Quantum physics, celebrated for its predictive success, has also become notorious for being an inscrutable mass of paradoxes.
One of the founders of the theory, Niels Bohr, stated that “those who are not shocked when they first come across quantum theory cannot possibly have understood it.” Nobel laureate Richard Feynman said, “I think I can safely say that nobody understands quantum mechanics.”
The shocking aspects of quantum theory can be summarized by three issues: uncertainty, nonlocality and the measurement problem (or the problem of “Schrödinger’s Cat”).
The first issue consists in the fact that the tiny objects described by quantum theory, such as the constituents of atoms — protons and electrons, for example — cannot be pinned down to definite locations and speeds at the same time. If one of these properties is definite, the other must be in a quantum superposition, a kind of “fuzziness” that we never see in the ordinary macroscopic world of experience.