Currently it is understood that all forces when traced back to their source find their origin in the electromagnetic field, that is all forces with the exception of gravity. Gravity is a rather strange force in that it can not be measured or to be more precise any measurement wherein gravity is the sole actor will yield zero. As an example astronauts undergo weightlessness simulations in an aircraft diving towards earth, during this experience they aren't subjected to any force yet they are accelerating with 9.81m/s2. Another example is when a spacecraft is accelerated through a slingshot effect around a planet where it undergoes a tremendous acceleration yet at no time is the spacecraft submitted to any force whatsoever. Compare these examples to powered acceleration, read acceleration caused by EM forces, where because of inertia the vehicle and its passengers are submitted to measurable forces. In science there is a rule which states 'if you can't see it it ain't real', gravity therefore isn't real, its an imaginary force.
As a side note, this makes the discussion about the speed of gravity void since there is no information to be transferred, the object being affected does not notice the affect taking place therefore no communication is taking place towards it.
If looked upon from a system point of view the dissimilarity between gravitation and the electromagnetic field makes sense. In order to have an active system you need two independent actors, an actor cannot act upon it self that would be self referential, it needs an external reference relative to which it can act, think of this as Baron Von Münchhausen pulling himself up by his own hair it can't be done. To be truly independent the two actors cannot have an image in each other, in other words they cannot share characteristics, one must be what the other is not, they must be complementary. They are references towards each other, one is a carrier for the other, meaning that the EMF exists within a gravitational universe and gravitation exists within an electromagnetic universe. If the two actors are fully complementary then those two universes will have exactly the same content because if you invert everything (opposite characteristics) then everything remains the same, you can compare this somewhat to the positive and negative of a picture.
We then are of the electromagnetic universe existing within the gravitational universe. Our sensory inputs are EM and those inputs depict an image of the gravitational universe. We do not interact with the gravitational universe because we aren't compatible with it.
To further understand the relationship between the two actors, gravity and the electromagnetic field, lets analyze their nature.
Gravity is a context independent force, two objects will attract each other in the same way no matter what is in between them or surrounds them. Gravity is also invariable, all it ever does is attracting it will never alter its behavior. An invariable context independent force is a chaos force, it will not create any kind of order because it is blind and even if it wasn't it wouldn't effect any corrections needed to maintain a situation since it won't alter its behavior.
The EMF is context dependent, whether and how objects influence each other is strongly affected by their surroundings since interaction occurs through the field and all objects to some degree modify that field. The EMF is also adaptive it can change the direction and sense (sign) of the forces it applies. As I understand it the electromagnetism is a force which wants not to be active, it has a strong tendency to isolate objects through the use of dual layers and to minimize energy expenditure by following paths of minimal resistance. A force which is context dependent and which has a sense of purpose will create order, it will have preferences and seek to maintain those.
The electromagnetic field then creates order and gravity keeps messing things up putting the universe in a balance between chaos and order.
Now consider a combustion engine. Within a cylinder an explosion takes place, a chaotic event. This explosion can be seen (simplified) as a movement in all directions. The cylinder will filter out the movement vectors in one direction and the cylinder head acts as a mirror giving sense (sign) to that movement thus creating power output. This same functionality can be mapped onto gravity and the EMF whereby gravity provides chaos input and the EMF provides direction via its magnetic field and sense via its electric field. True the functionality is not as absolute as it is in the combustion engine but is is there. Note that no energy is created, gravity exchanges momentum which is energy neutral and the magnetic and electric field will expend energy when providing direction and sense. What happens is that chaos is counteracted costing energy but also creating energy which is then projected to another location through an electric current.
So say you got an object, for example a planet, to/from which an electric current flows then a force will act upon that planet performing labor equal to the power output of that current. It is not that current which is responsible for the force rather it exists to maintain energy neutrality, the force is delivered by the local magnetic and electric field.
Thats my view to date, comments are apreciated
.