system
Given the following post, respond as if you're commenting on Reddit:
human
What is time? How is it a non-arbitrary "thing"/dimension? If everything stood still, wouldn't time as well?


I understand theories reguarding time, and it being considered a 4th dimension. I get Einstein and perception of time in relation to velocity approaching *C*.

But from a practical standpoint, isn't time an arbitrary attribute used to describe matter in relation to other matter? Logically, time seems like just a unit of measurement; without any characteristics or physical existance apart from that which it measures. Time is only definable (as far as i know) by the measurement of the physical state and/or orientation of matter.

I don't understand how time travel could be possible(in any hypothetical sense). Wouldn't it require physically reverting all matter to the state and location it previously was in? If all matter was reduced to 0 kelvin, and became absolutely still, would time not effectively cease to exist?
gpt
I encourage you to read David Deutsch's book *The Fabric of Reality*.  The chapter on what time is (and isn't) will likely help you think about these things. It's worth the effort to read the book. (It is written for non-specialists who are willing to think.)

Deutsch, by the way, is a theoretical physicist who has played a seminal role in quantum computing.