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In the beginning,
there was darkness...
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and then, bang...
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giving birth to an endless
expanding existence...
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00:00:10,051 --> 00:00:12,594
of time, space, and matter.
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00:00:12,637 --> 00:00:14,888
Now, see further
than we've ever imagined...
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00:00:14,931 --> 00:00:16,807
beyond the limits of our existence...
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00:00:16,850 --> 00:00:19,685
in a place we call "The Universe. "
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It is both mighty and meek.
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Humanity's quest is to harness
its power and escape its bonds.
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Holy cow!
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This is what an astronaut feels.
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It creates and breaks the stars,
the planets, the galaxies...
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00:00:47,756 --> 00:00:50,674
and directs their
cosmic roller coaster ride.
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00:00:52,635 --> 00:00:54,136
Gravity is our friend and our foe.
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00:00:54,179 --> 00:00:58,307
Without it,
life as we know it would end.
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The Earth would literally explode.
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00:01:02,020 --> 00:01:05,355
It is the magnificent
and mystifying force...
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00:01:05,398 --> 00:01:08,609
that rules the universe: Gravity.
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00:01:25,627 --> 00:01:29,088
Gravity is the most pervasive
force in the universe.
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It is at work on massive
and minute scales...
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on the routine and the extreme.
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A surfer needs it to hang ten.
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00:01:44,646 --> 00:01:47,106
When you ride a wave, you're
going to slide down the front...
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and you're going to use
that pull of gravity to get you going.
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It's your acceleration force.
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00:01:51,236 --> 00:01:53,570
It's your accelerator.
Gravity is your accelerator.
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00:01:55,615 --> 00:01:58,408
A skier uses it
to race downhill.
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00:02:00,787 --> 00:02:03,789
A snowboarder must have it
to get big air.
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00:02:05,500 --> 00:02:09,962
It acts on everything with mass,
including us, 24/7...
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00:02:10,004 --> 00:02:13,090
even when sleeping
or standing.
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00:02:14,926 --> 00:02:18,470
Gravity here on Earth, of course,
is always accelerating us down...
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toward the center of the Earth
at 32 feet per second squared.
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At a theme park,
gravity is the galactic gas...
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that makes roller coasters roar
and people scream.
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00:02:34,696 --> 00:02:37,322
The gravity of the Earth
pulls us down...
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00:02:37,365 --> 00:02:39,616
and that's going to make us go
really, really fast.
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00:02:45,999 --> 00:02:48,667
All objects
with mass or energy-
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00:02:48,710 --> 00:02:54,840
particles, people, planets,
stars, and galaxies-
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00:02:54,883 --> 00:02:57,551
produce gravity.
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Omnipotent and omnipresent...
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00:03:00,054 --> 00:03:05,434
gravity attracts, governs,
warps, shapes, makes...
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00:03:05,476 --> 00:03:10,898
and takes all matter and mass
in the universe.
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So it's pervasive.
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00:03:11,983 --> 00:03:16,028
It acts on all things through
extremely large distances...
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00:03:16,070 --> 00:03:18,363
and nothing escapes its pull.
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00:03:19,532 --> 00:03:23,368
It is gravity that holds
our solar system together.
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The force of gravity...
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is basically that thing
that holds us on the planet...
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keeps us from flying off.
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It is the cosmic glue that binds
all matter in the universe together.
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00:03:39,344 --> 00:03:42,137
If you were to imagine
taking two dice...
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and putting them perfectly at rest
out in the middle of space...
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and separating them
by a centimeter...
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00:03:49,437 --> 00:03:52,773
then what you'd see is that
over a course of an hour or so...
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those two dice would slowly
come together and touch.
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00:04:00,240 --> 00:04:03,242
Gravity made our world.
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00:04:03,284 --> 00:04:06,286
Our Sun formed
from a vast cloud of gas...
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00:04:06,329 --> 00:04:08,997
that gravitationally contracted.
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00:04:09,040 --> 00:04:13,085
Similarly, our Earth formed
through the gravitational attraction...
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00:04:13,127 --> 00:04:15,587
of little particles,
little bitty things...
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gradually growing
into a bigger and bigger object.
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00:04:20,760 --> 00:04:23,095
When it comes
to gravity's pulling power...
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mass and distance matter.
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It depends on the masses
of each object...
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the amount of matter
within each object.
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00:04:30,895 --> 00:04:34,273
So it's proportional to
the product of the two masses.
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00:04:35,900 --> 00:04:37,901
In other words, the bigger it is...
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00:04:37,944 --> 00:04:40,237
the harder it pulls
on other objects.
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00:04:41,322 --> 00:04:42,656
But that's not all.
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And it's inversely proportional...
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to the square of the distance
between them.
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00:04:48,579 --> 00:04:52,291
This means if you double the distance
between two objects...
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00:04:52,333 --> 00:04:56,712
the attraction or pull is only
a quarter of its original strength.
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00:04:59,757 --> 00:05:03,510
The pulling power of gravity lets
it direct the motion and movement...
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00:05:03,553 --> 00:05:08,390
of all matter, however massive,
in the universe.
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00:05:08,433 --> 00:05:10,559
So you have whole galaxies,
for example...
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in orbit around each other.
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Clusters of galaxies all orbit
around their common center of mass.
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00:05:26,117 --> 00:05:30,412
But it is the practical potential
of harnessing this relentless force...
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that has obsessed scientists
for centuries.
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It would literally fall to Galileo Galilei,
the 17th-century truth-seeker...
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to first recognize
that gravity even existed.
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00:05:45,720 --> 00:05:49,431
Galileo found that objects
having a different weight...
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fall at the same rate.
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So here's a very heavy steel ball...
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and a light ping-pong ball
of the same size.
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00:05:57,899 --> 00:06:00,192
And if I drop them
at the same time...
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00:06:00,234 --> 00:06:02,986
they hit the ground
at exactly the same time as well...
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00:06:03,029 --> 00:06:05,322
because they fall
at the same rate.
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00:06:09,243 --> 00:06:13,705
To illustrate Galileo's most profound
gravitational discovery...
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00:06:13,748 --> 00:06:18,210
that all objects, regardless of mass,
fall at the same rate...
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00:06:19,837 --> 00:06:23,965
we take a ride on the mega-fast
"Superman: The Escape"...
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at Six Flags Magic Mountain
in Southern California.
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The theme park ride
is the stage...
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for a spectacular
free-fall demonstration.
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It will show what happens
when a car full of people...
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and a tennis ball fall
from 415 feet in the air.
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Okay. Here we go.
All right.
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Oh, my. Oh, my God.
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00:06:55,248 --> 00:06:58,583
The riders are shot up
the 41-story-tall tower...
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at a hundred miles an hour.
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00:07:00,420 --> 00:07:04,965
With their eyes open, gravity
will help them see a superhero.
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00:07:09,095 --> 00:07:10,804
Oh, my God. Okay.
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00:07:10,847 --> 00:07:12,305
I'm going to drop this ball
now and-
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00:07:12,348 --> 00:07:14,057
Oh, my God,
it's floating around!
106
00:07:14,100 --> 00:07:15,725
It's floating!
It's floating!
107
00:07:19,981 --> 00:07:23,483
Oh, the wind blew the ball
away that time.
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00:07:23,526 --> 00:07:28,113
While we expect all objects to fall
freely together, regardless of mass...
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on a windy day,
results aren't always perfect.
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All right. Oh, my God.
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At the very top of the ride,
when upward motion has stopped...
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gravity takes over
and the downward free fall begins.
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I'm going to drop this ball...
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and it's going to float.
It's going to float.
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00:07:51,471 --> 00:07:53,138
Oh, it's floating.
It's floating.
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I'm going to
release this ball now.
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00:08:00,229 --> 00:08:02,522
And then,
for a few blissful seconds...
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theme park thrill-seekers
feel weightless...
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00:08:05,151 --> 00:08:10,530
as if they are free of gravity,
or in what scientists call zero-G.
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00:08:14,452 --> 00:08:17,704
Oh, that one floated well.
That one floated well.
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Oh, I'm going to try
dropping the ball.
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00:08:30,384 --> 00:08:32,636
But zero-G is just an illusion.
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00:08:32,678 --> 00:08:35,013
In reality, gravity is running this ride.
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It's the force that yanks the car,
the people, and the tennis ball...
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indifferent to their mass,
back down to Earth at the same rate.
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Oh, that's a fantastic ride.
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I mean, feeling oneself
drop is amazing.
128
00:08:53,491 --> 00:08:55,992
But what's really great
is dropping the ball...
129
00:08:56,035 --> 00:08:58,662
and seeing it floating
above my face.
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00:08:58,704 --> 00:09:01,206
Now-I mean, it's falling.
I know it's falling...
131
00:09:01,249 --> 00:09:03,416
but I'm falling
at exactly the same rate.
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00:09:03,459 --> 00:09:05,877
It doesn't matter
how massive something is.
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It falls, under the force of gravity,
at exactly the same rate.
134
00:09:13,261 --> 00:09:15,470
Thanks to experiments like this...
135
00:09:15,513 --> 00:09:19,182
we now know that objects
all fall at the same rate.
136
00:09:19,934 --> 00:09:23,645
But what would it take to launch
a cannonball into orbit?
137
00:09:30,861 --> 00:09:33,738
When the famous British
physicist Sir Isaac Newton...
138
00:09:33,781 --> 00:09:37,742
saw the apple fall that,
some say, hit him on the head...
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it changed the world.
140
00:09:40,746 --> 00:09:42,831
You got the apple
falling from the tree...
141
00:09:42,873 --> 00:09:46,543
and he looks up and sees the Moon
in orbit around the Earth...
142
00:09:46,586 --> 00:09:50,255
and judges that not only
is the apple falling to Earth...
143
00:09:50,298 --> 00:09:51,965
so too is the Moon.
144
00:09:56,637 --> 00:09:59,180
But could the Moon
really be falling?
145
00:10:01,183 --> 00:10:02,183
Load!
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00:10:02,977 --> 00:10:07,439
By thinking of a cannon
and the trajectory of the ball it shoots...
147
00:10:07,481 --> 00:10:11,192
Newton used math
to unlock a cosmic mystery.
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00:10:18,492 --> 00:10:24,873
It came in his landmark publication,
"Principia Mathematica," in 1687.
149
00:10:25,875 --> 00:10:27,709
Isaac Newton
has a famous drawing...
150
00:10:27,752 --> 00:10:30,462
and in it, he draws a planet
and a little mountain.
151
00:10:30,504 --> 00:10:32,589
There's a little projectile
first kicked off the mountain...
152
00:10:32,632 --> 00:10:34,215
and it falls down a little bit.
153
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You give it more speed,
it goes a little farther out.
154
00:10:37,345 --> 00:10:39,387
Now say you could just increase
the force all you wanted.
155
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It can go fifty miles,
it can go a hundred miles before it fell.
156
00:10:45,561 --> 00:10:50,148
By adding more gunpowder
and with just the right angle of fire...
157
00:10:50,191 --> 00:10:53,985
a cannonball can be made
to go faster and farther.
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00:10:56,072 --> 00:10:59,115
Inevitably, however, gravity wins...
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00:10:59,158 --> 00:11:03,036
pulling the cannonball
back down to Earth.
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00:11:03,079 --> 00:11:06,831
The Earth is round and not flat,
so Newton realized...
161
00:11:06,874 --> 00:11:11,294
that if the cannonball
is fired at sufficient speed...
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00:11:13,714 --> 00:11:16,049
the cannonball would
actually go into orbit.
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00:11:18,386 --> 00:11:20,637
For that to happen,
Newton determined...
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00:11:20,680 --> 00:11:23,139
the ball would need to be shot
out of the cannon...
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at 17,500 miles an hour.
166
00:11:27,687 --> 00:11:29,104
It starts curving
around the Earth...
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00:11:29,146 --> 00:11:32,273
and he realized
that there must be a speed...
168
00:11:32,316 --> 00:11:35,068
where it goes completely
around the Earth...
169
00:11:35,111 --> 00:11:36,486
and hits you
in the back of the head...
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never actually hitting
Earth's surface.
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00:11:40,074 --> 00:11:42,701
And if you duck,
it'll just keep going...
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00:11:42,743 --> 00:11:45,161
and lo and behold,
you have an orbit.
173
00:11:47,415 --> 00:11:50,083
But why doesn't the Moon
fall to Earth?
174
00:11:50,960 --> 00:11:54,129
The Moon also has
some sideways motion...
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so for every little bit
that it falls down...
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it also moves off
in this direction...
177
00:11:59,677 --> 00:12:05,765
and the sum of all those motions
is an orbit around the Earth.
178
00:12:07,893 --> 00:12:12,605
Newton also realized that the Earth
is in a giant freefall around the Sun.
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00:12:13,566 --> 00:12:16,943
With gravity forging the path,
our planet rounds the Sun...
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00:12:16,986 --> 00:12:20,113
like an endless cosmic
roller coaster ride.
181
00:12:22,491 --> 00:12:24,659
Newton cracked
the gravity code...
182
00:12:24,702 --> 00:12:29,748
and physicists are still using his ideas
to solve all sorts of problems...
183
00:12:33,919 --> 00:12:36,546
some of them
stranger than others...
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00:12:36,589 --> 00:12:40,675
like, what would happen if a person
tried to travel through a tunnel...
185
00:12:40,718 --> 00:12:43,261
from one side of the planet
to the other?
186
00:12:44,722 --> 00:12:46,181
In this wild scheme...
187
00:12:46,223 --> 00:12:48,516
you would have to drive
a straight-line tunnel...
188
00:12:48,559 --> 00:12:53,772
right through the Earth and use
gravity alone to propel a traveler...
189
00:12:53,814 --> 00:12:56,649
down this so-called
gravity express.
190
00:12:58,819 --> 00:13:00,361
So, suppose you've got
one of these tunnels...
191
00:13:00,404 --> 00:13:02,280
and you jump in.
192
00:13:02,323 --> 00:13:04,574
Initially, the Earth is pulling down.
193
00:13:04,617 --> 00:13:06,159
You're going toward
the center of the Earth...
194
00:13:06,202 --> 00:13:08,578
and so you're
accelerating toward it.
195
00:13:08,621 --> 00:13:10,955
But as you pass through
the center of the Earth...
196
00:13:10,998 --> 00:13:14,209
and start going out
toward the opposite side...
197
00:13:14,251 --> 00:13:17,045
the gravity of the Earth
is trying to pull you back...
198
00:13:17,087 --> 00:13:19,047
so it's decelerating you.
199
00:13:21,342 --> 00:13:23,927
So gravity's actually
having a braking effect.
200
00:13:24,637 --> 00:13:26,679
There's no fear
of shooting out the hole...
201
00:13:26,722 --> 00:13:28,890
on the other side of the Earth
at some tremendous velocity...
202
00:13:28,933 --> 00:13:30,725
and shooting yourself
back into space...
203
00:13:30,768 --> 00:13:34,229
but, in fact, you reach the surface
of the Earth exactly.
204
00:13:34,271 --> 00:13:36,231
You would coast
to a perfect rest.
205
00:13:36,273 --> 00:13:38,274
In forty-two minutes, you'd be there.
206
00:13:40,069 --> 00:13:43,154
Whichever two cities you connect
with a straight-line tunnel...
207
00:13:43,197 --> 00:13:46,783
it takes gravity exactly
forty-two minutes to get you there.
208
00:13:46,826 --> 00:13:50,870
The journey from Los Angeles
to Paris, forty-two minutes.
209
00:13:52,248 --> 00:13:54,499
Suppose you wanted to go
from Los Angeles to Tokyo...
210
00:13:54,542 --> 00:13:57,377
forty-two minutes.
211
00:13:57,419 --> 00:13:59,587
It doesn't matter which path
you take through the Earth.
212
00:13:59,630 --> 00:14:02,799
The journey is always
forty-two minutes long.
213
00:14:03,926 --> 00:14:08,263
It takes Newton's math
to figure out why this works.
214
00:14:08,305 --> 00:14:10,348
If we connect
Los Angeles to New York...
215
00:14:10,391 --> 00:14:12,350
digging a tunnel, obviously...
216
00:14:12,393 --> 00:14:13,518
a tunnel would not go
straight down...
217
00:14:13,561 --> 00:14:16,604
but it has to go down
at an angle.
218
00:14:16,647 --> 00:14:20,358
The angle slows
the speed of descent.
219
00:14:20,401 --> 00:14:21,818
But the distance
is also less.
220
00:14:21,861 --> 00:14:23,778
And if you work out
the equations...
221
00:14:23,821 --> 00:14:26,489
lo and behold,
the two effects cancel...
222
00:14:26,532 --> 00:14:28,658
and you still get there
in forty-two minutes.
223
00:14:29,577 --> 00:14:32,537
It takes forty-two minutes
regardless of the path you take.
224
00:14:32,580 --> 00:14:33,746
That's really cool.
225
00:14:37,126 --> 00:14:40,461
Newton figured out
what gravity does...
226
00:14:40,504 --> 00:14:43,464
but it took the brilliance
of physicist Albert Einstein...
227
00:14:43,507 --> 00:14:45,967
to work out why it was doing it.
228
00:14:49,638 --> 00:14:54,225
Einstein realized that gravity
is really caused by huge objects...
229
00:14:54,268 --> 00:14:58,771
like stars and planets,
literally bending space itself.
230
00:14:58,814 --> 00:15:00,982
Like a massive rubber sheet...
231
00:15:01,025 --> 00:15:05,069
space is curved
where massive objects sit in it.
232
00:15:05,112 --> 00:15:09,782
In fact, Einstein proposed that the path
planets take around their stars...
233
00:15:09,825 --> 00:15:14,954
their orbits, are all a direct result
of this curvature of space.
234
00:15:16,498 --> 00:15:17,582
He said that what an orbit is...
235
00:15:17,625 --> 00:15:19,417
is really something
traveling in a straight line.
236
00:15:19,460 --> 00:15:21,753
When something is free-falling
towards another object...
237
00:15:21,795 --> 00:15:24,547
it really is just traveling
in a straight line through space-time.
238
00:15:24,590 --> 00:15:29,761
However, the curvature of space-time
bends its path into a closed orbit...
239
00:15:29,803 --> 00:15:33,097
but space itself
curves it back in on itself.
240
00:15:34,183 --> 00:15:39,646
This revolutionary discovery came
when Einstein, in the early 191 Os...
241
00:15:39,688 --> 00:15:44,108
realized that orbits of stars and planets
in the observable cosmos...
242
00:15:44,151 --> 00:15:47,028
behave just
as Newton's math predicted...
243
00:15:47,071 --> 00:15:49,614
except one: Mercury.
244
00:15:51,617 --> 00:15:54,953
Its orbit essentially wobbles.
245
00:15:54,995 --> 00:15:59,415
Einstein described gravity
as a curvature in space and time...
246
00:15:59,458 --> 00:16:03,670
and the orbit of Mercury works perfectly
when you take that into account.
247
00:16:03,712 --> 00:16:07,632
Mercury isn't moving in flat space,
but curved space around the Sun.
248
00:16:07,675 --> 00:16:09,050
Then the orbit's perfect.
249
00:16:11,345 --> 00:16:15,974
This curvature of space is
at play in our own solar system.
250
00:16:16,016 --> 00:16:20,478
Earth is simply following
what it thinks is a straight-line path...
251
00:16:20,521 --> 00:16:22,397
the shortest distance
between two points...
252
00:16:22,439 --> 00:16:25,608
in this intrinsically
curved space.
253
00:16:27,528 --> 00:16:31,489
Einstein not only determined
that mass warps space...
254
00:16:31,532 --> 00:16:33,199
it warps time, too.
255
00:16:34,034 --> 00:16:36,452
So, henceforth,
Einstein proclaimed...
256
00:16:36,495 --> 00:16:39,998
physicists should not speak
of space and time separately...
257
00:16:40,040 --> 00:16:43,459
but of space-time
as one unified object.
258
00:16:45,087 --> 00:16:47,505
While it's uncomfortable to many
the first time you hear it...
259
00:16:47,548 --> 00:16:50,842
if you stop and think about it,
it's actually quite obvious.
260
00:16:50,884 --> 00:16:52,343
If I'm going to make
an appointment with somebody...
261
00:16:52,386 --> 00:16:55,096
I don't say,
"I'll meet you at 3:00."
262
00:16:55,139 --> 00:16:56,389
That's not enough information.
263
00:16:56,432 --> 00:16:58,307
There's got to be a question
that follows that.
264
00:16:58,350 --> 00:16:59,434
What is that question?
265
00:16:59,476 --> 00:17:00,518
Where?
266
00:17:02,229 --> 00:17:05,815
If I say,
"Meet you in room 203."
267
00:17:07,693 --> 00:17:08,985
When?
268
00:17:09,028 --> 00:17:13,072
Any time you intersect
with someone's else's life...
269
00:17:13,115 --> 00:17:16,284
you do so at a time
and at a place.
270
00:17:17,745 --> 00:17:21,164
Einstein's realization
that space is curved...
271
00:17:21,206 --> 00:17:24,459
and that time and space
are, in fact, intertwined...
272
00:17:24,501 --> 00:17:27,253
is now the very definition
of gravity.
273
00:17:28,630 --> 00:17:31,049
Liftoff of
the Space Shuttle "Discovery. "
274
00:17:31,091 --> 00:17:33,217
Unlocking the secrets of gravity...
275
00:17:33,260 --> 00:17:37,096
has enabled humanity to escape
our earthly shackles...
276
00:17:37,139 --> 00:17:40,016
and opened the universe
for exploration.
277
00:17:41,769 --> 00:17:45,021
But how can future astronauts
on the long way to Mars...
278
00:17:45,064 --> 00:17:48,941
survive the disabling effects
caused by zero-G?
279
00:17:59,953 --> 00:18:01,662
Gravity is our friend...
280
00:18:03,415 --> 00:18:04,957
and our foe.
281
00:18:07,211 --> 00:18:10,546
It is the fearsome force
that propels a skier...
282
00:18:10,589 --> 00:18:13,466
and the snowboarder
down the mountain...
283
00:18:13,509 --> 00:18:15,510
and shoots them into the air.
284
00:18:16,804 --> 00:18:19,639
With enough momentum,
an airborne snowboarder...
285
00:18:19,681 --> 00:18:22,225
can feel for fleeting moments...
286
00:18:22,267 --> 00:18:26,104
as if they are free
of Earth's gravitational pull.
287
00:18:26,146 --> 00:18:29,607
You're actually weightless
when you go off the jump.
288
00:18:29,650 --> 00:18:32,443
The period of weightlessness
is determined...
289
00:18:32,486 --> 00:18:37,240
by the duration of your trajectory
as a function of your velocity...
290
00:18:37,282 --> 00:18:40,409
so that the snowboarder
who gets really good big air...
291
00:18:40,452 --> 00:18:45,581
may achieve a second, two seconds,
even three seconds of weightlessness.
292
00:18:48,669 --> 00:18:51,087
But in the end, gravity wins...
293
00:18:51,130 --> 00:18:53,965
and the high-flying,
free-falling boarder...
294
00:18:54,007 --> 00:18:56,592
just like the ball
fired from the cannon...
295
00:18:56,635 --> 00:18:59,846
is eventually yanked
back down to Earth.
296
00:18:59,888 --> 00:19:02,014
This free fall
for the snowboarder...
297
00:19:02,057 --> 00:19:04,100
as he or she goes
over the jump...
298
00:19:04,143 --> 00:19:07,353
and creates this trajectory
is just as much free fall...
299
00:19:07,396 --> 00:19:09,188
as a cannonball
going through the air...
300
00:19:09,231 --> 00:19:11,482
and the trajectory
is determined...
301
00:19:11,525 --> 00:19:14,610
only by the velocity
and the force of gravity.
302
00:19:14,653 --> 00:19:17,613
Then, of course, what happens
on the landing is another story.
303
00:19:21,702 --> 00:19:23,536
But what if a snowboarder...
304
00:19:23,579 --> 00:19:25,913
aspired to reach
even greater heights?
305
00:19:26,748 --> 00:19:29,000
What if he wanted
to overcome gravity...
306
00:19:29,042 --> 00:19:32,003
and launch himself
right off the planet?
307
00:19:32,045 --> 00:19:34,172
You want to leave Earth
entirely and forever?
308
00:19:34,214 --> 00:19:37,175
Earth has what we call
the escape velocity...
309
00:19:37,217 --> 00:19:39,677
this magic speed
where if you pass that speed...
310
00:19:39,720 --> 00:19:44,223
you will escape Earth forever,
never to return.
311
00:19:46,101 --> 00:19:50,313
Escape velocity, the minimum speed
any object needs to reach...
312
00:19:50,355 --> 00:19:52,481
in order to escape
from the Earth...
313
00:19:52,524 --> 00:19:54,859
is about seven miles a second.
314
00:19:54,902 --> 00:19:57,945
That's 25,000 miles an hour.
315
00:20:00,407 --> 00:20:02,825
In theory, even a snowboarder...
316
00:20:02,868 --> 00:20:06,412
with enough momentum
and aimed in the right direction...
317
00:20:06,455 --> 00:20:08,748
can take offjust like a rocket.
318
00:20:13,253 --> 00:20:17,840
Escaping Earth's gravity may
not be realistic for a snowboarder...
319
00:20:17,883 --> 00:20:23,387
but it has proven possible to launch
people and projectiles into orbit.
320
00:20:23,430 --> 00:20:24,805
You can leave systems.
321
00:20:24,848 --> 00:20:27,099
You just need
enough energy to do so.
322
00:20:27,142 --> 00:20:30,728
And we've garnered enough energy
and technological know-how...
323
00:20:30,771 --> 00:20:33,481
to do just that
in our voyages to the Moon.
324
00:20:33,523 --> 00:20:36,609
And our hope is that that will
continue on to Mars and beyond.
325
00:20:38,362 --> 00:20:40,488
To get to Mars and beyond...
326
00:20:40,530 --> 00:20:43,366
mankind will have to harness
gravity's energy...
327
00:20:45,577 --> 00:20:49,580
just like we always do when
we're seeking thrills to the extreme.
328
00:20:52,084 --> 00:20:54,418
Gravity gives us
two types of energy...
329
00:20:56,630 --> 00:20:58,005
potential...
330
00:21:00,133 --> 00:21:01,300
and kinetic.
331
00:21:05,514 --> 00:21:07,598
Potential is just that.
332
00:21:07,641 --> 00:21:10,226
It is energy that's being stored...
333
00:21:10,269 --> 00:21:14,772
while kinetic is the result
of all that pent-up potential energy.
334
00:21:17,651 --> 00:21:21,487
This fantastic phenomenon
works on a roller coaster.
335
00:21:21,530 --> 00:21:24,824
As you're winched up on a hill,
your potential energy is increasing.
336
00:21:24,866 --> 00:21:26,951
You literally have more energy...
337
00:21:26,994 --> 00:21:28,494
at the top of the roller coaster
than at the bottom.
338
00:21:28,537 --> 00:21:30,997
It's not just a weird,
abstract thing.
339
00:21:31,039 --> 00:21:33,582
You actually possess
higher energy at the top...
340
00:21:33,625 --> 00:21:36,502
and that's turned into speed,
into kinetic energy...
341
00:21:36,545 --> 00:21:38,963
as you go down that hill
on the roller coaster.
342
00:21:40,257 --> 00:21:45,469
Pretty soon, I'll be converting
my potential energy to kinetic energy.
343
00:21:49,891 --> 00:21:53,185
When a surfer hits
that sweet spot on a wave...
344
00:21:53,228 --> 00:21:55,896
they're using
energy's double act.
345
00:21:59,109 --> 00:22:02,069
NASA also uses
this energy exchange principle...
346
00:22:02,112 --> 00:22:04,322
to add some speed
to their missions.
347
00:22:05,615 --> 00:22:08,659
As a spacecraft
nears the orbit of a planet...
348
00:22:08,702 --> 00:22:14,415
it, too, gathers kinetic energy
at the expense of potential energy.
349
00:22:14,458 --> 00:22:18,336
Then as it rounds the planet
on its cosmic coaster ride...
350
00:22:18,378 --> 00:22:20,296
the craft gets a slingshot effect...
351
00:22:20,339 --> 00:22:24,175
that punches it onward
with more kinetic energy.
352
00:22:25,385 --> 00:22:31,265
When the Voyager spacecraft
visited Jupiter in 1979, 1980...
353
00:22:31,308 --> 00:22:35,269
it flew past Jupiter,
and Jupiter tugged on it...
354
00:22:35,312 --> 00:22:39,857
giving it extra motion,
sort of a slingshot effect...
355
00:22:39,900 --> 00:22:42,026
not only changing
its direction of motion...
356
00:22:42,069 --> 00:22:44,695
so that it was aimed
towards Saturn...
357
00:22:44,738 --> 00:22:46,364
but also speeding it up.
358
00:22:48,283 --> 00:22:50,826
Knowing how to use
the power of gravity...
359
00:22:50,869 --> 00:22:55,623
will enable humanity to travel
further and faster across the universe.
360
00:22:58,543 --> 00:23:01,879
Having the physics formulated
and the technology available...
361
00:23:01,922 --> 00:23:06,384
is just one part of the preparation
for extraterrestrial travel.
362
00:23:06,426 --> 00:23:11,097
Readying people for the rigors
of space is the other.
363
00:23:13,100 --> 00:23:16,060
Far away from Earth's
gravitational pull...
364
00:23:16,103 --> 00:23:19,480
in a spaceship on the long
journey to Mars, for example...
365
00:23:19,523 --> 00:23:24,235
future astronauts will have to
learn to live, work, and play...
366
00:23:24,277 --> 00:23:28,155
in an environment free
of Earth's sizeable gravity...
367
00:23:28,198 --> 00:23:31,200
one where they
effectively feel weightless...
368
00:23:31,243 --> 00:23:34,578
and all objects
move equally and freely.
369
00:23:37,749 --> 00:23:39,583
One fun way to experience...
370
00:23:39,626 --> 00:23:42,962
the astronautical thrills
and spills of space travel...
371
00:23:43,004 --> 00:23:46,006
is to simulate it
on a zero-G flight.
372
00:23:46,049 --> 00:23:47,591
I'm really looking forward to this.
373
00:23:47,634 --> 00:23:49,635
This is going to be
an incredible experience.
374
00:23:50,220 --> 00:23:52,721
By riding the ultimate
roller coaster...
375
00:23:52,764 --> 00:23:57,268
a specially modified
zero-G Boeing 727 aircraft...
376
00:23:57,310 --> 00:24:03,983
astrophysicist Alex Filippenko
is about to go on the ride of his life.
377
00:24:04,025 --> 00:24:06,277
This is going to be like a ball
thrown up in the air...
378
00:24:06,319 --> 00:24:09,947
weightless because it will be
in free fall...
379
00:24:09,990 --> 00:24:15,244
so I'll be floating around as though
there's no ground holding me up.
380
00:24:17,456 --> 00:24:22,626
The zero-G flight flies between
24,000 and 32,000 feet.
381
00:24:22,669 --> 00:24:26,964
This is about the same altitude
as a regular commercial jet...
382
00:24:27,007 --> 00:24:29,800
but that is where
the similarity ends.
383
00:24:29,843 --> 00:24:31,218
The water's the next one?
384
00:24:31,261 --> 00:24:35,806
The path it follows is a series
of coaster-like rolling hills...
385
00:24:35,849 --> 00:24:37,349
in the stratosphere.
386
00:24:37,392 --> 00:24:40,144
Just like "Superman: The Ride"...
387
00:24:40,187 --> 00:24:43,772
the super zero-G plane
gathers potential energy...
388
00:24:43,815 --> 00:24:46,400
as it climbs up at forty-five degrees.
389
00:24:47,402 --> 00:24:49,904
Passengers feel this
as an increase in weight.
390
00:24:49,946 --> 00:24:50,946
Oh, yeah.
391
00:24:50,989 --> 00:24:54,783
Gravity is measured
in terms of g-forces.
392
00:24:54,826 --> 00:24:57,286
One G is the amount
of gravity we feel...
393
00:24:57,329 --> 00:24:59,079
standing on the surface
of the Earth.
394
00:24:59,122 --> 00:25:02,625
I'm going to get back down
like this and get ready.
395
00:25:02,667 --> 00:25:06,128
As the plane steeply climbs,
accelerating upward...
396
00:25:06,171 --> 00:25:09,548
the gravity G count rises
and people feel heavier.
397
00:25:09,591 --> 00:25:10,591
All right.
398
00:25:12,344 --> 00:25:14,803
The plane
is accelerating us upwards...
399
00:25:14,846 --> 00:25:18,933
at about 1.8 G at its maximum.
400
00:25:20,477 --> 00:25:24,355
As the flight approaches, then eases
around the apex of the arc...
401
00:25:24,397 --> 00:25:27,233
the plane, as well
as all the people inside it...
402
00:25:27,275 --> 00:25:29,568
are, in effect, in free fall.
403
00:25:32,614 --> 00:25:34,198
Zero-G comin' up.
404
00:25:34,241 --> 00:25:39,745
Oh, man,
what an indescribable feeling.
405
00:25:39,788 --> 00:25:41,205
Holy cow!
406
00:25:43,542 --> 00:25:47,002
Oh, I'm out in free space.
407
00:25:48,755 --> 00:25:50,089
Floating, just floating.
408
00:25:50,131 --> 00:25:51,757
This is what an astronaut feels.
409
00:25:52,884 --> 00:25:57,429
The plane's trajectory induces
weightlessness again and again...
410
00:25:57,472 --> 00:26:00,391
by flying a series
of these parabolic arcs.
411
00:26:00,934 --> 00:26:03,811
Even though they are
within the cabin of a plane...
412
00:26:03,853 --> 00:26:10,025
the zero-G passengers are freely falling
towards the Earth just like skydivers.
413
00:26:10,068 --> 00:26:12,987
But what creates the sensation
of weightlessness?
414
00:26:19,244 --> 00:26:21,161
It goes back to Galileo...
415
00:26:21,204 --> 00:26:24,540
who showed that all objects
fall at the same rate.
416
00:26:26,459 --> 00:26:31,046
So, as the plane and the people inside
fall freely toward Earth...
417
00:26:31,089 --> 00:26:34,425
they maintain the same position
relative to each other...
418
00:26:34,467 --> 00:26:37,303
and that is why
they feel weightless.
419
00:26:44,561 --> 00:26:47,354
The feeling lasted
twenty-five full seconds...
420
00:26:47,397 --> 00:26:51,567
because, for twenty-five seconds,
we were essentially in free fall.
421
00:26:51,610 --> 00:26:54,111
It was like Superman
just flying through the air.
422
00:26:54,154 --> 00:26:57,323
Oh, I cannot believe
how it feels.
423
00:26:59,576 --> 00:27:03,120
When the jet's engines reengage
and end the free fall...
424
00:27:03,163 --> 00:27:06,874
the passengers
feel their weight return.
425
00:27:06,916 --> 00:27:10,711
As Einstein would say,
weightlessness is but an illusion.
426
00:27:14,341 --> 00:27:18,093
This is so awesome!
So awesome!
427
00:27:18,136 --> 00:27:19,887
The zero-G plane
takes advantage...
428
00:27:19,929 --> 00:27:23,140
of something Einstein
worked out back in 1916...
429
00:27:23,183 --> 00:27:25,643
in his general theory of relativity...
430
00:27:25,685 --> 00:27:29,188
that acceleration is essentially
the same as gravity.
431
00:27:37,322 --> 00:27:40,949
When you are thrust upward
in a rocket or the zero-G plane...
432
00:27:40,992 --> 00:27:43,118
the G-forces you experience...
433
00:27:43,161 --> 00:27:45,746
are the same as you would feel
being tugged downward...
434
00:27:45,789 --> 00:27:49,124
by the gravity of a massive object
like a planet.
435
00:27:54,589 --> 00:27:58,842
So gravity and acceleration
create the same sensation.
436
00:27:58,885 --> 00:28:01,345
That's how the passengers
on a zero-G flight...
437
00:28:01,388 --> 00:28:03,180
can feel like an astronaut...
438
00:28:03,223 --> 00:28:06,433
and can experience
the joys of weightlessness.
439
00:28:16,069 --> 00:28:18,529
The ball and I
are just freely falling...
440
00:28:18,571 --> 00:28:22,825
according to our natural path
through curved space-time.
441
00:28:22,867 --> 00:28:25,202
This is what Einstein's theory says.
442
00:28:25,245 --> 00:28:29,707
Independent of the mass,
we all follow the same path.
443
00:28:29,749 --> 00:28:31,875
Oh, yeah, this is unbelievable.
444
00:28:33,294 --> 00:28:35,921
On the twenty-minute,
fifteen-parabola flight...
445
00:28:35,964 --> 00:28:39,425
there's time in between
the frights and delights...
446
00:28:39,467 --> 00:28:41,635
to further taunt
the laws of gravity.
447
00:28:44,764 --> 00:28:47,224
Look at that.
Look at that water.
448
00:28:47,267 --> 00:28:51,520
Oh, look at that water.
I'm going to catch some.
449
00:28:53,273 --> 00:28:55,607
Okay, here we go.
450
00:28:55,650 --> 00:28:57,985
As well as entertaining
weekend warriors...
451
00:28:58,027 --> 00:28:59,445
the parabolic flights...
452
00:28:59,487 --> 00:29:03,073
also inauspiciously called
"The Vomit Comet"...
453
00:29:03,116 --> 00:29:04,950
have a practical purpose.
454
00:29:05,994 --> 00:29:08,912
They prepare NASA astronauts
for working and living...
455
00:29:08,955 --> 00:29:11,749
in the zero-G environment of space.
456
00:29:13,710 --> 00:29:16,503
With these sensational
parabolic flights...
457
00:29:16,546 --> 00:29:19,840
humans have learned how to
simulate the absence of gravity.
458
00:29:21,050 --> 00:29:25,471
But is it also possible to create
artificial gravity in the lab?
459
00:29:25,513 --> 00:29:29,725
These experiments will lead
to a successful exploration of Mars.
460
00:29:29,768 --> 00:29:31,435
It is in our future.
461
00:29:37,650 --> 00:29:42,780
At the dawn of the 21 st century,
overcoming the bonds of gravity...
462
00:29:42,822 --> 00:29:46,617
and escaping Earth's sizeable
tug have been realized.
463
00:29:48,036 --> 00:29:51,622
The next step is to design
and build the technology...
464
00:29:51,664 --> 00:29:56,210
that will allow humans
to travel, work, and live...
465
00:29:56,252 --> 00:29:59,129
on exotic alien planets.
466
00:29:59,172 --> 00:30:00,964
And we've garnered
enough engineering know-how...
467
00:30:01,007 --> 00:30:03,759
to do just that
in our voyages to the Moon.
468
00:30:06,262 --> 00:30:08,472
Thanks to state-of-the-art
technology...
469
00:30:08,515 --> 00:30:14,770
humanity is on the brink of
a new era in space exploration.
470
00:30:15,814 --> 00:30:21,318
The trip to Mars is beginning
here at our laboratory at MIT.
471
00:30:21,361 --> 00:30:25,239
Artificial gravity may be one
of the ways that we overcome...
472
00:30:25,281 --> 00:30:27,324
the debilitating effects
of weightlessness.
473
00:30:28,493 --> 00:30:30,452
Since the advent
of the space age...
474
00:30:30,495 --> 00:30:33,664
scientists have been
concerned with minimizing...
475
00:30:33,706 --> 00:30:36,834
the life-threatening risks
and damaging effects...
476
00:30:36,876 --> 00:30:40,546
of being weightless at zero-G.
477
00:30:40,588 --> 00:30:44,466
The issues originally had to do
with human survivability.
478
00:30:44,509 --> 00:30:48,053
We didn't even know
back in the Apollo period...
479
00:30:48,096 --> 00:30:51,598
how people would react
to stays in space...
480
00:30:51,641 --> 00:30:53,058
of more than a few hours.
481
00:30:54,394 --> 00:30:57,855
There was all kinds of concern
about humans' ability...
482
00:30:57,897 --> 00:31:00,858
to control a vehicle after
being exposed to weightlessness...
483
00:31:00,900 --> 00:31:02,901
for a long period of time.
484
00:31:04,571 --> 00:31:07,531
A mission to Mars
would require astronauts...
485
00:31:07,574 --> 00:31:11,827
to be away from Earth's gravity
for at least two, maybe three years.
486
00:31:13,413 --> 00:31:15,789
The human frame
is simply not designed...
487
00:31:15,832 --> 00:31:19,960
for the absence
of terrestrial one-G gravity.
488
00:31:20,003 --> 00:31:25,257
The architecture of our bodies
is designed to withstand our weight...
489
00:31:25,300 --> 00:31:26,758
under the forces of gravity.
490
00:31:26,801 --> 00:31:30,178
Gravity determines how our
cardiovascular system reacts...
491
00:31:30,221 --> 00:31:31,722
so when you get out of bed...
492
00:31:31,764 --> 00:31:34,349
and you go from being supine
to upright...
493
00:31:34,392 --> 00:31:37,436
there's a regulatory system
that keeps the blood pressure...
494
00:31:37,478 --> 00:31:39,897
reacting
against the forces of gravity.
495
00:31:40,815 --> 00:31:44,860
Experience has shown that
being weightless for long periods...
496
00:31:44,903 --> 00:31:47,988
leads to bone loss,
muscle deterioration...
497
00:31:48,031 --> 00:31:50,532
and life-threatening blood clots.
498
00:31:51,784 --> 00:31:54,995
Aeronautical engineers
at NASA and MIT...
499
00:31:55,038 --> 00:31:57,998
are testing a personal
centrifuge system...
500
00:31:58,041 --> 00:32:01,126
that may mitigate
the very real dangers.
501
00:32:03,129 --> 00:32:05,422
They protect the heart,
the bones, their muscles.
502
00:32:05,465 --> 00:32:09,676
And even in these early experiments,
we have every reason to believe...
503
00:32:09,719 --> 00:32:11,929
that artificial gravity
with short-radius centrifuges...
504
00:32:11,971 --> 00:32:16,224
may be the universal antidote
that we're looking for...
505
00:32:16,267 --> 00:32:19,269
to protect people
on the long trip to Mars.
506
00:32:21,147 --> 00:32:23,065
Just like a theme park ride...
507
00:32:23,107 --> 00:32:27,235
spinning a subject
artificially creates g-forces.
508
00:32:28,821 --> 00:32:31,740
To prevent motion sickness
in the MIT ride...
509
00:32:31,783 --> 00:32:34,451
astronauts are conditioned
to keep their head still.
510
00:32:35,620 --> 00:32:38,956
By spinning a person
at thirty revolutions a minute...
511
00:32:38,998 --> 00:32:41,458
the centrifuge imparts one G...
512
00:32:41,501 --> 00:32:45,504
the same force felt pulling down
a person standing on Earth.
513
00:32:47,632 --> 00:32:51,927
Scientists hope that one day,
a trip to Mars will be a reality.
514
00:32:52,762 --> 00:32:55,764
Onboard, they believe there should be
a personal centrifuge.
515
00:32:56,933 --> 00:33:01,103
To get their Earthly gravity fill-up,
21 st-century astronauts...
516
00:33:01,145 --> 00:33:05,232
could then just spend
one hour a day on the machine.
517
00:33:05,274 --> 00:33:07,818
We get onto it
for a brief period every day...
518
00:33:07,860 --> 00:33:09,861
and get spun up quite fast...
519
00:33:10,697 --> 00:33:13,073
spun up in what I'll call
a spin in the gym.
520
00:33:13,116 --> 00:33:16,118
You go for your exercise,
you go for your workout...
521
00:33:16,160 --> 00:33:18,954
you get your G tonic,
your gravity tonic.
522
00:33:20,748 --> 00:33:24,042
While a trip to Mars
may still be decades away...
523
00:33:24,085 --> 00:33:27,838
astrophysicist and seasoned
skier Larry Young...
524
00:33:27,880 --> 00:33:31,550
can dream of big air
in the liberating gravity of Mars.
525
00:33:33,344 --> 00:33:36,972
On the surface, there is three-eighths
the tug of Earth's gravity.
526
00:33:38,808 --> 00:33:40,851
Everyone likes
to get some air.
527
00:33:40,893 --> 00:33:41,893
Everybody likes a little bit.
528
00:33:41,936 --> 00:33:44,980
Just think if we were on Mars.
529
00:33:47,900 --> 00:33:50,652
A person who weighs
100 pounds on Earth...
530
00:33:50,695 --> 00:33:53,947
would feel as if they weigh
38 pounds on Mars.
531
00:33:55,116 --> 00:33:57,951
Although a Martian skier
would fly down Olympus Mons...
532
00:33:57,994 --> 00:34:00,495
at a third of the speed
they would on Earth...
533
00:34:00,538 --> 00:34:02,873
the lower gravity also means
that they would get...
534
00:34:02,915 --> 00:34:06,043
at least three times the big air.
535
00:34:06,085 --> 00:34:07,919
In the case of gravity,
it's mass that matters.
536
00:34:07,962 --> 00:34:10,922
The more mass you have,
the stronger the pull of gravity.
537
00:34:10,965 --> 00:34:13,508
So when you think about what
your weight would be on the Earth...
538
00:34:13,551 --> 00:34:16,678
versus something more massive
than the Earth, it's pretty direct.
539
00:34:16,721 --> 00:34:18,430
If something were twice
as massive as the Earth...
540
00:34:18,473 --> 00:34:20,307
you'd weigh
about twice as much.
541
00:34:21,726 --> 00:34:25,062
The Big Kahuna
in our solar system is Jupiter.
542
00:34:25,104 --> 00:34:27,564
On that planet,
a 100-pound person...
543
00:34:27,607 --> 00:34:30,817
would weigh
a whopping 254 pounds.
544
00:34:31,778 --> 00:34:34,237
Even if Jupiter
had a solid surface...
545
00:34:34,280 --> 00:34:37,115
a skier there would have
to fight for big air.
546
00:34:38,284 --> 00:34:41,161
What we already know
about gravity, how it works...
547
00:34:41,204 --> 00:34:43,872
and how it can be used
for practical purposes...
548
00:34:45,124 --> 00:34:48,126
could, in theory,
even save the planet...
549
00:34:48,169 --> 00:34:50,796
from its
ultimate cataclysmic fate.
550
00:34:51,964 --> 00:34:54,633
Here's how gravity
can come to our rescue.
551
00:34:56,677 --> 00:34:59,596
Gradually,
in about five billion years...
552
00:34:59,639 --> 00:35:03,725
our Sun will brilliantly flare,
turn into a red giant...
553
00:35:03,768 --> 00:35:07,479
gloriously burn up and die.
554
00:35:07,522 --> 00:35:11,191
As this comes to pass,
our inner solar system is engulfed...
555
00:35:12,693 --> 00:35:16,571
and Earth's gravity and atmosphere
will be radically altered.
556
00:35:17,698 --> 00:35:21,660
At that point, life
on the blue planet will end.
557
00:35:24,497 --> 00:35:27,457
But astrophysicist
Greg Laughlin has a plan...
558
00:35:27,500 --> 00:35:30,627
to use gravity to save Earth.
559
00:35:30,670 --> 00:35:32,587
This environment
that we have here now...
560
00:35:32,630 --> 00:35:34,631
would look very similar
to the environment...
561
00:35:34,674 --> 00:35:37,092
that is holding sway
on Venus right now.
562
00:35:37,135 --> 00:35:39,219
A crushing carbon dioxide
atmosphere...
563
00:35:39,262 --> 00:35:41,263
temperatures hot enough
to melt lead.
564
00:35:43,391 --> 00:35:47,102
But rest assured,
if the worst hypothetical happens...
565
00:35:47,145 --> 00:35:50,939
gravitational science
could save mother Earth.
566
00:35:50,982 --> 00:35:53,775
The one thing that we could do
over the very long term...
567
00:35:53,818 --> 00:35:56,778
is to somehow move
the Earth's orbit...
568
00:35:56,821 --> 00:36:00,448
out to a larger distance
from the sun...
569
00:36:00,491 --> 00:36:02,701
where the temperature
isn't so hot.
570
00:36:02,743 --> 00:36:07,539
And a way that you can do that,
if you have enough time...
571
00:36:07,582 --> 00:36:10,625
if you have billions of years
available to you...
572
00:36:10,668 --> 00:36:14,629
is to use a comet
or an asteroid.
573
00:36:15,423 --> 00:36:18,925
This mega move would require
astronauts and engineers...
574
00:36:18,968 --> 00:36:22,846
aboard a spacecraft to maneuver
the comet or asteroid...
575
00:36:22,889 --> 00:36:25,348
just in front of the Earth.
576
00:36:25,391 --> 00:36:26,892
In order to be most effective...
577
00:36:26,934 --> 00:36:29,186
the comet has to fly
very close to the Earth...
578
00:36:29,228 --> 00:36:32,939
within orbital radius or so
of the Earth.
579
00:36:34,483 --> 00:36:36,735
Then on the cosmic roller coaster...
580
00:36:36,777 --> 00:36:42,365
potential and kinetic energy are
roused and gravity does the rest.
581
00:36:42,408 --> 00:36:46,703
If that happens, then the comet
pulls the Earth forward...
582
00:36:46,746 --> 00:36:48,538
the Earth pulls
the comet backward...
583
00:36:48,581 --> 00:36:52,834
and the net result is that
the Earth is given a boost.
584
00:36:52,877 --> 00:36:56,338
It's given a boost
to a slightly higher orbital radius...
585
00:36:56,380 --> 00:36:58,715
slightly larger distance from the Sun.
586
00:36:58,758 --> 00:37:01,676
And if you make
one of these adjustments...
587
00:37:01,719 --> 00:37:04,930
one of these passages
every 10,000 years or so...
588
00:37:04,972 --> 00:37:07,974
then the Earth,
over a period of a billion years...
589
00:37:08,017 --> 00:37:11,853
can move
at a fast enough pace outward...
590
00:37:11,896 --> 00:37:15,106
to keep track with
the steadily brightening sun.
591
00:37:16,734 --> 00:37:19,653
If however, the experts
get the math wrong...
592
00:37:19,695 --> 00:37:24,199
and the big gamble doesn't work,
all bets are off.
593
00:37:24,242 --> 00:37:27,244
And if you screw that up,
then you can have a collision...
594
00:37:27,286 --> 00:37:28,495
between the comet
and the Earth.
595
00:37:28,537 --> 00:37:31,915
So a hundred-kilometer object
crashing into the Earth...
596
00:37:31,958 --> 00:37:34,834
is absolutely
an extraordinary disaster.
597
00:37:34,877 --> 00:37:39,589
It's the kind of thing
that causes huge extinctions...
598
00:37:39,632 --> 00:37:42,259
of gigantic numbers of species.
599
00:37:43,970 --> 00:37:47,847
Of course, this is only
an extreme hypothetical scenario...
600
00:37:47,890 --> 00:37:49,599
but what is known for sure...
601
00:37:49,642 --> 00:37:52,894
is that our continued existence
today here on Earth...
602
00:37:52,937 --> 00:37:56,856
is contingent
on the presence of gravity.
603
00:37:56,899 --> 00:37:59,401
It allows for the perfect
conditions for life...
604
00:37:59,443 --> 00:38:02,570
and the pursuit of happiness.
605
00:38:02,613 --> 00:38:07,242
One G produces the surfer's dream:
A perfect wave.
606
00:38:10,329 --> 00:38:12,747
But the wild waters
enjoyed on Earth...
607
00:38:12,790 --> 00:38:16,293
are not the only kind
of gravity-generated waves.
608
00:38:16,335 --> 00:38:22,090
There are cosmic waves so large
they roll across the entire universe.
609
00:38:26,262 --> 00:38:32,058
Tidal torrents of gravity-boosted
particles roll across the cosmos.
610
00:38:32,101 --> 00:38:33,476
According to Einstein...
611
00:38:33,519 --> 00:38:37,314
these gravitational waves
wash through the universe.
612
00:38:38,858 --> 00:38:41,151
But what are they?
613
00:38:41,193 --> 00:38:42,986
Any change in the gravity...
614
00:38:43,029 --> 00:38:47,824
sends a ripple through
that fabric of space...
615
00:38:47,867 --> 00:38:49,743
then moves
at the speed of light.
616
00:38:50,328 --> 00:38:52,746
That would be a gravity wave.
617
00:38:52,788 --> 00:38:54,998
And why do they happen?
618
00:38:55,041 --> 00:38:58,168
If you have two objects,
two compact stars...
619
00:38:58,210 --> 00:39:00,754
each of which
curves space around them...
620
00:39:00,796 --> 00:39:03,214
and they're orbiting one another...
621
00:39:03,257 --> 00:39:06,843
then the result is, is that
these two curved regions...
622
00:39:06,886 --> 00:39:10,680
create a wave,
a ripple in the structure...
623
00:39:10,723 --> 00:39:14,017
in the shape of space
that moves outwards...
624
00:39:14,060 --> 00:39:16,186
carrying energy with it.
625
00:39:16,228 --> 00:39:18,730
That's called a gravitational wave.
626
00:39:19,899 --> 00:39:22,484
I mean, literally, you can
think about space and time...
627
00:39:22,526 --> 00:39:24,819
having a wave,
just like an ocean wave in it...
628
00:39:24,862 --> 00:39:26,946
that travels
through the universe.
629
00:39:26,989 --> 00:39:28,990
Gravity waves
are just the same.
630
00:39:31,577 --> 00:39:35,205
Any type of mass in motion,
big or small...
631
00:39:35,247 --> 00:39:38,041
generates a gravitational wave.
632
00:39:38,084 --> 00:39:40,543
And like the Earth's ocean tides...
633
00:39:40,586 --> 00:39:45,423
gravitational waves roll
ceaselessly across the cosmos.
634
00:39:46,342 --> 00:39:50,720
In theory, a surfer launched
into space could experience...
635
00:39:50,763 --> 00:39:53,181
an out-of-this-world
wipeout and warp.
636
00:39:54,433 --> 00:39:58,103
If a gravitational wave was
created in space or somewhere...
637
00:39:58,145 --> 00:40:00,730
and went through you,
what would happen...
638
00:40:00,773 --> 00:40:04,234
is you'd get fat
and then you'd get skinny...
639
00:40:04,276 --> 00:40:06,653
meaning that space
was distorted.
640
00:40:06,695 --> 00:40:09,280
Space in one direction
made you fatter.
641
00:40:09,323 --> 00:40:11,491
In the other direction,
it squashed you.
642
00:40:11,534 --> 00:40:12,784
And it goes back and forth.
643
00:40:16,163 --> 00:40:21,126
But for earthbound scientists
to detect any faint G-wave signals...
644
00:40:21,168 --> 00:40:23,461
the disturbance
needs to be propagated...
645
00:40:23,504 --> 00:40:25,630
by a massive cosmic object.
646
00:40:27,800 --> 00:40:30,802
Black holes and spinning
neutron stars can do it.
647
00:40:31,637 --> 00:40:33,138
Another thing
that can make a gravity wave...
648
00:40:33,180 --> 00:40:35,098
is an explosion,
say, a supernova.
649
00:40:35,141 --> 00:40:37,142
A star explodes
and it goes-whack-
650
00:40:37,184 --> 00:40:39,853
and that actually pushes
a gravity wave forward.
651
00:40:43,274 --> 00:40:48,653
The tool to catch the light-like signal
from a wave is the LIGO...
652
00:40:48,696 --> 00:40:52,824
the Laser Interferometer
Gravitational Wave Observatory.
653
00:40:54,493 --> 00:40:57,745
There are two identical,
ground-based LIGO labs.
654
00:40:57,788 --> 00:41:00,915
One is in Hanford, Washington...
655
00:41:00,958 --> 00:41:03,626
and the other is more
than 2,000 miles away...
656
00:41:03,669 --> 00:41:05,837
near Baton Rouge, Louisiana.
657
00:41:09,842 --> 00:41:14,846
If a wave comes by, each lab's results
will be vital to confirm the event.
658
00:41:16,348 --> 00:41:17,765
Here's how it works.
659
00:41:17,808 --> 00:41:22,979
Super polished glass mirrors are
at the fulcrum of the interferometer...
660
00:41:23,022 --> 00:41:24,481
which is a tool that basically...
661
00:41:24,523 --> 00:41:26,816
compares two
light wave measurements...
662
00:41:26,859 --> 00:41:30,153
and identifies the differences
between them.
663
00:41:30,196 --> 00:41:33,281
Precision laser light
is fired back and forth...
664
00:41:33,324 --> 00:41:37,285
and split between
two calibrated mirrors.
665
00:41:37,328 --> 00:41:40,830
In normal circumstances,
as the light bounces up and down...
666
00:41:40,873 --> 00:41:44,417
the 21/2-Mile long,
L-shaped vacuum tubes...
667
00:41:44,460 --> 00:41:47,128
the two laser beams
are basically in sync.
668
00:41:48,506 --> 00:41:51,925
This means the beams effectively
cancel each other out...
669
00:41:51,967 --> 00:41:53,968
and no light escapes the tunnel.
670
00:41:55,054 --> 00:41:56,971
But when a gravity wave
rolls through...
671
00:41:57,014 --> 00:42:01,017
space is ever so slightly stretched
or squashed.
672
00:42:01,060 --> 00:42:04,270
As a result, the laser beams
are thrown out of phase...
673
00:42:04,313 --> 00:42:08,191
and only then a small amount
of light is emitted...
674
00:42:08,234 --> 00:42:11,986
a tiny signal, less than
the diameter of a human hair...
675
00:42:12,029 --> 00:42:16,533
1/1000th the size
of a proton will register.
676
00:42:16,575 --> 00:42:19,035
Converted into a sound
and a light signal...
677
00:42:19,078 --> 00:42:21,663
it will be seen and heard.
678
00:42:23,123 --> 00:42:24,916
The scientists' greatest hope...
679
00:42:24,959 --> 00:42:29,212
is to catch the most massive event
that ever occurred in the universe...
680
00:42:29,255 --> 00:42:31,381
the Big Bang.
681
00:42:31,423 --> 00:42:33,967
Gravity waves may be
our best chance to look...
682
00:42:34,009 --> 00:42:36,803
very, very close to
the beginning of the universe.
683
00:42:36,845 --> 00:42:39,681
About 300,000 years
after the Big Bang...
684
00:42:39,723 --> 00:42:42,767
the universe was so dense,
it was actually opaque to light.
685
00:42:42,810 --> 00:42:45,895
Light could not travel through it.
686
00:42:45,938 --> 00:42:49,774
So if light can't travel
through the universe, what can?
687
00:42:49,817 --> 00:42:50,858
A gravity wave.
688
00:42:53,445 --> 00:42:56,781
The problem is a miniscule signal
from a gravity wave...
689
00:42:56,824 --> 00:42:59,075
has yet to be caught.
690
00:42:59,118 --> 00:43:00,577
It's clearly hard.
691
00:43:00,619 --> 00:43:05,873
In fact, when Einstein predicted them,
he thought it was a nice idea...
692
00:43:05,916 --> 00:43:08,209
but no one would ever
be able to detect them.
693
00:43:08,252 --> 00:43:11,921
It's only the advances of technology
that give us a chance.
694
00:43:13,007 --> 00:43:16,217
LIGO scientists,
like astrosurfers...
695
00:43:16,260 --> 00:43:18,720
live for the day
when they can hang ten...
696
00:43:18,762 --> 00:43:22,599
and ride their very own
perfect wave of gravity.
697
00:43:22,641 --> 00:43:25,268
We've seen what we think
are the effects of gravity waves...
698
00:43:25,311 --> 00:43:29,814
the loss of energy from a system
by way of gravity waves...
699
00:43:29,857 --> 00:43:31,649
but we never
directly detected one.
700
00:43:31,692 --> 00:43:33,693
That's one of the last frontiers.
701
00:43:34,862 --> 00:43:37,488
If the LIGO scientists' quest
is successful...
702
00:43:37,531 --> 00:43:41,909
and they catch a wave,
it could change science.
703
00:43:41,952 --> 00:43:45,580
So, I think that long term,
it's first to understand gravity...
704
00:43:45,623 --> 00:43:48,333
and then, even more interestingly,
to understand the universe.
705
00:43:52,171 --> 00:43:56,132
The force of gravity
has domain over our universe.
706
00:43:57,009 --> 00:44:01,554
It created and can destroy
the cosmos, the stars...
707
00:44:01,597 --> 00:44:04,974
the planets, and the people.
708
00:44:06,518 --> 00:44:13,024
It controls our lives,
our play, and our endeavors.
709
00:44:13,067 --> 00:44:15,109
And therein
is this cosmic ballet.
710
00:44:16,320 --> 00:44:19,697
Our collective future depends
on the grace and greatness...
711
00:44:19,740 --> 00:44:23,493
of the mighty ruler
of the cosmos, gravity.
60711
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