I had a theory once. It had to do with multi verses. What if bodies of gravity, such as galaxies reacted and multiplied the effects of gravity on they're prospective planes. It would be as if several millions if not billions of Milky Ways were stacked up on each other. Sure there would be "infinite", but the idea is that a number of galaxies would have moved in a different direction or some particular Milky Way didn't form properly...

There is no observational evidence for multi verses,,the universe,by definition,,contains all there is,,,you can not get "outside" of the universe. All current data heavily suggests the universe is infinite.

I had a theory too, that our theory of gravity is just wrong, at least at extreme scales. In other words, the law of gravity is still at the Newtonian motion stage, it's close enough for day-to-day and mid-range observations, but fails to provide accurate predictions at larger (and smaller) scales. This also explains why quantum mechanics and gravitation theory still have not been reconciled.

There is no observational evidence of dark matter (or dark energy) for that matter. They are the equivalent of fudge-factors...no, not the equivalent, they -are- fudge-factors, created out of thin air to try and make the numbers add up to the observations.

I have a theory; if I counted up the money in a cash register at the end of the day and came up short, then declared the difference was "dark money"...I'd lose my job.