Our universe has been ruled by weirdness for at least six centuries. If the quantum effects in a new experiment aren’t genuine, but are somehow caused by past meddling, then that is how long ago it must have happened – a finding that makes would-be alternatives to quantum theory even more unlikely.
But the quantum effects we see on tiny scales defy these descriptions. The properties of particles aren’t set in stone until we measure them, and their states can be
entangled – such that altering one affects the other much faster than light can travel between the two.
Their experiment exploits a standard test for locality: Bell’s inequality. It sets a limit on how often two entangled particles can end up in the same state just by chance – without quantum mechanics or some unknown “hidden variables” to guide them.
The first step is to create a pair of
entangled particles – often photons of light – then fire them off in different directions. Usually, a random number generator determines at the very last moment which property of each particle to measure. The detectors used are far enough apart that the arriving particles can’t “cheat” and coordinate their states – unless they can signal each other faster than light.
If the measurements tally more often than allowed by Bell’s rule, then the particles aren’t governed by locality. Previous experiments have shown this consistently, and so backed quantum mechanics.
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Few things are as comforting in the winter as sheltering from the bleak weather in the dark wood and creaking floorboards of a pub with a beer and some good company. 
