The universe we can see is only a fraction of the great cosmic beyond. Galaxies, stars, planets, humans, trees — all of it comprises just 5% of the energy and matter in the universe. Among tangible matter, as opposed to the mysterious cosmic rending force called dark energy, only about 15% is the stuff we can detect. As for the rest, it comes in the unknown form known as dark matter.

This substance cannot be seen or held, yet cosmologists are broadly confident dark matter exists, because it is a shepherd of galaxies. Vast halos of dark matter surround every galaxy, including ours, and this invisible material can act as a lens to redirect the light that emanates from other galaxies, warping our vision of deep space. Dark matter also guides galaxy clusters as they evolve and move through the cosmos.

But we have no idea what it looks like, what it weighs, or how it functions. For decades, physicists have searched for a particle of dark matter in locations that range from deep underground mines to the International Space Station. All efforts have turned up empty so far. In other words, we don’t know what the universe is.

This is all extremely complex, mathematically abstruse, philosophically profound and, to theorists like Cora Dvorkin, great fun.

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