In 2017, Chinese scientists did something that would have made Albert Einstein's head explode. They proved quantum entanglement across 1,200 kilometers. From a satellite.

The experiment used a spacecraft named Micius, after a fifth century Chinese philosopher who conducted the first known experiments with light. Fitting, given what came next.

Aboard the satellite, a beam of light was passed through a crystal. The crystal did something remarkable: it split the beam into pairs of photons, each pair sharing a quantum bond. One photon from each pair was beamed down to a research station in Delingha. Its partner was fired to a station in Lijiang, 1,200 kilometers away.

When researchers measured more than a thousand pairs of photons and compared the results from both stations, the photons showed opposite polarizations far more often than chance could explain. The entanglement had survived. Across 1,200 kilometers of open space, two particles were still sharing a secret.

Einstein called entanglement "spooky action at a distance" and spent years arguing it couldn't be real. The Chinese satellite is named after a philosopher who lived five centuries before Einstein was born.

The universe has a long memory, and apparently a sense of humor.