What is reality?

“What do we really describe in physics?” he [Zeilinger] asked. “Do we describe reality? Is it out there?”

Classical physicists would have said yes, resoundingly. Studying physics reveals nature’s workings, providing an explicit map of reality’s subtleties. Those subtleties would be there whether we figured out how to question and extract them.

But in the early part of this century, quantum mechanics put that happy belief on the chopping block. Quantum mechanics, for all its ability to describe the atomic and subatomic world, blurs the distinction between the observer and the observed. As a result, it calls into question the essence of scientific curiosity and inquiry.