In 2015, The LIGO Scientific Collaboration made the historic discovery of two coalescing black holes and the waves of curved space, gravitational waves, that erupted out of this cosmic explosion. It was the first discovery in what Kip Thorne called the violdent “warped side” of the universe, invisible to our observatories and space based cameras. And then, just two years later, Thorne, Rai Weiss and Barry Barish won the Nobel Prize in Physics for LIGO.

The discovery made by LIGO's two giant detectors in Louisiana and Eastern Washington State was the culmination of a half-century-long search.

Kip knew as early as 1978 that according to theory, LIGO would have to reach a sensitivity of 10-to-the-minus 18 meters in its measurement of the movement of the mirrors suspended at each end of each arm of each observatory. That is one with 17 zeros in front of it.

The gravitational waves sweep across the observatories, infinitesimally stretching and squeezing the arms — with their mirrors — as lasers measure the changes in the distances between them as they move. This dance of the mirrors traces, imprints, the signal of the colliding black holes or neutron stars.

It was Vladimir Braginsky, a Soviet scientist, and Kip, who were long ago concerned that once LIGO achieved that measurement in the quantum world, looming ahead was an impenetrable quantum barrier that might well be an ultimate limit to LIGO's sensitivity: A theoretical barrier that had stood firm for nearly a hundred years.

It was based on Werner Heisenberg's famous uncertainty principle of 1927, one of the pillars of quantum physics, which said that in a quantum world the precise continuous measurement of subatomic particles, such as electrons, or photons, the particles of light, was impossible. Because, once the position of a particle was measured, the uncertainty of its momentum or movement must be unknown, and vice versa.

These gravitational waves are so faint, it was like seeing one strand of hair on the surface of the nearest star, Alpha Centauri, 25 trillion miles away.

Bringing a measurement at the level of seeing one hair 25 trillion miles away to distances on Earth itself was like measuring a subatomic particle 10,000 times smaller than a proton in the nucleus of an atom. A quantum measurement, indeed.

So all continuous measurement here would be uncertain. Everything would be probability. A cloud of probabilities to only estimate the specific qualities of the laser light measuring the gravitational waves.

That Kip, Braginsky and others knew early on this was a severe limitation to how sensitive the LIGO observatories could ever become was another way of saying they feared there was an ultimate barrier to how far they could see into the warped side, the unknown side, of the universe.

In 2024, more than five decades later, LIGO succeeded in breaking this theoretically insurmountable barrier, known as the Standard Quantum Limit. This is the story of that astonishing achievement.