time-a quantitative matter

Entropy

Vis that’s really a good q and deserves much discussion

First of all it’s difficult to describe, it’s so basic a commodity it isn’t easily defined using words, we presently lack the semantic equipment

But it’s an objective phenom even though different organisms sense it differently, as exhibited by its dependence in relativity upon other quantum phenoma

But in an unsatisfactory answer to your q, it didn’t start, it was always there

However there’s a theory that expansion will reverse, slowing clocks and bringing together all matter into a huge ball of uniform composition until it reaches a state of infinite mass with zero dimension—when of course time has stopped— whereupon the next Big Bang

Of course I hasten to explain it isn’t shaped like a ball. In addition, the state of nothingness entails contradictions and paradox resolved however by its enjoying a duration of zero