# Faster than speed of light?

#### Akshay_Anti

Faster than speed of light??

Throughout my schooling ( middle school and beyond, to be precise) I've learnt and believed that nothing travels faster than speed of light.... But my university textbook of physics says that matter waves can travel faster than speed of light... Isn't this kind of a contradiction? And how is it possible? I am really confused now... Help needed...

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#### ZapperZ

Staff Emeritus
2018 Award
Re: Faster than speed of light??

Throughout my schooling ( middle school and beyond, to be precise) I've learnt and believed that nothing travels faster than speed of light.... But my university textbook of physics says that matter waves can travel faster than speed of light... Isn't this kind of a contradiction? And how is it possible? I am really confused now... Help needed...

Can you please cite the exact reference to your textbook (author, publisher, date of publication), and then cite the exact passage in your text that says this (including page number).

Zz.

#### e.chaniotakis

Re: Faster than speed of light??

The point of confusion must be the phase velocity vs the group velocity of the wave.
The group velocity is the one that "mediates the energy" of the wave from one spacetime point to the other , and its formula is ug=dω/dk. This velocity can never exceed the speed of light.
On the other hand , the phase velocity describes the "speed" with which the disturbance moves. (Disturbance=wave pattern). This has no physical meaning actually, since the disturbance is a mathematical entity,used to help us out.

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