Saturday, 26 January 2008

Strings, LQG and all that

During a week long business trip I have finished reading a book by Peter Woit, Not Even Wrong, about the failure of the String Theory. I have then augmented it by several articles by Carlo Rovelli (especially Notes for a brief history of quantum gravity, and A dialog on quantum gravity, Int. J. Mod. Phys., 2003, D12, 1509-1528). Just to preserve the balance I leafed through Brian Greene books and Leonard Susskind Cosmic Landscape.

Results? Of course I do not understand String Theory not Loop Quantum Gravity. But as for human side, it is quite interesting.

The situation seems more than lightly skewed. While Woit and Rovelli discuss at length the pros and cons of string theory and its alternatives, the proponents of string theory behave somewhat differently. For example, Susskind devotes a single paragraph (about six lines of text) to Loop Quantum Gravity,
stating that it `is an interesting proposal, but it is not nearly as well developed as String Theory'. He continues:
As much as I would very much like to balance things by explaining the opposing side, I simply can't find that other side.

Very similar stance is taken by Greene in The Elegant Universe. He devotes about four pages to `criticisms of String Theory', which he starts as follows:
Is string theory right? We don't know. If you share the belief that the laws of physics should not be fragmented into those that govern the large and those that govern the small, and if you believe that we should not rest until we have a theory whose range of applicability is limitless, string theory is the only game in town.
You might well argue, though, that this highlights only physicists' lack of imagination rather than some fundamental uniqueness of string theory. Perhaps. You might further argue that, like the man searching for his lost keys under a street light, physicists are huddled around string theory merely because vagaries of scientific history have shed one random ray of light in this direction.

But, as Greene argues, these arguments are less and less important as the theory climbs up the mountain of understanding. The fact that it does not have any connection with experiment and reality is, for Greene, but a temporary matter, a `historical asynchrony'. What he hopes is that soon experiment would be able to confirm the results. The book has been written before the number of solutions of String Theory grew so much that any solution became possible, somewhere within the immense landscape which made the falsification near impossible. But the departure from the classical ideal of falsifiability by experiment is not critical for many proponents. The beauty of String Theory with its self-consistent finite number of dimensions, slightly spoiled that the number is wrong, not four but ten or eleven, and deep mathematical relationships is for many enough to continue the work. Both books by Greene and Susskind (as well as the one by Woit) are of the popular science genre. Thus, they may be considered as examples of what the scientists want to communicate to the lay public. And in the proponents of the String Theory it is clearly the excitement of research but also a lot of Public Relations. Look, we are climbing the mountain! We're just below the summit! The critics voices, more sombre, point out the less optimistic perspective. Is this good PR? Should we, scientists, show the public that we might be spending their money without getting results? Should we admit that some efforts (and funds) are wasted on wrong theories and failed experiments? If one looks through most of the books on history of science we usually see an uninterrupted march of progress, leaping, from tree to tree, like the Monthy Pythons lumberjack. Yes, there are some pet `wrong theories', like the phlogiston, or Ptolemaic system to show that progress is sometimes at expense of old ideas. But finding the day-to-day struggle with failed concepts, with ideas that caught fire for a couple of years only to be forgotten after a decade, is much more difficult. And for anyone who does dig deeply enough into the history of science, it is soon clear that this waste of funds and effort is an indispensable part of the success of science. Discovery can be achieved only by going into unknown. And this, by definition, means traveling without paths, often in a wrong direction.

The String Theory controversy, even taking into account its relatively low profile and the disproportions in the numbers of critics and supporters, is one of the crucial disputes in modern science. First, because it touches issues of group behaviour, career development, freedom of research. The question is: how can we expect to boost creativity if all the money (from limited and shrinking funds) is directed into one approach? What is the result of all the young, enthusiastic physicists flocking into one path?

The second issue is the role of Public Relations in science. In which way should the work be portrayed, is is allowed to publicize the controversies and questions? At first glance the situation in String Theory looks like a perfect case study for the radical `science studies' proponents, the deconstructivists and others. There is a lot of political agenda visible, a lot of social and psychological motives. But then the question becomes: can we separate the human and political aspects from the scientific content of the debate? Ultimately, some of the equations, some of the experiments would show who was right and who was not. This is at least what most of the physicists on both sides of the dispute hope for. How, then, could a sociologist decide who is right today, without understanding the physical problems? I am quite sure that most of the hard words expressed by the participants of the debate result not from some character flaws or political agendas but from deep convictions about the nature of the Universe. Yet, on the other hand, the social phenomena, such as tenure track selection or funding decisions are real.

The third issue is more physical: can we expect that any of the theories would touch with any experiments or observations in a foreseeable future? It seems that a small (but very fundamental) part of physics has turned into speculative metaphysics, where theories are laced so far ahead of experiment, that decisive factors are mathematical beauty or popularity. Some people might think that these are sufficient motivations for support. Some disagree.
But whatever our human inclinations are, the real verdict is still out --- there is no Quantum Gravity today.

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