That the laws of physics are symmetric under time reversal[0], so any statement you make about how things should evolve "over time" also holds if you go backwar

That the laws of physics are symmetric under time reversal[0], so any statement you make about how things should evolve "over time" also holds if you go backwards in time. The apparent arrow of time is commonly thought to have to do with initial conditions. Entropy was low right after the Big Bang, creating an asymmetry between the two time directions. 0. Technically, the laws of physics are symmetric under stimultaneous inversion of time, flipping of all charges, and a mirror reflection of space.