While most of us take gravity for granted, physicists have a big problem with it. Their beef: As forces go, gravity is implausibly feeble. (Try asking a physicist why a kitchen magnet can pick up a paper clip even though the gravitational force of the entire Earth is pulling the clip down.) In 1999 University of Washington physicist Eric Adelberger heard a lecturer offer an intriguing explanation: Perhaps gravity only appears weak, because it operates in additional spatial dimensions beyond length, width, and height. These extra dimensions would be imperceptible in our macro world but might have a detectable influence on gravity at scales of less than the width of a hair.
That may seem like a wild notion, but Adelberger took it seriously. If extra dimensions exist, undiscovered particles and forces could be hiding within them. So he and his colleagues devised a way to test the idea. Their ...
