Like cops tracking the wrong person, physicists seeking to identify dark matter—the mysterious stuff whose gravity appears to bind the galaxies—may have been stalking the wrong particle. In fact, a particle with some properties opposite to those of physicists' current favorite dark matter candidate—the weakly interacting massive particle, or WIMP—would do just as good a job at explaining the stuff, a quartet of theorists says. Hypothetical strongly interacting massive particles—or SIMPs—would also better account for some astrophysical observations, they argue.

"We've been searching for WIMPs for quite some time, but we haven't found them yet, so I think it's important to think outside the box," says Yonit Hochberg, a theorist at Lawrence Berkeley National Laboratory and the University of California (UC), Berkeley, and an author of the new paper.

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