Re: [Phys-l] Why question(s), again?

[John Denker <jsd@av8n.com>]

On 01/11/2011 01:09 PM, Bernard Cleyet wrote:
> A teacher member of the PTSOS** list posted:
> ---------------
> We're discussing Special Relativity in my conceptual physics class,
> and a student asked WHY light goes at 300,000 km/s, and what limits it.
>
> Have you any recommendations for a response?


The answer to almost all such questions is the same:  
 -- The laws of motion must say what happens.
 -- They may or may not say how it happens.
 -- They rarely if ever say why it happens.

Usually when people as "why" they meant to ask (or should have 
asked) something more like 
 -- How do we know this?
 -- How do we make sense of this?
 -- How do we reconcile this with everything else we know?


In the case of special relativity, there is a speed "c" that is
an intrinsic part of the geometry and trigonometry of spacetime.
This "c" is to rotations in the XT plane as "radian" is to
rotations in the XY plane.  This "c" need not be defined in
terms of light.  It is best defined in terms of the geometry
and trigonometry of spacetime.

  As a corollary, if/when you happen to be interested in
  electromagnetism, it turns out the EM waves propagate in
  a vacuum at the speed "c".  But still, this is neither
  here nor there in terms of the foundations of relativity.

How do we know about "c"?  Because 
  a) There is a stunningly simple theory that allows us to
   reconcile 4-dimensional geometry, trigonometry, and 
   physics with everything we ever knew about 3-dimensional 
   geometry, trigonometry, and physics.
  b) There is overwhelming experimental evidence that the
   theory is correct to an excellent approximation.

The non-weirdness of special relativity, i.e. its consistency
with other things we know, is discussed in the opening section 
of
  http://www.av8n.com/physics/odometer.htm