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…