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Freeman: Eternity.
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It's an idea as old as religion.
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Perhaps as old as humankind.
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00:00:17,161 --> 00:00:21,331
But what can modern science
tell us about the end of time?
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00:00:24,835 --> 00:00:28,471
Will the Universe end
in a cosmic apocalypse?
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00:00:28,473 --> 00:00:32,142
Could time keep on
ticking forever...
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Or will eternity end?
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Space, time, life itself.
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The secrets of the cosmos
lie through the wormhole.
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Through the Wormhole 03x09
Will Eternity End ? Original Air Date on August 1, 2012
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== sync, corrected by elderman ==
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The Apocalypse.
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It's the day when Muslims,
Christians, and Jews
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believe the world will come
crashing down around us.
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Physicists now have their own
version of Apocalypse.
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In fact,
they have several of them.
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The sun will engulf the earth.
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Our star will fall
into a black hole.
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Our entire galaxy will collide
with another.
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But what if everything
came to an end?
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Destroyed in an Apocalypse
so complete
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that time itself
would disappear.
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I was just a young boy when time
ran out for my grandmother.
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The sun continued to rise
and set each day.
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The seasons cycled on.
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I wondered if time for my
grandmother really had ended,
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time when the Universe
carried on.
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In fact, it seemed impossible
that time itself could ever end.
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The ancient Greeks and Egyptians
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thought of eternity
as a place outside of time.
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They saw time as a giant circle,
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mirroring the passing
of the sun overhead
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and the rotation of the seasons.
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But today, we have rolled out
the circle of time into a line
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stretching from the distant past
to the far future.
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Now we are forced to contemplate
whether this timeline has an end
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or whether it can
stretch on forever.
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00:03:00,257 --> 00:03:02,659
But perhaps the riddle
of eternity
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is something we've created
in our heads.
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Anthropologist
Vera da Silva Sinha
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and linguistic psychologist
Chris Sinha
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spend their time thinking about
how people think about time.
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Chris: We have very large-scale,
complex societies.
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We could not make our society
take over
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if we didn't have a calendar
and a clock.
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So we think of time concepts
and ways of measuring time
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as being what we call
a "cognitive technology."
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It's a technology of the mind.
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Freeman: But Chris and Vera
have discovered
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this organized view of time
is not universal.
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It's an insight they gained
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from studying the language
and culture
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of an indigenous Amazonian tribe
called the Amondawa.
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The Amondawa people
live in Rondonia --
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the state of Brazil.
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They were contacted
by the Brazilian government
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in 1984.
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The Amondawa tribe
does not live by a calendar,
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and they don't use clocks.
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In fact, there isn't even a word
for time in their language.
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If you ask
an Amondawa speaker
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to give a translation
of the word "time,"
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the nearest thing
that they can think of --
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they will say "Sun."
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Or they say
"raining season,"
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or they say "summertime,"
but there is no...
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There's nothing which is
abstracted from that, right?
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To try and understand
the Amondawa's notion of time,
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Chris and Vera had them arrange
a series of paper plates.
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So, we found out
there is two seasons, yeah?
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Rain season
and dry season.
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So, and they would use
the plates
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to symbolize how these seasons
are divided.
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An Amondawa man
organizes the plates
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not according to days or months
but by the natural events
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that occur throughout
their two seasons.
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For each one of these small
subdivisions of a season,
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he'll tell a little story
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about what kind of planting
and harvesting goes on,
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also what fruits
are ripening
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and what's going on in
the forest and in the rivers.
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Is their level of the river
going up or going down?
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This kind of thing.
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Yeah. Yeah.
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It's a way of mapping out time
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that would make sense
to any farmer.
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But in our industrialized
cultures,
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a much more rigid system
has taken over.
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We might arrange plates
in a line of seven --
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one plate for each day
of the week.
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Or we would divide a day
into hours arranged in a circle.
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But the Amondawa don't arrange
events in any particular shape.
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Vera: He's not really worried
about the shape of the events.
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He worry about the contents
of each event.
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They don't think of time
as being analogous
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to a spacial dimension.
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They don't think of time
being a sort of line
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in which there is a future
that you look forward to
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and a past
that you look back to.
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In English, you can say, "Oh,
I look back to my childhood."
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However, in Amondawa, you don't
look back to your childhood.
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So, in your childhood,
you were there,
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so you don't look
back anymore.
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So [Chuckles]
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The Amondawa
don't look back on a line
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that traces their life
from past to present.
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But in Western cultures,
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we can't help but impose
this time geometry on our lives.
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A person's life is like a line
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that stretches
from birth to death,
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and so we imagine
the Universe, too,
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must have a timeline --
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from its birth in the Big Bang,
14 billion years ago
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to some far future date
when it will die.
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There was no time
before the beginning,
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and time will
eventually disappear
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when the Universe meets
its apocalyptic end.
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Theoretical physicist
Fotini Markopoulou,
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like the Amondawa,
rejects this idea.
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Well, if you are to say
that time will end,
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you also have to say
that time began.
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It's like death and birth.
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You really can't have deaths
and no births.
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So now you have to tell me
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where time came from
if there was no time.
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Freeman: Fotini is trying
to understand
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the fundamental nature of time,
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00:07:51,249 --> 00:07:55,618
which in the microscopic world
of subatomic particles
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becomes a tricky concept.
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00:07:57,722 --> 00:08:00,423
The theory of
Quantum Mechanics says
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that particles don't interact
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as if they are solid,
defined objects,
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00:08:05,296 --> 00:08:07,029
but as amorphous clouds.
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A particle can be both there
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and not there at the same time.
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And it's impossible to say
when two particles meet
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or whether they did at all.
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00:08:19,677 --> 00:08:23,513
If you try to apply the laws
of Quantum Mechanics
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00:08:23,515 --> 00:08:26,782
to large objects like people
or planets,
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00:08:26,784 --> 00:08:31,387
you can imagine some
very puzzling possibilities.
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00:08:31,389 --> 00:08:33,422
I'm sitting here,
and I'm talking to you.
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Now, if by some accident,
in our Universe,
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there was a huge black hole
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00:08:39,264 --> 00:08:42,031
that would suck me inside
the black hole,
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00:08:42,033 --> 00:08:43,499
according to Quantum Theory,
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that black hole behind me
should be there and not there.
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And, as a result, you are in
a position of our conversation
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having happened or not happened.
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Freeman: Many Quantum
physicists argue
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00:08:56,581 --> 00:09:00,483
this uncertainty over whether
the events really happened
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shows that time cannot be
a fundamental thing
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00:09:03,555 --> 00:09:04,754
in the Universe.
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00:09:04,756 --> 00:09:06,689
It's something we've made up.
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00:09:06,691 --> 00:09:10,660
Albert Einstein disagreed
with Quantum Mechanics.
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00:09:10,662 --> 00:09:12,695
He believed time is real,
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00:09:12,697 --> 00:09:17,400
that it is woven with space
into the fabric of the Universe.
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And, according to his disciples,
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space and time were born
together in the Big Bang.
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But Fotini thinks both
these views of time are wrong.
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She thinks that time is real
and eternal.
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But for that to be true,
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we have to reimagine
what space is.
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Okay, so let's say
that this is space --
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the world we live in --
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and the little red strings
are other stuff in our world.
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And the net represents
the distances between us
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in terms of connectivity.
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00:09:52,971 --> 00:09:55,304
So that means that,
for instance,
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if we say that this is me
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and this is my friend Oralia
and that's my fried Helmut,
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it takes me --
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00:10:02,380 --> 00:10:05,748
one, two, three, four, five,
six steps to get to Oralia.
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00:10:05,750 --> 00:10:09,051
And then I need -- 1, 2, 3, 4,
5, 6, 7, 8, 9, 10,
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00:10:09,053 --> 00:10:12,922
11, 12, 13, 14, 15 steps
to reach Helmut.
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00:10:12,924 --> 00:10:16,158
Freeman:
But right after the Big Bang,
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the net of space was not
spread out like this.
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00:10:19,864 --> 00:10:22,531
Perhaps, me here...
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00:10:22,533 --> 00:10:28,237
was actually just
one step away from Helmut
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00:10:28,239 --> 00:10:29,805
back in the early Universe,
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00:10:29,807 --> 00:10:34,110
and these two guys
were connected,
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00:10:34,112 --> 00:10:38,047
until everybody is really
on top of everybody else.
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Freeman: In the very hot
and dense Big Bang,
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00:10:41,452 --> 00:10:44,820
everything is shrunk down
to a single point.
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00:10:44,822 --> 00:10:48,891
The idea of space
is meaningless.
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00:10:48,893 --> 00:10:53,896
But time, Fotini is certain,
always exists.
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00:10:53,898 --> 00:10:56,799
If we throw out space,
we get to keep time.
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00:10:56,801 --> 00:11:00,603
Time was always there before.
It will always be there after.
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00:11:02,272 --> 00:11:04,940
Freeman:
If Fotini is right,
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00:11:04,942 --> 00:11:07,576
time can indeed tick on forever.
190
00:11:07,578 --> 00:11:12,548
But one scientist is deeply
troubled by an eternal Universe.
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00:11:12,550 --> 00:11:15,785
Because if time
never stops ticking,
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00:11:15,787 --> 00:11:20,456
our very existence
could make no sense at all.
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00:11:21,583 --> 00:11:23,550
Eternity.
194
00:11:23,552 --> 00:11:27,955
It used to be a word
that only made sense in religion
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00:11:27,957 --> 00:11:29,790
or to people in love.
196
00:11:29,792 --> 00:11:35,029
Now some scientists also believe
time really may last forever.
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00:11:35,031 --> 00:11:37,765
But if eternity does exist,
198
00:11:37,767 --> 00:11:41,835
[ echoing ]
some very strange things...
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00:11:41,837 --> 00:11:43,504
[ Normal voice ] could happen.
200
00:11:51,079 --> 00:11:53,347
Cosmologist Sean Carroll
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00:11:53,349 --> 00:11:56,517
from the California Institute
of Technology,
202
00:11:56,519 --> 00:11:59,920
often takes a drive into
the mountains above Los Angeles
203
00:11:59,922 --> 00:12:03,090
to get a better look
at the night sky.
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00:12:03,092 --> 00:12:04,558
And when he does,
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00:12:04,560 --> 00:12:08,862
he can't help but wonder what
that night sky will look like
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00:12:08,864 --> 00:12:10,931
trillions of years from now.
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00:12:10,933 --> 00:12:15,069
Carroll: Right now, we live in
a bright, comfortable Universe
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00:12:15,071 --> 00:12:18,872
with stars shining 100 billion
galaxies in the Universe
209
00:12:18,874 --> 00:12:21,709
with 100 billion stars
in every galaxy.
210
00:12:21,711 --> 00:12:23,944
But those stars
can't shine forever.
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00:12:23,946 --> 00:12:26,714
They burn up fuel.
They have a finite lifetime.
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00:12:26,716 --> 00:12:29,083
So, about 10 to the 15 years
from now,
213
00:12:29,085 --> 00:12:31,318
those stars
will all have burnt out.
214
00:12:31,320 --> 00:12:33,987
There'll be no more stars
shining in the sky.
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00:12:33,989 --> 00:12:37,057
Freeman: A million billion years
from now,
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00:12:37,059 --> 00:12:40,861
the only celestial object
remaining will be black holes.
217
00:12:40,863 --> 00:12:43,497
Carroll: You might think,
okay, now we're done.
218
00:12:43,499 --> 00:12:45,065
Black holes and empty space.
219
00:12:45,067 --> 00:12:46,834
But those black holes evaporate.
220
00:12:46,836 --> 00:12:48,202
They give off radiation,
221
00:12:48,204 --> 00:12:50,471
and the black hole itself
shrinks away.
222
00:12:50,473 --> 00:12:53,307
So it will take a long time,
but once that happens,
223
00:12:53,309 --> 00:12:56,176
there's nothing left
but a thin gruel of particles.
224
00:12:56,178 --> 00:12:58,712
And then we're faced
with the question,
225
00:12:58,714 --> 00:13:02,149
well, what happens in that
infinitely long future period
226
00:13:02,151 --> 00:13:04,384
after everything has
emptied out?
227
00:13:04,386 --> 00:13:06,720
What is life like
in empty space?
228
00:13:06,722 --> 00:13:12,893
Freeman: It turns out that empty
space is not truly empty.
229
00:13:12,895 --> 00:13:15,062
In 1998,
230
00:13:15,064 --> 00:13:18,766
astronomers discovered
a strange cosmic force
231
00:13:18,768 --> 00:13:20,534
called "dark energy,"
232
00:13:20,536 --> 00:13:26,073
an expansive pressure
existing everywhere in space.
233
00:13:26,075 --> 00:13:29,309
Even an empty universe,
in the far future,
234
00:13:29,311 --> 00:13:32,045
would be filled
with this energy.
235
00:13:32,047 --> 00:13:35,048
And the laws of
Quantum Mechanics say,
236
00:13:35,050 --> 00:13:36,984
wherever there is energy,
237
00:13:36,986 --> 00:13:41,054
particles can spontaneously
appear out of nothingness.
238
00:13:42,824 --> 00:13:45,993
Because that dark energy
is lurking in empty space,
239
00:13:45,995 --> 00:13:47,427
there's a temperature.
240
00:13:47,429 --> 00:13:50,597
The future of the Universe
is not at absolute zero.
241
00:13:50,599 --> 00:13:52,900
There's a tiny
thermal fluctuation,
242
00:13:52,902 --> 00:13:54,268
even in empty space.
243
00:13:54,270 --> 00:13:57,938
If we imagine this oven
represents the whole universe,
244
00:13:57,940 --> 00:14:00,874
we can look inside
and see things appear.
245
00:14:00,876 --> 00:14:04,945
So if we wait a long time,
about 10 to the 10 years --
246
00:14:04,947 --> 00:14:06,480
10 billion years --
247
00:14:06,482 --> 00:14:09,183
we'll see a single,
lonely photon
248
00:14:09,185 --> 00:14:11,885
propagating
through the Universe.
249
00:14:11,887 --> 00:14:14,955
Freeman: But give
the Universe more time,
250
00:14:14,957 --> 00:14:16,857
and more particles appear.
251
00:14:16,859 --> 00:14:22,529
Eventually, after 10 to the
power 10 to the power 30 years,
252
00:14:22,531 --> 00:14:24,231
something as complex
and unlikely
253
00:14:24,233 --> 00:14:26,700
as a perfectly wired
human brain
254
00:14:26,702 --> 00:14:28,902
could simply pop into existence.
255
00:14:30,972 --> 00:14:33,473
And if you wait even longer
than that,
256
00:14:33,475 --> 00:14:36,877
10 to the 10 to the 120 years,
257
00:14:36,879 --> 00:14:40,047
we'll see an entire
new Big Bang,
258
00:14:40,049 --> 00:14:42,916
an entire universe
fluctuating into existence
259
00:14:42,918 --> 00:14:44,718
out of the surrounding chaos.
260
00:14:44,720 --> 00:14:45,919
Freeman: For Sean,
261
00:14:45,921 --> 00:14:48,722
these random fluctuations
present a big problem.
262
00:14:48,724 --> 00:14:51,191
If the Universe lasts forever,
263
00:14:51,193 --> 00:14:53,393
an infinite amount of time
264
00:14:53,395 --> 00:14:56,964
means an infinite amount
of possibilities,
265
00:14:56,966 --> 00:15:01,034
which means everything you could
possibly imagine
266
00:15:01,036 --> 00:15:02,870
will indeed appear --
267
00:15:02,872 --> 00:15:05,405
including
another version of you,
268
00:15:05,407 --> 00:15:07,474
who thinks he got here first.
269
00:15:07,476 --> 00:15:10,944
Many, many copies of me
will fluctuate into existence,
270
00:15:10,946 --> 00:15:14,514
many of them with exactly
the same memories that I have.
271
00:15:14,516 --> 00:15:18,518
There will be another version of
me that thinks the same as I do
272
00:15:18,520 --> 00:15:21,488
and has the same set of memories
that I have.
273
00:15:21,490 --> 00:15:25,392
But for most of
those versions of me,
274
00:15:25,394 --> 00:15:28,095
they won't actually be embedded
in a sensible universe
275
00:15:28,097 --> 00:15:29,997
with a big bang
and other galaxies.
276
00:15:29,999 --> 00:15:32,666
Freeman:
Each one of these Seans
277
00:15:32,668 --> 00:15:36,303
assumes that he is the first
version of himself.
278
00:15:36,305 --> 00:15:39,706
They each think they grew up
in Pennsylvania,
279
00:15:39,708 --> 00:15:43,277
studied at Harvard,
and wrote books on physics.
280
00:15:43,279 --> 00:15:46,580
But they are really just
random fluctuations
281
00:15:46,582 --> 00:15:48,849
that have popped into existence,
282
00:15:48,851 --> 00:15:52,586
future imposters that
actually live in empty space.
283
00:15:54,289 --> 00:15:56,790
The scenario that the Universe
just lasts forever
284
00:15:56,792 --> 00:15:58,625
and there's all
these fluctuations
285
00:15:58,627 --> 00:16:00,594
into everything we can
possibly imagine
286
00:16:00,596 --> 00:16:03,697
means that we have no right to
accept and believe our memories.
287
00:16:03,699 --> 00:16:06,133
If people and galaxies
and universes
288
00:16:06,135 --> 00:16:08,669
can randomly fluctuate
into existence,
289
00:16:08,671 --> 00:16:11,104
the conclusion is
that this can't be
290
00:16:11,106 --> 00:16:13,440
the right picture
of the Universe.
291
00:16:15,543 --> 00:16:20,047
Freeman: If dark energy
keeps on expanding our cosmos,
292
00:16:20,049 --> 00:16:24,184
countless versions of all of us
will eventually come to be,
293
00:16:24,186 --> 00:16:27,821
stretching from here
to eternity.
294
00:16:27,823 --> 00:16:29,823
There's only one thing
295
00:16:29,825 --> 00:16:34,094
that could prevent
such a preposterous universe...
296
00:16:34,096 --> 00:16:37,698
A truly cosmic apocalypse.
297
00:16:37,700 --> 00:16:39,666
[ Pop! ]
298
00:16:43,283 --> 00:16:47,987
What does the word
"Universe" mean?
299
00:16:47,989 --> 00:16:50,756
It used to mean "everything."
300
00:16:50,758 --> 00:16:55,928
But now some scientists imagine
there is more to creation
301
00:16:55,930 --> 00:17:01,167
than all the stars and galaxies
we could ever hope to see.
302
00:17:01,169 --> 00:17:06,405
We might be just one tiny patch
of something much larger,
303
00:17:06,407 --> 00:17:08,574
a multiverse,
304
00:17:08,576 --> 00:17:11,377
a place that lasts forever,
305
00:17:11,379 --> 00:17:15,414
and where a little Universe
like ours
306
00:17:15,416 --> 00:17:19,552
comes and goes in the blink
of an eye.
307
00:17:21,321 --> 00:17:26,292
Raphael Bousso is one of a new
generation of cosmologists
308
00:17:26,294 --> 00:17:31,030
who grew up with the idea
that our Universe may not be
309
00:17:31,032 --> 00:17:34,433
the be all and end all
of existence.
310
00:17:34,435 --> 00:17:39,338
For him, other universes pop
into existence all the time
311
00:17:39,340 --> 00:17:43,275
and exist inside
a colossal multiverse.
312
00:17:43,277 --> 00:17:46,812
Bousso: The multiverse is made out
of many different regions.
313
00:17:46,814 --> 00:17:49,448
These individual regions
can be so large that,
314
00:17:49,450 --> 00:17:50,950
if you live in them,
315
00:17:50,952 --> 00:17:54,053
you're really like a fish in an
extremely large tank of water.
316
00:17:54,055 --> 00:17:57,089
You might think that there is
nothing else whatsoever.
317
00:17:57,091 --> 00:18:03,028
Freeman: Imagine the Universe
we live in is like a balloon.
318
00:18:03,030 --> 00:18:04,663
In the beginning,
319
00:18:04,665 --> 00:18:08,434
it was just a miniscule piece
of compact space.
320
00:18:08,436 --> 00:18:09,868
At the Big Bang,
321
00:18:09,870 --> 00:18:13,405
a powerful force called
inflation took over,
322
00:18:13,407 --> 00:18:15,841
expanding it in a split second.
323
00:18:15,843 --> 00:18:18,110
14 billion years later,
324
00:18:18,112 --> 00:18:21,847
we all live deep inside
its inflated walls,
325
00:18:21,849 --> 00:18:23,949
blind to what's outside.
326
00:18:25,885 --> 00:18:29,488
But Raphael believes inflation
is still at work
327
00:18:29,490 --> 00:18:32,558
outside of our balloon.
328
00:18:32,560 --> 00:18:37,863
It constantly takes tiny pieces
of space and expands them.
329
00:18:37,865 --> 00:18:40,432
So, this room
is what we can think of
330
00:18:40,434 --> 00:18:42,468
as the multiverse looking like,
331
00:18:42,470 --> 00:18:48,507
where every one of these
balloons is a single universe,
332
00:18:48,509 --> 00:18:51,910
and all these universes are here
because of inflation.
333
00:18:51,912 --> 00:18:55,080
Freeman: Raphael's understanding
of inflation
334
00:18:55,082 --> 00:18:58,684
stems from the view of reality
called "String theory,"
335
00:18:58,686 --> 00:19:02,588
which holds that there are not
three dimensions of space...
336
00:19:02,590 --> 00:19:05,491
but nine.
337
00:19:05,493 --> 00:19:07,192
In our Universe,
338
00:19:07,194 --> 00:19:12,865
six of the dimensions are curled
up billions of times smaller
339
00:19:12,867 --> 00:19:15,467
than the smallest particle.
340
00:19:15,469 --> 00:19:16,802
There might be some places
341
00:19:16,804 --> 00:19:19,204
where all nine spatial
dimensions have become large.
342
00:19:19,206 --> 00:19:20,472
There might be other places
343
00:19:20,474 --> 00:19:22,508
where fewer than three
have become large.
344
00:19:22,510 --> 00:19:27,946
So inflation stretches some,
but not necessarily all,
345
00:19:27,948 --> 00:19:29,581
of the dimensions of space.
346
00:19:29,583 --> 00:19:33,218
Freeman:
Just like an inflated balloon,
347
00:19:33,220 --> 00:19:35,688
inflated dimensions of space
348
00:19:35,690 --> 00:19:39,992
are intrinsically unstable
and will eventually...
349
00:19:39,994 --> 00:19:42,127
re-collapse.
350
00:19:42,129 --> 00:19:43,729
As I'm walking around this room,
351
00:19:43,731 --> 00:19:46,131
you can see that these balloons
are popping...
352
00:19:46,133 --> 00:19:48,701
ever so slowly,
one after the other.
353
00:19:48,703 --> 00:19:50,269
There are a lot of balloons,
354
00:19:50,271 --> 00:19:52,604
but if you train your eye
on one balloon,
355
00:19:52,606 --> 00:19:54,940
that balloon eventually
is going to pop.
356
00:19:54,942 --> 00:19:56,208
And just like that,
357
00:19:56,210 --> 00:19:58,744
our piece of space eventually
is going to decay.
358
00:19:58,746 --> 00:20:01,180
Freeman:
By studying how inflation
359
00:20:01,182 --> 00:20:03,982
mutates the curled-up dimensions
of space,
360
00:20:03,984 --> 00:20:06,352
Raphael has been able
to calculate
361
00:20:06,354 --> 00:20:09,421
that the rate of creation
of inflated universes
362
00:20:09,423 --> 00:20:12,124
is much higher
than their rate of decay.
363
00:20:12,126 --> 00:20:16,195
So, even though universes
are going...all the time,
364
00:20:16,197 --> 00:20:19,164
many more are always
being created.
365
00:20:19,166 --> 00:20:23,869
So the multiverse keeps on
growing and will last forever.
366
00:20:23,871 --> 00:20:27,506
This pattern is called
"eternal inflating multiverse."
367
00:20:27,508 --> 00:20:30,509
If you were watching this room
from the outside,
368
00:20:30,511 --> 00:20:31,910
time would be eternal.
369
00:20:31,912 --> 00:20:33,645
This would continue forever.
370
00:20:33,647 --> 00:20:36,949
Freeman:
This multiverse may be eternal,
371
00:20:36,951 --> 00:20:41,186
but it's an eternity no one
can ever hope to experience
372
00:20:41,188 --> 00:20:44,623
because no one can ever escape
the universe
373
00:20:44,625 --> 00:20:46,325
they were created in.
374
00:20:46,327 --> 00:20:48,293
You don't get the benefit
of seeing this eternity
375
00:20:48,295 --> 00:20:50,462
of more and more inflation
and more and more balloons.
376
00:20:50,464 --> 00:20:51,730
The speed-of-light limit
377
00:20:51,732 --> 00:20:54,400
prevents you from seeing
all these other balloons.
378
00:20:54,402 --> 00:20:56,268
You sit around
in this one balloon,
379
00:20:56,270 --> 00:20:58,337
and sooner or later
it's going to go "pop."
380
00:20:58,339 --> 00:20:59,772
[ Pop! ]
381
00:20:59,774 --> 00:21:03,575
Freeman: If you live in a
universe, like everything must,
382
00:21:03,577 --> 00:21:08,514
then Raphael believes your time
is definitely going to end.
383
00:21:08,516 --> 00:21:10,048
[ Pop! ]
384
00:21:10,050 --> 00:21:13,619
And all of the problems
of an eternal universe
385
00:21:13,621 --> 00:21:15,554
that worry Sean Carroll
386
00:21:15,556 --> 00:21:19,324
are problems our Universe
will never live to see.
387
00:21:19,326 --> 00:21:23,162
We can calculate how rapidly
space will decay.
388
00:21:23,164 --> 00:21:26,231
As long as that decay of
our Universe happens faster
389
00:21:26,233 --> 00:21:29,701
than these unbelievably unlikely
events are going to happen,
390
00:21:29,703 --> 00:21:32,404
then we know that
we don't have to worry about
391
00:21:32,406 --> 00:21:34,773
copies of ourselves
coming into being.
392
00:21:34,775 --> 00:21:38,210
When our Universe decays,
time really does end there.
393
00:21:38,212 --> 00:21:40,179
[ Pop! ]
394
00:21:40,181 --> 00:21:45,584
Is our universe destined to die
in a cosmic cataclysm?
395
00:21:45,586 --> 00:21:48,020
Perhaps not.
396
00:21:48,022 --> 00:21:51,957
Because time may not be
what we think it is,
397
00:21:51,959 --> 00:21:56,519
and all of eternity
might already exist.
398
00:21:58,659 --> 00:22:02,562
Physicists tell us that time
is the fourth dimension.
399
00:22:03,762 --> 00:22:07,764
But it's not like the other
three that we move around in.
400
00:22:07,766 --> 00:22:09,499
In space,
401
00:22:09,501 --> 00:22:12,469
I could walk from here...
402
00:22:12,471 --> 00:22:14,771
to here...
403
00:22:14,773 --> 00:22:18,642
and then turn around
and go back again.
404
00:22:18,644 --> 00:22:21,912
Time's dimension
seems different.
405
00:22:21,914 --> 00:22:25,816
We only move through itin one direction.
406
00:22:25,818 --> 00:22:30,153
But there may be a way to grasp
all of eternity
407
00:22:30,155 --> 00:22:34,458
if we stop thinking about
time as a dimension
408
00:22:34,460 --> 00:22:38,762
and start thinking about time
as a projection
409
00:22:38,764 --> 00:22:40,597
from the future...
410
00:22:40,599 --> 00:22:43,500
[ Echoing ] to the past.
411
00:22:46,237 --> 00:22:49,673
[ Normal voice ] For Harvard
physicist Andy Strominger,
412
00:22:49,675 --> 00:22:52,142
the difference between
the future and the past
413
00:22:52,144 --> 00:22:53,877
is a deep puzzle.
414
00:22:53,879 --> 00:22:56,847
Because, according to
the known laws of physics,
415
00:22:56,849 --> 00:22:59,883
they should be exactly the same.
416
00:22:59,885 --> 00:23:02,686
There's a very basic principle
of physics
417
00:23:02,688 --> 00:23:04,287
which begin with Newton.
418
00:23:04,289 --> 00:23:07,090
The past determines the future,
419
00:23:07,092 --> 00:23:12,195
and the laws of physics can be
run forward or backwards.
420
00:23:12,197 --> 00:23:16,933
So, if I take this motion
of this pendulum
421
00:23:16,935 --> 00:23:18,835
hanging from the pencil
422
00:23:18,837 --> 00:23:23,039
and you run the movie forward
or backwards,
423
00:23:23,041 --> 00:23:25,208
it looks exactly the same.
424
00:23:26,911 --> 00:23:31,915
But there's a huge white
elephant in the room of physics,
425
00:23:31,917 --> 00:23:34,718
and that's the Big Bang.
426
00:23:34,720 --> 00:23:37,587
So, the cartoon picture
of the Big Bang
427
00:23:37,589 --> 00:23:39,423
is that there was nothing.
428
00:23:39,425 --> 00:23:41,258
Somebody flipped a switch,
429
00:23:41,260 --> 00:23:42,793
and, all of a sudden,
430
00:23:42,795 --> 00:23:46,029
all the something that
we know of was present.
431
00:23:46,031 --> 00:23:48,231
So, the past of our Universe
432
00:23:48,233 --> 00:23:52,869
and the future of our Universe
look fundamentally different.
433
00:23:54,572 --> 00:23:57,474
Freeman:
To resolve this paradox,
434
00:23:57,476 --> 00:24:00,977
Andy began to imagine
the dimension of time
435
00:24:00,979 --> 00:24:02,879
a radical new way --
436
00:24:02,881 --> 00:24:05,816
as a hologram.
437
00:24:05,818 --> 00:24:08,985
Holograms are
two-dimensional plates
438
00:24:08,987 --> 00:24:13,557
from which a third dimension
of space appears to emerge.
439
00:24:13,559 --> 00:24:16,726
Andy wondered if he could
apply this idea
440
00:24:16,728 --> 00:24:19,729
not to space but to time.
441
00:24:19,731 --> 00:24:25,101
Perhaps a dimension of time is
just a holographic projection.
442
00:24:25,103 --> 00:24:27,337
Time is a kind of illusion.
443
00:24:27,339 --> 00:24:30,841
And the whole universe
is written at a hologram
444
00:24:30,843 --> 00:24:33,877
that is sitting there
at the end of time
445
00:24:33,879 --> 00:24:37,848
and projected backwards
through our present era
446
00:24:37,850 --> 00:24:39,716
back to the Big Bang.
447
00:24:42,753 --> 00:24:47,224
Freeman: The hologram that contains
everything the universe ever was
448
00:24:47,226 --> 00:24:51,428
and ever will be is like
this intricate ice crystal.
449
00:24:51,430 --> 00:24:53,063
According to Andy,
450
00:24:53,065 --> 00:24:55,165
it sits in the far future
451
00:24:55,167 --> 00:24:58,902
and projects information
back into the past.
452
00:24:58,904 --> 00:25:04,274
Strominger: So, this sculpture represents
the holographic plate,
453
00:25:04,276 --> 00:25:06,142
which contains all
the information
454
00:25:06,144 --> 00:25:08,345
about the entire lifetime
of the Universe.
455
00:25:08,347 --> 00:25:13,550
As I look at this very closely,
I can see more and more detail.
456
00:25:13,552 --> 00:25:16,686
From far away,
or more accurately,
457
00:25:16,688 --> 00:25:18,989
from further back in time,
458
00:25:18,991 --> 00:25:22,292
there would be
less and less detail,
459
00:25:22,294 --> 00:25:27,163
less and less information
present in the universe itself.
460
00:25:27,165 --> 00:25:31,034
Freeman: The further you get
from a holographic plate,
461
00:25:31,036 --> 00:25:33,837
the less information
you can read on it.
462
00:25:33,839 --> 00:25:37,607
So, as we travel back in time
from our present day,
463
00:25:37,609 --> 00:25:41,845
in a highly complex universe
of planets, stars, and galaxies,
464
00:25:41,847 --> 00:25:44,047
we move to a simpler past,
465
00:25:44,049 --> 00:25:48,318
to a universe the way it was
billions of years ago,
466
00:25:48,320 --> 00:25:52,088
filled with nothing more
than clouds of gas.
467
00:25:52,090 --> 00:25:54,057
Strominger:
And, eventually,
468
00:25:54,059 --> 00:25:56,393
if you go far enough
back in time,
469
00:25:56,395 --> 00:25:58,128
before the Big Bang,
470
00:25:58,130 --> 00:26:01,298
there is simply nothing there
at all.
471
00:26:01,300 --> 00:26:04,834
Freeman: Holographic time
is the only theory
472
00:26:04,836 --> 00:26:09,339
that logically explains how
our Universe began from nothing.
473
00:26:09,341 --> 00:26:13,843
Once you get too far back in
time from the holographic plate,
474
00:26:13,845 --> 00:26:17,213
it cannot project back
any more information.
475
00:26:17,215 --> 00:26:21,685
Before the Big Bang, there is
no information in the universe.
476
00:26:21,687 --> 00:26:25,121
In a holographically-emergent
universe,
477
00:26:25,123 --> 00:26:27,324
we don't have a Big Bang.
478
00:26:27,326 --> 00:26:30,927
There isn't a special moment
when, all at once,
479
00:26:30,929 --> 00:26:33,763
everything in the universe
came into being.
480
00:26:33,765 --> 00:26:37,534
Rather, we have
an ongoing continual bang,
481
00:26:37,536 --> 00:26:39,502
which started from nothing
482
00:26:39,504 --> 00:26:42,973
and kept banging and banging
onto the future.
483
00:26:42,975 --> 00:26:45,008
In the past, there was nothing.
484
00:26:45,010 --> 00:26:47,510
In the future,
there is everything.
485
00:26:47,512 --> 00:26:51,081
Freeman: The mathematics
behind Andy's theory
486
00:26:51,083 --> 00:26:52,649
are highly complex.
487
00:26:52,651 --> 00:26:57,020
Holographic time is not laid out
like any normal dimension.
488
00:26:57,022 --> 00:27:00,557
As you go further and further
into the future,
489
00:27:00,559 --> 00:27:05,195
the same increment of time moves
you less and less far forward.
490
00:27:05,197 --> 00:27:08,632
So it would take an infinite
amount of time
491
00:27:08,634 --> 00:27:12,102
to actually arrive
at the holographic plate.
492
00:27:12,104 --> 00:27:14,304
Strominger: In this picture,
493
00:27:14,306 --> 00:27:17,807
our Universe goes on forever
into the future
494
00:27:17,809 --> 00:27:19,876
and gets bigger and bigger
495
00:27:19,878 --> 00:27:23,380
and keeps growing
and creating new elements.
496
00:27:23,382 --> 00:27:27,851
So we don't know that
it describes our universe.
497
00:27:27,853 --> 00:27:30,153
We're very far from that.
498
00:27:30,155 --> 00:27:35,492
But we do know that it is
something which can be discussed
499
00:27:35,494 --> 00:27:40,130
with some mathematical precision
and consistency.
500
00:27:40,132 --> 00:27:42,899
And so that's a starting point.
501
00:27:45,469 --> 00:27:49,639
Freeman: Will our Universe
survive for an eternity?
502
00:27:49,641 --> 00:27:51,741
It depends on who you ask.
503
00:27:51,743 --> 00:27:54,778
Some say time
will go on forever.
504
00:27:54,780 --> 00:27:57,180
Others are sure it must end.
505
00:27:57,182 --> 00:27:59,849
But now another physicist thinks
506
00:27:59,851 --> 00:28:03,386
we might be able to decide
who is right,
507
00:28:03,388 --> 00:28:05,855
because the future
of the universe
508
00:28:05,857 --> 00:28:10,126
may be traveling back in time
to meet us.
509
00:28:12,239 --> 00:28:16,275
Is all eternity
already out there?
510
00:28:16,559 --> 00:28:21,028
Could the present and the past
be echoes of the future,
511
00:28:21,030 --> 00:28:22,930
rippling back in time?
512
00:28:22,932 --> 00:28:24,632
If that's the case,
513
00:28:24,634 --> 00:28:28,970
why is it you don't know
what I'm going to say next?
514
00:28:28,972 --> 00:28:30,037
The fact is,
515
00:28:30,039 --> 00:28:33,040
scientists think
they found evidence
516
00:28:33,042 --> 00:28:36,444
the future really does affect
the present.
517
00:28:36,446 --> 00:28:40,014
And knowledge about the fate
of the Universe
518
00:28:40,016 --> 00:28:43,017
may already be
right in front of us.
519
00:28:45,754 --> 00:28:50,291
Physicist Jeff Tollaksen
from Chapman University
520
00:28:50,293 --> 00:28:55,463
thinks the future is very much
connected to the present.
521
00:28:55,465 --> 00:29:00,601
The notions of time, eternity,
the end of time --
522
00:29:00,603 --> 00:29:04,171
these are some of the most
profound questions
523
00:29:04,173 --> 00:29:07,008
that we deal with
as human beings.
524
00:29:07,010 --> 00:29:09,110
But you have to listen
very carefully
525
00:29:09,112 --> 00:29:11,145
to what nature's
trying to tell you
526
00:29:11,147 --> 00:29:12,747
to discover fundamental truth.
527
00:29:15,751 --> 00:29:18,486
Freeman:
Jeff believes most physicists
528
00:29:18,488 --> 00:29:21,822
have failed to fully understand
the nature of time
529
00:29:21,824 --> 00:29:24,725
because of the way they insist
on doing experiments --
530
00:29:24,727 --> 00:29:28,729
smashing particles together
in giant accelerators.
531
00:29:28,731 --> 00:29:32,433
Maybe, instead of smashing
particles to bits,
532
00:29:32,435 --> 00:29:35,770
we just need to give them
a little push.
533
00:29:38,106 --> 00:29:44,345
What if more physicists took up
the gentle sport of curling?
534
00:29:44,347 --> 00:29:46,147
Tollaksen: As you can see
535
00:29:46,149 --> 00:29:48,649
what our athletes
are doing here,
536
00:29:48,651 --> 00:29:52,319
they set the stone going
and they sweep a little bit
537
00:29:52,321 --> 00:29:54,922
to try to direct the stone
going somewhere.
538
00:29:54,924 --> 00:29:56,390
In a sense,
539
00:29:56,392 --> 00:29:59,460
this sweeping is kind of like
a very gentle interaction.
540
00:29:59,462 --> 00:30:01,829
You're not actually
touching the stone.
541
00:30:01,831 --> 00:30:04,799
You're kind of making the ice
a little bit smoother
542
00:30:04,801 --> 00:30:06,200
or melting a little bit
543
00:30:06,202 --> 00:30:09,737
so it would tend to go
in one direction.
544
00:30:09,739 --> 00:30:13,774
Freeman: Jeff believes
you can understand everything
545
00:30:13,776 --> 00:30:16,744
about the way time really works
in the universe
546
00:30:16,746 --> 00:30:18,713
by watching curling.
547
00:30:18,715 --> 00:30:21,315
And you can begin
at the beginning,
548
00:30:21,317 --> 00:30:24,952
with the idea of time
Isaac Newton had.
549
00:30:24,954 --> 00:30:26,954
Tollaksen: So, the stone starts
550
00:30:26,956 --> 00:30:28,823
from some definite place
in the past,
551
00:30:28,825 --> 00:30:31,759
it goes to some definite place
in the present,
552
00:30:31,761 --> 00:30:34,361
and it goes to a definite place
in the future.
553
00:30:34,363 --> 00:30:37,665
So, from that perspective
of classical physics,
554
00:30:37,667 --> 00:30:40,234
the universe looks like
it's a big machine,
555
00:30:40,236 --> 00:30:44,071
like a big,
very perfectly tuned clock.
556
00:30:44,073 --> 00:30:47,208
Freeman: But then,
about a century ago,
557
00:30:47,210 --> 00:30:49,410
along came Quantum Mechanics.
558
00:30:49,412 --> 00:30:52,546
It took away all that certainty
from the universe
559
00:30:52,548 --> 00:30:55,750
by unmasking
the subatomic world.
560
00:30:55,752 --> 00:30:58,552
If these curling stones
were atoms,
561
00:30:58,554 --> 00:31:02,156
the rules of the game
would change dramatically.
562
00:31:02,158 --> 00:31:05,693
Tollaksen: So, the quantum world
is different.
563
00:31:05,695 --> 00:31:07,361
It makes different predictions
564
00:31:07,363 --> 00:31:09,430
from the classical view
of things.
565
00:31:09,432 --> 00:31:11,132
In Quantum Mechanics,
566
00:31:11,134 --> 00:31:14,135
you could start these stones
the same
567
00:31:14,137 --> 00:31:18,639
and you notice that, incredibly,
one stone goes to the left
568
00:31:18,641 --> 00:31:21,742
and the other stone
goes to the right.
569
00:31:21,744 --> 00:31:24,912
Freeman: In the microscopic
world of atoms,
570
00:31:24,914 --> 00:31:26,747
nothing is known for sure.
571
00:31:26,749 --> 00:31:29,483
Atoms are not solid,
defined objects.
572
00:31:29,485 --> 00:31:33,721
They are waves of probabilities
that tell you where,
573
00:31:33,723 --> 00:31:38,559
when you look for a particle,
you are most likely to find it.
574
00:31:38,561 --> 00:31:43,864
But in the 1960s,
quantum guru Yakir Aharonov
575
00:31:43,866 --> 00:31:47,668
dared to ask why atoms
are so unpredictable,
576
00:31:47,670 --> 00:31:50,037
why it's so hard to pin down
577
00:31:50,039 --> 00:31:53,507
what they're doing
at any given moment.
578
00:31:53,509 --> 00:31:55,643
And the answer, he discovered,
579
00:31:55,645 --> 00:31:59,513
was because the future
and the past are both involved
580
00:31:59,515 --> 00:32:01,549
in creating the present.
581
00:32:01,551 --> 00:32:07,721
Yakir showed that he could
reformulate Quantum Mechanics
582
00:32:07,723 --> 00:32:10,291
in a way that dealt
with the past
583
00:32:10,293 --> 00:32:13,260
and the future
on exactly equal footing.
584
00:32:13,262 --> 00:32:17,097
Future information, which is
impossible to know now,
585
00:32:17,099 --> 00:32:18,432
in principle,
586
00:32:18,434 --> 00:32:21,735
maybe that's already relevant
to the present moment.
587
00:32:21,737 --> 00:32:25,840
Freeman: Jeff and Yakir
have searched for evidence
588
00:32:25,842 --> 00:32:30,010
of this revolutionary idea
for the past two decades.
589
00:32:30,012 --> 00:32:34,081
They've learned to be very
gentle in their measurements.
590
00:32:34,083 --> 00:32:37,351
A subatomic particle
will move or disappear
591
00:32:37,353 --> 00:32:39,320
if it's observed directly.
592
00:32:39,322 --> 00:32:42,890
It's as if they have to put
a particle in a box,
593
00:32:42,892 --> 00:32:46,527
not look at it, and allow it
to carry on existing
594
00:32:46,529 --> 00:32:49,663
as they spread out
a wave of probability.
595
00:32:49,665 --> 00:32:51,098
When they do that,
596
00:32:51,100 --> 00:32:55,569
they can begin to see the effect
of the future on the present.
597
00:32:55,571 --> 00:32:59,039
So, we have the red boxes
that are going forward in time.
598
00:32:59,041 --> 00:33:04,812
And now you have to think about
the backward evolving state.
599
00:33:04,814 --> 00:33:08,749
So we're gonna represent that
by blue boxes.
600
00:33:08,751 --> 00:33:11,252
Same particle, right?
We have one particle.
601
00:33:11,254 --> 00:33:14,255
But coming from the future,
we're saying the present
602
00:33:14,257 --> 00:33:16,390
is created out of a combination
603
00:33:16,392 --> 00:33:19,927
of the forward evolving
and the backward evolving.
604
00:33:22,163 --> 00:33:24,732
Freeman:
As radical as it sounds,
605
00:33:24,734 --> 00:33:27,234
Jeff, Yakir,
and their colleagues
606
00:33:27,236 --> 00:33:30,004
have now tested this idea
in the lab.
607
00:33:30,006 --> 00:33:34,174
They give a series of
very gentle magnetic nudges
608
00:33:34,176 --> 00:33:36,210
to subatomic particles.
609
00:33:36,212 --> 00:33:39,780
They measure them at 2:00...
610
00:33:39,782 --> 00:33:42,082
and then at 2:30.
611
00:33:42,084 --> 00:33:46,120
They do this
over and over again.
612
00:33:46,122 --> 00:33:49,189
Some but not all
of the particles
613
00:33:49,191 --> 00:33:51,859
are also measured again at 3:00.
614
00:33:51,861 --> 00:33:56,864
And what they found is that
taking their measurement at 3:00
615
00:33:56,866 --> 00:34:00,167
seemed to influence
the apparently random readings
616
00:34:00,169 --> 00:34:02,770
they got at 2:30.
617
00:34:02,772 --> 00:34:06,373
The future seemed to affect
the present,
618
00:34:06,375 --> 00:34:09,610
even though
it hadn't happened yet.
619
00:34:09,612 --> 00:34:11,712
Tollaksen: If you're trying to
understand the present moment,
620
00:34:11,714 --> 00:34:14,848
the past is relevant,
as we knew before,
621
00:34:14,850 --> 00:34:18,552
but the future is just
as relevant to the present
622
00:34:18,554 --> 00:34:19,653
as the past.
623
00:34:19,655 --> 00:34:20,921
Freeman: So far,
624
00:34:20,923 --> 00:34:23,991
these experiments have only
been carried out
625
00:34:23,993 --> 00:34:25,726
on the microscopic level,
626
00:34:25,728 --> 00:34:29,797
and the effects of the future
on the present are very subtle.
627
00:34:29,799 --> 00:34:33,467
But to Jeff, it suggests
that buried somewhere
628
00:34:33,469 --> 00:34:36,737
in the apparently random motion
of all the particles
629
00:34:36,739 --> 00:34:41,909
in the Universe there is
such a thing as cosmic destiny.
630
00:34:41,911 --> 00:34:43,677
Tollaksen:
There's an ocean flowing here.
631
00:34:43,679 --> 00:34:44,878
There's a current flowing
632
00:34:44,880 --> 00:34:47,948
from past to future
and from future to past.
633
00:34:49,784 --> 00:34:54,254
Freeman: The Universe
may already have a destiny.
634
00:34:54,256 --> 00:34:57,224
But can we mere mortals
ever know it?
635
00:34:57,226 --> 00:35:00,160
One scientist thinks
he's discovered
636
00:35:00,162 --> 00:35:03,297
the mathematical limit
of human knowledge.
637
00:35:08,246 --> 00:35:11,380
Scientists have spent
3,000 years
638
00:35:11,680 --> 00:35:16,182
trying to learn as much as they
can about the world we live in.
639
00:35:16,184 --> 00:35:18,752
We've done pretty well.
640
00:35:18,754 --> 00:35:23,556
We understand how planets,
stars, and galaxies work.
641
00:35:23,558 --> 00:35:27,627
But to know the fate
of the entire universe,
642
00:35:27,629 --> 00:35:31,564
just imagine how much more
there is to know.
643
00:35:31,566 --> 00:35:36,703
So perhaps it's time to ask
ourselves an important question.
644
00:35:36,705 --> 00:35:41,307
Are there some things we just
aren't meant to understand?
645
00:35:45,046 --> 00:35:48,581
Theoretical physicist Tom Banks
646
00:35:48,583 --> 00:35:51,451
believes the best way
to understand eternity
647
00:35:51,453 --> 00:35:54,988
is to calculate how much
we can ever know.
648
00:35:54,990 --> 00:35:59,025
And what we can know
is what we can measure.
649
00:35:59,027 --> 00:36:03,029
So, you can see the Pacific
Ocean is here behind me,
650
00:36:03,031 --> 00:36:05,331
and the Pacific Ocean is huge.
651
00:36:05,333 --> 00:36:08,468
We couldn't possibly
measure it with rulers,
652
00:36:08,470 --> 00:36:11,271
so we measure it
by using trigonometry,
653
00:36:11,273 --> 00:36:12,639
all kinds of math.
654
00:36:16,777 --> 00:36:20,146
Freeman: The Pacific Ocean
may be massive,
655
00:36:20,148 --> 00:36:23,416
but we've traversed its length
and breadth
656
00:36:23,418 --> 00:36:27,220
and mapped out all of
its 64 million square miles.
657
00:36:27,222 --> 00:36:29,489
However, it isn't even a speck
658
00:36:29,491 --> 00:36:32,258
compared with
the entire universe.
659
00:36:32,260 --> 00:36:35,562
Banks: It is much too big for us
to physically measure.
660
00:36:35,564 --> 00:36:38,998
Our Universe -- we can't even
get out there to most of it.
661
00:36:39,000 --> 00:36:41,801
And we measure it by receiving
light from it,
662
00:36:41,803 --> 00:36:43,269
sending light out to it,
663
00:36:43,271 --> 00:36:45,438
and getting all kinds
of signals.
664
00:36:45,440 --> 00:36:47,674
And we figure out
where things are,
665
00:36:47,676 --> 00:36:49,109
how far away they are.
666
00:36:49,111 --> 00:36:54,147
Freeman: But the Universe does
not just stretch out over space.
667
00:36:54,149 --> 00:36:56,349
It also extends over time,
668
00:36:56,351 --> 00:36:59,385
from its beginning
in the Big Bang
669
00:36:59,387 --> 00:37:01,020
to the far future.
670
00:37:01,022 --> 00:37:04,290
What would it take
to know everything
671
00:37:04,292 --> 00:37:06,359
about such a vast place?
672
00:37:06,361 --> 00:37:10,730
Tom thinks he can calculate
the answer to that question
673
00:37:10,732 --> 00:37:15,235
using something he calls
"the theory of causal diamonds."
674
00:37:15,237 --> 00:37:19,405
Banks: I'm drawing
a schematic diagram,
675
00:37:19,407 --> 00:37:22,108
showing a causal diamond.
676
00:37:22,110 --> 00:37:25,311
This is my past.
This is my future.
677
00:37:25,313 --> 00:37:26,980
And this diamond represents
678
00:37:26,982 --> 00:37:29,582
everything I could've done
experiments on
679
00:37:29,584 --> 00:37:32,986
during that whole history
from the beginning to the end.
680
00:37:32,988 --> 00:37:36,256
That region in space-time,
681
00:37:36,258 --> 00:37:37,690
it forms a diamond shape
682
00:37:37,692 --> 00:37:40,627
because light goes out
in sort of a cone like this,
683
00:37:40,629 --> 00:37:43,263
and then if I look back
from the latest time,
684
00:37:43,265 --> 00:37:44,864
it goes backwards in a cone.
685
00:37:44,866 --> 00:37:46,933
You put those two
cones together,
686
00:37:46,935 --> 00:37:49,135
and they're sort of
a diamond shape.
687
00:37:49,137 --> 00:37:51,704
[ Clock ticking ]
688
00:37:51,706 --> 00:37:54,407
Freeman: A causal diamond
marks the limit
689
00:37:54,409 --> 00:37:57,377
of how much of the Universe
a measuring device
690
00:37:57,379 --> 00:37:59,012
could ever hope to reach.
691
00:37:59,014 --> 00:38:02,115
When that device sends out
a light beam,
692
00:38:02,117 --> 00:38:04,384
it heads out into the Universe,
693
00:38:04,386 --> 00:38:07,120
bounces off
some distant galaxies,
694
00:38:07,122 --> 00:38:11,357
and finally returns to the
device billions of years later.
695
00:38:11,359 --> 00:38:13,593
Tom has been able to calculate
696
00:38:13,595 --> 00:38:17,897
that the amount of information
existing inside that diamond
697
00:38:17,899 --> 00:38:20,266
is related to the area
of a sphere
698
00:38:20,268 --> 00:38:24,771
that just fits around it
at its widest point,
699
00:38:24,773 --> 00:38:28,474
a sphere he calls
"the holographic screen."
700
00:38:28,476 --> 00:38:30,677
Banks: So now we can ask
the question,
701
00:38:30,679 --> 00:38:33,346
suppose there was some machine
that lived forever
702
00:38:33,348 --> 00:38:35,915
from the beginning of
the Universe to the end?
703
00:38:35,917 --> 00:38:39,285
How big does the holographic
screen of the causal diamond
704
00:38:39,287 --> 00:38:42,188
of that infinitely long-lived
detector ever get?
705
00:38:42,190 --> 00:38:43,656
And it's very important,
706
00:38:43,658 --> 00:38:46,359
because that determines
how much information
707
00:38:46,361 --> 00:38:48,061
there could've possibly been
708
00:38:48,063 --> 00:38:50,196
in this region
of space and time.
709
00:38:50,198 --> 00:38:54,500
Freeman: Knowing absolutely
everything there is to know
710
00:38:54,502 --> 00:38:59,005
about every atom and every
subatomic particle in existence
711
00:38:59,007 --> 00:39:03,476
would mean collecting a truly
mind-blowing amount of data.
712
00:39:03,478 --> 00:39:07,647
Banks: This number is 10
to the 10 to the 123.
713
00:39:07,649 --> 00:39:11,484
It's a 1 with 10
to the 123 zeros after it.
714
00:39:11,486 --> 00:39:15,822
That number is so huge
that it's hard to imagine it.
715
00:39:15,824 --> 00:39:19,659
If I started trying to write
that number down
716
00:39:19,661 --> 00:39:22,295
and I wrote a zero every second,
717
00:39:22,297 --> 00:39:24,297
I would run out of time
718
00:39:24,299 --> 00:39:28,201
long before the whole history
of the Universe,
719
00:39:28,203 --> 00:39:30,703
and I would never get
to the end of it.
720
00:39:30,705 --> 00:39:34,007
Freeman: But could
an advanced civilization
721
00:39:34,009 --> 00:39:36,242
actually collect this much data
722
00:39:36,244 --> 00:39:39,145
and know everything
about the Universe
723
00:39:39,147 --> 00:39:40,947
and thus learn its fate?
724
00:39:40,949 --> 00:39:42,882
The answer, Tom believes,
725
00:39:42,884 --> 00:39:47,787
is contained
in this tiny cup of water.
726
00:39:47,789 --> 00:39:51,724
So, in this little bit of water
I just got out of the Pacific,
727
00:39:51,726 --> 00:39:53,493
there are sextillion atoms.
728
00:39:53,495 --> 00:39:55,428
That's trillions of trillions.
729
00:39:55,430 --> 00:39:58,031
If we wanted to measure
all those atoms,
730
00:39:58,033 --> 00:40:00,566
we'd have to have
a really big machine.
731
00:40:00,568 --> 00:40:04,637
We'd need a device that was
larger than the United States.
732
00:40:04,639 --> 00:40:08,474
Freeman: But collecting data
on the entire Universe
733
00:40:08,476 --> 00:40:11,477
is not just a monumental
engineering challenge.
734
00:40:11,479 --> 00:40:15,915
The laws of physics actually
prevent us from doing it.
735
00:40:15,917 --> 00:40:19,185
If we tried to measure
every atom in existence,
736
00:40:19,187 --> 00:40:21,988
we would end up
using so much equipment
737
00:40:21,990 --> 00:40:25,925
that we'd fill space with more
stuff than it could handle,
738
00:40:25,927 --> 00:40:29,896
and the entire experiment would
collapse into a black hole,
739
00:40:29,898 --> 00:40:32,765
destroying all that information
with it.
740
00:40:32,767 --> 00:40:34,434
Whoa!
741
00:40:36,470 --> 00:40:40,039
Tom has calculated
that we can measure no more
742
00:40:40,041 --> 00:40:43,643
than 10 to the 10 to the 90 bits
of information
743
00:40:43,645 --> 00:40:47,246
before we cause the entire
Universe to collapse
744
00:40:47,248 --> 00:40:48,748
into a black hole.
745
00:40:48,750 --> 00:40:51,384
This may seem like
a gigantic number,
746
00:40:51,386 --> 00:40:54,120
but it is actually just
a tiny fraction
747
00:40:54,122 --> 00:40:56,856
of 10 to the 10 to the 123,
748
00:40:56,858 --> 00:41:00,960
which is all that
there is to know.
749
00:41:00,962 --> 00:41:04,597
That number is so incredibly
smaller than this number,
750
00:41:04,599 --> 00:41:07,567
that there's no hope
that any civilization,
751
00:41:07,569 --> 00:41:09,469
no matter how sophisticated,
752
00:41:09,471 --> 00:41:12,572
could possibly measure all
of the information
753
00:41:12,574 --> 00:41:16,542
that there is in the Universe
throughout its entire history.
754
00:41:16,544 --> 00:41:20,546
Freeman: All we can ever learn
about the Universe
755
00:41:20,548 --> 00:41:24,517
is an impossibly tiny morsel
of what's out there.
756
00:41:24,519 --> 00:41:25,952
And Tom argues,
757
00:41:25,954 --> 00:41:30,423
trying to predict the future
based on such scant knowledge
758
00:41:30,425 --> 00:41:31,991
is utterly futile.
759
00:41:31,993 --> 00:41:37,463
So, perhaps we should quit
worrying about the end of time
760
00:41:37,465 --> 00:41:40,366
and learn to live for the now.
761
00:41:40,368 --> 00:41:43,870
Banks: It's natural for us
to want to know everything.
762
00:41:43,872 --> 00:41:48,341
And we like to make up stories
about everything.
763
00:41:48,343 --> 00:41:51,144
And those stories
are often wrong.
764
00:41:51,146 --> 00:41:53,312
So people...are people.
765
00:41:53,314 --> 00:41:56,282
We're finite.
We're not Gods.
766
00:41:56,284 --> 00:41:58,785
We're -- we don't own
the Universe.
767
00:41:58,787 --> 00:42:01,554
We're a very tiny portion
of the Universe.
768
00:42:01,556 --> 00:42:05,358
And we've now discovered that
we're a much tinier portion
769
00:42:05,360 --> 00:42:07,527
than we might've thought before.
770
00:42:07,529 --> 00:42:10,296
We don't have the right,
in some sense,
771
00:42:10,298 --> 00:42:13,766
to expect to know everything
that there is to know.
772
00:42:18,238 --> 00:42:21,674
Will the Universe last forever?
773
00:42:21,676 --> 00:42:24,177
Is eternity already out there,
774
00:42:24,179 --> 00:42:28,714
projecting the present back
to us from the far future?
775
00:42:28,716 --> 00:42:32,685
Or will a cosmic apocalypse
destroy everything
776
00:42:32,687 --> 00:42:34,687
in the blink of an eye?
777
00:42:34,689 --> 00:42:38,458
We don't know,
and we probably never will,
778
00:42:38,460 --> 00:42:42,462
because some questions
require more knowledge
779
00:42:42,464 --> 00:42:44,397
than we can ever get.
780
00:42:44,399 --> 00:42:47,733
And maybe that's not so bad.
781
00:42:47,735 --> 00:42:51,971
After all,
what fun would life be
782
00:42:51,973 --> 00:42:55,608
if we already knew
how it was going to end?
783
00:42:55,633 --> 00:42:59,633
== sync, corrected by elderman ==
784
00:42:59,683 --> 00:43:04,233
Repair and Synchronization by
Easy Subtitles Synchronizer 1.0.0.0
63090
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