The idea is simple.
What I know of light is that there exist different penetration depths. So inspired by light. I guess there is a connection between light and gravity. Because gravity also seem to have a great penetration depth. Or so I assume.
I wonder therefore if you can differentiate between forces in general to include those who have a varying degree of penetration. That is. Those who do not only affect the surface but go deeper inside the body.
So I speculate that there should exist deep forces.