Hi Max, Thanks for your submission, which I think is an excellent one for stimulating some discussion about what people who like Bohmian mechanics find valuable about it. I have actually found Bohmian mechanics very illuminating in thinking about several of the things you mentioned, and when I first read your submission I thought “It would be good to write up a little note explaining, for example, how Bohmian mechanics helped me stop losing sleep over the delayed choice quantum eraser.” As it happens, I then went looking around some of the other discussion threads and found a nice post by Daniel Rohrlich, in the “time-symmetric theories” forum, where he claims that “retro-causality is intrinsic to quantum mechanics”. The example turns out to be closely related to the quantum eraser (and some other things) so I figured I’d kill two birds with one stone and talk about Rohrlich’s specific example instead.
But first, I wanted to say something more general about why I like Bohmian mechanics. It’s true that it provides, I think, a very illuminating concrete model against which to judge claims of the form “Quantum mechanics conclusively establishes X!” (where X is, for example, the failure of determinism, or the existence of parallel worlds, or the metaphysically creative role of observation or consciousness, or …). That is, Bohmian mechanics provides a very convenient way of seeing that many, many claims that one hears about what QM proves/establishes/requires, are actually just wrong. The available data simply do not require those things. This sort of debunking is the purpose to which I’ll put the theory in my comments about Rohrlich’s example below. But to me that’s kind of a polemical side benefit, rather than the central reason that one should actually like the theory. That central reason is: it might be true. And what I mean by that is: Bohmian mechanics is the kind of theory that might actually be “the final word” about how things really work (at least, to the extent that you pretend that non-relativistic QM is empirically adequate). Orthodox QM, by contrast, has no chance (in my opinion) of being that final word — it is to me just unbelievable that there are really two different worlds (one “quantum” and one “classical”) with distinct ontologies and dynamics and then only vaguely-defined ad hoc rules for how those two worlds interact when they meet. That just can’t be right. It’s instead clear that orthodox QM is some kind of phenomenological makeshift that, virtuous and accurate though it may be in terms of its predictions, simply can’t be the final description of what’s happening in the world.
Of course, Bohmian mechanics is not the only such viable candidate “description of what’s happening in the world”. There are a couple of different flavors of GRW type theories that are viable candidates; maybe (I’m skeptical, but maybe) Everett’s many worlds picture is such a candidate; and of course there are presumably many such viable candidate theories that we just haven’t thought of yet.
I’m not sure if Bohmian mechanics is (again leaving aside issues about extensions to QFT, etc.) true. But it *might* be true. And that mere possibility is a remarkable achievement — something that many/most extant “interpretations of QM” cannot match. This is, in a sense, the same point that people have in mind when they claim that Bohm’s theory solves the measurement problem. But that, to me, is too negative a way to put it, so I’m trying to rephrase that point in more positive terms. Anyway, that’s what I regard as the central virtue of the theory. It might actually be true.
Since this preamble got long, I’ll comment about Rohrlich’s example in a separate post…
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