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♪♪
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Something is hiding
in the darkness.
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Invisible objects
of unimaginable power
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00:00:09,599 --> 00:00:15,098
that could hold the key to
solving the mysteries of space,
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time, and the universe itself.
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To me, a black hole is
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the greatest exhibition
of nature's mysterious powers.
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You literally can't see them.
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And that's what makes them
extremely mysterious.
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They are bizarre quirks
of nature.
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When we're studying black holes,
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we're right on the edge
of human knowledge.
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00:00:40,343 --> 00:00:43,245
And yet, they are sculptors
of the cosmos.
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The jets from black holes are so
powerful, they can affect
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the whole shape and nature
of a galaxy.
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Even shaping our own galaxy,
the Milky Way.
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We had hints that black holes
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were at the center of all
of galaxies, like our own.
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Can we lift the veil...
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Forget the one-way trip to Mars.
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I'm going in the black hole.
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And reveal their secrets?
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Fermi revealed something
completely astonishing
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and unexpected.
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We've never seen anything
like it.
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Finding these little pieces
of the puzzle that did not fit
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is super-exciting.
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But if you really want to
understand
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the deepest questions
of the universe,
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you have to understand
black holes.
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♪♪
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"Black Holes,"
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right now, on "NOVA."
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♪♪
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♪ See me when I float
like a dove ♪
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♪ The skies above are lined
with trees ♪
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♪ I'm on my knees,
begging please ♪
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♪ Come and take me away ♪
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♪♪
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As we gaze out at the Milky Way,
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our eyes are drawn to the light.
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Hundreds of billions of stars
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serenely spinning through
the cosmos.
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When we look up
at the night sky,
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the stars and planets that
we see are beautiful.
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But actually,
it's in the space between these,
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in the dark patches,
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that some of the most
fascinating things lie.
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00:03:00,148 --> 00:03:04,272
♪♪
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In places where there is
no light,
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objects of profound mystery
bide their time.
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Awesome in their simplicity
and perfection,
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we call them black holes.
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A black hole
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is an infinitely dense point
in space from which nothing
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00:03:26,669 --> 00:03:29,353
can escape, not even light.
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00:03:29,388 --> 00:03:31,843
It's extraordinary to think
that black holes are everywhere
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in the universe,
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that they have existed from very
early times in the universe.
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When quiet, they are almost
impossible to detect.
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We're talking about a region
of space
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where, if something falls in,
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we'll never know about it
ever again.
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♪♪
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They hold the power to shred
stars and worlds,
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but also, the potential to shape
galaxies...
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00:04:01,380 --> 00:04:04,163
Black holes are one of the most
fundamentally important
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00:04:04,195 --> 00:04:08,123
singular objects that might
dictate how galaxies
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form and evolve.
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00:04:10,529 --> 00:04:12,123
It's natural to fear them,
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but we're learning that
they're essential.
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You can't live with them,
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but you also can't live without
them.
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♪♪
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And they may hold the secret
to the ultimate fate
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of the universe.
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Black holes,
on a fundamental level,
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00:04:27,549 --> 00:04:31,161
challenge our understanding
of physics,
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of the way that everything
in the universe works.
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Black holes are the most
mysterious objects
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in the universe, fullstop.
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♪♪
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To understand black holes, we
have to start at the beginning.
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00:04:50,455 --> 00:04:55,125
At the moment of birth.
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Black holes that are a few times
the mass of the sun
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probably formed from giant stars
that were maybe about
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20 to 30 times
the mass of the sun.
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00:05:05,747 --> 00:05:09,489
♪♪
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Enormous stars burning bright
blue with intense heat.
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00:05:16,113 --> 00:05:20,782
But the brightest stars
are the shortest-lived.
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00:05:20,816 --> 00:05:23,566
A star is a big ball of gas,
right?
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There's outward gravity
pushing in, right?
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The thing wants to collapse
in on itself
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00:05:26,894 --> 00:05:28,553
under its own self-gravity.
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00:05:28,590 --> 00:05:30,695
But the fusion that's happening
within the star's core
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liberates so much light that
the outward radiation pressure
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prevents the collapse
of that star.
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00:05:38,571 --> 00:05:42,149
But eventually, that gives up.
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A star like that can burn
through its nuclear fuel
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00:05:47,593 --> 00:05:50,375
in just a few million years.
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♪♪
102
00:06:01,446 --> 00:06:03,934
And when its power source runs
out,
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00:06:03,973 --> 00:06:10,115
it collapses under its own
gravitational pull.
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00:06:10,147 --> 00:06:12,962
There's so much material
that's collapsing during
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00:06:12,994 --> 00:06:17,435
their final few moments
that they create this massive
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00:06:17,473 --> 00:06:19,775
dense ball of neutrons
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that continues to collapse.
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A star 20 times the mass
of our sun or larger...
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crushed by the force of gravity,
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until the star disappears,
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leaving only a ghost behind.
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♪♪
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A black hole.
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♪♪
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This transformation does not
await all stars.
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Smaller, less massive stars,
like our sun,
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00:07:02,742 --> 00:07:06,287
eventually become burnt-out
dwarves when their fusion stops:
118
00:07:06,325 --> 00:07:12,020
slowly fading cinders.
119
00:07:12,052 --> 00:07:14,473
But it's possible that almost
all the massive stars
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00:07:14,515 --> 00:07:18,257
that dominated the early
universe formed black holes
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00:07:18,289 --> 00:07:22,861
when they died.
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Because black holes are simply
what happens when enough matter
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00:07:26,512 --> 00:07:30,342
is crushed into a small enough
volume,
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00:07:30,383 --> 00:07:34,212
dramatically warping the space
around it.
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00:07:34,253 --> 00:07:36,439
A river is a great analogy
for the area right around
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a black hole.
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Here I am far upstream,
and the water is fairly placid.
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It's not moving too fast.
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00:07:45,067 --> 00:07:47,555
If I were to get into the water
here and swim across,
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00:07:47,594 --> 00:07:50,856
I'd be able to do that
very easily.
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In the same way, if you're
far away from a black hole,
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you'll be able to get around
with just a normal spacecraft
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without too much trouble
and simple propulsion.
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♪♪
135
00:08:04,710 --> 00:08:06,717
But the closer you get
to the black hole,
136
00:08:06,758 --> 00:08:11,100
the stranger things become.
137
00:08:11,140 --> 00:08:13,508
The collapsed massive star
crushes down
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00:08:13,540 --> 00:08:15,962
so small and so dense,
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00:08:16,195 --> 00:08:19,708
it ceases to have a physical
surface at all,
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00:08:19,746 --> 00:08:24,416
becoming an infinitely small
point in space,
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00:08:24,449 --> 00:08:31,126
exerting a profound effect
on the space-time around it.
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00:08:31,168 --> 00:08:34,648
As the water gets closer
to the waterfall,
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00:08:34,686 --> 00:08:37,850
the speed of the water
increases.
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00:08:37,886 --> 00:08:41,813
If I were to jump into the water
right here,
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00:08:41,852 --> 00:08:44,187
the speed of the current
would be so intense
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that I wouldn't be able to swim
against it,
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00:08:46,683 --> 00:08:49,530
and I would be gradually pulled
closer to the edge
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of the waterfall till I reach
a point of no return.
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00:08:51,994 --> 00:08:54,677
And that's the same around
a black hole.
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♪♪
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Just outside the black hole,
the fabric of space itself
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00:09:02,328 --> 00:09:05,492
actually stretches inward
towards the center.
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00:09:08,502 --> 00:09:12,910
Not even stars, planets, people,
even light cannot escape
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00:09:12,948 --> 00:09:15,021
the pull of a black hole.
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00:09:15,060 --> 00:09:17,614
It's like a waterfall
in the fabric of the universe.
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00:09:21,234 --> 00:09:26,668
The black hole's gravitational
reach is not infinite.
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00:09:26,705 --> 00:09:29,291
People have this idea
that black holes suck,
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in the sense that they suck
everything into them,
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00:09:31,312 --> 00:09:32,971
but that's not true.
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Black holes can only eat things
that are within
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00:09:36,015 --> 00:09:38,917
a certain distance away
from them.
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If you're further away,
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then the black hole has no way
of eating you.
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But once in its grasp,
you are lost forever.
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And this is the key
to their mystery.
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The black hole's interior
is hidden from view,
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cut off from the rest of the
universe by a boundary in space:
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00:10:03,879 --> 00:10:07,589
the event horizon.
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00:10:07,623 --> 00:10:10,470
Beyond this point,
there is no escape.
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00:10:12,837 --> 00:10:17,115
♪♪
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As we approach
the event horizon,
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we get our first glimpse of the
true weirdness of black holes.
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Ever since Einstein,
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we've viewed the fabric of the
universe
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00:10:32,576 --> 00:10:36,853
not as something static, but
instead something that's fluid,
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something that bends and warps
around objects with mass.
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00:10:41,438 --> 00:10:46,010
We call this space-time,
a combination of space and time.
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00:10:46,044 --> 00:10:49,972
See, Einstein's insight was to
realize that these two things
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00:10:50,012 --> 00:10:52,216
are intimately connected.
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00:10:52,252 --> 00:10:56,659
That when an object has mass,
it not just bends space,
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but changes the passage of time
itself.
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00:11:00,473 --> 00:11:04,597
In particular, the effect of a
mass is to slow time down.
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00:11:07,256 --> 00:11:09,525
In the region around
the black hole,
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the warped space-time
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elongates light waves,
distorting color.
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00:11:16,246 --> 00:11:19,541
The event horizon is the place
at which time stops
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when seen from far away.
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Someone who's outside
the black hole will see you get
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redder and redder...
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And your time will slow down.
191
00:11:28,402 --> 00:11:29,787
And you'll kind of pass through
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00:11:29,810 --> 00:11:31,217
the horizon, disappear forever.
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♪♪
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00:11:49,837 --> 00:11:54,409
♪♪
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00:12:08,904 --> 00:12:15,843
Black holes are like waterfalls
in the fabric of the universe,
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00:12:15,878 --> 00:12:20,995
where space contorts and time
itself grinds to a halt,
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ensnaring light,
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00:12:24,324 --> 00:12:29,277
making them lockboxes for the
universe's ultimate secrets.
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00:12:32,194 --> 00:12:37,245
♪♪
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00:12:43,743 --> 00:12:48,085
It is said that fact is
sometimes stranger than fiction,
201
00:12:48,126 --> 00:12:51,771
and nowhere is that more true
than in the case of black holes.
202
00:12:54,556 --> 00:12:57,622
Black holes are stranger
than anything dreamed up
203
00:12:57,660 --> 00:12:59,962
by science fiction writers,
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00:12:59,995 --> 00:13:02,646
but they are firmly matters
of science fact.
205
00:13:10,328 --> 00:13:13,362
The vast majority of black holes
are small...
206
00:13:13,399 --> 00:13:17,109
Less than 20 miles across...
207
00:13:17,142 --> 00:13:22,128
And they usually wander alone
through space.
208
00:13:22,357 --> 00:13:25,259
But if we turn our gaze towards
the center of the Milky Way
209
00:13:25,301 --> 00:13:27,406
and journey inwards,
210
00:13:27,444 --> 00:13:33,106
through the gas and dust
that shroud the galactic core,
211
00:13:33,139 --> 00:13:36,848
signs of something altogether
different appear.
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00:13:36,881 --> 00:13:38,704
If you simply observe
213
00:13:38,737 --> 00:13:42,664
the stars in the very heart of
our galaxy over about 20 years,
214
00:13:42,704 --> 00:13:44,843
you will observe them orbiting
nothing.
215
00:13:48,271 --> 00:13:52,100
At the center of this swarm of
stars is darkness.
216
00:13:52,141 --> 00:13:54,476
It's a void.
217
00:13:54,509 --> 00:13:59,877
Scientists name this invisible
enigma Sagittarius A-star,
218
00:13:59,915 --> 00:14:02,763
although it is not a star
at all.
219
00:14:02,794 --> 00:14:03,908
Can you imagine
220
00:14:03,947 --> 00:14:07,689
how massive that object
has to be to be able to pull
221
00:14:07,722 --> 00:14:09,413
entire stars into orbit?
222
00:14:12,425 --> 00:14:14,280
They believe it to be
a black hole
223
00:14:14,312 --> 00:14:18,239
more than four million times
the mass of our sun...
224
00:14:18,279 --> 00:14:19,709
Many thousands of times
more massive
225
00:14:19,943 --> 00:14:23,009
than any other in the Milky Way.
226
00:14:23,046 --> 00:14:24,388
How did this monster
227
00:14:24,421 --> 00:14:27,040
come to live at the heart
of the Milky Way?
228
00:14:27,077 --> 00:14:32,510
Sagittarius A-star
is a supermassive giant
229
00:14:32,547 --> 00:14:36,922
around which the entire galaxy
spins,
230
00:14:36,962 --> 00:14:41,119
raising intriguing new questions
about the role of black holes
231
00:14:41,153 --> 00:14:44,536
in our galaxy and the universe.
232
00:14:44,576 --> 00:14:46,464
How did it get there?
233
00:14:46,495 --> 00:14:49,757
How did it get so big?
234
00:14:49,791 --> 00:14:52,180
And what can it tell us
about how black holes
235
00:14:52,222 --> 00:14:55,005
shape the cosmos?
236
00:14:55,037 --> 00:14:56,467
Would we even be here today
237
00:14:56,509 --> 00:14:57,939
without Sagittarius A-star?
238
00:15:04,219 --> 00:15:05,636
Just a few minutes away
from the 26th flight
239
00:15:05,659 --> 00:15:07,121
of the shuttle Columbia,
240
00:15:07,162 --> 00:15:08,657
with a crew of five.
241
00:15:08,890 --> 00:15:12,817
♪♪
242
00:15:15,960 --> 00:15:19,026
I think a night launch
is particularly exciting.
243
00:15:19,064 --> 00:15:22,064
Go for engine start.
244
00:15:22,102 --> 00:15:25,747
We have booster ignition
and lift-off of Columbia.
245
00:15:25,782 --> 00:15:27,441
Roger roll, Columbia,
we're looking in.
246
00:15:29,717 --> 00:15:32,106
Chandra is huge.
247
00:15:32,149 --> 00:15:33,523
It's about the size of
a school bus.
248
00:15:33,556 --> 00:15:34,964
It's the largest telescope
249
00:15:34,995 --> 00:15:37,330
to ever be launched
by the space shuttle.
250
00:15:37,363 --> 00:15:41,640
♪♪
251
00:15:41,682 --> 00:15:45,391
SRB separation is confirmed.
252
00:15:45,425 --> 00:15:46,970
You're stressed about
the astronauts onboard
253
00:15:46,993 --> 00:15:49,710
that are literally risking
their lives to help us
254
00:15:49,743 --> 00:15:51,653
get a better view
of the universe.
255
00:15:56,910 --> 00:16:00,074
In the summer of 1999,
256
00:16:00,109 --> 00:16:03,338
NASA's flagship telescope
for X-ray astronomy
257
00:16:03,372 --> 00:16:07,114
sets off from the space shuttle
cargo bay.
258
00:16:07,148 --> 00:16:12,482
♪♪
259
00:16:12,522 --> 00:16:15,173
Even two decades into its voyage
of discovery,
260
00:16:15,209 --> 00:16:18,984
Chandra remains by far
the most powerful observatory
261
00:16:19,016 --> 00:16:20,904
that we have to observe
the high-energy universe.
262
00:16:26,247 --> 00:16:30,753
Almost 83,000 miles
above the Earth's surface,
263
00:16:30,790 --> 00:16:36,386
at its highest orbit,
Chandra scans the sky
264
00:16:36,420 --> 00:16:39,354
with eight high-precision
mirrors engineered
265
00:16:39,395 --> 00:16:44,064
to detect X-rays emitted
from extremely hot regions
266
00:16:44,098 --> 00:16:45,243
of the universe.
267
00:16:47,905 --> 00:16:53,207
For 14 years, it searches
among the exploding stars
268
00:16:53,247 --> 00:16:55,801
and clusters of galaxies.
269
00:16:58,878 --> 00:17:03,351
But then, on September 14, 2013,
270
00:17:03,389 --> 00:17:08,953
Chandra chances on something
else entirely.
271
00:17:08,987 --> 00:17:10,842
Chandra wasn't looking for this
at all...
272
00:17:10,875 --> 00:17:12,436
Just happened to be looking
nearby.
273
00:17:12,474 --> 00:17:14,100
So it was a total surprise.
274
00:17:14,139 --> 00:17:19,768
♪♪
275
00:17:19,800 --> 00:17:24,437
As the telescope gazes into the
constellation of Sagittarius,
276
00:17:24,472 --> 00:17:28,246
it aims to observe a large cloud
of hot gas.
277
00:17:28,279 --> 00:17:32,948
But unexpectedly,
278
00:17:32,981 --> 00:17:37,967
it records a flash of X-rays
just a few pixels across
279
00:17:38,004 --> 00:17:43,852
coming from the seemingly empty
space in the galactic core.
280
00:17:43,891 --> 00:17:48,593
♪♪
281
00:17:53,040 --> 00:17:54,680
When we see something get very
hot for a very short period
282
00:17:54,703 --> 00:17:57,551
of time, we get very excited.
283
00:17:57,583 --> 00:17:59,972
Something is causing it...
Something we can't see.
284
00:18:00,014 --> 00:18:04,521
♪♪
285
00:18:08,812 --> 00:18:12,739
Some scientists believe
the flash seen by Chandra
286
00:18:12,780 --> 00:18:15,366
is caused by an asteroid...
287
00:18:17,098 --> 00:18:22,019
♪♪
288
00:18:22,057 --> 00:18:25,352
Ripped apart and burning up
in a blaze
289
00:18:25,384 --> 00:18:30,086
hundreds of times brighter
than the sun,
290
00:18:30,119 --> 00:18:34,396
releasing a burst of X-rays
that Chandra can detect
291
00:18:34,438 --> 00:18:39,293
almost 26,000 light-years away.
292
00:18:39,333 --> 00:18:41,517
If we see a level of X-rays
being produced that's so bright,
293
00:18:41,540 --> 00:18:43,198
it can't be explained
294
00:18:43,236 --> 00:18:45,789
by any other process,
then we know that there must be
295
00:18:45,827 --> 00:18:48,063
a black hole there.
296
00:18:48,098 --> 00:18:50,880
It's the behemoth at the center
of our galaxy.
297
00:18:55,009 --> 00:18:57,398
Sagittarius A-star.
298
00:19:00,735 --> 00:19:06,680
♪♪
299
00:19:06,910 --> 00:19:09,495
You can take a telescope like
Chandra and watch a black hole
300
00:19:09,533 --> 00:19:11,443
have a small snack,
301
00:19:11,484 --> 00:19:13,906
maybe like a human might have a
little biscuit in the afternoon.
302
00:19:13,948 --> 00:19:16,632
And it's something like
an asteroid.
303
00:19:16,667 --> 00:19:18,404
And there will be a small
sort of X-ray signature
304
00:19:18,427 --> 00:19:19,408
from that event.
305
00:19:19,451 --> 00:19:21,044
So it's incredible
306
00:19:21,082 --> 00:19:23,733
that we can actually observe
Sagittarius A-star,
307
00:19:23,769 --> 00:19:26,191
which lies 26,000 light-years
away,
308
00:19:26,232 --> 00:19:31,120
actually eating something.
309
00:19:31,159 --> 00:19:32,927
But Chandra does not only look
inwards.
310
00:19:32,950 --> 00:19:38,896
It also looks out,
beyond the Milky Way.
311
00:19:38,933 --> 00:19:43,635
At the center of almost every
large galaxy Chandra peers into,
312
00:19:43,668 --> 00:19:48,402
it finds evidence that our
galaxy is hardly unusual.
313
00:19:48,435 --> 00:19:51,054
We started to spot
314
00:19:51,090 --> 00:19:54,156
X-ray sources of light
everywhere around the sky,
315
00:19:54,194 --> 00:19:56,583
and we started to realize
something weird was going on
316
00:19:56,817 --> 00:19:57,852
in the centers of galaxies.
317
00:20:01,295 --> 00:20:03,881
At the heart of most galaxies,
318
00:20:03,919 --> 00:20:05,992
we think now there are
supermassive black holes,
319
00:20:06,031 --> 00:20:07,959
black holes that weigh millions
or billions of times
320
00:20:07,982 --> 00:20:10,404
what our sun does.
321
00:20:10,445 --> 00:20:14,155
It's incredible that our modern
X-ray telescopes, like Chandra,
322
00:20:14,188 --> 00:20:16,676
allow us to map out
323
00:20:16,716 --> 00:20:20,425
where these fascinating black
holes are across the universe.
324
00:20:20,459 --> 00:20:22,499
♪♪
325
00:20:22,730 --> 00:20:26,079
Supermassive black holes seem
to be an integral feature
326
00:20:26,122 --> 00:20:29,024
of the cosmos.
327
00:20:29,065 --> 00:20:33,571
But these supermassive objects
raise questions.
328
00:20:33,608 --> 00:20:35,877
How do they form?
329
00:20:35,911 --> 00:20:40,253
And why are they so big?
330
00:20:40,293 --> 00:20:43,589
These things form over millions
to billions of years.
331
00:20:43,621 --> 00:20:45,857
So we can't watch this
happening.
332
00:20:45,892 --> 00:20:48,227
We can only see it at various
different stages
333
00:20:48,260 --> 00:20:50,083
throughout the universe.
334
00:20:50,115 --> 00:20:54,458
And so we have to just piece it
together like a jigsaw puzzle.
335
00:20:54,498 --> 00:20:58,328
Some scientists theorize
that the biggest and oldest
336
00:20:58,369 --> 00:21:03,420
black holes did not start life
as stars at all.
337
00:21:03,456 --> 00:21:05,977
In the very early universe,
we believe that
338
00:21:06,015 --> 00:21:08,536
you could have formed
very massive black hole seeds
339
00:21:08,574 --> 00:21:11,836
by direct collapse of gas.
340
00:21:11,870 --> 00:21:15,579
So these black holes are called
direct-collapse black holes.
341
00:21:15,613 --> 00:21:19,704
But the jury is still out.
342
00:21:19,739 --> 00:21:21,944
It's possible that
Sagittarius A-star formed
343
00:21:21,979 --> 00:21:25,111
by direct collapse of material.
344
00:21:25,146 --> 00:21:28,277
What I think is more likely
is that it formed by
345
00:21:28,314 --> 00:21:30,583
the death of a star.
346
00:21:30,617 --> 00:21:35,854
However Sagittarius A-star was
born, one thing is certain:
347
00:21:35,896 --> 00:21:37,719
it had to grow.
348
00:21:37,751 --> 00:21:44,591
♪♪
349
00:21:44,630 --> 00:21:49,779
The newly formed Sagittarius
A-star begins to feast,
350
00:21:49,812 --> 00:21:55,114
gorging itself on not just
asteroids,
351
00:21:55,154 --> 00:22:01,319
but bigger game, like stars
and massive clouds of gas.
352
00:22:01,361 --> 00:22:03,085
As it snacks on these
353
00:22:03,121 --> 00:22:06,951
nearby objects that wander
into its path, it gets bigger
354
00:22:06,992 --> 00:22:08,967
and bigger and bigger.
355
00:22:11,855 --> 00:22:15,303
The black hole gains more mass
356
00:22:15,342 --> 00:22:20,099
and more gravitational power.
357
00:22:20,141 --> 00:22:22,858
But black holes that are a few
times the mass of the sun
358
00:22:22,891 --> 00:22:25,161
can never grow to be
a supermassive black hole
359
00:22:25,195 --> 00:22:27,530
just by eating gas and stars.
360
00:22:31,402 --> 00:22:36,835
How did Sagittarius A-star speed
up its growth?
361
00:22:36,872 --> 00:22:41,182
On September 14, 2015,
an international team
362
00:22:41,223 --> 00:22:45,478
of astronomers finds a clue,
363
00:22:45,510 --> 00:22:50,244
the aftershock of a truly
titanic interaction:
364
00:22:50,277 --> 00:22:54,586
two colliding black holes.
365
00:22:54,628 --> 00:22:56,940
So the merger of two black
holes, as you might imagine,
366
00:22:56,963 --> 00:23:01,120
is spectacularly energetic.
367
00:23:01,154 --> 00:23:04,024
It is so energetic that it
causes ripples in the fabric
368
00:23:04,065 --> 00:23:05,066
of space-time itself
that propagate outward
369
00:23:05,089 --> 00:23:06,912
at the speed of light.
370
00:23:06,944 --> 00:23:10,687
And we have detected these
ripples here on Earth
371
00:23:10,719 --> 00:23:14,581
with something we call LIGO.
372
00:23:14,622 --> 00:23:18,365
LIGO is an instrument that works
by sending laser beams
373
00:23:18,397 --> 00:23:21,496
that bounce off of mirrors.
374
00:23:21,532 --> 00:23:26,747
When a gravitational wave
passes by the Earth,
375
00:23:26,779 --> 00:23:30,074
this changes the timing
of the interaction
376
00:23:30,107 --> 00:23:32,474
of those laser beams.
377
00:23:32,506 --> 00:23:34,960
The stretching caused by
a merger here on Earth
378
00:23:35,002 --> 00:23:36,824
is absolutely minuscule.
379
00:23:36,857 --> 00:23:38,680
But with advanced technology,
380
00:23:38,712 --> 00:23:40,174
LIGO was able to do it.
381
00:23:40,216 --> 00:23:44,918
♪♪
382
00:23:50,997 --> 00:23:55,405
Many scientists now think that
mergers like this are the key
383
00:23:55,444 --> 00:23:57,965
to how supermassive black holes,
384
00:23:58,003 --> 00:24:03,022
like our own, grow so big.
385
00:24:03,058 --> 00:24:07,760
♪♪
386
00:24:14,383 --> 00:24:19,053
When another black hole wanders
towards Sagittarius A-star,
387
00:24:19,086 --> 00:24:25,763
they become locked in a
gravitational embrace.
388
00:24:25,804 --> 00:24:28,707
First, it is sort of
an intriguing dance.
389
00:24:28,748 --> 00:24:30,920
They kind of dance around
each other,
390
00:24:30,955 --> 00:24:35,712
lose energy, and slowly spiral
into each other.
391
00:24:35,754 --> 00:24:40,031
♪♪
392
00:24:40,072 --> 00:24:42,001
This dance gets faster and
faster and faster and faster
393
00:24:42,024 --> 00:24:44,097
until they finally merge.
394
00:24:44,136 --> 00:24:50,081
♪♪
395
00:24:50,119 --> 00:24:53,152
Sagittarius A-star cannibalizes
its cousin...
396
00:24:58,596 --> 00:25:04,030
creating ripples in the
fabric of the universe itself.
397
00:25:04,066 --> 00:25:07,001
These mergers were fundamental
to making Sagittarius A-star
398
00:25:07,042 --> 00:25:09,312
the monster that we see today.
399
00:25:09,345 --> 00:25:11,833
They happened billions of years
ago, right at the beginning
400
00:25:11,873 --> 00:25:13,215
of Sagittarius A-star's life.
401
00:25:13,249 --> 00:25:17,045
♪♪
402
00:25:17,088 --> 00:25:18,365
More meals follow.
403
00:25:21,406 --> 00:25:25,050
Stars, gas clouds...
404
00:25:25,085 --> 00:25:27,452
Whatever strays too close.
405
00:25:31,100 --> 00:25:35,191
And as our black hole's mass
and influence grows,
406
00:25:35,227 --> 00:25:38,773
its surroundings
are changing, too.
407
00:25:38,810 --> 00:25:42,869
♪♪
408
00:25:45,880 --> 00:25:49,229
The sea of stars and gas
around the black hole
409
00:25:49,272 --> 00:25:52,021
continues to grow...
410
00:25:54,486 --> 00:25:58,795
gradually evolving
into the familiar spiral disk
411
00:25:58,837 --> 00:26:02,731
we call home:
412
00:26:02,771 --> 00:26:06,088
the majestic Milky Way
with the supermassive
413
00:26:06,323 --> 00:26:09,618
Sagittarius A-star at its core.
414
00:26:19,791 --> 00:26:21,221
So when Sagittarius A-star
415
00:26:21,263 --> 00:26:23,336
becomes a supermassive
black hole,
416
00:26:23,374 --> 00:26:26,058
it really comes of age,
and it acquires the ability
417
00:26:26,094 --> 00:26:28,582
to have a transformational
impact
418
00:26:28,622 --> 00:26:31,655
on the evolution
of the entire galaxy.
419
00:26:31,693 --> 00:26:34,278
Black holes are the ultimate
engines in the universe.
420
00:26:34,316 --> 00:26:36,356
When you think about a car,
421
00:26:36,396 --> 00:26:38,152
the first thing
you're interested in is,
422
00:26:38,187 --> 00:26:40,129
how does it work?
423
00:26:40,170 --> 00:26:43,847
You open the hood and you look
at the engine of the car.
424
00:26:43,881 --> 00:26:45,921
With a black hole,
you're asking,
425
00:26:45,960 --> 00:26:49,157
"I want to lift the hood up
on an entire galaxy.
426
00:26:49,192 --> 00:26:52,574
How does a galaxy power itself
at its very heart?"
427
00:26:52,615 --> 00:26:56,925
♪♪
428
00:27:00,741 --> 00:27:02,946
The center of the young galaxy
429
00:27:02,980 --> 00:27:06,777
is rich with swirling gas
and dust:
430
00:27:06,819 --> 00:27:10,081
more offerings to feast on.
431
00:27:15,073 --> 00:27:19,994
♪♪
432
00:27:20,224 --> 00:27:23,802
This is a gluttonous period,
433
00:27:23,839 --> 00:27:27,897
a new era for
Sagittarius A-star...
434
00:27:30,781 --> 00:27:36,051
when the invisible giant has
the power to sculpt the galaxy.
435
00:27:36,092 --> 00:27:39,889
♪♪
436
00:27:42,298 --> 00:27:44,884
As Sagittarius A-star
is gorging on food,
437
00:27:44,922 --> 00:27:47,224
the food that
it's waiting to eat
438
00:27:47,257 --> 00:27:50,105
is swirling around the
central supermassive black hole
439
00:27:50,137 --> 00:27:53,879
in this violent, energetic disk,
440
00:27:53,911 --> 00:27:59,345
and the matter is ripped apart
by the gravity,
441
00:27:59,574 --> 00:28:01,614
which causes the protons
and electrons to then make
442
00:28:01,654 --> 00:28:04,501
these twisted
magnetic field lines.
443
00:28:04,533 --> 00:28:05,917
Everything is rotating and
orbiting,
444
00:28:05,940 --> 00:28:08,330
so at the center
of this black hole,
445
00:28:08,372 --> 00:28:09,714
this accretion disk,
446
00:28:09,748 --> 00:28:12,650
you have
a twisted magnetic field,
447
00:28:12,690 --> 00:28:14,600
almost like a tornado.
448
00:28:14,642 --> 00:28:16,105
Right before material
449
00:28:16,146 --> 00:28:18,863
approaches that event horizon...
That,
450
00:28:18,897 --> 00:28:21,264
that eternal prison,
if you will...
451
00:28:21,297 --> 00:28:25,606
It can be redirected instead.
452
00:28:25,648 --> 00:28:27,032
And from the blazing tumult,
453
00:28:27,055 --> 00:28:29,903
the super-heated material
454
00:28:29,934 --> 00:28:32,204
is thrown out
along the magnetic poles...
455
00:28:34,541 --> 00:28:41,000
two high-powered jets
launched out into the cosmos.
456
00:28:41,035 --> 00:28:42,804
They can reach hundreds of
thousands of light-years
457
00:28:42,827 --> 00:28:43,863
from the black hole itself.
458
00:28:47,914 --> 00:28:50,980
It's only recently
that we've begun to grasp
459
00:28:51,017 --> 00:28:55,807
the huge influence of
Sagittarius A-star on our galaxy
460
00:28:55,848 --> 00:28:58,663
and the role that those
super-powered jets
461
00:28:58,695 --> 00:29:00,190
may have played.
462
00:29:00,230 --> 00:29:01,954
Engines start.
463
00:29:01,990 --> 00:29:04,543
One, zero, lift-off.
464
00:29:08,932 --> 00:29:13,024
The Delta rocket carrying
a gamma ray telescope
465
00:29:13,059 --> 00:29:16,769
searching for unseen physics
in the stars of the galaxies.
466
00:29:19,361 --> 00:29:23,638
♪♪
467
00:29:26,080 --> 00:29:29,341
Just over a decade ago,
468
00:29:29,375 --> 00:29:34,808
astronomers made a completely
unexpected discovery.
469
00:29:34,846 --> 00:29:36,505
It was
this whole piece of our galaxy
470
00:29:36,541 --> 00:29:39,443
that we never knew
was there before.
471
00:29:39,485 --> 00:29:41,594
It would be like finding
a brand-new continent on Earth.
472
00:29:46,490 --> 00:29:50,997
The Fermi space telescope was
built to detect gamma rays,
473
00:29:51,033 --> 00:29:55,310
the most energetic radiation
in the universe.
474
00:29:55,353 --> 00:29:57,720
Fermi is roughly
100 times as sensitive
475
00:29:57,752 --> 00:29:59,661
as previous
gamma ray telescopes.
476
00:29:59,704 --> 00:30:01,679
So it has the sensitivity
477
00:30:01,719 --> 00:30:06,508
to see things that we
just simply couldn't see before.
478
00:30:06,549 --> 00:30:10,641
Orbiting the Earth
once every 96 minutes,
479
00:30:10,677 --> 00:30:14,474
Fermi constructs
a map of the cosmos
480
00:30:14,516 --> 00:30:18,313
and uncovers
an invisible landscape...
481
00:30:18,355 --> 00:30:21,355
The most energetic regions
of the galaxy
482
00:30:21,394 --> 00:30:25,616
highlighted across the sky.
483
00:30:25,649 --> 00:30:27,471
So we pointed
the Fermi telescope
484
00:30:27,504 --> 00:30:30,504
towards our very own
supermassive black hole,
485
00:30:30,543 --> 00:30:33,805
and we had a picture of what
that area sort of looked like...
486
00:30:33,839 --> 00:30:34,821
In our minds, at least.
487
00:30:35,054 --> 00:30:38,055
But then Fermi
revealed something
488
00:30:38,094 --> 00:30:40,461
completely astonishing
and unexpected.
489
00:30:43,180 --> 00:30:46,247
Emerging from the plane of
the Milky Way
490
00:30:46,284 --> 00:30:50,081
are two enormous bubbles,
491
00:30:50,123 --> 00:30:56,232
each one stretching
25,000 light-years,
492
00:30:56,265 --> 00:30:59,614
together reaching
half the width of the galaxy.
493
00:31:03,048 --> 00:31:04,528
If you could see in gamma rays,
494
00:31:04,551 --> 00:31:05,958
the Fermi bubbles would be about
495
00:31:05,991 --> 00:31:07,966
the biggest thing
you see on the sky.
496
00:31:08,006 --> 00:31:10,146
They look like huge dumbbells
497
00:31:10,182 --> 00:31:11,524
going straight up
and straight back
498
00:31:11,557 --> 00:31:16,346
from the center of
the black hole.
499
00:31:16,388 --> 00:31:19,705
The bubbles match the imprint
scientists expect
500
00:31:19,747 --> 00:31:22,747
an enormous eruption
from Sagittarius A-star
501
00:31:22,786 --> 00:31:27,390
to leave on the galaxy.
502
00:31:27,425 --> 00:31:30,425
We had had some clues that
the Milky Way might have had
503
00:31:30,464 --> 00:31:33,334
a more energetic
and active past,
504
00:31:33,375 --> 00:31:35,863
but the incredible thing about
the Fermi bubbles
505
00:31:35,903 --> 00:31:39,580
was that they suddenly gave us
concrete evidence
506
00:31:39,614 --> 00:31:42,265
that the Milky Way
was much more energetic
507
00:31:42,302 --> 00:31:44,724
at some time in its history.
508
00:31:55,802 --> 00:32:01,016
♪♪
509
00:32:01,049 --> 00:32:04,432
When our black hole gorges,
510
00:32:04,472 --> 00:32:09,141
it unleashes a towering inferno
of super-heated matter.
511
00:32:13,589 --> 00:32:15,019
A supermassive black hole
512
00:32:15,061 --> 00:32:17,396
can impart something
like a trillion,
513
00:32:17,428 --> 00:32:19,665
trillion atomic bombs'
per second
514
00:32:19,700 --> 00:32:21,871
worth of energy.
515
00:32:21,908 --> 00:32:24,047
If we were to be
in the line of fire
516
00:32:24,083 --> 00:32:26,156
of one of those jets,
517
00:32:26,386 --> 00:32:27,118
it would be catastrophic for us.
518
00:32:27,346 --> 00:32:29,735
We'd be vaporized.
519
00:32:29,777 --> 00:32:34,512
♪♪
520
00:32:44,653 --> 00:32:46,694
Every planet in the jet's path
521
00:32:46,733 --> 00:32:49,483
could have its atmosphere
stripped away.
522
00:32:55,435 --> 00:32:59,745
♪♪
523
00:33:10,279 --> 00:33:11,506
But further out in the galaxy...
524
00:33:16,549 --> 00:33:20,292
these violent outbursts from
Sagittarius A-star
525
00:33:20,324 --> 00:33:23,740
may have played
a surprising role.
526
00:33:37,696 --> 00:33:42,714
Because the hot gas displaced by
the supermassive black hole
527
00:33:42,751 --> 00:33:47,507
has a calming effect
on the galaxy that hosts it.
528
00:33:47,549 --> 00:33:49,011
In order for stars to form,
529
00:33:49,053 --> 00:33:52,980
you need
very cold and very dense gas,
530
00:33:53,020 --> 00:33:55,737
because stars form through
the collapse of material.
531
00:33:55,771 --> 00:33:58,673
So, instead, if you have
532
00:33:58,715 --> 00:34:01,432
something like
a supermassive black hole
533
00:34:01,466 --> 00:34:04,052
that is sending out
these hot jets
534
00:34:04,281 --> 00:34:06,256
into the galaxy around it,
535
00:34:06,297 --> 00:34:09,166
those jets are going to
heat up the gas.
536
00:34:09,208 --> 00:34:11,696
Now the gas is
no longer cold enough
537
00:34:11,735 --> 00:34:13,197
to collapse
and then form a star.
538
00:34:15,990 --> 00:34:18,357
There's a symbiotic relationship
539
00:34:18,390 --> 00:34:20,278
between the supermassive
black hole at the center
540
00:34:20,309 --> 00:34:23,212
and its host galaxy.
541
00:34:23,252 --> 00:34:25,554
And this relationship determines
542
00:34:25,588 --> 00:34:28,271
the rate at which stars form,
planets form,
543
00:34:28,307 --> 00:34:30,827
and ultimately, in some sense,
544
00:34:30,867 --> 00:34:32,329
why we are here.
545
00:34:32,370 --> 00:34:36,680
♪♪
546
00:34:45,711 --> 00:34:50,413
♪♪
547
00:34:53,453 --> 00:34:55,755
After spending billions of years
548
00:34:55,788 --> 00:35:01,155
consuming the gas, dust,
and stars around it,
549
00:35:01,195 --> 00:35:03,562
there is little left
to feast on.
550
00:35:08,712 --> 00:35:11,713
Our black hole falls dormant.
551
00:35:14,631 --> 00:35:20,741
Today, the Milky Way
has entered an era of calm
552
00:35:20,774 --> 00:35:25,411
and Sagittarius A-star
is a sleeping giant,
553
00:35:25,444 --> 00:35:29,274
the enormous bubbles spotted by
the Fermi telescope
554
00:35:29,316 --> 00:35:32,764
echoes of a lively past.
555
00:35:32,803 --> 00:35:34,028
You never want to assume that
556
00:35:34,051 --> 00:35:36,539
you live at a special time
in the history of the universe.
557
00:35:36,578 --> 00:35:39,545
But it is kind of a special time
558
00:35:39,585 --> 00:35:41,789
that, right now,
the black hole is very quiet,
559
00:35:41,825 --> 00:35:43,254
and it must have been
much more active
560
00:35:43,296 --> 00:35:46,558
a few million years ago.
561
00:35:51,454 --> 00:35:53,461
As our understanding has grown,
562
00:35:53,693 --> 00:35:57,239
our picture of black holes
has transformed,
563
00:35:57,276 --> 00:36:01,368
no longer sinister monsters,
564
00:36:01,403 --> 00:36:03,825
but agents of
change and creation.
565
00:36:03,867 --> 00:36:07,664
Sculptors of the cosmos.
566
00:36:07,706 --> 00:36:08,722
We are far from
567
00:36:08,762 --> 00:36:11,250
unlocking all the secrets
568
00:36:11,289 --> 00:36:13,908
of our galaxy's
supermassive black hole.
569
00:36:13,944 --> 00:36:16,497
And in fact,
the stuff that remains
570
00:36:16,728 --> 00:36:18,801
is probably
the most interesting:
571
00:36:18,839 --> 00:36:22,254
what happens inside
a supermassive black hole
572
00:36:22,486 --> 00:36:24,941
and at its event horizon.
573
00:36:30,772 --> 00:36:34,601
Black holes challenge
the most basic principle
574
00:36:34,643 --> 00:36:37,938
about the predictability of
the universe
575
00:36:37,970 --> 00:36:40,424
and the certainty of history.
576
00:36:40,465 --> 00:36:43,662
♪♪
577
00:36:43,697 --> 00:36:47,112
Nothing could get out of
a black hole.
578
00:36:47,152 --> 00:36:48,811
Or so it was thought.
579
00:36:54,318 --> 00:36:55,726
Black holes are where
580
00:36:55,757 --> 00:37:01,954
two of our greatest theories
collide and clash.
581
00:37:01,996 --> 00:37:04,866
So you've got these two
primal forces in the universe:
582
00:37:04,907 --> 00:37:08,802
gravity, which we all understand
and feel with our bones.
583
00:37:08,842 --> 00:37:10,631
And then you've got
quantum mechanics,
584
00:37:10,666 --> 00:37:13,982
which governs
the theory of the ultra-small,
585
00:37:14,025 --> 00:37:15,782
how atoms
and nuclei come together.
586
00:37:15,816 --> 00:37:18,151
The black hole
587
00:37:18,184 --> 00:37:22,111
is where gravity and
quantum mechanics finally meet.
588
00:37:22,151 --> 00:37:25,135
SYLVESTER JAMES GATES, JR.:
When we try to take the
mathematics of the very large
589
00:37:25,158 --> 00:37:26,882
and try to combine that with
590
00:37:26,917 --> 00:37:28,706
the mathematics of
the very small,
591
00:37:28,741 --> 00:37:31,262
instead of matching...
592
00:37:31,301 --> 00:37:32,992
They get into a fight.
593
00:37:33,029 --> 00:37:35,931
And so we don't have a
consistent way to describe both.
594
00:37:39,042 --> 00:37:41,759
We can begin to probe
this deep mystery
595
00:37:41,794 --> 00:37:45,438
by investigating the heart of
Sagittarius A-star.
596
00:37:50,112 --> 00:37:55,774
Scientists have studied
dozens of stars in its orbit,
597
00:37:55,807 --> 00:37:59,123
some passing just
a few billion miles
598
00:37:59,165 --> 00:38:02,330
from the event horizon,
599
00:38:02,365 --> 00:38:06,675
a hair's width
on galactic scales.
600
00:38:06,716 --> 00:38:10,360
And these fly-bys could have
catastrophic consequences...
601
00:38:17,688 --> 00:38:20,110
♪♪
602
00:38:20,153 --> 00:38:24,462
Because some of these stars
likely have planets in orbit.
603
00:38:28,246 --> 00:38:32,785
Planets that
may stray too close.
604
00:38:33,013 --> 00:38:35,402
Moths to a flame.
605
00:38:40,435 --> 00:38:43,119
Pulled from their parent stars
606
00:38:43,154 --> 00:38:46,220
towards the abyss.
607
00:38:46,450 --> 00:38:48,686
So imagine you're some
alien civilization
608
00:38:48,721 --> 00:38:51,503
looking up at your lovely
home star, S2, in the sky.
609
00:38:51,536 --> 00:38:55,660
And one day, the thing starts
wandering closer and closer
610
00:38:55,695 --> 00:38:57,670
to what we call
the tidal disruption radius
611
00:38:57,711 --> 00:38:59,140
of Sagittarius A-star,
612
00:38:59,182 --> 00:39:03,786
this four-million-solar-mass
black hole.
613
00:39:03,821 --> 00:39:05,796
If you fell into a black hole,
614
00:39:05,836 --> 00:39:08,739
you'd pass the event horizon,
and actually,
615
00:39:08,780 --> 00:39:11,497
bizarrely, you'd see nothing.
616
00:39:11,531 --> 00:39:16,320
There's no physical barrier,
there's no big line in space
617
00:39:16,362 --> 00:39:20,191
saying
"point of no return."
618
00:39:20,233 --> 00:39:23,080
You would just drift
very casually, gently
619
00:39:23,112 --> 00:39:25,894
across the event horizon.
620
00:39:27,783 --> 00:39:29,671
If we could stand on
621
00:39:29,703 --> 00:39:33,216
such a planet and look outwards,
622
00:39:33,253 --> 00:39:36,636
we'd see something spectacular.
623
00:39:36,677 --> 00:39:43,354
♪♪
624
00:39:43,395 --> 00:39:45,949
You would see a distorted
universe,
625
00:39:45,986 --> 00:39:49,020
and in fact,
you'd see it distorted
626
00:39:49,058 --> 00:39:53,182
in both time and space.
627
00:39:53,216 --> 00:39:55,289
You'd see it playing out
628
00:39:55,328 --> 00:39:59,419
at an amazingly fast speed.
629
00:39:59,455 --> 00:40:01,910
The rest of time would
play out unbelievably fast
630
00:40:01,950 --> 00:40:03,674
in front of your eyes.
631
00:40:03,710 --> 00:40:07,059
♪♪
632
00:40:07,101 --> 00:40:10,679
But eventually,
tidal and gravitational forces
633
00:40:10,908 --> 00:40:13,494
become too strong...
634
00:40:13,531 --> 00:40:17,361
♪♪
635
00:40:17,402 --> 00:40:22,453
Stretching space
and everything in it.
636
00:40:22,489 --> 00:40:24,464
Your feet would be pulled
637
00:40:24,505 --> 00:40:26,360
more strongly by gravity
than your head,
638
00:40:26,392 --> 00:40:30,418
so you'd be stretched out
into a giant string,
639
00:40:30,455 --> 00:40:34,611
and eventually, you'd be
one long string one atom thick.
640
00:40:34,646 --> 00:40:39,283
We call this spaghettification.
641
00:40:39,317 --> 00:40:42,351
Boulders become rocks.
642
00:40:42,580 --> 00:40:44,206
Rocks become sand,
643
00:40:44,243 --> 00:40:46,961
whose very atoms
644
00:40:46,995 --> 00:40:52,330
are then pulled apart.
645
00:40:52,369 --> 00:40:57,071
Gravity and
the quantum world collide.
646
00:40:57,104 --> 00:41:00,519
Ahead, the heart of
the black hole...
647
00:41:00,559 --> 00:41:04,236
The singularity,
648
00:41:04,271 --> 00:41:08,526
where all journeys in terminate.
649
00:41:08,558 --> 00:41:09,718
Our idea of a singularity
650
00:41:09,741 --> 00:41:11,629
is that everything is compressed
651
00:41:11,660 --> 00:41:14,410
beyond what it can be
until it's nothing,
652
00:41:14,444 --> 00:41:16,386
but yet still exists.
653
00:41:16,427 --> 00:41:18,632
That is...
654
00:41:18,667 --> 00:41:21,002
Wow.
655
00:41:34,567 --> 00:41:36,607
♪♪
656
00:41:44,229 --> 00:41:46,204
Over trillions of years,
657
00:41:46,244 --> 00:41:49,506
all the stars around
Sagittarius A-star
658
00:41:49,539 --> 00:41:52,386
will gradually fade
out of existence.
659
00:41:55,586 --> 00:42:00,092
♪♪
660
00:42:04,895 --> 00:42:08,506
Long after the last-ever sun
sets on any planet,
661
00:42:08,542 --> 00:42:10,055
black holes will continue
to roam the universe.
662
00:42:10,078 --> 00:42:13,787
♪♪
663
00:42:17,660 --> 00:42:19,286
The final dark age.
664
00:42:26,329 --> 00:42:27,426
If nothing can ever escape,
665
00:42:27,449 --> 00:42:30,100
if this is some eternal prison,
666
00:42:30,137 --> 00:42:31,249
is that the end of the story?
667
00:42:34,967 --> 00:42:37,040
Perhaps not.
668
00:42:37,079 --> 00:42:40,243
Because scientists
now believe that even
669
00:42:40,278 --> 00:42:42,188
Sagittarius A-star will die.
670
00:42:48,468 --> 00:42:52,395
And its death
will come at the hands of
671
00:42:52,435 --> 00:42:55,533
what might seem an
inconsequential effect
672
00:42:55,570 --> 00:42:58,537
first described
almost five decades ago.
673
00:43:00,816 --> 00:43:01,995
So in 1975,
674
00:43:02,032 --> 00:43:05,709
Stephen Hawking
published this amazing paper
675
00:43:05,744 --> 00:43:10,926
showing that black holes aren't
absolutely, completely black.
676
00:43:10,959 --> 00:43:14,406
They glow very, very faintly.
677
00:43:14,446 --> 00:43:19,050
They have a temperature
associated with them.
678
00:43:19,084 --> 00:43:21,539
And you can write
that temperature
679
00:43:21,579 --> 00:43:27,208
very simply in an equation
680
00:43:27,242 --> 00:43:28,966
that's just beautiful.
681
00:43:29,001 --> 00:43:31,652
It links together so many
different parts of physics.
682
00:43:31,689 --> 00:43:33,544
It's got gravity in it.
683
00:43:33,577 --> 00:43:35,911
It's got the mass
of the black hole in it.
684
00:43:35,944 --> 00:43:37,886
It's got the speed of light.
685
00:43:37,928 --> 00:43:40,710
It's got constants relating to
atomic physics,
686
00:43:40,743 --> 00:43:42,237
the microworld.
687
00:43:42,279 --> 00:43:45,890
And it's putting
all of these together
688
00:43:45,925 --> 00:43:48,031
and giving us a temperature.
689
00:43:48,069 --> 00:43:51,200
Hawking's equation
has huge implications
690
00:43:51,236 --> 00:43:53,570
for the future
of the black hole.
691
00:43:53,603 --> 00:43:56,025
So if something
has a temperature,
692
00:43:56,067 --> 00:43:58,140
it's glowing, it's radiating.
693
00:43:58,370 --> 00:43:59,627
Like when you put your hand
close to a fire,
694
00:43:59,650 --> 00:44:00,992
you can feel it.
695
00:44:01,025 --> 00:44:03,840
And that losing energy,
696
00:44:03,873 --> 00:44:06,775
for a black hole like
Sagittarius A-star,
697
00:44:07,008 --> 00:44:09,594
over timescales
that are hugely long,
698
00:44:09,631 --> 00:44:13,886
it's going to evaporate away.
699
00:44:13,918 --> 00:44:16,340
It's going to disappear.
700
00:44:16,381 --> 00:44:20,505
♪♪
701
00:44:30,042 --> 00:44:31,668
Very gradually,
702
00:44:31,706 --> 00:44:34,008
this Hawking radiation
703
00:44:34,041 --> 00:44:39,889
will erode away
Sagittarius A-star
704
00:44:39,927 --> 00:44:43,986
until, many trillions
and trillions of years
705
00:44:44,022 --> 00:44:45,811
into the future...
706
00:44:53,108 --> 00:44:55,497
in a final burst of light...
707
00:45:00,819 --> 00:45:06,666
our black hole will disappear.
708
00:45:06,705 --> 00:45:09,607
And then the Milky Way
will be completely dark
709
00:45:09,648 --> 00:45:12,267
for all eternity.
710
00:45:15,759 --> 00:45:17,133
So why does it matter
711
00:45:17,166 --> 00:45:18,727
if these black holes
disintegrate
712
00:45:18,765 --> 00:45:21,995
in the far distant future?
713
00:45:22,029 --> 00:45:25,804
Well, the discovery of
Hawking radiation
714
00:45:25,835 --> 00:45:28,869
raised some
profound questions in physics.
715
00:45:28,907 --> 00:45:31,690
If I was to set fire
to this piece of paper
716
00:45:31,722 --> 00:45:34,112
with Stephen Hawking's equation
written on it...
717
00:45:37,385 --> 00:45:39,840
what happens to all that
information as it burns away,
718
00:45:39,880 --> 00:45:42,269
as it radiates away?
719
00:45:42,311 --> 00:45:47,548
Do we lose it
from the universe forever?
720
00:46:00,003 --> 00:46:05,054
Maybe if I could sweep up
all the ash,
721
00:46:05,090 --> 00:46:08,570
if I could find all the photons
722
00:46:08,609 --> 00:46:12,057
and reconstruct them,
723
00:46:12,096 --> 00:46:16,188
maybe I could reconstruct
that piece of paper,
724
00:46:16,223 --> 00:46:20,500
even the equation written on it.
725
00:46:20,542 --> 00:46:23,444
So does this also apply to
black holes?
726
00:46:23,485 --> 00:46:26,333
What happened to
all the information
727
00:46:26,364 --> 00:46:28,601
contained on all the material
728
00:46:28,636 --> 00:46:30,709
that ever fell into
a black hole?
729
00:46:30,747 --> 00:46:35,220
And as a black hole evaporates,
what happens to it?
730
00:46:42,009 --> 00:46:46,711
Black holes ain't as black
as they are painted.
731
00:46:46,744 --> 00:46:49,940
They are not the eternal prisons
they were once thought.
732
00:46:54,645 --> 00:46:59,282
So if you feel you are in
a black hole, don't give up.
733
00:47:03,251 --> 00:47:05,586
There's a way out.
734
00:47:12,593 --> 00:47:16,335
If information somehow escapes
from Sagittarius A-star
735
00:47:16,368 --> 00:47:18,539
as it evaporates away,
736
00:47:18,576 --> 00:47:22,885
the implication is profound.
737
00:47:22,926 --> 00:47:25,992
Scientists now believe
that every star,
738
00:47:26,029 --> 00:47:27,972
asteroid,
739
00:47:28,013 --> 00:47:29,770
planet...
740
00:47:29,804 --> 00:47:33,830
Everything that ever fell into
Sagittarius A-star...
741
00:47:33,867 --> 00:47:36,835
May live on,
742
00:47:36,874 --> 00:47:39,296
every aspect and position
743
00:47:39,338 --> 00:47:43,910
of every particle
encoded as information.
744
00:47:46,409 --> 00:47:48,416
All that you would
theoretically need
745
00:47:48,456 --> 00:47:51,107
to put the whole back together.
746
00:47:53,766 --> 00:47:56,385
So the memory of
every single thing
747
00:47:56,421 --> 00:47:58,396
that's "fallen into,"
become part of,
748
00:47:58,437 --> 00:47:59,566
Sagittarius A-star
in the Milky Way
749
00:47:59,589 --> 00:48:00,800
hasn't been lost.
750
00:48:00,837 --> 00:48:02,397
It's still there.
751
00:48:02,436 --> 00:48:05,600
It's just that
we can't access that now.
752
00:48:05,635 --> 00:48:10,010
But maybe we might be able
to read the ashes of that memory
753
00:48:10,051 --> 00:48:13,367
in the far future of
the universe.
754
00:48:13,409 --> 00:48:18,559
But how can anything escape
a black hole's grip?
755
00:48:18,592 --> 00:48:20,479
The defining fact of
a black hole
756
00:48:20,511 --> 00:48:22,454
is that nothing
should be able to get out.
757
00:48:22,495 --> 00:48:25,430
And yet when you look at
Hawking radiation,
758
00:48:25,470 --> 00:48:28,405
it seems to be suggesting
that quantum physics
759
00:48:28,445 --> 00:48:32,187
does connect up the inside
back to the outside.
760
00:48:32,221 --> 00:48:37,305
We just don't really know how.
761
00:48:37,339 --> 00:48:39,827
Black holes force us to
762
00:48:39,866 --> 00:48:45,616
consider nature in entirely new
and mind-bending ways.
763
00:48:45,657 --> 00:48:48,407
People aren't at all certain
about the resolution
764
00:48:48,441 --> 00:48:51,605
to what happens when we
throw things into black holes,
765
00:48:51,639 --> 00:48:52,768
as far as where
the information goes.
766
00:48:52,791 --> 00:48:54,318
It's still an open question.
767
00:48:54,359 --> 00:48:57,042
Maybe it gets sent to
a portal to another dimension,
768
00:48:57,079 --> 00:48:59,501
maybe it gets pumped
into some other branch
769
00:48:59,734 --> 00:49:02,352
of a larger multiverse.
770
00:49:02,388 --> 00:49:04,593
Some people imagine that
black holes are really
771
00:49:04,628 --> 00:49:08,425
just a kind of quantum fuzz,
a fuzzball.
772
00:49:08,467 --> 00:49:10,332
Some people think that
all the information
773
00:49:10,355 --> 00:49:11,419
that fell into the black hole
774
00:49:11,442 --> 00:49:12,687
is somehow encoded on
its surface
775
00:49:12,722 --> 00:49:15,537
in a hologram.
776
00:49:15,570 --> 00:49:18,320
But we're not really privy to
any of this information.
777
00:49:18,352 --> 00:49:20,117
And if we want to find out,
we'd have to go in.
778
00:49:22,895 --> 00:49:24,805
Whatever the solution
proves to be,
779
00:49:24,847 --> 00:49:26,888
it will have ramifications
780
00:49:26,927 --> 00:49:30,539
far beyond
the black hole itself.
781
00:49:30,573 --> 00:49:34,021
♪♪
782
00:49:34,060 --> 00:49:38,217
This theory of quantum gravity
that's so elusive right now,
783
00:49:38,251 --> 00:49:40,139
that is what we would need
to describe
784
00:49:40,171 --> 00:49:43,237
what's happening
inside black holes,
785
00:49:43,274 --> 00:49:45,544
could either be
the most exciting development
786
00:49:45,577 --> 00:49:50,334
to happen in the next decade or
maybe even the next century,
787
00:49:50,376 --> 00:49:53,605
or it could be an alarm bell
going off in our heads
788
00:49:53,640 --> 00:49:56,390
that maybe
Einstein's theory of gravity
789
00:49:56,423 --> 00:50:00,449
is not
the final word on gravity.
790
00:50:00,486 --> 00:50:03,203
Solving the mystery of
black holes
791
00:50:03,238 --> 00:50:07,613
may be our best chance to
complete the picture of nature
792
00:50:07,652 --> 00:50:10,881
that has eluded us
for the last century.
793
00:50:10,916 --> 00:50:12,012
So perhaps the important thing
794
00:50:12,035 --> 00:50:14,370
isn't what the answer
turns out to be.
795
00:50:14,594 --> 00:50:16,635
The important thing is
that we will gain
796
00:50:16,674 --> 00:50:18,431
a fuller understanding of
the cosmos
797
00:50:18,465 --> 00:50:19,846
by studying
these remarkable objects.
798
00:50:19,874 --> 00:50:24,445
Studying the universe has
completely changed our universe.
799
00:50:24,480 --> 00:50:28,670
We have to rethink everything
over and over again.
800
00:50:28,703 --> 00:50:30,567
Like, it's almost, like,
tear up the universe we know
801
00:50:30,590 --> 00:50:34,867
and write a new one.
802
00:50:34,909 --> 00:50:36,950
We're still a long way from
803
00:50:36,989 --> 00:50:42,074
fully comprehending
the secrets of black holes,
804
00:50:42,107 --> 00:50:44,050
but we're beginning to
lift the veil.
805
00:50:48,282 --> 00:50:52,243
Far from being
mere cosmic aberrations,
806
00:50:52,281 --> 00:50:56,820
black holes fundamentally
shape our universe.
807
00:50:59,767 --> 00:51:00,767
So it's extraordinary
to think that
808
00:51:00,790 --> 00:51:02,285
we might be
fundamentally connected
809
00:51:02,326 --> 00:51:04,214
to something that
we didn't know existed
810
00:51:04,246 --> 00:51:06,188
for the vast span of
human history.
811
00:51:06,421 --> 00:51:10,480
♪♪
812
00:51:10,516 --> 00:51:12,208
The beautiful thing about
black holes
813
00:51:12,244 --> 00:51:14,187
is that they're such a
rich source of information.
814
00:51:14,227 --> 00:51:17,009
We've learned so much
about the universe
815
00:51:17,043 --> 00:51:18,472
from studying black holes:
816
00:51:18,515 --> 00:51:20,522
space, time,
817
00:51:20,562 --> 00:51:22,253
the very fundamental nature of
reality.
818
00:51:24,369 --> 00:51:26,638
Bit by bit revealing
819
00:51:26,672 --> 00:51:30,895
the deepest mysteries of
the cosmos.
820
00:51:30,927 --> 00:51:34,276
We're in a golden age of
discovery about black holes.
821
00:51:34,318 --> 00:51:36,261
We understand how they merge,
822
00:51:36,301 --> 00:51:38,669
we've discovered
their colossal jets,
823
00:51:38,701 --> 00:51:40,295
and we're beginning to see them
824
00:51:40,333 --> 00:51:43,945
not just as destroyers,
but also as creators
825
00:51:43,979 --> 00:51:46,729
and sculptors.
826
00:51:46,763 --> 00:51:49,665
And all that
is just the beginning.
827
00:51:49,706 --> 00:51:51,714
Our story's happening now,
828
00:51:51,754 --> 00:51:54,656
but black holes,
they're going to outlive us
829
00:51:54,697 --> 00:51:57,283
by trillions of years.
830
00:51:57,320 --> 00:51:59,622
Their story
is just getting started.
62897
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