(Ross A. Finlayson) wrote in message . com...
Why is c the speed limit?

Is it because the mass of a particle and its waviness increases as it
approaches c?

Is Cerenkov radiation ever faster than c? It's just faster than light
when light is slowed, nearer to c.

Two point light sources coincidentally start emission at the same time
towards each other. Does not each photon hurtle at c thus that their
relative velocity is 2c?

Yes ... that's corect, and two physical bodies can have a relative
closing velocity as seen by a third observer as arbitrarily close to
2c. I can also prearrange to have a long line of flash bulbs go off
at 10c. So?

The sources disappear and the photons
remain, why is not one at rest and the other moving at 2c?

Nothing moving at c every defines a proper rest frame... but we soon
start talking in slogans at this rate.

The
visible universe has many light sources.

How would you define a tachyon, and what are its properties?

http://scienceworld.wolfram.com/physics/Tachyon.html

It's kind of like c is 1, and massy particle obeying Newton's inertia
law speed is infinitesimal, and tachyon speed infinite, and particle
and tachyon speed are reciprocal.

Yeah. It's kinda like that. :-)