Unable To Speak The Name

Albro Swift wrote:
 ...to synchronize events at the two ends of a uniform stationary 
 rod, we can simply tap the rod at its midpoint and let the sound 
 waves (in the rod) propagate out to the ends, where they will
 arrive simultaneously....

Brian Jones wrote:
 But where is your proof that they arrive simultaneously?

The above constitutes a _definition_ of simultaneity, a temporal
relation such as exists between two symmetrical sound waves reaching
the ends of a uniform stationary rod from its midpoint.  You've
asked for a "proof" that the waves arrive simultaneously, but the
word "simultaneously" is simply a variant of "simultaneity", so
your question is asking for a proof of a definition.  Needless to
say, definitions are stipulated rather than proven, so your question
is unintelligible.

You might have meant to express an objection to the stated 
definition, but it's worth noting that the definition in question 
is the one *you* have been advocating.  The "stationary rod" has 
velocity V=0 which, based on your hypothetical absolute velocity, 
will yield "true" synchronization according to your definition.

The point of my post at which you *should* have objected was not 
this definition, but the subsequent paragraphs that discussed the 
applicability of this definition to a larger class of reference 
frames, and the consequences of NOT applying this operational 
definition to all inertial frames.  That's the point at which 
your views differ from both the classical and the relativistic 
interpretations.


Brian Jones wrote:
 The length of a rod has nothing to do with any kind of clock
 synchronization. 

Ah, we've identified the source of your confusion.  Now all you
need to do is learn why your statement above is false, and you'll 
be on your way to understanding relativity.


Brian Jones wrote:
 What proposal? Are you sure that you read my article?

Quite sure.  Your proposal is for a definition of time that provides
unique simultaniety for events, viz, you would surely reject any 
synchronization procedure that fails to yield this result.  Hence,
even though you've provided no means of accomplishing this 
synchronization (which, by the way, isn't really very difficult) 
we can still assess the consequences of it.  Any sync procedure 
that satisfies the "uniqueness" criterion automatically yields highly 
anisotropic lengths and mechanical operations in all but (at most) 
one single inertial frame.  This is the essential physical content 
of special relativity.  The fact that you claim lengths have nothing 
to do with synchronization simply reveals that this essential 
content has eluded you.


On 13 Aug 1997 Brian Jones wrote:
 There are only two inertial relativity theories:[1] Galileo's 
 mechanical one, and [ii] E's optical one.

I specifically presented the relativistic definition of simultaneity 
in terms of mechanical sound waves, in an apparently wasted effort 
to show you that there is nothing inherently "optical" about it.  
Forget light rays!  Take a solid uniform stationary bar and tap its 
midpoint.  By symmetry, uniformity, and the principle of sufficient 
cause (all classical criteria) we are justified in defining the two 
waves as reaching the opposite ends simultaneously.  (Please note 
the words "uniform", "stationary", and "midpoint", whose definitions 
are all significant here.)  Both classical and relativistic theories 
use this *mechanical* definition.  The difference between them is 
simply that classically it was assumed you could apply this same 
spatially isotropic-based procedure to any frame and the resulting 
relations of simultaneity would be the same, whereas it was realized 
around the turn of the century that this is not the case.  To put it 
succinctly, it was found that

  The assumption of spatial and mechanical isotropy in all 
  inertial frames is *empirically* incompatible with the 
  assumption of unique simultaneity in all inertial frames.

Again, this is the essential physical content of special relativity.