Steven D'Aprano wrote:
(1) General relativity tells us that not all observers will agree on the space-time coordinates of two objects, since not all observers agree on a single frame of reference.
But that doesn't mean they won't agree about whether objects are identical or not! The coordinates they use to describe spacetime locations may differ, but they will agree on whether or not they are equal. A Lorentz transformation can't cause a single point in spacetime to split into two, or two distinct points to merge into one.
(2) Quantum mechanics tells us that objects are not located at a single space-time coordinate. Objects are "smeared out" over space (and time). We cannot really talk about the location of an object, but only about the probability of a measurement registering the object at a certain location.
But that doesn't mean you can stuff two objects into the same space at the same time. What we perceive as solid objects are composed of fermions, which obey the Pauli exclusion principle. That means you can't have more than one of them in a given quantum state. While you *could* have two of them equally spread out over all of space, they would then have to be separated in some other dimension such as momentum or spin. So if you replace "space-time coordinates" with "quantum state", the original statement remains essentially true. -- Greg -- https://mail.python.org/mailman/listinfo/python-list