gjphw (08/06/82)
Intended reply to houti!trc about ants
The issue of relativity is not an examination of what changes but
a formula for how things change. Special relativity is a misnomer; it
is more properly called the study of invariants.
As for our ant friend, there is never any claim that accelerations
are relative. Einstein's General Theory of Relativity (named this way
to distinguish it from other "relativity theories") merely assumes the
equivalence of an accelerating reference frame and gravity (one of many
assumptions). Both Special Relativity and Newton's physics treat
accelerations as non-relative quantities (accelerations don't transform
to other reference frames).
You do have a case for reference frames that have constant relative
velocities with respect to one another. Relativity does apply here.
Unfortunately for this whole discussion, rotation is not unaccelerated
motion (the velocity vector is constantly changing direction, and changing
velocity is the definition of acceleration).
What an ant on a rotating wheel experiences is a pseudo-force due
to its particular reference frame. How might one decide if they are
experiencing a pseudo-force? If they can transform to a different frame
of reference where the force goes away, then the force must have been
fictitious. The ant experiences centrifugal force because it assumes
that its own reference frame is fixed. If it were to transform to a frame
that does not rotate, it would notice that the force it is experiencing
is due to its motion (rotational motion with a constantly changing velocity
vector). While this transformation may be easy for us to visualize, it
may not be so for the ant. Can we decided about our own reference frame?