From the future here, gravity is just light reflecting off of stellar bodies, which causes the universe to "bend" space/time in all directions, just different strengths based on the reflectiveness of whatever it hit and the strength of the light source. The reason that a whole bunch of nothingness between planets keeps them spinning around one another is just light and the sheer force it applies by bumping into objects and then reflecting into the next one. Don't think of just one beam of light, think of a cacophony of endless bounces of light in varying degrees of strength.
Light is without mass, but not without energy. That energy causes what you could describe as "propulsion". Even the slightest bit of propulsion in the emptiness of space will cause matter to move around.
It's like light being a big ladle. And using that ladle to spin the water + tiny floating objects in a bath. They will all affect one another until the heat death of the bath occurs and all life grinds to a halt.
Light is without mass, but not without energy. That energy causes what you could describe as "propulsion". Even the slightest bit of propulsion in the emptiness of space will cause matter to move around.
It's like light being a big ladle. And using that ladle to spin the water + tiny floating objects in a bath. They will all affect one another until the heat death of the bath occurs and all life grinds to a halt.