Talk:String theory/Archive 4

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I don't really get how strings work.

Anything that is infinitely thin like a string and has mass seems strange, because the smaller the volume of it that you look at, the more dense it appears. The smallest point of it would be so dense its escape speed would exceed the speed of light and it would become a black hole, losing its material properties since black holes only have gravity and rotation. 154.20.194.233 (talk) 06:19, 15 June 2010 (UTC) ...

It is possible on subatomal levels to go faster than speed of light. Mass is the string property which depends of the wave level.

Basecaly, string is a fast moving source (which can even be in more than one place at the same time) which is a source of the wave-particle field. All the properties of the coresponding particle depend on the oscilations on that source string.Čeha (razgovor) 09:01, 6 July 2010 (UTC)

I don´t like the first picture

It puts me off reading. I would remove the picture or change it with another one. —Preceding unsigned comment added by 190.188.3.11 (talk) 01:24, 14 July 2010 (UTC)

What's new ?

Anything new in string theory in the last 10 years? —Preceding unsigned comment added by Alphachapmtl (talk • contribs) 20:31, 5 August 2010 (UTC)

Critical dimension and consistency

The article currently states that the critical dimension of string theory is not fixed by any consistency condition. This is pretty much orthogonal to what I know about string theory. My understanding is that the critical dimension follows from the requirement that the conformal anomaly present in string theory is absent, and that this only happens if there are 26 (or 10 for superstrings) spacetime dimensions. Of course, my info on this may be dated, but my gut feeling is that the work on super-/subcritical string theories is getting WP:UNDUE weight.TimothyRias (talk) 15:35, 6 September 2010 (UTC)

What?

This needs to be simplified greatly. I'm an university student who is used to tackling complex academic texts (granted, mostly humanities related), but this makes no sense to me. Layman's terms simplified explanation would be useful. The way I see it encyclopedia is aimed at general public, it is not reference tool for theoretical physicists. 203.206.49.48 (talk) 15:50, 22 March 2010 (UTC)

only amenable to a mathematical explanation. --Dc987 (talk) 05:46, 31 March 2010 (UTC)

I agree with the OP, its not like its impossible to explain string theory in "layman's terms"; there's plenty of sources where such explanations can be found. We shouldn't force users to research the theory off-site to understand it. What's the point of putting an article in language that only a person who already knows about the subject can understand? Deliberately phrasing the description of a theory to make it seem complicated and advanced should violate some Wikipedia standards about giving undue weight. You don't see the evolution or gravity theory pages expressed in such complicated terms, at least not within their respective headers. --IronMaidenRocks (talk) 03:39, 15 May 2010 (UTC)

I agree as well. I can read msot of it fine, but it sometimes requires me to re-read sentences. I think that has to do with the terrible word placements rather than "difficult words." 64.234.0.101 (talk) 17:49, 31 July 2010 (UTC)

Definition of 'science' - theoretical physicists have to realise that experiment is not the criterion for science. In geohysicsa, astronomy and in many fields of human sciences (history, political sciences) events occur only once and cannot be repeated: you cannot experiment of various possible leads of Sarajevo shots that started the WW I. You cannot experiment with Tungusta impact. You cannot experiment with WTC attack. You can only observe them. That's why I modified the end of the first chapter. —Preceding unsigned comment added by Martti Muukkonen (talk • contribs) 19:58, 30 October 2010 (UTC) ÷

Testable does not mean just laboratory experiments, it includes observations of events such as astronomical ones and historical ones. So if someone came up with a new theory of comets, which could be confirmed by examining past impact records including the Tungusta impact. The text you added seemed to confuse this somewhat: yes, repeatable laboratory experiments are better from the point of view of proving something, but that's not always possible. Often science has to be done after the event, for a whole number of reasons. Nor is this a particular property of physics, it's a property of all science.

The weakness of string theory is it makes no predictions at all, or at least none that are different from existing theories such as QM and relativity at energies we can measure. But this well understood b←y all scientists, and as this article is intended for quite an advanced readership I don't think it needs elaborating further. It is explained further down at some length, as it's an important aspect of the theory, but much of that is too advanced for the introduction.--JohnBlackburne^words_deeds 20:31, 30 October 2010 (UTC)

there is no reference to other sources that can help the reader clarify the concepts, linear algebra works with multiple dimensions, but it is not even mentioned as a starting point for clarification. —Preceding unsigned comment added by 130.76.64.117 (talk) 02:01, 19 November 2010 (UTC)

Cutting the lead

While the lead was clear and very nice in wording, it was way too long, so I cut it so it has max. 4 paragraphs and should fit in 1 screen. It can be still shrinked a bit, however I don't think simply removing more content from the lead would be any good. In my opinion the better approach would be to put more work into enlarging "Overview" section, so some informations just won't be needed in the lead anymore. So if someone is inclined to make a longer general introduction, please do it in this section. I will happily make further compactification of the lead. -- kocio (talk) 14:54, 6 September 2010 (UTC)

One thing to be aware of is that WP:LEAD also requires that the lead reflects the content of the article.TimothyRias (talk) 15:37, 6 September 2010 (UTC)

For me "how long is the lead?" and "is it a good summary?" are two somehow orthogonal questions. The {{Lead too short}} template currently includes the summary problem, however in my opinion "may not adequately summarize its contents" doesn't always mean "expanding the lead to provide an accessible overview of the article's key points". It's rather a problem of consistency with the rest of the article, not the length of the lead, even if it's related most of the time. In case of such a big and non-obvious article someone really should overlook the whole article and make a new lead out of it to satisfy both rules, which is unfortunately far beyond my skills. kocio (talk) 10:48, 8 September 2010 (UTC)

Consciousness as vibrating strings

Is it true that in string theory consciousness is like electromagnetic waves and electromagnetic brain waves are the same thing as vibrating very long strings in space? So Consciousness in string theory is vibrating strings and sinusoid with many over waves of those vibrating strings is the same as electromagnetic brain waves sinusoid with many over waves? —Preceding unsigned comment added by 84.240.9.58 (talk) 17:57, 23 October 2010 (UTC)

No. 66.66.5.195 (talk) 02:29, 14 December 2010 (UTC)

That sounds more BS than string theory. But perhaps only slightly. —Preceding unsigned comment added by 121.209.152.190 (talk) 19:10, 2 January 2011 (UTC)

History

What has happend since late 1990s? I don't see any more in the history section. Is it still thought of as a viable theory? —Preceding unsigned comment added by 74.180.160.27 (talk) 14:18, 20 November 2010 (UTC)

Exaggeration regarding testability and science

"The theory has yet to make testable experimental predictions, which a theory must do in order to be considered a part of science."

That sounds suspiciously like some kind of advocacy of a particular position. If mathematics is not "a part of science", then someone had better tell that to the College of Natural Sciences at my local university. Also, I've heard string theorists make all kinds of predictions, just mostly not ones that can be tested at any currently-reasonable cost. Can someone with less bias please find a more neutral way to phrase this? 146.6.204.155 (talk) 18:58, 7 February 2011 (UTC)

Possible strings as fibers instead of circles.

I have a proposal for those with open minds: If you look at the way a transmitting antenna works, different lengths produce different frequencies. I think it may be possible these strings are in fact different lengths of fibers, not circles, vibrating at different frequencies and different strengths that harmonically interact with one another and either attract or repel on a sonic level. — Preceding unsigned comment added by Dgm76513 (talk • contribs) 08:57, 11 March 2011 (UTC)

Testable?

Brian Greene was on NPR recently talking about how this maybe tested. That nasty little sentence is out of date.

As mentioned under falsifiability, Particle physicists from the Vienna University of Technology and Institut Laue-Langevin (ILL) have developed a new technique named Gravity Resonance Spectroscopy Netdragon (talk) 19:53, 23 April 2011 (UTC)

I'm removing that sentence. It's fallicious. Netdragon (talk) 19:53, 23 April 2011 (UTC)

Falsifiability

First, there's a question about whether Popper required that falsifiability be specific to the theory in question. The answer is no (at least to my knowledge), he didn't, because such a criterion would make no sense. How would you decide which theory is the "original", and therefore legitimately falsifiable, and which is the derivative one?

Second, someone asserted that falsifiability is necessary but not sufficient for a theory to be scientific. I don't think that's the case (and by the way, wiki contradicts itself on that - in one place at least it agrees with that, but in others it contradicts it and says theories are scientific by Popper's criteria if and only they are falsifiable). Popper himself says the following:

"In this way, the recognition of unilaterally decidable statements allows us to solve not only the problem of induction (note that there is only one type of argument which proceeds in an inductive direction: the deductive modus tollens), but also the more fundamental problem of demarcation, a problem which has given rise to almost all the other problems of epistemology. For our criterion of falsifiability dis- tinguishes with sufficient precision the theoretical systems of the empirical sciences from those of metaphysics..." (The Logic of Scientific Discovery, op. 316)

This seems quite clear to me - falsifiability is (according to Popper) sufficient (and of course necessary) to distinguish between science and metaphysics. Therefore as far as I can tell that section is correct as written, and I will remove those tags after some time unless someone else comments here and disagrees.Waleswatcher (talk) 18:28, 14 January 2011 (UTC)

• Correct. Popper didn't intend for it to be a strict requirement. IN FACT, Popper was a stark critic of logical positivism even though logical positivism was founded off Popper falsifiability. Netdragon (talk) 19:52, 23 April 2011 (UTC)
• Correct. Falsifiability is sufficient but can be overkill
  • I think the way it was described is fine and left it alone. The original writer isn't saying falsifiability isn't enough, but that it just isn't compelling if there are no unique predictions. See if the way I re-organized things makes this more clear (and didn't make a direct statement that string theory has no unique predictions (yet it still is implied so maybe a slight rewording is in order) Netdragon (talk) 20:39, 23 April 2011 (UTC)
• Furthermore, the argument that there is no way to test quantum gravity is bogus and outdated. Particle physicists from the Vienna University of Technology and Institut Laue-Langevin (ILL) have developed a new technique named Gravity Resonance Spectroscopy which will serve that purpose Netdragon (talk) 19:52, 23 April 2011 (UTC)
  • Added Netdragon (talk) 20:39, 23 April 2011 (UTC)
• Hence, the whole section on testability needs to be overhauled Netdragon (talk) 19:52, 23 April 2011 (UTC)
  • I cleaned it up, but only removed quotes (note references). The rest was just moving things around other than adding a note about Gravity Resonance Spectroscopy. Netdragon (talk) 20:39, 23 April 2011 (UTC)

"11-dimensional space" was corrected to "11-dimensional spacetime"

In the opening introduction, it mistakenly referred to "11-dimensional space". I corrected it to "11-dimensional spacetime". - Brad Watson, Miami 72.153.60.84 (talk) 12:47, 14 April 2011 (UTC)

I would agree with 11 dimensions. — Preceding unsigned comment added by 203.83.248.32 (talk) 05:55, 3 June 2011 (UTC)

Good Article

How do you nominate an article to be good? --Gilderien (talk) 06:43, 9 May 2011 (UTC)

See WP:GAN.TR 12:03, 9 May 2011 (UTC)

Formula?

What's the central formula of this theory? I mean, there has to be something likem a Lagrange density or something similar... --91.4.236.151 (talk) 18:09, 20 July 2011 (UTC)

To start, check out the pages on Nambu-Goto action or Polyakov action. Isocliff (talk) 21:31, 20 July 2011 (UTC)

I was just looking over this article and the talk page. Im thinking this article could benefit from a little more meat, i.e. specific formulas. This question came to mind, and seems to reinforce the need. Im thinking the article could benefit from at least a few of the basic formulas, i.e. how the p-brane worldvolume action generalizes the point particle worldline action, and just a few basic statements about the Nambu-Goto action and Polyakov action.... Im aware that this article shouldn't be a treatise on all the math of string theory, but these definitely seem appropriate. Thoughts? Isocliff (talk) 23:21, 4 September 2011 (UTC)

How to test it.

One way to test string theorys predictions about hidden dimensions would be to produce photons with a wavelength shorter than the size of the hidden dimensions. The energy problem can be solved by firing multiple laser beams at a single nanoparticle, heating it to locally extreme temperatures. The ultra-hot nanoparticle would radiate a small number of ultra-short photons, but the photons would make up in energy what they lack in numbers. Since string theory predict that gravity and electromagnetism unify in hidden dimensions, the test should involve gravimeters. — Preceding unsigned comment added by 109.58.249.18 (talk) 08:26, 29 July 2011 (UTC)

"Correct"

From the lead section:

"Five major string theories were formulated. The main differences among them were the number of dimensions in which the strings developed and their characteristics. All of them appeared to be correct, however."

I find the statement "All of them appeared to be correct" slightly strange and at odds with the rest of the article, which says that the theory has not even made any testable experimental predictions. So, in what sense is "correct" being used? 86.179.1.213 (talk) 01:29, 2 September 2011 (UTC)

It's being used in a theoretical sense Dauto (talk) 02:10, 2 September 2011 (UTC)

And what does correct mean in a theoretical sense? (I think this sentence should be rephrases.)TR 05:52, 2 September 2011 (UTC)

(OP) I agree. Perhaps it just means "consistent"?? 86.160.208.79 (talk) 11:17, 2 September 2011 (UTC)

Since there have been no further comments, and pending clarification of exactly what it means, I have removed the sentence. At the moment I feel it does more harm than good because to the ordinary reader "correct" means "an accurate model of the real physical world". 86.160.212.182 (talk) 17:02, 6 September 2011 (UTC)

Unified Strings (u21s19) Theory - NASA Conference Presentation

I added the following to Online Material...

• Watson II, Richard 'Brad'shaw. Identifying 'True Earth-like Planets' - All New Worlds Are Built On 7_4 (like Earth) Or 6_4 http://exep.jpl.nasa.gov/exep_exoMtgPosters.cfm Presentation at the NASA Conference Missions for Exoplanets 2010-2020 held in Pasadena, CA on April 21-23, 2009 - Unified Strings (u21s19) Theory is presented with the aspects of 1-dimensional time symmetry. Indirect evidence of strings is documented for the first time and u21s19 theory is used to predict the characteristics of all 'true Earth-like planets'. - Brad Watson, Miami 66.229.56.118 (talk) 13:31, 16 September 2011 (UTC)

That's a very strange paper. I wonder how stuff like that gets on a NASA conference. It reminds me of the timecube guy Bhny (talk) 14:30, 16 September 2011 (UTC)

Bhny, your comment reminds me of those that attacked Galileo's, Newton's, and Einstein's theories. - Brad Watson, Miami 66.229.56.118 (talk) 14:42, 16 September 2011 (UTC)

How is the string theory scientific?

This article claims that the string theory is a scientific theory even though the string theory does not adhere to the scientific method (has no testable predictions) and is by definition pseudo-scientific.

It's possible for something to be falsifiable and still have no testable predictions. According to this article I can say that anything is scientific if it relies on the truth of General Relativity or Quantum Mechanics even if it has no testable predictions, which is obviously nonsense.

Using this article's reasoning we can conclude that Intelligent Design is scientific.

So why are the authors of this article biased towards making the string theory appear scientific? --96.255.71.164 (talk) 04:42, 4 September 2011 (UTC)

You're just misinformed. String theory has testable predictions. Dauto (talk) 04:53, 4 September 2011 (UTC)

The article has a lot of criticism and the intro doesn't say that it is a "scientific theory", it says it's a research framework that is a contender for a theory of everything. I think it's safe to call it scientific research. Bhny (talk) 15:20, 4 September 2011 (UTC)

It would also be safe to call it a scientific theory but the article chooses to be conservative which is fine. Dauto (talk) 15:28, 4 September 2011 (UTC)

For some reason the Wikipedia editors have blocked out my response, so go read it here http://en.wikipedia.org/wiki/User_talk:96.255.71.164#String_theory_not_scientific

--96.255.71.164 (talk) 05:54, 30 September 2011 (UTC)

If anything the article leans heavily to the conservative side. String theory is falsifiable which by definition means that it makes experimental predictions. The only question is how novel or significant those predictions are, which is debatable and under active research. So the last sentence of the first paragraph seems to be incorrect. Isocliff (talk) 22:23, 4 September 2011 (UTC)

In what way exactly is the sentence wrong? It says "testable predictions". Obviously string theory makes predictions. Isn't the big problem that the predictions haven't been testable?

(the weasel words- "some scientists" need to be fixed) Bhny (talk) 02:14, 5 September 2011 (UTC)

Well one important example is gravity and general relativity. These can be viewed as "obvious" today or "postdictions", but its still true that every time we test general relativity, as in the recent frame-dragging experiments by Gravity Probe B, we are doing experiments that could falsify string theory if they produced the wrong result. The same can be said of the experiments that have been done in recent years verifying the exactness of the Lorentz symmetry. So one could make a case that the ways to test string theory are so far not yet sufficiently convincing, but its wrong to assert categorically that its untestable, unfalsifiable, unscientific, or anything like that.

It would be nice to be able to say it predicts us to observe particle X at exactly Y energy, but there doesn't seem to be any justification for expecting this would be the case. Im not an expert on the phenomenology or anything, but its clear that string theory is compatible with all kinds of particle physics content, but there also exist a lot of very firm rules (such as dictated by dualities, etc) that can be checked in principle. To check them to a significant degree probably requires very high energy collisions, but the fact that these tests are economically inconvenient to humans is not the same thing as being untestable. Isocliff (talk) 04:22, 5 September 2011 (UTC)

String theory is scientific by any definition I know of, the best of which is Popper's. To be scientific, theories (according to Popper) only need to be falsifiable. But as is mentioned in the article, this is obviously the case for string theory. For instance string theory is locally Lorentz invariant. Many experiments have been done to check whether this holds for nature or not. If any of those experiments (past or future) show that nature isn't locally Lorentz invariant, string theory is falsified. So it's clearly scientific by that criterion. Obviously string theory is more than just Lorentz invariance, and so to convincingly confirm that it's right we need to do more than just check that nature is Lorentz invariant. There's a discussion of that in there too.

I don't think the fact that string theory is mathematical belongs in that section. Mathematics is too general to be falsified, it's just the logical consequences of various sets of axioms, and axioms cannot be falsified.Waleswatcher (talk) 14:07, 30 November 2011 (UTC)

Before further changes get made to the testability section, perhaps we should discuss them here. Something close to the language that's there now was extensively discussed and finally agreed on several years ago. There are some basic facts relevant here: string theory is quantum mechanical, all known versions of it reduce to Einstein's general relativity (the full, non-linear theory) in the low energy limit, and all string theories are fundamentally Lorentz invariant. That makes them falsifiable, full stop. Therefore, they are scientific according to Popper. There's no debate I'm aware of on that, because these really are basic facts about the theory. The problem of string theory is that it probably doesn't make predictions that are falsifiable with current technology AND that are "new", meaning not shared by other putative theories that are QM, Lorentz invariant, and reduce to GR (never mind that no other such theory exists....). Waleswatcher (talk) 17:04, 8 December 2011 (UTC)

Two small points on history

Useful article. Comments:

1. The term "bootstrap program" is used but undefined and meaningless to outsiders.

2. Has actually nothing worth noting happened since 1997? Or is the jury still out? Recent controversies would be of interest.

Burressd (talk) 21:14, 30 November 2011 (UTC)

I added a link to "bootstrap model". I find the wording redundant "...complete the bootstrap program for this model". Could we change it to "complete the bootstrap model"? Bhny (talk) 22:15, 30 November 2011 (UTC)

widely believed to be consistant?

Since string theory is widely believed[who?] to be a consistent theory of quantum gravity, many hope that it correctly describes our universe, making it a theory of everything.

Really? It widely believed to be consistant? Consistant with itself? That means no divergences or infinities? Did somebody prove that? Or it's widely believed that somebody has proved that, even though nobody has actually proven that? I suppose we need a cite that many people believe something that isn't true. SBHarris 06:20, 8 December 2011 (UTC)

The phrase "consistent with itself" is a tautology. These questions are the subject of countless papers that you may read, and yes all conceivable kinds of self-consistency checks have been passed. In practice, establishing consistency means checking in detail that all rigorously derivable conclusions are consistent with one another, its much more difficult to prove that all possible logical inferences that may ever be drawn will all be consistent, but so far there is no consistency problem whatsoever. If you want to be precise, the consistency of quantum field theory isn't a rigorously derivable truth either, but that doesn't mean its inconsistent. In fact there's a huge amount of evidence that it is consistent. So you're "who" tag doesn't make much sense. – Isocliff (talk) 06:47, 8 December 2011 (UTC)

QFT (or more precisely, non-Abelian guage theories without anomalies) are renormalizable and free of infinities. This basically makes the entire standard model (all forces but gravity), renormalizable, as t'Hooft proved in 1971. [1] No string theory that predicts fermions has been proven finite and free of divergences beyond the 3-loop case. So the idea that string theories that are candidates to be theories of everything are "consistent," is rather like claiming that Fermat's theorum has so far passed all consistancy checks because the integers 3, 4 and 5 have been checked! [2]. (Yes, I know Fermat's theory was finally proven for all integers, but that's not what has happened to any string theory that has any chance of being a discription of nature). Smolin's paper on these problems, that later was expanded into a popular book (The Trouble With Physics) is available here: [3]. Here's what is says about consistancy, and it quotes from the group that has actually computed terms.

(from page 34) "As it does not appear to be widely appreciated that the consistency of string perturbation theory is still open [26], I quote here from a recent paper by experts in the field, which announced the proof of consistency at the two loop level: (quote follows) Despite great advances in superstring theory, multiloop amplitudes are still unavailable, almost twenty years after the derivation of the one-loop amplitudes by Green and Schwarz for Type II strings and by Gross et al. for heterotic strings. The main obstacle is the presence of supermoduli for world-sheets of non-trivial topology. Considerable efforts had been made by many authors in order to overcome this obstacle, and a chaotic situation ensued, with many competing prescriptions proposed in the literature. These prescriptions drew from a variety of fundamental principles such as BRST invariance and the picture-changing formalism, descent equations and Cechco homology, modular invariance, the light-cone gauge, the global geometry of the Teichmueller curve, the unitary gauge, the operator formalism, group theoretic methods, factorization, and algebraic supergeometry. However, the basic problem was that gauge-fixing required a local gauge slice, and the prescriptions ended up depending on the choice of such slices, violating gauge invariance. At the most pessimistic end, this raised the undesirable possibility that superstring amplitudes could be ambiguous, and that it may be necessary to consider other options, such as the Fischler-Susskind mechanism[131].

As Smolin makes clear, the problem with the (infinite number of) string theories is not what they show, but what people THINK they show. No, Mandelstam did NOT show that any string theory is free of all infinities, or even that it is free to the extent of what t'Hooft did for guage theories. Smolin himself believed prior to his review what this colleagues had been telling him, that at least some versions of 3-D string theory that describe actual known particles, or are capable of it, were free of infinities (which means they might possibly be true). So far, none has actually been proven to be so.

So, string theory is DIFFERENT from guage theory QFTs describing the 3 non-gravity forces of the standard model. So, in what sense does your sentence make sense?

As a second problem, what is this stuff about "theories of everything"? Because all string theories are dependent on a Minkowski SR background which does not change in time, so far there are no quantum gravity theories that are free of infinities for even strong field gravity waves, which are the needed kind to deal with. After all, the flat-space-limit weak-field spin-2 gravity quantum was presented in 1930, and nobody needs strings to describe it-- you can read about weak field "gravitons" in Misner-Thorne-Wheeler. The "gravitons" in all string theories today are this same weak-field gravity quanta, so the fact these particular gravitons have no infinities, is not very interesting, since weak gravity waves are obviously not strong enough to have any contact with a "theory of everything," and certainly are not "quantum gravity" as we need it. Plain old general relativity describes gravitational waves far more powerful than this, but of course by that time, the field is not quantizable. Weak field gravitons never had any infinities before anybody had thought of string theories, but then, they also never had enough energy to need anything but a linearized GR field description anyway-- so what's the point? In other words, if string theories reduce to linearized gravity (as they all do), but not general relativity (which they most certainly by definition do NOT do, as Smolin points out), then what's the point? All that means, is these theories reduce to a field theory that isn't even as accurate as the field theory Einstein came up with, in 1915. Einstein's generalization has passed tests (linear gravity doesn't predict Mercury's precession). String theory (if you can call it a theory) has passed no tests, but if it reduces in the end to linear gravity, as all 10¹⁵⁰⁰ versions of it do, it can't be a candidate for a theory of everything (TOE), since it isn't even a candidate for describing the orbit of Mercury, let alone more interesting physics. So again, which people hope which string theory will be a theory of everything, and which theory is it, that they have hopes for? There are more string theories than particles in the universe by far, but the right one certainly cannot be any of the background dependent-ones. And if Smolin is right, all proposed classes of string theories are background dependent (they live in 4-d asymptotically flat space-time, even if they do have extra dimensions), which means NONE of them can possibly be candidates for TOEs.

To put this another way: You see those loops that are supposed to be the "gravitons" in string theories? Do you see them actually bending the space-time through which they move? No? That's right, you don't. And that's a HUGE problem. Since in any "Theory of Everything," they must. SBHarris 21:42, 9 December 2011 (UTC)

Despite your frequent use of the caps lock, almost every sentence you wrote is wrong. All string theories (or more precisely, all corners of string theory) possess general relativity as their low energy limits, not linearized gravity. This is a completely unambiguous, quantitative conclusion you can see worked out in detail in any string theory textbook. You should not be using a popular level book as you singular resource in order to dispute the most basic facts about what string theory implies, especially if its a book written by a person whose sole purpose is to reduce the stature of string theory and get more people to work on his own idea. String theories are fully diffeomorphism-invariant, i.e. they possess the same gauge symmetry as general relativity, and frequently this freedom is used to gauge fix to flat space in order to make calculation easier, but any suggestion that string theory is wedded to flat space is quite far removed from reality. If this was true, string theory would not have anything remotely approaching the interest and activity that it does. (and again its pretty hard not to notice if you step one inch into actually learning the subject)

This means that string theory is fully background-independent in any physical sense of the word, because any change in the background is shown to be equivalent to a particular condensation of matter within it. The only case you can really make, and its a legitimate one, is that we should try to find a language that makes the background-independence manifest. As Joe Polchinski (who wrote one of the best textbooks on the subject) has said [4] "In string theory it has always been clear that the physics is background-independent even if the language being used is not, and the search for a more suitable language continues."

Im not going to debate the merits of string theory with you here, but your statements are demonstrably, factually wrong. If you want to get any kind of informed opinion about string theory then reading some textbooks on the subject would be advisable. Or if you will only read popular level accounts I strong suggest taking Smolin with a grain of salt and get some other books. For example, Hawking's book is mentioned in the introduction of this article. But I would not recommend reading any books that get major facts wrong. Disclaimer: I am not promising to correct all your misimpressions and you seem to have quite a few others remaining. For example, you seem to think that stabilizing moduli is some kind of major unsolved problem. Well its not. – Isocliff (talk) 00:49, 10 December 2011 (UTC)

Stabalizing moduli is a major unsolved problem. And since you quote Polchinski on Smolin, I may as well quote Smolin's answer back [5]:

Regarding background independence, Polchinski claims that, “(as Smolin belatedly notes), Maldacena duality provides a solution to this problem, one that is unexpected and powerful.” This exaggerates and distorts the situation. What is true-and what I acknowledge, is that if the strong form of the AdS/CFT conjecture is shown to be correct, then a very weak, and limited form of background will have been achieved. But for reasons just mentioned, which I explain in detail in the book, this is still a big if.

What has been shown so far relies on the fact that one can use the fact that SUSY N=4 Yang-Mills has the same global super-symmetry as perturbative physics on a background AdS5 X S5 spacetime, to express some physical quantities in the latter in terms of observables of the former. This is great mathematical physics and a great achievement, but the whole point of general relativity and quantum gravity is that the generic solutions are governed by no global symmetries because the geometry of spacetime is completely dynamical. This has two implications. First it makes it very non-trivial to show the strong form of the Maldacena conjecture, because it must extend to solutions of supergravity arbitrarily far from those with global symmetries in the bulk. However, if this is possible at all it will be because the full algebra of global super-symmetries remain on the boundary. The case of asymptotically flat will be much harder because there the asymptotic symmetries of the generic case are very different from the global symmetries of the ground state, and indeed there are no proposals for a gauge-gravity duality in this case. The case of positive cosmological constant-which appears to be the physical case-is harder still. And we have not even yet touched the real meaning of background independence, which is that fixed classical fields or global symmetries play absolutely no role in the formulation of the dynamics or observables of the theory.

The latter is what is meant by background independence in the rest of the classical and quantum gravity world, and so far string theory and the AdS/CFT conjectures do not come close to addressing it. It was in fairness to string theory that I was willing to acknowledge that the strong form of the AdS/CFT conjecture, if true, would provide a very limited and weak form of background independence. One would hope that in fairness to the truth string theorists who make this point would also hasten to acknowledge how far this would be from the real, full meaning of background independence. Brian Greene does acknowledge this when he proposes that the latter idea be distinguished by calling it “manifest background independence.”

Polchinski also acknowledges the difference, when he says, “In string theory it has always been clear that the physics is background-independent even if the language being used is not, and the search for a more suitable language continues.” But this is not the most accurate way to put it. It would be more accurate to say, “Some string theorists believe that the formulations of perturbative string theories and dualities between them that they study concretely are approximations to a deeper, background independent formulation. This missing background independent formulation is not just a different t language for the theory, it is hoped to be the statement of the principles and laws that define the theory, from which everything studied so far would be derived as an approximation. Despite this belief, only a few concrete proposals have been made for the laws and principles of this conjectural background independent formulation of string theory and none has gained wide support.” [end of quote]

You can read the whole thing on the link. String theory is not wedded to flat space, but neither is it completely free of needing a space to back it. Indeed as you know, the various anti de Sitter spaces in AdS/CFT become more and more difficult to use in theories when the global universe they are supposed to explain is a manifestly de Sitter universe, with a positive cosmological constant. Something just being discovered by the Hubble Space Telescope as Maldacina made his first conjecture (alas). Which is still a conjecture. At least Ed Witten has admitted that string theories giving rise to de Sitter universes like ours, don't look like anything thought of, so far. SBHarris 03:59, 10 December 2011 (UTC)

Again, Im not going to sort through all of your misconceptions and resolve them all for you, but what you say is wrong and demonstrably so. You can quote Smolin all day long, but these are quantitative questions that have been decided in papers, not in popular-level books. The AdS/CFT is not in any way critical to these arguments and I didn't bring it up. The key point was that string theory possesses the same diffeomorphism symmetry as general relativity, and implies Einstein's equations as a low energy limit. Those are two unambiguous facts that are true of string theory as it exists today, not some dreamed about completion of it. They are pretty important things to know about it, and I cant guarantee I will continue conversing with someone who wont acknowledge these basic characteristics of the topic in question. Again, your wrong statements include your assertion that de Sitter space and moduli are "major unsolved problems". Does the actual literature written on these topics matter at all? I will leave a few recommended selections here. [6] [7] [8] [9] – Isocliff (talk) 05:06, 11 December 2011 (UTC)