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    • CommentRowNumber1.
    • CommentAuthorUrs
    • CommentTimeJan 6th 2013

    I started putting down some thoughts at theory (physics). Not meant to be comprehensive or anything, but just a quick note. I am not claiming that the state the entry is in is the state it should remain in at all. But maybe it’s a start that helps to develop something.

    • CommentRowNumber2.
    • CommentAuthorzskoda
    • CommentTimeJan 7th 2013

    I agree with Toby that physical theory may be better prime name of the page with redirect theory (physics). Though I do not feel strong about it.

    • CommentRowNumber3.
    • CommentAuthorUrs
    • CommentTimeJan 7th 2013
    • (edited Jan 7th 2013)

    I think an entry should be called the way the term is called by its practitioners. In physics you don’t say “physical theory” just as in logic you don’t say “logical theory”.

    It’s “quantum theory” and not “quantum physical theory”, it’s “theory of relativity” and not “physical theory of relativity”. It’s “This theory has chiral fermions.” and not “This physical theory has chiral fermions.” It’s “string theory” and not “string physical theory”.

    Indeed, you’ll get into heated arguments when you say that “string theoy is a physical theory” but everybody will agree that “string theory is a theory in physics”.

    If the nnLab had more contributors with a physics background and fewer with a pure math/logic background we would likely have had theory first describe what is now at theory (physics) and later people would have argued whether to create theory (logic), too.

    I remember similar issues when signature was created. Everybody says “signature” and takes the context to be understood. Nevertheless it means entirely different things in different contexts. But the official term in each case is just that, “signature”. You would complain if I asked you to say “logical signature”, I think.

    That said, I don’t bother too much what the title of an entry is as long as it has the right redirects. But if sombody cares strongly, and if we are to continue having discussinons like “Why didn’t you name the entry differently?” then maybe those who do care migth try to work out a list of criteria by which to decide. If possible.

    • CommentRowNumber4.
    • CommentAuthorTobyBartels
    • CommentTimeJan 8th 2013

    you’ll get into heated arguments when you say that “string theory is a physical theory”

    Yes, I see what you mean. This is an important and different sense of the word ‘physical’.

    everybody will agree that “string theory is a theory in physics”

    Well, the most extreme detractors might dispute even this. (^_^)

    • CommentRowNumber5.
    • CommentAuthorUrs
    • CommentTimeJan 8th 2013
    • (edited Jan 8th 2013)

    Well, the most extreme detractors might dispute even this. (^_^)

    If you meet one who is disputing, ask if he or she considers the Ising model a model in physics.

    \langle begin argument with myself \rangle

    If the distractor is good he or she might make the point that there is a distinction between physics and theoretical physics. That would be a good point, I think. I’d be willing to rename theory (physics) and field (physics) into theory (theoretical physics) and field (theoretical physics).

    On the other hand, the same would then be necessary for all other entries such as physics itself, higher category theory and physics etc.

    Ah, bah. No we shouldn’t do that.

    \langle end argument with myself \rangle

    • CommentRowNumber6.
    • CommentAuthorDavid_Corfield
    • CommentTimeJan 8th 2013

    I can’t imagine any workable distinction between a ’theoretical’ physical theory and ’real’ (or whatever the contrast would be) physical theory. Aside from the issues of idealisation, abstraction, and universality classes, it would strike me as wrong to decree in timeless fashion the remit of physics. For one thing, we may have apparently unreal models (say string theoretic models) finding use in other regimes (say condensed matter physics), perhaps by applying some duality to the former.

    More grandly, it may turn out that consideration of the whole space of theories in which is found a particular one describing our universe well is illuminating for the one ’real’ theory. And, for all we know, we may be reasonably led to believe in a multiverse realising the whole range of theories.

    • CommentRowNumber7.
    • CommentAuthorzskoda
    • CommentTimeJan 8th 2013

    I like many thing about strong theory, do not consider it really physics yet and I do consider Ising model physics as it is something what gives insight about practical, real, everyday physics.

    • CommentRowNumber8.
    • CommentAuthorUrs
    • CommentTimeJan 8th 2013
    • (edited Jan 8th 2013)

    The Ising model was introduced as an unrealistic theoretical model the interest in which was purely theoretical. Playing with it helped theoreticians understand general properties of QFT methods in statistical physics.

    This only changed later when with some effort physical systems were found that were reasonably well described by the Ising model. For instance from the introduction of

    For many years the Ising model and its variants were regarded as theoretical simplifications, designed to model the essential aspects of cooperative systems, but without detailed correspondence to specific materials. In the early 1950’s pure rare earth elements became more readily available and this stimulated the study of new magnetic materials. Some of these were soon recognized as close approximations to the Ising model.

    In contrast, the Veneziano model (out of which string theory grew) was a genuine attempt to describe observed physics. The fact that later it was realized to describe something different than originally intended notwithstanding.

    And the list of results at string theory results applied elsewhere shows that the insight into observed physics gained from string theory is considerably larger than that gained from the Ising model. Not to mention that only the study of string theory led to the understanding of the Ising model and other rational conformal field theories on non-trivial genus.

    (To all readers who know both terms: of course to compare the Ising model with string theory is as to compare an electron to a galaxy, but I am doing it here anyway for the sake of argument that it is inconsistent to regard the Ising model as theoretical physics, but not string theory.)

    • CommentRowNumber9.
    • CommentAuthorzskoda
    • CommentTimeJan 8th 2013
    • (edited Jan 8th 2013)

    The Ising model was introduced as an unrealistic theoretical model the interest in which was purely theoretical.

    The overcome consideration before I was born are not deciding for me what I consider realistic physics. I learned Ising model from real contemporary condensed matter physicists and in the context of a family of related models in magnetism; the considerations were felt there as understanding, getting feeling of real physics. It is hard to string theorists to point out anything that close.

    inconsistent

    This is not about a logic, but practice. If a person wants to get insight into something what is for sure physics, it is much more sure bet learning Ising model, especially when taking into account the amount of time needed to spend for abstracies out of the usual physics language and practice. On the other hand, I surely agree that the difference is not fundamental.

    • CommentRowNumber10.
    • CommentAuthorUrs
    • CommentTimeJan 8th 2013

    I believe what all those who think that “string theory is not theoretical physics” are confused about is the distinction between a theory in theoretical physics and the false und unbased claims that have been made over decades about what string theory has to say about physics as now seen at the LHC. The huge discussion that revolves aorund the latter has skewed the perspective of many.

    In this context I find it most refreshing to read David Corfield’s thoughts above. Sticking to pure reasoning, David shows here a much clearer picture of theoretical physics and the role of string theory in it that I have seen with many full-time theoretical physicists and mathematicians.

    Theoretical physics is independent of what happens in the blogs and mass media. The 90s had string theory hype in the media, which was all wrong and uninformed, and now the 2000s have string theory anti-hype, all wrong and uninformed. This has nothing to do with theory. But nevertheless it affects the thinking of many who should know better.

    • CommentRowNumber11.
    • CommentAuthorTobyBartels
    • CommentTimeJan 8th 2013

    I did not intend to start an argument about string theory! Just a joke with a smiley.

    References for this sense of ‘physical theory’: λϕ 4\lambda \phi^4 theory is unphysical (well established fact), string theory is unphysical (highly controversial opinion). It's not just a question of whether it applies to anything in the real world but whether it could have a coherent interpretation allowing one to hypothetically apply it.

    • CommentRowNumber12.
    • CommentAuthorUrs
    • CommentTimeJan 8th 2013
    • (edited Jan 8th 2013)

    Hi Toby,

    that blog post is confused. It says:

    A central point to understanding string theory is that it cannot be formulated the way all other fundamental theories are

    On the contrary, perturbative string theory (and that’s all there is and which everybody means) is modeled precisely on the basic construction by which all other fundamental theories are formulated: the Feynman perturbation series. It’s premise is to replace in this the sum over correlators of a 1d QFT on 1d graphs with those of a 2d QFT on 2d graphs.

    This may or may not be realistic. But as far as theories go it is perfectly admissible. In fact it is better than most of the Feynman perturbation series that are considered in QFT, because the string perturbation series is degreewise finite hence automatically renormalized.

    And that’s of course the whole point of what it means to find a UV-completion of unrenromalizable effective theories such as gravity.

    I see this confusion “there are no equations of string theory” all around the web reproduced in laymen articles. I am not sure where this meme originates in and why it is so contagious. But it is confused.

    If we are to continue this discussion (maybe we shouldn’t, I am not sure, and I won’t have much more time for it anyway) then I suggest we stay away entirely from random opinions voiced on various blogs and stick to founded arguments.

    • CommentRowNumber13.
    • CommentAuthorzskoda
    • CommentTimeJan 8th 2013
    • (edited Jan 8th 2013)

    I believe what all those who think that “string theory is not theoretical physics”

    As far as this general statement may be also addressed to me, I beg you to carefully read what I wrote. I wrote that there is no fundamental distinction and I agree with you. I also said what I now detail that on the practical level, for a condensed matter physicist to go one week or several into a toy model like Ising to get some test feeling similar to what one is doing when attacking a concrete system from application is completely different activity where one person sees the advance in his own problem soon after spending that short period in a toy model, while going into excursion of string theory means spending years for a model, and progress to concrete things in applications takes efforts of so many people and a single person who is not a specialist will hardly ever get any use. You do not need to be an expert for integrable systems to get into textbook with Ising model, or more realistically, a Hubbard model and get something you use successfully next semester. This is the frustration of a real physicist why not going there. Nothing fundamental in this argument, but in real life it is very strong argument.

    Edit: one is not loosing a feeling to be a physicist if one is making breaks of several days doing tools which are not physics properly but if one is making a break of several years. So, it is different touch with physics for a condensed matter theortician and string theoretician. This I find psychologically very important.

    • CommentRowNumber14.
    • CommentAuthorUrs
    • CommentTimeJan 8th 2013
    • (edited Jan 8th 2013)

    As far as this general statement may be also addressed to me,

    If you think that string theory is not a theory in physics, then I suppose you would be subsumed. In the end, only you can know if you do, but that’s how I could interpret your sentence above.

    I am not sure how to discuss this kind of claim. One thing we could do to proceed constructively might be the following:

    once I tried to explain at string theory what string theory is. I just wrote that in a leisurely minute, so it’s far from perfect or comprehensive. But maybe we could go through it together, paragraph-by-paragraph, see what the statements are, if we follow them, agree on them, and how we can improve them.

    • CommentRowNumber15.
    • CommentAuthorTobyBartels
    • CommentTimeJan 9th 2013

    The unfounded opinion that I cited is cited only as an example of usage of the word ‘physical’. (It was the top Google hit for unphysical string theory.)

    It is perhaps a bad sign that this was easier to find than a discussion of λϕ 4\lambda \phi^4 theory.

    • CommentRowNumber16.
    • CommentAuthorUrs
    • CommentTimeJan 9th 2013
    • (edited Jan 9th 2013)

    Sorry if I misinterpreted what you said. Though I am still not entirely sure what you meant to say, for instance what the “bad sign” is alluding to? As we both know, I can find blog posts on the web for every claim about string theory and its opposite. For some mysterious reason discussion of this topic on the web tends to be irrational in many ways. What does pointing to it mean? I don’t understand. One gets tens of thousands of Google hits for “Einstein was wrong”. Is that a bad sign of anything?

    But if there is any interest in having a reasoned exchange on these questions, I’d be interested in having it! And I am interested in having the nnLab pages on these matter have decent and critical information and arguments. If disussion here leads to that, I’d be happy.

    • CommentRowNumber17.
    • CommentAuthorDavid_Corfield
    • CommentTimeJan 9th 2013

    Leaving aside the physics, and of course there’s a vast amount to be said there, e.g., Matthias Blau, String theory as a theory of quantum gravity – A status report(pdf), it seems utterly clear that the investigation of the space of QFTs via string theoretic considerations is good for mathematics. (Shame we didn’t have someone at the ASPECTS conference.)

    I’m not completely sure why, but I found the observation that geometric Langlands is a case of S-duality particularly striking. It’s something along the lines of: God wouldn’t give us a physically-inspired theory which pointed to the deepest parts of number theory, but which led to nothing further important physically.

    • CommentRowNumber18.
    • CommentAuthorUrs
    • CommentTimeJan 9th 2013
    • (edited Jan 9th 2013)

    God wouldn’t give us a physically-inspired theory which pointed to the deepest parts of number theory, but which led to nothing further important physically.

    I believe this summarizes a more wide-spread feeling well.

    There is a rather charming little video Newton medal winner 2010: Edward Witten of well-invested 25 minutes.

    Somewhere half-way through or so he expresses pretty much the above feeling (in different words of course, I’d have to watch it again to remember) as a young researcher and how he then thought to himself that given such a chance from the heavens it is not to be wasted. Towards the very end he speaks about geometric Langlands explicitly, I think.

    (Of course others feel entirely differently. I am just mentioning this to David and those who enjoy it. Let’s maybe not discuss feelings about God and the heavens further :-)

    • CommentRowNumber19.
    • CommentAuthorUrs
    • CommentTimeJan 9th 2013
    • (edited Jan 9th 2013)

    I have always felt the following. I have always felt very lonely with this view, too, but try to give it a chance:

    I always felt that string theory is in QFT physics as category theory is in mathematics:

    Lots of cross-relations flow from it and only with it is a unified picture available. And practitioners in any given subfield tend to be unhappy when told so. Also, lots of nonsense is written about it and in the name of it.

    ;-)

    • CommentRowNumber20.
    • CommentAuthorDavid_Corfield
    • CommentTimeJan 9th 2013

    Re #18, one can replace talk of God by the space of possibilities.

    Witten starts talking about amazing coincidences at 13:30, e.g., Green-Schwartz mechanism 1984.

    We hear of the importance of string theory in shedding light on existing theories.

    At18:50 there’s more on coincidences.

    String theorists have insights into geometry, not because they’re especially good geometers, but because they have string theory.

    Khovanov homology is what is spoken of explicitly.

    • CommentRowNumber21.
    • CommentAuthorDavid_Corfield
    • CommentTimeJan 9th 2013

    Similar sentiments here:

    I would love to understand “why” string theory really exists and remains well-behaved regardless of the directions (not only on its configuration space) in which we take it. Because string theory’s spectrum and parameter spaces and lists of objects etc. (and even lists of relevant branches of mathematics) change as you move on its moduli space (or as you switch in between dual descriptions), the proof – if there’s any – must say something about the continuity and closedness of a highly flexible, chameleon-like mathematical structure.

    • CommentRowNumber22.
    • CommentAuthorUrs
    • CommentTimeMar 29th 2015
    • (edited Mar 29th 2015)

    I gave theory of everything a little stand-alone entry with some minimum comments, for the moment such as to have a way to link to this term. Also added minimum cross-links with related entries.

    • CommentRowNumber23.
    • CommentAuthorUrs
    • CommentTimeJul 7th 2018

    added pointer to

    diff, v19, current

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