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).
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There is no such thing as “Time” as an independent “thing”. There is no such thing as “Space” as an independent “thing” either. There is only Spacetime.
Spacetime has 4 dimensions (leaving out the theoretical ones from other theories), x, y, z, and t. If you want to know where you are in spacetime, you need those 4 numbers. T = time. So time is not it’s own “thing”, it is a dimension of spacetime.
As for time dilation, the simplest way to explain it (which isn’t TOTALLY correct but accurate enough to be useful) is one given by Brian Greene in his book The Fabric of the Cosmos.
You body is made of matter. Matter is energy, so we can say you body is made up of X energy. At rest, X energy is moving through the Time dimension of Spacetime (at the speed of light). Now, lets say you walk across the room. You are now spending Y energy to move through a different dimension of Spacetime (a spatial one, up, down, left, right, etc). Since energy can neither be created nor destroyed, the energy needed to move through that spatial dimension of spacetime has to come from somewhere. It comes from the energy that was being used to move you through Time, so before you moving through Time with X energy, now you are moving through time at X – Y energy, which is slower.
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