The distinction between past, present, and future is only a stubbornly persistent illusion.

Einstein wrote this in a condolence letter (March 21, 1955) to the family of his close friend Michele (Michael) Besso after Besso’s death. He was expressing a relativity-informed view that the usual human sense of time flowing and being divided into past/present/future does not reflect how physics can represent events in spacetime.

From the standpoint of relativity, events can be treated as part of a single spacetime structure rather than something that objectively “moves” from future to present to past. Einstein’s remark suggests that the sharp boundaries we feel between past, present, and future are psychologically compelling but not fundamental features of physical reality.

For us believing physicists, the separation between past, present and future has only the meaning of an illusion, albeit a tenacious one.

People like us, who believe in physics, know that the distinction between past, present and future is only a stubbornly persistent illusion.