So I'm a dozen or so pages into Einstein's Mirror and the start is all about light and time and what not...
The authors keep talking about time and distance and how far and fast light travels etc etc.
So, nothing travels faster than light but... does light always HAVE to travel at that speed or is it possible (even if just in theory, of course) to slow down the speed of light and if light is able to slow down does it cease to be light and become some other form of energy/particle/wave/whatever?