I was just wondering... "All entities travelling at lightspeed must have zero mass and can never travel at any other speed. They are collectively called luxons."
If this is true, how is it that they have supposedly slowed light? There have been many stories lately of labs slowing light. So is the above impossiblily no longer impossible? Or have they not really slowed the light but just made it take a longer rout, and not really slowed it at all, despite their claims? Or am I missing something else really obvious
The speed of light is constant in a vacuum. All you have to do is change several different properties of a medium to change the speed light travels within that medium; the difference in speed will cause light to refract when it changes media. This is why objects under water appear distorted, for example: light travels more slowly through water, so a wave of light bends upon exiting the water and entering the air.
You should note that in the vacuum between atoms, light travels at c. The reason it slows, IIRC, is because it is absorbed and reemitted by the atoms in the medium, which takes time. The constancy of the speed of light in a vacuum is necessary for Maxwell's equations governing electromagnetism to hold.
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You could also say that light moves in extremes. It always takes either the minimum amount of time to get between two points or in rarer cases, the maximum amount of time. So a being made of light would always move around in such a way that it takes the minimum time to get there. Chances are, this makes going for a walk for them kind of boring.
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Well, at the very bottom level, it is true that light always moves at the maximum constant rate. However, when it moves through a medium, the light excites a motion in the material which cancels the leading part of the wave and adds in a part later... effectively slowing it down.
The retarded green function of electromagnetism (which is at root where the speed of light comes from) doesn't change the slope of its light cone for media. But the media do provide interference.
