{"id":3628,"date":"2018-02-03T07:41:16","date_gmt":"2018-02-03T13:41:16","guid":{"rendered":"https:\/\/scottaaronson.blog\/?p=3628"},"modified":"2018-02-13T05:49:39","modified_gmt":"2018-02-13T11:49:39","slug":"interpretive-cards-mwi-bohm-copenhagen-collect-em-all","status":"publish","type":"post","link":"https:\/\/scottaaronson.blog\/?p=3628","title":{"rendered":"Interpretive cards (MWI, Bohm, Copenhagen: collect ’em all)"},"content":{"rendered":"

I’ve been way<\/em> too distracted by actual research lately from my primary career as a nerd blogger—that’s what happens when you’re on sabbatical.\u00a0 But now I’m sick, and in no condition to be thinking about research.\u00a0 And this morning, in a thread that had turned to<\/a> my views on the interpretation of quantum mechanics called “QBism,”<\/a> regular commenter Atreat asked me the following pointed question:<\/p>\n

Scott, what is your<\/em> preferred interpretation of QM? I don\u2019t think I\u2019ve ever seen you put your cards on the table and lay out clearly what interpretation(s) you think are closest to the truth. I don\u2019t think your ghost paper<\/a> qualifies as an answer, BTW. I\u2019ve heard you say you have deep skepticism about objective collapse theories and yet these would seemingly be right up your philosophical alley so to speak. If you had to bet on which interpretation was closest to the truth, which one would you go with?<\/p>\n

Many people have asked me some variant of the same thing.\u00a0 As it happens, I’d been toying since the summer with a huge post about my views on each major interpretation, but I never quite got it into a form I wanted.\u00a0 By contrast, it took me only an hour to write out a reply to Atreat, and in the age of social media and attention spans measured in attoseconds, many readers will probably prefer that short reply to the huge post anyway.\u00a0 So then I figured, why not promote it to a full post and be done with it?\u00a0 So without further ado:<\/p>\n

\n

Dear Atreat,<\/p>\n

It\u2019s no coincidence that you haven\u2019t seen me put my cards on the table with a favored interpretation of QM!<\/p>\n

There are interpretations (like the \u201ctransactional interpretation<\/a>\u201d) that make no sense whatsoever to me.<\/p>\n

There are \u201cinterpretations\u201d like dynamical collapse<\/a> that aren\u2019t interpretations at all, but proposals for new physical theories.\u00a0 By all means, let\u2019s test QM on larger and larger systems, among other reasons because it could tell us that some such theory is true or—vastly more likely, I think—place new limits on it! (People are trying.)<\/p>\n

Then there\u2019s the\u00a0deBroglie-Bohm theory<\/a>, which does lay its cards on the table in a very interesting way, by proposing a specific evolution rule for hidden variables (chosen to match the predictions of QM), but which thereby opens itself up to the charge of non-uniqueness: why\u00a0that<\/i>\u00a0rule, as opposed to a thousand other rules that someone could write down?\u00a0 And if they all lead to the same predictions, then how could anyone ever know which rule was right?<\/p>\n

And then there are dozens of interpretations that seem to differ from one of the \u201cmain\u201d interpretations (Many-Worlds, Copenhagen, Bohm) mostly just in the verbal patter.<\/p>\n

As for Copenhagen, I’ve described it as “shut-up and calculate except without ever shutting up about it”! \u00a0I regard Bohr’s writings on the subject as barely comprehensible, and Copenhagen as less of an interpretation than a self-conscious anti-interpretation: a studied refusal to offer any account of the actual constituents of the world, and—most of all—an insistence that if you<\/em> insist on such an account, then that just proves that you cling na\u00efvely to a classical worldview, and haven’t grasped the enormity of the quantum revolution.<\/p>\n

But the basic split between Many-Worlds<\/a> and Copenhagen<\/a> (or better: between Many-Worlds and \u201cshut-up-and-calculate\u201d \/ \u201cQM needs no interpretation\u201d \/ etc.), I regard as coming from two fundamentally different conceptions of what a scientific theory is supposed to do for you.\u00a0 Is it supposed to posit an objective state for the universe, or be only a tool that you use to organize your experiences?<\/p>\n

Also, are the ultimate equations that govern the universe \u201creal,\u201d while tables and chairs are \u201cunreal\u201d (in the sense of being no more than fuzzy approximate descriptions of certain solutions to the equations)?\u00a0 Or are the tables and chairs \u201creal,\u201d while the equations are \u201cunreal\u201d (in the sense of being tools invented by humans to predict the behavior of tables and chairs and whatever else, while extraterrestrials might use other tools)?\u00a0 Which level of reality do you care about \/ want to load with positive affect, and which level do you want to denigrate?<\/p>\n

This is not like picking a race horse, in the sense that there might be no future discovery or event that will tell us who was closer to the truth.\u00a0 I regard it as conceivable that superintelligent AIs will\u00a0still<\/i>\u00a0argue about the interpretation of QM \u2026 or maybe that God and the angels argue about it now.<\/p>\n

Indeed, about the only thing I can think of that might definitively settle the debate, would be the discovery of an even deeper level of description than QM\u2014but such a discovery would \u201csettle\u201d the debate only by completely changing the terms of it.<\/p>\n

I will say this, however, in favor of Many-Worlds: it\u2019s clearly and unequivocally the best interpretation of QM,\u00a0as long as we leave ourselves out of the picture!<\/b>\u00a0 I.e., as long as we say that the goal of physics is to give the simplest, cleanest possible mathematical description of the world that somewhere<\/i> contains something<\/i> that seems to correspond to observation, and we\u2019re willing to shunt as much metaphysical weirdness as needed to those who worry themselves about details like \u201cwait, so are we postulating the physical existence of a continuum<\/em> of slightly different variants of me, or just an astronomically large finite number?\u201d (Incidentally, Max Tegmark\u2019s \u201cmathematical multiverse\u201d<\/a> does even better than MWI by this standard.\u00a0 Tegmark is the one waiting for you all the way at the bottom of the slippery slope of always preferring Occam’s Razor over trying to account for the specificity of the observed world.)\u00a0 It\u2019s no coincidence, I don’t think, that MWI is so popular among those who are also eliminativists about consciousness.<\/p>\n

When I taught my undergrad Intro to Quantum Information course last spring—for which lecture notes are coming soon, by the way!—it was striking how often I needed to resort to an MWI-like way of speaking when students got confused about measurement and decoherence. (\u201cSo then we apply this unitary transformation U that entangles the system and environment, and we compute a partial trace over the environment qubits, and we see that it\u2019s as if the system has been measured, though of course we could in principle reverse this by applying U-1<\/sup>\u00a0\u2026 oh shoot, have I just conceded MWI?\u201d)<\/p>\n

On the other hand, when (at the TAs\u2019 insistence) we put an optional ungraded question on the final exam that asked students their favorite interpretation of QM, we found that there was no correlation whatsoever between interpretation and final exam score\u2014except<\/i>\u00a0that students who said they didn\u2019t believe any interpretation at all, or that the question was meaningless or didn’t matter, scored noticeably higher than everyone else.<\/p>\n

Anyway, as I said, MWI is the best interpretation if we leave ourselves out of the picture.\u00a0 But you object: \u201cOK, and what if we\u00a0don\u2019t<\/i>\u00a0leave ourselves out of the picture?\u00a0 If we dig deep enough on the interpretation of QM, aren\u2019t we ultimately also asking about the \u2018hard problem of consciousness,\u2019 much as some people try to deny that? So for example, what would it be like to be maintained in a coherent superposition of thinking two different thoughts A and B, and then to get measured in the |A\u27e9+|B\u27e9, |A\u27e9-|B\u27e9 basis?\u00a0 Would it even be like anything?\u00a0 Or is there something about our consciousness that depends on decoherence, irreversibility, full participation in the arrow of the time, not living in an enclosed little unitary box like AdS\/CFT<\/a>\u2014something that we\u2019d necessarily destroy if we tried to set up a large-scale interference experiment on our own brains, or any other conscious entities?\u00a0 If so, then wouldn\u2019t that point to a strange sort of reconciliation of Many-Worlds with Copenhagen\u2014where as soon as we had a superposition involving different subjective experiences,\u00a0for that very reason<\/i>\u00a0its being a superposition would be forevermore devoid of empirical consequences, and we could treat it as just a classical probability distribution?\u201d<\/p>\n

I\u2019m not sure, but\u00a0The Ghost in the Quantum Turing Machine<\/a>\u00a0will probably have to stand as my last word (or rather, last many words) on those questions for the time being.<\/p>\n","protected":false},"excerpt":{"rendered":"

I’ve been way too distracted by actual research lately from my primary career as a nerd blogger—that’s what happens when you’re on sabbatical.\u00a0 But now I’m sick, and in no condition to be thinking about research.\u00a0 And this morning, in a thread that had turned to my views on the interpretation of quantum mechanics called […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"advanced_seo_description":"","jetpack_seo_html_title":"","jetpack_seo_noindex":false,"jetpack_seo_schema_type":"","_jetpack_newsletter_access":"","_jetpack_dont_email_post_to_subs":false,"_jetpack_newsletter_tier_id":0,"_jetpack_memberships_contains_paywalled_content":false,"_jetpack_feature_clip_id":0,"_jetpack_memberships_contains_paid_content":false,"footnotes":"","jetpack_publicize_message":"{title}\n\n{excerpt}\n\n{url}","jetpack_publicize_feature_enabled":true,"jetpack_social_post_already_shared":false,"jetpack_social_options":{"image_generator_settings":{"template":"highway","default_image_id":0,"font":"","enabled":false},"version":2},"_wpas_customize_per_network":false,"jetpack_post_was_ever_published":false},"categories":[12,3,4],"tags":[],"class_list":["post-3628","post","type-post","status-publish","format-standard","hentry","category-metaphysical-spouting","category-procrastination","category-quantum"],"jetpack_publicize_connections":[],"jetpack_featured_media_url":"","jetpack_sharing_enabled":true,"_links":{"self":[{"href":"https:\/\/scottaaronson.blog\/index.php?rest_route=\/wp\/v2\/posts\/3628","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/scottaaronson.blog\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/scottaaronson.blog\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/scottaaronson.blog\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/scottaaronson.blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=3628"}],"version-history":[{"count":4,"href":"https:\/\/scottaaronson.blog\/index.php?rest_route=\/wp\/v2\/posts\/3628\/revisions"}],"predecessor-version":[{"id":3637,"href":"https:\/\/scottaaronson.blog\/index.php?rest_route=\/wp\/v2\/posts\/3628\/revisions\/3637"}],"wp:attachment":[{"href":"https:\/\/scottaaronson.blog\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=3628"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/scottaaronson.blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=3628"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/scottaaronson.blog\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=3628"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}