The problem is that entanglement violates how the world ought to work. Information can’t travel faster than the speed of light, for one. But in a 1935
paper, Einstein and his co-authors showed how entanglement leads to what’s now called
quantum nonlocality, the eerie link that appears to exist between entangled particles. If two quantum systems meet and then separate, even across a distance of thousands of lightyears, it becomes impossible to measure the features of one system (such as its position, momentum and polarity) without
instantly steering the other into a corresponding state.
Up to today, most experiments have tested entanglement over spatial gaps. The assumption is that the ‘nonlocal’ part of quantum nonlocality refers to the entanglement of properties across space
. But what if entanglement also occurs across
time? Is there such a thing as temporal nonlocality?
The answer, as it turns out, is yes. Just when you thought quantum mechanics couldn’t get any weirder, a team of physicists at the Hebrew University of Jerusalem
reported in 2013 that they had successfully entangled photons that never coexisted. Previous experiments involving a technique called ‘entanglement swapping’ had already showed quantum correlations across time, by delaying the measurement of one of the coexisting entangled particles; but Eli Megidish and his collaborators were the first to show entanglement between photons whose lifespans did not overlap
at all.
In other words, time is fluid. The past can change the future and the future can go back and alter the past.
