- Gravity is capable of producing waves.
Now, we've never seen these things.
So the challenge is to see them.
And just like other forms of waves,
you get frequency.
So, you know, I can talk like this,
or I can talk like this.
You can change the frequency of sound.
And for light, the analog of frequency is color.
Blue's at one end of the frequency; red's at the other.
So you can change the frequency of waves.
So gravity waves come in different frequencies
caused by different events.
So, the analog of blue, I'm sorry, of red,
would be the waves of gravity that were caused
around the time of the Big Bang.
Now, can we see those?
That's the question.
Or you can consider supermassive black holes.
There are these things called black holes
that are predicted by this (mumbles).
You could imagine looking at supermassive black holes
as they interact with galactic nuclei.
Can you detect those kinds of waves?
The frequencies are gonna be different.
Or you could look at things
like binary stars in our galaxies.
And so there's a whole range of frequencies
in which these waves can occur.
Question is, can we find them?
And that's what I'm gonna close on.
Well, first of all, it's more math, right?
Because that's what Einstein actually gave us,
a piece of mathematics.
And those of us who like to play with mathematics
beat the math to death to get it to tell us a story.
And then go talk to our friends
who are very clever at measuring things,
because typically those of us who are really good at math
are terrible at measuring.
It's almost an exclusion principle.
(students laugh)
And so you have to talk to people
really good at measuring things.
And your friends who are really good at measuring things
go out and build these very sophisticated devices.
Although the LHC which measured the Higgs'
was not invented for measuring gravity,
it's one of the most complicated devices
that has ever been constructed.
So you talk to people who can build complicated devices.
And like I said, normally the people who understand the math
are not the people who can build the devices.
And there's a third group that's sort of in-between the two.
In our community, we call them phenomenologists.
They're the people who understand the math,
understand devices.
They kind of act as the glue to make sure
that the whole edifice works to discover new science.
So this is what the math of these waves look like.
It's the last thing.
Let me point out there's a factor of two here
whereas when I looked at electromagnetic waves,
there was a factor of one.
And when I look at sound waves, there was no term
like this at all.
This is again telling us we can track the spin
of these waves by looking at the trigonometric dependence
on a certain variable.
So, in March of this year,
there was an announcement.
The announcement was that an experiment called BICEP2
had seen evidence of gravity waves
in the early universe.
So how do we translate that the ordinary people speak?
Because we're all ordinary people here.
So the idea is,
if I had a cup of latte
and I put a spoon in it and I stirred the cup up,
If I look at the suds and foam on the top of the latte,
I can see the pattern there.
And so the idea here was that in the early universe,
remember in our radiation picture,
we always saw all these modes
that were looking like circles?
If they were there in the early universe,
they would have stirred the early universe
and therefore any picture taken of the early universe
would show the evidence of this stirring.
And that's what the BICEP2 experiment was claiming,
that they could see the evidence of the gravitational waves
stirring the early universe
by looking at the cosmic microwave background.
That's what was up.
Now unfortunately, we now think that was wrong.
And I wish David Spergel was here,
because this is really in David's realm.
David was here last year, and in fact, he and I talked a bit
about various things related to this.
But there's lots of evidence that they blew it.
Because we humans aren't perfect.
We cannot do everything perfectly all the time.
It's just not in our human capacity to do it.
So in science, we try to do the best we can,
and as we tell you scientific stories,
they're the best possible things
we can tell you at the time.
So, BICEP2 didn't seem to find this effect,
but there's another experiment called Polar Bear
where they may be seeing an (mumbles) effect.
There's a recent piece of research out
that maybe they're seeing the stirring
in the cosmic microwave background
caused by these primordial gravity waves.
So these are some pictures of the actual,
this is the BICEP2 experiment.
This picture is a illustration of the Polar Bear Experiment.
What other ways could see these waves?
Well, I have a little movie here.
In this movie, what we have,
what we imagine are two start, but not too ordinary stars,
but two massive neutron stars
that are orbiting about each other.
Now, neutron starts are every interesting
because they have these beam-like structures
that come out top.
If they're massive enough, they will generate
waves of gravity, and if you,
unfortunately the lights are too high,
but you can kind of see there's some kind of something here
that's rolling and it's coming to, like,
a familiar blue marble and its companion,
namely us.
Passing the moon.
And when this wave gets to the ground,
if it's really there, it's gonna do something,
Now, if it happened to hit at two places
in the United States when,
and the Hanford nuclear reservation in Washington,
or, near Louisiana, New Orleans.
It'll come down and find an L-shaped building.
This L-shaped building is a scientific experiment called LIGO.
The Laser Interferometry Gravitational wave observatory.
All of you who are taxpayers in this room
you spent probably by now about 500 million dollars on this.
So you might want to know where some of your money went.
This is where you were spending it.
Actual pictures of LIGO look like.
On the left of this we have the site in Johnson, Paris
and Louisiana north
and west of New Orleans.
On the right we have the one in the state of Washington
at the old Hanford Nuclear Reservation.
Now, as you can see there's this big, L-shaped building.
And if you watch the end of my movie,
Which you would have noticed the building was not at rest,
it was actually flexing.
And the reason that it was flexing
is because these waves from the neutron star,
if the mathematics is right, tells us that space is flexing,
But if something is in space, then that thing has to flex.
So the idea with this experiment is that
you can measure the flexing in this L-shaped building.
1.7 long, kilometer long arms.
You can try to measure how the arms are stretching
when one of these waves comes down and strikes it.
Now, the changes that you're trying to measure
are remarkable.
They're like a thousand times the sme,
a thousand times smaller than the nucleus of a helium atom.
That's pretty small.
And so, LIGO has been in operation.
It's just recently had an upgrade that will allow it
to continue to run, and we're looking
for the effect of these waves.
So the waves will be changing the lengths of these arms.
We use lasers, by the way, to measure the links.
That's why it's laser interferometry
gravitational wave observatory.
And we look and see, do these two arms
get a little bit smaller,
in a way that's consistent with these mathematics.
That's a hard experiment, clearly.