- Einstein really made some waves.
Or at least he predicted them.
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When Einstein published his theory
of general relativity a century ago,
one of the predictions in that theory
was something called gravitational waves.
This was an idea Einstein had where giant,
violent activities in the universe,
like black holes colliding, or neutron stars
rotating around each other rapidly
would cause ripples in space time,
and those ripples would move out from the source
at the speed of light, and those ripples
are what we call gravitational waves.
But here's the thing, Einstein was pretty sure
we would never be able to detect them,
because they're invisible and their effects
are so small as to be almost unimaginable.
But here's the really cool news,
we detected them anyway, take that, Einstein!
So how did we do it?
Well, you have to understand a peculiar thing
gravitational waves do when it ripples this space time.
It actually changes the distance between two points.
Now, if we were to magnify this effect
a billion billion billion times,
you could actually see it in action.
In reality, the effect is much much smaller.
For example, if a supernova were to explode
in the Milky Way galaxy, and keep in mind,
that's our home turf, the gravitational waves
from this event would only be large enough to change
the distance between the Earth and the sun
by the diameter of a hydrogen atom.
So how on Earth did we detect such a thing?
The answer is with the LIGO observatory.
Now, the observatory has a pair of enormous detectors.
One of them is in Louisiana,
and the other is in Washington state.
What's really cool about LIGO is its elegant design.
Each of these detectors is built
in an L shape of vacuum tubes.
Those tubes are 2.5 miles long, or four kilometers.
At the end of each tube is a mirror,
and at the crux of the L is a beam splitter.
So they fire a laser through that splitter,
one half of the laser beam goes down one vacuum tube,
the other half goes down the other.
They bounce off the mirrors at the end,
and because both halves are traveling
the exact same distance, they return
to the crux at the same moment.
Their wavelengths cancel each other out,
and no light is emitted, but when a gravitational wave
moves through, one arm of the vacuum tube
gets longer, the other gets shorter,
because they're perpendicular to each other.
That means the laser has further to travel
in one direction and shorter on the other,
and that also means they don't meet up
at the same time at the crux, some light gets emitted.
A light detector picks this up,
and that's the information scientists use to determine
whether or not a gravitational wave has moved through.
So why are there two detectors,
and why are they so far apart?
Well, it's to make sure that it's not a false positive.
You see, if one detector picks up a hit
but the other one doesn't, that suggests
some sort of local event has set off the detector.
Maybe seismic activity,
or even just a heavy truck rolling by.
But if one detector picks up a gravitational wave
and the other picks it up within 1o milliseconds,
you know you've got something.
And that's what happened in September 2015.
Now, scientists took their time analyzing this data,
and they didn't announce the discovery
until February 11th, 2016.
That's when we found out the gravitational wave
they detected was from a pair of colliding black holes
that hit each other 1.3 billion years ago.
And now everything has changed.
We have a new way to observe the universe.
We can listen to it.
This is like being alive when the telescope was invented,
and it could be the gateway to learning
about everything from dark matter to black hole behavior
to the origins of the universe itself,
and my mind is blown.
But I've got a question for you guys.
What scientific endeavor do you think astronomers
and physicists should dedicate themselves to next?
Dark matter, maybe cosmic inflation, moon cheese?
Let me know in the comments below.
Thanks to Toyota for sponsoring this show
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