Reality Conditions

Wednesday, November 01, 2006

On not taking a stance

After a typically excellent explanation of the hierarchy of energy scales that is crucial to allow life as we know it to exist in the universe, Sean Carroll says:

Because we don’t yet fully understand the origin of these fantastic hierarchies, we can conclude that God exists. Okay, no we can’t. Really we can conclude that we live in a multiverse in which all of the constants of nature take on different values in different places. Okay, we can’t actually conclude that either. What we can do is keep thinking about it, not jumping to too many conclusions while we try to fill one of those pesky “gaps” in our understanding that people like to insist must be evidence for their personal favorite story of reality.



This is exactly the kind of thing I was going to say in a post scheduled to write one of these days, but not on the fine-tuning problem but on the interpretation of quantum mechanics.

Just as in the fine-tuning problem we have theologians pressing on one side that the most rational solution is to accept the existence of God, and people like Leonard Susskind pressing on the other side that the only rational solution is to accept the real existence of the multiverse, on the interpretation of quantum mechanics we are also pressed on all sides by people who want to convince us of accepting "their personal favorite story of reality". Many physicists insist that we should give up the goal of a physical theory that describes reality "as it really is" and accept that theories are only tools to predict experimental outcomes. Some others urge that the most rational interpretation of quantum mechanics is one that allows a complete and deterministic description like in classical physics, even if this requires nonlocal hidden variables or backwards causation. Still others think that the only reasonable thing is to expect orthodox quantum mechanics to break down at a certain level, replacing unitary evolution of the state vector by a real, physical "collapse". And many others vehemently insist that the only interpretation that makes justice to quantum theory as it is, without adding any extra element nor relinquising realism, is the Everettian one that implies that millions of copies of us "branch out" into other universes at every minute.

And I... find every one of these alternatives unpalatable. And I don't think I am rationally required to take a stance and accept one of them, not even provisionally, any more here than in the fine-tuning case. The day we have a final theory of nature (meaning one that predicts correctly and explains all actual and possible experiments we can think of, including quantum gravity and everything else under the sun), and if it still includes quantum mechanics in its present form, I will have to decide which interpretation to suscribe to. But meanwhile, I think it is perfectly acceptable to go on, using quantum mechanics as every other physicist does, but without accepting any interpretation of it; not even the pragmatical one that rejects all interpretations as a matter of principle.

There is still much we don't know, and not only just "facts" but also whole realsm of nature we do not know how to think coherently about; not the lesser one, spacetime itself at a quantum level. It seems to me a reasonable expectation that a correct theory of quantum gravity could involve changes in the very structure of quatum theory, that would reveal the theory as we know it to be a weak-energy limit of some other kind of physics, with a conceptual structure we cannot even guess at the moment, but which would not be as "paradoxical" and "un-interpretable" as quantum mechanics as we know it, while not involving in any sense a return to classical (pre-quantum) notions.

Someone might say that this (and the similar position on the fine-tuning issue) is just a cop-out. If all the alternative ways of understanding something are on the table, and I can't think of any other, am I not supposed to decide which of the alternatives seems most likely to be true, and accept it until something else comes up? Am I? But why? There is a similar and very familiar fallacy commited by Intelligent Design defenders: if they point to some biological system which we can't explain at present how it evolved, then the only available explanation for the moment is God and we ought to accept it until we can give an evolutionary explanation. The fallacy is much more obvious here, because in the biological case we have already a good idea of what kind of explanation is needed, and we have excellent reasons to believe that with more research we will find it. While in the physical problem I discussed we have no idea at present of how to develope deeper theories that may solve them, which makes some people insist that quantum mechanics as we know it (and particle physics, string theory and cosmology as we know them) are final; that we have already reason to believe that we will be no further revolutionary overturning of our knowledge on those areas. This sounds hubristic to me. If the history of science shows something, it is that Nature is cleverer than we are.

I have a particular historical analogy on my side. When Newton proposed his theory of gravity, it was considered a strong criticism against it that it involved action at distance. The prevailing philosophy of nature, Cartesianism, implied that all physical action occured by direct contact, and the idea of a body exerting a gravitational force directly on another one, without any intermediate, seemed philosophically absurd. When it became clear the Newton's theory predicted accurately the planetary orbits, people had to come to grips with the fact of action at distance; and sure enough, just as with quantum mechanics there were many that said: "You are not supposed to understand how it works -that is a metaphysical question! It predicts the movements we observe, what else do you want?" Still others try to develope theories that mimic Newton's Law starting fom Cartesian models, like Le Sage's theory, and these efforts (which ultimately failed) can be compared to the "hidden variables" or the "physical collapse" models for quantum mechanics, which try to limit the weirdness going back to something more familiar. And there were certainly no lack of people who thought that the model of particles affecting each other at distance was there to stay forever; I think some even said that it could be known a priori that Nature behaved in that way, which shows how much familiarity with an initially weird idea can make for you. (I have seen also a priori deductions of quantum mechanics.) What finally happened, of course, was that Einstein came up with General Relativity, which explained how the gravitational force is transmitted through spacetime using mathematical tools, concepts, and a whole way of seeing nature which were completely unthinkable in the 18th century. The puzzle was finally solved when a much deeper and comprehensive theory was found. That, exactly, is what I am hoping for the puzzle of quantum mechanics

[Note: Does the expression "to take a stance" strike native speakers of English as an eggcorn? I hesitated between it and "take a stand"; checking Dictionary.com only the latter phrase appeared, but Google finds results for "take a stance" in a ratio of 1/10 to it. Which seems high enough to be linguistically acceptable, and it sounded much better to my ears. What do you think?]

6 Comments:

  • I'm a native speaker of E. and "taking a stance" sounds OK to me.
    (since you asked)

    By Anonymous Who, at 12:24 AM, November 04, 2006  

  • "which shows how much familiarity with an initially weird idea can make for you. "

    which shows what familiarity with an initially weird idea can do for you.

    "develope"

    develop

    "suscribe"

    subscribe

    "relinquising"

    relinquishing

    "There is still much we don't know, and not only just "facts" but also whole realsm of nature we do not know how to think coherently about;"

    There is still much we don't know, and it is not simply that we don't know the "facts": we also do not know how to think coherently about the whole reality of nature;

    "not the lesser one, spacetime itself at a quantum level."

    not least about spacetime itself at a quantum level.

    =====================
    The next passage interests me very much and I quote it not to suggest changes in the English but to call attention.
    It reminds me of Lee Smolin's recent paper about QM being a limit or approximation of a more fundamental theory. You say

    It seems to me a reasonable expectation that a correct theory of quantum gravity could involve changes in the very structure of quantum theory, that would reveal the theory as we know it to be a weak-energy limit of some other kind of physics, with a conceptual structure we cannot even guess at the moment, but which would not be as "paradoxical" and "un-interpretable" as quantum mechanics as we know it, while not involving in any sense a return to classical (pre-quantum) notions.

    That idea seems intuitively right to me. Perhaps you will help discover the more fundamental theory.

    Smolin's paper is
    http://arxiv.org/abs/quant-ph/0609109
    "Could quantum mechanics be an approximation to another theory?"

    You write a good English style which is why I am moved to offer emendations.

    By Anonymous Marcus, at 1:03 AM, November 04, 2006  

  • Funny, the same historical analogy came to my mind many times while discussing QM in Marseilles. Obviously those working on it directly prefer the analogy of EM and SR.

    By Anonymous fh, at 9:57 AM, November 04, 2006  

  • Who: thanks, that is conforting.

    FH: that is the problem with historical analogies replacing real arguments, isn't it? It is often easy to find one that supports your preferred position.

    Marcus: thanks for the corrections. "Make for you", "suscribe" and "develope" are real mistakes; "relinquising" is just a typo. I still stand by my choice of words in the last to quotes (after correcting the obvious typo "realsm" => "realms"). Quantum spacetime is one of those realms, and not the lesser one; what it wrong with that?

    When I started the blog I used to run the spell checker on the posts before posting them. I gave up because there are too many physical/philosophical terms that it doesn't recognize, but maybe I should start using it again.

    By Blogger Alejandro, at 11:24 AM, November 04, 2006  

  • 'Taking a stance' is eggcorn-like, I think. But I wouldn't worry too much about it; 'stance' and 'stand' are synonyms or near-synonyms -- they just differ in their associations. So it's linguistically acceptable. Many eggcorns are, and this is only a borderline eggcorn if it's one at all.

    On Marcus's point about the phrase 'not the lesser one': the phrasing suggests that you are talking about two and only two realms of nature (the lesser one and the one that's not the lesser one). The reason it jars a bit on the ear is that the phrase in the previous clause (There are whole realms of nature) makes it sound like you are talking about many realms of nature. It would sound better if either the first part of the sentence read "There is a whole realm of nature" or the second part read "not one of the lesser ones".

    By Blogger Brandon, at 5:41 PM, November 04, 2006  

  • Thank you for the great story.

    Annuaire | Nettoyage | dardenac | Annuaire | Maternelle | Referencement | arianax | Deenox | Vin bergerac | Qrom | pagerank

    By Anonymous Raphaël CONFIANT, at 6:04 PM, April 07, 2010  

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