## Saturday, August 20, 2011 ... /////

### Unity and uniqueness of string theory became a heresy

At the beginning of the year, I was kind of amazed by the quality of Physics Stack Exchange. There were actual experts over there and meritocracy mostly worked worked. So I have also answered 661 questions and became the highest-score user on that server.

But sometimes in Spring, I couldn't overlook that the percentage of extremely stupid questions and bad answers was dramatically increasing. This inevitably had to mean that the professional physicists would leave because the environment was becoming low-brow, marginally hostile, and visits became a waste of time. And they did leave. So did I.

I was reassured that my decision not to visit the website too often was sensible when I answered a question about the early history of string theory yesterday.

You know, I have sketched the usual stuff that the hadrons seem to live in a jungle without rules and partial patterns were being noticed - like the Regge trajectories (the dependence between the angular momentum of a particle and its squared mass etc.). Veneziano found his amplitude which agreed with the Regge trajectories and also satisfied the (world sheet) duality, a principle whose importance was correctly guessed by Veneziano in his search for his amplitude.

Susskind and others were able to find out that the tower of resonances came from many harmonic oscillators living "inside" the particles and the particles were ultimately one-dimensional vibrating objects, strings. The picture of strings automatically explains the (world sheet) duality because it unifies the $s$-channel and $t$-channel diagrams into one stringy diagram.

The end of my answer sketched the modern history since 1997 which showed that the idea to use string theory as a description of the strong force was revived and put on firm ground by the AdS/CFT correspondence which shows that string theory on certain backgrounds is exactly equivalent to particular gauge theories. So the initial concepts - mesons as open strings etc. - were also right but one had to use a higher-dimensional, curved, and more structured background of string theory to describe QCD - or, more reliably, the $N=4$ gauge theory.

They were initially satisfied, happy, nice answer, blah blah blah, but it became quickly clear that the satisfaction is fake. They clearly didn't understand a word.

New battles begin

A user named Ron Maimon complained that the one-dimensional character couldn't possibly explain the world sheet duality because of some clearly flawed arguments in which Maimon was saying "rubber band" but he really meant "generic point-like particles with interactions designed in the same way as for generic point-like particles". So I was telling him that he was using a term but he didn't really take the term into account. He was saying one-dimensional but he was thinking zero-dimensional. I learned that this attempt to explain some trivial things to him couldn't lead anywhere because the well-known insight issues obviously violate some religious sensibilities of this guy.

Well, I still tried a few more times. ;-)

This exchange with him gradually transformed to the debate on uniqueness of string theory. Can you add random ad hoc point-like-particle-like interactions to string theory? So I was trying to explain him that you can't do it because that would cripple the consistency - well-definedness in the UV or unitarity or Lorentz symmetry - of the theory. Again, this irrational person just can't get it. It's like trying to explain to a fundamentalist Muslim that Mohammed was primarily an aggressive medieval terrorist. Certain things are taboos for certain people.

I don't know why they are but they are.

Needless to say, the uniqueness of string theory - the impossibility to deform it without spoiling its consistency - is a key technical property of the theory. It means a very specific thing, may be demonstrated by very specific techniques, and understanding why it's true is completely essential to understand why the term "string theory" exists and why physicists study it at all. If something prevents you from learning the technical insights linked to this point, you can't really start to understand what string theory is.

Everything we know about string theory may be classified as parts of our knowledge of the answer to a question that could a priori have many answers - except that we may use maths and logic and the criteria of consistency to figure out that the answer isn't arbitrary and we may show which of the answers may occur and which of them can't. For example, a maximally decompactified superstring/M-theory background could have any spacetime dimension. But the right answer is $D=10$ or $D=11$, respectively. When a background is fully specified, or initial conditions are fully specified, everything is determined.

This is really true not just in string theory - it's true in all sciences and any rational reasoning that makes any sense. We ask questions that may a priori have almost arbitrary answers but we may collect evidence, arguments, proofs, and calculations that show that some (or almost all) answers are impossible (or at least disfavored, if the arguments are not as rock solid as in string theory) and only one (or a subset) of answers is possible (or preferred).

Obviously, if someone still thinks that he can add arbitrary interactions similar to those of point-like particles to string theory without spoiling its consistency, it shows that he has understood neither the point, nor the power, nor 1% of the material in basic textbooks on string theory. Obviously, if this were possible, i.e. if "anything goes" were a valid assumption, it would be completely silly to study string theory (or any other theory, for that matter). "String theory" would actually be a meaningless term because its meaning could be modified in any way you want.

But string theory can't be modified, not even by an infinitesimal mutation. It can't be deformed. This property may be unusual because all previous theories could have been deformed but string theory can't, OK?

The exchanges with a user named Marek - apparently some grad student in Prague or something like that (whom I do not know) - became equally hopeless. He said that string theory can't really be a theory of hadrons, so what it is? So I reiterated that with the AdS/CFT correspondence, it was understood that the original motivation of string theory is also valid because string theory offers an alternative - and equally accurate - description of the strong force i.e. an equivalent description of physics of gauge theories. It's not quite settled for ordinary QCD but it is totally established for many supersymmetric examples among which the $N=4$ theory is the most familiar representative.

This has been known for almost 15 years and before this exchange, I wouldn't believe that this could possibly be controversial on a physics server in 2011. Well, it surely is! So when I said that string theory is both a theory of quantum gravity as well as a theory of all interactions as well as a theory of the strong force only, depending on the background, I was told that my comment was an "ideology" and "propaganda". I guess that the tobacco industry is behind this one, too. Well, it's because I also learned that Mr Marek had an "allergy" towards similar statements. ;-)

Holy cow, what is "propagandistic" or "ideological" about these totally technical statements? Something like 17,000 papers show that the AdS/CFT correspondence works in any test that has become doable and there are very many of them and they became very diverse. It shows that string theory - a quantum gravitational theory - is a perfectly valid and accurate description of seemingly non-gravitational phenomena in nuclear physics (and elsewhere).

If someone is "allergic" when it comes to demonstrably correct answers to questions he has asked himself, he should obviously not be trying to do science because such an "allergy" is a condition that is entirely incompatible with science - or any rational reasoning, for that matter. Science is about learning new things so you should better not be allergic when it comes to new insights.

Similar pompous "allergic" fools exist everywhere but make no doubts about it, the continuing socialist Academia in the Czech Republic is an incubator of this stuff (fortunately not a big one). It's a place that is de facto inevitably producing worthless science kibitzers of the Shmoit kind - imagine hundreds of Shmoits within the socialist physics institutes in the Czech Republic who are inventing irrational excuses and "allergies" so that they don't have to learn anything and they can be getting salaries without doing any research that makes any sense. The real high-energy physics at the top universities is also bad and produces "allergies", doesn't it? So we in Prague don't have to do that.

This "active opposition" wasn't quite created during communism. It's a sign of low-quality scientific institutions we had even in the 19th century. Almost all key historical scientific figures on the Czech territory were either German-speaking or imported from other countries or both. In 19th century, we had this Czech Shmoit - a very high-positioned Czech "physicist" - who was producing lots of rants arguing how Maxwell was not even wrong about everything.

Needless to say, the persistent tolerance for this attitude and active justifications of low quality - and for people who don't hide that they don't want to do science properly and who want to sling mud at the most important research throughout their lives instead (and bring emotions to the stupid masses) - is one of the main reasons why the Czech high-energy theoretical physics has produced pretty much no results before the era when Czech string theorists began to leave the sterile environment.

All those obvious observations made it even harder for me to understand how someone in the U.S. could possibly justify the vitriol by various Shmoits. Those people - often working just meters from real top physicists - are the American counterparts of the post-socialist sterile useless semi-educated unproductive parasites who may only complain about the evil imperialists while they haven't produced and will not produce anything beyond shit in their whole life. I have been immensely offended by the first and second person who indicated that I should be treated on par with these Shmoits - and I am still offended by such suggestions. They're just idiotic worthless piles of feces - how could you possibly say something along these lines?

But there are many stupid "ordinary" people who love to buy such thing because they hate that someone is smarter than they are. They hate when someone finds an important result, especially if they couldn't find it themselves.

#### snail feedback (2) :

Was always looking for answers from the educated. It's too bad it's falling away from an ideal for you Lubos. I wish I had know earlier it existed.

Best,

Hi Lubos, It's Ron Maimon.

I read this blog post with amusement, because I am amazed that you think that I was somehow against string theory uniqueness. You will not find a more adamant defender of string theory than me. I am 100% sure that the theory is consistent, nondeformable, unique, everything everyone says.

What I was trying to tell you is that this uniqueness does not come from the 1 dimensional nature of the string. It comes from another assumption that is glossed over by people nowadays, for essentially political reasons.

The only reason that string theory is unique and non-deformable and all that is that it is a holographic theory, that it obeys the gravitational holographic principle. No holographic principle, no string theory. No holographic principle, no uniqueness. The holographic principle is to string theory as the equivalence principle is to GR, it is the unifying physical insight that gives the theory credibility as a theory of everything.

The original statement of a proto-holographic principle was Geoffrey Chew's S-matrix principle, that the spectrum of the theory should be determined by the fact that the exchange of particles in the spectrum is what determines the interaction, and that these interactions then lead to self-consistency conditions that determine the spectrum. All of early string theory was devoted to making the bootstrap work.

From the bootstrap, you learn that the worldsheet exchange is Regge-soft in Regge limits, and that it is double-counting to sum over T-channel and S-channel string exchange.

Without the bootstrap, only assuming a string spectrum with some free action at some energy range, you don't get doodly squat.
There are bazillion theories of 1-d extended objects, with a string-like spectrum, but which are not dual strings, because they interact through point-particle exchange. At high energies, you resolve the point-nature of the strings. The string excitations do not include the full spectrum, but they can include a significant fraction of the low energy spectrum, perhaps all of it.

These fake-strings, I call them rubber-bands to distinguish them from honest to goodness dual strings, are boring and non-unique. They have nothing to do with the real string theory, except as a counterexample to the ridiculous claim that to derive string theory all you need is the assumption that objects are extended in 1 dimension.

Once you have the bootstrap, the bootstrap demands that the only interaction of the string is through the exchange of string states which are found in the spectrum. This gives such great constraints on the spectrum that the full string theory is uniquely determined. But this condition cannot be derived from the spectrum itself.

The best way to state this assumption nowadays is to state it in full holographic form: the string must be considered to be a 1d extended extremal black hole, so that every object in the theory is an oscillation mode of the string, because every object in the theory can fall into a black hole. This guarantees that summing over string exchange is summing over everything, and that summing over ultraviolet strings with high energies is the same as summing over infrared long strings, so that the theory is ultra-violet soft.

The world-sheet duality is a property of dual-string exchange which comes directly from the bootstrap. It is deemphasized in modern treatments because people want to dismiss the contributions of Geoffrey Chew, Stanley Mandelstam, and all the other S-matrixers who were laughed at for so long.

You should celebrate their amazing achievements instead of dismissing them. They didn't get string theory by fluke. They got it because the bootstrap is fundamentally the only correct way to do fundamental physics.