Entropy increases over time. This is the basis on of the second law of thermodynamics = the tendency that over time, differences in temperature, pressure, and chemical potential equilibrate in an isolated physical system. A change in the entropy (S) of a system is the infinitesimal transfer of heat (Q) to a closed system driving a reversible process, divided by the equilibrium temperature (T) of the system. The entropy of an isolated system that is in equilibrium is constant and has reached its maximum value.
You can prove this yourself as a house of cards (which is very low entropy) would always prefer to be a pile of random cards (representing high entropy)
Therefore, disorder increases as time passes. At the heart of every difference between the past and future — memory, aging, causality, free will — is the fact that the universe is evolving from order to disorder. Entropy is increasing, as we physicists say. There are more ways to be disorderly (high entropy) than orderly (low entropy), so the increase of entropy seems natural. But to explain the lower entropy of past times we need to go all the way back to the Big Bang. We still haven’t answered the hard questions: why was entropy low near the Big Bang, and how does increasing entropy account for memory and causality and all the rest?