The Stone is a forum for contemporary philosophers on issues both timely and timeless.
This is a response by the author to readers of his recent post for The Stone, "Nothing to See Here: Demoting the Uncertainty Principle."
Thanks to readers of The Stone for their feedback. The point of the article was essentially twofold: (a) to pry apart what the uncertainty relations actually say from the typical "Copenhagen interpretation" gloss given to them, and (b) to point out that when one does so, then the uncertainty relations are still downright strange, but they don't support the kind of metaphysical excesses commonly assumed. I hoped that the Stingy Oddsmaker metaphor usefully performed (a) and that the examples of "quantum theory without observers" supported (b).
Many readers bridle against the idea that measurement fundamentally is unimportant in quantum mechanics. In expressing my frustration with this idea, I can't do any better than to quote the physicist J.S. Bell:
It would seem that the theory is exclusively concerned about "results of measurement," and has nothing to say about anything else. What exactly qualifies some physical systems to play the role of "measurer"? Was the wavefunction of the world waiting to jump for thousands of millions of years until a single-celled living creature appeared? Or did it have to wait a little longer, for some better qualified system … with a Ph.D.? If the theory is to apply to anything but highly idealized laboratory operations, are we not obliged to admit that more or less "measurement-like" processes are going on more or less all the time, more or less everywhere. ("Against 'Measurement' ")
I admit that we are usually taught that the observer is fundamentally important when learning quantum physics. But that is an artifact of history. There is no reason for it anymore. Quantum mechanics can be formulated in ways that treat the observer as part of the quantum system. Doing so is not merely an aesthetic desideratum, but instead necessary if the theory is to be applied to the cosmos as a whole, as in quantum gravity. Readers with further interest in "quantum mechanics without observers" might find Shelly Goldstein's paper of that title useful.
Other comments quite rightly point out that the Stingy Oddsmaker metaphor isn't mathematically precise. Nowhere do I mention Planck's constant or conjugate variables, never mind the many fancier mathematical formulations available or these recent experiments. This is not because, as some suggested, I am a philosopher, but because I was writing an essay for a general audience, not for a physics journal. Equations tend to put off readers who are not familiar with them. The Stingy Oddsmaker metaphor expresses what's odd about the uncertainty relations when they are shorn of metaphysical mischief. Adding the technical details is obviously deeply important to physics, but not for communicating my main point. Those desiring more detail can read this wonderful article by the physicist and philosopher Jos Uffink.
Some comments make sophisticated claims about the physics that I believe it's important to correct. One reader writes that Bell proved that formulations of quantum theory such as de Broglie-Bohm can't reproduce quantum statistics. To such a reader it will then come as a surprise that Bell himself strongly endorsed de Broglie-Bohm. Were there two "Bell"'s, one approving the theory while the other showed it impossible? No, Bell proved that no local so-called "hidden variable" theory would work, but de Broglie-Bohm is non-local (and in agreement with experiments). Another reader insists that de Broglie-Bohm is false because it violates relativity and another that it doesn't extend to quantum field theory. Here I can only point out that the theory agrees with experiment and has been developed along these lines in various ways (see here and here), but that I agree there are challenges in satisfactorily extending the theory. Even if false, however, there are other formulations of quantum mechanics without observers.
Finally, some readers worried that I characterized a straw man. Were that only so! By beginning with television shows and films, I can see how one might get that impression. Alas, wild mischaracterizations of uncertainty seem to be the rule, not the exception, in academia outside physics. A Google Scholar search of "uncertainty principle" coupled with various buzzwords from social theory will quickly reveal some. I was just too much of a gentleman to name names.
Craig Callender is chair of the philosophy department at the University of California, San Diego. He recently edited "The Oxford Handbook for the Philosophy of Time," and he is finishing a book on time and physics entitled "What Makes Time Special."
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