News and views about philosophy, the academic profession, academic freedom, intellectual culture, and other topics. The world’s most popular philosophy blog, since 2003.
We haven’t discussed this in our department (lower ranked PGR but tend to get highly competitive/very large applicant pool) but…
If you were the head recruiter for a professional basketball team, would you require height and weight measurements for prospective…
I wonder if people are familiar with Fred Schauer’s essay on Kelsen and Fuller. https://papers.ssrn.com/sol3/papers.cfm?abstract_id=3607099
If knowledge is sociologically conditioned, then what, exactly, happens to the truth-status of the sociology of knowledge itself? This is…
To a large degree, Kuhn’s Structure is an attempt to deliver on the descriptive task of epistemology as Reichenbach conceived…
I concur to a certain extent. I also scored very low on the writing section. Back then, GRE was required…
Thanks, I’ll check it out!
The physicist Steven Weinberg (Texas) comments. I'd be interested to hear what philosophers make of this. (Thanks to Phil Gasper for the pointer.)
There are actual experts in QM and its philosophy which can chime in, but note: as far as I can tell once again (contrary to Einstein's use) physicists like Weinberg are using "measurement" and "realism" in sort of non-standard ways, which might get some of the mysteriousness of what is claimed out if "interaction" and "single-valuededness" or the like are instead used. (Some time ago there was a publication of such a "translation manual"; the particle physicist Vic Stenger for example once did part of one.)
Also, as for probabilities – there are two possibilities as I see it: (a) the probabilities are, as Peirce guessed, just there in nature (why shouldn't they be?) or (b) they are non-local statistical effects like Smolin seems to think.
Weinberg is a brilliant physicist and his thoughts are worth listening to. (And in this matter they are quite common among physicists.)
I feel Everett (many-worlds) is by far the most sensible take on QM, though it certainly has its open questions. Weinberg's objections to it are (1) he'd prefer only one world, and (2) he doesn't see how probabilities come out of a deterministic theory. (1) is not a very good objection. (2) is a very real worry, but there are certainly ways of seemingly deriving the correct probability rule. E.g. decision theory:
http://www.preposterousuniverse.com/blog/2012/04/16/quantum-mechanics-and-decision-theory/
or self-locating uncertainty:
I think Weinberg does rather a good job of setting out the basic issues, and the basic responses, and the trouble with those responses…It's welcome indeed that—as a renowned physicist—he's come to the recognition that there are indeed significant problems to be faced in coming to an understanding of quantum mechanics. (The troubles are not so much to do with understanding each of the available options, but rather in deciding which of the options one should adopt. Sometimes that is because an approach which works well in one physical regime— e.g. non-relativistic particle mechanics—may not have a straightforward extension to other domains (e.g. high energy physics) so more actual physics needs to be done to construct the extensions and to check that all works well. Sometimes it is for more straightforwardly philosophical reasons, such as having to decide whereabouts on the spectrum between realism and anti-realism in the philosophy of science one can bear comfortably to sit.)
Aficionados will note that i) Weinberg is perhaps a little too quick to drop instrumentalist approaches on the grounds of anthropocentrism; one can develop instrumentalist approaches which do not have *that* fault (this would involve e.g. just fixing some parameter regime at which collapses kick-in (somewhat as one does in the dynamical collapse approaches Weinberg moots at the end of his essay)); ii) he also seems to leave out so-called 'hidden variable' completions of quantum mechanics which add further parameters bobbing along under the wavefunction (the best known such theory is due to de Broglie (1927) and Bohm (1952)). Hidden variable theories are quite tightly constrained by various 'no-go' theorems—proofs that any such theory would have to violate such-and-such a classical-physics or otherwise-intuitively-seemingly-desirable feature. So whatever one does, there is no going back to classical physics in this direction. Which makes life all the more interesting.
Finally: Weinberg is right to emphasise the interest of trying to develop experiments or subtle scenarios which would probe small departures from the standard laws of quantum mechanics. This can be (and is being) done both in the case he mentions of dynamical collapse theories, and also for the case of certain hidden variable theories. (This is something that my own group—amongst others—has been working on, in collaboration with colleagues in physics and materials science here in Oxford.)
I'm a physicist (though with philosophy envy) so maybe it's reasonable for me to say that Weinberg, while obviously a brilliant physicist, seems to me to occasionally go a little off the rails in his pronouncements about philosophy. But this seemed like a reasonable assessment of a fairly wide spectrum of views in the physics community re. whether interpretation of QM is a relevant issue. But he did leave one thing out, brought up by Chris Timpson above, that I think has gained adherents over the years, i.e. the de Broglie, Bohm theory.
While it's true, as Chris Timpson, states that it's held up as a sort of prototypical hidden variable theory, I think that aspect (i.e. the use of hidden variables) is less important than it initially was. What's important is that it is a deterministic theory about classical style variables, i.e. positions and velocities of particles, and seems to me to have the logical status, in terms of interpretability, of a classical theory. Some, rightly, consider the price too high, in that is saddled with the non locality that Bell showed hidden variable theories require (given that any such theory must satisfy Bell's other constraints, deemed necessary by the results of recent experiments). Some also consider it a bit inelegant in requiring more dynamical equations, i.e. the Schrodinger equation for the evolution of the "weird" (in the sense of treating de Broglie, Bohm theory as a classical theory), non-local potential, as well as the equations of motion for the particles in that potential.
For whichever reason, interest in the de Broglie, Bohm theory has grown very slowly. The price, either the inelegance or the strange non-local potential (but though that may be weird for a classical theory, instrumental or many worlds formalisms also "suffer" non-locality), may indeed be too high re. it's broader adoption but the logical coherence gained seems to make it at least worth considering seriously.
The aforementioned omission of Bohm is certainly strange to me. I've had in philosophy a narrow exposure to this area so I don't have an appropriate feel for how widely accepted a given theory generally is, but from my interactions and readings, Bohm (and to a lesser extent GRW) has been more popular than all the other competitors. David Wallace mentions anecdotally in a paper that in physics, Everett and traditional Copenhagian interpretations are most popular, with Everett being largely rejected in philosophy though making some amount of a comeback in the U.K. This might explain Weinberg's inclusions/exclusions.
I'll add some concern that Weinberg's criticism of Everett plays a bit too closely for me with connecting Everett to the pop-science understanding of Everett's "Many Worlds Interpretation." (Weinberg writes: In effect the history of the world has split into two streams, uncorrelated with each other… This inconceivably huge variety of histories has provided material for science fiction, and it offers a rationale for a multiverse, in which the particular cosmic history in which we find ourselves is constrained by the requirement that it must be one of the histories in which conditions are sufficiently benign to allow conscious beings to exist. But the vista of all these parallel histories is deeply unsettling, and like many other physicists I would prefer a single history.)
Wallace (http://philsci-archive.pitt.edu/8888/1/Wallace_chapter_in_Oxford_Handbook.pdf) and Alyssa Ney (in her introduction to The Wave Function: Essays on the Metaphysics of Quantum Mechanics), give good accounts of Everett, with Ney's being particularly suited for newcomers. Her whole introduction in fact is essentially a thorough introduction to this whole area that Weinberg's piece is on, so I'd recommend her introduction for anyone interested in what Weinberg writes. After which, one could consult David Albert's Quantum Mechanics and Experience which'll go even a bit deeper into the same material, though still serving as an introduction for philosophers.
As someone whose limited knowledge of QM has come adjunct to studies in the philosophy of mind and action theory (reading e.g., Henry Stapp, Hans Halvorson, etc.), I find it puzzling that Weinberg seems to equate assigning consciousness an essential role to play in QM with instrumentalism (in the first two paragraphs of section 3 of his article). The more-or-less dualist-leaning folks I’ve read on this treat the wave function not merely, as Weinberg puts it, as “an instrument that provides predictions of the probabilities of various outcomes when measurements are made,” but as describing a very real deterministic, physical system with which a non-physical mind can causally interact in “measurement,” thereby causing wave-function collapse. David Chalmers, who of course does not endorse this view but gives a fair assessment of it in “Mind and Its Place in Nature,” says:
"The collapse dynamics [of QM] leaves a door wide open for … [a dualist-]interactionist interpretation. Any physical nondeterminism might be held to leave room for nonphysical effects, but the principles of collapse do much more than that. Collapse is supposed to occur on measurement. There is no widely agreed definition of what a measurement is, but there is one sort of event that everyone agrees is a measurement: observation by a conscious observer. Further, it seems that no purely physical criterion for a measurement can work, since purely physical systems are governed by the linear Schrodinger dynamics. As such, it is natural to suggest that a measurement is precisely a conscious observation, and that this conscious observation causes a collapse. … [Thus] quantum mechanics appears to be perfectly compatible with such an interpretation. In fact, one might argue that if one was to design elegant laws of physics that allow a role for the conscious mind, one could not do much better than the bipartite dynamics of standard quantum mechanics: one principle governing deterministic evolution in normal cases, and one principle governing nondeterministic evolution in special situations that have a prima facie link to the mental."
Whatever one might make of this perspective, it seems clearly a mistake to equate it with an instrumentalist interpretation of QM. It seems to me that what Weinberg is really objecting to in this perspective is not instrumentalism, but the fact that it is non-naturalistic and non-deterministic(see the 3rd paragraph in section 3). However, he slides from worrying over instrumentalism to worrying over non-naturalism without clearly noting that they are entirely different views, pertaining to entirely differ matters.
Oops! The Chalmers' reference should be to "Consciousness and its place in nature." "Mind and it's place in nature" is the book by C.D. Broad to which Chalmers' title alludes.
A further thought, following P. Christian Adamski, about how Everett is portrayed in popular media and sci-fi: the division between "worlds" in those depictions is much cleaner and more stark than anything a physicist might countenance. Just reading the Wiki article on decoherence ( https://en.wikipedia.org/wiki/Quantum_decoherence ) convinced me that Everett was much more elegant and credible than its sci-fi imitations.
The issue of "Interpretations of quantum mechanics" is similar to the issue of "paradigms" of Thomas Kuhn.
Debates on "interpretations of quantum mechanics" show what is incommensurability (in Kuhn's sense.)
Thomas Kuhn, ''The Structure of Scientific Revolution'':
[T]he proponents of competing paradigms practice their trades in different worlds. … Practicing in different worlds, the two groups of scientists see different things when they look from the same point in the same direction.
This is not bad description of the issue of "interpretations"…
—–
KEYWORDS:
Primary Blog
Leave a Reply