It occurs to me that one consequence of learning about QM from the sequence (as many people are doing), is that you then need to un-learn wavefunction realism, if you want to think about the subject for yourself. A better way to learn QM is to approach it as an incomplete classical-looking theory. E.g. a particle isn’t really a wavefunction; it’s a particle, with a position and momentum that we only know imprecisely, and the wavefunction is a calculating device that gives you the probabilities. Once you’re clear on that picture, then you can say “this theory is manifestly incomplete; what’s the actual physical reality, and why does this wavefunction thing work?” And then you’re in a position to consider whether the wavefunction itself could somehow be the actual physical object. But because the sequence presupposes wavefunction realism from the beginning—even the Copenhagen interpretation is mostly portrayed as being about an objectively existing wavefunction with two modes of evolution—it would take an unusually careful reader to come to the sequence with no prior knowledge of QM, and still notice the possibility that wavefunctions aren’t real.
What you describe is the hidden-value theory of QM, which has been invalidated experimentally. Any interpretation of QM must be inherently “weirder” than observers merely bring in a state of ignorance about the velocity and position of billiard ball particles.
Probably true. That said, I’m not sure how many readers could approach QM as a “classical-looking theory” and notice the possibility that particles aren’t real. I’m also not sure there’s a way to approach QM—or, indeed, anything else—that doesn’t bias the reader in favor of some ontology.
Incidentally, New Scientist (“Ghosts in the atom: Unmasking the quantum phantom”, Aug 2, 2012) are now reporting that theoretical breakthroughs have disproved non-realist interpretations of QM. Its been shown that different interpretations of QM have different empirical consequences, and the naive version of the Copenhagen interpretation contradicts empirical data.
“Now Matthew Pusey and Terry Rudolph of Imperial College London, with
Jonathan Barrett of Royal Holloway University of London, seem to
have struck gold. They imagined a hypothetical theory that
completely describes a single quantum system such as an atom but,
crucially, without an underlying wave telling the particle what to
do.
Next they concocted a thought experiment to test their theory, which
involved bringing two independent atoms together and making a
particular measurement on them. What they found is that the
hypothetical wave-less theory predicts an outcome that is different
from standard quantum theory. “Since quantum theory is known to be
correct, it follows that nothing like our hypothetical theory can be
correct,” says Rudolph (Nature Physics, vol 8, p 476).
Some colleagues are impressed. “It’s a fabulous piece of work,” says
Antony Valentini of Clemson University in South Carolina. “It shows
that the wave function cannot be a mere abstract mathematical
device. It must be real—as real as the magnetic field in the space
around a bar magnet.”
The Pusey-Barrett-Rudolph result was published (and much discussed) last year. Matt Leifer has a nice, non-sensationalist discussion of the theorem, and he argues convincingly that the theorem does not rule out any interpretation of QM held by contemporary researchers.
It occurs to me that one consequence of learning about QM from the sequence (as many people are doing), is that you then need to un-learn wavefunction realism, if you want to think about the subject for yourself. A better way to learn QM is to approach it as an incomplete classical-looking theory. E.g. a particle isn’t really a wavefunction; it’s a particle, with a position and momentum that we only know imprecisely, and the wavefunction is a calculating device that gives you the probabilities. Once you’re clear on that picture, then you can say “this theory is manifestly incomplete; what’s the actual physical reality, and why does this wavefunction thing work?” And then you’re in a position to consider whether the wavefunction itself could somehow be the actual physical object. But because the sequence presupposes wavefunction realism from the beginning—even the Copenhagen interpretation is mostly portrayed as being about an objectively existing wavefunction with two modes of evolution—it would take an unusually careful reader to come to the sequence with no prior knowledge of QM, and still notice the possibility that wavefunctions aren’t real.
What you describe is the hidden-value theory of QM, which has been invalidated experimentally. Any interpretation of QM must be inherently “weirder” than observers merely bring in a state of ignorance about the velocity and position of billiard ball particles.
Probably true.
That said, I’m not sure how many readers could approach QM as a “classical-looking theory” and notice the possibility that particles aren’t real.
I’m also not sure there’s a way to approach QM—or, indeed, anything else—that doesn’t bias the reader in favor of some ontology.
Incidentally, New Scientist (“Ghosts in the atom: Unmasking the quantum phantom”, Aug 2, 2012) are now reporting that theoretical breakthroughs have disproved non-realist interpretations of QM. Its been shown that different interpretations of QM have different empirical consequences, and the naive version of the Copenhagen interpretation contradicts empirical data.
“Now Matthew Pusey and Terry Rudolph of Imperial College London, with Jonathan Barrett of Royal Holloway University of London, seem to have struck gold. They imagined a hypothetical theory that completely describes a single quantum system such as an atom but, crucially, without an underlying wave telling the particle what to do.
Next they concocted a thought experiment to test their theory, which involved bringing two independent atoms together and making a particular measurement on them. What they found is that the hypothetical wave-less theory predicts an outcome that is different from standard quantum theory. “Since quantum theory is known to be correct, it follows that nothing like our hypothetical theory can be correct,” says Rudolph (Nature Physics, vol 8, p 476).
Some colleagues are impressed. “It’s a fabulous piece of work,” says Antony Valentini of Clemson University in South Carolina. “It shows that the wave function cannot be a mere abstract mathematical device. It must be real—as real as the magnetic field in the space around a bar magnet.”
The Pusey-Barrett-Rudolph result was published (and much discussed) last year. Matt Leifer has a nice, non-sensationalist discussion of the theorem, and he argues convincingly that the theorem does not rule out any interpretation of QM held by contemporary researchers.
Probably better to cite a description rather than blurbs. Scott Aaronson’s post was linked on LW, and is a really good description.
Quick summary: what the paper shows is that the “wave-function as knowledge” description is incompatible with QM.