Monday, January 28, 2013

A theory of everything is an important research project

Richard Feynman stressed that we shouldn't make preconditions about how our future description of Nature is going to look like:



Lisa Randall, a top phenomenologist whom I know very well, gave an interview to Nude Socialist in which she says that it's an illusion that physics is mostly about the search for the final theory (among other things: read it). To a large extent, her answers are similar to Feynman's.

Phil Gibbs wrote that we need to find a TOE, after all.




Despite the contradictions in the "spirit" of their answers, I agree with all these three folks but I still think that some of the uncertainty in the first two people's comments are, to a certain extent, obsolete.

So, I agree with Feynman that it can't a priori be clear whether the Universe obeys the laws of a concise final theory that may be found after a finite time. It's critically important in science not to confine your reasoning by some assumptions whose validity isn't really certain – and sometimes not even justified – i.e. by dogmas.

On the other hand, I think that the evidence has accumulated that the alternative non-TOE scenario of the onion with infinitely many layers can't operate in Nature. Ken Wilson taught us to organize the phenomena in Nature according to their characteristic distance scale (or time scale or energy scale).

We may seemingly go to ever shorter distances and discover new and previously unknown layers of the onion, matryoshkas inside the larger matryoshkas, and so on. However, I am confident that we pretty much know that this "seemingly infinite" process inevitably stops at some point – the Planck scale. There are no distances shorter than the Planck scale that may be physically resolved, that make sense in the usual physical sense.

So once you describe all the effective theories – layers of the onion of knowledge – for all distance scales up to (longer than or equal to) the Planck scale, that's the end of the story. The last layer – the explanation how Nature behaves at the scale of the quantum gravity – will be the only task that you have to solve fully. No additional infinite hierarchy of effective theories can be squeezed over there. Because of the uncertainty principle's impact on the proper length that becomes severe and of order 100% near the Planck scale, energies that exceed the Planck energy no longer allow you to probe shorter distance scales and qualitatively new physical phenomena; instead, if the center-of-mass energy of a collision dramatically exceeds the Planck scale, you create a black hole (an ever larger one if you increase the energy) whose rough behavior is captured by the low-energy effective equations once again. No new physics emerges.

These were general comments boiling down to the Renormalization Group and the existence of gravity in our quantum world. But we have been collecting some precious, much more specific evidence for a few decades when it looked increasingly indisputable that string/M-theory is the final theory of everything. It apparently possesses everything that a final theory needs to have. It seems to be 100% robust and predictable: there's no way to "deform it" without spoiling its consistency. It allows no adjustable yet non-dynamical continuous dimensionless parameters. It seems that everything that's left is to understand string/M-theory more completely (including persistently confusing aspects such as the initial conditions and Big Bang singularity and the vacuum selection mechanisms in general if there are any) and isolate the solution that is relevant for the environment seen in Nature around us.

I could spend lots of time with mostly linguistic disclaimers that I don't find too deep or interesting here.

Of course, the term "theory of everything" has to be interpreted correctly – we/physicists don't know "everything", just the elementary laws to which (plus the knowledge of the initial state and "the right questions") everything may be reduced in principle. I think that people realize that a TOE has to be interpreted this carefully (as the theory about the elementary forces and building blocks – or the maths replacing them – only) and science doesn't completely stop when you find a TOE (lots of complex questions always remain) which is why I think that the opposition to the term TOE because of this reason is really unsubstantiated. Also, it's obvious that even in particle physics, many physicists are working on many things that have almost nothing to do with the search for a final theory – and that don't even depend on its existence in any way.

Still, the fact that physicists are working on various things doesn't mean that they're equally important. I agree with Phil that the search for a TOE is a very important research industry in physics, one that – according to the present evidence – should be solvable in principle but one that is so ambitious that it's clearly impossible to promise any deadlines for the date when the problem will be fully solved. We're not there yet but the "TOE research program" has already generated lots of profound spin-offs that have been valuable even for those who don't give a damn about a TOE.

I have always found the possibility that there is a TOE important enough for much of my thinking time to be occupied by questions related to this project – although the particular things one is thinking about are always much more concrete, limited, and modest than overarching claims about a TOE (a fact that the laymen may easily misunderstand, too: physicists are simply not meditating about a TOE, OM, TOE for hours in their office, they're looking at well-defined, seemingly more special, questions). On the other hand, Lisa Randall isn't passionate about a TOE – a fact that is correlated with her being a phenomenologist rather than a string theorist. Needless to say, I view both approaches as important ones but the TOE-focused, string-theoretical approach to be significantly more successful as a generator of progress in the last 35 years or so, a trend that is more likely than not to continue in the coming years, I think.

20 comments:

  1. And what is the goal within String theory? I guess people are trying to find the non perturbative formulation of the Quantum theory which has as low energy limit the 11D supergravity? This will be the TOE we are looking for?

    If yes I don't see progress or hints of progress in that direction. Are there any proposals for such theory?

    Alternatively someone could say that the TOE is some SCFT due to gauge/gravity duality?

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  2. even if string theory is right, most likely won't be able to do as many things as it was being advertised. one of the problems is that people trying to push it were saying things about string theory could do that they knew they were probably not true. some of the "cool" names in string theory that helped its marketing also maybe did damage in the long term.


    a Greek is responsible for the damage done by many of the "cool" sounding names.


    it's a problem when scientists give terms and talk like bullshit artists that give business advice.

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  3. i don't have a clue if string theory is right, wrong or partly right. i don't know about string theory. but in my opinion some people promoting it were overhyping it. it would be very nice if i was wrong and it is a GUT or whatever.

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  4. "You clearly have no clue what you're talking about"

    Maybe I didn't make myself clear. I meant progress towards identifying the specific Quantum theory which has as low energy limit the 11D supergravity (or some of its basic characteristics).

    For example one step forward was Matrix theory but that was 15 years ago. I don't see concrete progress in that direction anymore. Maybe some bits and pieces here and there. Higher Spin gauge theory could be seen as a significant development though.

    There was progress with AdS/CFT e.g. ABJM but here I'm talking about the QG theory in the bulk.

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  5. Hi Lumo,

    I look forward to read this later, conversely to some comments you seem to get :-/, this article looks like a very nice reading.

    Not sure because I have not yet read it, but maybe it would make a nice and much needed (to prevent people from trolling) answer here too?

    http://physics.stackexchange.com/q/52385


    However, for some reason I dont like this question very much, maye because he cites the Nude Scientist ...

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  6. "My noble partner [Lubos] You greet with present grace and great prediction Of noble having and of royal hope,

    That he seems rapt withal. To me you speak not [scientificaly news]. If you can look into the seeds of time And say which grain [research program in ST] will grow and which will not, Speak, then, to me (...)".

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  7. Dilaton, i happen to sell video games. video game consoles like the Playstation 3 and XBOX 360 happen to have fanboys that many of them not only trash each others' console but many cannot accept criticism about the console they own and its exclusive games.


    i own a Playstation 3 but i find the XBOX 360 controller better for most games except its D-pad and it has many exclusive games that are better than most Playstation 3 exclusives.


    judging and trolling are different things.

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  8. George, I have been reading LM's blog for three or four years. Being merely
    an ex physics and maths student, I have not thought to post any "judgements" on
    string theory.

    you say "judging and trolling are different things" but that's only when the person doing the "judging" has some idea of what they're talking about.

    If you don't understand why LM is strict about posting then look at other physics blogs/forums, where every topic is clogged with people "judging".

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  9. "The CFT at strong 't Hooft coupling *is* string theory."

    The CFT at strong 't Hooft coupling is Supergravity:-).

    Anyway (the above was a joke) I know what you mean but for example we know that due to gauge/gravity duality information is conserved in a black hole, don't you to know though the exact mechanism in the bulk?

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  10. well, Jeremy i am hardly just an ex physics and maths student and the opinions i expressed are hardly of physics and math students and if you had a clue you would understand that from my answers.

    no matter what, my answers made much more sense than his that were also inappropriate.

    i won't spend the time to analyse each point i made or his points.


    no matter if i had a clue or not it was my opinion and it is probably also right.


    most experts say similar things i have said and i have never said it is wrong.

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  11. Any scope in physics for hyperreals, infinitesimals in particular?

    At a practical level, the latter might come in handy for dickless wonders like girly-boy Toni Bliar in casual crotch adjustment below the Planck length.

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  12. Exactly, the comment sections of other nice physics blogs become unreadable, as soon as the owner of the site dears to mention any BSM physic, SUSY, ST, etc :-/

    Certain keywords immediately make whole armys of trolls jumping out of the nowhere which prevents prevent by "judging" any reasonable scientifgic discussion about the physics topic the original article was about ...
    It regularly happens on Prof. Strassler's blog, Phil Gibbs's site, and any site where the comments are not properly moderated.

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  13. Nope, this is just not true. You clearly lack the completely basic knowledge about AdS/CFT. The CFT is never just supergravity, after all, supergravity is an inconsistent theory.

    At strong coupling, the physics of CFT is that of string theory, with all the excited strings, branes, and everything else. All these things have been known pretty much from the first year of the AdS/CFT.

    The 't Hooft limit of the CFT - N going to infinity while g^2*N is kept fixed and large - is equivalent to the planar limit of type IIB string theory.



    Concerning the question, your wording is loaded because it suggests that there is a mechanism that is expressible in the bulk - by which one really means that the effects have to be associated with particular places in the bulk. But it's not true; the bulk string theory isn't exactly local and the best (and possibly only) description of its nonlocality could be the CFT. There could also be another description that is more local in the bulk and quantifies the deviations from the locality via some well-defined degrees of freedom and their nonlocal behavior - but it's in no way guaranteed that such an extra description exists and this extra description is in no way necessary for the theory to be well-defined and "competely understood". It's just a working hypothesis that there is something else to be found, not a fact.

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  14. Physics is not done by opinion, and it is very bad that today every dimwit thinks who has no clue what he is talking about has the right to spit and spat on the work of bright people, insult them, etc ...


    Lumo should really ban you if you do not stop your arrogant attacks

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  15. John F. HultquistJan 28, 2013, 9:12:00 PM

    You might find this BBC story interesting” “Quantum biology:
    Do weird physics effects abound in nature? – Sorry to be O/T.

    http://www.bbc.co.uk/news/science-environment-21150047

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  16. George, I’m sure you are a nice guy but you are way, way over your head here. Unless you are willing to admit your limitations you will either disappear or continue jousting at windmills. Please don’t do that.

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  17. To me, this video of Feynman is a distillated display of how and why he was a most agreeable fellow - as far as his personality and philosophical outlook on "science v.s. mysticism or theistic beliefs" is being outlined in it.

    I can very well see why you, Lubos, have a great affinity to him and have him as a kind of role model (given that he too grew up to be a brilliant theoretical physicist who apparently was good at living/enjoying life in an unusually wide variety of ways).

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  18. It seems to me first and foremost to solve problem of
    Planck units.



    I mean to separate smart Planck unit from senseless
    Planck units.



    Does all Planck units are sacred or only one?



    We don't have guarantee G, c, are real constants or not,
    during the evolution of the Univertse.



    We don't have guarantee they depend of each other or
    not,or 2 sides the same coin.



    Imagine that G and c simultaneously vary,because
    permittivity of vacuum vary following the evolution.Doesn't matter the Universe
    shrinking or expanding.



    But we believe naive:



    1.Schwarshild black hole R radius G/c^2



    2.Planck unit L of length G/c^3



    3.Planck unit T of time G/c^5



    4.Planck unit M of mass c/G



    What is correspond to real world?



    If all,it would be absurd.



    To my opinion only #4 linear link between G and c is
    real,eternal



    and vary synchronously.



    And #1,2,3 are fake that only teasing physicists



    Conclusion:



    1.Only Planck unit of mass(10-5g) have sense.



    2.Only h is fundamental constant.



    Sincerely

    Yuri

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  19. Yes IIB Supergravity and not any Supergravity but anyway that was supposed to be a joke.

    In any case it just happened that these days I'm reading Gubser's 'Little book of String theory' and today I read in his book at page 94:

    "M-theory, I remind you, is the quantum mechanical theory that includes eleven-dimensional supergravity as its low energy limit. Although M-theory is more than ten years old at the time of writing this book, the statement I've just made is still the most important thing we know about it. I would not hesitate to say that this is a disappoiment."

    This confirms my impression that there is no significant progress in identifying M-theory.

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  20. do you kiss your mother with that mouth?

    ReplyDelete