Einstein didn't like it

Quantum mechanics that is.

Excerpt from latest book I'm reading, Brian Greene's "The Frabric of the Cosmos":

Einstein's viewpoint is very compelling. What could be more natural to expect a particle to be located at, or, at the very least, near to where it's found a moment later?

But Neils Bohr and the QM entourage disagreed, such reasoning they argued, is rooted in conventional thinking according to which each particle follows a definite path as it wanders to and fro.

But the two slit experiment shows us that particles act as waves, if they wandered about in some definite path then no interferance pattern would be seen (and one is seen).

The particle has a position in the usual sense only when we look at it. Rather contrary to what you would expect, the particle simply does not have a definite position before the measurement is taken.

This is a radically strange reality. In this view, when we measure the particles position we are not measuring an objective, pre-existing feature of reality. Rather, the act of measurement is deeply enmeshed in creating the very reality it is measuring.

Einstein never liked QM and over a period of years tried to discredit it with some neat thought experiments - all of which were refuted, the refutations being agreed to by Einstein. In the end Einstein had to admit that QM holds water but was never completely satisfied by it.

Reality used to be a friend of mine !