## Links, proofs, talks, jokes

July 30th, 2019For those who haven’t yet seen it, Erica Klarreich has a wonderful article in *Quanta* on Hao Huang’s proof of the Sensitivity Conjecture. *This* is how good popular writing about math can be.

Klarreich quotes my line from this blog, “I find it hard to imagine that even God knows how to prove the Sensitivity Conjecture in any simpler way than this.” However, even if God doesn’t know a simpler proof, that of course doesn’t rule out the possibility that **Don Knuth** does! And indeed, a couple days ago Knuth posted his own variant of Huang’s proof on his homepage—in Knuth’s words, fleshing out the argument that Shalev Ben-David previously posted on this blog—and then left a comment about it here, the first comment by Knuth that I know about on this blog or any other blog. I’m honored—although as for whether the variants that avoid the Cauchy Interlacing Theorem are actually “simpler,” I guess I’ll leave that between Huang, Ben-David, Knuth, and God.

In *Communications of the ACM*, Samuel Greengard has a good, detailed article on Ewin Tang and her dequantization of the quantum recommendation systems algorithm. One warning (with thanks to commenter Ted): the sentence “The only known provable separation theorem between quantum and classical is sqrt(*n*) vs. *n*” is mistaken, though it gestures in the direction of a truth. In the *black-box* setting, we can rigorously prove all sorts of separations: sqrt(*n*) vs. *n* (for Grover search), exponential (for period-finding), and more. In the non-black-box setting, we can’t prove any such separations at all.

Last week I returned to the US from the FQXi meeting in the Tuscan countryside. This year’s theme was “Mind Matters: Intelligence and Agency in the Physical World.” I gave a talk entitled “The Search for Physical Correlates of Consciousness: Lessons from the Failure of Integrated Information Theory” (PowerPoint slides here), which reprised my blog posts critical of IIT from five years ago. There were thought-provoking talks by many others who might be known to readers of this blog, including Sean Carroll, David Chalmers, Max Tegmark, Seth Lloyd, Carlo Rovelli, Karl Friston … you can see the full schedule here. Apparently video of the talks is not available yet but will be soon.

Let me close this post by sharing two important new insights about quantum mechanics that emerged from my conversations at the FQXi meeting:

(1) In Hilbert space, no one can hear you scream. Unless, that is, you scream the exact same way everywhere, or unless you split into separate copies, one for each different way of screaming.

(2) It’s true that, as a matter of logic, the Schrödinger equation does not imply the Born Rule. Having said that, if the Schrödinger equation were leading a rally, and the crowd started a chant of “BORN RULE! BORN RULE! BORN RULE!”—the Schrödinger equation would just smile and wait 13 seconds for the chant to die down before continuing.