You can imagine reality as if it was an empty picture frame, with a string made of the fabric of space and time strung from one side of the frame to the other. The space above the string is our reality and is made of matter. The space below the string is the other reality, one made up of antimatter. Now if someone plucked this string, things get interesting. The moment where the string is closer to the bottom of the frame represents the moments where our universe is expanding. On the flip side of this when the string is closer to the top of the frame it represents moments like the big bang/bounce. This remains the same on the other side too. As the string oscillates up and down with time, each time it changes direction are moments between the two realities where the differences between the two are so great that matter or antimatter may tunnel itself through the string into its opposite reality. This so far would explain why in our reality there ended up being more matter than antimatter right after our big bang/bounce and the event itself. Now in addition to this, make the string a taut piece of fabric, taut even though it is technically still oscillating like when it was the string. If you push a finger against the fabric, on the side of your hand there is a gravity well, like the one for Earth. On the flip side of this, there is a gravity mountain. A spot of gravity that pushes you away like two objects of the same polarity. There even could be a chance that this relates to dark matter. Now, this theory is just a thought, it could have been thought up of before, but it might not have been. I am no expert either, but I like to think this theory of mine has just as much chance to be true as the one where we are living in a simulation.