How to Make Light Late ⚡ экспресс
The Shapiro delay—one of the classic tests of general relativity—allows constraining the PPN parameter γ, which equals 1 in GR. So far, all measurements have been astrophysical and planetary, with an accuracy of 10⁻⁵. This work proposes a Sagnac fiber interferometer for ground-based measurement of the Shapiro delay, with sensitivity approaching 10⁻⁹. This method enables a laboratory determination of γ, representing an independent test of GR in a previously unexplored experimental regime.
Mass curves spacetime like a heavy stone pressing into an asphalt road. Light passing by skirts around this dent, its path lengthens, and it arrives late. Astronomers have observed this Shapiro effect many times near the Sun and planets.
A new plan proposes to recreate this delay on a lab bench. Two beams are simultaneously launched into a closed fiber-optic loop: one clockwise, the other counterclockwise. A massive object placed nearby curves space within the loop, and one of the beams arrives with a delay of billionths of a second. The technology is well-honed: similar devices already detect vibrations of space.
Instead of satellites and telescopes, Einstein's theory of gravity could be tested in an ordinary room. The precision is enough to spot deviations hinting at new physics. Remarkably, the light delay near bodies was originally proposed by Einstein himself in 1916—long before the first spaceflights.
🎯 The strongest Shapiro effect from our star: a signal to Venus and back is delayed by about 200 microseconds due to the Sun's gravity.