Concerning quantum entanglement Wikipedia says:
Measurements of physical properties such as position, momentum, spin, and polarization, performed on entangled particles are found to be correlated. For example, if a pair of particles is generated in such a way that their total spin is known to be zero, and one particle is found to have clockwise spin on a certain axis, the spin of the other particle, measured on the same axis, will be found to be counterclockwise, as is to be expected due to their entanglement. However, this behavior gives rise to seemingly paradoxical effects: any measurement of a property of a particle performs an irreversible collapse on that particle and will change the original quantum state. In the case of entangled particles, such a measurement will be on the entangled system as a whole.
I am worried about the phrase "measured on the same axis". If one particle is measured on the earth on a certain axis and the other is measure on the moon (or somewhere near Alpha Centauri) how does one set up the measuring devices so that both are measured on the "same axis"? It seems this would require some kind of parallel transport which might be difficult or impossible to do--especially if curvature of space-time must be taken into account.
And what if the two measuring locations are a billion or so light years apart. Must we wait for a settled theorem of quantum gravity to deal with this case?
I imagine something like a Stern-Gerlach apparatus as measuring device.
In the EPR experiments done on the surface of the earth, what devices are used and how are they aligned.