Time and Motion

If everything in the universe stopped moving, would time pass? You couldn't tell how long the stillness lasted: your clock wouldn't move [a]; you couldn't experience the stop: your neurons wouldn't be firing; you couldn't check via calander: the Earth's rotation and orbit would pause; you couldn't age or check corrosion since no bacteria would live to eat away at your body and no chemical reactions could tarnish metal or rot at anything.

What we call "time" is just the procession of motion; today we use atomic clocks and this measure time as the regular vibration of caesium atoms but in the past of course we used other (less regular, less perfect) events such as the Earth's rotation, but these regular movements are not time themselves any more than a yardstick is itself distance. It's all just commeasurable ratios of periods of motion.

I used to think that speed was a construct. What I mean by this is that we have this equation linking speed, distance and time, which goes like this:

v = d / t
That is, the speed of an object is equal to the distance covered divided by the time it took to travel that distance. Now I thought speed was a construction in that it was something we made up to describe what we saw, purely determined by the other two variables. You could change the distance something travelled, or the time it took to travel but if you tried to change speed directly you would only do that by changing the other two. Now I understand that it's really the other way around,
t = d / v
You can change speed, it's time that is the construct. Only motion actually exists and time is just something we perceive to explain this. Generally, all that happens when you measure the speed of an object is you're measuring the speed of this object compared to another object (probably a caesium atom or quartz crystal) which acts as a common measure. In this sense you could say the measurement of speed is a construct in that a "metre per second" doesn't really exist, since we made up "seconds" from photons and use the motion of light as a common measure for other motions.

As such, to say we exist in "spacetime" or whatever is meaningless. We don't live "in time", time is not a thing in itself, we live in a physical world where objects (matter) are/is capable of motion. Anything that could be described as "outside of time" is really being described as "outside of motion" or really "outside of matter" (since matter - or energy, since they're the same thing - is always what is moving). Something that is eternal is really just something that never moves or changes - seems obvious but sometimes people think of this as being a consequence of something being eternal rather than the state of being eternal as a consequence of these properties.

Example

Think about this: if you had a universe that consisted entirely of a ball in some otherwise empty space, and moved the ball somewhere else, all you would have to do to "roll back time" would be to simply move the ball back to where it was (assuming literally there is nothing else in the universe). The same is true for our universe, which is obviously much more complex and intricate. The comparable example would be like moving something like 1080 balls back, but if you could do that, there is nothing to say that time would not completely have materially reversed in the universe.

Notes

a: That is, the quartz crystal or caesium atom wouldn't move, not just the clock hands or LEDs