Thomas Larsson wrote in a comment mentioning a news story that appeared early this past summer in the Deseret Morning News (yes, that’s Deseret, not Desert; this is a name Mormons use to refer to Utah). The news story is about a conference on “String Geometry” held at Snowbird, Utah in June. Evidently at Andy Strominger’s talk at this conference someone actually mentioned that there were people who were skeptical about string theory and asked him to comment. His response was that “I hope they’re wrong, but I can’t prove it, and I bet my life work on their being wrong” , which I guess characterizes the attitude of many string theorists these days (“things don’t look good, but I’ve got too much invested in this to give up, so I’ll keep on engaging in wishful thinking even though I no longer have much of an argument for why I’m doing this”).
Many of the talks at the conference are online. These include a couple of interesting talks by Gukov and Spradlin about recent work on twistor theory and perturbative Yang-Mills amplitudes, as well as the usual Michael Douglas talk with its wishful thinking that analyzing the astronomically large “landscape” will somehow lead to some sort of prediction of something. There’s also a talk by Radu Tatar about non-Kahler superstring theory backgrounds. I’ve always wondered about this since I hear from an algebraic geometer colleague that although no one knows whether there are an infinite number of Calabi-Yaus in the Kahler case, if you relax the Kahler condition there definitely are an infinite number of them. If these non-Kahler backgrounds make sense, you can stop worrying about whether the landscape contains 10^100 or 10^500 possibilities.
Tomorrow here at Columbia my colleague Brian Greene is giving a colloquium on “The State of String Theory”. His abstract says he’ll “assess both its current shortcomings and major achievements”.
Offend? I must up my flippancy daemon priority.
But seriously, I like to know who’s saying what.
My apologies on not giving a name. My intent was not to offend. If it makes you feel better, I am not a regular poster being coy, but merely a casual reader who was posting a flippant comment. If I happen to post something of substance I’ll be sure to give a name.
But, since you asked, I’ll just say that Georgi isn’t a loon at all. Actually I loved the class I took with Georgi, and him as a person as well.
That is true, although I do have a nice letter from Georgi from my teenage days. He isn’t (wasn’t?) a loon. In fact I can’t remember ever meeting a math/physics loon before the advent of this Internet thing.
(Simple request – can we please use names here? There’s nothing to be afraid of. I’d like to think/pretend this isn’t the run-of-the-mill free- republic-type anony-blog.)
“He’s a loon with a professorship at Harvard.
How’d that happen?”
You’ve clearly not spent any time as a physics student at Harvard…
Serenius, I have no doubt that most string theorists and LQG’ists alike are nice people. Motl may be an exception, but Gell-Mann does not give a particularly nice impression neither. This is not important. Besides, I think that Motl has a point about LQG, more politely expressed by Hellig-Policastro.
Nobody doubts that most string theorists are nice and bright, only that they are right. To call Strominer a loon is certainly not fair.
He’s a loon with a professorship at Harvard.
How’d that happen?
I don’t think that Strominger’s attitude is wrong. He has a hunch that string theory is right and he is following that up. He has infinitely more reason to be triumphal about [eg] black hole entropy than Lubos Motl or others of that ilk, yet I have never heard that he has tried to exaggerate the real but modest achievements of string theory in that direction. He’s a good guy and a sensible one.
Speaking of LM, this is from his proposed entry on loop gravity in wikipedia [the online encyclopaedia, http://en.wikipedia.org/wiki/Main_Page%5D:
most loop quantum gravity advocates are not good physicists, and they try to avoid learning anything from particle physics and other fields even though it is clearly necessary for a proper understanding of many questions in quantum gravity. They believe that a very narrow-minded understanding of reality that they propose – and that has not made any real progress for decades – is everything we need. They are making incorrect mental links between different concepts and they are unable to learn better.
This was spiked by the wikipedia people on the grounds that it was “over the top”. LM has reached the stage where even non-physicists can tell that he’s a loon.
It is due to phenomenology that N=1 susy to many people seems/seemed to be a very attractive property of an effective field theory of the fundamental forces.
The potential to shed light on the hierarchy problem as well as apparently better gauge unification properties are what made many people consider supersymmetric extensions of the standard model. And models like that drop out of string theory if six of ten dimensions are compactified on a CY manifold.
However, there is no known dynamical reason within string theory that six dimensions should spontaneously compactify as a CY space. This does not necessarily mean that such a dynamical mechanism does not exist, but these questions concerning the dynamical choice of string ‘vacuum’ are not at all well understood. For these reasons people just choose a CY compactification for phenomenological reasons and proceed from there.
This choice is compoletely analogous to (but somewhat more complex than) choosing a value for the parameter k in the Friedman-Robertson-Walker cosmological solutions of plain GR. For each value of k one obtains a valid solution, but one does not have (yet) a dynamical explanation why one value of k is observed in nature while the others are not. So one chooses the parameter that is preferred phenomenologically and then proceeds from there.
The math of supersymmetry as an abstract concept is extremely nice and supersymmetry concepts play an important role in many branches of physics and mathematics that are not directly related to high energy phenomenology. However, the supersymmetric extensions of the standard model and the scattering computations done in them are far from being very elegant. They have a plethora of free parameters and many new particles and interactions. Even though supersymmetry still ensures certain cancelations and makes some computations quicker, in general supersymmetry phenomenology is a mess.
Urs (or anybody), why is N=1 SUSY so compelling? Suely it can’t be because of phenolenology. Is it just that the math is graceful?
Are there any backgrounds which break ALL the supersymmetry, without introducing any additional “diseases” to string theory?
The condition that after the compactification of 1oD string theory down to four dimensions the remaining effective field theory has precisely N=1 supersymmetry is that the compactified 6 dimensions form a Calabi-Yau space, which is in particular Kähler. Relaxing that means not having N=1 susy in four dimensions (at high energy before 4d susy breaking).
In principle there is no compelling reason that the ten susystring dimensions must be compactified such that the resulting 4d theory has N=1 susy. This is just the scenario that people find/found most interesting. (Because susy in 4d is/was considered attractive and N=1 (as opposed to higher N) is the only choice not in contradiction with observation from the outset).
Peter,
If you relax the Kahler condition, do you get an aleph_0 infinity of backgrounds or an aleph_1 infinity or beyond?
Physics wise what would be the dire consequences of relaxing the Kahler condition, besides definitely having an infinite number of backgrounds?