"Henry Spencer" wrote ...
In article ,
wrote:

I don't understand the above statements.
The mirror will definitely still be accelerated even if an arbitrary
observer is attached to it.

Accelerated *with respect to who*? Not with respect to the observer, by
definition. (It is not meaningful to speak of whether it is "really"
accelerated or not; all such statements must be made relative to a
specific observer.)

Er, didn't Einstein have something to say on that subject?
/Velocity/ is only meaningful relative to a particular observer, but
"is this accelerating / not accelerating" is a meaningful question.

Dealing with
non-inertial frames of reference gets messy.

Quite.