This article should really be called "Patching the argumentative flaw in the Sequences created by the Quantum Physics Sequence".
There's only one big thing wrong with that Sequence: the central factual claim is wrong. I don't mean the claim that the Many Worlds interpretation is correct; I mean the claim that the Many Worlds interpretation is obviously correct. I don't agree with the ontological claim either, but I especially don't agree with the epistemological claim. It's a strawman which reduces the quantum debate to Everett versus Bohr - well, it's not really Bohr, since Bohr didn't believe wavefunctions were physical entities. Everett versus Collapse, then.
I've complained about this from the beginning, simply because I've also studied the topic and profoundly disagree with Eliezer's assessment. What I would like to see discussed on this occasion is not the physics, but rather how to patch the arguments in the Sequences that depend on this wrong sub-argument. To my eyes, this is a highly visible flaw, but it's not a deep one. It's a detail, a bug. Surely it affects nothing of substance.
However, before I proceed, I'd better back up my criticism. So: consider the existence of single-world retrocausal interpretations of quantum mechanics, such as John Cramer's transactional interpretation, which is descended from Wheeler-Feynman absorber theory. There are no superpositions, only causal chains running forward in time and backward in time. The calculus of complex-valued probability amplitudes is supposed to arise from this.
The existence of the retrocausal tradition already shows that the debate has been represented incorrectly; it should at least be Everett versus Bohr versus Cramer. I would also argue that when you look at the details, many-worlds has no discernible edge over single-world retrocausality:
- Relativity isn't an issue for the transactional interpretation: causality forwards and causality backwards are both local, it's the existence of loops in time which create the appearance of nonlocality.
- Retrocausal interpretations don't have an exact derivation of the Born rule, but neither does many-worlds.
- Many-worlds finds hope of such a derivation in a property of the quantum formalism: the resemblance of density matrix entries to probabilities. But single-world retrocausality finds such hope too: the Born probabilities can be obtained from the product of ψ with ψ*, its complex conjugate, and ψ* is the time reverse of ψ.
- Loops in time just fundamentally bug some people, but splitting worlds have the same effect on others.
I am not especially an advocate of retrocausal interpretations. They are among the possibilities; they deserve consideration and they get it. Retrocausality may or may not be an element of the real explanation of why quantum mechanics works. Progress towards the discovery of the truth requires exploration on many fronts, that's happening, we'll get there eventually. I have focused on retrocausal interpretations here just because they offer the clearest evidence that the big picture offered by the Sequence is wrong.
It's hopeless to suggest rewriting the Sequence, I don't think that would be a good use of anyone's time. But what I would like to have, is a clear idea of the role that "the winner is ... Many Worlds!" plays in the overall flow of argument, in the great meta-sequence that is Less Wrong's foundational text; and I would also like to have a clear idea of how to patch the argument, so that it routes around this flaw.
In the wiki, it states that "Cleaning up the old confusion about QM is used to introduce basic issues in rationality (such as the technical version of Occam's Razor), epistemology, reductionism, naturalism, and philosophy of science." So there we have it - a synopsis of the function that this Sequence is supposed to perform. Perhaps we need a working group that will identify each of the individual arguments, and come up with a substitute for each one.
Hello, I'm posting this because I saw some earlier comments about PTI that needed correcting.
PTI does not have 'world branches' like MWI. If you read the material at the end of my FoP article (http://arxiv.org/abs/1204.5227)
and my new book, http://www.cambridge.org/us/knowledge/discountpromotion/?site_locale=en_US&code=L2TIQM
Chapters 3 and 6 in particular, you will see that there is already a 'transaction eater' in PTI (if I understood that notion correctly); i.e., something that really does result in 'collapse'. These are the absorbers, properly understood (and I give a precise definition of what an 'absorber' is.) PTI was developed to better define 'absorber,' to extend TI to the relativistic domain, and to address the fact that multiparticle q. states are 3N-dimensional, too 'big' to fit into spacetime. So I view them as physical but sub-empirical possibilities -- something 'more real than ideas' but 'less real than things of the facts', as Heisenberg first suggested.
So the possibilities in PTI are not 'other worlds' containing sets of macroscopic object including observers. Rather, each possibilitiy is just a possibility for a transaction resulting in a single spacetime event. The set of spacetime events that we experience as our macroscopic world are the actualized transactions corresponding to specific individual events. So this is definitely not just another version of MWI. Thank you for your interest in TI and PTI. Best wishes, RK
I have a problem with your Possibilist TI that I also had with original TI, and with almost every ontological interpretation except for Bohmian mechanics - I can't figure out what the ontology is; nor even what the mathematical object is, that represents reality in the theory.
If Einstein had had his way, reality would have been described by classical fields on a manifold. Mathematically the universe would be represented by some particular exact solution of the equations of motion. Even given that, we could still ask the ontological questions like, what is... (read more)