Physicists don’t know much about dark matter. They can’t agree on what it’s made of, how much a single particle weighs, or the best way to construct a Play-Doh diorama of it. (How would you do it? Dark matter is invisible—light doesn’t interact with it at all.) Nobody has ever caught a dark matter particle on Earth. But after 30-plus years of telescope observations, most researchers do agree on one thing: The universe contains a lot of it.

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