across space and time

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Everyone knows that quantum physics is weird—but it just got weirder. 
Because a team of scientists from the University of Jerusalem have used quantum entanglement to allow two photons that never existed at the same time to communicate with each other.

Quantum entanglement is a weird old phenomena that means some particles, like photons and electrons, can interact with each other physically once, and yet still go on to share states—like spin or polarization—even when they're separated. That's what led Einstein to refer to the idea as "spooky action at a distance", because changes at one point are instantly mirrored in another physical location.

But the University of Jerusalem researchers have gone further, creating a pair of photons that were entangled not across space—but across time. In reality, the process didn't just use two photons to achieve the feat, but rather four.

First, the team used a laser to entangle two photons, call 'em P1 and P2. Then they measured the polarization of P1—in turn destroying it. Then they created a second pair of entangled photons, P3 and P4, and then entangled P2 and P3.

Following all this, the researchers claim that P4 demonstrated entanglement with P1—despite the fact that P1 was destroyed before P4 was even created. The researchers explain:

“In the scenario we present here, measuring the last photon affects the physical description of the first photon in the past, before it has even been measured. Thus, the 'spooky action' is steering the system’s past. 

Another point of view that one can take is that the measurement of the first photon is immediately steering the future physical description of the last photon. In this case, the action is on the future of a part of the system that has not yet been created."

It's the first time researchers have experimentally shown action at a distance can work not just across space but time, too. Of course, it's not really clear what the hell this finding can be used for—but sometimes science for science's sake is cool. And photons communicating from beyond the grave? That's cool.


—jamie condliffe 

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