But this overwhelming success comes with a peculiar price tag: Use this theory; lose Reality.
The deepest unsolved question of quantum theory is this: how can we properly conceive a model of the world for which quantum theory is a correct description? No one has posed the Quantum Reality Question better than UCSC professor Bruce Rosenblum who says: "Classical physics could explain the world but got some of the details wrong; quantum physics gets all the details right but can't explain the world."
Quantum theory describes the world in two ways, depending on whether it's being measured or not. When not measured, it's described by a wave of probabilities (called the psi-function); when it's measured, it turns into actual particles.
The Quantum Reality Question resolves itself into two parts:
1) The Interpretation Question: what does the psi-function actually stand for? What in the world is going on when we aren't making measurements?
2) The Measurement Problem: what happens during a measurement when (in the theory at least) waves turn into actual particles?
A successful Quantum Reality would tell us: 1) what the world is like when it's not looked at and 2) how the act of looking changes the unobserved world into the world we see.
In my book Quantum Reality: Beyond the New Physics I consider eight candidate models for a viable way of conceptualizing the world including Hugh Everett's Many-Universe Model (QR #4) and Werner Heisenberg's version (QR #8).
In Everett's Many-Universe Model, the psi-function describes not possibilities but actualities--Everything that can happen really does happen in one universe or another. That's what's going on in the world when you don't look. When you look, the universe you happen to be in splits into all possible outcomes of the measurement you chose to make but you are conscious of inhabiting only one of these branching paths. As preposterous as this model appears it ranks as the most detailed and mathematically consistent model of Quantum Reality yet put forth. The fact that such an outlandish model of reality is taken seriously by smart people is a measure of how desperate physicists have become in their quest to solve the Quantum Reality Question.
Heisenberg's Model proposes that there is only one world. But when nobody looks it's just a world of possibilities. Whenever somebody looks, one of these possibilities becomes actual. Heisenberg fails to tell us though, how the first real look happened in a world of pure possibility, nor does he say what a look looks like--that is, which sorts of interactions in the world qualify as "looks" and which are merely inconsequential dances of possibilities.
Unlike many popular physics books that trumpet the colorful successes of physics, Quantum Reality focuses single-mindedly on physics' most conspicuous failure--the Quantum Reality Question as the most embarrassing skeleton pushed way into the back of physics' secret closet. Quantum Reality explores in great detail a deep and glaringly unsolved problem located not in the hidden recesses of elementary particles or in some galaxy far away but right here at home--an unsolved mystery located literally everywhere we look.
None of the eight proposed Quantum Realities (and others since invented) feels right to me. No one today, I think, really knows how this world works. One easy way to fluster a physicist: ask what he/she thinks of the Measurement Problem.
Quantum Reality has been translated into German, Japanese and Portuguese. Nick gets about $1 in royalties for every copy sold. Recently made available (Dec 2011) as an E-book.