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$E=mc2$Edit

Is light speed really the fastest speed anything can go in the universe? Nothing can move faster than the speed of light (except possibly tachyons with negative mass, but they cannot slow down to the speed of light) but there is no limitation on how fast spacetime itself can travel. That explains how the Universe could expand faster than the speed of light just after Big Bang, and also opens the possibility of faster than light travel through wormholes and warp drives. And why is it that light speed is 299,792,458 metres per second and not faster or slower than that? Is it because photons gain relativistic mass when they are created, and then whatever it is that causes them to accelerate in the first place gets cancelled out?

Answer: No. Photons have no mass. The speed of light is just a speed limit.
That is not necessarily correct. See here. Photons have no rest mass, but it is possible that once in motion photons gain mass from weak interactions with other mediating particles; possibly the Higgs Field. If the speed of light is "just" a speed limit, then we need to know what the limiting factor is, whether that be the size of the universe, or the limitations of photon interaction with spacetime, or any of the other factors.

Accelerating lightEdit

Do photons go instantly from the moment they are created to light speed? Or is there an acceleration curve?

Answer: They travel instantly at the speed of light, without any acceleration curve.
What is your proof of this? Keith 14:28, November 24, 2010 (UTC)
Proof: They move at the speed of light unstopped by relativistic mass increase, and therefore they have no acceleration curves.