Hi Siva Prasad Kodukula ,

theoretically, both the group and the phase velocity of inhomogeneous plane (evanescent) waves (surface waves) can be less than c.

There are some experimentally proven phenomena which involve evanescent waves (e. g. Goos-Hänchen effect), and I assume any discrepancy between theory and results would have attracted further attention which it hasn't as far as I know.

In the thesis behind the following link, on waves along a kind of Goubau wire, theoretical and experimental results match well (see chapter 6); the wavelengths are compared which are proportional to the phase velocities:

https://thesis.library.caltech.edu/6597/3/Yeh_c_1962.pdf

With the advent of metamaterials, we can dispersion-engineer synthetic structures to achieve almost any desired phase/group velocities, including imaginary and/or negative values.

However, this is only for guided-wave modes. If you're referring to plane-wave propagation in a vacuum, the medium is dispersionless and therefore all waves propagate at the same rate.

@Joerg Fricke, Thank you Sir.. If necessary I will come back to you...

The reason behind this question is -

"While I am working on consciousness and brain, as per quantum information calculations of my model, I got a conclusion that wave of 10^-6hzfrequency is the main cause to originate consciousness. But as per uncertainty principle the energy of that wave cannotsupport to complete that ossilation. So it will not come out as an electromagnetic wave with velocity 'c'. If its energy is less its frequency will be less but instead of enlarging its wavelength, its velocity will be redused. Combination of such waves(one million waves) produces as 1hz and can get it byEEG. The lesser frequencies if comes out seperately their velocity must be less than 'c'. Itcontains quantum information that will be processed in brain. If right answer is available, it can be used in experimental verifications...

What do you think the velocity of a wave travelling through a coaxial cable from the antenna on your roof to your television receiver amounts to?

Denis Jaisson , it depends on the material between inner and outer conductor. Usually, it has a relative permittivity of about 4, and a relative permeability of 1, which results in a velocity of about c / 2.

Thank you, Jörg... What I meant to do, actually, was to prompt Siva to ponder on the abyssal depth of his ignorance of what he claims to be one of his specialties, that is theoritical physics.

@Denis Jaisson,.... it is better not to use ignorance like words -"I know that the velocity of em wave depends on permittivity and permeability of medium. That is the reason the velocity is light velocity in vacuum or space. So such low velocity em waves can not exist in this space(you may call it as vacuum). But still there is a possibility of existence of Space with different parameters. Its consequences can be observed and reverse analysis can be done.Such spaces are possible in quantum mechanics and waves related to quantum particles.

I was about to suggest you attend an undergraduate course in Physics, but an English course might be a good start, actually. Regardless, it would be as dishonest as clumsy on your part, to try to make your original question sound different, now that feel it was a silly one.

@Denis, Thank you for your understanding of the question. I am not interested in argument with you... no.. use...

Nor am I interested to argue with you. This web site is for qualified engineers and scientists, by the way.

Ok. Once again thank you...

EM waves can be slowed down enormously, and even stopped, but only in special matter, not in free space. I think it is unlikely that this would happen in the brain. What do you mean by saying that if you combine 10^6 waves of 10^-6Hz you get 1 Hz. This doesn't make sense. You would only get 1 Hz from 10^6 pulses with repetition rate 10^-6 Hz, and to get this the pulses would need to be less than 1 s wide so would contain a wide range of frequencies including frequencies close to 1 Hz. You might (I don't know if it actually could happen) also get it from simultaneous collision and conversion of 10^6 photons to one photon, but if it is possible this is so unlikely to happen it probably won't ever happen anywhere in the life of the universe, let alone in everyone's brains.

If you are talking about space with different parameters, then many things are possible, but there is no evidence for it, and what can happen in it is guesswork.

Dear Mr.Malcolm White,

Thank you for your explanation.

1. Yes .I am discussing about velocity of EM Wave in free space. Here the space means, the space in which we are living, the space which is termed as 4 dimensional space in theoretical physics, the space whose curvature is considered as gravity in General Theory of Relativity and in some cases called as vacuum).

2. Electromagnetic wave equation is a second order partial differential equation describing propagation of EM wave in medium. For free space(vacuum) The universal constant appearing in the equations is dependent on permittivity and permeability of free space. That constant is ‘c’ and is equal to velocity of light in vacuum. In my opinion this constant and the relation between permittivity and permeability lead Einstein’s intuition to propose postulates of ‘special theory of Relativity’. Permittivity is the measure of materials ability to store an electric field and permeability is the resistance of material against the formation of magnetic field. Above defined space can not keep up that wave as an electromagnetic wave in free space with velocity less than that of light and it must move with velocity c due to its permittivity and permeability. At the same time due to Uncertainty principle of physics, the quantum of this space can not complete its wave length to maintain velocity of light and the plank energy equation and wave velocity equation can not be valid at the same time. So electromagnetic velocities less than that of light are not possible in the space defined above.

3. As per my earlier claims and proposals (Ref:paper entitled “New Hypothesis on consciousness-Brain as quantum processor”-In my profile of research gate), the energy that producing in the brain is very less it cannot emerge as an electromagnetic wave and at the same time the complete process is in coherence till a thresh hold time. And the energy originated in brain is not continuous it is quantized and equivalent to 10^-6 Hz. Thus the Energy increases until it can deliver 1 hz electromagnetic wave in to this space.

4. I have used different spaces since the ‘Fundamental forces of nature’ will represent different space time densities(I have explained in my earlier papers –provided in Research gate for reference) and different space time parameters which originate quantum particles by their interactions.

You are true. My works are guess works only.

My knowledge is limited. I have to clarify my basic doubts with experts like you only. Then only I can decide to go further in my probe of these fundamentals.

I am substantiating my guess work by clarifications from the experts like you and making them in to hypothesis. These hypotheses will emerge as theories by bright minds who cooperate me and my beliefs.

Thank you that you have clarified my doubt with your practical and confident advise.