Dimitri
random3f

Commenting on the observation that he “doesn’t blog all that often”, Matt Leifer had the following to say:
Most bloggers think of their blog like a newspaper column… what I find interesting is that you don’t have to think …

Yes there are. That’s part of the technical programme and is probably the most substantial contribution of decoherence theory to foundational studies. The review article focusses mainly on conceptual/interpretational issues, but it does discuss one model by Zurek as an example, which fits into the “less realistic” category. However, you can find references to the extensive technical literature in the review.

One of the most impressive achievements is that decoherence can select different types of “basis” depending on the relative strengths of the system-environment and internal system Hamiltonians (I use quotation marks because the states selected can be overcomplete). If the internal Hamiltonian is much stronger then the energy basis tends to be selected and if it is much weaker then something approximating the position basis is often found. In intermediate regimes, things like coherent states can be selected. This corresponds well to what we see in the lab, and has significant explanatory power. The fact that other approaches to emergence cannot reproduce this yet is a significant point in favor of the decoherence explanation.

“Re: ontology, I would feel more comfortable if I knew any operational way of deciding whether any specific ontology is “correct”, or even a reason to expect that a fully satisfactory solution exists…”

I more or less agree with you. A good choice of ontology should eventually lead to an experimental prediction that it would have been incoceivable to make without it. This might not happen in current QM itself, but perhaps in future theories like quantum gravity. However, in this post, I left the question of what constitutes a “good” ontology open, because different people have different requirements. For example, one could weaken your operational requirement and just say that the ontology should have explanatory power, i.e. be a good way of thinking about the theory that aids intuition. I also don’t have a big problem with having more than one ontology available, so long as you can account for the terms of one ontology consistently in terms of the other. Arguably, we have this stiuation in classical mechanics because the different formulations, e.g. Newton’s laws, Hamiltonian mechanics, Largrangian mechanics, etc. suggest taking different quantities as the fundamental entities of the theory. On the other hand, we shouldn’t end up with competing ontologies that give radically different pictures of what is going on in reality and appear to be genuinely irreconcilable. Arguably, this is the case with current interpretations of QM.

Re: ontology, I would feel more comfortable if I knew any operational way of deciding whether any specific ontology is “correct”, or even a reason to expect that a fully satisfactory solution exists…

thanks,

Moshe