Does space-time emerge from a network of quantum bits? That’s the theory behind emergent gravity, an idea most recently proposed by Erik Verlinde, a theoretical physicist at the University of Amsterdam. His theory does away with the need for dark matter — unseen particles that appear to affect the behavior of galaxies and other large-scale structures in the universe. But a recent test of emergent gravity shows that it doesn’t appear to do as good a job of describing the motions of astronomical objects as its theoretical rival.
Kris Pardo, a graduate student working under the astrophysicist David Spergel at Princeton University, assembled a sample of 81 isolated dwarf galaxies. These small galaxies appear to have an especially high concentration of dark matter, and so provide a unique astrophysical laboratory in which to compare various theories. He then measured how quickly those galaxies rotate. The more dark matter that exists in a galaxy — or the stronger the effects of emergent gravity — the faster the galaxy should spin. “Isolated dwarf galaxies are the cleanest test you can get,” Pardo said. “It’s the best we can do right now.”
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