Two coins are flipped in different cities, but they always land the same way. Physicists call this entanglement: particles behave as if an invisible thread connects them. But what if the thread isn't instantaneous, just very fast — still not faster than light? Then some signal could slip between measurements, and the coincidences would be explained without any magic.
The authors of the new work built an experiment where two detectors were placed at varying distances, and a precise time signal was sent over an ordinary wire. If a slow signal were flying between particles, it wouldn't have time to travel from one station to the other before the measurement ended. But correlations held at any distance. So there's no hidden 'mailman.'
This result closes the last fundamental loophole in tests of quantum nonlocality. Now we can more confidently say that the world, at its most fundamental level, doesn't obey the familiar logic where everything propagates no faster than light.
In early entanglement experiments, detectors sat in the same room, and a 'signal' could have slipped between them. Now the distance is varied from meters to hundreds of meters without touching the rest of the setup.
In the series 'Dark,' entanglement allows communication across time, but real experiments show that no information carrier between particles is needed.