I’ve got a question for any of you geeks out there. Recently I’ve been troubled by a bit of a paradox. First, some background: It is possible to entangle the quantum properties of two particles. Doing so means that both particles will exist in a superposition of two states, but that the resolution of one superposition will force the resolution of the other particles wavefunction. All experiments to date have indicated that this phenomenon is instantaneous.
So, here’s the setup: I entangle two particles, then send one on orbit around the earth at some significant percentage of the speed of light, then bring it back to the lab with the other particle. Then I carry out a measurement on the particle that remained stationary, thus causing a collapse of the superposition.
The question: Does the traveling particle’s wavefunction collapse simultaneously in the stationary frame of the lab? Or will there be a delay associated with the time shift it would have experienced while orbiting? If it’s the former, what does that imply about space-time curvature and causality (i.e. the future, in this case the stationary particle, affecting the past)? If it’s the later, what if we measure both particles simultaneously (in the frame of the stationary particle/lab)? Is it possible to “break” entanglement, and have the two superpositions resolve to the same state? (If not, isn’t that the same as the former situation with entanglement crossing time barriers?)
EDIT:
This has been done by the group of Nicolas Gisin in Geneva:
http://prola.aps.org/abstract/PRA/v63/i2/e022111
They used a spinning absorbing wheel as their “detector” that caused projection and then a stationary real detector to collect light that wasn’t blocked by the absorber. Not ideal, of course, compared to moving the whole lab, but that was the principle. As expected, the results were not affected.
Huh. Interesting.