Re: Divergence of opinion by experts on SR

Bill Hobba wrote:
> 
>  EjP wrote:
> > When you realize that relativity is ultimately about observation,
> > the 4,5,7, and 8 are more or less equivalent (with some qualification).
> > Although 2 and 3 sound contradictory, it depends on your definition
> > of "real" (believe it or not, "real" is not a well-defined term,
> > scientifically).  Some people would consider a "real" length
> > contraction to be something involving some sort of physical
> > compression, understandable in terms of the bulk modulus, and
> > by that definition, the length contraction is
> > not "real". On the other hand if "real" means that I could
> > devise an experiment to measure the length contraction of
> > something that is moving in my frame, the it is *real*, but
> > now "real" is entirely consistent
> > with 4,5,7, and 8.   I believe this distinction is what Eddington
> > was alluding to in comment 1.
> 
> For those that doubt length contraction simply analyze a current carrying
> wire.  If length contraction occurs  then magnetic forces appear - exactly
> as found from experiment - if length contrition does not occur then magnetic
> forces do not appear - in disagreement with experiment.
> 
> Thanks
> Bill

This is not a good example. If you do the math you'll find that length
contraction cancels out of the equation, leaving the force as due to
only the relative velocity and proximity of the respective lines of
charge. Thus your example is actually a counter-argument to the
'reality' of length contraction, i.e. length contraction is unnecessary
and has nothing to do with the measured force. As an analogy let's
suppose that instead of length contraction we substitute line density
increase via spontaneous creation of extra electrons. Now it should be
obvious that this will provide exactly the same outcome, since the
relativistic length contraction hypothesis  provides just this same line
density increase. Now let's suppose that instead of either of these we
postulate that the lines of charge simply 'appear' closer to each other
from their respective points of view when they are in relative motion.
Again we get the same result. In short, any ad hoc presumption that will
increase the force as a function of relative velocity will work equally
as well as any other that does the same, each will provide correctly for
the observed force. 

Thus I trust you'll see that the development of this force is no proof
or even the slightest indication that length contraction is real.

Now look at 
http://www.cswnet.com/~rper
and you'll find a mathematical treatment of this force that makes no
assumptions at all about the 'cause' of the force, it simply quantifies
it directly as a function of relative velocity (in a sense this reduces
to the actual cause), and thus by virtue of Ockham's Razor, it is a much
superior approach, eliminating as it does all of the excess baggage that
you brought along above.

Richard Perry