Whoa, dude. Check out those killer equations. Sweet. These realities are experienced separately by each individual. As far as either can tell, the other one doesn’t exist.
This seems weird to us, because each of us only experiences an individual existence, and we don’t get to see other branches. It’s as if each of us, like Schrödinger here, are a kind of coral branching into different possibilities. The mathematics of quantum mechanics tells us this is how the world works at tiny scales. It can be summed up in a single sentence: Everything that can happen, does. That’s quantum mechanics. But this does not mean everything happens. The rest of physics is about describing what can happen and what can’t. What physics tells us is that everything comes down to geometry and the interactions of elementary particles. And things can happen only if these interactions are perfectly balanced.