Not long after physicists on experiments at the Large Hadron Collider at CERN laboratory discovered the Higgs boson, CERN Director-General Rolf Heuer was asked, “What’s next?” One of the top priorities he named: figuring out dark matter.

Dark matter is five times more prevalent than ordinary matter. It seems to exist in clumps around the universe, forming a kind of scaffolding on which visible matter coalesces into galaxies. The nature of dark matter is unknown, but physicists have suggested that it, like visible matter, is made up of particles.

Dark matter shows up periodically in the media, often when an experiment has spotted a potential sign of it. But we are still waiting for that Nobel-Prize-triggering moment when scientists know they finally have it.

Here are four facts to get you up to speed on one of the most exciting topics in particle physics:

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