[Phys-L] Re: "moving clock runs slower" (yes)

[John Denker <jsd@AV8N.COM>]

Bob Sciamanda wrote:
> Consider the simple "bouncing photon" clock.  In its proper frame, a photon
> bounces back and forth, in one dimension, between two parallel mirrors -
> registering one tick per round trip.  As viewed from a moving frame this
> photon travels a longer, "triangular" path through space.  Since the photon
> speed is numerically the same (c) as measured in both frames, the clock must
> tick at a slower rate when viewed from the second frame (when compared to an
> identical clock at rest in the second frame).

I would say that the _projection_ of the clock's tick-events
onto the laboratory's time-axis is slow, i.e. the _projected_
tick-marks are farther apart.

> What is it about this effect that is not real, and only an appearance

The projection is quite nontrivial.

It is profoundly analogous to viewing a ruler nearly end-on.

> - must
> we say that the invariance of vacuum light speed is not real, and only an
> appearance?

No, "c" is the same in all frames.  All the projection operators you
can make from the Lorentz group leave "c" unchanged.  Under a Lorentz
transformation, the x axis tilts up just as much as the t axis tilts
over, so that the diagonal remains unchanged.  Draw the diagram.  Or
look at mine:
   http://www.av8n.com/physics/twins.htm#fig-twins-joe
   http://www.av8n.com/physics/twins.htm#fig-twins-out
   http://www.av8n.com/physics/twins.htm#fig-twins-in
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