The first technique capable of measuring the pull of gravity on a particle just microns in diameter could aid the quest for a quantum theory of gravity – a longstanding goal in physics. The new experiment uses a superconducting quantum interference device (SQUID) to detect the force on the particle at ultralow temperatures and suppresses vibrations that might interfere with motion due to gravity.

Gravity differs from the other fundamental forces because it describes a curvature in space-time rather than straightforward interactions between objects. This difference explains, in part, why theoretical physicists have long struggled to reconcile gravity (as described by Einstein’s general theory of relativity) with quantum mechanics. One of the main sticking points is that while the latter assumes space-time is fixed, the former states that it changes in the presence of massive objects. Since experiments to determine which description is correct are extremely difficult to perform, a theory of quantum gravity remains out of reach despite much theoretical effort in areas such as string theory and loop quantum gravity.