Gravitational Lensing as the Universe's Double-Slit: Wave-Optics Proofs, Interference Conditions, and Astrophysical Evidence - Weber

This work reframes gravitational lensing as nothing less than the cosmos performing Young’s double-slit experiment at astronomical scales.Starting from the scalar wave equation in a weak-field spacetime, the paper derives the Fresnel–Kirchhoff diffraction integral, proves that the phase difference between lensed images is exactly proportional to their time delay, and establishes quantitative criteria for interference visibility in both electromagnetic and gravitational waves. With rigorous theorems, order-of-magnitude estimates, and astrophysical examples, the paper demonstrates why quasars appear incoherent, while fast radio bursts, astrophysical masers, black hole photon rings, and gravitational-wave chirps are prime candidates for observing gravitationally induced interference fringes. The analysis unites classical GR lensing, quantum interference, and modern observational astronomy into a single framework: spacetime itself provides the “slits,” and the carriers — photons or gravitons — do the rest.This is not speculation: the observational data already exist in radio telescopes, gravitational-wave detectors, and mm-VLBI arrays. The framework outlined here provides immediate, testable predictions for current and next-generation facilities, positioning gravitational lensing as the ultimate natural interferometer. RJW