Lots More Landscape

Various things from the past couple days related to Susskind, the Landscape, and his book The Cosmic Landscape:

The paper Computational Complexity of the Landscape I by Frederik Denef and Michael Douglas is out. They show that even in simplified models of string theory vacua the problem of finding a model with CC in the anthropically determined range is NP-hard. This strongly indicates that in practice you can’t ever do what landscapeologists have optimistically hoped might be possible: pick out those vacua with anthropically acceptable values of the CC, and somehow use them to make predictions. Denef and Douglas end by bringing up a peculiar possibility: what if direct evidence for string theory is found (they’re kind of vague on how this going to happen…), but the problem of actually identifying our vacuum state remains intractable?

This raises the possibility that we might someday convince ourselves that string theory contains candidate vacua which could describe our universe, but that we will never be able to explicitly characterize them.

Lubos has a posting about this, including an exchange of comments with Frederik. On the whole I tend to see eye to eye with Lubos about the Landscape, although not here, where he’s frantically trying to dismiss the Denef-Douglas results, which look pretty solid to me.

The Philadelphia Enquirer has an editorial entitled A scientific leap, but without the faith, by Amanda Gefter, who did the recent interview with Susskind in New Scientist. Gefter tries to argue that string theory, unlike intelligent design, is science despite not being falsifiable. I don’t have the time or energy here to do justice to her argument or the problems I have with it (for one thing, she thinks string theory is breathtakingly beautiful). Science and Theology News has an article about the Gefter editorial called Intelligent design versus string theory which kind of misses the point, claiming that string theory can be falsified.

This month’s American Scientist has a review of Susskind’s book by cosmologist John Peacock entitled A Universe Tuned for Life . The review is pretty much uncritical, and mainly happy that Susskind is anti-religion:

These obligatory small criticisms should in no way detract from Susskind’s tremendous achievement. This book is a fine piece of popular science writing, but it is particularly significant for the timeliness of its message. Susskind emphasizes that the whole structure of the universe requires an active Creator no more than does the human eye or the temperature of the Earth. At a time when more and more people seem happy with a creation that took place 6,009 years ago, this lesson needs repeating.

Peacock actually feels that Susskind doesn’t go far enough in trashing the 20th century idea that there is some simple, compelling physical theory that explains the way the world works:

But if life on Earth is a random accident in a universe where only chance yielded laws of physics suitable for life, why stop there? Perhaps string theory itself is nothing special and only part of a wider spectrum of possible prescriptions for reality. If the search for a unique and inevitable explanation of Nature has proved illusory at every step, is it really plausible that suddenly string theory can make everything right at the last? Reading Susskind’s book should make you doubt that possibility, in which case we may have reached the end of the search for underlying simplicity that has driven physics since the beginning.

Finally, last night’s new papers on the arXiv included the surprising inclusion of one on Emergent Gravity by Jack Sarfatti. Famously, supposedly Sarfatti had been banned from publishing on the arXiv, but now I guess the arXiv has changed it standards. I still haven’t heard from them about why they’re banning trackbacks to this site, but perhaps there’s an explanation as to why they have finally found a paper by Sarfatti acceptable. It includes exactly two references, one to a 1976 paper about defects in condensed matter physics, the second to, you guessed it, Susskind’s The Cosmic Landscape.

Update: Chris W. correctly points out that I mistakenly had Gefter referring to string theory as “strikingly beautiful”, when it was general relativity she was referring to in this context.

Update: As a commenter pointed out, there’s a long, uninformed discussion of string theory and intelligent design over at The Panda’s Thumb. Many of the people commenting over there seem to believe that string theory is testable, and even invoke the latest SLAC story. Please don’t bring that particular discussion over here now. If you’re in the mood, contribute over there. Unfortunately I don’t have the time or energy at the moment…

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19 Responses to Lots More Landscape

  1. Chris W. says:

    Gefter was referring to general relativity when she used the phrase “breathtakingly beautiful”. Regarding string theory, she says:

    …, string theory is lacking in testable predictions, but more important, it is lacking some underlying principle to give it deep explanatory power. Still, scientists pursue it because they see paths of unification, shards of beauty, glimmers of ultimate reality.

  2. Michael says:

    http://en.wikipedia.org/wiki/Jack_Sarfatti

    interesting bit on wikipedia about Dr. Sarfatti. he seems like a cool guy.

  3. Alejandro says:

    There is a nice discussion on the “ID vs String Theory” debate going on at The Panda’s Thumb.

  4. JP says:

    When was Sarfatti banned from ArXiv.org? What was the reason?

  5. The “convince ourselves” parragraph is strinkingl similar to arguments about continuum hipothesis.

  6. woit says:

    I don’t know the whole history of Sarfatti’s interactions with the arXiv, and I’d rather not have a thread here about the conflicts he and others have had with them in the past. The interesting question of the moment is why they seem to have changed their policy, exactly when he starts writing about the landscape and referring to Susskind.

    Privately I have heard through another party that Sarfatti sent out many requests for endorsements, and that he himself doesn’t know how many of them led to endorsements, or why the arXiv has changed its policy towards him. I’ve certainly noticed in recent months some rather, let us to be polite say “non-mainstream” articles being posted, even in hep-th, of a sort that I believe in the past were not allowed. What they had in common was that they somehow claimed to be about string theory. This has raised the question in my mind of whether the landscape pseudo-science gaining ground in the mainstream particle theory community is starting to infect the arXiv in general, leading to a breakdown in long-held understandings of what is legitimate theoretical physics worthy of inclusion in the arXiv, and what isn’t.

    If anyone actually knows what is going on at the arXiv on this issue, I’d be interested in hearing about it.

  7. Amanda says:

    I’ve certainly noticed in recent months some rather, let us to be polite say “non-mainstream” articles being posted, even in hep-th, of a sort that I believe in the past were not allowed.

    Really? Can you give some examples? Of topics, if you prefer not to be too specific.

  8. woit says:

    I didn’t keep specific track of these as I saw them, but here’s one example:

    hep-th/0601104

    This seems to me very much the sort of thing that traditionally would not be allowed on hep-th, with the fact that “string theory” is mentioned the only reason it got on there.

  9. Hal says:

    I know that anthropic and multiverse theories are not well thought of around here, for understandable reasons. Nevertheless there are philosophical arguments that can provide guidance through even the thicket of an infinite multiverse. The basic principle is this: that the universe should be as complex as necessary to create intelligent life, but no more so. Justifying and defending this principle obviously takes more room than is available here in the margin :) so I will just point to the works of Max Tegmark and Jurgen Schmidhuber.

  10. One can have a David Deutsch-like multiverse without a Susskind-like anthropic landscape and that’s a good thing.

  11. Luboš Motl says:

    I am happy that you consider the newest paper about the anthropic principle and the meta-statistical analysis of the vacua solid, Peter. Why is it good news that Peter Woit goes anthropic? It’s because we have finally some kind of diversity in the blogosphere, and I don’t have to worry that Michael’s and Frederik’s attitudes to the vacuum selection issues are underrepresented. ;-)

  12. Well, my own papers had got a good historical record of “unappropiateness” in the ArXiV, and recently I have found they are passing more smoothly. So either my writting is going better, or the arxiv has revamped some criteria after the appointment of new supervisors last year.

  13. Chris W. says:

    From Peter:

    I’ve certainly noticed in recent months some rather, let us to be polite say “non-mainstream” articles being posted, even in hep-th, of a sort that I believe in the past were not allowed. What they had in common was that they somehow claimed to be about string theory. This has raised the question in my mind of whether the landscape pseudo-science gaining ground in the mainstream particle theory community is starting to infect the arXiv in general, leading to a breakdown in long-held understandings of what is legitimate theoretical physics worthy of inclusion in the arXiv, and what isn’t.

    How about these: Papers by the author of A Solution to the Fermi Paradox: The Solar System, part of a Galactic Hypercivilization?:

    Besides these simple solutions there are many more exotic proposals. For example, a rather drastic expansionist solution is given by the theoretical physicist Cumrun Vafa, at Harvard University, who thinks that the fact that we do not see aliens around could be the first proof of the existence of brane worlds: all advanced aliens would have emigrated to better parallel universes [7].

  14. woit says:

    Chris W.

    That is one of the best arguments for brane worlds I know of. Note that this author’s papers in recent years have been on in the unmoderated “physics” sections rather than one of the moderated sections like hep-th. What I’m interested in is whether their moderation policy has changed or is changing.

  15. woit says:

    Correction: the “physics” section is also moderated, although presumably in a somewhat different way than the other sections.

  16. Well I am happy that at least it has been changing or changed during the last year, because it let me to arxive some things I can need to check in the future -lot of susy and/or topcondensation going on-, and it is important to have them handy and public even if not in “publishable” form. I hope it will remain at the current moderation level and no go back to the old ages.

    PS: Alejandro, could you please to use at least the initial of your surname, to avoid confusion?
    PS2: It seems that a Sarfatti has answered to this thread in a different one.

  17. Christine says:

    P.C.W. Davies submitted this paper recently to astro-ph:

    The problem of what exists. The abstract is:

    Popular multiverse models such as the one based on the string theory landscape require an underlying set of unexplained laws containing many specific features and highly restrictive prerequisites. I explore the consequences of relaxing some of these prerequisites with a view to discovering whether any of them might be justified anthropically. Examples considered include integer space dimensionality, the immutable, Platonic nature of the laws of physics and the no-go theorem for strong emergence. The problem of why some physical laws exist, but others which are seemingly possible do not, takes on a new complexion following this analysis, although it remains an unsolved problem in the absence of an additional criterion.

  18. woit says:

    Christine,

    Thanks a lot for pointing out the Davies multiverse paper, I hadn’t noticed it.!

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