very natural for it to increase
er det meget naturligt for den at stige,
04:21
because there's more ways to be high entropy.
fordi der er flere måder at få høj entropi på.
04:23
What he didn't explain
Det, han ikke forklarede,
04:26
was why the entropy was ever low in the first place.
var, hvorfor entropien nogensinde var lav i første omgang.
04:28
The fact that the entropy of the universe was low
Det faktum, at universets entropi var lav,
04:31
was a reflection of the fact
var en refleksion over det faktum,
04:33
that the early universe was very, very smooth.
at det tidlige univers var meget, meget glat.
04:35
We'd like to understand that.
Vi kunne godt tænke os at forstå det.
04:37
That's our job as cosmologists.
Det er vores job som kosmologer.
04:39
Unfortunately, it's actually not a problem
Desværre er det faktisk ikke et problem,
04:41
that we've been giving enough attention to.
som vi har givet nok opmærksomhed.
04:43
It's not one of the first things people would say,
Det er ikke en af de første ting, folk ville sige,
04:45
if you asked a modern cosmologist,
hvis man spurgte en moderne kosmolog,
04:47
"What are the problems we're trying to address?"
"Hvilke problemer forsøger vi at besvare?"
04:49
One of the people who did understand that this was a problem
En af de folk, der forstod, at dette var et problem,
04:51
was Richard Feynman.
var Richard Feynman.
04:53
50 years ago, he gave a series of a bunch of different lectures.
For 50 år siden gav han en serie af en bunke forskellige foredrag.
04:55
He gave the popular lectures
Han gav de populære foredrag,
04:57
that became "The Character of Physical Law."
der blev til "The Character of Physical Law."
04:59
He gave lectures to Caltech undergrads
Han gav foredrag til Caltech førsteårsstuderende,
05:01
that became "The Feynman Lectures on Physics."
som blev til "The Feynman Lectures on Physics."
05:03
He gave lectures to Caltech graduate students
Han gav foredrag til Caltech kandidatstuderende,
05:05
that became "The Feynman Lectures on Gravitation."
der blev til "The Feynman Lectures on Gravitation."
05:07
In every one of these books, every one of these sets of lectures,
I hver eneste af disse bøger, hver eneste af disse foredragssæt
05:09
he emphasized this puzzle:
understregede han denne gåde:
05:12
Why did the early universe have such a small entropy?
Hvorfor havde det tidlige univers så lav en entropi?
05:14
So he says -- I'm not going to do the accent --
Så han siger -- jeg vil ikke gengive accenten --
05:17
he says, "For some reason, the universe, at one time,
han siger, "Af en eller anden grund havde universet på et tidspunkt
05:19
had a very low entropy for its energy content,
en meget lav entropi i forhold til dets energiindhold,
05:22
and since then the entropy has increased.
og siden da er entropien steget.
05:25
The arrow of time cannot be completely understood
Tidspilen kan ikke blive fuldstændigt forstået
05:27
until the mystery of the beginnings of the history of the universe
før mysteriet om universets histories begyndelse
05:30
are reduced still further
bliver reduceret endnu mere
05:33
from speculation to understanding."
fra spekulation til forståelse."
05:35
So that's our job.
Så det er vores job.
05:37
We want to know -- this is 50 years ago, "Surely," you're thinking,
Vi vil gerne vide -- dette er for 50 år siden, "Jamen," tænker I,
05:39
"we've figured it out by now."
"vi har vel fundet ud af det nu."
05:41
It's not true that we've figured it out by now.
Det er ikke sandt, at vi har fundet ud af det nu.
05:43
The reason the problem has gotten worse,
Grunden til, at problemet er blevet værre
05:45
rather than better,
i stedet for bedre
05:47
is because in 1998
er, at i 1998
05:49
we learned something crucial about the universe that we didn't know before.
lærte vi noget meget vigtigt om universet, som vi ikke vidste før.
05:51
We learned that it's accelerating.
Vi lærte, at det accelererer.
05:54
The universe is not only expanding.
Universet udvider sig ikke kun.
05:56
If you look at the galaxy, it's moving away.
Hvis man ser på galaksen, bevæger den sig væk.
05:58
If you come back a billion years later and look at it again,
Hvis man kommer tilbage en milliard år senere og ser på den igen,
06:00
it will be moving away faster.
vil den bevæge sig hurtigere væk.
06:02
Individual galaxies are speeding away from us faster and faster
Individuelle galakser styrter væk fra os hurtigere og hurtigere,
06:05
so we say the universe is accelerating.
så vi siger, universet accelererer.
06:08
Unlike the low entropy of the early universe,
I modsætningen til det tidlige univers' lave entropi,
06:10
even though we don't know the answer for this,
selvom vi ikke kender svaret på dette,
06:12
we at least have a good theory that can explain it,
har vi i det mindste en god teori, der kan forklare det,
06:14
if that theory is right,
hvis den teori er korrekt,
06:16
and that's the theory of dark energy.
og det er teorien om mørk energi.
06:18
It's just the idea that empty space itself has energy.
Det er bare idéen, at tomt rum i sig selv har energi.
06:20
In every little cubic centimeter of space,
I hver lille kubikcentimeter rum,
06:23
whether or not there's stuff,
uanset om der er noget eller ej,
06:26
whether or not there's particles, matter, radiation or whatever,
uanset om der er partikler, stof, stråling eller andet eller ej,
06:28
there's still energy, even in the space itself.
er der stadig energi, selv i rummet selv.
06:30
And this energy, according to Einstein,
Og denne energi udøver ifølge Einstein
06:33
exerts a push on the universe.
et skub på universet.
06:35
It is a perpetual impulse
Det er en uophørlig impuls,
06:38
that pushes galaxies apart from each other.
der skubber galakser væk fra hinanden.
06:40
Because dark energy, unlike matter or radiation,
For mørk energi, i modsætningen til stof eller stråling,
06:42
does not dilute away as the universe expands.
tynder ikke ud som universet udvider sig.
06:45
The amount of energy in each cubic centimeter
Mængden af energi i hver kubikcentimeter
06:48
remains the same,
forbliver den samme,
06:50
even as the universe gets bigger and bigger.
selv som universet bliver større og større.
06:52
This has crucial implications
Dette har meget vigtige implikationer
06:54
for what the universe is going to do in the future.
for, hvad universet vil gøre i fremtiden.
06:57
For one thing, the universe will expand forever.
For det første vil universet udvide sig for evigt.
07:00
Back when I was your age,
Dengang da jeg var på jeres alder,
07:02
we didn't know what the universe was going to do.
vidste vi ikke, hvad universet ville gøre.
07:04
Some people thought that the universe would recollapse in the future.
Nogle folk troede, at universet ville falde sammen igen i fremtiden.
07:06
Einstein was fond of this idea.
Einstein var tilhænger af denne idé.
07:09
But if there's dark energy, and the dark energy does not go away,
Men hvis der er mørk energi, og den mørke energi ikke forsvinder,
07:11
the universe is just going to keep expanding forever and ever and ever.
vil universet bare fortsætte med at udvide sig for evigt og altid og altid.
07:14
14 billion years in the past,
14 milliarder år i fortiden,
07:17
100 billion dog years,
100 milliarder hundeår,
07:19
but an infinite number of years into the future.
men et uendeligt antal år i fremtiden.
07:21
Meanwhile, for all intents and purposes,
Imens, til alle hensigter og formål,
07:24
space looks finite to us.
ser rummet endeligt ud for os.
07:27
Space may be finite or infinite,
Rummet kan være endeligt eller uendeligt,
07:29
but because the universe is accelerating,
men fordi universet accelererer,
07:31
there are parts of it we cannot see
er der dele af det vi ikke kan se
07:33
and never will see.
og aldrig vil se.
07:35
There's a finite region of space that we have access to,
Der er en endelig del af rummet, som vi har adgang til,
07:37
surrounded by a horizon.
omringet af en horisont.
07:39
So even though time goes on forever,
Så selv om tiden fortsætter for evigt,
07:41
space is limited to us.
er rummet begrænset for os.
07:43
Finally, empty space has a temperature.
Endelig har rum en temperatur.
07:45
In the 1970s, Stephen Hawking told us
I 1970'erne fortalte Stephen Hawking os,
07:48
that a black hole, even though you think it's black,
at et sort hul, selvom man tror det er sort,
07:50
it actually emits radiation
faktisk afgiver stråling,
07:52
when you take into account quantum mechanics.
når man tager kvantemekanik med i overvejelserne.
07:54
The curvature of space-time around the black hole
Krumningen af rumtiden omkring det sorte hul
07:56
brings to life the quantum mechanical fluctuation,
bringer de kvantemekaniske fluktuationer til live,
07:59
and the black hole radiates.
og det sorte hul stråler.
08:02
A precisely similar calculation by Hawking and Gary Gibbons
En præcist lignende udregning af Hawking og Gary Gibbons
08:04
showed that if you have dark energy in empty space,
viste, at hvis man har mørk energi i tomt rum,
08:07
then the whole universe radiates.
så stråler hele universet.
08:10
The energy of empty space
Det tomme rums energi
08:13
brings to life quantum fluctuations.
bringer kvantefluktuationer til live.
08:15
And so even though the universe will last forever,
Og derfor, selvom universet vil vare for evigt,
08:17
and ordinary matter and radiation will dilute away,
og normalt stof og stråling vil blive udvandet til det forsvinder,
08:19
there will always be some radiation,
vil der altid være noget stråling,
08:22
some thermal fluctuations,
nogle termiske fluktuationer,
08:24
even in empty space.
selv i tomt rum.
08:26
So what this means
Så det, det her betyder,
08:28
is that the universe is like a box of gas
er, at universet er som en kasse med gas,
08:30
that lasts forever.
der varer evigt.
08:32
Well what is the implication of that?
Nå, hvad er implikationen af det?
08:34
That implication was studied by Boltzmann back in the 19th century.
Den implikation blev studeret af Boltzmann tilbage i det 19. århundrede.
08:36
He said, well, entropy increases
Han sagde, altså, entropi stiger,
08:39
because there are many, many more ways
fordi der er mange, mange flere måder
08:42
for the universe to be high entropy, rather than low entropy.
for universet at have høj entropi end at have lav entropi.
08:44
But that's a probabilistic statement.
Men det er en probabilistisk udtalelse.
08:47
It will probably increase,
Den vil sandsynligvis stige,
08:50
and the probability is enormously huge.
og sandsynligheden er enormt stor.
08:52
It's not something you have to worry about --
Det er ikke noget, man skal bekymre sig om --
08:54
the air in this room all gathering over one part of the room and suffocating us.
at luften i dette rum alt sammen skulle samle sig ovre i én del af rummet og kvæle os.
08:56
It's very, very unlikely.
Det er meget, meget usandsynligt.
09:00
Except if they locked the doors
Bortset fra hvis de låste dørene
09:02
and kept us here literally forever,
og holdt os her bogstaveligt talt for evigt,
09:04
that would happen.
ville det ske.
09:06
Everything that is allowed,
Alt, der er tilladt,
09:08
every configuration that is allowed to be obtained by the molecules in this room,
enhver konfiguration, det er tilladt for molekylerne at opnå i dette rum,
09:10
would eventually be obtained.
ville eventuelt blive opnået.
09:13
So Boltzmann says, look, you could start with a universe
Så Boltzmann siger, altså, man kunne starte med et univers,
09:15
that was in thermal equilibrium.
der var i termisk ligevægt.
09:18
He didn't know about the Big Bang. He didn't know about the expansion of the universe.
Han kendte ikke til Big Bang. Han kendte ikke til universets udvidelse.
09:20
He thought that space and time were explained by Isaac Newton --
Han troede, at rum og tid blev forklaret af Isaac Newton --
09:23
they were absolute; they just stuck there forever.
de var absolutte; de sad der bare for evigt.
09:26
So his idea of a natural universe
Så hans opfattelse af et naturligt univers
09:28
was one in which the air molecules were just spread out evenly everywhere --
var en, hvori luftmolekylerne bare var spredt jævnt ud overalt --
09:30
the everything molecules.
alt-molekylerne.
09:33
But if you're Boltzmann, you know that if you wait long enough,
Men hvis man er Boltzmann, ved man, at hvis man venter længe nok,
09:35
the random fluctuations of those molecules
vil de molekylers tilfældige fluktuationer
09:38
will occasionally bring them
af og til bringe dem
09:41
into lower entropy configurations.
ind i konfigurationer med lavere entropi.
09:43
And then, of course, in the natural course of things,
Og så, selvfølgelig, efter tingenes naturlige rækkefølge,
09:45
they will expand back.
vil de udvide sig tilbage.
09:47
So it's not that entropy must always increase --
Så det er ikke fordi, entropi altid skal stige --
09:49
you can get fluctuations into lower entropy,
man kan få fluktuationer til lavere entropi,
09:51
more organized situations.
mere organiserede situationer.
09:54
Well if that's true,
Jamen hvis det er sandt,
09:56
Boltzmann then goes onto invent
går Boltzmann så videre til at opfinde
09:58
two very modern-sounding ideas --
to idéer, der lyder meget moderne --
10:00
the multiverse and the anthropic principle.
multiverset og det antropiske princip.
10:02
He says, the problem with thermal equilibrium
Han siger, problemet med termisk ligevægt
10:05
is that we can't live there.
er, at vi ikke kan leve der.
10:07
Remember, life itself depends on the arrow of time.
Husk, livet selv afhænger af tidens pilen.
10:09
We would not be able to process information,
Vi ville ikke være i stand til at bearbejde information,
10:12
metabolize, walk and talk,
fordøje, gå og tale,
10:14
if we lived in thermal equilibrium.
hvis vi levede i termisk ligevægt.
10:16
So if you imagine a very, very big universe,
Så hvis man forestiller sig et meget, meget stort univers,
10:18
an infinitely big universe,
et uendeligt stort univers
10:20
with randomly bumping into each other particles,
med partikler, der tilfældigt støder ind i hinanden,
10:22
there will occasionally be small fluctuations in the lower entropy states,
vil der af og til være små fluktuationer til tilstande med lavere entropi,
10:24
and then they relax back.
og så falder de tilbage igen.
10:27
But there will also be large fluctuations.
Men der vil også være store fluktuationer.
10:29
Occasionally, you will make a planet
Af og til vil man lave en planet
10:31
or a star or a galaxy
eller en stjerne eller en galakse
10:33
or a hundred billion galaxies.
eller et hundrede milliarder galakser.
10:35
So Boltzmann says,
Så Boltzmann siger,
10:37
we will only live in the part of the multiverse,
vi kun vil leve i den del af multiverset,
10:39
in the part of this infinitely big set of fluctuating particles,
i den del af dette uendeligt store sæt af fluktuerende partikler,
10:42
where life is possible.
hvor liv er muligt.
10:45
That's the region where entropy is low.
Det er den region, hvor entropi er lav.
10:47
Maybe our universe is just one of those things
Måske er vores univers bare en af disse ting,
10:49
that happens from time to time.
der sker fra tid til anden.
10:52
Now your homework assignment
Nå jeres hjemmeopgave
10:54
is to really think about this, to contemplate what it means.
er virkelig at tænke over dette, at overveje hvad det betyder.
10:56
Carl Sagan once famously said
Carl Sagan sagde som bekendt engang,
10:58
that "in order to make an apple pie,
at "for at lave en æbletærte,
11:00
you must first invent the universe."
må man først opfinde universet."
11:02
But he was not right.
Men han tog fejl.
11:05
In Boltzmann's scenario, if you want to make an apple pie,
I Boltzmanns scenarie hvis man vil lave en æbletærte,
11:07
you just wait for the random motion of atoms
venter man bare på, at atomernes tilfældige bevægelser
11:10
to make you an apple pie.
laver en æbletærte til en.
11:13
That will happen much more frequently
Det vil ske meget oftere,
11:15
than the random motions of atoms
end at atomernes tilfældige bevægelser
11:17
making you an apple orchard
laver en æbleplantage til en
11:19
and some sugar and an oven,
og så noget sukker og en ovn,
11:21
and then making you an apple pie.
og så laver en æbletærte til en.
11:23
So this scenario makes predictions.
Så dette scenario laver forudsigelser.
11:25
And the predictions are
Og forudsigelserne er,
11:28
that the fluctuations that make us are minimal.
at fluktuationerne, der laver os, er minimale.
11:30
Even if you imagine that this room we are in now
Selv hvis man forestiller sig, dette rum, vi er i nu,
11:33
exists and is real and here we are,
eksisterer og er virkeligt, og her er vi,
11:36
and we have, not only our memories,
og vi har ikke bare vores minder,
11:38
but our impression that outside there's something
men vores indtryk, at udenfor er der noget,
11:40
called Caltech and the United States and the Milky Way Galaxy,
der hedder Caltech og USA og Mælkevejen,
11:42
it's much easier for all those impressions to randomly fluctuate into your brain
er det meget lettere for alle disse indtryk tilfældigt at fluktuere inde i ens hjerne,
11:46
than for them actually to randomly fluctuate
end at de rent faktisk tilfældigt fluktuerer
11:49
into Caltech, the United States and the galaxy.
til Caltech, USA og galaksen.
11:51
The good news is that,
De gode nyheder er, at
11:54
therefore, this scenario does not work; it is not right.
derfor virker dette scenario ikke; det er ikke rigtigt.
11:56
This scenario predicts that we should be a minimal fluctuation.
Dette scenario forudser, at vi skulle være en minimal fluktuation.
11:59
Even if you left our galaxy out,
Selv hvis man fjernede vores galakse,
12:02
you would not get a hundred billion other galaxies.
ville man ikke få hundrede milliarder andre galakser.
12:04
And Feynman also understood this.
Og Feynman forstod også dette.
12:06
Feynman says, "From the hypothesis that the world is a fluctuation,
Feynman siger, "Fra hypotesen, at verden er en fluktuation,
12:08
all the predictions are that
er alle forudsigelserne, at
12:12
if we look at a part of the world we've never seen before,
hvis vi ser på en del af verden, vi aldrig har set før,
12:14
we will find it mixed up, and not like the piece we've just looked at --
vil vi se den som blandet, og ikke som delen vi lige så på --
12:16
high entropy.
høj entropi.
12:18
If our order were due to a fluctuation,
Hvis vores orden skyldtes en fluktuation,
12:20
we would not expect order anywhere but where we have just noticed it.
ville vi ikke forvente orden nogen andre steder end der, vi lige har bemærket det.
12:22
We therefore conclude the universe is not a fluctuation."
Vi konkluderer derfor, at universet ikke er en fluktuation."
12:24
So that's good. The question is then what is the right answer?
Så det er godt. Spørgsmålet er så, hvad er det rigtige svar?
12:28
If the universe is not a fluctuation,
Hvis universet ikke er en fluktuation,
12:31
why did the early universe have a low entropy?
hvorfor havde det tidlige univers lav entropi?
12:33
And I would love to tell you the answer, but I'm running out of time.
Og jeg ville elske at give jer svaret, men jeg er ved at løbe tør for tid.
12:36
(Laughter)
(Latter)
12:39
Here is the universe that we tell you about,
Her er universet, som vi fortæller jer om,
12:41
versus the universe that really exists.
versus universet, der virkelig eksisterer.
12:43
I just showed you this picture.
Jeg har lige vist jer dette billede.
12:45
The universe is expanding for the last 10 billion years or so.
Universet har udvidet sig i de sidste 10 milliarder år sådan ca.
12:47
It's cooling off.
Det køler af.
12:49
But we now know enough about the future of the universe
Men vi ved nu nok om universets fremtid
12:51
to say a lot more.
til at sige meget mere.
12:53
If the dark energy remains around,
Hvis mørk energi fortsætter med at være tilstede,
12:55
the stars around us will use up their nuclear fuel, they will stop burning.
vil stjernerne omkring os opbruge deres kernebrændsel, de vil stoppe med at brænde.
12:57
They will fall into black holes.
De vil falde sammen til sorte huller.
13:00
We will live in a universe
Vi vil leve i et univers
13:02
with nothing in it but black holes.
med intet i sig ud over sorte huller.
13:04
That universe will last 10 to the 100 years --
Det univers vil vare 10 opløftet i 100 år --
13:06
a lot longer than our little universe has lived.
meget længere end vores lille univers har levet.
13:10
The future is much longer than the past.
Fremtiden er meget længere end fortiden.
13:12
But even black holes don't last forever.
Men selv sorte huller varer ikke evigt.
13:14
They will evaporate,
De vil fordampe,
13:16
and we will be left with nothing but empty space.
og vi vil blive tilbage med intet ud over tomt rum.
13:18
That empty space lasts essentially forever.
Det tomme rum varer grundlæggende set evigt.
13:20
However, you notice, since empty space gives off radiation,
Men I bemærker, eftersom tomt rum afgiver stråling,
13:24
there's actually thermal fluctuations,
er der faktisk termiske fluktuationer,
13:27
and it cycles around
og det kører i ring
13:29
all the different possible combinations
alle de forskellige mulige kombinationer
13:31
of the degrees of freedom that exist in empty space.
af grader af frihed, der eksisterer i tomt rum.
13:33
So even though the universe lasts forever,
Så selvom universet varer evigt,
13:36
there's only a finite number of things
er der kun et endeligt antal af ting,
13:38
that can possibly happen in the universe.
der kan lade sig gøre i universet.
13:40
They all happen over a period of time
De sker allesammen over en tidsperiode
13:42
equal to 10 to the 10 to the 120 years.
på 10 opløftet i 120 år.
13:44
So here's two questions for you.
Så her er to spørgsmål til jer.
13:47
Number one: If the universe lasts for 10 to the 10 to the 120 years,
Nummer et: Hvis universet varer i 10 opløftet i 10 opløftet i 120 år,
13:49
why are we born
hvorfor er vi født
13:52
in the first 14 billion years of it,
i de første 14 milliarder år af den tid
13:54
in the warm, comfortable afterglow of the Big Bang?
i Big Bangs varme, behagelige efterglød?
13:57
Why aren't we in empty space?
Hvorfor lever vi ikke i tomt rum?
14:00
You might say, "Well there's nothing there to be living,"
I kunne sige, "Jamen, der er ingenting til at leve,"
14:02
but that's not right.
men det er ikke rigtigt.
14:04
You could be a random fluctuation out of the nothingness.
I kunne være en tilfældig fluktuation ud af intetheden.
14:06
Why aren't you?
Hvorfor er I ikke?
14:08
More homework assignment for you.
Mere hjemmearbejde til jer.
14:10
So like I said, I don't actually know the answer.
Så som jeg sagde, kender jeg faktisk ikke svaret.
14:13
I'm going to give you my favorite scenario.
Jeg vil give jer mit yndlingsscenario.
14:15
Either it's just like that. There is no explanation.
Enten er det bare sådan. Der er ingen forklaring.
14:17
This is a brute fact about the universe
Dette er et hårdt faktum om universet,
14:20
that you should learn to accept and stop asking questions.
som man bør lære at acceptere og stoppe med at stille spørgsmål.
14:22
Or maybe the Big Bang
Eller måske er Big Bang
14:26
is not the beginning of the universe.
ikke universets begyndelse.
14:28
An egg, an unbroken egg, is a low entropy configuration,
Et æg, et ubrudt æg, er en konfiguration med lav entropi,
14:30
and yet, when we open our refrigerator,
og når vi alligevel åbner vores køleskab,
14:33
we do not go, "Hah, how surprising to find
siger vi ikke, "Hah, hvor overraskende at finde
14:35
this low entropy configuration in our refrigerator."
denne konfiguration med lav entropi i vores køleskab."
14:37
That's because an egg is not a closed system;
Det er fordi et æg ikke er et lukket system;
14:39
it comes out of a chicken.
det kommer fra en høne.
14:42
Maybe the universe comes out of a universal chicken.
Måske kommer universet fra en universal høne.
14:44
Maybe there is something that naturally,
Måske er der noget, der helt naturligt,
14:48
through the growth of the laws of physics,
ved vækst fra fysikkens love,
14:50
gives rise to universe like ours
giver anledning til et univers som vores
14:53
in low entropy configurations.
med konfigurationer med lav entropi.
14:55
If that's true, it would happen more than once;
Hvis det er sandt, ville det ske mere end én gang;
14:57
we would be part of a much bigger multiverse.
vi ville være del af et meget større multivers.
14:59
That's my favorite scenario.
Det er mit yndlingsscenario.
15:02
So the organizers asked me to end with a bold speculation.
Så arrangørerne bad mig om at slutte med en dristig spekulation.
15:04
My bold speculation
Min dristige spekulation
15:07
is that I will be absolutely vindicated by history.
er, at jeg bliver fuldstændigt bekræftet engang.
15:09
And 50 years from now,
Og om 50 år fra nu
15:12
all of my current wild ideas will be accepted as truths
bliver alle mine lige nu vilde idéer accepteret som sandheder
15:14
by the scientific and external communities.
af de videnskabelige og eksterne samfund.
15:17
We will all believe that our little universe
Vi vil alle tro på, at vores lille univers
15:20
is just a small part of a much larger multiverse.
bare er en lille del af et meget større multivers.
15:22
And even better, we will understand what happened at the Big Bang
Og endnu bedre vil vi forstå det, der skete ved Big Bang
15:25
in terms of a theory
med en teori,
15:28
that we will be able to compare to observations.
som vi vil være i stand til at sammenligne med observationer.
15:30
This is a prediction. I might be wrong.
Dette er en forudsigelse. Jeg kunne tage fejl.
15:32
But we've been thinking as a human race
Men vi har tænkt som menneskerace
15:34
about what the universe was like,
over, hvordan universet var,
15:36
why it came to be in the way it did for many, many years.
hvorfor det blev på den måde, det blev i mange, mange år.
15:38
It's exciting to think we may finally know the answer someday.
Det er spændende at tænke på, vi måske endelig kommer til at kende svaret engang.
15:41
Thank you.
Tak.
15:44
(Applause)
(Bifald)
15:46

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About the speaker:

Sean M. Carroll - Physicist, cosmologist
A physicist, cosmologist and gifted science communicator, Sean Carroll is asking himself -- and asking us to consider -- questions that get at the fundamental nature of the universe.

Why you should listen

Sean Carroll is a theoretical physicist at Caltech in Pasadena, California, where he researches theoretical aspects of cosmology, field theory and gravitation -- exploring the nature of fundamental physics by studying the structure and evolution of the universe.

His book on cosmology and the arrow of time, From Eternity to Here: The Quest for the Ultimate Theory of Time, was published in 2010. He keeps a regular blog at Cosmic Variance.

More profile about the speaker
Sean M. Carroll | Speaker | TED.com