if an event happens at the exact moment of another for a single observer, what does instantaneous mean? This stems from a question i posed about the speed at which two entangled particles collapse into one definite state when one is measured. It got m thinking what does zero time and instantaneous really mean. Can any two events truly be said to happen in an instant with zero time elapsing between them. I know we cannot measure zero time, we could only measure down to the planck scale. So do we know that events can happen with zero time between them for a single observer?