One of the weirder aspects of quantum mechanics could be explained by an equally weird idea – that causation can run backwards in time as well as forwards.
What Einstein called “spooky” action at a distance could theoretically be evidence of retrocausality, which is the particle equivalent of you getting a stomach ache today thanks to tomorrow’s bad lunch.
A pair of physicists from the US and Canada took a closer look at some basic assumptions in quantum theory and decided unless we discovered time necessarily ran one way, measurements made to a particle could echo back in time as well as forward.
We all know quantum mechanics is weird. And part of that weirdness comes down to the fact that at a fundamental level, particles don’t act like solid billiard balls rolling down a table, but rather like a blurry cloud of possibilities shifting around the room.