A few decades ago we actually saw explosions
in the sky somewhere out in space that we
really didn’t understand at all.
They gave intense bursts to something called
gamma rays.
And gamma rays are the highest energy kind
of light that is possible.
Now you probably heard of, you know, ultraviolet
rays from the sun, they give you sunburn.
And then there are things like x-rays.
Gamma rays are even more energetic and more
dangerous to us than that.
But gamma rays are only created in the universe
by things that are naturally in the billions
of degrees.
And we saw these little gamma ray pops going
off in space.
At first we wondered well are they nearby?
Could they be in our own galaxy or are they
very far away?
We really didn’t know.
And a few decades ago we actually realized
that these gamma-ray bursts were coming from
very, very distant galaxies.
Galaxies that in most cases were billions
of light-years away.
A light-year is about six trillion miles,
the distance that light travels in one year.
So billions of light-years away.
And so something was creating a lot of gamma
rays because they were bright enough to measure
from that distance.
And incredibly some of these explosions were
so intense – there was one I believe it
was in 2007 that NASA observed.
There was a little flash of visible light
that came with the gamma rays and it was actually
visible with the naked eye for a couple of
minutes.
If you were actually in the southern hemisphere
on that night you would have seen a little
star turn on and off for a couple of minutes
and then it would have been gone.
And that explosion happened about seven billion
light-years away.
Something blew up seven billion years ago
on almost the other side of the observable
universe and it was bright enough to see with
the unaided eye.
We had discovered something unbelievable.
What could possibly be that bright?
What could possibly be that violent?
That little explosion for a few minutes outshone
the rest of the observable universe.
Just one thing.
So we really didn’t know what could possibly
create that much energy.
And the theoretical physicists got to work
and they started just kind of guessing.
I mean what could explode that could make
that much energy?
And it turns out that if you have these things
called neutron stars.
Neutron stars are the leftover compressed
cores of dead stars.
They are amazing monsters.
They’re about ten miles across and they
have a density that if you had about a teaspoonful
of the material that that would be about as
much as the mass as Mount Everest crushed
into a teaspoonful.
They’re amazing things and we observe hundreds,
thousands of these things in space.
And so people sort of theorize that if two
of these things spiral together and collided
you would actually be able to get that much
energy out.
It seemed unlikely but, you know, maybe that
does happen sometime in the universe, the
two of these things collide.
Now Einstein came up with this wonderful idea
that space and time is almost kind of like
a fabric that connects everything in the universe.
And what gravity is is gravity is kind of
a pulling and a stretching on that fabric.
And if you have two really massive things
moving around each other very fast before
they collide.
Say two neutron stars spiraling in.
They should actually make ripples in this
fabric.
So as they spiral closer and closer together
they actually make ripples that actually go
out through space at the speed of light.
And these are called gravitational waves.
And they are very, very hard to find.
I mean lucky for us masses moving around only
create tiny little distortions in space and
time.
The fabric of space and time itself.
So what happens is we actually started building
instruments that were sensitive enough.
Sensitive enough to detect this tiny little
wobble in space and time itself.
And to give you an idea about how hard this
is to detect we used an instrument called
LIGO, the Laser Interferometric Gravitational-Wave
Observatory.
And LIGO has two lasers and the lasers are
about two miles long and they’re actually
at a right angle.
So two-mile long lasers at a sort of a corner
shape.
And the idea was that if one of these ripples
in space and time comes through one of the
sides of the laser in this corner construction
would actually be warped a little more than
the other and you’d actually see that space
and time itself were changing a little more
in one direction as this ripple came through.
The ripple is so small that over a two-mile
laser the distance space and time changes
is by about a thousandth of a diameter of
a proton.
We have an instrument that can measure that
and amazingly we started seeing these ripples
coming from many different places in the sky
as these neutron stars collided and spiraled
together.
And the thing that was so wonderful – this
only happened last year – is that one of
these gamma-ray bursts, one of these ultraviolet
explosions that we have no idea really what
they could be went off.
And at the same time at the speed of light
with those gamma rays came that ripple, that
signal that exactly matched two neutron stars
spiraling together.
We had guessed that the only thing that could
actually make that much energy were these
two dead stars colliding and now we had evidence.
And the evidence was a ripple in space and
time a thousand times smaller than a proton.
