• Is it possible that string theory strings are geons? This may be an overly speculative or naive question, but is there an obvious reason why not? Both strings and geons seem to have roughly the same length scale (comparing the rq from here to thePlanck length).
  • $\begingroup$ It's usually best to stick to one question per post, or at least ensure that if there are multiple questions per post, that they're very closely related. I think this would be much better off split into a few different posts. $\endgroup$ – David Z Jan 14 '12 at 23:37
  • $\begingroup$ Did I not explain myself clearly enough? I think the questions are very closely related: all are about geons. $\endgroup$ – user1247 Jan 15 '12 at 0:23
  • $\begingroup$ Just being about the same thing does not make multiple questions related. If one is an immediate prerequisite for another, that might make them related, but I don't believe that's the case here. Each of your bullet points is a separate question. A good rule of thumb (I think) is that if you can't distill the contents of your post into a single question to put in the post title, it's probably better off split up. $\endgroup$ – David Z Jan 15 '12 at 0:33
  • $\begingroup$ My main concern is that this topic is extremely specialized, and that it would be poor form to spam the forum with a whole lot of separate questions about a specialized topic. Also, I'm worried that some of the questions, the 2nd and the last 3 particularly (I guess basically all of them), will be interpreted differently if not in the context provided by the other questions. $\endgroup$ – user1247 Jan 15 '12 at 1:24
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    $\begingroup$ It's best to edit this question to only contain one logical question, and then make a separate post for each other question you want to ask. Of course you don't have to literally copy and paste the text of each bullet point; you can add extra text to give the context, including linking to other related questions. And it's not poor form at all to post a lot of questions about a specialized topic; that's exactly what this site (not a forum) is for. You're not spamming the site as long as the questions are on topic, which these are. $\endgroup$ – David Z Jan 15 '12 at 2:32

The classical objects which correspond to quantum strings have been identified, they are extremal black holes. Geons are (unstable) gravitationally bound configurations of massless fields, and they cannot be identified well with strings because they are not primitive holographic objects, as black holes are.

The physics of string world sheet, with its emission vertex operators which correspond to all the spectrum of the theory, is only sensibly interpreted as a holographic reconstruction on the world-sheet of the surrounding space-time theory. The connections between world-sheet physics and space-time physics was one of the seeds that led to AdS/CFT, and there is no longer any confusion regarding the classical notion corresponding to the world sheet--- it is an extended charged black hole.

The correspondence is more general, so that the D0 branes of IIA theory used to construct the matrix version of M-theory are point black holes, while the D3 branes are described by 4d gauge theory, and most recently, that the M2 branes by a strange 3 dimensional Chern Simons theory.

  • $\begingroup$ I am having trouble understanding from your answer whether or not the relationship between strings and black holes are merely a mathematical duality, or if it really makes physical sense to equate the two dual objects as one and the same. Is the black hole that is dual to the string that forms an electron (for example) of roughly the same size and charge and so on, so that the two objects can be physically identified? $\endgroup$ – user1247 Jan 15 '12 at 6:09
  • $\begingroup$ Slightly off topic @Ron Maimon (sorry): Reading Your answer I`m wondering again why there can only be even OR odd dimensional D-branes in a theory ...? Prof. Susskind said this in a video-lecture without further justification while explaining how turning up the string coupling constant can lead to the emergence of an additional dimension from S-duality. $\endgroup$ – Dilaton Jan 15 '12 at 10:45
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    $\begingroup$ This is just an accident of type II string theory. The odd dimensional branes and even dimensional branes swap under T-duality (making one dimension small). The dimensions of the branes in type IIA can be understood from the dimensional reduction of the form field in 11 dimensional supergravity, plus the Kaluza-Klein field of a circle, which gives 0 branes carrying momentum along the small circle. These 0 branes reveal the circle to be there. everything in supergravity is insanely constrained--- it is a miracle that 11 dimensional SUGRA exists at all, same for 10D SUGRA's. It's all form dim's. $\endgroup$ – Ron Maimon Jan 15 '12 at 17:48
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    $\begingroup$ @user1247: Yes, the two can be identified. The electron is a small quantum black hole. $\endgroup$ – Ron Maimon Jan 19 '12 at 2:49

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