The Order of Time

by Carlo Rovelli

The usual way of interpreting the relation between time and the state of equilibrium is to think that time is something absolute and objective; energy governs the time-evolution of a system; and the system in equilibrium mixes all configurations of equal energy. The conventional logic for interpreting this relation is therefore: time → energy → macroscopic state5 That is: to define the macroscopic state we first need to know the energy, and to define energy we first need to know what is time. In this logic, time comes first and is independent from the rest. But there is another way of thinking about this same relationship: by reading it in reverse. That is, to observe that a macroscopic state, which is to say a blurred vision of the world, may be interpreted as a mingling that preserves an energy, and this in its turn generates a time. That is: macroscopic state → energy → time