Twenty Years After

We are at present at a very exciting and interesting juncture of time in the world of physics. It is one hundred years now when Einstein published his theory of special relativity in 1905 and the four dimensional spacetime was introduced. He published four other papers in the same year each of which broke fresh ground and is considered fundamental in its own right. One of them on the photoelectric effect won him a Nobel Prize in 1921. The physicists are memorializing the centenary of Einstein’s publications in the year 1905 in their own ways. One of them is weblogging

According to Quantum Diaries, January 13, 2005 (http://www.math.columbia.edu/~woit/blog/), “The world of particle physics web logging expanded by about an order of magnitude today, as a new web site called Quantum Diaries came on-line. 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 web logs so people can follow what they do during 2005.” But I am not writing about Einstein’s work here; on the other hand, I am writing about the string theory.

The string theory was conceived around 1970 and the mathematicians and physicists were excited about it. They hoped it would lead to the unification of the fundamental forces but concerted efforts to this end led nowhere. To start with, they realized that the theory required 26 dimensions, which appeared totally outlandish. And the theory was pock-marked by several anomalies as well. Consequently, the scientists lost interest in it. By 1980, only a few of them were seriously working in this field.

Then John Schwarz and Michael Greene considered wedding supersymmetry with the string theory and the theory of Superstrings was born in 1985. The theory opened up new possibilities and generated new interest. This event is now called ‘the first revolution in string theory’. It is twenty years when this revolution occurred; hence the title of this article. (The title was inspired by Alexander Dumas’ novel ‘Twenty Years After’).

I have previously published a few articles at chowk.com describing the string theory. In them, I tried to capture the excitement of the proponents of the theory and also describing the views of some naysayers. The proponents and the naysayers include some celebrated physicists in their ranks. 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 the fundamental forces, the controversy continues.

Although the theory is nowhere near its goal and nobody is able to see the end of the road, if indeed there is any end of the road, it doesn’t mean that the theory remained stagnant. It went through a second revolution in 1995 with the advent of the M-theory (M for Magic, Mystery, or Matrix), which is the extended version of the string theory. The first revolution created five different superstring theories. The theory thus suffered from its excessive richness. This caused a great deal of dismay and frustration in the ranks of the string theorists. Then Ed Witten was able to demonstrate that all the 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 euphorically called it the mother of string theories). The theory was back on track again and on the move. However after a decade now, it doesn’t have much to show for itself. The criticism of the naysayers persists and the theorists are again wistfully waiting for a new revolution.

In the mean time, there was a tiny ray of gleaming optimism. The Harvard physicists, Vafa and Strominger were able to deduce an entropy formula for the black holes which agreed exactly with the previous independent and different derivation by Bekenstein and Hawking. According to Strominger (Black Holes and Beyond, http://www.sciencewatch.com/may-june99/sw_may-june99_page3.h tm), “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 position of the 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 the cosmological constant should probably be at least 55 orders of magnitude larger than experimental bounds. 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,” (Peter Woit).

The biggest criticism of the string theory hinges on two points, which are:

1. The theory is not testable.
2. The theory doesn’t make predictions so it cannot be falsified.

The theory seems to have made some predictions, which are unrealistic, trivial or not very crucial. One of such predictions is in regards to the cosmological constant, which has already been mentioned in the above. Mocking at the 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 was any string theorists, so I don’t take that as a prediction,” (http://www.pbs.org/wgbh/nova/elegant/view-glashow.html).


The critics’ claim that the 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 M-theory, Ed Witten had remarked “M stands for Magic, Mystery or Matrix.” Dismayed that it has probably hit a stone wall in as much as unification is concerned, he says now “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 the string theory remarked about string theory, “It’s really too early to have any kind of final picture. We don’t even know what string theory is.”

Glashow remarked appositely, “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. The string theory may also produce something equally useful. May. So it is science, it is physics, it is mathematics. It does stimulate ideas in related fields.”

Naysayers and Aye-Sayers

The people who are on record to condemn the string theory are many and some of them are Nobel Laureates in particle physics. Likewise, those who have shown faith in it even though they may not be directly working on the theory are many and distinguished. Professors Salam (deceased) and Weinberg are the believers although they have expressed their doubts if the theory could be directly tested because the energy required for this purpose is so very 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 the particle physicists. Michael Greene and John Schwarz, the founders of the first revolution, also belong to the older generation. Ed Witten, the harbinger of the second revolution, is still active in the field.

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

The naysayers, likewise, are many and some of them are very distinguished. I have mentioned Glashow herein and in my previous articles on string theory, and the late Richard Feynman had no faith in the string theory. Both of them are theoretical physicists and have won Nobel Prize for their theoretical work. David Gross, one of the winners of the 2004 Nobel Prize in Physics, has listed 25 most important questions in physics. One of them is “the nature of string theory.” He questioned: what is it..? Some are simply indifferent.

Despite this gloomy view, many young physicists are attracted by the galore of the string theory and they have staked their careers on the possibility of shining light on the dark areas in the theory. There is another attractive feature of the string theory. It is probably the only theory, which embraces gravity naturally and thus seems to have the potential for discovering a unified theory. But there is no guarantee that such a theory will indeed emerge from it.

Glashow is dismayed that most of the young physicists have left the theory which deals with experimental data (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 the 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 the young theoretical physicists are doing string theory and ain’t interested in the results of the experiments. Not now, and not then.”

Peter Woit (Department of Mathematics, Columbia University) is another severe critic of the string theory. He suggests, “Many physics researchers do not believe in the 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,”.

Concluding Remarks

Although string theory seems to have failed, or not yet succeeded, in its fundamental goal, it has a history of ‘stop and go’. It went through two revolutions, may be some more are in the offing. This hope keeps the interest of the young theorists alive. The mathematics of the string theory is very complex and is still unraveling. Probably this is also a source of alienation between the ‘smart alecs’ of the 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 the string theory delivers what it set to do, in the first place – unify the fundamental forces. It took more than three hundred years to prove that there was no solution of Fermat’s Last theorem (x^n + y^n = z^n) for all integral values of n greater than 3. I hope the string theory will not meet that fate.