If matter is quantum, why does the everyday world appear solid and definite, never blurred across possibilities? Part of the answer is decoherence, the leaking of quantum coherence into the environment.
At the microscopic level, physics runs equally well forward and backward; the film of colliding particles looks lawful in reverse.
Erasing a bit of information is not free.
Among physical laws one stands apart for caring about direction.
The laws of physics look the same run forward or backward, yet time plainly flows one way.
Some quantities never change, whatever else does.
That the laws of nature look the same from different viewpoints is no mere elegance.
To understand a system one need not track every detail.
Cool water and at a precise point it becomes ice, its character transformed.