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Dance Your PhD: Two Black Holes Merging with Kari Alison Hodge

The relationship between art and science is something we talk a lot about on this show. Today we bring you a guest who is a wonderful illustration of it…

Kari Alison Hodge didn’t take her first physics class until she was a junior in college at USC, but now she is at Caltech finishing up her PhD in Gravitational Wave astronomy. Kari did something really interesting, she took her thesis and made it an interpretive dance. It’s called Dance Your PhD, a yearly competition where you choreograph a dance around your thesis, film it and set it to music. It is then judged by a panel of scientists and dancers. I’ll be talking to Kari about gravitational wave astronomy, how you dance it, and the intimate relationship between art and science. 

Here's a link to the video.


Transcript:

 

Brittney Gallagher

What is gravitational wave astronomy?

Kari Alison Hodge

Traditionally, humans have looked for things in our galaxy and beyond, using light, like radio waves, x-rays, light in the visible spectrum. And this is a whole new way of looking for things. Instead of looking for photons, we are measuring space-time here on earth, and when an event happens far away, it creates these ripples in space-time that travel toward us, and then when they reach us, they stretch and squeeze space-time.

So, gravitational wave astronomy relies on Einstein’s general theory of relativity, which describes what we feel as gravity as simply mass and energy curving space time. There’s an analogy that’s used a lot. You have a rubber sheet, and you put a bowling ball in it, and the rubber sheet stretches because of the weight of the bowling ball. And then if you roll a marble on that rubber sheet, it falls into the bowling ball, much like how things fall into a black hole.

So now, think if you have bowling balls moving around on that sheet. If you dropped a stone into water, you see ripples traveling away from the stone, telling you that the stone was dropped in the water.

So in particular what I’m looking for are two black holes that are orbiting each other, and they’re getting closer and closer together, and finally they merge and become one black hole. Originally you had two separate bowling balls, and in the end, you have one in the middle. And the information about that change and where the black holes were travels to us on Earth.

Brittney Gallagher

Tell us about dancing your PhD.

Kari Alison Hodge

Once I heard of it, I knew I had to do it. I mean, every time I go to a conference, like a gravitational wave conference, I always...

Brittney Gallagher

Are there a lot of those?

Kari Alison Hodge

There are. Several a year, in fact.

Kari Alison Hodge

 I organize a dance party for the people attending the conference.

Brittney Gallagher

Are gravitational wave astronomers big dancers? Is that something we didn’t know about?

Kari Alison Hodge

Yes. They are very good. They all have their own style.

Another reason why is that the gravitational waveforms that I’m looking for are in the audio band. So you can transform them from that pattern of light into music. So, my thesis especially was just asking to be danced.

Brittney Gallagher

Describe how you danced your PhD.

Kari Alison Hodge

I started off in space with the cosmic ballet of the two black holes orbiting each other, finally merging, and then ringing down as they settle into their new form of being one black hole. And that produces ripples in the fabric of space-time which are carried from space to our detector sitting on Earth, which is LIGO, which stands for Laser interferometer Gravitational Wave Observatory, by our gravitational wave messengers.

These are new messengers, because usually we are looking to photons to see things in space. But you actually could not even use photons to sense black holes colliding, because photons would just fall into the black hole. They wouldn’t bounce off and come back into your eye.

When the gravitational wave goes by our detector on Earth, it uses the fact that light interferes with itself to measure the lengths of the arms of the el extremely accurately. So, in my dance, I have four of my friends lying on the ground. It’s a very sunny day, and I’m making them lay face up in the sun, and I’m yelling at them, “X-arm contract! Y-arm lengthen! X-arm contract! Y-arm lengthen!” As I have these other people, the gravitational wave messengers, pushing the sheet up and down, making a little wave pattern.

As the gravitational wave passes by, it produces a pattern of light out of the vortex of the el. And I zoom into that light, where I am then dancing representing the data that you are extracting from that pattern of laser light that represents the gravitational wave that’s gone by.

I do a very specific wiggly dance that represents the wiggles that come when the black holes are spiraling into each other, then different wiggles when they merge, and then a subtle ring down. And I have a friend who has made a vocal track to go over that, that goes from low frequency to high frequency, because as the black holes are getting closer together, the gravitational waves are going from low frequency to high frequency and also from quiet to loud. It’s known as a chirp signal, like, “whoo-ip.”

So then we get to the problem of other things causing light to escape the interferometer. I have my thesis advisor, who has kindly agreed to be an electromagnetic glitch in the detector. We had made this big magnet out of foam, and gave it to him, and he runs over to the detector, and does a little hula dance, and wiggles it, and as he does that, my characters playing the detector shake on the ground. A new pattern of light comes out. And once again, I am dancing the signal that you see in the data, that is due to an electromagnetic glitch happening in the detector.

So the question is, how do we distinguish the wiggles from the merger of black holes, from those due to an environmental glitch or glitch within the detector itself?  And we have sensors all over the detector.

So I put on a bunny suit. The purpose of a bunny suit is to make sure that none of your sweat or skin or dust particles gets out onto the equipment that you’re working with. So, dancing in a bunny suit on a hot day is a terrible idea. And, play the humpty dance. On repeat. Go and taken measurements from each of the components of my detector.

I take the temperature of one of my actors. I connect a multimeter to the head of another. And I place a little seismometer next to one. And that’s representing what I’m doing a lot of in my thesis, which is looking at what’s happening in those sensors, to say, if the pattern of light we’re seeing is due to an environmental or instrumental glitch.

For example, we have airplanes, or an earthquake in China. All shake the detector a little bit, cause light to escape, that looks kind of like the light that would escape from the merger of two black holes.

Brittney Gallagher

So...you’ve never actually found a gravitational...

Kari Alison Hodge

Right. It’s very important that I say that we have never found a gravitational wave.

Brittney Gallagher

But you know they’re there in theory.

Kari Alison Hodge

Yeah.

Brittney Gallagher

Do you know what a black hole would look like?

Kari Alison Hodge

We do, calculated based on the basic principles of Einstein’s general relativity, [know] what the gravitational wave form would look like from two neutron stars orbiting and merging, versus two black holes. We’ve got the wave forms for all these different systems.

Brittney Gallagher

How does the video end?

Kari Alison Hodge

We end with my advisor leading the official LIGO dance. As I mentioned, when a gravitational wave passes by the detector, one arm of the el gets shorter while the other gets longer, So the LIGO dance is just putting your arms out in a V and doing a little shimmy like that.

Brittney Gallagher

What is your interest in the relationship between art and science?

Kari Alison Hodge

I think it’s really funny when people are shocked whenever science and art interact, because they’re actually very similar in a lot of ways. There’s an analytical component to them, and there’s a part where you have to make some crazy leap and just see if it works. They both have that. That’s at the heart of both of them.

Dancing your PhD is a perfect example of the marriage of art and science.

What’s great about projects like that is that it makes your science more understandable to non-scientists.

Brittney Gallagher

Now that you’ve danced your PhD, and you’re actually almost finished with your PhD, what are your plans for the future with art and science?

Kari Alison Hodge

I love science. I think it’s fascinating and so important. But, I’m also an actor. I’m actually also writing a script, which is tentatively titled, Women in Physics.

Brittney Gallagher

That’s very exciting. So you’re definitely taking your physics background and springing it into essentially, art.

Kari Alison Hodge

Yes, it goes both ways.



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