Quantum Mechanics Smackdown

Greetings from the Big Apple, where the World Science Festival got off to a swinging start with the announcement of the Kavli Prize winners. The local favorite will of course be the Astrophysics prize, which was awarded to Alan Guth, Andrei Linde, and Alexei Starobinsky for pioneering the theory of cosmic inflation. But we should also congratulate Nanoscience winners Thomas Ebbesen, Stefan Hell, and Sir John B. Pendry, as well as Neuroscience winners Brenda Milner, John O’Keefe, and Marcus E. Raichle.

I’m participating in several WSF events, and one of them tonight will be live-streamed in this very internet. The title is Measure for Measure: Quantum Physics and Reality, and we kick off at 8pm Eastern, 5pm Pacific. The live-stream is here, but I’ll also try to embed it and see how that goes:

The other participants are David Albert, Sheldon Goldstein, and Rüdiger Schack, with the conversation moderated by Brian Greene. The group is not merely a randomly-selected collection of people who know and love quantum mechanics; each participant was carefully chosen to defend a certain favorite version of this most mysterious of physical theories.

  • David Albert will propound the idea of dynamical collapse theories, such as the Ghirardi-Rimini-Weber (GRW) model. They posit that QM is truly stochastic, with wave functions really “collapsing” at unpredictable times, with a tiny rate that is negligible for individual particles but becomes rapid for macroscopic objects.
  • Shelly Goldstein will support some version of hidden-variable theories such as Bohmian mechanics. It’s sometimes thought that hidden variables have been ruled out by experimental tests of Bell’s inequalities, but that’s not right; only local hidden variables have been excluded. Non-local hidden variables are still very viable!
  • Rüdiger Schack will be telling us about a relatively new approach called Quantum Bayesianism, or QBism for short. (Don’t love the approach, but the nickname is awesome.) The idea here is that QM is really a theory about our ignorance of the world, similar to what Tom Banks defended here way back when.
  • My job, of course, will be to defend the honor of the Everett (many-worlds) formulation. I’ve done a lot less serious research on this issue than the other folks, but I will make up for that disadvantage by supporting the theory that is actually true. And coincidentally, by the time we’ve started debating I should have my first official paper on the foundations of QM appear on the arxiv: new work on deriving the Born Rule in Everett with Chip Sebens.

(For what it’s worth, I cannot resist quoting David Wallace in this context: when faced with the measurement problem in quantum mechanics, philosophers are eager to change the physics, while physicists are sure it’s just a matter of better philosophy.)

(Note also that both Steven Weinberg and Gerard ‘t Hooft have proposed new approaches to thinking about quantum mechanics. Neither of them were judged to be sufficiently distinguished to appear on our panel.)

It’s not accidental that I call these “formulations” rather than “interpretations” of quantum mechanics. I’d like to see people abandon the phrase “interpretation of quantum mechanics” entirely (though I often slip up and use it myself). The options listed above are not different interpretations of the same underlying structure — they are legitimately different physical theories, with potentially different experimental consequences (as our recent work on quantum fluctuations shows).

Relatedly, I discovered this morning that celebrated philosopher Hilary Putnam has joined the blogosphere, with the whimsically titled “Sardonic Comment.” His very first post shares an email conversation he had about the measurement problem in QM, including my co-panelists David and Shelly, and also Tim Maudlin and Roderich Tumulka (but not me). I therefore had the honor of leaving the very first comment on Hilary Putnam’s blog, encouraging him to bring more Everettians into the discussion!

This entry was posted in Philosophy, Science. Bookmark the permalink.

53 Responses to Quantum Mechanics Smackdown

  1. Ray Gedaly says:

    Fermi Paradox implies either that faster-than-light communications (or travel) is impossible, or that the universe is not infinite (Type 1 multiverse). Were it possible to communicate ftl, then a civilization beyond the observable universe could communicate with us. Were the universe infinite, then there is a certainty that there would be an infinite number of civilizations with ftl technology who would want to communicate with us. Thus we don’t live in a universe (or Type 1 multiverse) where both of these are true.

  2. Quantum Mechanics Smack-down, a fun name :) based upon the contentions and rivalry of the vastly different factions of Quantum Theory. As can be seen by the likes and dislikes of comments on this thread, there may be no mainstream topic in physics more divisive than Quantum Theory.

    “….only local hidden variables have been excluded. Non-local hidden variables are still very viable!”

    Regarding the quote above, although nearly all theorists would agree with this statement above there are still those that theorize that even local hidden variables have not been ruled out, and some that non-local hidden variables are highly improbable (somewhat the opposite of the quote above). Such local hidden variable theories usually involve a type of aether. Today’s aether-like theories for such explanations might include dark matter, dark energy, Higgs particles as a Higgs field, gravitons, quantum foam, and many other theorized possibilities. .

    Although Einstein and others of his time disagreed with the premises of QM, most did not invoke aether to explain observations in the quantum world. But for those that today propose an aether in one form or another for this or other reasons, examples as mentioned above, some theorize that there may be nothing mysterious about the quantum world, including wave-particle duality, quantum entanglement etc., that cannot be readily explained by an aether of some kind – proposing that the universe is a far simpler place than most versions of Quantum Theory otherwise contend.

  3. Pingback: Quantum Mechanics In Your Face | Sean Carroll