A binary pulsar is a cosmic metronome, setting the beat for the Universe's two 'ears'. These objects were discovered by Jocelyn Bell Burnell and studied by Russell Hulse. Radio telescopes (radio astronomy) hear the pulses, delayed by spacetime curvature near a massive neutron star — that's how we compute the orbital tilt. The second 'ear' — gravitational wave detectors, like LISA, catch the trembling of space, shifting mirrors by a fraction of an atomic nucleus using interferometry. By comparing the 'sound' and the 'echo', we test Einstein's theory.

Numerical simulations yield an accuracy of 0.004 for two neutron stars; with a black hole, it's even sharper. White dwarfs stay silent. Any discrepancy would point to hidden fields of dark matter or dark energy.