You can't have a field variation without some sort of current. Light is most definitely "electric" in nature. Then you employ pair production to make electrons and positrons. The electron has spin and angular momentum. It's essentially half the original photon wrapped up and trapped by itself. You now have a standing electromagnetic field instead of a field variation, and if you move this thing you have direct current.
All of this is what we'd call electrodynamics. Einstein's first relativity paper was On the electrodynamics of moving bodies. When you move on to gravity you see Einstein saying things like c = c0 (1 + Φ/c²) in 1911, see http://www.relativitybook.com/resources ... avity.html, and die Ausbreitungsgeschwindigkeit des Lichtes mit dem Orte variiert in 1916. That's in chapter 22 of Relativity: the Special and General Theory. You can translate it via google: http://translate.google.com/translate_t ... ry_state0=# . It translates to the speed of light varies with the locality. Then you look at Z0 = √(μ0/ε0) and c = √(1/ε0μ0) and you realise what gravitational time dilation actually is. It's just the light going slower, and a gravitational field is just inhomogeneous space, like Einstein said in his 1920 Leyden address:
"According to this theory the metrical qualities of the continuum of space-time differ in the environment of different points of space-time, and are partly conditioned by the matter existing outside of the territory under consideration. This space-time variability of the reciprocal relations of the standards of space and time, or, perhaps, the recognition of the fact that “empty space” in its physical relation is neither homogeneous nor isotropic, compelling us to describe its state by ten functions (the gravitation potentials gμν)..."
And then near the bottom you read Einstein talking about how important it would be to comprehend both gravity and electromagnetism, and what an advance it would be:
"Of course it would be a great advance if we could succeed in comprehending the gravitational field and the electromagnetic field together as one unified conformation. Then for the first time the epoch of theoretical physics founded by Faraday and Maxwell would reach a satisfactory conclusion. The contrast between ether and matter would fade away, and, through the general theory of relativity, the whole of physics would become a complete system of thought, like geometry, kinematics, and the theory of gravitation".
And then a chill runs down your spine, because it's all so simple and easy. A gravitational field isn't curved spacetime, because that's the effect, not the cause. The cause is a gradient in space, caused by the central matter/energy of a star or planet. But the electric field is curved space, because light travels in straight lines, but pair production creates an electron where the photon is going round in circles. It's an electric universe, and all the mysteries start tumbling like dominoes.
Who wants to talk about it? If you want to find out more about what I've been saying, a good primer is an article about "black swans", see http://physicsworld.com/cws/article/print/38468. That's on the Institute of Physics PhysicsWorld website. Of course, some will say that the geometrical model is just an ugly duckling, but not everybody. Take a look at some other physicsworld page such as http://physicsworld.com/cws/article/news/40714 and look at the bottom right hand corner where you see an advert for this:

http://www.amazon.co.uk/RELATIVITY-Theo ... 0956097804
That's me. If you can see the dedication to the unsung heroes of science, you can see that I take pains to stress that it isn't all my own work. This is not "my theory", instead it's a synthesis where I've joined a few dots. It's easy reading, intended for the layman, painting a coherent simple picture, and it's in line with Einstein and others such as Feynman, Schrodinger, Dirac, Maxwell, Faraday, and Newton. It's so very simple and logical that nobody seems able to offer any rational argument as to why the thrust of it is incorrect. What's particularly interesting is that it's somewhat similar to http://en.wikipedia.org/wiki/Quantum_topology, which Ed Witten was working on in the nineties. I'm not sure why he dropped it, but I suspect that's the sort of rigor that now needs to be applied. Another interesting approach is David Hestenes' geometric calculus. I really ought to learn about it. So much to do.

