March 19, 2005

TODAY we are at a very exciting and interesting juncture in time. It is one hundred years since Albert Einstein published his theory of special relativity and introduced the four-dimensional spacetime. He published four other papers the same year, each of which broke fresh ground and were considered important in their own right.

One of them, dealing with the photoelectric effect, won him a Nobel Prize in 1921. Physicists throughout the world are commemorating the centenary of Einstein’s 1905 publications in their own special styles. One of them is weblogging.

According to the Quantum Diaries of Jan. 13 : “The world of particle physics weblogging expanded by about an order of magnitude today, as a new website called Quantum Diaries came online. The idea seems to be to celebrate the 100th anniversary of Einstein’s remarkable 1905 papers by getting 25 physicists from around the world to set up weblogs so that people may follow what they do during 2005.”

Let me clarify, however, that I am not writing about Einstein’s work here. On the other hand, I am writing about string theory.

The string theory was conceived around 1970 and mathematicians and physicists were initially very excited about it. They hoped it would lead to the unification of the fundamental forces but concerted efforts to this end largely led nowhere.

To start with, they realized that the theory required 26 dimensions, which appeared totally outlandish. In addition, the theory was pockmarked by several anomalies. Consequently, scientists soon lost interest in it. By 1980, only a few of them were seriously working in the field.

Then John Schwarz and Michael Greene considered wedding supersymmetry with string theory and the theory of superstrings was born in 1985. The theory opened new possibilities and generated new interest. This event is often called “the first revolution in string theory.” It is twenty years since this development.

The theory has a fair share of naysayers. To be sure, both the theory’s supporters and sceptics include some celebrated physicists. The theory is thus polemical and attracts passionate views from both sides. Since it has so far failed to achieve its fundamental goal, namely the unification of fundamental forces, the controversy continues.

Although it is nowhere near its goal and nobody can see where the journey will end, or how, the theory has been far from stagnant. It went through a second revolution in 1995, with the advent of M-theory (M for Magic, Mystery, or Matrix), which represents its extended version.

The first revolution had created five different superstring theories. The theory, therefore, suffered from excessive richness. This caused a great deal of dismay and frustration in the ranks of string theorists. Then Ed Witten was able to demonstrate that all five theories were dualities of one another; each one of them was a different image of the same fundamental theory, which he called the M-theory. Some even called it the “mother of string theories.”

String theory was thus back on track and on the move. However, despite the passage of a full decade since the last revolution, string theory does not have much to show for itself. Criticism from naysayers persists and string theorists are waiting anxiously for a new revolution.

In the intervening period, there was a tiny ray of gleaming optimism. Harvard physicists Vafa and Strominger were able to deduce an entropy formula for black holes, which was in line with a previously independent but different derivation by Bekenstein and Hawking. According to Strominger (Black Holes and Beyond, ): “The first example we could solve was in five dimensions —although by now many other cases, including four dimensions, have been solved. We found that we were able to give a complete description of a five-dimensional black hole by building it out of strings and macroscopic objects called D-branes….” This is still a far cry from the ultimate goal.

‘Not even wrong’
The status of string theory is best described with Pauli’s phrase “it’s not even wrong.” “No one has managed to extract any sort of experimental prediction from the theory other than that the cosmological constant should probably be at least 55 orders of magnitude larger than experimental bounds. The string theory not only makes no predictions about physical phenomena at experimentally accessible energies, it makes no predictions whatsoever…It’s not even clear that there is any possible theoretical development that would falsify the theory,” remarked Peter Woit.

The biggest criticism of the theory hinges on two points, which are: the theory cannot be tested, and; it does not make concrete predictions so it cannot be falsified.

It’s not that it is without predictions altogether. It does seem to have made some predictions, but these are mostly unrealistic, trivial or not very crucial. One such prediction pertains to the cosmological constant.

Mocking at string theorists, Nobel laureate Sheldon Glashow remarked: “They will say ‘we predicted the existence of gravity’. Well, I knew a lot about gravity before there were string theorists, so I don’t take that as a prediction”.

The sceptics claim that “string theory isn’t even wrong” may be an apt description of its present status. Even its strongest proponent, Ed Witten, admits: “It isn’t an established theory. My personal opinion is that there are circumstantial reasons to suspect that it’s on the right track.”

When he propounded the M-theory, Ed Witten had said: “M stands for Magic, Mystery or Matrix.” Dismayed that it has probably hit a stonewall in as much as unification is concerned, he now says: “But it (M) also sometimes is seen as standing for Murky because the truth about M-theory is murky.”

Michael Atiyah, a celebrated mathematician whose K-theory is being used in string theory, remarked about it: “It’s really too early to have any kind of final picture. We don’t even know what string theory is.”

Glashow said, “One never knows, just as number theory —the most useless of the mathematical sciences — has given us cryptography and has given us a secure way to encode information, string theory may also produce something equally useful. So it is science, it is physics, it is mathematics. It does stimulate ideas in related fields.”

Sceptics and supporters
The people who are on record as condemning the theory are many, some of whom are Nobel laureates in particle physics. Likewise, those who have shown faith in it, though they may not be directly working on it, are several and distinguished. Professors Salam and Weinberg are the believers although they have expressed doubts if the theory could be directly tested because the energy required for the purpose is so high that it cannot be produced with the available technological resources. Stephen Hawking is an optimistic believer.

All of them belong to the older generation of particle physicists. Michael Greene and John Schwarz, the founders of the first revolution, belong to this generation. Ed Witten, the facilitator of the second revolution, is still active in the field.

Some of the younger proponents include Brian Green (The Elegant Universe), Cumrun Vafa and Andrew Strominger (String Theory of Black Holes) and Juan Malcedena, besides junior associates of Vafa and Strominger — namely Shiraz Minwala and Lubos Motl.

As already mentioned, Glashow is a nonbeliever and the late Richard Feynman also did not believe in the theory. Both are theoretical physicists who have won Nobel Prize for their work. David Gross, one of the winners of the 2004 Nobel Prize in physics, has listed 25 most important questions. One of them is: “The nature of string theory.”

Despite all the gloom, many young physicists are attracted towards the theory and they have staked their careers on the possibility of a breakthrough. There is an attractive feature of the theory, though. It is probably the only theory that embraces gravity naturally and, thus, seems to have the potential for discovering a unified theory. However, there is no guarantee that such a theory will indeed emerge one day.

Glashow is dismayed that most young physicists have left the theory that deals with experimental data, the standard model. He complained: “There is a big accelerator, the Large Hadron Collider (LHC), which is scheduled to be completed in another five years or so. That should make lots of discoveries. Who will be interested in trying to fit these discoveries into theory?

“It will be people like me, except we may be dead by then or if not we’ll be rather old. Or it will be the young, theoretical physicists, but they are doing string theory and ain’t interested in the results of experiments. Not now and not then.”

Peter Woit of Columbia University is another detractor. He suggests: “Many physics researchers do not believe in string theories but work on it anyway. They are intimidated intellectually by the fact that some leading string theorists are undeniably geniuses, and professionally by the desire to have a job, get grants, go to conferences and generally have an intellectual community in which to participate.”

Conclusion
Although string theory seems to have failed, or not yet succeeded, in achieving its fundamental goal it has a history of “stop and go.” It went through two revolutions, may be more are in the offing. This keeps the interest of the young theorists alive.

The mathematics of string theory is very complex which is still being unveiled. This probably is another source of the chasm between the “smart alecs” of string theory and the conventional theoretical physicists.

Glashow described this situation rather eloquently by stating: “At Harvard today (2000) there’s a very strong group of string theorists upstairs on the fourth floor of the Jefferson Laboratory. Each week, there are visitors from around the world giving lectures. I’ve occasionally attempted to attend these lectures. I can’t understand the titles, and I can’t understand the lectures, and it’s not just me. I think most theoretical physicists who are not themselves string theorists could not possibly follow these lectures.”

Only time will tell if string theory delivers what it originally set out to do — unify the fundamental forces. It took more than three hundred years to prove that there was no solution to Fermat’s last theorem (x^n + y^n = z^n) for n greater than 3. Let’s hope the string theory does not meet the same fate.

The writer akramgill@yahoo.com has a PhD in civil engineering from University of London. He works for the Detroit Water and Sewerage Department, Detroit, US

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