[pdonis]

> Circular motion is not, it is absolute.

What is absolute is not circular motion, but proper acceleration and vorticity of a particular congruence of worldlines. But you can describe those phenomena perfectly well in a reference frame in which, for example, a person riding along on a rotating platform is at rest. The reference frame will not be inertial, but that does not mean it is any less valid. For that matter, we routinely describe phenomena on Earth using a reference frame in which the entire Earth is at rest, not just its center; that is perfectly valid as well.

[ars]

> but proper acceleration and vorticity of a particular congruence of worldlines.

This is a side note, but you really think that's a good way to describe something? You sound like you found some buzzwords and wanted to make a sentence out of them.

> But you can describe .... will not be inertial, but that does not mean it is any less valid. ... that is perfectly valid

Sure it's valid, but that was never the question in the first place.

It still has an absolute component. And in the context of this discussion (time travel) that absolute component means you will have to take the motion into account, as opposed to relative motion.

[pdonis]

> you really think that's a good way to describe something? You sound like you found some buzzwords and wanted to make a sentence out of them.

No, I just used standard terminology in physics.

> It still has an absolute component.

Yes, but "motion" is not part of what is absolute.

> in the context of this discussion (time travel) that absolute component means you will have to take the motion into account, as opposed to relative motion.

No, it doesn't, because there is no such thing as "motion" apart from relative motion. So the time travel device can't be using "motion" to determine what it does. It could use the other things I described, but not "motion".