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Hi, I am a string theorist and a publicist.


Aug
28
awarded  Good Answer
Aug
27
awarded  Nice Answer
Aug
21
comment Why are the antimatter compositions of neutrons and protons different? Why by about 1%? References?
Hi, the keyword you may want to search is "parton distribution functions" (acronym PDF; too many references). They are functions telling you how many quarks, antiquarks, and gluons with various momenta are included in the proton or neutron. Because $p$ and $n$ differ by one quark, $u$ and $d$, and because the mass of these two quarks differs - 4 or 7 MeV and equally for the antiquarks, it follows that the heavier antiquark (anti d) will start to disappear faster etc.
Aug
21
comment What are the details around the origin of the string theory?
Dear @Ron, it's very interesting. But could you please be a little bit specific what the "hidden [bootstrap] assumptions" are? It's hard to imagine anything real behind your words at this point. I was just innocently stating that the particular deformation of string interactions you proposed was inconsistent. As far as I can say, one can prove it without any assumptions that would have to remain "hidden". You: "The fractal dimension of the embedding might be nonsense for real strings, but that's not the point." - OK, but what is your point then? Fractal dimension depends on UV physics.
Aug
20
comment What are the details around the origin of the string theory?
By the way, your "counting of the intersection dimension" in string theory is crap, too. There is absolutely no reason why such ad hoc concepts should be well-defined in a physical theory and they're not. Much more generally, the concept of "total spacetime dimension" is extremely subtle - the number of "Planckian" or "stringy" sized dimensions is always ambiguous and different dual descriptions generally yield different answers: ST isn't a fully local QFT, after all. Only large dimensions - much larger than the string/Planck scale - can be "unambiguously" counted.
Aug
20
comment What are the details around the origin of the string theory?
Dear Ron, you write: "I can construct an example field theory with low energy 'strings' and high energy crap". Great. You may construct such a "theory". But I may easily prove why it is crap and not a consistent theory i.e. not string theory. You can't modify string theory at high energies or low energies without spoiling its consistency. Of course, you may produce lots of crap but crap isn't the same thing as a theory in physics. One may prove that string theory can't be added ad hoc point-like-particle-like interactions without spoiling its consistency.
Aug
20
comment What are the details around the origin of the string theory?
Dear @Ron, Brandenberger-Vafa or string gas cosmology etc. isn't a paper about the existence and character of fundamental interactions in string theory; it is a paper about the "derived" impact of geometrical arrangement of strings on cosmology. Whether the strings are intersecting or not is irrelevant and the rules for the interactions of strings are independent of the spacetime dimension and they work in such a way that you may neglect the possibility of self-intersection as a measure-zero problem: the world sheet is always smooth around the interaction "point", even in $d=2$.
Aug
20
comment What are the details around the origin of the string theory?
Dear @Marek, the statement that string theory is a single theory is not ideology: it is a key technical property of the theory. Even if you decided to call it ideology - be my guest - it is a totally crucial ideology to understand what the theory actually is and what it is not. So it's just too bad if someone cannot learn these crucial technical things without "allergies". Arivero, Ramond's string - and Neveu-Schwarz string - wasn't really an "origin of string theory". String theory had "origin" as bosonic string theory which has no fermions. All SUSY/fermioncs strings are "new".
Aug
19
comment What are the details around the origin of the string theory?
What I want to say is that it is the opposite of the truth to suggest that string theory might be a theory of "anything". All previous theories in physics admitted some deformations or continuous parameters that were labeling different theories - but string theory doesn't. For example, interactions of rubber bands that would be nonlocal on the world sheet would also break spacetime locality and spacetime unitarity and spacetime Lorentz symmetry, and so on. Consistency prohibits all pathological mutations of the theory and string theory is totally determined by consistency.
Aug
19
comment What are the details around the origin of the string theory?
Concerning your second comment, @Ron, once you adopt the assumption that the physical objects are made out of strings, the rest of the theory - including all the details about the ways how these things may interact - is completely determined by consistency - unitarity or, equivalently in the light-cone gauge, Lorentz symmetry. There is not a tiny bit of choice or freedom to "adjust" string theory. String theory is a single, totally rigid structure without any adjustable dimensionless parameters and it has a totally well-defined set of solutions. There's no way to "deform" string theory.
Aug
19
comment What are the details around the origin of the string theory?
Dear @Ron, 1-dimensional objects almost never self-intersect in spacetime of higher dimension of 3+1, e.g. $D=26$ or $D=10$, so this is a measure zero problem and you may completely forget about it. An even more obvious "measure zero" situation that may be ignored is when all atoms of a rubber end are located at the same point - which, by the way, can't happen at all if the rubber bands are made out of atoms such as the real rubber bands. The bulk of the dynamics of a string or a rubber band - it's totally analogous in both cases - is given by the dynamics of 2-dimensional world sheets.
Aug
19
comment What are the details around the origin of the string theory?
In other words, @Marek, the key comment is that string theory is a "theory of everything" - which I didn't really use: I said that it was both a theory of gravity as well as the strong force, and the strong force emerges from string theory in several different ways, either as a "part" of a full description of all forces, or - via AdS/CFT - as "just QCD" from an AdS background. This seems to be the very point of your question, at least the followup questions you added. So I can't understand why you're so hysterically trying to hide your head to the sand when I am telling you the answer.
Aug
19
comment What are the details around the origin of the string theory?
Dear @Marek, you write: "I have no interest in terms such as 'theory of everything'". If you're not interested, why did you ask a question exactly about this question on Physics Stackexchange? Your comments about your being interested in a particular "model" shows that you still misunderstand the structure of string theory. String theory is not "many models". String theory is a single, unified, totally inseparable theory. You can't cherry-pick string theory. It's one set of equations that has a large landscape of solutions. All of them are valid, all of them show different phenomena.
Aug
19
comment What are the details around the origin of the string theory?
Just to be sure, non-SUSY QCD is ill-behaved from many viewpoints but there are many other gauge theories with as low as N=1 supersymmetry whose string theory dual is understood more or less rigorously, almost on par with the N=4 case. Various bases of the conifolds, Einstein spaces, etc., and one gets gauge theories with various kinds of chiral supermultiplets. So as I have tried to emphasize, but apparently unsuccessfully, the original motivation of string theory was proved correct as well, one just needed some extra work and understanding of subtleties of the right backgrounds.
Aug
19
comment What are the details around the origin of the string theory?
Dear @Marek, well, not quite, as I have indicated, the right background of string theory is the correct theory of hadrons. We call it the "QCD dual". This isn't quite perfectly and accurately understood for ordinary real QCD but it is beautifully understood for a very similar theory, the N=4 gauge theory in d=4, which is exactly equivalent to type IIB string theory on AdS5 x S5. The equivalence is known as AdS/CFT. So strings can work as those things - this is what much of the last 15 years were all about. String theory is all of these things and much more.
Aug
19
comment What are the details around the origin of the string theory?
Ron, when you say that rubber bands could distinguish the s-channel and the t-channel, it seems that you are using the word "rubber band" but you are actually not treating them as rubber bands. Rubber bands, by definition, are one-dimensional objects. One-dimensional objects inevitably have 2-dimensional histories in spacetime - world sheets or "rubber sheets" - and these histories "geometrically" always work like in the string case, and this geometry is enough to see that no qualitative separation of s-channel and t-channel diagrams may exist.
Aug
19
comment What are the details around the origin of the string theory?
Dear Ron, I don't think that your comment is right. Strings in string theory are "relativistic rubber bands" while normal rubber bands are made out of atoms that pick a special frame and obey a Lorentz-breaking world volume theory, but this is the only difference. Rubber bands, much like strings, would still respect the world sheet duality. Well, at least any rubber bands that could be continued to the Euclidean spacetime. In particular, you can't create a whole rubber band at a single point. Rubber bands are 1-dimensional so you may only create them 1 point/atom at a time, one after another.
Aug
19
comment What are the details around the origin of the string theory?
Dear Marek, string theory always contains gravitons when it's studied correctly and consistently, so the confusing massless spin-2 mode was always there and was always confusing for anyone who tried a strong interaction-like interpretations. In fact, the bosonic string theory also had a tachyon which is much worse. ;-) For a few years, there was a confusion about such things - whether you could move the spectrum, choose any spacetime dimension you wanted etc. so there was a lot of unjustified hope it would work. Within years, $D=26$ and tachyon+graviton's inevitable existence was settled.
Aug
19
answered What are the details around the origin of the string theory?
Aug
19
awarded  quantum-mechanics