Sunday, December 03, 2006

String theory tied up in knots?

Two new books, Peter Woit’s “Not Even Wrong” and Lee Smolin’s “The Trouble With Physics” – both have been published this year – have created ripples of controversy because the two criticise string theory for its unsubstantiated big claims to pave the way for the Holy Grail of physics – the Theory of Everything (TOE). Theere is nothing much new in the criticism, because since its inception in the 1970s, it has been viewed with scepticism by many theoretical physicists.Woit teaches mathematics at Columbia University, and Smolin is a theoretical physicist at Waterloo in Canada,.

What seems to raise eyebrows in the latest round of fireworks is Woit’s argument that for lack of anything better, many young physicists as well as science funding agencies are putting money in string theory research, and that not much attention is being paid to competing theories.

Smolin is pursuing his own picture of the sub-atomic world known as “loop theory”, facilitated by a particular formulation of the theory of relativity developed by his friend Abhay Ashtekar, a much respected theoretical physicist teaching in the United States.

But string theorists are not willing to yield ground. Two of the prominent members of the significantly large string theory group in India, Prof. Sunil Mukhi of the Tata Institute of Fundamental research (TIFR), and Prof. Ashoke Sen of the Harish Chandra Institute of Mathematics, Allahabad, in their email responses sought to deflect the attacks mounted by Woit and Smolin..

In response to the query whether the disllusionment with string theory as expressed by Woit and Smolin spells the end of string theory, Mukhi says:”The ‘disllusionment’ consists mainly of two recently published books, one by Peter Woit and the other by Lee Smolin. I don’t believe either of these authors has ever particularly subscribed to string theory, indeed they have been negative about it for a long time.”

Sen is of the view that string theory has not reached a dead-end. He says: “While a lot of the effort in string theory is now diverted towards the issue of different possible phases of string theory and trying to see what kind of information can be extracted from these, a lot of the effort is also geared towards various conceptual issues. As far as I can see, there is a still a lot to be done in string theory.”

A strong criticism against string theory has been that it has not offered any experimental evidence, and that this is the biggest handicap. Mukhi accepts the demand for experimental verification as a fair one. He says that string theory’s ‘supersymmetry’ will be tested at the Large Hadron Collider in Geneva next year.

Meanwhile, Sen explains the scope of string theory: “The debate is about how much one can calculate in string theory. There is a hint that string theory contains many different phases (just like a theory of water molecules have ice, water and vapour phases) and the measurable parameters depend on which particular phase of theory we are living in. If this is the case then the most likely picture of the universe is that different parts of the universe can be in different phases of string theory (just as different parts of the world can be in ice, water and vapour phases) and unless we know which of the phases describe the part of the universe we are living in we cannot calculate the fundamental constants of nature with absolute certainty.”

So, is the anger or dissastisfaction with the string theory due to the fact that it has not delivered on the big promise of presenting the theory of everything? Or, is it a momentary irritation? Mukhi does not think that two dissenting books will seriously challenge the string theory. He emphatically notes: “ We are constantly engaged in critical assessments of the theory. I don’t really know why two books written for a lay audience would change anything. The only thing that would change the situation would be a new idea to address the ‘why’ questions, and for the moment there is no signs of that.” He admits that “the public could well feel angered that string theorists have not answered the big ‘why’ questions in two decades, but they need to realise that the questions are important and difficult, and 20 years might not be enough time to solve them.”

It may not be strictly right to say that there are no other competing views. Smolin has one up his sleeve, as it were. He came up with his own road map for TOE in 1995. It is called "nonperturbative quantum gravity”, and it seeks to combine, like string theory, general relativity and quantum mechanics.

Smolin explains the idea: “In this work, we've been combining a very beautiful formulation of Einstein's general theory of relativity discovered by my friend Abhay Ashtekar with some ideas about how to construct a quantum theory of the geometry of space and time in which everything is described in terms of loops. That is, rather than describing the world by saying where each particle is, we describe it in terms of how loops are knotted and linked with one another. This approach to quantum theory was invented by another friend — Carlo Rovelli — and myself, and also by the very interesting Uruguayan physicist Rodolfo Gambini.”

Of course, as in the case of the theory of strings, the experimental evidence for loop theory has been hard to come by as well..

Woit made a pungent observation in an article in Amercian Scientist in 2001: After enumeratng the various drawbacks of the theory, he concludes: “String theory has, however, been spectacularly successful on one front: public relations. For example, it's been the subject of the best-selling popular science book of the past couple years: The Elegant Universe by Brian Greene, one of my colleagues at Columbia…And The New York Times and other popular publications regularly run articles on the latest developments in string theory.”

It is true that string theory has been one of the major science stories that makes it to the mainstream media because of its novelty, and its suggestion that the universe comprises not just the four dimensional space-time of Einsteinian vintage but there are six other dimensions. Of course, the 10-dimensions idea is as yet a postulate, something that theoretical physicists, like the economists, always set up to test their assumptions.
The other major criticism, apart from the one on specifically scientific grounds, is that string theory is so dominating that other approaches are being blocked, and that this is not such a good thing for the progress of theoretical physics. Smolin in an interview has described it in terms of a landscape. He says that each theory stands for a hill interspersed with valleys. He thinks that many reach the top of their respective hills, but they are not willing to cross the valleys and reach out to those on the other hills.

It seems that it is more a question of lack of communication between groups of theoretical physicists, each guarding their own territory. What Woit and Smolin wanted to do, perhaps, was to create a bit of mayhem by attacking string theory, hoping that when the dust settles there would be better communication among bands trekking their way to the theoretical mountain of TOE.

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