On Gravity Waves

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This week I'm going to talk a bit about the research I've been doing here at Penn State for the last couple of years. I figure I'll spend this entry and the next one talking about the actual sciency stuff, then move on after that to give some general observations about what it's like to do research. Also, I figure this should be a pretty easy entry to write, as I was up until some depressing hour of the morning writing about this stuff in my thesis. Anyway, on to the science.

General Relativity says a lot of weird stuff about the way gravity works. It replaces Newton's good old force equation with the idea that space and time are curved. You may have heard it explained using the "rubber sheet" analogy, which says that massive objects distort space like a bowling ball dropped onto a rubber sheet, which causes smaller objects to roll down towards it. 

Well, it turns out that this is kind of a lousy analogy. What exactly is pulling the bowling ball "down" onto the rubber sheet anyway? But, lousy or not, it'll have to do since explaining what's really going on requires a lot of math that I don't want to get into (and, in fact, barely understand myself). The important thing is that matter bends space, and that makes gravity happen.

It also makes some other odd things happen. It turns out that whenever a mass accelerates, it leaves behind little tiny distortions which travel away as waves. Now, whenever you have a wave you need to have something doing the waving. For sound waves, that's the air, and for light waves, that's electric and magnetic fields. For gravity waves the thing that's waving is actually length. Weird concept I know. When a gravity wave passes through something, nothing actually moves, but the distances between things get longer or shorter. Don't feel bad if that thought gives you a headache. Here's a picture of what it would look like if a gravity wave passed through a circle of objects.  The wave in this case is coming out of your computer screen:
Gravity Wave.gif

So, if these waves happen every time a mass accelerates, why doesn't the world go all loopy every time you drop something? Well, the bouncing around in that picture up there is much, much, much, much bigger than any real gravity wave could produce. Even the strongest sources, things like a pair of colliding black holes, only make distortions on the scale of the diameter of a proton. That's really small and really, really hard to see, and since scientists like to try to see really hard to see things, there's a massive project underway to try to find these little distortions

The main way people are trying to find them is with a set giant interferometers. When I say "giant", I'm not kidding.

That's a LIGO (Laser Interferometer Gravitational wave Observatory) interferometer. Those lines stretching off into the distance are 4 km long vacuum tubes. They bounce big lasers down those tubes, which lets them measure the lengths of those arms insanely accurately. When a gravity wave passes by, the arm lengths change a tiny little bit, creating a signal which scientists can measure.

Now we (finally) get to the point where I come in. The data from LIGO have crazy amounts of noise. Any minuscule vibration anywhere near the observatory will also set it off. That makes it quite hard to get anything useful out of LIGO data. I'm one of a bunch of people working on ways to try and pull a meaningful signal out of all that noise. It's a bit like trying to find a needle in a stack of needle-shaped hay, but I've been working on some nifty statistical tricks which seem to have some potential. 

If we can find gravity waves, we can look at things like black holes and neutron stars which are almost invisible to normal electromagnetic telescopes. We could even see leftovers from when the Big Bang set the universe ringing like the biggest bell you can imagine. So gravitational wave astronomy is a field that combines lasers, distortions in the fabric of reality itself, black holes, and the formation of the universe. That's cool.

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