Saturday, December 04, 2004

String theory gets real?

The Science magazine has a new article ...

called "String theory gets real - sort of". The link above will only work at Harvard, so you will have to find the article elsewhere.

The article recalls the glorious moments 20 years ago, in 1984 - the year when the first superstring revolution started. In Aspen, Colorado, Michael Green and John Schwarz were working on the type I anomalies. Thunderstorm started and Michael Green said:
  • "We must be getting pretty close because God is trying to prevent us from finding the truth."
Unfortunately, this story is not from that article.

The text in the Science magazine says a lot of standard comments that string theory is our best hope to reconcile GR and QM, it requires extra dimensions, it can deal with the quantum foam, and so forth. It also explains how enthusiastic (or naive) people were right after the first revolution, and how much many people today dream about a more direct contact with experiments.

Problems with that text

However, the article says many strange things, too. First, the author argues that until today, no one was interested in string phenomenology, and Gordon Kane seems to support this statement by his authority. Today the group of string phenomenologists is growing.

That's ridiculous, of course. String theory has always been a physical theory dominated by phenomenological motivations - and roughly one third of the activity in string theory is more or less directly trying to answer questions related to experiments. It started as a temporarily failed attempt to describe the strong interactions; then it was identified by Scherk and Schwarz to be a theory of quantum gravity. In 1984 its ability to join gauge theory with quantum gravity was revealed by Green and Schwarz, and in 1985 the first semi-realistic models based on the heterotic strings (Gross, Harvey, Rohm, Martinec) compactified on Calabi-Yau spaces (Candelas, Horowitz, Strominger, Witten) have revolutionized the field. Of course, there have been thousands of papers that studied various phenomenological aspects of string theory.

Comment added later: Thanks to Arvind Rajaraman for correcting the heavily misspelled word "Witten" in a previous version of this article. :-)

Andy Strominger makes a very nice comment about their N=1 heterotic vacua on the Calabi-Yau space that gave us the first realistic stringy SUSY/GUT model with the correct spectrum of fermions:
  • "It was like hitting a golf ball from 200 yards away and coming within a centimeter of the hole. There was a feeling that it was going to take only one more shot to get it in."
If they say this nice comment of Andy, why did they also claim that string phenomenology did not exist until recently?

Concerning the recent developments, they describe the moduli stabilization; the hopes associated with the LHC (supersymmetry as a hint of string theory, not the final test); and the landscape problems.

The landscape's main goal is honestly described as a tool to calculate the cosmological constant. I say "honestly" because without knowing that the cosmological constant is very tiny but nonzero, no one would have attempted to believe the stories about a huge number of virtually unpredictable vacua.

Scott Thomas is cited as the person who favors "probabilistic statistical predictions" from the landscape - well - and Jeff Harvey even proposes that we will have to "rethink what it means for a theory to explain experimental data". Such comments really do not sound terribly encouraging!

Eva Silverstein reveals the fact that the relation between phenomenology and string theory is healthier today. M-theory is described as a completely mysterious theory - well, this is the kind of sentence that leads people like Peter Woit to say misled statements such as "M-theory does not exist". John Schwarz declares that we will need "many more" string revolutions, and volleyball matches, grilling, and beer drinking by the participants at the workshop in Aspen are mentioned.

Brent Nelson from Penn State makes a rather embarassing statement "As a teenager, I could not understand why people believed something so outlandish... and I still don't know why I should believe it."

Peter Woit's comments about the article are here.


  1. The landscape's main goal is honestly described as a tool to calculate the cosmological constant. I say "honestly" because without knowing that the cosmological constant is very tiny but nonzero, no one would have attempted to believe the stories about a huge number of virtually unpredictable vacua. The `huge number of vacua' is a result of string theory. A mathematical prediction, if you will. And people have known for a long time that string theory has a huge number of vacua. I find it strange that you think no one believed in their existence until faced with the urgency of a nonzero CC. Perhaps you mean that no one believed that there would be no real `principle' to choose one or a few from among the vacua, and the AP would be only one available?


  2. Right. I just wanted to say that the belief that there exists a large number of equally good vacua - and there is no vacuum selection mechanism to choose one or a few - has been a marginal belief in the community, and the only real reason why this belief became so much stronger today is the small but positive value of the cosmological constant. You know that the "proofs" of the large classes of vacua are incomplete, and without the anthropic C.C. ideology, virtually everyone would bet that any of the small gaps in this proof will be realized and it will invalidate the proof.

    I still find it very conceivable that once quantum cosmology (and/or supersymmetry breaking) is properly understood in string theory, there will be a rather small number of candidates to choose from.

  3. Hi Lubos,

    Fill in the blank: Candelas, Horowitz, Strominger and _______ :-)


  4. Hi Arvind! You have excellent reading skills. Someone must have hacked this blog, or I am getting insane. ;-) Thanks, Lubos

  5. the strings are contained in the -4-dimensional topological geometry with "exotics" structures given by the connection of TIME9 (SPINORS with rotations of degrees) with the space generaten the 4-dimensional manifolds with exotic structures that is the space continuos