NARRATOR: It is both
mighty and meek. Whoa! NARRATOR: Humanity's quest
is to harness its power and escape its bonds. Holy cow! This is what an astronaut feels. NARRATOR: It creates and
breaks the stars, the planets, the galaxies, and directs their
cosmic roller coaster ride. NEIL DEGRASSE TYSON: Gravity
is our friend and our foe. NARRATOR: Without it, life
as we know it would end. DAVID SANDWELL: The Earth
would literally explode. NARRATOR: It is the magnificent
and mystifying force that rules the universe-- gravity. [theme music] Gravity is the most pervasive
force in the universe. It is at work on massive
and minute scales, on the routine and the extreme. A surfer needs it to hang 10. DAVID SANDWELL: When
you ride a wave, you're going to
slide down the front, and you're going to use
that pull of gravity to get you going. It's your acceleration force. It's your accelerator. Gravity's your accelerator. NARRATOR: A skier uses
it to race downhill. A snowboarder must
have it to get big air. It acts on everything with
mass, including us, 24/7, even when sleeping or standing. LAWRENCE YOUNG: Gravity
here on Earth, of course, is always accelerating us down
toward the center of the earth at 32 feet per second squared. NARRATOR: At a
theme park, gravity is the galactic gas that makes
roller coasters roar and people scream. ALEX FILIPPENKO: The gravity
of the Earth pulls us down, and that's going to make
us go really, really fast. NARRATOR: All objects
with mass or energy-- particles, people, planets,
stars, and galaxies-- produce gravity. Omnipotent and omnipresent,
gravity attracts, governs, warps, shapes, makes
and takes all matter and mass in the universe. ALEX FILIPPENKO:
So it's pervasive. It acts on all things through
extremely large distances, and nothing escapes its pull. NARRATOR: It is gravity
that holds our solar system together. DAVID SANDWELL: The force
of gravity is basically the thing that holds
us on the planet, keeps us from flying off. NARRATOR: It is the cosmic
glue that binds all matter in the universe together. GREGORY LAUGHLIN: If you were
to imagine taking two dice and putting them perfectly at
rest out in the middle of space and separating them by a
centimeter, then what you'd see is that over a course
of an hour or so, those two dice would slowly
come together and touch. NARRATOR: Gravity
made our world. ALEX FILIPPENKO: Our sun formed
from a vast cloud of gas that gravitationally contracted. Similarly, our
Earth formed through the gravitational attraction
of little particles, little, bitty things gradually
growing into a bigger and bigger object. NARRATOR: When it comes to
gravity's pulling power, mass and distance matter. ALEX FILIPPENKO: It
depends on the masses of each object, the amount
of matter within each object. So it's proportional to the
product of the two masses. NARRATOR: In other words, the
bigger it is, the harder it pulls on other objects. But that's not all. ALEX FILIPPENKO:
And it's inversely proportional to the square
of the distance between them. NARRATOR: This means if you
double the distance between two objects, the
attraction, or pull, is only a quarter of
its original strength. The pulling power
of gravity lets it direct the motion and
movement of all matter, however massive,
in the universe. NEIL DEGRASSE TYSON: So you have
whole galaxies, for example, in orbit around each other. Clusters of galaxies all orbit
around their common center of mass. [rocket blast] NARRATOR: But it is
the practical potential of harnessing this relentless
force that has obsessed scientists for centuries. It would literally fall
to Galileo Galilee, the 17th century truth
seeker, to first recognize that gravity even existed. ALEX FILIPPENKO: Galileo
found that objects having a different weight
fall at the same rate. So here is a very heavy steel
ball and a light ping pong ball of the same size. And if I drop them
at the same time, they hit the ground at
exactly the same time as well because they
fall at the same rate. NARRATOR: To illustrate
Galileo's most profound gravitational discovery
that all objects, regardless of mass, fall at
the same rate, we take a ride on the
mega-fast Superman The Escape at Six Flags
Magic Mountain in Southern California. The theme park ride is the
stage for a spectacular freefall demonstration. It will show what happens when a
car full of people and a tennis ball fall from 450
feet in the air. OK, here we go. All right. Oh, boy. NARRATOR: The riders are shot
up the 41-story-tall tower at 100 miles an hour. With their eyes open, gravity
will help them see a superhero. [yelling] Oh my god. OK, I'm gonna drop this ball
now and-- oh, yeah, it's floating around. It's floating.
It's floating. It's floating! Oh, the wind blew the
ball away that time. NARRATOR: While we expect
all objects to fall freely together, regardless of
mass, on a windy day, results aren't always perfect. ALEX FILIPPENKO: All right. Oh my god. NARRATOR: At the
very top of the ride, when upward motion has
stopped, gravity takes over and the downward
freefall begins. [inaudible] I'm
gonna drop this ball. It's gonna float. It's gonna float. Oh, it's floating. It's floating! I'm gonna release this ball now. I'm gonna release it. NARRATOR: And then, for
a few blissful seconds, theme park thrill
seekers feel weightless, as if they are free of gravity,
or in what scientists call, zero G. ALEX FILIPPENKO: Oh,
that one floated well. That one floated well. Oh, man. Oh. [laughing] I'm gonna try dropping the ball. Oh! NARRATOR: But zero G
is just an illusion. In reality, gravity
is running this ride. It's the force that yanks the
car, the people, and the tennis ball, indifferent to their
mass, back down to Earth at the same rate. ALEX FILIPPENKO: Oh,
that's a fantastic ride. I mean, feeling one's
self drop is amazing. But what's really great
is dropping the ball and seeing it floating
above my face. Now, I mean, it's falling. I know it's falling,
but I'm falling at exactly the same rate. It doesn't matter how
massive something is. It falls under the
force of gravity at exactly the same rate. NARRATOR: Thanks to
experiments like this, we now know that objects
all fall at the same rate. But what would it take to
launch a cannonball into orbit? When the famous British
physicist Sir Isaac Newton saw the apple fall that some
say hit him on the head, it changed the world. NEIL DEGRASSE TYSON: You got
the apple falling from the tree, and he looks up and sees the
moon in orbit around the Earth and judges that not only is the
apple falling to Earth, so too is the moon. NARRATOR: But could the
moon really be falling? Hold! NARRATOR: By
thinking of a cannon and the trajectory of the ball
it shoots, Newton used math to unlock a cosmic mystery. [cannon fire] It came in his landmark
publication "Principia Mathematica" in 1687. NEIL DEGRASSE TYSON: Isaac
Newton has a famous drawing, and in it, he draws a planet
and a little mountain. There's a little projectile
first kicked off the mountain, and it falls down a little bit. You give it more speed, it
goes a little farther out. MICHELLE THALLER: Now, say
you could just increase the force all you wanted. It could go 50 miles, go
100 miles before it fell. NARRATOR: By adding more
gunpowder and with just the right angle of
fire, a cannonball can be made to go
faster and farther. [cannon fire] Inevitably, however, gravity
wins, pulling the cannonball back down to Earth. ANTHONY ZEE: The Earth
is round and not flat, so Newton realized that
if the cannonball is fired at sufficient
speed, [cannon fire] the cannonball would
actually go into orbit. NARRATOR: For that to
happen, Newton determined, the ball would need to
be shot out of the cannon at 17,500 miles an hour. NEIL DEGRASSE TYSON: It starts
curving around the Earth, and he realized that there
must be a speed where it goes completely
around the Earth and hits you in the
back of the head, never actually hitting
Earth's surface. And if you duck,
it'll just keep going. And lo and behold,
you have an orbit. NARRATOR: But why doesn't
the moon fall to Earth? ALEX FILIPPENKO: The moon
also has some sideways motion. So for every little
bit that it falls down, it also moves off
in this direction. And the sum of all those motions
is an orbit around the Earth. NARRATOR: Newton also
realized that the Earth is in a giant freefall
around the sun. With gravity forging
the path, our planet rounds the sun like an endless
cosmic roller coaster ride. Newton cracked the gravity
code, and physicists are still using his ideas to solve all
sorts of problems, some of them stranger than others, like what
would happen if a person tried to travel through a tunnel
from one side of the planet to the other? In this wild scheme,
you would have to drive a straight-line
tunnel right through the Earth and use gravity alone
to propel a traveler down this so-called
gravity express. ALEX FILIPPENKO: So suppose
you've got one of these tunnels and you jump in. Initially, the Earth
is pulling down. You're going toward the
center of the Earth, and so you're
accelerating toward it. But as you pass through
the center of the Earth and start going out
toward the opposite side, the gravity of the Earth
is trying to pull you back. So it's decelerating you. So gravity is actually
have a braking effect. There's no fear of shooting
out the hole on the other side of Earth at some
tremendous velocity and shooting yourself
back into space. But in fact, you reach the
surface of the Earth exactly. You are close to a perfect rest. In 42 minutes, you'll be there. NARRATOR: Whichever
two cities you connect with a straight-line tunnel,
it takes gravity exactly 42 minutes to get you there. The journey from Los
Angeles to Paris, 42 minutes. Suppose you wanted to go
from Los Angeles to Tokyo. 42 minutes. It doesn't matter which path
you take through the Earth. The journey is always
42 minutes long. NARRATOR: It takes Newton's math
to figure out why this works. If we connect Los Angeles
to New York digging a tunnel, obviously, a tunnel would
not go straight down, but it has to go
down at an angle. NARRATOR: The angle slows
the speed of descent. ANTHONY ZEE: But the
distance is also less. And if you work out the
equations, lo and behold, the two effects cancel, and you
still get there in 42 minutes. ALEX FILIPPENKO: It takes 42
minutes regardless of the path you take. That's really cool. NARRATOR: Newton figured
out what gravity does, but it took the brilliance
of physicist Albert Einstein to work out why it was doing it. Einstein realized
that gravity is really caused by huge objects
like stars and planets literally bending space itself. Like a massive
rubber sheet, space is curved when massive
objects sit in it. In fact, Einstein proposed
that the path planets take around their stars,
their orbits, are all a direct result of
this curvature of space. MICHELLE THALLER: He said
that what an orbit is is really something
traveling in a straight line. When something is free-falling
towards another object, it really is just traveling
in a straight line through spacetime. However, the
curvature of spacetime bends its path into
a closed orbit, but space itself curves
it back in on itself. NARRATOR: This
revolutionary discovery came when Einstein,
in the early 1910s, realized that orbits
of stars and planets in the observable cosmos
behave just as Newton's math predicted, except one-- Mercury. Its orbit essentially wobbles. MICHELLE THALLER:
Einstein described gravity as a curvature in space and
time, and the orbit of Mercury works perfectly when you
take that into account. Mercury isn't
moving in flat space but curved space around the sun. Then the orbit's perfect. NARRATOR: This
curvature of space is at play in our
own solar system. ALEX FILIPPENKO: Earth is
simply following what it thinks is a straight-line path, the
shortest distance between two points, in this
intrinsically curved space. NARRATOR: Einstein
not only determined that mass warps space. It warps time, too. ANTHONY ZEE: So henceforth,
Einstein proclaimed, physicists should not speak of space
and time separately, but of spacetime as
one unified object. NEIL DEGRASSE TYSON: While it's
uncomfortable to many the first time you hear it, if you
stop and think about it, it's actually quite obvious. If I'm going to make an
appointment with somebody, I won't say I'll meet
you at three o'clock. That's not enough information. There's gotta be a
question that follows that. What is that question? Where? If I say meet you
in room 203, when? Anytime you intersect
with someone else's life, you do so at a time
and at a place. NARRATOR: Einstein's
realization that space is curved and that time and space
are in fact intertwined is now the very
definition of gravity. MAN: Liftoff of space
shuttle Discovery. NARRATOR: Unlocking
the secrets of gravity has enabled humanity to
escape our Earthly shackles and opened the universe
for exploration. But how can future astronauts
on the long way to Mars survive the disabling
effects caused by zero G? Gravity is our
friend and our foe. It is the fearsome
force that propels a skier and the snowboarder
down the mountain and shoots them into the air. With enough momentum,
an airborne snowboarder can feel, for fleeting moments,
as if they are free of Earth's gravitational pull. You're actually weightless
when you go off the jump. The period of weightlessness
is determined by the duration of your trajectory as a
function of your velocity, so that the snowboarder who
gets really good, big air may achieve a second, two
seconds, even three seconds of weightlessness. NARRATOR: But in the
end, gravity wins and the high-flying,
free-falling boarder, just like the ball
fired from the cannon, is eventually yanked
back down to earth. This freefall for
the snowboarder, as he or she goes over the jump
and creates this trajectory, is just as much
freefall as a cannonball going through the air. And the trajectory is
determined only by the velocity and the force of gravity. And then, of course, what
happens on the landing is another story. NARRATOR: But what
if a snowboarder aspired to reach
even greater heights? What if he wanted to overcome
gravity and launch himself right off the planet? NEIL DEGRASSE TYSON:
You want to leave Earth entirely and forever? Earth has what we call
the escape velocity, this magic speed where
if you pass that speed, you will escape Earth
forever, never to return. NARRATOR: Escape velocity, the
minimum speed any object needs to reach in order to
escape from the Earth, is about 7 miles a second. That's 25,000 miles an hour. In theory, even a snowboarder,
with enough momentum and aimed in the right
direction, can take off, just like a rocket. Escaping Earth's gravity may not
be realistic for a snowboarder, but it has proven possible to
launch people and projectiles into orbit. NEIL DEGRASSE TYSON:
You can leave systems. You just need enough
energy to do so, and we've garnered enough energy
and technological know-how to do just that in our voyages
to the moon and our hope that that will continue
on to Mars and beyond. NARRATOR: To get
to Mars and beyond, mankind will have to
harness gravity's energy, just like we always do
when we are seeking thrills to the extreme. Gravity gives us two types of
energy, potential and kinetic. Potential is just that. It's energy that's being
stored, while kinetic is the result of all that
pent-up potential energy. This fantastic phenomenon
works on a roller coaster. MICHELLE THALLER: As you're
winched up on a hill, your potential
energy is increasing. You literally have more energy
at the top of the roller coaster than at the bottom. It's not just a
weird, abstract thing. You actually possess
higher energy at the top, and that's turned into
speed, into kinetic energy, as you go down that hill
on the roller coaster. Pretty soon, I'll be
converting my potential energy to kinetic energy! Woo! NARRATOR: When a surfer hits
that sweet spot on a wave, they're using
energy's double act. NASA also uses this energy
exchange principle to add some speed to their missions. As a spacecraft nears
the orbit of a planet, it too gathers kinetic
energy at the expense of potential energy. Then, as it rounds the planet
on its cosmic coaster ride, the craft gets a
slingshot effect that punches it onward
with more kinetic energy. ALEX FILIPPENKO: When the
Voyager spacecraft visited Jupiter in 1979, 1980,
it flew past Jupiter, and Jupiter tugged on it,
giving it extra motion, sort of a slingshot effect, not
only changing its direction of motion so that it was
aimed towards Saturn, but also speeding it up. NARRATOR: Knowing how to
use the power of gravity will enable humanity to
travel further and faster across the universe. Having the physics formulated
and the technology available is just one part
of the preparation for extraterrestrial travel. Readying people for the
rigors of space is the other. Far away from Earth's
gravitational pull, in a spaceship on the
long journey to Mars, for example, future
astronauts will have to learn to
live, work, and play in an environment free of
Earth's sizable gravity, one where they effectively
feel weightless and all objects move equally and freely. One fun way to experience
the astronautical thrills and spills of space travel is
to simulate it on a 0 G flight. I'm really looking
forward to this. This is going to be an
incredible experience. NARRATOR: By riding the ultimate
roller coaster, a specially modified 0 G Boeing
727 aircraft, astrophysicist
Alex Filippenko is about to go on the
ride of his life. ALEX FILIPPENKO: This is
gonna be like a ball thrown up in the air-- weightless, because it
will be in a freefall. So I'll be floating
around as though there's no ground holding me up. NARRATOR: The 0 G flight flies
between 24,000 and 32,000 feet. This is about the same altitude
as a regular commercial jet, but that is where
the similarity ends. ALEX FILIPPENKO: The
water's the next one. NARRATOR: The path that
follows is a series of coaster-like rolling
hills in the stratosphere. Just like Superman The
Ride, the super 0 G plane gathers potential energy as
it climbs up at 45 degrees. Passengers feel this as
an increase in weight. Oh, yeah. NARRATOR: Gravity is measured
in terms of G-forces. 1 G is the amount of
gravity we feel standing on the surface of the Earth. I'm gonna get back down
like this and get ready. NARRATOR: As the plane steeply
climbs, accelerating upward, the gravity G count rises,
and people feel heavier. All right. Oh, the plane is accelerating
us upwards at about 1.8 G at its maximum. NARRATOR: As the
flight approaches then eases around the apex
of the arc, the plane, as well as all the
people inside it, are, in effect, in freefall. ALEX FILIPPENKO: 0 g coming up. Oh, man, what an
indescribable feeling. Holy cow! Oh, I'm out in free space. Holy cow. I'm floating. This is what an astronaut feels. NARRATOR: The plane's trajectory
induces weightlessness again and again by flying a
series of these parabolic arcs. Even though they are within
the cabin of a plane, the 0 G passengers are freely
falling towards the Earth, just like skydivers. But what creates the
sensation of weightlessness? [inaudible] Oh, man! Oh! NARRATOR: It goes
back to Galileo, who showed that all objects
fall at the same rate. So as the plane and the
people inside fall freely toward Earth, they
maintain the same position relative to each other, and that
is why they feel weightless. ALEX FILIPPENKO: The feeling
lasted 25 full seconds because for 25 seconds, we
were essentially in freefall. It was like Superman just
flying through the air. Oh, I cannot believe
how it feels. NARRATOR: When the jet's engines
re-engage and end the freefall, the passengers feel
their weight return. As Einstein would
say, weightlessness is but an illusion. This is so awesome! So awesome! NARRATOR: The 0 G plane takes
advantage of something Einstein worked out back in 1916 in his
general theory of relativity, that acceleration is
essentially the same as gravity. When you are thrust upward
in a rocket or the 0 G plane, the G-forces you
experience are the same as you would feel
being tugged downward by the gravity of a massive
object like a planet. So gravity and acceleration
create the same sensation. That's how the passengers
on a 0 G flight can feel like an astronaut
and can experience the joys of weightlessness. The ball and I are
just really falling according to our natural path
through curved spacetime. This is what
Einstein's theory says. Independent from the the mass,
we all fall at the same time. Oh, yeah. This is unbelievable. NARRATOR: On the 20-minute,
15-parabola flight, there's time
in-between the frights and delights to further
talk the laws of gravity. Look at that. Look at that water. Whoa, look at that water! I'm going to catch some. OK, here we go. Oh, man. NARRATOR: As well as
entertaining weekend warriors, the parabolic flights,
also inauspiciously called the "vomit comet," have
a practical purpose. They prepare NASA astronauts for
working and living in the 0 G environment of space. With these sensational
parabolic flights, humans have learned how
to simulate the absence of gravity, but is it
also possible to create artificial gravity in the lab? LAWRENCE YOUNG:
These experiments will lead to a successful
exploration of Mars. It is in our future. NARRATOR: At the dawn of
the 21st century, overcoming the bonds of gravity and
escaping Earth's sizable tug have been realized. The next step is to design
and build the technology that will allow humans to
travel, work, and live on exotic alien planets. NEIL DEGRASSE TYSON: And we've
garnered enough engineering know-how to do just that
in our voyages to the moon. NARRATOR: Thanks to
state-of-the-art technology, humanity is on the brink of a
new era in space exploration. LAWRENCE YOUNG: The trip
to Mars is beginning here at our laboratory at MIT. Artificial gravity
may be one of the ways that we overcome
the debilitating effects of weightlessness. NARRATOR: Since the
advent of the space age, scientists have been
concerned with minimizing the life-threatening risks
and damaging effects of being weightless at 0 G. LAWRENCE YOUNG: The
issues originally had to do with human
surviveability. We didn't even know back
in the Apollo period how people would react
to stays in space of more than a few hours. There was all kinds of
concern about humans' ability to control the vehicle after
being exposed to weightlessness for a long period of time. NARRATOR: A mission to Mars
would require astronauts to be away from Earth's
gravity for at least two, maybe three years. The human frame is simply
not designed for the absence of terrestrial 1 G gravity. LAWRENCE YOUNG: The
architecture of our bodies is designed to
withstand our weight under the forces of gravity. Gravity determines how our
cardiovascular system reacts. So when you get
out of bed and you go from being supine
to upright, there's a regulatory system that keeps
the blood pressure reacting against the forces of gravity. NARRATOR: Experience has
shown that being weightless for long periods leads to bone
loss, muscle deterioration, and life-threatening
blood clots. Aeronautical engineers
at NASA and MIT are testing a personal
centrifuge system that may mitigate the very real dangers. LAWRENCE YOUNG: They protect
their heart, their bones, their muscles. And even in these
early experiments, we have every reason to
believe that artificial gravity and short radius centrifuges
may be the universal antidote that we're looking for to
protect people on the long trip to Mars. NARRATOR: Just like
a theme park ride, spinning a subject
artificially creates G-forces. To prevent motion
sickness in the MIT ride, astronauts are conditioned
to keep their heads still. By spinning a person at
30 revolutions a minute, the centrifuge imparts
1 G, the same force felt pulling down a
person standing on Earth. Scientists hope that one day, a
trip to Mars will be a reality. Onboard, they
believe there should be a personal centrifuge. To get their Earthly
gravity fill-up, 21st century astronauts could
then just spend one hour a day on the machine. LAWRENCE YOUNG: You get onto
it for a brief period every day and get spun up quite
fast, spun up in what I'll call a spin in the gym. You go for your exercise. You go for your workout. You get your G tonic,
your gravity tonic. NARRATOR: While a trip to Mars
may still be decades away, astrophysicist and
seasoned skier Larry Young can dream of big air and the
liberating gravity of Mars. On the surface, there is 3/8
the tug of Earth's gravity. LAWRENCE YOUNG: Everybody
likes to get some air. Everybody likes [inaudible]. But just think if
we were on Mars. NARRATOR: A person who
weighs 100 pounds on Earth would feel as if they
weigh 38 pounds on Mars. Although a Martian
skier would fly down Olympus Mons at a third of
the speed they would on Earth, the lower gravity also means
they could get at least three times the big air. MICHELLE THALLER: In
the case of gravity, it's mass that matters. The more mass you have, the
stronger the pull of gravity. So when you think about
what your weight would be on the Earth versus something
more massive than the Earth, it's pretty direct. If something were twice
as massive as the Earth, you'd weigh about twice as much. NARRATOR: The big kahuna in
our solar system is Jupiter. On that planet, a
100-pound person would weigh a
whopping 254 pounds. Even if Jupiter had
a solid surface, a skier there would have
to fight for big air. What we already know about
gravity, how it works and how it can be used
for practical purposes, could, in theory,
even save the planet from its ultimate
cataclysmic fate. Here's how gravity can
come to our rescue. Gradually, in about
5 billion years, our sun will brilliantly
flare, turn into a red giant, gloriously burn up, and die. As this comes to pass, our
inner solar system is engulfed, and Earth's gravity
and atmosphere will be radically altered. At that point, life on
the blue planet will end. But astrophysicist Greg
Laughlin has a plan to use gravity to save Earth. GREGORY LAUGHLIN: This
environment that we have here now would look very similar to
the environment that is holding sway on Venus right
now-- crushing carbon dioxide, atmosphere
temperatures hot enough to melt lead. NARRATOR: But rest assured, if
the worst hypothetical happens, gravitational science
could save Mother Earth. GREGORY LAUGHLIN: The one thing
that we could do over the very long term is to somehow move the
Earth's orbit out to a larger distance from the sun, where
the temperature isn't so high. And a way that you can do that,
if you have enough time, if you have billions of years
available to you, is to use a comet
or an asteroid. NARRATOR: This mega move
would require astronauts and engineers
aboard a spacecraft to maneuver the comet
or asteroid just in front of the Earth. In order to be most
effective, the comet has to fly very close to the
Earth, within orbital radius or so of the Earth. NARRATOR: Then, on the
cosmic roller coaster, potential and kinetic
energy are roused and gravity does the rest. If that happens, then the
comet pulls the Earth forward. The Earth pulls
the comet backward. And the net result is that
the Earth is given a boost. It's given a boost to a slightly
higher orbital radius, slightly larger distance from the sun. And if you make one of
these adjustments, one of these passages every
10,000 years or so, then the Earth, over a
period of a billion years, can move at a fast enough
pace outward to keep track with a steadily brightening sun. NARRATOR: If, however, the
experts get the math wrong and the big gamble doesn't
work, all bets are off. And if you screw
that up, then you can have a collision between
the comet and the Earth. So a 100-kilometer object
crashing into the Earth is absolutely an
extraordinary disaster. It's the kind of thing that
causes huge extinctions of gigantic numbers of species. NARRATOR: Of
course, this is only an extreme
hypothetical scenario. But what is known for sure is
that our continued existence today here on Earth is
contingent on the presence of gravity. It allows for the perfect
conditions for life and the pursuit of happiness. 1 G produces the surfer's
dream, a perfect wave. But the wild waters
enjoyed on Earth are not the only kind of
gravity-generated waves. There are cosmic
waves so large, they roll across the entire universe. Tidal torrents of
gravity-boosted particles roll across the cosmos. According to Einstein,
these gravitational waves wash through the universe,
but what are they? NEIL DEGRASSE TYSON: Any
change in the gravity sends a ripple through
that fabric of space that moves at the speed of light. That would be a gravity wave. NARRATOR: And why
do they happen? ALEX FILIPPENKO: If you have
two objects, two compact stars, each of which curves
space around them, and they're orbiting
one another, then the result is that these
two curved regions create a wave, a ripple
in the structure, in the shape of space
that moves outwards, carrying energy with it. That's called a
gravitational wave. MICHELLE THALLER: I
mean, literally, you can think about space
and time having a wave, just like an ocean
wave in it, that travels through the universe. Gravity waves are just the same. NARRATOR: Any type of mass
in motion, big or small, generates a gravitational wave. And like the
Earth's ocean tides, gravitational waves roll
ceaselessly across the cosmos. In theory, a surfer launched
into space could experience an out-of-this-world
wipeout and warp. BARRY BARISH: If a gravitational
wave was created in space or somewhere and went through
you, what would happen is you'd get fat, and then you'd
get skinny, meaning that space was distorted. Space in one direction
made you fatter. In the other direction,
it squashed you. And it goes back and forth. NARRATOR: But for Earthbound
scientists to detect any faint G-wave
signals, the disturbance needs to be propagated by
a massive cosmic object. Black holes and spinning
neutron stars can do it. MICHELLE THALLER:
Another thing that could make a gravity wave is
an explosion, say a supernova. A star explodes and goes
whack, and that actually pushes a gravity way forward. NARRATOR: The tool to catch the
light-like signal from a wave is the LIGO, the
Laser Interferometer Gravitational-Wave Observatory. There are two identical
ground-based LIGO labs. One is in Hanford,
Washington, and the other is more than 2,000 miles away,
near Baton Rouge, Louisiana. If a wave comes by,
each lab's results will be vital to
confirm the event. Here's how it works. Super-polished glass
mirrors are at the fulcrum of the interferometer, which is
a tool that basically compares two light-wave
measurements and identifies the differences between them. Precision laser light
is fired back and forth and split between two
calibrated mirrors. In normal circumstances, as
the light bounces up and down the 2 and 1/2 mile long
L-shaped vacuum tubes, the two laser beams
are basically in sync. This means the beams effectively
cancel each other out, and no light escapes the tunnel. But when a gravity
wave rolls through, space is ever so slightly
stretched or squashed. As a result, the laser beams
are thrown out of phase, and only then a small
amount of light is emitted. A tiny signal, less
than the diameter of a human hair, 1/1000 the
size of a proton, will register. Converted into a sound
and a light signal, it will be seen and heard. The scientists' greatest hope is
to catch the most massive event that ever occurred
in the universe-- the Big Bang. MICHELLE THALLER: Gravity
waves may be our best chance to look very, very close to
the beginning of the universe. About 300,000 years
after the Big Bang, the universe was so dense it
was actually opaque to light. Light could not
travel through it. So if light can't travel
through the universe, what can? A gravity wave. NARRATOR: The problem is a
minuscule signal from a gravity wave has yet to be caught. BARRY BARISH: It's clearly hard. In fact, when Einstein
predicted them, he thought it was a nice
idea, but no one would ever be able to detect them. It's only the
advances of technology that give us a chance. NARRATOR: LIGO scientists, like
astro-surfers, live for the day when they can hang 10 and ride
their very own perfect wave of gravity. NEIL DEGRASSE TYSON: We've
seen what we think are the effects of gravity waves-- the loss of energy
from a system by way of gravity waves-- but we
never directly detected one. That's one of the
last frontiers. NARRATOR: If the LIGO
scientists' quest is successful and they catch a wave,
it could change science. BARRY BARISH: So I
think the long term is first to understand gravity, and
then even more interestingly, to understand the universe. NARRATOR: The force of gravity
has domain over our universe. It created and can destroy the
cosmos, the stars, the planets, and the people. It controls our lives, our
play, and our endeavors. NEIL DEGRASSE TYSON: And
therein is this cosmic ballet. NARRATOR: Our collective
future depends on the grace and greatness
of the mighty ruler of the cosmos-- gravity.
