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Relaxed informative Witten interview of June 18 at Cern

  1. Jun 18, 2009 #1


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    For general pubic so the language is entirely nontechnical.
    Don't expect a lot but you might be glad you watched just for general perspective.

    Witten gave a talk at CERN not long ago and the slides are available online.
    It had an interesting title, something vaguely like "prospects for new physics away from the high energy frontier." [my emphasis on the "away", which caught my attention.] Observational cosmology and astroparticle physics were the first things he focused on, as I recall. The potential of astro observations for turning up new stuff. I will post the link to the slides if I come across it. If you find it before I do please post. Nothing new but the talk too contains a sense of perspective and the relative importance of different things.

    I found it:
    Last edited: Jun 18, 2009
  2. jcsd
  3. Jun 18, 2009 #2
    Has Witten ever commented on LQG, besides his paper on Lee's Kodama?
  4. Jun 19, 2009 #3
    Yes, the other day at one of our lunches we talked with him about LQG, and his comment was: "are they still working on it?"
  5. Jun 19, 2009 #4
    But that can have two opposite meanings, depending on his face reaction.

    1- "are they still working on it?" -- like, "how stupid these people are; I can't believe they are still working on it!" :yuck:


    2- "are they still working on it?" -- like, "great, I think I'll have a look on their progress then". :approve:

    Well, yet I suppose I know which one you referred too.... :eek:
  6. Jun 19, 2009 #5
    Definitely 1).... and this the opinion not only of him, but of all colleagues I was talking to on this subject.
  7. Jun 19, 2009 #6
    Yes, opinions. We all have opinions. It's good to have opinions. I like my opinions. I suppose that you like yours too.

    I think that we always get back to the starting point. Whatever theory of nature one devises, its consistency should be verified and it ultimately must be tested against nature. All present theories related to quantum gravity (string theory, LQG, etc) are work in progress, no? Technical issues must be solved in all of them. At this point one may have opinions on them. But nature does not care about opinions. Until we do not have a theory consistent with observations/experiments, everyone is free to have opinions. I have no problems with that, as far as someone else's work is not criticized based on opinions only.

    BTW that is my opinion. :biggrin:
  8. Jun 19, 2009 #7


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    I agree to what you say, but unfortunately quantum gravity (I am not talking about a specific theory but about the general subject) ist different from all other physical theories / approaches / models studied so far.

    There ist not one single experiment that contradicts the standard model + general relativity and forces us to develop any new theory! Instead all approaches are driven by theoretical considerations regarding consistency (they do that from very different perspectives and there are different opninions, but these opinions are not directly related to nature - they are related to theoretical frameworks; that's what you are saying, right?)

    So the problem is that theoretical physics today (in ST, LQG) lacks the input from the experimental side - except for experimental results like "the universe exists and seems to be rather old", "we observe 3 spatial dimensions", "there are three generations of fundamental fermions", ...
  9. Jun 19, 2009 #8
    There was a specific question about Witten's opinion resp. comments, and I transferred his opinion, and not primarily my own (which happens to be the same).

    Some people believe that all opinions are equal, others, like me, believe that the opinions of educated and knowledgeable people are more relevant than those of laymen, and thus that it is very legitimate and informative to inquire about the opinion of Witten. And as I can tell you, the opinions of Vafa, Ooguri and others are no different, and these are not simple a sociological phenomenon (as some people seem to try to convey here), but there are good scientific reasons for taking LQG (or Lisi theory, or whatever) not seriously, it is as simple like that.
  10. Jun 19, 2009 #9
    Thanks for the link Marcus, Ed Witten is really delightful. "It's hard to assign probabilities to things that happen only once." :biggrin:
  11. Jun 19, 2009 #10


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    I just started the discussion https://www.physicsforums.com/showthread.php?t=320853". I would be very happy if you could step in and explain these scientific reasons to me.

    Last edited by a moderator: Apr 24, 2017
  12. Jun 19, 2009 #11
    personally i wish witten would write an article (technical or popular) summarizing his assessment of lqg
  13. Jun 19, 2009 #12


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    I agree! Witten - or anybody else who can speak for the string community: Schwarz, Polchinski, Vafa, ...
  14. Jun 19, 2009 #13
    I recall that some of them re LQG as not very promising in re: Smolin & Woit
  15. Jun 19, 2009 #14
    I wish Witten would write more articles, period!

    He hasn't even written a single article this millenium that has recieved over 500 citations (he used to put out a few of those per year), I hope he isn't slowing down for good.

    I can't say why people in general like Ed so much, but I like him because he writes with such lucidity and clarity, that just reading one of his articles makes me feel smarter. In relative comparison most other articles I read seem as obsfucated as encrypted scrawls from Newton's era.

    If any one would like to experience some non-string writing of Ed's, I recommend his description of the Yang Mill's mass gap millenium prize problem (cowritten with Jaffe, another great author):

    http://www.claymath.org/millennium/Yang-Mills_Theory/ [Broken]

    also not to be missed are the two big papers that started topological QFT:


    (sorry couldn't find a free link for this one)

    One thing about all the string theorists I have met is that there attitude towards science is very humble, from my viewpoint the depth of the mathematical problems that they are facing must be what humbles them. Naturally such a disposition does not lend itself well to criticism (positive or negative) of other people's research without being fully immersed in the field.
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  16. Jun 22, 2009 #15


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    Has anybody asked Witten to comment on LQG? Is it absurd to hope that e.g. Witten and Rovell could start some sort of discussion?
  17. Jun 22, 2009 #16
    ... read above.

    Most likely... but you wouldnd't really hope for that, or?
  18. Jun 22, 2009 #17
    In the past, Smolin reported he and Witten corresponded via email re: Kodama state.

    More recently, Randano cited and thanked Witten for his insights in LQG's Kodama state, and Witten's paper on it. I believe it is stated on his phD thesis on Kodama.

    So if Witten did say "people are still working on it" Witten would know, as he helped recently one phD student (Andrew Randono) complete a thesis paper on LQG-Kodama. He also wrote a paper recently on QG, where he lists LQG as a footnote, but w/ no additional comments other than a citation.
  19. Jun 22, 2009 #18
    "the opinions of educated and knowledgeable people are more relevant than those of laymen"

    Yes, in the realm of opinions, opinions have a spectra of values. Being a genius, Witten's opinion certainly have much more value than, e.g., mine.

    But what I mean is that what really matters is the scientific method. An opinion may guide a scientist at some length, yes, but it will always be an opinion. Unless one is ready to change the notion of science, opinions should not value more than the scientific method.

    Another thing: objective criticism is different from opinion. It is part of science as well.

    Anyway, at the present stage, I believe we all agree that quantum gravity is mostly limited to the search for a consistent theoretical framework, but it needs clear predictions along with it. And so it needs input from observations/experiments in order to close the cycle of the scientific method. Whether we will be able to close this cycle is unknown. But theories without clear predictions are not theories in the sense of the scientific method. I would like to know whether there are disagreements here and why...
  20. Jun 22, 2009 #19


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    I fully agree!

    In my opinion the most serious problem of quantum gravity is that there are no known experimental results forcing us to develop quantum gravity. There are "only" mathematical considerations regarding inconsistencies in the present framework of GR + QFT. The question is if one can develop a physical theory which is purely based on 1) requirements regarding consistency, 2) post-dictions and 3) predictions inaccesible to experiments

    I doubt that this will work!
  21. Jun 22, 2009 #20


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    The vast majority of what is written on the Beyond The Standard Model board is about opinions, not about physics or maths. So you should not apologize for your post!
  22. Jun 22, 2009 #21
    If Witten were to write a paper outline novel arguments against LQG/SF/CDT, and prove it's a dead end, then many working on LQG might switch to strings

    this statement depends on this

    Originally Posted by ccdantas View Post

    But that can have two opposite meanings, depending on his face reaction.

    1- "are they still working on it?" -- like, "how stupid these people are; I can't believe they are still working on it!"


    2- "are they still working on it?" -- like, "great, I think I'll have a look on their progress then".

    Well, yet I suppose I know which one you referred too....

    Definitely 1).... and this the opinion not only of him, but of all colleagues I was talking to on this subject.
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    Last edited: Jun 22, 2009
  23. Jun 23, 2009 #22


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    Here's another opinon.

    I share Christines comment on science and opinion. I even think that could be interpreted to mean more even to the new physics that perhaps was meant here. From the inside perspective, the own opinon is always what you have.

    If someone is to understand the actions of a physical systems, or for that matter my actions, then it's the my "inside view" opinon that is the key. Even if I listen to Witten, and realise that he is knowledgable and in some sense are expected by most to be more likely to be right than me, this still doesn't instantly revise my own opinon to his - why?

    Is this because I am irrational? No hardly, on the contrary. I have to evaluation the input from Witten by the same logic I evalute all other information, with my own critical system (it's all I have at hand). And thus someone trying to predict my actions, need to understand this logic. Similary I think someone wanting to understand the action of a subatomic particle, or any other system, needs to understand not what witten knows, but what this SYSTEM knows of it's own environment, that can be the only reasonable key to understanding.

    In that line, I belong to those that think that new theories could possibly tested in applications we didn't think of so far, which is complex systems interacting.

    The traditional way is to look at to extremes, the high energy limit at higher and higher energies, or the cosmological large scale more and more remote. Both have problems which is possibly the key to making it interesting for new theoris, the first has the problem of expending alot of energy and the problem of the latter is that statistics must be given a new meaning, as repeatable experiments of the universe at large isn't as straightforward as in particle physics.

    But, if you consider an intrinsic information of one system, action on it's environment then there is probably another simulation of cosmological scale domains - which is a small system observing a large complex system.

    I think the key more than "absolute scales" are relative complexity, of observer and observed. Maybe new predictions come come in the areas of complex systems selforganisation which previously was considered as just too "chaotic" or possible candidates for AI algorithms to be successfully modelled? These experiements might be in between the extremes. But the problem is this approach might instead be computing power. But that is also the point, what theory is the best survivor given a limited computing power? The proof would be outperfoming any old style models.

    These types are probably what I would personally considerd to be the most immediate new predictions after we have unified all forces etc if someone claims that the latter was "constructed" :)

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