Proper Distance, Rest Length: What to Know

[JD96]

Hello,

Could someone check my following statement: The proper distance between two spacelike separated events can be thought of as the rest length of a rod that connects both events in an inertial frame in which both events happen simultaneous.

Thanks in advance!

 

[vanhees71]

That's correct, and you can always find this frame of reference, by choosing the spacelike vector as one of the basis vectors of an inertial reference frame in Minkowski space.

 

[JD96]

Okay, that makes sense :) Thanks for the quick reply!

 

[Matterwave]

One should note that this does not necessarily work in GR. In SR where there are global inertial frames, one can always define a rest frame for such a rod, in GR if the two space like points are too far apart, there may not be a unique way to measure the distance between them (different "straight line paths" may connect the same two points).