Ripples in the fabric of spacetime
Einstein predicted in 1916 that accelerating masses create ripples in the fabric of spacetime — gravitational waves. These waves travel at the speed of light, stretching and squeezing space as they pass. In 2015, LIGO made the first direct detection: the merger of two black holes 1.3 billion light-years away, opening an entirely new window on the universe.
Two compact objects — neutron stars or black holes — spiral toward each other, radiating energy as gravitational waves. As they lose energy, the orbit tightens: the frequency and amplitude increase in a distinctive chirp. The spiral accelerates until the objects merge in a cataclysmic event, followed by a ringdown as the merged remnant settles.
Try it: Watch two objects spiral inward while ripples propagate through the spacetime mesh. The color encodes strain — blue for compression, amber for stretching. Adjust the mass ratio and playback speed to explore different scenarios.
Gravitational waves have two polarization modes. The plus mode (h+) stretches space along one axis while compressing the other. The cross mode (h×) does the same but rotated 45°. Together, they describe any gravitational wave.
LIGO uses laser interferometry to detect length changes of 10⁻¹⁸ meters — one-thousandth the diameter of a proton. Two 4 km arms form an L shape. A gravitational wave stretches one arm while compressing the other, creating an interference pattern in the laser light.
LIGO uses laser interferometry to detect gravitational waves. A laser beam is split and sent down two 4-km perpendicular arms. When a gravitational wave passes, it stretches one arm and compresses the other, changing the interference pattern at the detector. The GW150914 signal shown is the first-ever direct detection of gravitational waves from a binary black hole merger.
The gravitational waveform from a binary inspiral encodes the masses and distance of the system. The chirp mass determines how the frequency sweeps upward. Listen to the chirp — when sped up to audible frequencies, it sounds like a rising tone that ends abruptly at merger.
The gravitational wave "chirp" signal from a compact binary inspiral. As the two objects spiral closer, the orbital frequency and wave amplitude increase until coalescence. Click "Play Chirp" to hear a sonified version mapped to audible frequencies. The chirp mass Mc = (m1m2)3/5 / (m1+m2)1/5 determines the evolution.