Comments on: The 9/11 Flip http://asymptotia.com/2007/09/11/the-911-flip/ Wed, 07 Jan 2009 18:54:41 +0000 http://wordpress.org/?v=2.5.1 By: Javier http://asymptotia.com/2007/09/11/the-911-flip/#comment-78767 Javier Fri, 14 Sep 2007 06:37:54 +0000 http://asymptotia.com/2007/09/11/the-911-flip/#comment-78767 Just to stay that teh reason non-critial strings theories are in the news is because their prediction of a dispersion relation for vacuum lightspeed and the MAGIC observatory which has, maybe, found partial experimental evidences of it. Just to stay that teh reason non-critial strings theories are in the news is because their prediction of a dispersion relation for vacuum lightspeed and the MAGIC observatory which has, maybe, found partial experimental evidences of it.

]]> By: Clifford http://asymptotia.com/2007/09/11/the-911-flip/#comment-78544 Clifford Wed, 12 Sep 2007 23:16:10 +0000 http://asymptotia.com/2007/09/11/the-911-flip/#comment-78544 I'm not sure what natural or generic mean, really. Depends upon your goals, for a start. I think it is certainly very interesting to study and explore in its own right, whether or not it is perceived as better (by some measure I'm not sure how best to define) than the CY approach. Sorry to be vague on this, I just don't have a strong opinion one way or another. Cheers, -cvj I’m not sure what natural or generic mean, really. Depends upon your goals, for a start. I think it is certainly very interesting to study and explore in its own right, whether or not it is perceived as better (by some measure I’m not sure how best to define) than the CY approach. Sorry to be vague on this, I just don’t have a strong opinion one way or another.

Cheers,

-cvj

]]> By: mark http://asymptotia.com/2007/09/11/the-911-flip/#comment-78540 mark Wed, 12 Sep 2007 22:51:25 +0000 http://asymptotia.com/2007/09/11/the-911-flip/#comment-78540 Hi Clifford, Do you think that compactifying M-theory on a manifold with G2 holonomy where there are no U(1) isometries is more "natural"/"generic" than compactifying it on a circle times a Calabi-Yau? Thanks you! Hi Clifford,
Do you think that compactifying M-theory on a manifold with G2 holonomy where there are no U(1) isometries is more “natural”/”generic” than compactifying it on a circle times a Calabi-Yau?

Thanks you!

]]> By: Clifford http://asymptotia.com/2007/09/11/the-911-flip/#comment-78515 Clifford Wed, 12 Sep 2007 18:00:37 +0000 http://asymptotia.com/2007/09/11/the-911-flip/#comment-78515 Ok.... what I meant to say was that as ten dimensional theories the distinction needn't be made for this discussion. Cheers, -cvj Ok…. what I meant to say was that as ten dimensional theories the distinction needn’t be made for this discussion.

Cheers,

-cvj

]]> By: Clifford http://asymptotia.com/2007/09/11/the-911-flip/#comment-78507 Clifford Wed, 12 Sep 2007 16:58:59 +0000 http://asymptotia.com/2007/09/11/the-911-flip/#comment-78507 That's just type I (as is type IB) The distinction is not so crucial at this level.. I could say more, but have to run. -cvj That’s just type I (as is type IB) The distinction is not so crucial at this level.. I could say more, but have to run.

-cvj

]]> By: Alejandro Rivero http://asymptotia.com/2007/09/11/the-911-flip/#comment-78504 Alejandro Rivero Wed, 12 Sep 2007 16:43:19 +0000 http://asymptotia.com/2007/09/11/the-911-flip/#comment-78504 No role in the puzzle for "type IA"? No role in the puzzle for “type IA”?

]]> By: Clifford http://asymptotia.com/2007/09/11/the-911-flip/#comment-78503 Clifford Wed, 12 Sep 2007 16:38:48 +0000 http://asymptotia.com/2007/09/11/the-911-flip/#comment-78503 Hi, It is very tempting to give a humourous answer based on the term "critical" versus "non-critical" string theory, but I will resist. They are all part of the same thing. I've mentioned non-critical strings before in some blog posts, but it is probably easier to write something again than try to find it, so here goes: String theory (like many theories) comes with a large set of symmetries. These symmetries allow you to sometimes find nice computational schemes to make progress some places. Critical string theory arises from using the symmetries to pick a particularly nice framework that allowed a lot of progress to be made on many aspects. The price you pay for this is the remarkable fact that the string theory likes to choose to propagate in ten dimensions (if supersymmetric or 26 if bosonic), and all dimensions are on the same footing -ten dimensional local Lorentz invariance (the symmetry of Special Relativity) is built in. Those are the famous "critical" numbers of dimensions that people talk a lot about. Then there's the whole wonderful and interesting endeavour to understand how to get four dimensional physics from this, by doing various things to the other six dimensions. Somehow, a most people forgot that there are other choices that can be made. These allow you to end up in other dimensions right at the outset. But that's ok, since who (or what experiment) said that we need anything more than four dimensional Lorentz invariance? It was just a simplifying assumption. In fact, most of the activity in critical string theory goes about messing up that local Lorentz invariance in the higher dimensions anyway, so why fight hard to keep it? So you can give that up, finding that some directions are different than others... typically the string coupling and other fields can have preferred dependences on some directions, and so forth. The price is that it is very hard to understand those string theories in many settings (although there are some where we understand a lot), and for some dimensions (including four dimensions) we don't even know how to formulate it. I suspect that this is an important clue, and we ought to return to that problem to learn interesting things - maybe about our world. I'm pleasantly surprised to hear that non-critical strings are in the news, since it is high time that we told more of the story of string theory, and stopped being so hung up on the idea that we have to start with ten dimensions, which is really quite an over-simplification of the issues. This is one of the many reasons why -again and again- I keep trying to remind people here and elsewhere that there is so much wonderful stuff to figure out in string theory. It is not only a work in progress, it might just have barely begun. Cheers, -cvj Hi,

It is very tempting to give a humourous answer based on the term “critical” versus “non-critical” string theory, but I will resist.

They are all part of the same thing. I’ve mentioned non-critical strings before in some blog posts, but it is probably easier to write something again than try to find it, so here goes:

String theory (like many theories) comes with a large set of symmetries. These symmetries allow you to sometimes find nice computational schemes to make progress some places. Critical string theory arises from using the symmetries to pick a particularly nice framework that allowed a lot of progress to be made on many aspects. The price you pay for this is the remarkable fact that the string theory likes to choose to propagate in ten dimensions (if supersymmetric or 26 if bosonic), and all dimensions are on the same footing -ten dimensional local Lorentz invariance (the symmetry of Special Relativity) is built in. Those are the famous “critical” numbers of dimensions that people talk a lot about. Then there’s the whole wonderful and interesting endeavour to understand how to get four dimensional physics from this, by doing various things to the other six dimensions.

Somehow, a most people forgot that there are other choices that can be made. These allow you to end up in other dimensions right at the outset. But that’s ok, since who (or what experiment) said that we need anything more than four dimensional Lorentz invariance? It was just a simplifying assumption. In fact, most of the activity in critical string theory goes about messing up that local Lorentz invariance in the higher dimensions anyway, so why fight hard to keep it? So you can give that up, finding that some directions are different than others… typically the string coupling and other fields can have preferred dependences on some directions, and so forth. The price is that it is very hard to understand those string theories in many settings (although there are some where we understand a lot), and for some dimensions (including four dimensions) we don’t even know how to formulate it. I suspect that this is an important clue, and we ought to return to that problem to learn interesting things - maybe about our world.

I’m pleasantly surprised to hear that non-critical strings are in the news, since it is high time that we told more of the story of string theory, and stopped being so hung up on the idea that we have to start with ten dimensions, which is really quite an over-simplification of the issues. This is one of the many reasons why -again and again- I keep trying to remind people here and elsewhere that there is so much wonderful stuff to figure out in string theory. It is not only a work in progress, it might just have barely begun.

Cheers,

-cvj

]]> By: cecil kirksey http://asymptotia.com/2007/09/11/the-911-flip/#comment-78496 cecil kirksey Wed, 12 Sep 2007 15:52:08 +0000 http://asymptotia.com/2007/09/11/the-911-flip/#comment-78496 Dr. Johnson: This maybe a little off subject but can you explain in lay (engineering background) terms the differences between critical and non-critical string theory? Do both relie on a common set of assumptions but just use different mathematical techniques to arrive at a final theory? Non-critical strings has been in the news lately but with no clear cut statement as to the viability of this aspect of string theory. Is non-critical string theory part of string theory or not? Are you a supporter of this approach? Dr. Johnson:
This maybe a little off subject but can you explain in lay (engineering background) terms the differences between critical and non-critical string theory? Do both relie on a common set of assumptions but just use different mathematical techniques to arrive at a final theory?

Non-critical strings has been in the news lately but with no clear cut statement as to the viability of this aspect of string theory. Is non-critical string theory part of string theory or not? Are you a supporter of this approach?

]]> By: Clifford http://asymptotia.com/2007/09/11/the-911-flip/#comment-78484 Clifford Wed, 12 Sep 2007 14:23:26 +0000 http://asymptotia.com/2007/09/11/the-911-flip/#comment-78484 Hi Robert, Yes. There's no question that the concept goes to much earlier. I'm talking about the <em>terminology</em> "9/11 flip". I think that the term's wide use came as a result of their matrix string paper and subsequent lectures. (I edited your comment slightly. Chief result: it now has the latex you desired. Look in the sidebar for [tex]\LaTeX[/tex] instructions.) Cheers, -cvj Hi Robert,

Yes. There’s no question that the concept goes to much earlier. I’m talking about the terminology “9/11 flip”. I think that the term’s wide use came as a result of their matrix string paper and subsequent lectures.

(I edited your comment slightly. Chief result: it now has the latex you desired. Look in the sidebar for \LaTeX instructions.)

Cheers,

-cvj

]]> By: Robert http://asymptotia.com/2007/09/11/the-911-flip/#comment-78473 Robert Wed, 12 Sep 2007 12:15:27 +0000 http://asymptotia.com/2007/09/11/the-911-flip/#comment-78473 I remember Hermann Verline using this term extensively at the 1998 Trieste spring school (where somebody else was giving lectures with musical lecture notes). But I would agree with David that the concept (the realization that the [tex]S\in SL(2,Z)[/tex] of the IIB S-duality is geometric in M-Theory) obviously predates matrix string theory. I remember Hermann Verline using this term extensively at the 1998 Trieste spring school (where somebody else was giving lectures with musical lecture notes). But I would agree with David that the concept (the realization that the S\in SL(2,Z) of the IIB S-duality is geometric in M-Theory) obviously predates matrix string theory.

]]> By: Clifford http://asymptotia.com/2007/09/11/the-911-flip/#comment-78387 Clifford Wed, 12 Sep 2007 07:39:02 +0000 http://asymptotia.com/2007/09/11/the-911-flip/#comment-78387 The technique is a lot older, yes, but the term itself is what I'm talking about (I should be sure to emphasize). It certainly took off in a big way after that paper of theirs and their use of the term in a lot of their talks on the subject, and lectures at various schools. But I can certainly believe that the term also started from earlier, but I do not know who. Yes, it would be nice if anyone who has some clues or guesses can comment.... maybe point to a paper where the term is used. Cheers, -cvj The technique is a lot older, yes, but the term itself is what I’m talking about (I should be sure to emphasize). It certainly took off in a big way after that paper of theirs and their use of the term in a lot of their talks on the subject, and lectures at various schools. But I can certainly believe that the term also started from earlier, but I do not know who. Yes, it would be nice if anyone who has some clues or guesses can comment…. maybe point to a paper where the term is used.

Cheers,

-cvj

]]> By: David http://asymptotia.com/2007/09/11/the-911-flip/#comment-78384 David Wed, 12 Sep 2007 07:34:55 +0000 http://asymptotia.com/2007/09/11/the-911-flip/#comment-78384 Hi, Not sure the name 9/11 flip is due to the either Verlinde or Robbert. If I recall it was a supergravity person; part of the solution generating business in supergravity and almost predating m-theory though I might go for Hull and Townsend U-duality paper. Does anyone know? David Hi,

Not sure the name 9/11 flip is due to the either Verlinde or Robbert. If I recall it was a supergravity person; part of the solution generating business in supergravity and almost predating m-theory though I might go for Hull and Townsend U-duality paper. Does anyone know?
David

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