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> Putting the universe back as it was except for you is time travel. You've traveled your state to a different time (previous state) of the universe. > Your se

> Putting the universe back as it was except for you is time travel. You've traveled your state to a different time (previous state) of the universe. > Your semantic game sounds very clever, but is actually just inconsistent and borderline ignorant of what people mean by those terms. I don't think that's how most people think of time travel. For example, say I proceeded to invoke reactions to get all particles back to exactly how they were on Jan.1 2000. Say this took me a year, and finally, in 2018, I execute the final reaction that places the last particle, so that the universe is exactly like it was Jan.1, 2000. Have I been time travelling for a year? Does making 2018 look like 2000 what people generally think of as time travel? What about that you yourself did not change, where are those particles coming from? What about the old you existing in that time as well, there aren't enough particles in the universe to have two you's. What about the time you travelled from remaining in existence while you're gone, and the changes you invoke in the "past" propagating there? I get that it would provide a similar experience in many ways, but it doesn't involve travelling, nor time, just changes in particle positions - which is the nuance I am highlighting.

SomeStupidPoint 10y ago
You have to give up the idea of a universal clock: you only have a local one. In your example: since you erased the elapsed computation in other regions, you (by putting the particles back) are literally rewinding every clock but yours. In whatever sense they were ever in 2000, they're back there, though you're in (your) 2018. Having your 2018 be their 2000 seems like a sensible definition of time travel. (And yes, you'd have spent a year time traveling, though in many senses you always are time traveling forward, and you just happened to spend a year going fast "backwards".) For the rest of your points, I agree that they're sensible objections to being able to do it, but they don't make the concept not mean anything, which was your original point. Why would the future remain? You destroyed it when you time traveled, and any changes in the future would require time traveling forward to see. (Forward is less erasure heavy, because you're just stalling instead of rewinding.) It's not just a similar experience, it's the literal definition of what that term means. > nor time, just changes in particle positions Uh... It's comments like this which makes me question your position. Changes in particle positions is time! Literally: time is just that thing a clock does, which is tick. If particles change position, that's (by definition) time.

SomeStupidPoint 10y ago

You have to give up the idea of a universal clock: you only have a local one. In your example: since you erased the elapsed computation in other regions, you (by putting the particles back) are literally rewinding every clock but yours. In whatever sense they were ever in 2000, they're back there, though you're in (your) 2018. Having your 2018 be their 2000 seems like a sensible definition of time travel. (And yes, you'd have spent a year time traveling, though in many senses you always are time traveling forward, and you just happened to spend a year going fast "backwards".) For the rest of your points, I agree that they're sensible objections to being able to do it, but they don't make the concept not mean anything, which was your original point. Why would the future remain? You destroyed it when you time traveled, and any changes in the future would require time traveling forward to see. (Forward is less erasure heavy, because you're just stalling instead of rewinding.) It's not just a similar experience, it's the literal definition of what that term means. > nor time, just changes in particle positions Uh... It's comments like this which makes me question your position. Changes in particle positions is time! Literally: time is just that thing a clock does, which is tick. If particles change position, that's (by definition) time.