Shapiro Time Delay — Radar Signal Slowed by Gravity

Fire a radar pulse from a source, past a massive body, to a target and back, and watch general relativity's fourth classical test play out: the pulse's coordinate travel time grows the closer it grazes the mass, exactly as Irwin Shapiro predicted in 1964 and radar-echo experiments to Mercury, Venus and the Cassini spacecraft later confirmed. Adjust the central mass, the impact parameter and the two path distances — or load a real preset — and read the live one-way delay, round-trip echo delay and equivalent excess path length computed straight from the Shapiro-delay formula Δt = (4GM/c³)·ln(4r₁r₂/b²).