Can a particle really be in many places at the same time?
Is the Universe continually dividing itself into parallel worlds, each with an alternative version of ourselves?
Is there such a thing as an objective reality at all?
Philosophers and mystics, East and West, are in agreement with modern quantum theory: that objective existence of the world is an illusion.
But jut what is the Reality behind this illusion, then?
I don't know, nor, at this point, does anyone else.
So people say, let's not worry about the big question.
But some physicists worried anyway. By the 1930s, Albert Einstein had rejected the Copenhagen interpretation — not least because it allowed two particles to entangle their wavefunctions, producing a situation in which measurements on one could instantaneously determine the state of the other even if the particles were separated by vast distances. Rather than accept such “spooky action at a distance”, Einstein preferred to believe that the particles' wavefunctions were incomplete. He was wrong.
The problem with QM it is like a giant smooth mountain with no footholds, no way to ascend.