Some physicists believe time is a function of Entropy
https://en.m.wikipedia.org/wiki/Entropy
https://en.m.wikipedia.org/wiki/Entropy_(arrow_of_time)
The 3 arrows of time:
1. Psychological. We remember only the past, not the future.
2. Entropy. Always increases overall as time moves forward.
3. Cosmological. Universe expands into the future. (This one might need some qualification in some other universe, but definitely the case in ours.)