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Physics has a bit of a messy problem.

There's matter missing in our universe.

Something's there that we can't see, but we can detect it.

This mysterious substance behaves a lot like the matter we know,

you know, the matter that makes up you, me, the sun, the planets, and the stars, at least in the way that matter attracts other matter.

Stars can orbit other stars, galaxies, collections of billions of stars, can orbit other galaxies.

And looking at those orbits or the way things move around other things in space

can tell us how massive the object in the center is.

But sometimes we can't see what is really causing that movement.

When we look at how stars move in galaxies, they move as if there is a lot of matter there that we can't see.

That's Chonda Prescott Weinstein. She's a theoretical particle physicist at the University of New

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