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But antigravity avoids that problem, Chardin says, and it could also do away with two of the biggest puzzles in cosmology: the mysterious dark matter whose gravity keeps the galaxies intact and the even weirder dark energy that is stretching space and accelerating the expansion of the universe.

Gabriel Chardin, a cosmologist with CNRS, France’s national research agency, says, “It’s a beautiful experiment by outstanding people” and “a blow” to speculative theories that assume antimatter experiences antigravity—but not yet a fatal wound.

For example, in 2012 Chardin and a colleague hypothesized that the universe might contain equal amounts of matter and antimatter, with the latter subject to antigravity.

“Pure antigravity is excluded,” Chardin says.

The new result might seem to torpedo Chardin’s model, as it rules out antigravity equal in strength to gravity.