Why does time exist?

Question

So I have been thinking about some subjects and one of it involves time.

And I tried writing a story/question on here to summarize the bigger picture but it's not going to happen it's too complicated for that.

But basically one of the questions in that bigger picture was based on a comment I heard from a physicist in a video that said "people sometimes say that time is there to stop everything from happening all at once".

And that was a pretty weird comment in my opinion. But it got me thinking about it.

So then one of more basic questions that I had was, if you speed everything in the universe up with the same amount. Like, speed it up by the same magnitude. Wouldn't that be like going faster and everything ending up the same way that it will now, only faster?

Or would it alter things?

And in the end, my bigger picture ended up with kind of like... a link appearing between time itsself and the subjective experience of being alive. Consciousness. But I don't know if such a question is really answerable. So... Is there a link in that? Or is it too complicated for that?

Answer 1

Snap your fingers. Wait. Snap them again. Physically speaking, time is a measurement which distinguishes between these two different events (finger snaps) which happen non-simultaneously (snap, wait, snap) at the same spacial location. There is no reference frame in which these events happen simultaneously.

That's the simplest way I know to define time. Why does time exist? Because there are events which will always be non-simultaneous, no matter the reference frame. Time measures non-simultaneity.

Answer 2

"Why" is never a physics question, but we can replace it with "What is time?", which is.

"Time" is that which a suitable clock shows.

It's not some abstract, undefinable philosophical notion that magically "makes things happen". Time in physics is a stream of steadily increasing numbers coming from suitable experiments that measure time. We call those experiments "clocks". The definition of "time" is inseparable from the definition of "clock" in just the same way as the definition of "distance" is inseparable from the definition of "yardstick".

Once we have built good (enough) clocks, we can then correlate other numbers against the time numbers and that's how we do all physical dynamics. Now your question comes down to "When can I build clocks?" and the answer to that is given by thermodynamics: as long as the universe is not in thermodynamic equilibrium. If it were, there would be no useful notion of "time".