Zoom out to the level of the whole universe, if you can imagine that. Looking at the whole thing at once, you might notice that there's a lot that you actually cannot see. We can observe this same quandary at smaller scales: Stars in galactic systems rotate as if much more mass is present than the stars could contain. So where is this mass? This mysterious stuff is what astrophysicists call dark matter, but as University of New Hampshire theoretical physicist Chanda Prescod-Weinstein points out in our cover feature ("Enter the Axion," pages 158-165), that moniker is really a misnomer. As she says, we can see light bouncing off dark objects, but so-called dark matter doesn't interact with electromagnetic radiation at all. It's more hidden to us than if it were simply dark.
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