Halloween is long over so we might as well finish up the discussion of spooky action at a distance. We were left last time wondering if a particle that finds itself distantly removed from another particle can act as if both particles can still talk instantly to one other.
Einstein was not a believer in such “nonlocality.” Note it is well known that two particles can feel each other’s presence through reasonable means. For example, when we talk on the phone to a friend/relative in another continent we all know that there are delays brough on by the distance. After each reply we have to allow a couple of extra seconds for the signal to travel to the recipient and make it past the various delays.
Another example of a reasonable means of communication is by gravity. For example, a star can know of the presence of another very distant star because stars are heavy and release gravitational waves. Gravitational waves travel at the speed of light, so after a certain amount of time corresponding to the time it takes for light to travel between the two stars, both stars will know about each other. This will effect, for example, their overall trajectory through space.
We are all fine with that. What is bothersome about action at a distance is that the communication would be instantaneous. Einstein attempted to understand action at a distance by introducing the concept of quantum entanglement. If two particles shared a similar origin, then maybe even when they got separated they will still somehow manage to stay tangled up to the other
Physicist John Bell found a way to test for this kind of behavior and only found evidence in support of action at a distance. Was Einstein wrong? There is one new idea out there that we may live in a more holistic universe in which the pieces of space are organized into patterns not separated by vast distances in the usual sense but instead assembled in piecemeal fashion like a realization of a kaleidoscope. The jury is still out, and in the meanwhile there is still much that one can contribute to solve this fundamental problem.
