## Tuesday, December 07, 2004 ... /////

### NY Times: 20 years of strings

David Goss has pointed out to me a big, two-page article in the Science section of the New York Times.

http://www.nytimes.com/ ... 07stri.html

A shorter version of this article by Dennis Overbye has appeared in the International Herald Tribune:

http://www.rednova.com/ ...
http://www.iht.com/ ... string.html

It was written by Dennis Overbye who is already an experienced string theory writer - and I must say that this article looks much better to me than the articles in the Time magazine or the Science magazine that appeared recently.

Overbye starts with a cute story from Aspen, Colorado, in 1984 - a story I've heard from John Schwarz, and it's good that someone finally used it in a popular article. The first public announcement of the Green-Schwarz anomaly cancellation - the discovery that started the first superstring revolution - was a theater play. John Schwarz entered the stage as a madman who was babbling about having discovered a theory capable to explain everything, and he was carried away by several men in white suites. People were laughing because they did not realize at that point that there would be at least 20 years in which the madman will be proved increasingly right by hundreds or maybe thousands of similar madmen.

It is a good article because it not only summarizes the right discoveries, but it chooses the right, important ideas and the right people. By the right people I mostly mean the leaders, of course, such as Strominger, Vafa, Schwarz, Witten, Polchinski, Gross, Shenker, Greene, and others - and all of them have interesting things to say. The article focuses on the important insights found during the last 20 years, and does not go into recent semi-religious speculations. The conjectured huge number of solutions predicted by string theory is referred to as a possible problem which is what it always has been - instead of an opportunity to compete with the quasi-theories about Gods and Aliens, as other articles argued.

Some details mentioned in the article

• Holography (Bousso, Maldacena) and space as an illusion
• Kaluza-Klein theory and extra dimensions - and music of strings
• String theory is a 21st century science that accidentally fell into the 20th century, and therefore we will need 22nd century mathematics to solve it (I did not know the punch line!) ;-)
• Gross says that the research in string theory feels like if we were doing experiments
• Strominger says that 20 years ago no one could predict where string theory would develop in the following 20 years - how it would affect other fields in science
• We are as far from finishing the theory of everything as ever
• The Veneziano amplitude and the strong interactions at the beginning
• The Schwarz-Scherk interpretation of string theory as quantum gravity
• M-theory and the braneworlds
• Strominger-Vafa black hole entropy calculation as the most important single calculation in string theory, as Brian Greene puts it
• Cosmological implications of string theory, cosmic strings (Polchinski) and other signals (Greene)
• The LHC and the meaning of a possible discovery of supersymmetry
The article also includes an appropriate portion of a text about loop quantum gravity - a few percent. The most relevant recent discovery in loop quantum gravity was done, according to the article, by Vafa, Neitzke, Gukov, and Dijkgraaf, and Cumrun explains that if loop quantum gravity is correct, it must be a part of string theory. I am sure that our loop quantum gravity colleagues will agree wholeheartedly. ;-)

Overbye compares the relation between string theory and loop quantum gravity to the rivalry between the Windows and the Apples. Although I am a Windows fan, it does not seem as the most appropriate comparison because Apples work after all, and they are able to do all things expected from a computer - for example they can sum up diagrams that give you a scattering amplitude, at least in the perturbative expansion. That's not the case of loop quantum gravity. A better comparison could have been the rivalry between the USA and Cuba.

Lawrence Krauss, a cosmologist from Cleveland, is cited as a critic of string theory, calling string theory "a colossal failure", but otherwise I don't think that he has an interesting argument to offer. (Incidentally, Lawrence Krauss is the type of a cosmologist who believes that the most important task for high energy physicists is to identify which particles constitute dark matter, but as far as I see, it's not mentioned in the article.) Overbye compensates Krauss' inability to say a meaningful statement about string theory, and he at least explains that it is difficult to test string theory because the strings are so small.

I also liked the story at the end - Steve Shenker says that it would be great to prove string theory right. Brian Greene replies from the audience: "Would not it be great either way?" Steve responds: "Are you kidding me, Brian? How many years have you sweated on this?" Brian continued: "But if string theory is wrong, don't you want to know it, so that we can move on?" Well, Steve Shenker was forced to modify his original statement: "It would be great to have an answer; it would be even better if it's the right one."

Dennis Overbye has proved that he knows what he's talking about, at the popular level - the most bizarre formulation I noticed was the "violation of cause and effect" that Green and Schwarz also showed to be absent in string theory. I suppose it was a violation of causality - the relation between a cause and its effect - but at any rate, it is a bit confusing because their anomaly computation does not seem to deal with a violation of causality. Am I missing something?

#### snail feedback (12) :

Yes, the string-LQG analogy is much better paraphrased as that between USA-Cuba. Because then, according to Cumrun Vafa, if Cuba is right it must be part of the USA. ;)) I like that!

"If Cuba is right, it must be a part of the USA." Very funny!! :-)

Cuba used to be a part of the US. A colony of the US, if you will. But then it turned left' and stopped being right', and is no longer part of the US. :-)

Even now the Cuban `right' lives in the US, so the analogy is actually true in this case. :-)

I suppose it was a violation of causality - the relation between a cause and its effect - but at any rate, it is a bit confusing because their anomaly computation does not seem to deal with a violation of causality. Am I missing something?---------------

I think you are in the same position Gerard t'hooft is, in considering this panel? The last statement he makes there would set up one's thinking, would it not?

Can you activate the <-br-> tag to separate your wording, from comments? I am using this to separate-----

Good article for considerations as you spell out the historical questions, in today's langauage

Dear Plato,

I did not say that you cannot find a random slide on the internet that contains the word "acausal". I was saying that the Green-Schwarz anomaly cancellation computation does not seem to compute any violation of causality. May I ask you to try to take all the words in the sentence into account? Thanks! ;-)

Lubos

I should have posted this statement/question first, of Gerard's

Perhaps Quantum Gravity can be Handled by thoroughly reconsidering Quantum Mechanics itself?I just assumed, that this is what string theorists had always been doing?

When you think about the quantum mechanical discription, it is not so random is it?:)

The limitations that glast discribes makes LQGist's feel very comfortable, but in concert with the change string theorists have applied, how would superposition now demonstrate itself in the string theorist's mind?

You've altered the concept?:)

First of all, the discussion in the NYT and on my blog was not about quantum mechanics as such. It was about the Green-Schwarz anomaly calculation, and you can't expect that a random speculative comment remotely related to quantum mechanics will be relevant for a discussion about the Green-Schwarz mechanism.

OK, so this is why your comments are not relevant for the topic under consideration. Nevertheless, I can still try to answer your question "when you consider QM, it is not random, is it?" Of course that it is. It's a basic point of quantum mechanics that events are random and only the probabilities can be predicted. But I may have misunderstood which sort of "randomness" you were asking about.

Finally, I am absolutely confused what your following sentence involving GLAST, LQG, and superpositions has to do with anything written above, or with itself, for that matter, so I can't respond.

I will find the information from Greene and post then. Until then, I have enjoyed your exchange with Peter.

Sometimes defending ones position reveals more of the intricacies of thinking about this subject, then one could have randomly presented?:)

Hi Plato! Your observation sounds good - it is often very constructive to be forced to say something / defend one's positions - in order to clarify one's own ideas. The people who enjoy writing papers, regardless of any direct need from others, may have other mechanisms to refine their own thinking. ;-)

Some rather simple ideas are only put together once you really start to write them up in such a way that others might understand it.