While i am all for proving Elon Musk wrong, i can't say i'm satisfied that the our experience of reality can't be a computer simulation because keeping track of all the particles would require more particles than is in the universe. It seems a particularly uncreative analysis, and it certainly isn't thought out like someone who would program a simulated reality. In a simulation, occom's razor doesn't work out the same way. It's not the simplest solution to keep track of every atom in my sofa. And the subroutine IfPhysicistIsLooking can introduce the atoms at time of need.
I'm sure i'm missing something. Maybe Elon Musk believes the simulation began with the big bang?