Gravity Makes Time Local: Atomic Clocks Detect Millimeter-Scale Time Differences
The most precise optical atomic clocks can now detect gravitational time dilation over a mere millimeter in a lab: clocks at the bottom run slightly slower than those at the top, enabling direct tests of general relativity at human scales. With precision around one part in 10^21—roughly one second in 30 billion years—this landmark achievement opens practical avenues for gravimetry, geophysics, and possibly redefining the second, signaling that time is locally shaped by gravity rather than universally uniform.
