| Why? Because they don't, as proven experimentally. If they did, then
| supraluminal velocities would certainly be possible (as for example, an
| electron traveling at 0.9999c in the lab frame emitting a forward
| photon at relative velocity c). This fact can be predicted, it can be
| shown, starting from the two postulates of special relativity:
| a) that the laws of physics are identical in all inertial frames;
| b) that the speed of light in a vacuum is c, regardless of inertial
| frame.
|
| It turns out that in *this* cosmos (not my cosmos), velocities add
| according to
|       v(tot) = [v1 + v2]/[1 + (v1*v2/c^2)].
|
| This shows that when v1, v2 are much smaller than c, then
|       v(tot) = v1 + v2 
| is a good approximation, but only an approximation.
|
| You should check out the answer when
|       v1 = v2 = c.
|
| PD

How can I check this ?