Better than the light traveling through time experiment, is Tom Van Baak’s experiment in which he outfitted his family minivan with high-precision cesium clocks to demonstrate to his kids that they gained 22 nanoseconds of vacation time on their mountain road trip, compared with readings on clocks left back at home. Time travel in action.
As a collector of vintage and modern atomic clocks, I discovered it was possible, using gear found at home, to convert our family minivan into a mobile high-precision time laboratory, complete with batteries, power converters, time interval counters, three children, and three cesium clocks. We drove as high as we could up Mount Rainier, the volcano near Seattle, Washington, and parked there for two days. The trip was continuously logged with the global positioning system; the net altitude gain was +1340 meters.
Given the terrestrial blueshift of 1.1 Ã— 10-16 per meter mentioned by Kleppner and integrating our altitude profile, we predicted the round-trip time dilation to be +22 nanoseconds. This is remarkably close to what we experimentally observed when, after we returned, the ensemble of portable cesium clocks was again compared with atomic clocks left at home.