Faster than speed of light

[JimmyThyJoker]

Phase velocity can be faster the speed of light while the group velocity can't.
Which waves of the group are actually travelling at the phase velocity? If we can find them, aren't we going to be able to break the speed barrier?

[dochang]

An arbitrary wave can be decomposed mathematically into a summation of sines and cosines. Sometimes the decomposition can result in waves that have phase velocities faster than the speed of light. This is a completely mathematical procedure and doesn't always have any physical meaning.

[socratus]

Quantum Duality.
Photon (quantum-particles) can be ''wave'' and ''particle'' simultaneously.
#
If photon has constant speed (c) - it doesn't produce waves.
If photon does produce wave - it speed must be another.
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[kronotsky]

Quantum Duality.
Photon (quantum-particles) can be ''wave'' and ''particle'' simultaneously.
#
If photon has constant speed (c) - it doesn't produce waves.
If photon does produce wave - it speed must be another.
======

Have you ever heard of a "linear dispersion relation"?