Just a query - not a theory - I'm no boffin, just interested.
I was wondering about Dark matter - could it be a form of pure Gravity?
I was thinking of a very massive object - say a Galaxy! charging through space churning up Space/time and spinning bits of it into swirling vortexes like eddies in a river.
I know planets drag Spacetime as they spin.
I also thought of a blackhole spinning and doing crazy stuff to Spacetime but simultaneously in motion as the Universe expands - what would the effect on Gravity that it leaves in it's wake be like?
As stated not a theory just an innocent question to ponder.