Viewed an interesting utube last eve on antimatter. Said that at the moment of the big bang, there was equal amounts of matter and antimatter, and then discussed the various scenarios of what happened to the antimatter.
Other than the center of the milky way, there apparently is little antimatter in its stars and planets. Probably the same in the galaxies of the visible universes.
Perhaps there is a companion universe comprised of all the antimatter. Where that one would have a smattering of matter, just like we have antimatter here.
I knew a guy that built the best gravity meters in the world. He was hired by the military to try to measure “anti-gravity” as a solution to why the missiles weren’t landing where they were supposed to. This was years ago, and perhaps before the idea of dark matter was invented.
He couldn’t measure any anti-gravity (too difficult in actual on-site field experiments) - but he didn’t discount the idea. Although I guess that dark matter is the opposite of anti-gravity. Although the idea of anti-gravity may account for the variations that they observe?
All of the other natural forces (magnetic, electro-magnetic, etc.) have positive and negative attractions, so why wouldn’t gravity?