What is time, physically?

Question

I’ve been thinking about relativity where the passage of time depends on your velocity, but I don’t really understand what this means physically. I understand that the clocks of two different people traveling at different relative speeds will be different, but what does this really mean? Does this imply that time is a physical quantity, like energy, and that depending on your speed you have less of it? To make this more complicated, my understanding is that it’s not just clocks that will be different, it’s the actual “age” of physical things; ex: if I’m traveling at the speed of light I can go infinite distance and to me it would be like waking from a coma, I would have no memory of traveling at all, so as far as I was concerned it didn’t happen. I guess I just don’t really understand what this means about the physical nature of time; is it a tangible quantity like matter or is it more like a byproduct of something else and what we call “the passage of time” is just how we measure it (ex: if I heat up a gas and the atoms get more disordered then it’s entropy has increased, but I can measure temperature and use that as a proxy for entropy).

In: 11

Answer 1

Time is merely a measure of motion. You can base it on any regular movement – the sun across the sky, the hands of a clock, the radioactive decay of an atom, whatever. It isn’t actually a real thing in and of itself. When people say time goes slower as you speed up, what they mean is that the internal molecular motion of the thing going fast slows down.

Now, you can use time as a mathematical variable, and in some instances the formulas it is used in will correctly predict reality. But, like any mathematical formula, you can play around with them beyond the limits of the physical context where they actually work. Most of the fantastic and nonsensical theories about time travel are like this. Take formula A that works under conditions X to describe the real world, switch the conditions to impossible thing Y, then pretend that you can still translate that into a description of physical reality.