{"id":14144,"date":"2024-09-26T15:05:00","date_gmt":"2024-09-26T19:05:00","guid":{"rendered":"https:\/\/www.math.columbia.edu\/~woit\/wordpress\/?p=14144"},"modified":"2024-11-07T09:20:06","modified_gmt":"2024-11-07T14:20:06","slug":"is-spacetime-unraveling","status":"publish","type":"post","link":"https:\/\/www.math.columbia.edu\/~woit\/wordpress\/?p=14144","title":{"rendered":"Is Spacetime Unraveling?"},"content":{"rendered":"<p>Quanta magazine has just put out an impressive package of material under the title <a href=\"https:\/\/www.quantamagazine.org\/the-unraveling-of-space-time-20240925\/\">The Unraveling of Space-Time<\/a>.  Much of it is promoting the &#8220;Spacetime is doomed&#8221; point of view that influential theorists have been pushing for decades now.  A few quick comments about the articles:<\/p>\n<ul>\n<li>String theory is barely even mentioned.<\/li>\n<li>There is one article giving voice to an opposing point of view, that spacetime may not be doomed, an <a href=\"https:\/\/www.quantamagazine.org\/can-space-time-be-saved-20240925\/\">interview with Latham Boyle<\/a>.<\/li>\n<li>The big problem with the supposedly now conventional view that spacetime needs to be replaced by something more fundamental that is completely different is of course: &#8220;replaced with what?&#8221;.  A lot of attention is given to two general ideas.  One is &#8220;holography&#8221;, the other Arkani-Hamed&#8217;s amplitudes program.  But these are now very old ideas that show no signs of working as hoped.\n<p>Thirty years ago Lenny Susskind was writing about <a href=\"https:\/\/arxiv.org\/abs\/hep-th\/9409089\">The World as a Hologram<\/a>.  The idea wasn&#8217;t new then and seems to be going nowhere now.  It was 17 years ago that Arkani-Hamed started re-orienting his research around the hope that new ways to compute scattering amplitudes would show new foundations for fundamental physics that would replace spacetime. Years of research since then by hundreds of theorists pursuing this have led to lots of new techniques for computing amplitudes (twistors, the amplituhedron, the associahedron, now surfaceology), but none of this shows any signs of giving the hoped for new foundations that would replace spacetime.<\/li>\n<\/ul>\n<p>Instead of saying any more about this, it seems a good idea to try and lay out a very different point of view which I think has a lot more evidence for it. This point of view starts by noting that our current best fundamental theory has been absurdly successful.  There are questions it doesn&#8217;t answer so we&#8217;d like to do better, but the idea that this is going to happen by throwing the whole thing out and looking for something completely different seems to me completely implausible.<\/p>\n<p>One lesson of the development of our best fundamental theory is that the new ideas that went into it were much the same ideas that mathematicians had been discovering as they worked at things from an independent direction.  Our currently fundamental classical notion of spacetime is based on Riemannian geometry, which mathematicians first discovered decades before physicists found out the significance for physics of this geometry.  If the new idea is that the concept of a &#8220;space&#8221; needs to be replaced by something deeper, mathematicians have by now a long history of investigating more and more sophisticated ways of thinking about what a &#8220;space&#8221; is.  That theorists are on the road to a better replacement for &#8220;space&#8221; would be more plausible if they were going down one of the directions mathematicians have found fruitful, but I don&#8217;t see that happening at all.<\/p>\n<p>To get more specific, the basic mathematical constructions that go into the Standard Model (connections, curvature, spinors, the Dirac operator, quantization) involve some of the deepest and most powerful concepts in modern mathematics. Progress should more likely come from a deeper understanding of these than from throwing them all out and starting with crude arguments about holograms, tensor networks, or some such.<\/p>\n<p>To get very specific, we should be looking not at the geometry of arbitrary dimensions, but at the four dimensions that have worked so well, thinking of them in terms of the spinor geometry which is both more fundamental mathematically, and at the center of our successful theory of the world (all matter particles are described by spinors).  One should take the success of the formalism of connections and curvature on principal bundles at describing fundamental forces as indicating that this is the right set of fundamental variables for describing the gravitational force.  Taking spin into account, the right language for describing four-dimensional geometry is the principal bundle of spin-frames with its spin-connection and vierbein dynamical variables (one should probably think of vectors as the tensor product of more fundamental spinor variables).<\/p>\n<p>What I&#8217;m suggesting here isn&#8217;t a new point of view, it has motivated a lot of work in the past (e.g. Ashtekar variables).  I&#8217;m hoping that some new ideas I&#8217;m looking into about the relation between the theory in Euclidean and Minkowski signature will help overcome previous roadblocks.  Whether this will work as I hope is to be seen, but I think it&#8217;s a much more plausible vision than that of any of the doomers.<\/p>\n<p><strong>Update<\/strong>:  John Horgan has some commentary <a href=\"https:\/\/johnhorgan.org\/cross-check\/the-beyond-spacetime-meme\">here<\/a>, taking the point of view that discussions of &#8220;Beyond Space-time&#8221; are fine, as long as you realize what you&#8217;re doing is &#8220;ironic science&#8221; not science.<\/p>\n","protected":false},"excerpt":{"rendered":"<p>Quanta magazine has just put out an impressive package of material under the title The Unraveling of Space-Time. Much of it is promoting the &#8220;Spacetime is doomed&#8221; point of view that influential theorists have been pushing for decades now. A &hellip; <a href=\"https:\/\/www.math.columbia.edu\/~woit\/wordpress\/?p=14144\">Continue reading <span class=\"meta-nav\">&rarr;<\/span><\/a><\/p>\n","protected":false},"author":2,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"jetpack_post_was_ever_published":false,"_jetpack_newsletter_access":"","_jetpack_dont_email_post_to_subs":false,"_jetpack_newsletter_tier_id":0,"_jetpack_memberships_contains_paywalled_content":false,"_jetpack_memberships_contains_paid_content":false,"footnotes":""},"categories":[1],"tags":[],"class_list":["post-14144","post","type-post","status-publish","format-standard","hentry","category-uncategorized"],"jetpack_featured_media_url":"","jetpack_sharing_enabled":true,"_links":{"self":[{"href":"https:\/\/www.math.columbia.edu\/~woit\/wordpress\/index.php?rest_route=\/wp\/v2\/posts\/14144","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.math.columbia.edu\/~woit\/wordpress\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.math.columbia.edu\/~woit\/wordpress\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.math.columbia.edu\/~woit\/wordpress\/index.php?rest_route=\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/www.math.columbia.edu\/~woit\/wordpress\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=14144"}],"version-history":[{"count":14,"href":"https:\/\/www.math.columbia.edu\/~woit\/wordpress\/index.php?rest_route=\/wp\/v2\/posts\/14144\/revisions"}],"predecessor-version":[{"id":14184,"href":"https:\/\/www.math.columbia.edu\/~woit\/wordpress\/index.php?rest_route=\/wp\/v2\/posts\/14144\/revisions\/14184"}],"wp:attachment":[{"href":"https:\/\/www.math.columbia.edu\/~woit\/wordpress\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=14144"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.math.columbia.edu\/~woit\/wordpress\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=14144"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.math.columbia.edu\/~woit\/wordpress\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=14144"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}