Physicists are remarkably frank: they don’t know what dark matter is made of. “We’re all scratching our heads,” says physicist Reina Maruyama of Yale University. “The gut feeling is that 80 percent of it is one thing, and 20 percent of it is something else,” says physicist Gray Rybka of the University of Washington. Why does he think this? It’s not because of science. “It’s a folk wisdom,” he says.
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