Scientists just invented an entirely new way of observing the universe, and it's not with light, because what we've detected is waves in actual space.

That is, the stretching and compression of space itself in a ripple passing by us.

And as soon as we turn on the detector, we saw the merge of two black holes.

Scientists have been dreaming of this for a long time.

Einstein first proposed his theory of general relativity over 100 years ago, stating that gravity is really just the curvature of space and time, or spacetime.

In other words, a huge mass like a star curves space and time like this ball placed on a sheet.

And if mass could bend space, then accelerating or moving masses could send out ripples in the sheet, and we call those gravitational waves.

Einstein came up with all the math to describe this over 100 years ago.

Then, nearly 75 years later in 1992, scientists founded LIGO, the Laser Interferometer Gravitational Wave Observatory, to search for these waves.

But it wasn't until 2015 that gravitational waves were finally detected from the event where two black holes about 30 times the mass of the sun collided, sending out shock waves that reached us 1.3 billion years later.

The technology had to come so far for this to be possible.

Check it out.

In the LIGO detector, you've got two vacuum tunnel arms with lasers that go back and forth reflecting off of mirrors on the other end.

Depending on the distance those laser beams travel after reflecting off the mirrors, when they meet back up again you get interference, like waves that interfere in water making patterns.

If space is stretched or squeezed in one of these directions by passing gravitational waves, the laser beams in that arm will travel for more or less time, affecting how the two beams interfere when they meet back up.

And we can tell space has been stretched.

But this detector has to be so sensitive, it's affected by quantum mechanical vibrations in the mirrors.

So sensitive, it was picking up vibrations from trucks driving on roads nearby.

But scientists found ways to cut out that noise.

And in addition, there are two labs, one in Louisiana and one in Washington, making sure that the signal detected wasn't from something local.

That moment when those two detections matched up perfectly was the goosebumps moment when scientists realized we had heard a true signal.

Scientists have been using the term "heard", which I think helps set the technology apart from anything we've ever done, usually with light.

But the waves don't actually make a sound, because sound doesn't travel through empty space.

But scientists did take the waveform and turn it into a sound waveform to make the chirp heard 'round the world.

But the way this chirp affects us is not immediately obvious to all.

I mean, as little as you might follow biology or anthropology, it's easier to see the importance or excitement in finding the first hominid skeleton, or finally sequencing the entire human genome, because it opens doors.

The observation of gravitational waves in and of itself is exciting, but these waves have hypothetically been passing through the universe since way before humans existed and we've never known for sure.

It's like being deaf your entire life and finally able to hear for the first time.

That's what we've done for gravity.

That's what we've done for the field of astronomy.

And we can look out at the universe with an entirely new metaphorical lens, and at extreme violent events, and at objects that we know very little about, like black holes.

Plus, the technology is the most precise instrument ever developed.

It's improved cryogenics, optics, and made contributions to a number of other fields.

And who can forget that, though Einstein was ironically uninterested in the applications of his theory of relativity, we rely very heavily on it for the multi-billion dollar industry surrounding GPS.

And lastly, I'm going to venture so far as to say that we should care because it's relevant.

It's just cool.

If physics no longer had any practical applications, we'd probably still keep doing it because we are curious.

We want to know about our world.

This is how the universe works, the same universe that works in such a way that it's possible for you and me to exist.

Spacetime is the landscape in which we live, and we've just created a new way to understand it.

Thank you for watching this episode of "Physics Girl", and happy physicsing.