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Narrator: Islands have edges.
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Planets have edges.
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Even galaxies have edges.
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But what about the universe?
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As explorers,
as curious humans that we are,
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we're obsessed with boundaries
and limits.
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And we want to know,
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"does the whole thing,
the universe, have a limit?"
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does the universe have an edge?
Well, the answer is yes and no.
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It depends on
what you mean by edge.
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Narrator:
The edge of what we can see?
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The edge of where we can go?
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Or the edge of reality itself?
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Thaller: Looking out to the edge
of the universe
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is tremendously important
to understand
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our place
in the universe itself.
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Bullock: We're talking
about our universe.
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We're talking about the thing
that we exist within.
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The most fundamental
thing there is,
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we're driven to understand it.
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There is always a desire to push
the knowledge to the edge.
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Narrator:
So, can we ever find
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the edge of the universe?
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-- Captions by vitac --
www.Vitac.Com
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captions paid for by
discovery communications
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♪
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2016,
the hubble space telescope
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turned toward
a dark patch of sky
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in the constellation ursa major.
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It captured an image
of an indistinct blob of light.
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The glow is from a distant
galaxy called gn-z11...
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♪
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...The most distant galaxy
we've ever observed.
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But is this the edge
of the universe?
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Thaller: The universe all around
us is filled with galaxies,
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so it's kind of natural to say,
"would there be a final galaxy?
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If you traveled far enough away,
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would you finally be at the very
last galaxy in the universe
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looking out into empty space?"
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narrator: That's a difficult
question to answer.
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Because there's a limit
to how far we can see.
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It all comes down
to the speed of light
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and the age of the universe.
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The key to understanding
the edge of the universe
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is that light travels
very, very fast,
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but not infinitely fast.
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It takes time for it
to get from one place
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in the universe to the other.
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You open the curtains,
light fills the room.
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It doesn't seem
to travel at all.
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But over the vast distances
of the universe,
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you actually notice
this travel time.
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Even the sun
93 million miles away,
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the light takes eight minutes
to get to us.
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When you look out at the stars,
we start to think of distance
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in terms of light-years
because it takes years
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for the light
to get from those stars to us.
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Then when you look at galaxies,
then you're talking about
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millions
or billions of light-years.
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Narrator: When we look at the
light from galaxy gn-z11,
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we're seeing light emitted
13.4 billion years ago.
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You can't really
even find a galaxy
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too much farther away than that
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because the universe
is only 13.8 billion years old,
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and it takes a certain amount of
time for galaxies to even form.
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So we're not going to find
too many more galaxies
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farther away than this.
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If things are far enough away,
there is no way that light
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can get to us
in the age of the universe.
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What this means
is there's a hard limit
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to the edge of the universe
that we can see,
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and this is set
by the age of the universe.
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Narrator: Gn-z11 sparked
into life
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early in the history
of the universe,
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just 400 million years
after the big bang.
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Before that, there were no stars
to send out light.
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Thaller: If you look
in any direction at all,
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you get all the way back to
when there were no stars,
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no galaxies,
nothing but very, very hot gas,
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and that sort of forms
a shell around us.
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Narrator: That outer shell is
the cosmic microwave background.
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It is the oldest light
in the universe,
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the echo of the birth
of the universe,
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the big bang.
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The edge of our universe,
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the very furthest thing
that we can see,
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is one of the earliest relics
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of the formation
of the universe itself.
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That is the cosmic microwave
background.
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Narrator: We call this the edge
of our observable universe.
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So we have an observable
universe, but beyond that,
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even if there
are things out there,
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there's no way we can see them
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because the light just could
not have gotten to us by now.
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Narrator: As the name states,
the observable universe
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is simply the part
of the universe we can see.
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We can think
of the observable universe
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sort of like a spotlight
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centered on wherever
you're standing right now
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and you can see to the edge of
your spotlight and not beyond.
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But if you move a little bit
to the left,
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a little bit to the right,
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your observable universe
actually moves with you.
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Narrator: For someone living
in galaxy gn-z11,
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a totally different part of the
universe would be observable.
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So that distant galaxy is at the
edge of our observable universe,
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and we are at the edge
of their observable universe.
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We have different spotlights.
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One of the wonderful things
to think about
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is that there are other spheres
around other galaxies,
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there are other aliens
looking up into the sky tonight
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wondering what the true
extent of the universe is.
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Narrator: The true extent
of our universe
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doesn't end with galaxy gn-z11.
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But when astronomers use
the hubble space telescope
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to accurately measure
the distance to gn-z11,
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they find something shocking.
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It's 32 billion
light-years away,
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three times further
than thought possible.
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Plait: So if nothing can travel
faster than light
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00:07:00,154 --> 00:07:03,355
and we measure the distance
to this galaxy,
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00:07:03,357 --> 00:07:06,358
how can it be
32 billion light-years away?
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Narrator:
There hasn't been enough time
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in the history of the universe
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for light from gn-z11
to reach us.
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There must be some mistake here.
Right?
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Plait: At this point,
your brain
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00:07:21,074 --> 00:07:22,674
is probably thinking
of leaping out
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00:07:22,676 --> 00:07:24,776
of your skull
and running around screaming.
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Trust me, I know.
I'm an astronomer.
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I've been doing this
my whole life,
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and this stuff twists
my imagination up.
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It's really hard to grasp this.
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How do we see a galaxy that's
32 billion light-years away
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and only 13.4 billion years old?
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Narrator: Gn-z11 is further away
than it should be
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because something strange
is going on with our universe.
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It's expanding.
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00:07:57,244 --> 00:07:59,845
And if the universe
is expanding,
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then where does its edge lie
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and can we ever reach it?
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♪
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narrator:
13.8 billion years ago,
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00:08:26,273 --> 00:08:29,174
a speck of energy
burst into life.
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We call it the big bang --
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space and time
pushed out in all directions.
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Ever since, our universe
has expanded.
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But the way it's expanding
makes finding an edge
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a major challenge.
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The universe is expanding
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and expands according
to a very simple law
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that the farther away a galaxy
is from us,
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the faster it appears
to be receding away from us.
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00:09:03,977 --> 00:09:08,013
Narrator: The furthest galaxies
are moving at very high speeds.
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The most distant galaxy
we've ever spotted, gn-z11,
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seems to have moved 32 billion
light-years away from us
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in just 13.4 billion years.
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That's faster than
the speed of light.
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00:09:26,033 --> 00:09:28,667
We can measure the speeds
with which galaxies
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are moving away from us,
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and many, many galaxies
are moving away from us
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at speeds faster
than the speed of light.
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This sounds like
it's breaking the law, right?
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There's this idea
that you've all been told
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that relativity
says nothing goes faster
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than the speed of light.
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Okay, you've been lied to.
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Plait: Space itself can do
what it wants.
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It makes the rules,
it can break the rules.
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That rule applies to matter,
not to space itself.
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Space can expand
at whatever rate it wants.
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Simple way to think of this
expansion law is imagine
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00:10:02,202 --> 00:10:04,669
standing on
an infinite rubber sheet
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00:10:04,671 --> 00:10:06,838
that stretches all the way out
into the distance
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00:10:06,840 --> 00:10:08,373
and you're standing
on the same place.
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You can mark it
with a little "x."
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00:10:10,477 --> 00:10:14,446
now, all the sheet expands
in every direction.
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So if it expands
by a factor of two,
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another galaxy that was, say,
one foot away from you
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00:10:19,753 --> 00:10:22,954
is now two feet away from you
as we stretch the sheet,
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but another galaxy
was 10 feet away from you.
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Expand that by a factor of 2
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and now
it's 20 feet away from you.
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00:10:29,363 --> 00:10:33,231
So in the same amount of time,
one galaxy moved one foot,
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where another galaxy
moved 10 feet.
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00:10:36,036 --> 00:10:37,869
So the more stuff there is,
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the more elastic
between you and another galaxy,
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00:10:40,540 --> 00:10:43,074
the more it seems
to expand away from you.
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Narrator: Expansion means
our observable universe
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stretches for a colossal
46 billion light-years
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00:10:52,953 --> 00:10:57,255
in all directions,
92 billion light-years across...
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00:10:59,760 --> 00:11:02,327
...And getting bigger
by the second.
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00:11:06,566 --> 00:11:09,567
Bullock: This number is
so incomprehensibly large
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00:11:09,569 --> 00:11:12,971
that it's difficult to wrap
your brain around.
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00:11:12,973 --> 00:11:16,675
There are trillions of galaxies
within this volume.
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00:11:16,677 --> 00:11:18,143
It's staggering.
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00:11:18,145 --> 00:11:22,180
It's so much larger than
anything we're familiar with.
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00:11:22,182 --> 00:11:23,748
Narrator:
If we were to travel
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00:11:23,750 --> 00:11:27,018
to the edge
of the observable universe,
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00:11:27,020 --> 00:11:31,589
we would enter even more
unfamiliar territory.
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00:11:31,591 --> 00:11:34,793
Imagine we're in
an ultra-fast spaceship.
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00:11:34,795 --> 00:11:37,929
We leave the solar system,
then the milky way.
203
00:11:40,400 --> 00:11:43,668
As we travel deeper
into intergalactic space,
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00:11:43,670 --> 00:11:46,171
things start to get
really weird.
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00:11:49,676 --> 00:11:53,845
For every million light-years
we go from the milky way,
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00:11:53,847 --> 00:11:56,648
the galaxies move away from us
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00:11:56,650 --> 00:12:00,518
at around 13 miles
per second faster.
208
00:12:02,889 --> 00:12:05,890
We have to accelerate
just to keep up.
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00:12:05,892 --> 00:12:10,829
But the galaxies keep on moving,
always beyond our reach.
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00:12:10,831 --> 00:12:20,305
♪
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00:12:20,307 --> 00:12:24,776
♪
212
00:12:24,778 --> 00:12:27,145
plait: Imagine you're a sprinter
on a racetrack.
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00:12:27,147 --> 00:12:28,646
If you're running towards
the finish line,
214
00:12:28,648 --> 00:12:30,882
it may take you a few seconds
to cross it.
215
00:12:30,884 --> 00:12:34,452
But now imagine that that finish
line is moving away from you.
216
00:12:34,454 --> 00:12:36,821
If it's moving away from you at
the same speed you're running,
217
00:12:36,823 --> 00:12:38,189
you'll never reach it.
218
00:12:38,191 --> 00:12:41,292
And if it's moving faster
than the runner,
219
00:12:41,294 --> 00:12:43,528
then even faster runners
won't reach it.
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00:12:43,530 --> 00:12:47,732
And that's sort of what we're
seeing here with the universe.
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00:12:47,734 --> 00:12:49,334
Narrator:
Beyond a certain distance,
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00:12:49,336 --> 00:12:54,506
galaxies are racing away from us
faster than the speed of light.
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00:12:54,508 --> 00:12:58,109
It's a line called
the cosmic event horizon.
224
00:13:00,347 --> 00:13:05,483
And 97% of galaxies we see
in the observable universe
225
00:13:05,485 --> 00:13:08,853
are beyond this line
and unreachable,
226
00:13:08,855 --> 00:13:11,556
including gn-z11.
227
00:13:13,126 --> 00:13:14,926
They're sort of teasing us
to say, "look at me,
228
00:13:14,928 --> 00:13:16,494
what a nice piece
of real estate."
229
00:13:16,496 --> 00:13:19,631
but we know even if we started
going there now,
230
00:13:19,633 --> 00:13:21,266
we could never reach them.
231
00:13:24,004 --> 00:13:26,738
Narrator: Anything that has
crossed the cosmic event horizon
232
00:13:26,740 --> 00:13:29,374
is out of our reach forever.
233
00:13:29,376 --> 00:13:31,075
But that's not the full picture
234
00:13:31,077 --> 00:13:34,546
because the expansion rate
of the universe is changing.
235
00:13:36,483 --> 00:13:39,217
A little over 20 years ago,
astronomers discovered
236
00:13:39,219 --> 00:13:42,320
that the current rate
of the universe's expansion
237
00:13:42,322 --> 00:13:44,589
is accelerating,
it's speeding up.
238
00:13:46,626 --> 00:13:51,396
Narrator: Astronomers suspect
a mysterious force is at work --
239
00:13:51,398 --> 00:13:54,432
dark energy.
240
00:13:54,434 --> 00:13:58,269
Dark energy is what we think
is pushing the universe apart,
241
00:13:58,271 --> 00:14:01,406
causing this
accelerating expansion.
242
00:14:01,408 --> 00:14:05,610
And the origin and true
physical nature of dark energy
243
00:14:05,612 --> 00:14:07,245
is a big mystery.
244
00:14:09,683 --> 00:14:12,750
Narrator: Thanks to dark energy,
more and more galaxies
245
00:14:12,752 --> 00:14:15,119
are crossing
the cosmic event horizon
246
00:14:15,121 --> 00:14:17,655
and leaving
the observable universe.
247
00:14:20,427 --> 00:14:22,327
These galaxies...
248
00:14:22,329 --> 00:14:24,796
Are lost to us forever.
249
00:14:27,467 --> 00:14:30,301
Plait: There are galaxies
that we can see today
250
00:14:30,303 --> 00:14:33,805
that in a few million years,
say, we won't be able to see
251
00:14:33,807 --> 00:14:35,673
because the edge of
the observable universe
252
00:14:35,675 --> 00:14:39,077
has basically moved in closer
than that galaxy.
253
00:14:39,079 --> 00:14:40,812
That's going to happen
all the time.
254
00:14:40,814 --> 00:14:43,381
And in a trillion years
or something like that,
255
00:14:43,383 --> 00:14:45,450
all these galaxies
that we see in our sky
256
00:14:45,452 --> 00:14:46,985
will be completely invisible
257
00:14:46,987 --> 00:14:50,054
because they'll be beyond
the edge of the universe.
258
00:14:53,126 --> 00:14:55,927
Thaller: So eventually,
every last galaxy
259
00:14:55,929 --> 00:14:57,729
will be so far away from us
260
00:14:57,731 --> 00:15:01,332
that light cannot reach us
through that expanding space.
261
00:15:01,334 --> 00:15:04,102
It's almost as if you're driving
through a dark desert
262
00:15:04,104 --> 00:15:06,838
in your car
and the very, very last town
263
00:15:06,840 --> 00:15:08,706
that ever exists
has gone over the horizon
264
00:15:08,708 --> 00:15:10,975
and they'll never be
any light again.
265
00:15:14,347 --> 00:15:16,814
We can see less
and less of the universe
266
00:15:16,816 --> 00:15:18,983
as we go into the future.
267
00:15:18,985 --> 00:15:21,019
What a strange thought.
268
00:15:21,021 --> 00:15:25,189
So that means we should build
all the telescopes we can now.
269
00:15:27,227 --> 00:15:29,894
Narrator: There's a limit
to the universe we can see,
270
00:15:29,896 --> 00:15:33,731
even with the most
advanced telescopes.
271
00:15:33,733 --> 00:15:36,234
But what lies beyond
272
00:15:36,236 --> 00:15:39,137
is one of the biggest
mysteries in astronomy.
273
00:15:41,241 --> 00:15:44,509
The greater universe
could be stranger
274
00:15:44,511 --> 00:15:46,611
than our wildest imagination.
275
00:15:48,982 --> 00:15:50,181
Plait:
When you stand on the beach
276
00:15:50,183 --> 00:15:51,416
and you look at the horizon
277
00:15:51,418 --> 00:15:53,818
and you kind of think,
"oh, what beautiful lands
278
00:15:53,820 --> 00:15:55,286
are there beyond the horizon?
279
00:15:55,288 --> 00:15:58,589
Things I've never
imagined before."
280
00:15:58,591 --> 00:15:59,891
it's so natural.
281
00:15:59,893 --> 00:16:03,294
It's so human to ask,
"what lies beyond that?
282
00:16:03,296 --> 00:16:05,830
What is the true extent
of the universe?"
283
00:16:15,608 --> 00:16:21,145
♪
284
00:16:21,147 --> 00:16:23,147
narrator:
The observable universe
285
00:16:23,149 --> 00:16:25,350
contains trillions of galaxies.
286
00:16:27,921 --> 00:16:31,122
It's about 92 billion
light-years across...
287
00:16:33,360 --> 00:16:34,892
...But astronomers believe
288
00:16:34,894 --> 00:16:37,762
this isn't the full extent
of the universe.
289
00:16:41,001 --> 00:16:44,268
What we don't know is how much
of the universe
290
00:16:44,270 --> 00:16:46,270
is our observable universe.
291
00:16:46,272 --> 00:16:49,307
It could be a tiny,
microscopic speck of this
292
00:16:49,309 --> 00:16:51,776
much more vast universe.
293
00:16:51,778 --> 00:16:53,845
We just don't know.
294
00:16:53,847 --> 00:16:56,114
Carroll: We have no idea
how much stuff there is
295
00:16:56,116 --> 00:16:57,582
outside the observable universe,
296
00:16:57,584 --> 00:17:01,419
but because by definition, it's
outside the observable universe,
297
00:17:01,421 --> 00:17:04,222
we really don't know right now.
298
00:17:04,224 --> 00:17:06,290
Narrator:
So what is out there?
299
00:17:06,292 --> 00:17:10,695
One theory says that space
outside the observable universe
300
00:17:10,697 --> 00:17:16,134
is pretty much the same
as our own cosmic neighborhood.
301
00:17:16,136 --> 00:17:18,636
It's just more universe.
It's just like here.
302
00:17:18,638 --> 00:17:21,239
It's just far enough away
that we can't see it.
303
00:17:21,241 --> 00:17:24,709
So it's not like there's bizarre
places where time runs backwards
304
00:17:24,711 --> 00:17:27,078
or aliens have two heads,
well, yeah, maybe.
305
00:17:29,549 --> 00:17:30,948
Narrator: But further out
306
00:17:30,950 --> 00:17:33,451
in the deepest parts
of the greater universe,
307
00:17:33,453 --> 00:17:35,386
all bets are off.
308
00:17:37,657 --> 00:17:40,558
We expect that as you go sort of
twice or three times
309
00:17:40,560 --> 00:17:42,060
beyond the observable universe,
310
00:17:42,062 --> 00:17:44,929
it's probably very similar
to the universe we inhabit.
311
00:17:44,931 --> 00:17:48,433
But if you go a thousand times
or a million times farther,
312
00:17:48,435 --> 00:17:50,134
who knows what you might see?
313
00:17:52,172 --> 00:17:55,206
It might be very, very different
if we go far enough away.
314
00:17:57,844 --> 00:17:59,777
Narrator: Strangely,
it all comes back
315
00:17:59,779 --> 00:18:02,213
to the expansion of the universe
316
00:18:02,215 --> 00:18:05,383
and one crucial detail
in that process.
317
00:18:08,054 --> 00:18:09,153
There was a brief moment
318
00:18:09,155 --> 00:18:11,289
in the very early history
of the universe
319
00:18:11,291 --> 00:18:15,326
where its expansion
accelerated hugely.
320
00:18:15,328 --> 00:18:17,395
This acceleration
is called inflation,
321
00:18:17,397 --> 00:18:20,832
and in a brief moment,
the universe itself expanded
322
00:18:20,834 --> 00:18:23,534
at multiple times
the speed of light.
323
00:18:25,805 --> 00:18:29,440
Narrator: Inflation was
a formative moment
324
00:18:29,442 --> 00:18:31,008
for our universe.
325
00:18:31,010 --> 00:18:32,477
By the time it stopped,
326
00:18:32,479 --> 00:18:35,513
the universe's basic
characteristics were set.
327
00:18:37,917 --> 00:18:39,851
There are these
fundamental constants
328
00:18:39,853 --> 00:18:42,587
that describe the phenomena
in our universe,
329
00:18:42,589 --> 00:18:46,491
the fundamentals of matter
and light and space-time.
330
00:18:48,128 --> 00:18:49,794
Narrator:
But some scientists think
331
00:18:49,796 --> 00:18:52,396
there could be regions
of the greater universe
332
00:18:52,398 --> 00:18:54,866
where inflation
has never stopped.
333
00:18:57,137 --> 00:19:02,240
The idea is the greater universe
is expanding at an insane speed,
334
00:19:02,242 --> 00:19:05,409
but here and there,
occasionally a little region
335
00:19:05,411 --> 00:19:10,748
will stop inflating and
just expand at the normal rate.
336
00:19:10,750 --> 00:19:12,750
Inflation can end somewhere
337
00:19:12,752 --> 00:19:15,019
and that gives rise
to the universe we live in,
338
00:19:15,021 --> 00:19:18,956
while inflation
continues somewhere else.
339
00:19:18,958 --> 00:19:21,058
Narrator:
Parts of the greater universe
340
00:19:21,060 --> 00:19:22,360
that continued to inflate
341
00:19:22,362 --> 00:19:25,630
would be left
with different laws of physics.
342
00:19:27,267 --> 00:19:29,333
This incredibly violent
inflation process
343
00:19:29,335 --> 00:19:33,371
is actually monkeyed with
the very fabric of space itself,
344
00:19:33,373 --> 00:19:35,273
so that a lot of the things
that we were taught
345
00:19:35,275 --> 00:19:39,977
that are laws of physics
are different there.
346
00:19:39,979 --> 00:19:41,279
Carroll: So in an essence,
347
00:19:41,281 --> 00:19:43,181
inflation gives us
a very natural way
348
00:19:43,183 --> 00:19:46,083
to make this patchwork quilt of
different parts of the universe
349
00:19:46,085 --> 00:19:48,953
where things seem different.
350
00:19:48,955 --> 00:19:52,089
So what we could imagine
is a super large-scale structure
351
00:19:52,091 --> 00:19:55,660
where there's different regions
of the universe, domains,
352
00:19:55,662 --> 00:19:58,963
and each domain has different
local laws of physics.
353
00:20:01,935 --> 00:20:03,467
Narrator: These different parts
of the universe
354
00:20:03,469 --> 00:20:07,538
are separated by frontiers
called domain walls.
355
00:20:11,344 --> 00:20:14,178
We have similar boundaries
on earth.
356
00:20:14,180 --> 00:20:17,014
Whenever you have something that
can be in many different states,
357
00:20:17,016 --> 00:20:19,884
you can end up with domain wall.
358
00:20:19,886 --> 00:20:25,523
If our fish swimming around
in the arctic near an iceberg,
359
00:20:25,525 --> 00:20:27,225
there will be a domain boundary
360
00:20:27,227 --> 00:20:29,493
between the water
being in the liquid state
361
00:20:29,495 --> 00:20:33,297
where I am and the solid state
inside the ice.
362
00:20:33,299 --> 00:20:36,867
So a domain wall is just a wall
between two domains.
363
00:20:36,869 --> 00:20:38,836
If it's water,
this could be ice,
364
00:20:38,838 --> 00:20:39,904
this could be liquid.
365
00:20:39,906 --> 00:20:41,339
If you're talking about space,
366
00:20:41,341 --> 00:20:43,908
this could be a kind of space
maybe you can live in.
367
00:20:43,910 --> 00:20:47,712
This could be a kind of space
where you don't want to be.
368
00:20:47,714 --> 00:20:51,616
Narrator: Crossing a domain wall
would be very bad news
369
00:20:51,618 --> 00:20:54,385
for anyone who dared to try.
370
00:20:54,387 --> 00:20:57,021
Cross that domain wall
and the laws of physics
371
00:20:57,023 --> 00:20:59,323
could change dramatically.
372
00:20:59,325 --> 00:21:01,325
The number of dimensions
could change.
373
00:21:01,327 --> 00:21:03,928
If we were somehow able to
travel to places in the universe
374
00:21:03,930 --> 00:21:05,329
where the laws of physics
are different,
375
00:21:05,331 --> 00:21:07,698
we would die
376
00:21:07,700 --> 00:21:10,501
because all of the chemistry
going on in our bodies
377
00:21:10,503 --> 00:21:15,106
depends very, very sensitively
on the laws of physics.
378
00:21:15,108 --> 00:21:19,043
So you could just dissipate like
thanos snap and you're gone.
379
00:21:21,047 --> 00:21:22,747
Narrator: Domain walls
might be the closest
380
00:21:22,749 --> 00:21:25,383
we get to locating
an edge in the universe.
381
00:21:26,953 --> 00:21:29,320
Depends on how
you define the edge.
382
00:21:29,322 --> 00:21:32,690
If it is the realm where the
laws of our universe operate,
383
00:21:32,692 --> 00:21:36,627
then these domain walls are in
essence the age of the universe.
384
00:21:40,767 --> 00:21:42,700
Narrator:
But this is all just theory.
385
00:21:46,572 --> 00:21:48,406
If we ever really are
to work out
386
00:21:48,408 --> 00:21:50,875
what the true size
and shape of the universe is,
387
00:21:50,877 --> 00:21:54,545
we're going to have to look
for clues that are close to us.
388
00:21:54,547 --> 00:21:58,049
Narrator: Clues that could
answer the ultimate question,
389
00:21:58,051 --> 00:22:01,952
how big is the rest
of the greater universe
390
00:22:01,954 --> 00:22:04,822
and could it go on forever?
391
00:22:13,533 --> 00:22:20,404
♪
392
00:22:20,406 --> 00:22:22,807
narrator:
For tens of thousands of years,
393
00:22:22,809 --> 00:22:28,145
mankind has gazed in wonder
at the vastness of the cosmos,
394
00:22:28,147 --> 00:22:32,483
but just how extensive is it?
395
00:22:32,485 --> 00:22:34,185
If we could answer
that question,
396
00:22:34,187 --> 00:22:39,357
it might help us to understand
our place in the universe.
397
00:22:39,359 --> 00:22:41,692
One of the fundamental
questions in science
398
00:22:41,694 --> 00:22:44,995
is how big is the universe?
399
00:22:44,997 --> 00:22:47,732
O'dowd: To answer the question,
"how big is the universe?"
400
00:22:47,734 --> 00:22:51,068
we have to answer the question,
"what shape is the universe?"
401
00:22:51,070 --> 00:22:53,003
and by shape, I mean geometry.
402
00:22:53,005 --> 00:22:57,775
I mean, how is the universe
curved on its largest scales?
403
00:22:57,777 --> 00:23:00,177
Sutter: If we are to discover
that the universe
404
00:23:00,179 --> 00:23:04,215
does have some
sort of geometric curvature,
405
00:23:04,217 --> 00:23:09,754
then this might imply that it
wraps around in on itself
406
00:23:09,756 --> 00:23:12,390
over incredibly large distances.
407
00:23:12,392 --> 00:23:16,127
And that if you could travel
in one direction long enough,
408
00:23:16,129 --> 00:23:18,129
you would end up
at your starting point.
409
00:23:18,131 --> 00:23:19,797
Another version is
that the universe
410
00:23:19,799 --> 00:23:22,633
is more like
an infinite flat plane.
411
00:23:22,635 --> 00:23:25,136
Okay?
No curvature at all.
412
00:23:25,138 --> 00:23:27,671
The further you travel,
well, the further you get
413
00:23:27,673 --> 00:23:30,541
and you never get back
to where you started.
414
00:23:32,779 --> 00:23:34,378
Narrator: To work out the shape
of something,
415
00:23:34,380 --> 00:23:37,481
we would normally just step back
and take a look.
416
00:23:37,483 --> 00:23:42,753
But clearly moving outside
the universe is a nonstarter.
417
00:23:42,755 --> 00:23:44,155
Bullock:
You can't jump on a rocket
418
00:23:44,157 --> 00:23:47,391
and fly a thousand times larger
than our cosmic horizon
419
00:23:47,393 --> 00:23:49,226
and see what the shape
of the universe is.
420
00:23:49,228 --> 00:23:51,128
We just can't do that.
421
00:23:51,130 --> 00:23:54,165
Thaller: Our human perspective
on the larger universe
422
00:23:54,167 --> 00:23:55,466
is so limited.
423
00:23:55,468 --> 00:23:57,601
So if we want to figure out
what the larger shape
424
00:23:57,603 --> 00:23:59,603
and scale of the universe is,
425
00:23:59,605 --> 00:24:01,939
we're going to have to be
very clever indeed.
426
00:24:04,777 --> 00:24:06,577
Narrator:
One way to be clever
427
00:24:06,579 --> 00:24:08,979
is to think of the geometry
of the universe
428
00:24:08,981 --> 00:24:11,749
in its simplest terms.
429
00:24:11,751 --> 00:24:14,084
Bullock: When we talk about
the geometry of the universe,
430
00:24:14,086 --> 00:24:16,620
we really are talking
about geometry.
431
00:24:16,622 --> 00:24:19,790
In order to do geometry,
you have to take measures.
432
00:24:19,792 --> 00:24:21,992
You need a cosmic ruler
to do this,
433
00:24:21,994 --> 00:24:24,395
and it turns out
there's a great cosmic ruler
434
00:24:24,397 --> 00:24:27,231
known as baryon
acoustic oscillations.
435
00:24:29,669 --> 00:24:32,436
Narrator: Baryonic acoustic
oscillations are ripples
436
00:24:32,438 --> 00:24:36,173
in the cosmic
microwave background,
437
00:24:36,175 --> 00:24:38,642
the oldest light
in the universe.
438
00:24:40,947 --> 00:24:42,680
As the universe expanded,
439
00:24:42,682 --> 00:24:47,284
these ripples were imprinted
in space in a uniform way.
440
00:24:48,754 --> 00:24:50,654
They provide a cosmic ruler
441
00:24:50,656 --> 00:24:53,858
to measure vast
distances over time,
442
00:24:53,860 --> 00:24:56,193
so we can gauge
if the universe expands
443
00:24:56,195 --> 00:24:59,897
in curved space
or over a flat plane.
444
00:25:02,802 --> 00:25:04,835
Bullock:
When we use these cosmic rulers
445
00:25:04,837 --> 00:25:07,104
to try to back out
the shape of the universe,
446
00:25:07,106 --> 00:25:09,340
we're sure
to a few percent accuracy
447
00:25:09,342 --> 00:25:12,943
that the universe is flat.
448
00:25:12,945 --> 00:25:15,079
Narrator:
If the universe is flat,
449
00:25:15,081 --> 00:25:17,848
we could set off
traveling into the cosmos
450
00:25:17,850 --> 00:25:20,551
and continue traveling forever.
451
00:25:22,655 --> 00:25:26,357
There may be no edge
to our universe
452
00:25:26,359 --> 00:25:30,928
because a flat universe
can be an infinite universe.
453
00:25:30,930 --> 00:25:32,963
Now we're thinking of
the universe as something
454
00:25:32,965 --> 00:25:34,832
that really does
go on forever,
455
00:25:34,834 --> 00:25:38,869
that the stars and galaxies
never have an end,
456
00:25:38,871 --> 00:25:42,973
and how can something
truly infinite really exist?
457
00:25:42,975 --> 00:25:47,711
Infinity is weird
because it's a concept of,
458
00:25:47,713 --> 00:25:50,047
because it's endless.
459
00:25:50,049 --> 00:25:52,783
What does that mean? Who knows?
I don't know.
460
00:25:55,488 --> 00:25:59,056
Plait: Infinity is a concept
more than anything else.
461
00:25:59,058 --> 00:26:01,025
Our brains aren't
evolved for that.
462
00:26:01,027 --> 00:26:03,794
We evolved living in the plains.
463
00:26:03,796 --> 00:26:06,430
We were apes looking for food.
464
00:26:06,432 --> 00:26:09,433
We weren't evolved to think
about the universe
465
00:26:09,435 --> 00:26:12,169
and all of this stuff.
466
00:26:12,171 --> 00:26:14,572
Oluseyi: I just can't stop
contemplating this stuff.
467
00:26:14,574 --> 00:26:17,474
The idea of infinity
and these large numbers
468
00:26:17,476 --> 00:26:19,510
and even the tininess
of everything.
469
00:26:19,512 --> 00:26:20,978
It's nuts.
470
00:26:20,980 --> 00:26:24,114
Yeah, thinking about infinity
makes my head hurt a little bit.
471
00:26:28,421 --> 00:26:31,589
Narrator: An infinite universe
has profound implications
472
00:26:31,591 --> 00:26:34,291
for understanding our place
in the cosmos.
473
00:26:36,362 --> 00:26:39,296
It guarantees we're not alone.
474
00:26:40,900 --> 00:26:42,933
Carroll:
But if the universe is infinite,
475
00:26:42,935 --> 00:26:44,868
then there could be
an infinite number of galaxies
476
00:26:44,870 --> 00:26:49,306
that have planets with life,
an infinite number without life,
477
00:26:49,308 --> 00:26:51,642
then because life
did appear here on earth,
478
00:26:51,644 --> 00:26:53,077
it's physically possible,
479
00:26:53,079 --> 00:26:54,612
therefore,
it will definitely happen
480
00:26:54,614 --> 00:26:57,081
elsewhere in the universe.
481
00:26:57,083 --> 00:26:58,415
Narrator: In a flat universe,
482
00:26:58,417 --> 00:27:03,387
alien life could come in
an infinite number of forms,
483
00:27:03,389 --> 00:27:07,625
but there is an altogether
stranger guarantee.
484
00:27:07,627 --> 00:27:10,728
If the universe has no edge,
this means that
485
00:27:10,730 --> 00:27:14,665
things that seem like they are
impossible become possible.
486
00:27:17,370 --> 00:27:20,237
Every possible arrangement
of matter,
487
00:27:20,239 --> 00:27:23,240
every possible history.
488
00:27:23,242 --> 00:27:27,711
A galaxy of a solar system
of a planet like earth
489
00:27:27,713 --> 00:27:28,979
is possible
490
00:27:28,981 --> 00:27:32,583
and is happening right now
in parallel to us
491
00:27:32,585 --> 00:27:35,052
somewhere over there.
492
00:27:36,589 --> 00:27:39,490
Freese: So that means that there
has to be another place
493
00:27:39,492 --> 00:27:42,960
that has a galaxy just like ours
494
00:27:42,962 --> 00:27:44,862
and it would have an earth
just like ours.
495
00:27:44,864 --> 00:27:49,700
It would have people who would
have another version of you,
496
00:27:49,702 --> 00:27:51,168
another version of me.
497
00:27:51,170 --> 00:27:55,372
It's 100% guaranteed that there
is another max tegmark out there
498
00:27:55,374 --> 00:27:58,776
having exactly this conversation
and in fact many of them.
499
00:28:00,846 --> 00:28:03,547
Narrator: An infinite universe
full of max tegmarks
500
00:28:03,549 --> 00:28:05,616
may be a strange concept,
501
00:28:05,618 --> 00:28:08,152
but what's truly mind-bending
is understanding
502
00:28:08,154 --> 00:28:11,221
the physics of a flat universe.
503
00:28:11,223 --> 00:28:14,558
If the universe is infinite
and it's expanding,
504
00:28:14,560 --> 00:28:20,197
what's it expanding into
and what did it expand from?
505
00:28:20,199 --> 00:28:24,635
Was there ever an edge
to the universe?
506
00:28:24,637 --> 00:28:28,806
Fortunately, the answer is that
it doesn't make sense
507
00:28:28,808 --> 00:28:30,774
to ask that question.
508
00:28:30,776 --> 00:28:33,077
Everything is expanding,
509
00:28:33,079 --> 00:28:36,113
including the universe
that we exist within.
510
00:28:36,115 --> 00:28:39,083
So in fact, it's not expanding
into anything
511
00:28:39,085 --> 00:28:40,684
because it is everything.
512
00:28:40,686 --> 00:28:45,656
♪
513
00:28:45,658 --> 00:28:47,758
narrator: To help understand
what's going on
514
00:28:47,760 --> 00:28:49,359
in an infinite universe,
515
00:28:49,361 --> 00:28:51,595
we need to go back
to the big bang.
516
00:28:54,266 --> 00:28:57,601
We want to think of the big bang
as an explosion in space,
517
00:28:57,603 --> 00:28:59,336
like it happened someplace,
518
00:28:59,338 --> 00:29:02,239
but there wasn't any place
before the big bang.
519
00:29:02,241 --> 00:29:05,509
Space existed inside
of the big bang itself.
520
00:29:05,511 --> 00:29:07,778
So it's not an explosion
in space,
521
00:29:07,780 --> 00:29:10,280
it's an explosion of space.
522
00:29:10,282 --> 00:29:12,349
We're sometimes told that
at the big bang,
523
00:29:12,351 --> 00:29:15,786
the universe started out very,
very small and then got big,
524
00:29:15,788 --> 00:29:19,723
but how can a finite point
become infinite?
525
00:29:19,725 --> 00:29:21,759
Well, if the universe
is infinite,
526
00:29:21,761 --> 00:29:25,529
then it was also infinite
at the big bang.
527
00:29:25,531 --> 00:29:27,831
This is a tough thing
to think about.
528
00:29:27,833 --> 00:29:29,299
Think about it this way.
529
00:29:29,301 --> 00:29:31,902
In an infinite universe,
the galaxies go on forever
530
00:29:31,904 --> 00:29:35,572
and now there's a great
distance between every galaxy.
531
00:29:35,574 --> 00:29:36,607
But once upon a time,
532
00:29:36,609 --> 00:29:38,108
the galaxies
were closer together,
533
00:29:38,110 --> 00:29:40,711
say half their current
distance apart,
534
00:29:40,713 --> 00:29:42,079
but they still went on forever.
535
00:29:42,081 --> 00:29:45,749
The universe was still infinite.
536
00:29:45,751 --> 00:29:47,184
Narrator:
In a flat universe,
537
00:29:47,186 --> 00:29:51,855
space was infinite
from the beginning.
538
00:29:51,857 --> 00:29:54,358
There was never
a single point in space
539
00:29:54,360 --> 00:29:56,994
where the big bang happened.
540
00:29:56,996 --> 00:30:00,597
It happened everywhere.
541
00:30:00,599 --> 00:30:05,602
An infinite universe offers
infinite possibilities
542
00:30:05,604 --> 00:30:08,038
but no edge to space.
543
00:30:11,177 --> 00:30:14,111
But there may be
another kind of edge,
544
00:30:14,113 --> 00:30:18,649
one that will only reveal itself
if the universe dies.
545
00:30:30,930 --> 00:30:37,401
♪
546
00:30:37,403 --> 00:30:42,339
narrator: We live in an infinite
and expanding universe.
547
00:30:42,341 --> 00:30:46,009
Space has no edge.
It goes on forever.
548
00:30:46,011 --> 00:30:51,014
♪
549
00:30:51,016 --> 00:30:55,919
but there could be a different
kind of edge to our universe,
550
00:30:55,921 --> 00:30:59,056
an edge of time.
551
00:30:59,058 --> 00:31:01,191
The universe seems to have begun
552
00:31:01,193 --> 00:31:03,260
13.8 billion years ago
in the past,
553
00:31:03,262 --> 00:31:06,363
so there's some inclination,
some impression,
554
00:31:06,365 --> 00:31:08,165
that it's finite in time.
555
00:31:08,167 --> 00:31:12,035
What we call the big bang is,
as far as we understand it,
556
00:31:12,037 --> 00:31:14,638
a beginning,
a start of the universe.
557
00:31:14,640 --> 00:31:16,907
The universe has a finite age.
558
00:31:16,909 --> 00:31:20,644
Now, does it have an edge
in the future?
559
00:31:20,646 --> 00:31:22,546
Narrator: We used to think
that time would someday
560
00:31:22,548 --> 00:31:25,148
come to a catastrophic end,
561
00:31:25,150 --> 00:31:28,518
along with the planets,
galaxies,
562
00:31:28,520 --> 00:31:30,754
and all life in the universe.
563
00:31:33,425 --> 00:31:35,692
If we know there's a big bang,
if we know the universe started,
564
00:31:35,694 --> 00:31:38,528
it expanded and cooled,
it's very natural to wonder
565
00:31:38,530 --> 00:31:40,764
whether or not someday
the expansion will stop,
566
00:31:40,766 --> 00:31:44,001
reverse, and come back,
and that's a big crunch.
567
00:31:44,003 --> 00:31:49,105
♪
568
00:31:49,107 --> 00:31:50,340
narrator: In a big crunch,
569
00:31:50,342 --> 00:31:53,777
our expanding universe
would begin to contract.
570
00:31:53,779 --> 00:31:56,680
Stars and planets would smash
into each other.
571
00:31:58,851 --> 00:32:02,119
Galaxies would collide,
572
00:32:02,121 --> 00:32:05,389
and all of the life left
in space would be compressed
573
00:32:05,391 --> 00:32:08,926
with all the other matter
into a singularity.
574
00:32:08,928 --> 00:32:17,567
♪
575
00:32:17,569 --> 00:32:20,270
if this theory is true,
then the universe
576
00:32:20,272 --> 00:32:25,742
would have both a beginning
and an end of time.
577
00:32:25,744 --> 00:32:27,945
If we live in a universe
that will expand,
578
00:32:27,947 --> 00:32:30,881
stop expanding,
and then go back into a crunch,
579
00:32:30,883 --> 00:32:34,284
then it has,
in effect, two edges.
580
00:32:34,286 --> 00:32:38,655
Narrator: But there's a much
stranger possibility.
581
00:32:38,657 --> 00:32:41,692
Perhaps the end is
but a beginning,
582
00:32:41,694 --> 00:32:43,794
where the universe
is a oscillating universe.
583
00:32:43,796 --> 00:32:45,696
It has a big bang
like beginning,
584
00:32:45,698 --> 00:32:47,431
it expands to a maximum size,
585
00:32:47,433 --> 00:32:49,433
and then goes back
into a big crunch
586
00:32:49,435 --> 00:32:51,768
and does that over and over.
587
00:32:53,505 --> 00:32:55,539
Narrator: We could be residents
of a universe
588
00:32:55,541 --> 00:32:58,709
created from the ashes
of another,
589
00:32:58,711 --> 00:33:03,413
a single universe in a stream
of bouncing universes...
590
00:33:06,552 --> 00:33:11,455
...Each full of galaxies,
planets, and life.
591
00:33:11,457 --> 00:33:14,992
But our most recent observations
of the universe suggest
592
00:33:14,994 --> 00:33:17,928
a big crunch isn't in the cards.
593
00:33:20,099 --> 00:33:23,567
Once again, dark energy is key.
594
00:33:26,238 --> 00:33:30,340
For a while we didn't know
if the expansion of the universe
595
00:33:30,342 --> 00:33:32,676
was going to slow, stop,
596
00:33:32,678 --> 00:33:35,312
and reverse itself
because of gravity.
597
00:33:35,314 --> 00:33:36,713
There are all these galaxies
in the universe
598
00:33:36,715 --> 00:33:38,849
and they're pulling on
each other by their gravity.
599
00:33:38,851 --> 00:33:40,517
And if the expansion
isn't fast enough,
600
00:33:40,519 --> 00:33:43,153
that gravity might be strong
enough to stop the expansion
601
00:33:43,155 --> 00:33:44,921
and re-collapse the universe.
602
00:33:44,923 --> 00:33:46,223
Now with dark energy,
603
00:33:46,225 --> 00:33:48,658
we know that there's no way
that can happen.
604
00:33:48,660 --> 00:33:51,194
The universe is going
to expand forever
605
00:33:51,196 --> 00:33:55,032
because dark energy is
pumping it full of acceleration.
606
00:33:55,034 --> 00:33:57,534
In order for there
to be a big crunch,
607
00:33:57,536 --> 00:34:01,138
our understanding of dark energy
would have to change a lot.
608
00:34:01,140 --> 00:34:03,740
That is, dark energy would have
to be extremely weird
609
00:34:03,742 --> 00:34:07,911
and turn off in some very funny
way for the universe
610
00:34:07,913 --> 00:34:10,914
to suddenly stop expanding
and re-collapse.
611
00:34:13,252 --> 00:34:14,885
Narrator:
Without a big crunch,
612
00:34:14,887 --> 00:34:19,256
there is no future edge to time.
613
00:34:19,258 --> 00:34:20,957
Carroll: The universe is not
only expanding,
614
00:34:20,959 --> 00:34:22,692
but it's being driven
by dark energy
615
00:34:22,694 --> 00:34:26,063
to expand faster and faster
and the dark energy
616
00:34:26,065 --> 00:34:28,532
doesn't dilute away,
as far as we can tell.
617
00:34:28,534 --> 00:34:31,001
So the simplest idea
is that the universe
618
00:34:31,003 --> 00:34:34,738
will simply continue to expand
eternally toward the future.
619
00:34:36,909 --> 00:34:41,711
Narrator: Just like space,
time will go on forever.
620
00:34:41,713 --> 00:34:46,116
That might sound like a better
fate for life and the universe,
621
00:34:46,118 --> 00:34:47,751
but it's not.
622
00:34:50,022 --> 00:34:53,056
Freese: One of the consequences
of this dark energy
623
00:34:53,058 --> 00:34:56,026
that's causing the acceleration
of the universe
624
00:34:56,028 --> 00:35:01,598
is that we eventually are
headed towards the big chill.
625
00:35:01,600 --> 00:35:05,302
I should say, "we're eventually
headed towards the big chill."
626
00:35:05,304 --> 00:35:08,438
so the universe is getting
colder and colder
627
00:35:08,440 --> 00:35:11,441
and things are getting more
and more spread out.
628
00:35:11,443 --> 00:35:13,743
So the accelerated and continual
629
00:35:13,745 --> 00:35:16,012
and forever expansion
of our universe
630
00:35:16,014 --> 00:35:19,716
might make for a frankly
depressing end to time itself.
631
00:35:19,718 --> 00:35:23,253
The ultimate entropy-based
heat death of the universe
632
00:35:23,255 --> 00:35:27,858
where you would walk out
and see no stars in the sky,
633
00:35:27,860 --> 00:35:29,526
see absolutely nothing.
634
00:35:29,528 --> 00:35:32,596
There will come one day when the
very last star in the universe
635
00:35:32,598 --> 00:35:35,432
just fizzles out and that is it.
636
00:35:38,303 --> 00:35:40,303
Narrator: In the future,
637
00:35:40,305 --> 00:35:44,074
space will be a cold, dark
and infinite void,
638
00:35:44,076 --> 00:35:47,844
where time goes on forever.
639
00:35:47,846 --> 00:35:49,746
There will be nothing to do
640
00:35:49,748 --> 00:35:53,216
but suffer
in the eternal expanse.
641
00:35:53,218 --> 00:35:56,887
It's our inevitable fate
that there's no future edge
642
00:35:56,889 --> 00:36:00,824
of time in the universe.
643
00:36:00,826 --> 00:36:04,127
But even if there isn't an edge
to the universe,
644
00:36:04,129 --> 00:36:09,866
could there be edges
within the universe?
645
00:36:09,868 --> 00:36:12,402
If you wanted to visit the edge
of the universe,
646
00:36:12,404 --> 00:36:15,839
then go find your nearest
black hole and jump on in
647
00:36:15,841 --> 00:36:18,008
because that's a one-way trip.
648
00:36:18,010 --> 00:36:21,811
Narrator: If you cross this
edge, you will never return.
649
00:36:29,254 --> 00:36:33,757
♪
650
00:36:33,759 --> 00:36:36,159
[ applause ]
651
00:36:36,161 --> 00:36:38,295
narrator: April 2019,
652
00:36:38,297 --> 00:36:40,497
an international team
of astronomers
653
00:36:40,499 --> 00:36:42,866
makes a special announcement.
654
00:36:42,868 --> 00:36:46,469
And we are delighted to be able
to report to you today
655
00:36:46,471 --> 00:36:51,541
that we have seen and taken
a picture of a black hole.
656
00:36:51,543 --> 00:36:52,809
Here it is.
657
00:36:52,811 --> 00:36:54,411
[ applause ]
658
00:36:54,413 --> 00:36:58,982
♪
659
00:36:58,984 --> 00:37:02,252
narrator: It's a picture
of a supermassive black hole
660
00:37:02,254 --> 00:37:07,324
at the center of the m87 galaxy
54 million light-years away.
661
00:37:09,161 --> 00:37:14,130
It may also be the first image
of an edge in the universe.
662
00:37:15,400 --> 00:37:18,001
Black holes create
a really interesting scenario
663
00:37:18,003 --> 00:37:22,906
when we think about space
and the universe having edges.
664
00:37:22,908 --> 00:37:27,844
Narrator: The edge between space
outside and inside a black hole
665
00:37:27,846 --> 00:37:31,114
is called the event horizon.
666
00:37:31,116 --> 00:37:32,582
Bullock: The event horizon
of a black hole
667
00:37:32,584 --> 00:37:36,152
is a region within which,
once you cross inside,
668
00:37:36,154 --> 00:37:38,755
the gravitational tug
is so strong
669
00:37:38,757 --> 00:37:43,393
that even light cannot escape,
which means nothing can escape
670
00:37:43,395 --> 00:37:46,296
once you cross
inside the event horizon.
671
00:37:46,298 --> 00:37:48,665
So that really
is sort of an edge
672
00:37:48,667 --> 00:37:51,234
because it really does
create a boundary.
673
00:37:51,236 --> 00:37:56,306
♪
674
00:37:56,308 --> 00:37:59,709
narrator: The event horizon is
not a physical barrier in space.
675
00:38:01,913 --> 00:38:04,314
Event horizon is an edge
of the part of the universe
676
00:38:04,316 --> 00:38:06,283
we can visit,
but it's not an edge
677
00:38:06,285 --> 00:38:09,185
in the sense
that there's anything there.
678
00:38:09,187 --> 00:38:10,553
You would just pass
right through it
679
00:38:10,555 --> 00:38:12,722
if you actually got right up
to that place.
680
00:38:12,724 --> 00:38:15,158
So it's sort of
a conceptual boundary
681
00:38:15,160 --> 00:38:19,129
between two different parts
of the universe.
682
00:38:19,131 --> 00:38:22,532
Narrator: If we sent a man to
probe into a black hole,
683
00:38:22,534 --> 00:38:24,301
it would be a one-way trip.
684
00:38:26,738 --> 00:38:31,541
The event horizons of
black holes are a sort of edge
685
00:38:31,543 --> 00:38:34,611
because, once you pass through
an event horizon,
686
00:38:34,613 --> 00:38:38,214
you are cut off
from the rest of the universe.
687
00:38:38,216 --> 00:38:40,784
You can never go back out.
688
00:38:40,786 --> 00:38:45,155
You are outside of our universe.
689
00:38:45,157 --> 00:38:46,990
Once you've crossed
inside that region,
690
00:38:46,992 --> 00:38:50,360
you are never coming back out,
and that's an edge.
691
00:38:52,197 --> 00:38:54,197
Narrator:
Once inside the black hole,
692
00:38:54,199 --> 00:38:58,301
the probe would be in
a separate part of space,
693
00:38:58,303 --> 00:39:02,339
cut off from the rest
of the universe.
694
00:39:02,341 --> 00:39:04,374
Sutter: Falling through the
event horizon of a black hole
695
00:39:04,376 --> 00:39:07,644
is like jumping over
the edge of a cliff.
696
00:39:07,646 --> 00:39:10,580
You can see the edge
and you can see the edge go by,
697
00:39:10,582 --> 00:39:13,149
and then when you're at
the bottom, you can look up
698
00:39:13,151 --> 00:39:15,618
and see what's happening
at the top of the cliff,
699
00:39:15,620 --> 00:39:17,354
but you can never go back.
700
00:39:19,491 --> 00:39:21,891
Narrator: At the bottom
of this black-hole cliff
701
00:39:21,893 --> 00:39:24,694
sits a singularity,
702
00:39:24,696 --> 00:39:30,567
a region of space where the laws
of physics go off the rails.
703
00:39:30,569 --> 00:39:33,403
Deep toward that singularity
could be as surprising
704
00:39:33,405 --> 00:39:36,339
as you might imagine
and yet still a possibility.
705
00:39:36,341 --> 00:39:38,808
If you map the space-time
around a black hole
706
00:39:38,810 --> 00:39:40,377
in a very particular way,
707
00:39:40,379 --> 00:39:44,347
there emerges a sort of mirror
universe, a parallel universe,
708
00:39:44,349 --> 00:39:46,015
on the other side
of the black hole,
709
00:39:46,017 --> 00:39:50,787
identical to our own and
traversable by the black hole.
710
00:39:50,789 --> 00:39:56,059
♪
711
00:39:56,061 --> 00:40:01,197
narrator: So black holes are not
just edges to our universe,
712
00:40:01,199 --> 00:40:06,569
they may also be gateways
to other universes.
713
00:40:06,571 --> 00:40:08,138
Bullock: It's highly conjecture,
714
00:40:08,140 --> 00:40:12,375
but if there's ever going
to be a space, or region,
715
00:40:12,377 --> 00:40:15,545
where you're making connections
with, say, some other universe,
716
00:40:15,547 --> 00:40:18,314
a black hole, in principle,
could be a portal to that.
717
00:40:22,354 --> 00:40:23,753
Narrator:
But it's highly unlikely
718
00:40:23,755 --> 00:40:24,954
that anyone will ever want
719
00:40:24,956 --> 00:40:29,592
to venture beyond
an event horizon to find out,
720
00:40:29,594 --> 00:40:33,029
and our pursuits of the other
edges in the cosmos
721
00:40:33,031 --> 00:40:35,965
offer little hope either.
722
00:40:35,967 --> 00:40:41,137
We can never travel beyond
the cosmic event horizon.
723
00:40:41,139 --> 00:40:44,340
We will never be able
to see beyond the edge
724
00:40:44,342 --> 00:40:47,744
of our observable universe.
725
00:40:47,746 --> 00:40:51,915
So can we ever hope to discover
the true edge
726
00:40:51,917 --> 00:40:56,186
of the greater universe
or find out if it even has one?
727
00:40:58,023 --> 00:41:00,423
My feeling is that probably
we should not think
728
00:41:00,425 --> 00:41:03,226
about edges for the universe.
729
00:41:03,228 --> 00:41:05,929
Everything you've ever seen
in your life is finite,
730
00:41:05,931 --> 00:41:10,099
it has an inside
and the outside, it has an edge.
731
00:41:10,101 --> 00:41:11,901
The universe
might not be like that.
732
00:41:11,903 --> 00:41:13,369
It's probably not like that.
733
00:41:13,371 --> 00:41:16,506
There's probably no sense in
which the universe has an edge.
734
00:41:19,544 --> 00:41:22,111
We used to think that
the ultimate limits
735
00:41:22,113 --> 00:41:24,948
on the future life
were set by nature,
736
00:41:24,950 --> 00:41:26,249
we couldn't get off the planet,
737
00:41:26,251 --> 00:41:29,452
or there was nothing beyond
our solar system.
738
00:41:29,454 --> 00:41:31,921
Now we realized
we have this vast,
739
00:41:31,923 --> 00:41:35,258
vast cosmos out there
and that the ultimate limits
740
00:41:35,260 --> 00:41:38,461
are actually simply
our own imagination
741
00:41:38,463 --> 00:41:41,231
and our ability
to do great things with it
742
00:41:41,233 --> 00:41:42,932
rather than self-destruct.
743
00:41:42,934 --> 00:41:46,069
Our future destiny
is in our own hands
744
00:41:46,071 --> 00:41:49,873
and I find that very empowering.
745
00:41:49,875 --> 00:41:52,208
Thaller:
It is beautifully frustrating
746
00:41:52,210 --> 00:41:53,943
to realize how limited we are,
747
00:41:53,945 --> 00:41:56,613
to realize that we're probably
never going to get a true view
748
00:41:56,615 --> 00:41:58,515
of the real extent
of the universe.
749
00:41:58,517 --> 00:42:00,583
We should keep an open mind,
we should be humble,
750
00:42:00,585 --> 00:42:02,452
but I think that we should
give up on the idea
751
00:42:02,454 --> 00:42:03,887
that things should have edges
752
00:42:03,889 --> 00:42:05,355
because that's what
we're familiar with.
753
00:42:05,357 --> 00:42:08,124
The universe
is something special.
754
00:42:08,126 --> 00:42:12,896
Sutter: What matters to us, and
will only ever matter to us,
755
00:42:12,898 --> 00:42:15,298
is the observable universe
756
00:42:15,300 --> 00:42:18,001
because that's the limit
of what we can see
757
00:42:18,003 --> 00:42:19,903
and that is the limit
of what we can know.
758
00:42:19,905 --> 00:42:22,171
So there is an edge
to the universe,
759
00:42:22,173 --> 00:42:24,173
there's an edge
to what we can know.
68097
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