We often hear it said that time began with the Big Bang. The phrase sounds precise, scientific, even definitive. But when you slow down and examine it carefully, it conceals a quiet confusion. Time is not a thing that can begin. It is not a substance, a field, or a container waiting to be filled. Time is a measure — a way of ordering events. And ordering already presupposes that something has happened.
If nothing changes, there is no time to begin.
What physics actually describes, when it talks about the “beginning of time,” is not the birth of time itself, but the emergence of something much more specific: irreversible change. Before that, there may have been dynamics, laws, even structure — but no accumulation, no records, no history. Time does not precede events. It follows from them.
The key insight is simple but easily missed: facts are more basic than time. Time does not produce facts. Facts produce time. Only when something becomes true in a way that cannot be undone — when alternatives are closed and a commitment is made — does a before and an after come into existence. Time is not the stage on which reality unfolds; it is the bookkeeping that becomes necessary once reality can no longer erase what it has done.
This is why not all change creates time. A perfectly reversible process, whether in classical mechanics or quantum evolution, does not age. It leaves no scars. It produces no history. Quantum superpositions evolve, interfere, and recombine — but until a result becomes irreversible, nothing has happened in the historical sense. The system changes, but it does not grow older.
From this perspective, the Big Bang marks not the start of existence, but the onset of commitment — the moment the universe began to leave marks it could not take back. That transition, from reversible possibility to irreversible fact, is what gives rise to time’s arrow. Without it, “before” and “after” are empty words.
Time did not begin.
What began was irreversibility.
And once the universe could no longer undo itself, time appeared — not as a flowing river or a cosmic container, but as the order imposed by facts that cannot be erased.