>The photon receives no special treatment in QM. If we know
>its location with 100% certainty, we are 100% uncertain of it's
>speed, like every other particle.
>
>>From "QED" by Richard Feynman:
>
>"You found out in the last lecture that light doesn't only
>go in straight lines; now, you find out that it doesn't go
>only at the speed of light!"
OK - light can travel at any speed. You are right, of course.
BUT. Energy/mass conservation is also not true. Or momentum
conservation. Particles do not necessarily have positive
kinetic energy too (e.g., tunneling). All these are features
of QM.
But. None of these apply to macroscopic measurements. Normally
when one uses phrases like 'the speed of light', one means the
macroscopic vacuum value (which someone pointed out is well known
and will presumably become even better known as time goes on).
ken
(Unfortunately, i have no idea where or why this discussion began -
and w/o context am unsure if this message is particularly relevant.)