No. 19: Jan-Feb 1982
How do physically separated subatomic particles (and devices based on them) communicate with one another? Somehow one subatomic particle knows what a distant compatriot is doing and reacts accordingly. Physical experiments have confirmed this seemingly impossible situation. No fields, wires, or any other sort of communication line connects the two particles; yet they behave as though there were. Quantum mechanics has an explanation of sorts but it still leaves the situation with an aura of mystery.
(Mermin, N.D.; "Bringing Home the Atomic World: Quantum Mysteries for Anybody," American Journal of Physics, 49:940, 1981.)
Comment. This digest is greatly oversimplified, and readers are encouraged to read the whole article. It is an important type of physical experiment because some have suggested it may help explain ESP, assuming ESP exists.