🚀 go-pugleaf

rscott@csws1.ic.sunysb.edu (Robert Scott) writes:

>ROBERT FIRTH WRITES:

>WELL, MAYBE I DIDN'T MAKE MYSELF CLEAR.  I WASN'T TRYING TO SAY THAT
>THE ORTHODOX VERSION OF SPECIAL RELATIVITY IS WRONG AND THAT IT NEEDS
>TO BE REPLACED BY A COMMON-SENSE VERSION IN WHICH EVERYTING IS
>EXPLAINED AS A SIMPLE RESULT OF SPEED-OF-LIGHT DELAYS.  RATHER, I WAS
>TRYING TO SAY THAT THE ORTHODOX VERSION OF SPECIAL RELATIVITY _IS_ A
>COMMON-SENSE VERSION IN WHICH EVERYTHING IS EXPLAINED AS A SIMPLE
>RESULT OF SPEED-OF-LIGHT DELAYS, REGARDLESS OF HOW MUCH SOME TEACHERS
>AND TEXTBOOKS TRY TO OBFUSCATE THIS POINT. 
 
[description of a Poincare-and-dilations-symmetric game, with
programmable robots exchanging light-speed signals, deleted]

One way to make yourself clear might be to say that everything
in relativistic kinematics is a logical consequence of signal
delays *combined with* the postulate that c is the same in all
frames.  It sounded (though it doesn't any more) like you were
claiming that SR was a theory of optical effects due to finite
signal speed in an otherwise Galilean world.

As an example of this, say that your (really nice) idea for a
"relativistic Robot Wars" game is implemented, and you build
a light clock consisting of two robots that fly parallel to
each other at the same speed and exchange signals.  One bounce
of the signal is one tick of the clock.  Time dilation immediately
manifests itself from the "God's eye" view; the clock runs more
slowly in frames where it's moving with respect to God's eye.
If you don't want to refer to that symmetry-breaking feature,
you can set up twin-paradox-style situations involving multiple
clocks and see that the right answers come out.  

What still isn't clear is that this is a good clock for all
physical phenomena.  If the physics is just point masses exchanging
light-speed signals -- if the world of the game is all the physics
there is-- then this is all of SR kinematics, and it could be argued
that ordinary matter is just this sort of thing, since it consists
of electrons and nuclei that interact electromagnetically.
(I think that this was one way of explaining Lorentz
contraction as a purely electromagnetic phenomenon before
Einstein put special relativity on a more universal footing.)

On smaller scales, though, things get muddier, and it's possible
to have phenomena that don't necessarily consist of the exchange
of speed-of-light signals in any obvious way.  The postulate that
physics, including c, is the same in all frames is equivalent to
stating that this kind of clock really is a good one, that
special relativity applies to more than electromagnetism, and that
time dilation and all the other assorted phenomena are of
general validity.

The game would, IMHO, be lots of fun to play with-- it's fun
just to think about!  The light clock provides a nice
demonstration of how the addition of proper-time clocks would
break dilation symmetry.  If the robots have proper-time
clocks, they can tell how fast their light clock runs, and 
consequently how far apart they are in their rest frame.
 
-- 
Matt McIrvin, professional gradgrind, amateur Usenet drifter