Frequently Asked Questions (of a scientific, sociological, or other nature) -- :
1. How do you know string theory is true ?
2. How do I learn string theory ?
3. How will string theoy affect our daily lives, and what is its use ?
4. What's up with the Sokal Affaire ?
1." How do you know string theory is true ?"
The simple answer to this question is: we do not yet know whether nature is described by string theory or not.
1a) "So, why are so many scientists working on it then ? Isn't it more important to work on theories of which we know they are true ?"
Scientists work on string theory because they believe it has a very good chance of being true. In other words, the theory is compellingly beautiful and resourceful, to experts, and it is convincingly consistent. Moreover, it addresses problems that theoretical and other physicists believe need to be examined, and it does this in rigorous fashion. All these scientists believe it is also important to work, for instance, on delving deeper into the guts of the quantum field theories of the standard model (i.e. a theory which has been experimentally established), but they have chosen to follow an alternative path. There is a much larger community of physicists that do work on theories that are known to describe nature accurately. Some try to go beyond this framework, because this has been proven to be instructive, useful and interesting in the past. That is well-established methodology.
1b) "Why don't you just do the right experiment, and check whether string theory is true or not ?"
We should consider the fact that we have continuously tried to heighten the energy scale at which we can do experiments. This becomes more and more difficult to realize. If a new particle accelerator is constructed, we are happy with a gain of a factor of ten in energy scale -- a lot of new physics can be hidden in the new energy range that will be accessible to us after it is operational. But, this costs a lot of energy, money, time, knowledge, engineering skill, etc. We should not underestimate the resources that we put into this enterprise.
Simultaneously, string theorists try to lower the energy scale at which string theory can predict spectacular new phenomena. We're happy each time we can pinpoint a new peculiar phenomenon that would be indicative of the existence of strings, and that could be observed at relatively low energy scales.
But, the gap between theory and experiment is still large in the sense that the new phenomena that string theory predicsts MAY happen at low energy scales (i.e. energy scales that we will soon be able to access with sufficient political and public support), but that this is not guaranteed to be the case (i.e. the energy scales at which these spectacular signs would pop up could be much higher than the ones that will be accessible in near future experiments).
1c) Moreover, it should be stressed that even when string theory is verified, we wouldn't claim to have solved all problems in nature. Perhaps string theory will be our best approximation to experiment at some point -- we should be aware though that presumably new theoretical problems will then be discovered on the horizon -- in fact, we can already discern some now, and we are already trying to address them. We should be weary of people predicting the end of physics, the theory of everything, or the answer to the question of life, the universe and everything. Therefore, a statement as: "I know string theory to be true and final" cannot reasonably be expected of a serious scientist. Clarity does not always spell truth, and the truth is not always cristalclear. Perhaps this is one of the reasons that trained scientists have a reputation of being vague, careful, slow and deliberate.
2) How do I learn string theory ?
It is very welcome that we often get this interested and enthousiastic question. Indeed, we need people to learn string theory in order for it to survive, as is the case for most of the knowledge gathered by humanity. However, it is necessary to warn on beforehand that the road to learning string theory is hard and painful, as well as rewarding.
Often I encounter people who have plowed through the standard works that popularize string theory (including this site), and they remain hungry for more, and understandably so. And one might think that beyond the ten books or so aimed at the non-expert about string theory, there is not much else to recommend. Once those books are read, one is done ?
That is obviously false. One road might be to recommend the many more popularizing books that make the pillars on which string theory rests more accessible to the public. Another piece of advice could be to actually draw the path that most string theorists themselves took in learning string theory in order for people to be able to follow up on it. To make that road transparent is a difficult matter. It may not obvious, but to learn quantum mechanics, one does need some linear algebra. To compute probabilities, one does need to know how to multiply complex numbers. To understand the fabric of space and time deeply, one needs to study differential geometry. To really learn string theory, one does need to learn math.
In other words, learning string theory often starts out with learning elementary math, and its physical applications. And to appreciate the physics of math actually does not take too much effort. You surely can find an elementary physics text book explaining the link between velocity and acceleration, and derivatives of the distance function. Or between the distance traveled and an integral of the velocity. Etc. Once one masters elementary links between physics and mathematics, I'm sure it's easier to appreciate the long road towards learning string theory. As an intermediate goal for the very enthousiastic reader, I would propose to try to master the link between second order differential equations (Newton's law) and the movement of the planets around the sun. I learned the link when I was eighteen, and I'm still impressed by the beauty and simplicity of this piece of physics/math. How about learning this piece of physics first, then to tackle the rest ?
3) How will string theory affect our daily lives, and what is it's use ?
The above question can be paraphrased as: "What is string theory good for, really ?". In answering this question, we venture in the realm of the human sciences, and we're aware of the fact that the answer differs depending on believes, values, and convictions. For instance, you might answer this question with: "for nothing, really, or at least nothing I can think of, nothing concrete, anyway not in my life". That would be a reasonable answer. I prefer another one.
Firstly, science, and any attempt to better understand our world is a goal by itself. It needs no further justification. As far as I'm concerned, it is an integral and important part of human nature that we try to extend the knowledge we have at any given moment in time. This is sufficient reason to study string theory (given the fact that I judge it to be a very reasonable and important attempt to extend our knowledge).
On a second level, science has many consequences outside the realm of science itself, which are of great importance. However assesing these consequences for string theory may be premature. When we ignore this fact and still attempt to draw consequences, several come to mind. String theory, when confirmed (and even before being confirmed) would change our perception of reality. Associated to the (possible) appearance of extra dimensions, we could imagine a whole new world opening up -- every point in the room we are in, we would then think of as a little ball, so small that we cannot see it -- but we would know it is there if string theory is confirmed. That is only one example of how knowledge can change our daily perception of our environment.
However, frequently one is asked about the practical daily use of string theory. What are the concrete applications ? For instance, in the case of general relativity, one can point to GPS systems which would not be practical without our extensive knowledge of the laws of gravity. No such applications are patented for string theory as of now (to my knowledge). As usual, one first acquires knowledge about the laws governing certain physical processes, before we are able to transfer those laws into technical abilities, and an ability to manipulate the physics at those scales. The time-delay between knowledge and manipulative ability can be quite large. For example, the physics of atoms has been known for quite a while -- almost a hundred years --, but only in our days are we learning how to manipulate individual atoms well. We usually first try to find applications for the laws of physics that operate at scales slightly smaller than the scale ath which we have already found applications (say, the atomic scale) -- and that is what people do now. Theoretical scientists and experimental scientists and engineers all work at their own scale, and each group advances, step by step. Some visionaries try to jump ahead, but they seldom succeed in doing so realistically. Thus, the question about the immediate practical use of string theory can be considered a good and reasonable question, but perhaps ill-timed.On a more indirect abstract level, it should be said that the theoretical use of string theory, both as a breeding ground for new ideas in mathematics and physics, as well as as a training ground for excellent scientists, teachers, physicists, or even financial analysts has been demonstrated. (I refer for instance to the detailed history of the American physics community during the second world for the irrefutable proof of the versatility of a theoretical physics training.)
4) "What's up with the Sokal affair, and is it true that there is a counterpart in the Bogdanov affair ? How can I take science seriously after these affairs, and what is written about them in the newspapers ? "
I refer to the linked internet pages for a thorough discussion of some of the facts. But, I believe that most of the discussions of these affairs are missing some substantial points which shed a more reasonable and pragmatic light on the issues at hand. These points are presented below, and should be read as complementary to the extensive debate which is easily followed by using Google.
One of the basic assumptions underlying the serious discussions regarding the publication of these papers in respected journals is the idea that all refereed papers that are published are considered sensible by the experts of the field. That idea is false, and it should be clear that once this fact is accepted, the affairs lose a lot of their interest. They are instances of the violation of the above belief which were blown out of proportion, and this is possible because the belief is held so strongly, although it is false.
So, first, let's see why the belief that all refereed papers are considered sensible by the field's experts is wrong. To realize this fact, it is sufficient to be acquainted with everyday scientific practice. Since I am a scientist, I can testify to the following rare facts. I know that some of the editors of respected journals are extremely busy people who do research, teach, give lectures, write papers, guide PhD students, attend seminars, etc. In fact, they may have extremely little time left to consider in detail the full content of one particular edition of the journal they edit. Secondly, I know that some refereeing is done very casually. I've seen instances of scientists having no time whatsover left to read in detail a long paper they have had lying on their desk for weeks, and for which they are supposed to hand in a referee-report within 24 hours. I've known instances in which capable referees have refused papers, and in which those same papers were allowed to be published by other capable referees. I have very little doubt that some referees, on some very rare occasions have accepted papers they have not at all read, although it would have been rather careless of them to inform me of this fact. As stated, these facts may be rare, but they certainly allow for many papers slipping through the mazes of the referee-net. It should not be difficult to identify a small but non-zero number of non-sensical papers in the stream of papers publised monthly. (It is not common among scientists to state the above facts, and the reason should be clear from the further discussion.)
How is this possible ? Well, refereeing is not paid for by anybody. Like with many real work, if it is paid poorly, or not at all, it might be done badly (however: see below). Why is done at all then ?
Well, this is closely connected to why the above belief in the referee system is so widely spread. The referee-system is still in place because many scientists believe it frequently (as opposed to rarely -- see above) gives a good indication of the level of a paper to check in what refereed journal it was published. Moreover, this belief has been carried over into the administrative and poltical world, and is used extensively to provide criteria for the distribution of money. The latter circumstance has terrifying consequences on how serious the scientific community has to take the referee-system. A system that indirectly influences how scientific money is spent, is all of a sudden under pressure to be flawless. Within the scientific community the referee-ing system is supplemented with many other ways of judgement which are hardly accesible for non-experts, but which are necessary for a more balanced view on scientific merit. Unfortunately, these complementary corrective measures are difficult to translate into politics and administration (unless by incorporating willing and able scientists into these activities).
Let's summarize. The referee-system is not flawless. It might be improved if more money was spent on it. And, most of the time, although little money is spent on it, it works fine, because most of the time scientific referees take their jobs seriously. Is it surprising that this is not always the case ? No. Thus the believe on which the discussion of the affairs is based is wrong, and the reasons for this believe are interesting and could be the subject of a social text.
Given the undermining of the above first approach to the interpretation of the affairs (which is: the referee-system and editing-system is extremely serious business, and should be more or less flawless, and yet, nonsense is allowed to pass, and this is very upsetting), what are we to think of the affairs ? Well, unfortunately, the affairs were not drawn out long enough to really judge them. Let me explain what I mean. The whistle was blown on the Sokal affair just after publication. This is a pity, because I would like to replace the referee-system judgement by another criterium for the scientific succes of a hoax: whether the hoax-paper is taken up by the community, seriously studied, followed up on by many papers, whether the author is invited to discuss his results, to extend them in collaborations, and whether after a number of years (say ten) has passed, the scientific community remembers, using its collective memory that the paper exists. Certainly, the Sokal-affair was not drawn out long enough to make this judgement call. (In other words, it could be that the Sokal paper after publication would simply not have found any following.) In the Bogdanov-affair, I know for a fact that their work is not succesful, by ordinary scientific standards (which differ from the referee-system). Therefore, there really is no affair to speak of.
In fact, what I have wished to argue is that a judgement of the Sokal-hoax and the Bogdanov-affair is much more subtle than the discussions put forward in the newspapers. I have wished to indicate that an acquaintance with scientific practice in both the physics and the philosophical community would be necessary to make a reasonable judgement-call, and that wrong criteria are used to claim success for a hoax, or "affair". Secondly, the false succes is used to draw dangerous conclusions, which I have tried to undermine -- there is no reason to lose your faith in science after reading about stories of affairs like these. I argued that the whole debate surrounding these affairs is interesting, but warned for drastic and early conclusions. And, finally, I testify that the Bogdanov-affair perhaps would be worrysome if frequently repeated, but, that at the present (very limited) rate, it is a normal statistical aberation in a on the whole very healthy scientific community with reasonable criteria for scientific success.