{"id":964,"date":"2015-05-25T12:54:46","date_gmt":"2015-05-25T17:54:46","guid":{"rendered":"http:\/\/blog.richmond.edu\/physicsbunn\/?p=964"},"modified":"2015-05-25T13:49:44","modified_gmt":"2015-05-25T18:49:44","slug":"nature-is-at-it-again","status":"publish","type":"post","link":"https:\/\/blog.richmond.edu\/physicsbunn\/2015\/05\/25\/nature-is-at-it-again\/","title":{"rendered":"Nature is at it again"},"content":{"rendered":"

Last week, Nature<\/em> ran a piece under the headline Quantum physics: What is really real?<\/a>\u00a0I obnoxiously posted this on Facebook (because I’m too old and out of touch to be on any of the hipper social media sites):<\/p>\n

\"Screenshot<\/a><\/p>\n

I have now read the piece, and I can report that there’s no need for a recantation. As expected,\u00a0Nature<\/em> is making grandiose claims about quantum mechanics and the nature of reality that go beyond anything supported by evidence.<\/p>\n

Nature<\/em> writes pretty much the same story every couple<\/a> of years<\/a>. The main idea behind all of these articles is the question of whether the quantum mechanical wavefunction describes\u00a0the way a system really is\u00a0<\/em> or merely\u00a0our knowledge of the system.\u00a0<\/em>In philosophy-of-science circles, these two points of view\u00a0are sometimes known as the psi-ontic and psi-epistemic stances. More specifically, all three of these articles have to do with a theorem published<\/a> (in one of the\u00a0Nature <\/i>journals) by Pusey et al.<\/em> that claims to provide an experimental way of distinguishing between these possibilities. After Pusey et al.<\/em> published this theoretical result, others went ahead and performed the proposed experimental tests, leading to the (claimed) conclusion that the wavefunction describes actual reality, not merely our knowledge.<\/p>\n

You should of course be skeptical of any claim that an experimental result reveals something about the deep nature of reality. Sure enough, if you dig down just a little bit, it becomes clear that these results do no such thing. The Pusey et al.<\/em> theorem proves that\u00a0a certain class<\/em> of psi-epistemic theories make predictions that differ from the predictions of standard quantum mechanics. The subsequent experiments confirmed the standard predictions, so they rule out that class of theories.<\/p>\n

The problem is that ruling out a specific class of psi-epistemic theories is not the same thing as ruling out the psi-epistemic point of view as a whole. We now know that that class of theories is wrong, but that’s all we know. To make matters worse, the class of theories ruled out by these experiments, as far as I can tell, does not contain any theories that any proponents of psi-epstemicism actually believe in. The theories they tested are straw men.<\/a><\/p>\n

In particular, the most prominent proponents of the psi-epistemic point of view are the advocates of something called quantum Bayesianism<\/a>\u00a0(QBism). QBism\u00a0is an interpretation of quantum mechanics, as opposed to an alternative theory — that is, it makes predictions that are identical to those of standard quantum mechanics. There is, therefore, no experimental result that would distinguish QBism from psi-ontic versions of quantum mechanics.<\/p>\n

Not all psi-epistemicists are QBists, of course, but as far as I can tell even the others never\u00a0advocated for any theories in the class considered by Pusey et al<\/em>. If I’m wrong about that, I’d be interested to know.<\/p>\n

 <\/p>\n","protected":false},"excerpt":{"rendered":"

Last week, Nature ran a piece under the headline Quantum physics: What is really real?\u00a0I obnoxiously posted this on Facebook (because I’m too old and out of touch to be on any of the hipper social media sites): I have now read the piece, and I can report that there’s no need for a recantation. … Continue reading Nature is at it again<\/span><\/a><\/p>\n","protected":false},"author":12,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1],"tags":[],"class_list":["post-964","post","type-post","status-publish","format-standard","hentry","category-uncategorized"],"jetpack_featured_media_url":"","_links":{"self":[{"href":"https:\/\/blog.richmond.edu\/physicsbunn\/wp-json\/wp\/v2\/posts\/964","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/blog.richmond.edu\/physicsbunn\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/blog.richmond.edu\/physicsbunn\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/blog.richmond.edu\/physicsbunn\/wp-json\/wp\/v2\/users\/12"}],"replies":[{"embeddable":true,"href":"https:\/\/blog.richmond.edu\/physicsbunn\/wp-json\/wp\/v2\/comments?post=964"}],"version-history":[{"count":0,"href":"https:\/\/blog.richmond.edu\/physicsbunn\/wp-json\/wp\/v2\/posts\/964\/revisions"}],"wp:attachment":[{"href":"https:\/\/blog.richmond.edu\/physicsbunn\/wp-json\/wp\/v2\/media?parent=964"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/blog.richmond.edu\/physicsbunn\/wp-json\/wp\/v2\/categories?post=964"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/blog.richmond.edu\/physicsbunn\/wp-json\/wp\/v2\/tags?post=964"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}