By Sebastian Anthony on March 7, 2013
A team of Chinese physicists have clocked the speed of spooky action at a distance — the seemingly instantaneous interaction between entangled quantum particles — at more than four orders of magnitude faster than light. Their equipment and methodology doesn’t allow for an exact speed, but four orders of magnitude puts the figure at around 3 trillion meters per second.
Spooky action at a distance was a term coined by Einstein to describe how entangled quantum particles seem to interact with each other instantaneously, over any distance, breaking the speed of light and thus relativity. As of our current understanding of quantum mechanics, though, it is impossible to send data using quantum entanglement, preserving the theory of relativity. A lot of work is being done in this area, though, and some physicists believe that faster-than-light communication might be possible with some clever manipulation of entangled particles.
Now, thanks to these Chinese physicists — the same ones who broke the quantum teleportation distance record last year — we know that spooky action at a distance has a lower bound of four orders of magnitude faster than light, or around 3 trillion meters per second. We say “at least,” because the physicists do not rule out that spooky action is actually instantaneous — but their testing equipment and methodology simply doesn’t allow them to get any more accurate.
To get this figure, the physicists entangled pairs of photons at a base station, and then transmitted half of each pair to two receiving sites. The receiving sites were 15.3 kilometers (9.5mi) apart, and aligned east-west so as to minimize the interference from the Earth’s rotation (which is significant, when measuring speed on this scale). One half of the pair was then observed, and the time for the other half to assume the same state is measured. This process was repeated continuously for 12 hours to generate enough data to accurately divine the speed of spooky action.
As cool as this sounds, it's actually kind of blase at this point. There have been experiments where one particle was measured AFTER the first was detected and no longer exists. In that case, the effect was more than instantaneous, it happened before the cause.
One experiment that was done recently (last 1/2 year or so) was to take two pairs of entangled photons, and measure one photon from each pair for polarization. These are uncorrelated. Then, the two remaining photons - one from each pair - go on after the first two are measured. Sometime later, those two photons can be operated on in such a way as to entangle them, which (retroactively) entangles the first two photons that were measured for polarization. This "swaps" the entanglement.
When the entanglement is swapped, the polarizations of the first photons will HAVE BEEN measured to correlate with each other, even though the decision as to whether to swap the entanglement as made after the measurement when the two original photons no longer exist.
Another experiment moved entanglement from one photon to the next, to the next, and then measures it. The entanglement works even though the partner hasn't existed across several transfers of entanglement.
My conclusion is that entanglement not only doesn't care about spacial separation, it doesn't care about temporal separation - which according to Einstein is kind of the same thing. The world is not what we think it is.