🚀 go-pugleaf

jcr@milton.u.washington.edu (Mr. EuStress) writes:

[concerning two objects moving toward a point from opposite
directions at close to c]

>    Remember my "IF"s -- "if the one system could `observe'
>    the other".  The one system cannot observe the other
>    because observations can only made within *ONE*
>    single (Lorentz transformed) system.  But,
>    **observation does not make reality**.

Whose relative velocity would you have be the "real" one?  Are
relative velocities only to be calculated by adding together
velocity vectors in some arbitrary frame?

The relative velocity of the two objects, as found by a
Lorentz transform into the rest frame of one object, isn't
just an illusion caused by signal delays, or some such
thing.  What do you mean when you say that one system cannot
observe the other?  Someone riding on one object *could*
observe the other, and after allowing for effects due to
signal delays, would calculate a real relative velocity less
than c.
 
>      If two things, both moving near the speed of light,
>    hit each other the real velocity is near 2c.
>    The observed would be under c, but that observation
>    does not change the "reality".

If they hit each other, the real relative velocity would be 
less than c.  The physical situation experienced by one
of the objects would be *exactly* the same as that
in which it is stationary and the other object comes in
to collide with it at the velocity calculated by a Lorentz 
transformation.  What better definition of a real relative
velocity is there?

-- 
Matt McIrvin  mcirvin@husc.harvard.edu 
"Robber bands stretched across the land, snapping up ill-gotten loot."
                                      -- "The Lone Stranger and Porky"