Here is the answer to Einstein’s question about the moon. Yes, it is there when no one observes it – because the environment is already, and without cease, ‘measuring’ it. All of the photons of sunlight that bounce off the moon are agents of decoherence, and more than adequate to fix its position in space and give it a sharp outline. The universe is always looking.

[W]hereas we might have been content enough to believe that electrons in a bright beam are wave-like and can be diffracted by the double slits, it is hard to understand how one-by-one passage of what seem to be particles (judging from the discrete bright spots that appear on the screen) can produce wave-like interference. We’re forced to conclude that ‘wave-like’ electrons can interfere with themselves.

[A]tomic nuclei are pretty hard to peer into. But that’s not the root of the problem. It’s that we simply can’t, for quantum processes, talk about a historical progression of events that led to a given outcome. There’s no story of how it ‘got’ to be that way.

We know that measurements of a quantum system seem to collapse the wavefunction. We most certainly don’t know how, or why, or indeed if that actually happens.

Quantum objects may in principle have a number of observable properties, but we can’t gather them all (Copenhagenists might in fact say ‘elicit them’) in a single go, because they can’t all exist at once. And by gathering some we may scramble the values of others.

[T]he probabilistic nature of the Schrödinger equation, which predicts only the likelihood of different experimental outcomes, leaves it offering no reason why one specific outcome is observed instead of another. In effect, it says that quantum events (the radioactive decay of an atom, say) happen for no reason.

[T]he wavefunction of the electron in [a] box can penetrate into the walls. If the walls aren’t too thick, the wavefunction can actually extend right through them, so that it still has a non-zero value on the outside. What this tells you is that there is a small chance – equal to the amplitude of the wavefunction squared in that part of space – that if you make a measurement of where the electron is, you might find it within the wall, or even outside the wall.