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Missing mass? Not on our watch—Dr. Paul Sutter explains dark matter ctm magazine


Produced and directed by Corey Eisenstein. Click here for transcript.

Greetings, Arsians! We have something special for you today: the premiere of a new science series we’re creating, called Edge of Knowledge. We’ve recruited physicist and author Dr. Paul Sutter (Google Scholar link) to be our host and guide on an eight-episode romp through the mysteries of the cosmos, touching on topics that we at Ars find fascinating. This means we’ll have episodes on black holes, the future of climate change, the origins of life, and, one of my favorite topics for our premiere: dark matter.

Dark matter: The universal majority

As Ars readers, you’re all probably familiar with Douglas Adams’ “Space is big” opening to The Hitchhiker’s Guide to the Galaxy, but “big” only tells part of the story. You might assume that, as a corollary to all that bigness, space should also be generally vast and empty, with just an occasional stray hydrogen atom whipping its way through an otherwise perfect vacuum of nothingness—but nothing could be further from the truth.

Because that’s the thing—empty space isn’t empty at all. It’s absolutely chock full of all kinds of stuff we don’t have a solid understanding of—stuff so weird that we have a difficult time even looking at it to try to learn about it. In fact, if scientists are doing their math right, it turns out that there’s so much of this weird stuff that what we think of as the “normal” stuff in the Universe—things like protons and neutrons and electrons that make up all of the observable matter in the Universe—account for only a tiny fraction of the Universe’s overall mass.

We call some of this weird stuff “dark matter,” because it’s difficult-to-impossible to measure or observe. Despite its invisibility, it is truly ubiquitous—as Paul explains in the video, there’s dark matter everywhere. There’s dark matter streaming through your body right now. But one of dark matter’s key features—the feature that makes it so difficult to observe, in fact—is its stubborn unwillingness to interact in almost any meaningful way with “normal” matter.

(Dark matter isn’t the only weird thing that exists in enormous abundance everywhere—there’s also the apocalyptic creepiness of dark energy, but we’re saving dark energy for another video in the series.)

Pull my strings

I say dark matter is stubbornly unwilling to interact with “normal” matter in almost any meaningful way, but it turns out that there is one very important way in which dark matter does interact with us, and that’s through gravity. Dark matter exerts gravity proportional to its mass, just like “normal” matter, and this is what led to its initial discovery. The only way to explain a bunch of large-scale observations of the Universe—including the way galaxies rotate around their central black hole cores—is if there’s a whole buttload of mass floating around that we can’t directly observe, and dark matter is about the only thing that fits the bill.

There’s lots more to learn about this weird undetectable stuff—including the ways in which we’re getting closer to actually detecting it. If you have a few minutes, please kick back and enjoy Paul’s explanations about one of the Universe’s fundamental mysteries.

And stay tuned—we have seven more episodes on the way!



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