I feel-
The body of 3rd demensional matter, arms legs blood head ect, has evolved over many many years in this 3rd demension. From single cell to human. This body, sustained of 3rd demensional matter, has been created to collect sensory memory. When one dreams, and makes the trip across into the dream body or light body, sometimes the 3rd demensional body will act as an anchor and disable the light body slightly. A good example of this is the phenomona of "not being able to run" in your dreams. What is happening is the connection between the to 2 bodys is strong, the sleeping body in the bed is weighing down the dreaming light body.
Just like a good hit of spice, when one attains lucid dreaming, one will experience a rush very similar to spice, and the connection between the sleeping body and light body is severed and one will experience the complete freedom of the light body coupled with the imagination.

Now if we eject the 'human relevance in this equation, and replace the word "sleeping body" with "entire 3rd demensional universe" and "light body" with "dream universe" or something to that effect, what you get is an entity of absolute consciousness, ping ponging back and forth between the 2 demensions. The body in the 3rd demension that has evolved into a self aware creature of sorts, is being used as a vessel and tool for absolute consciousness,the same way it uses other animals and plants to peer thru into this 3rd demension ,walk around and collect memory and sensory experience.

I feel that absolute consciousness has been making this trek back and forth between the 2 demensions long before humans and most animals. The very first animal or plant to dream on this planet was like a break thru moment, a pouring thru or fusion of the 2 demensions. The first constructed bits of a bridge. (maybe the very basic components of matter have been making this voyage back and forth since the beginning?, example would be a photon changing from a wave (dream) into matter (3rd demension)??

Im going to go out on a limb here and suggest that, as the 3rd demension evolves, it starts to look more and more like the thing thats making it evolve.

But back to your question about the "force" what is that force? I feel it is the aculmination of all collected sensory memory, arms and legs have evolved to experience the effects of gravity ect. This memory is used to construct a body in the dream/spice demension, for gravity I feel relies on memory , and when you make the voyage from one demension to the other, your exchanging one gravity for the other or experiencing them both at the same time.