Natural Science Forum / Physics / Relativity / June 2006

I agree with you, I couldn't find any physics book that explains this
genre of cylinder problems either.
David

I'm going to try to get a copy of Wheeler's book.  Vast majority of
relativity books don't discuss the problems like I posted on 6/1/2006
titled "For Paul Anderson" and like I posted on 6/18/2006 titled
something like "Simple length measurement for Todd ...

It seems like raising simple questions is verboten.  And its not clear
if there are any answers - if there were, someone like yourself could
post the one or two sentence answer that explains things, instead of
the 50 non-physics posts that serve no purpose.  The length
measurement post where the straight wire as measured in the moving
frame is length L' before attachment and it is L' after attachment yet
the wire undergoes stretching doesn't make sense to me.  And all
points of a wire that is cut to the correct length so no stretching
occurs cannot  be attached simultaneously to the cylinder as measured
in the moving frame.  And the wire that is L' before attachment and L'
+ some positive delta after attachment doesn't undergo any stretching
seems completely backwards to me. Or why the unattached wire of the
problem in the "For Paul Anderson" thread keeps rotating around the
cylinder eventhough nothing keeps it attached to the cylinder. Someone
like yourself could post a few sentences why that makes sense to you -
but most people don't know or are afraid of criticism from their
peers.   Of course, those answers aren't easy to come by, but that's
the kind of book I'm looking for.  Run of the mill books don't
generally discuss those topics.

And even the top physicists give mis-information.  For example Stephen
Hawking in the Brief History of Time states that Michelson-Morley
measured  the speed of light to be constant.  When I looked up
Michelson's original paper and then Michelson-Morley's paper when the
experiment was repeated with more precision, what they measured was
that there was no shift in the interference pattern of interacting
waves as two perpendicular optical paths were rotated relative to the
earth's motion.  In their experiment the optical paths have unequal
lengths when viewed from frames have a velocity wrt the earth.  The
simplest explanation to their experiment is that the velocity of light
depends on the velocity of the light source (this is apparently not
allowed to be stated in any SR book).  But then Lorentz pointed out
that a length contraction (of physical objects) of objects moving
through space might occur in the direction of motion which provided a
different explanation of the same experiment.  Einstein then
hypothesized that Lorentz's notions could be properties of space
itself.   But that is a far cry from Hawking's statement that MM
measured the speed of light to be constant.

Likewise, in reading Einstein's books, he suggests that someone in an
enclosed box could not determine whether that box was in a
gravitational field or was being accelerated by a rope pulling the
box.   Of course we all know that is not true - it can be
experimentally determined whether the acceleration is due to a rope or
to gravity.  He should have said that the box analogy provides
insights to the way we should think about gravity, but that analogy is
not physically correct.

David