[gondramB]

>>I would actually be most grateful to learn what it is you had in mind as "a thing which can move faster then the speed of light" (even if it has no mass.)<<

Glad to...

"Something" traveling faster is best illustrated with a thought experiment. Imagine a round room 186,000 miles around - the distance light can travel in one second. Imagine a laser pointer sitting on a turntable in the center pointing at the wall.

If the turntable rotates once per second, the spot on the wall travels 186,000 miles each second. Now, double the speed of the turntable and the dot on the wall travels 372,000 miles each second or double the speed of light. This is called the phase velocity.

Addendum for nerds:
1. A thought experiment (a calque or English loanword based on both the German/Latin compound Gedankenexperiment and its German equivalent Gedankenversuch[1]) is a proposal for an experiment that would test a hypothesis or theory but cannot actually be performed due to practical limitations; instead its purpose is to explore the potential consequences of the principle in question. Famous examples of thought experiments include Schrödinger's cat, illustrating quantum indeterminacy through the manipulation of a perfectly sealed environment and a single radioactive atom, and Maxwell's demon, in which a supernatural being is instructed to attempt to violate the second law of thermodynamics.

2. The phase velocity (or phase speed) of a wave is the rate at which the phase of the wave propagates in space. This is the speed at which the phase of any one frequency component of the wave travels....

The phase velocity of electromagnetic radiation may under certain circumstances (e.g. in the case of anomalous dispersion) exceed the speed of light in a vacuum, but this does not indicate any superluminal information or energy transfer. It was theoretically described by physicists such as Arnold Sommerfeld and Leon Brillouin. See dispersion for a full discussion of wave velocities.

[mrjesse]

If the turntable rotates once per second, the spot on the wall travels 186,000 miles each second. Now, double the speed of the turntable and the dot on the wall travels 372,000 miles each second or double the speed of light. This is called the phase velocity.

Thanks for the nice reply, gondramB. I guess with a little stretch of the imagination the difference in time of arrival is a "thing" :-)

I'd actually already read about that one and concluded that it wasn't really faster then the speed of light. Indeed the same experiment could be done with two glass marbles shot at two points which were 1 light second away from each other. The first marble might hit 1mS ahead of the other in which case the point of contact would have moved at a thousand times the speed of light. Or if they had hit at the same time, it would have "moved" at an infinite speed. The problem I have is that "it" doesn't exist as a thing, and it didn't move - because it was really two incidences - or as you put it, phase speed or whatever.

Thanks anyway, though!

-Jesse