The String Coffee Table

Very nice review, fair and balanced.

One quip, the SuSy calculations on the CC while they do cut the problem in half are rather troubling, b/c in principle there is absolutely nothing wrong with the calculation. They seem robust! Whereas for the vanilla SM such a calculation is rather unnatural and one could speculate about all sorts of ways out of it. 120 orders of magnitude or 60 orders of magnitude is still (at least to my mind) god returning ‘error, man made mistake’

I think that is what Dr Woit was reffering too -shrug-

“Because of the sensitivity to the UV cutoff?”

Yea more or less. Also that the hamiltonian in globally supersymmetric field theory is an absolute quantity (related to the supercharges rather trivially with the antibracket) so the whole thing is calculated explicitly and rather trivially with a simple scalar potential and the vaccuum fluctuations.

You might worry that the setting is absurd as well, since all of this is flat spacetime calculations. The SUGRA calculation in curved spacetime thus is far more robust and you still retain the rather nice satisfying and clear form the hamiltonian has as well as the ease of the calculation. Its hard to imagine what went wrong.

Aaron,

It seems likely that the S.T. community can expect more of the kinds of critiques that are coming from Woit and Smolin. Woit has the advantage of not noisily promoting a particular alternative, and therefore being more likely to be seen as objective.

I think that outsiders are more likely to be convinced by thoughtful reviews of Peter’s book, such as the one you just posted, which explains your reasons for studying String Theory, rather than the outright dismissal of all opponents as crackpots, morons or losers.

Aaron, thanks for the sensible review. I’ll try and write up a bit of a response on my blog.

Haelfix,

Yes, you’re right about the point I was trying to make. Before you bring in gravity, in the SM the vacuum energy is ill-defined, in a supersymmetric theory the vacuum energy is the order parameter for SSYM breaking and we know it has to have a scale of at least 100s of Gev. Your quantum gravity theory has to somehow have a plausible way of making this go away.

Especially given the other serious problems caused by supersymmetry breaking, this seems to me evidence that going to supersymmetric extensions of the SM doesn’t improve matters, but introduces new, intractable problems.

I realize this is splitting hairs and everyone knows this already and the statement is rather silly.

Its just that the SUGRA calculation is sort of the natural setting where you would think the CC problem would be well formulated. You have gravity and you can have curved space, and the statements are now measurable. And from an aesthetic point of view, its simply two terms that have to conspire to cancel to fantastic accuracy. All I was getting at, was that simple statement that it didn’t seem like there was much wiggle room there.

This entire thread just reassures me that I made the right decision to leave physics and go to work on Wall Street :)

You know it is not easy for us lay people following these discussions.

If there has been some solifdification of the “points of view” here having read Aaron’s work, could there be a “short list” summarized/synopsized, as to why Peter’s book may not be suitable for/against the references to “string theory people” who are doing research in regards to quantum gravity?

As you know, some of us lay people are not that smart and could have easily fell under the spell of delusions, perpetrated by scientists for and against the use and advancement by way model apprehensions.:)

This thread exhibits some remarkable self-similarity properties. Has anyone ever considered studying critical exponents of blog threads?

The first full paragraph on page 4 of Aaron’s review starts with

It is true [..] that there really is no such thing as ‘string theory’. It is, rather, a collection of partial theories and calculational techniques bound by physical intuition and conjecture.

I was surprised when I read this first. A “collection of partial theories bound by intuition and conjecture” does not sound like anything which would allow tests like described in the next sentence:

[…] this skein is remarkably robust. Calculations that have the possibility of destroying this structure invariably turn out to reinforce it.

Of course I immediately agree that the study of string theory involves a lot of partial theories, the links of which are often conjectural.

But I think it is important to point out that there is, apart from - and above - intuition and conjecture a binding force, which distinguishes the study of “string theory” from the study of a subjective menu of partial ideas that happen not to contradict each other.

Compare with some other field of physics. Say classical mechanics. There is a unifying essence, namely Newton’s laws, or Hamilton’s equations, if you like. People want to study this.

But only in the most simplest of situations can one actually practically study this essence itself. Most interesting phenomena in the world are - or at least have been for a considerable time of history - not directly accessibly using the fundamental equations. Often, they require inventing “new theories”, like thermodynamics, theory of friction, theory of fluid dynamics.

Today most of these “new theories” can be derived pretty well from first principles. But for various periods of history, scientists believed in the correctness of Newton’s laws but had to accompany them nevertheless by a “collection of partial theories and calculational techniques bound by physical intuition and conjecture”. Bound - that is - among each other, but, most importantly, bound by conjecture and intuition to the essence that they are thought to be derivable from in principle, namely some microscopic dynamics following Newton’s laws, or maybe following the laws of quantum mechanics, if that’s necessary.

If I remember correctly, there are aspects of something as ordinary as friction (certain special sorts of friction for certain materials) which even today remain puzzling, in that it is not clear precisely how they follow from a microscopic description.

The same case could be made for particle physics. While it is believed that the essence of particle physics is the study of the standard model, it is a fact of life that for describing most interesting phenomena, notably bound states of nucleons, one needs to resort to “theories ” (models) that are bound to the standard model only by intuition and conjecture. We expect them to be derivable from the essential concept itself, but we do not know how to do it.

I am emphasiziing this point because on the blogosphere one could frequently here various layman ask rethorically for “the equations” of string theory, implying precisely that the whole thing is made up from subjective choices without really being a “theory” which you could hand somebody with the words “this is what I mean by string theory, study this”. Like, for instance, you could do with classical gravity by handing somebody the Einstein-Hilbert functional.

For this reason it might be worthwhile to state clearly in a popular account like the above review is, what precisely it is in essence that people are studying when they are studying string theory, notwithstanding that this essence may incarnate itself in various different guises.

And - please correct me if you think I am wrong - the essence is this:

The study of string theory is the study of quantum theories that have a perturbative expansion which is given by a loop expansion in terms of Feynman-2-graphs computed using 2-dimensional gravity.

Whatever else you do, if it is not bound, maybe just by conjecture or intuition, to this essential principle, you will hardly be doing string theory.

For instance one can go ahead and study linearly-extended objects governed by an action principle involving a BF-theory ($\to$). Working out the dynamics, one finds that it does indeed describe propagation of string-like objects.

In a world where “string theory” would be just anything bound by intuition and conjecture, one could happily go ahead and declare that this particular theory is one of the many that constitute “string theory”.

But that’s not what happens. The dynamics of the strings in these BF-theories is not governed by Feynman-2-graphs with amplitudes governed by worldsheet gravity. So it’s something else, not “string theory”.

Of course it could happen, and I would be positively intrigued if it were true, that these BF-theory strings are related to one of the satellite theories that are indeed, slightly by conjecture and intuition, related to essential string theory proper: namely to the theory of D-branes and D-strings in particular.

With some “string theory” papers on DBI-actions and things like that, describing D-brane dynamics, one could get the impression that the theory investigated in these papers is just yet another random theory, that we happen to like to add into our “string theory” portfolio.

But of course this is not a matter of our free choice. The DBI-action, while it can be studied just by itself, is, by more or less robust arguments, believed to be derivable from the assumption that there is a theory whose perturbative expansion is given by a string theory S-matrix.

The same applies to all other topics studied in string theory. For instance, people are very interested in extensions of classical gravity which involve fields known as RR-fields. (Of course Aaron and Jacques know all this, much better than I do. I am just stating it for the record and for the general reader)

This is curious, as precisely for those fields it is not known how to relate such theories to a worldsheet description. But it is strongly believed that, while not known at the moment, it is possible in principle. Hence the “theory of RR-backgrounds” is related to the main body of string theory, partly by conjecture and intuition.

If, however, there were no indication at all that RR-backgrounds arise in quantum theories that have perturbatiuve expansion involving a string theory S-matrix, then we would not consider RR-backgrounds part of string theory. Would we?

Similar comments apply to Matrix Theory, AdS/CFT and so on.

I apologize for having probably emphasized the obvious. It just struck me as an important point in the discussion of the raison d’être of string theory.

Unfortunately, I am a rogue student who needs lots of help sometimes. :)

All the points presented Urs, while demonstrating the materialization of “new methods (strings),” helps, not deters people from expanding the frontiers of science?

Historically, and most notably Newton and calculus?

So the method of maths gain ground when it is put into perspective. From Weinbergs first three mintues, to the microseconds that “strings constitue” in the expression of our universe? A microscopic/quantum analysis.

That, is advancement in our thinking. Qui! Non?

Where a dictionary proceeds in a circular manner, defining a word by reference to another, the basic concepts of mathematics are infinitely closer to an indecomposable element”, a kind of elementary particle” of thought with a minimal amount of ambiguity in their definition…also..Each generation builds a mental picture” of their own understanding of this world and constructs more and more penetrating mental tools to explore previously hidden aspects of that reality.

It’s interesting to note the prominent String theorists reaction to books like
“Not Even Wrong” and “The Trouble With Physics”. Case in point, Lubos Motl’s “review” of Lee Smolins’s book - “The Trouble with Physics”. About all that Motl has to say in review is that
it is a very weird book, full of non-sense, that made him very angry. Probably that’s because string theory is a rather weird piece of nonsense itself, and now Lubos Motl and his motley crew of strung-out cohorts will have to find some new,
but equally irrelevant and mathematically
elegant pretense at doing physics.

I think it’s no fair to layfolk to say one has computed the entropy of black holes when one really means extremal or near-extremal black holes - purely theoretical entities that don’t exist in our universe. Layfolk would never guess you meant this. Why not just be clear?

Btw, I think somewhere you wrote “without precendence” when you meant “without precedents”.

I just finished reading this book. The author correctly describes the current status of string theory. However, he does not specify some achievements in other directions and how string theorists try to suppress these achievements. For more info about them visit http://archivefreedom.org/.

Also in page 181 he writes that “Einstein devoted most of his career to fruitless attempt to unify electromagnetism and gravity using the sort of geometric techniques that had worked in the case of GR.” However, in 2002 a Russian scientist (S. Shahverdiyev) formulated geometry underlyuing electromagnetism and proposed unified model of electromagnetism and gravitation using principle of geometrization, at least at the classical level. For detailes see hep-th/0205224.

Any comments and corrections are greatly appreciated.

OK, Aaron, here goes :)

1) With 10^500 possible “string theories” one can easily say string theory predicts nothing. Indeed, when “Pope” Witten falsely claims ST “predicts gravity” it’s clearly a self-serving claim made to secure more funding. No, neither ST nor LQG actually “predict” gravity.

2. After 25+ years, ST has yet to make a SINGLE falsifiable prediction - it’s a dead-end.

3). Recently Lenny Suskind said that the existence of gravity, the existence of particles, and the existence of natural laws “prove” ST - what nonsense! The breath-taking lack of logic amazes me. He further went on to indulge in ad hominem attacks on Woit and Smolin. Personal attacks are apparently what string theorists do best, since they can’t produce any real science.

4). ST can’t even decide the dimensionality of space-time - is it 10,11,26, all of the above, none of the above?

5). “Stringers” claim the missing dimensions are rolled up into tiny CY manifolds too small to be measured. How convenient! The problem is real science deals with measureable properties. One might as well say some unobserved planet somewhere is made of green cheese…