Talk:The speed of light

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I just had to archive a recent Chez Watt nomination here:

> "Maybe we are seeing light that hasn't reached us yet. Why does light
> have to reach us for us to see it? Couldn't we see it on it's
> approach?"

-- Steinsky 13:14, 18 Sep 2003 (BST)

Answer: To perceive light, there has to be stimulation in the optic nerve. For there to be stimulation in the optic nerve, a photon must hit a rod or cone on the retina. Therefore, to see light it has to hit our eyes.

Question: I've heard of scientists slowing down light, i thought that was impossible?

Answer: Light is only a constant speed in a vacuum. When passing through material such as air and water, it does slow down. The amount by which it is slowed down is called the refractive index of the medium and is always greater than 1.

Question: If Einstein was right about the speed of light always going the speed of light faster then you are traveling, then the speed of light would be faster then normal for someone observed you observing the speed of light while traveling at some speed?

Moved discussion here. BTW, the last question does not parse. --tk 09:28, 2 Mar 2005 (UTC)

He's confused about the very nature of relativity, applying the "common sense" Newtonian mechanics to the situation and finding a contradiction, not realizing that it is common sense that is wrong.

Consider this, you are travelling at half the speed of light, with a flashlight on the front of your vehicle. According to Einstein, the speed of light is the same regardless of perspective. That is, if you were to read the speed of light leavnig that flashlight, you would find it was moving away FROM YOU at the speed of light. However, since the ship is moving away from Earth at .5C, then the speed of the light leaving the space ship would have to be 1.5C, from the perspective of Earth.

But, it doesn't work that way. Relativity overturns newtonian mechanics on this point by taking an obvious point and making something stunningly not obvious about it: Light going away from the earth from the front of the space ship WILL NEVER be seen from earth. From earth's perspective, it's not travelling at 1.5C, it's not travelling at all, it doesn't even exist!

I'm explaining this badly as I'm not a physicist.

--Suttkus 23:05, 4 June 2006 (BST)