Any extra dimensions of space curled inside the three that humans inhabit are less than 50 micrometers in diameter, physicists reported February 15.

Ted Cook of the University of Washington in Seattle and colleagues used a torsion pendulum, two rotating disks strategically riddled with holes whose gravitational tugs on each other can be precisely tracked, to probe how gravity works at small scales. If the force’s strength differs from expected when objects are very close, it could indicate that gravity leaks into extra dimensions. Earlier work showed that gravity’s pull is normal when objects are 56 micrometers apart, meaning any extra dimensions must be smaller than that.

But Cook’s setup is twice as sensitive, allowing him to winnow the limit even further. He eventually hopes to push the limit below 30 micrometers.

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