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When I was a little girl I got lost in
the jungle.
I heard the ocean in the distance
somewhere far away.
The sound of the waves carried me out of
the trees, out of the darkness, to safety.
We talk a lot about the things we see.
But what we hear can guide us, comfort us,
even amaze us. My name is Lucia and I'm
getting a PhD in physics. Well, I'm hoping
to get a PhD in physics anytime now! If
I've learned anything in the last few
years it's that things are not as simple
as we think. The ocean can seem calm and
tranquil, gently changing with the tides.
But the ocean can be violent. Waves can
churn under the surface in intricate and
complex ways.
Even simple things are more complex than
we thought. Like the way gravity keeps us
grounded. Since the time of Newton we
have thought of gravity as a force
pulling objects toward earth. Check this
out!
But then in grad school they taught us
that Einstein described gravity as more
like the ocean: dark, complex, mysterious.
Just like the ocean gravity can turn
violent.
And like a drop in the ocean
gravity can become a wave. My advisor and
I are researching extreme gravity and
gravitational waves. Gravitational waves
have a story to tell about the most
extreme systems in the universe. This
story is so complex that it can only be
understood using complicated mathematics
and computer simulations. Imagine:
colliding neutron stars. Merging black
holes.
Giant exploding stars. For the first time
we can listen to these amazing stories.
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Einstein wrote the equations that
describe gravity as we understand it
today.
Between 1905 and 1915 Einstein created
his masterpiece: the Theory of General
Relativity. The cornerstone of this
theory is that space and time form a
continuum called space-time. Space-time
can stretch and curve due to the
presence of dense objects like planets
or stars. Gravity, to Einstein, was not a
force as Newton imagined. Rather it was a
result of the curvature of space-time.
if this were true,
Einstein reasoned, then space-time could
also vibrate and undulate. Like when an
object falls into water--there are
ripples created on the surface.
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Gravitational waves are ripples in
gravity itself.
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How do we know Einstein’s theory is true?
In 100 years of testing Einstein's
theory scientists have yet to find one
experiment that disagrees with the
predictions of his masterpiece.
Not even one! How crazy is that?
I have a cool example: for years
scientists were confused about the orbit
of mercury. All the planets in our solar
system move in ellipses around the Sun.
But Mercury's orbit is crazy elliptical
with a little wobble thrown in. We call
that wobble precession. Here's how Einstein’s
theory of space-time can explain
Mercury's strange orbit. The Sun is so
massive that it curves space-time. A lot!
Since mercury is the closest planet to
the Sun, its orbit is the most affected.
In one of my grad classes we calculated
the orbit of mercury using Einstein's
theory of general relativity. We learned
that it is the curvature of space-time
created by the Sun that causes Mercury's
wobbly orbit. Einstein's theory also
predicts other effects.
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If space-time is really curved then
light should follow a curved path as it
travels from distant stars to earth. And
if the Sun was between Earth and the
Stars -- stay with me here --
then the star light would have to bend
around the Sun before reaching us,
right? Einstein made a prediction this
would happen.
Not only that he calculated exactly how
much the light would bend. And this was
before anybody observed this effect. In
1919 Einstein's light bending prediction
was confirmed by a team led by English
Royal Astronomer Sir Arthur Eddington.
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Here is what happened. During a solar
eclipse
Eddington photographed stars very close
to the Sun. Those are here. Six months
later when the Sun was not between Earth
and the stars
Eddington photographed the same stars
again. Without the Sun bending space-time
those same stars appeared here.
The stars were not in the same place. It
is as if the stars had moved a vast
distance in the six months between
observations. That's impossible!
It must have been starlight bending
during the first observation and not
during the second.
In other words Eddington found exactly
the effect that Einstein predicted.
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Experiments and observations were
telling us that Einstein was right.
Space-time bends and curves
significantly around massive objects
like stars. Wait a second. Okay-- that's
better!
So that's why the light produced by this
star looks like a ring instead of a
point. Light is bending on its way to
Earth.
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Scientists from all around the world
started to use Einstein's theory to make
amazing discoveries. Here's a great
example. Using Einstein’s formulas
scientists reasoned that if an object in
space is really dense it will collapse
onto itself and become a new type of
star: a dark star -- a black hole. Imagine if
you took the Sun, which could fit 1.3
million earths inside it, and compressed
it down to the size of 32 football
fields. That would create a black hole.
The curvature of space-time-- gravity-- is
so strong in a black hole that nothing--
not even light-- can escape. I like to
think of black holes as the corpses of
dead stars that shine no more. I know,
very poetic of me! When two black holes
collide space-time is forced to undulate
and vibrate. Waves are formed and
propagate away from the black hole at
the speed of light. These are
gravitational waves. And they are
produced at other times.  Like when
stars explode in amazing supernova.
Or when neutron stars collide and
produce short bursts of radiation. These
gravitational waves fill Einstein's
universe in a quiet symphony of
incredible activity and dynamic range.
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Einstein's theory predicted the
existence of gravitational waves. And a
hundred years later the detection of
gravitational waves by advanced LIGO is
one more confirmation that Einstein was
right all along.
Gravitational waves help us answer some
huge questions. Like how do stars die? How
are black holes born? Gravitational waves
paint a whole new picture of our
universe. But here's an interesting thing:
It is a picture that we cannot see.
gravitational waves are not light waves
so we can't just point a telescope to
observe them. We don't see gravitational
waves; we hear them. But how? We use
special equipment to amplify the waves.
That is what you are listening to right
now: this is the sound of colliding
neutron stars. This is the sound of
merging black holes. And this is the
sound when you add music!
Detecting them is more complicated than
hearing ocean waves. Here's how we do it.
Scientists built two intersecting
tunnels with mirrors at the ends.
They shoot lasers down the tunnels,
bounce them off the mirrors, then let the
laser light recombine. When a
gravitational wave is passing through
Earth, the wave stretches one tunnel and
compresses the other. When that happens
the lasers get out of phase. They don't
line up when they recombine. These laser
interferometers are antennae listening
stations for gravitational waves.
There are several sites like this around
the world.
Now imagine these listening stations in
space!
Scientists plan to launch a laser
interferometer antenna into space to
expand our understanding of
gravitational waves.
Scientists from the European Space
Agency and NASA are leading the mission.
Years of experience launching rockets
and satellites will help guide these
efforts.
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By using powerful lasers and other tools
to detect gravitational waves we can
continue to listen to the symphony of
The universe.
When I was a little girl, the sound of
the ocean led me out of the jungle.
Hearing can be just as important as
seeing.
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There are things in the universe we
cannot see. We cannot see black holes, but
we have strong evidence they are there.
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We can hear the gravitational waves
black holes produce when they collide
with each other.
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The universe is becoming audible! These
sounds can give us a new understanding
of how the universe was formed, and how
it continues to change. The waves tell an
unseen story. But we don't know how the
story will end. Observing gravitational
waves will lead to discoveries and
technologies that we can only dream
about. Let's close our eyes,
imagine our future, and listen!
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