RAY WEISS: Einstein's view of gravitation
was very different than Newton.
Newton was thinking of forces between objects,
and he didn't quite imagine how the forces would project
from one object to another.
That was always a mystery.
On the other hand, Einstein replaced that spookiness
with, probably, something that's just a spooky,
and that was this notion of gravitational waves.
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GABRIELA GONZALEZ: LIGO stands for Laser Interferometer
Gravitational-Wave Observatory.
The W didn't fit in there, so we just hyphenate.
LIGO's goal is to detect gravitational waves.
Gravitational waves were predicted by Einstein's theory,
but they have never been directly detected.
We have very strong indirect evidence,
and we all believe his theory.
But we'd never saw these waves, directly.
So that's what we want to measure them.
MIKE ZUCKER: Newton's description of gravity
was, basically, that it was a force that
was proportional to the masses of bodies
and inversely proportional to the square of their separation.
Einstein's concept was to look at the body's influence
on the space they're embedded in.
And so in Einstein's picture, a massive body
makes a depression in the spacetime around it,
so that other bodies, following their natural paths,
tend to be attracted to this depression.
The two ideas sort of come up with the same answer
when we're describing, say, the orbit
of the Earth around the sun, or the moon around the Earth,
or the falling of an apple.
But they differ if you think about,
what is the effect of a very rapid change.
For example, if two stars collide or a star explodes,
somehow the change in the mass distribution--
the presence or absence of the star
where there was one before--
has to somehow be communicated throughout the whole universe.
And in Newton's picture, there's a problem with that.
Because there isn't any way for that information
to take some finite amount of time.
Somehow, the whole universe must know about everything,
instantaneously.
It's called the problem of action at a distance.
So going back to Einstein's picture,
if you think of it in terms of massive bodies
affecting the spacetime, you can immediately
think of a way to communicate information about those bodies
from place to place through ripples in spacetime.
RAY WEISS: The waves can be represented by this object
I found on a wine bottle.
And it's a mesh that you can see, and the waves cause,
transverse of the direction in which they're moving--
they're moving forward--
and transverse to that, the space gets tugged like this,
and collapses like that, tugs like this.
And if you look carefully at this,
and I'll do this a few times, you'll
notice that the little squares in this
are how they're exercising a motion where,
along one direction--
it's obvious which direction, I mean
the direction I'm pulling in--
space is getting expanded.
But transverse to that, up and down,
space is getting contracted.
That's the key to the whole thing.
LIGO LIGO is laid out in an L shape.
And each side of the L is four kilometers long.
Four kilometers was chosen because the American taxpayers
are willing to pay for it, and it's far enough
to get an effect that we think we can see.
The reason it's an L shape is because gravitational waves
cause objects to get closer in one axis
and farther in a perpendicular axis, and then vice versa.
So we fill the two arms with light
from a laser in the corner station.
And the light spends about 1/100 of a second in this arm
and 1/100 of a second in the other arm.
And then the light comes back to the corner station.
And the light that spent time in this arm comes back a little
bit before or a little bit after the light that
spent time in the other arm.
And that's how we would detect the effect.
GABRIELA GONZALEZ: A lot of people
tried to think about how to produce gravitational waves,
so you could measure them.
And then you have an experiment like you do with radio.
You produce the waves, you detect them,
and then you prove that they exist.
But with gravitational waves, it turns out
that you need a lot of mass and very high accelerations
in order to make any distance change at all,
by even a minuscule amount that you can measure.
So everything produces gravitational waves.
But it's only big things sound out.
It's big black holes, big neutron stars,
that are accelerating, and colliding, and exploding.
And it's that kind of event that produce
gravitational waves of such magnitude
that we can measure them.
MIKE ZUCKER: The prediction is that gravitational waves
are always occurring.
The reason why we don't notice them
is that they're exceedingly weak.
They're very hard to imagine how weak they are.
But for our detector, for LIGO, we're looking for displacements
of the test masses at the two ends that will be something
like 1,000th the diameter of a proton,
over a scale of 2 and 1/2 miles on a side.
So we're looking for substantially smaller
displacements than the kind of things
that people normally experience and measure.
GABRIELA GONZALEZ: When we begin detecting gravitational waves,
it's going to be in the newspaper
everywhere, because it's going to be the first time we
see gravitational waves.
But once we begin seeing them routinely,
and we can classify it-- and these come from black holes,
these come from neutron stars, these comes from supernovas--
then we can learn a lot about these sources.
MIKE ZUCKER: I think one of the really big motivations
for looking for gravitational waves, in addition
to all the wonderful forms of energy that we observe
our universe in, is precisely this fact that they're
entirely responsive to the distribution of matter.
And so if we can detect them, we'll
see what's going on in the course of the objects, the most
dense and the most active parts.
And even though it's quite challenging
and it hasn't been done before, the promise is that we'll
reveal, effectively, a different universe than we've
seen before.
RAY WEISS: And that's what makes it so exciting for most
of the people in this business.
It isn't just one number you're looking for.
This experiment isn't over when one makes one discovery.
It has a lovely, distant, wonderful future
with many, many new things that will come.