# Speed of light that is traveling away from the observer

The second postulate of Special Relativity states:

The speed of light in a vacuum is the same for all observers, regardless of their motion relative to the source.

Now imagine the observer that is looking at the light which is traveling away from him in a direction he is looking. In this case, the light should look somewhat like a "dot" to such observer - not really moving at any direction for him. However according to postulate above the light should move at the speed of c (if we are in vacuum to be precise).

What is wrong with this reasoning? Or is it just some kind of exception from the rule?

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You only see light when it actually hits your eye. – Keep these mind Mar 24 '14 at 20:58
My guess is that in your reasoning you "projected out" the dimension in which light was moving. How do you measure the speed of the "dot" if don't have any clue what distance it moves in a given time ? – Dominique Mar 24 '14 at 21:04
Thanks Nick, I think your comment is closest to the answer after all. As I understand it now, the light is still going at the speed c for the observer, he is just not able see that direction. What helped me to understand was the idea of something moving at the speed (v,0,0) in some frame of reference (coordinate system). Then consider observer standing in the origin of such coordinate system. He wouldn't see the actual movement, but that wouldnt change the fact that the object is moving at the speed of v relative to his frame of reference. – RelentlessAsker Mar 29 '14 at 18:38
You have to consider the observer's "reference frame", not her point of view – Sunghyuk Park Mar 30 '14 at 11:19