Faster than the speed of light.

Main Question or Discussion Point

http://science.howstuffworks.com/news-item6.htm

this says that u can speed light to 300 times the natural speed of light, and theoretically one could see a moment in time before it took place.

what do you think??

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a light beam itself which exceeds c? Perhaps, probable, I don't really know myself. But something which have mass like you and me would have difficulty going faster than c cos' of imaginary mass and all?

yes, i know that im talking about the seeing a moment in time before it happened

I've seen these experiments. A powerful pulse of some duration is sent through a filter that blocks most of the pulse. What comes out is a much shorther pulse, the beginning of which is later than the beginning of the input pulse, but the center of the much shorther pulse is before the center of the input pulse. The output pulse's time duration is completely within the time duration of the input pulse.

To me this is just the dyanamics of the medium. The speed of light is not exceeded.

russ_watters
Mentor
You are correct, Vern - that's a surprisingly misinformed article from howstuffworks.

This is very common, the error is to consider that the 2nd postulate of special relativity says that the speed of the light in the vacuum is the top speed. But this is not exactly correct. The 2nd postulate says:

The maximum speed of information transmission is the speed of the light in the vacuum.

In waves, the group velocity and phase velocity don't contains any information about the wave, so both can be greather than "c", and this complains with the 2nd postulate.

See http://www.physicsweb.org/articles/news/8/11/10/1

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