What assumptions are made about radio waves in relation to mechanical waves such as sound?
Don’t listen to anyone (including a text book) who says electromagnetic waves don’t need a medium; all waves need a medium. If you assume that radio waves have no medium, you would be wrong. The medium of sound is a fluid, and fluids have no shear strength, therefor they can only be longitudinal (pressure) waves. Electromagnetic waves are transverse (shear) waves, so their medium (ether) has to be solid. The formula for the speed of a transverse wave in a solid is c = √(G/ρ), where G is the shear modulus (stiffness) and ρ is the inertial density of the medium. If we knew the density of the ether, we could calculate its shear modulus from the known speed of light, and vice versa. Evidently, the ether is ultra dense—perhaps a googol times denser than a neutron star. That’s inertial density; the ether probably has no gravity of its own, as (I believe) it is also the medium of gravity, and all the other forces.
