Phase velocity faster than light?

[shanepitts]

I am currently taking an undergrads course in atomic physics, and I have just grazed the concepts of matter wave functions, group waves, group velocity, and phase velocity. For the latter, it has been stated that phase velocity can exceed the speed of light. I don't fathom this. Could anyone please help me with this concept?

 

[Drakkith]

Does this help?

Per wiki: http://en.wikipedia.org/wiki/Faster-than-light#Phase_velocities_above_c

The phase velocity of an electromagnetic wave, when traveling through a medium, can routinely exceed c, the vacuum velocity of light. For example, this occurs in most glasses at X-ray frequencies.[11] However, the phase velocity of a wave corresponds to the propagation speed of a theoretical single-frequency (purely monochromatic) component of the wave at that frequency. Such a wave component must be infinite in extent and of constant amplitude (otherwise it is not truly monochromatic), and so cannot convey any information.[12] Thus a phase velocity above c does not imply the propagation of signals with a velocity above c.[13]

 

[shanepitts]

Thanks

 

[bhobba]

I am currently taking an undergrads course in atomic physics, and I have just grazed the concepts of matter wave functions, group waves, group velocity, and phase velocity. For the latter, it has been stated that phase velocity can exceed the speed of light. I don't fathom this. Could anyone please help me with this concept?

Its purely a mathematical artefact - nothing is really traveling FTL.

Also matter waves was simply an interim theory on the way to full blown Quantum Mechanics that appeared when Dirac published his transformation theory.

Don't spend too long on what is just really of historical interest. Try, as soon as possible, to come to grips with the correct theory. So you understand its REAL basis check out:
http://www.scottaaronson.com/democritus/lec9.html

Your course may not get to this for a while, or indeed at all, depending on its depth, but just keep in the back of your mind this is what QM is REALLY about - the rest is basically historical background.

Thanks
Bill

 

[sardar]

I can understand your confusion about the concept of phase velocity exceeding the speed of light. This idea goes against our understanding of the fundamental laws of physics, such as the theory of relativity which states that nothing can travel faster than the speed of light.

However, in the context of matter waves and quantum mechanics, the concept of phase velocity exceeding the speed of light is not violating any physical laws. This is because the phase velocity refers to the velocity at which the phase of a wave moves, while the speed of light refers to the velocity at which information can be transmitted.

In matter waves, the phase velocity can exceed the speed of light because it is not carrying any information, but rather represents the probability amplitude of the wave function. This means that even though the phase velocity may be faster than light, it does not violate the fundamental laws of physics.

It is important to note that this concept is still being studied and researched, and there is ongoing debate and discussion among scientists about the implications of phase velocity exceeding the speed of light. So while it may seem counterintuitive, it is a valid concept in the field of quantum mechanics.

I would recommend continuing to explore and learn about matter waves and their properties, and keeping an open mind to new and potentially groundbreaking discoveries in the field of atomic physics.