[SOLVED] the nature of electric magnetic radiation,it's rest mass and potential to sl Some people look at light as photons I look at light simular to radio waves except at a higher frequency,so if you analyse light from the point of from radio waves you get a much better picture as to whats going on.If you have wire carrying DC current it has a magnetic field around it,since this field is something it must have mass although extremely small.When an AC current is fluctuated at a low frequecy in an antenna this magnetic field collaspes around the the antenna, as the frequency increases the speed at which the field expands and contracts increases. At certian frequency the waves propagate where the veloctity of the expanding magnetic field is c and the contractive force of the magnetic field is overcome. Since magnetic fields have mass and light is made up of magnetic fields,then light must have rest mass. Therefore at c light waves have a value of mass and can therfore be slowed down. Light from a distant star can be slowed down by the contractive force of the magnetic portion of light acting on the expanding electromagnetic radiation after it's covered vast distances. This should show up as red shifting of a distant star. Replying to the comment does a magnetic field have mass, I assumed that since a magnetic exists it would follow that it would have mass. The proof that I can offer you is this, if you take a superconducting air core toriodal inductor and charge it with a powerful magnetic field,then energy x will have gone into the toriod,since no energy was dissipated in the toriod windings,the energy must be stored in the toriod.Relying on energy mass equivalency the toriod with the magnetic field is going to have more mass than the one without the field.So therefore it is safe to assume that a magnetic field has mass. Further correction, could it be possible that a magnetic field is stored potential energy and has no mass? I think it's time that science investigates this situation, it will answer a lot of questions.