B What is the theory of relativity?

[Ross Arden]

Is the Theorey of relativity that there is no absolute movement, only movement of one frame relative to another or that there is absolute movement but we cannot measure it ?

 

[Ibix]

What would be the difference?

As I understand it, the former is vanilla SR; the latter is Lorentz Ether Theory. The latter is generally deprecated because it has an extra assumption, but it makes no difference to the maths.

 

[Orodruin]

This is part of relativity, yes. But it is not exclusive to special and general relativity as it is also the case in classical mechanics.

 

[PeterDonis]

Is the Theorey of relativity that there is no absolute movement, only movement of one frame relative to another or that there is absolute movement but we cannot measure it ?

Experimentally, the two are indistinguishable, and there is an interpretation of special relativity that takes the second option; however, that interpretation (usually referred to as "Lorentz Ether Theory") is not used in modern SR and is not a suitable topic for discussion here:

https://www.physicsforums.com/insights/pfs-policy-on-lorentz-ether-theory-and-block-universe/

 

[Ross Arden]

so if you have three space ships one pointing along the x axis, one on the y-axis and one on the z axis and then they all blast off, surely the assumption can credibly be made that one of them must be moving in an absolute sense, not in a relative sense?

 

[Ibix]

Depends on whether or not "absolute motion" means anything. Vanilla SR says it doesn't.

 

[PeterDonis]

surely the assumption can credibly be made that one of them must be moving in an absolute sense

You can make this assumption, but since it has no experimental consequences at all, there's no point.

 

[PeterDonis]

Closing this thread as discussions of LET are out of bounds, per the link already provided.