Permittivity, permeabiltiy and gravity

[Chronos]

The speed of light is theoretically constrained by the pemittivity and permeability of the medium through which it travels. It seems counterintuitive that pemittivity and permeabilty also constrain the speed of gravity since neither electric or magnetic fields appear to have any influence on gravitational fields. My apologies if this sounds like a cranky question, but, it has me confused - which is not necessarily a difficult accomplishment.

 

[atyy]

Any massless relativistic free wave, electromagnetic or not, will travel at "the speed of light".

If the photon has mass, it will travel at less than "the speed of light". (Actually, its speed will depend on its wavelength, that is the meaning of "mass" applied to waves. The relation of the "mass" of a wave to the mass of a particle is via the de Broglie relations.)

 

[DrDu]

T It seems counterintuitive that pemittivity and permeabilty also constrain the speed of gravity since neither electric or magnetic fields appear to have any influence on gravitational fields.

Who claims this to be the case?

 

[Mentz114]

Who claims this to be the case?

A number of people have made this or similar claims. See here

http://en.wikipedia.org/w/index.php?title=Polarizable_vacuum&oldid=56603531

and contrast with the current entry

http://en.wikipedia.org/wiki/Polarizable_vacuum

 

[Meir Achuz]

"Fringe physics" is an apt description.

 

[DrDu]

Ok, without a context, the question is hard to understand. But magnetic and electric fields have a non-vanishing energy momentum tensor which produces a gravitational field. So electromagnetic and gravitational fields are coupled.