Re: c = constant

On 12/3/2003 3:08 PM, Brian Kennelly wrote:
> HenriWilson wrote:
>>Do you really believe a rod changes its physical length every time a
>>differently moving observer looks at it?
> 
> No, I believe that the rod has a length that depends on velocity, not on 
> who is looking at it.

In SR (and GR), the rod has an intrinsic length that is independent of
the rod's motion wrt anything[#], and its measured length is independent
of WHO is looking at it, but depends upon HOW it is measured.

        [#] neglecting stresses induced by accelerations.

The normal way an observer measures the length of a moving rod is by
marking both ends of the rod on a ruler that is at rest wrt the
observer, and both marks are made simultaneously to the observer. In SR
(and GR) this is a PROJECTION of the rod's intrinsic length onto the
coordinate system of the observer; such projections can obtain values
different from the intrinsic length of the ruler itself. In SR this
specific projection is called length contraction, but a better name
would be length projection.


Tom Roberts     [EMAIL PROTECTED]