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selfAdjoint

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No experimental evidence in favor of SST. Theoretical discovery of huge number, maybe infinite number, of inequivalent vacua causes dismay among some SST physicists and circle-the-wagons psychology in others. Revisions to estimated mass of top quark (experimental, from Tevatron) tighten the window for Higgs mass and may force supersymmetry theorists into unwanted fine tuning.Ratzinger said:

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George Jones

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String theory seems to be mathematically consistent only when there are extra (to those normally perceived) spatial dimensions. How could these extra spatial dimensions be detected? One way is by look for modifications (for semi-technical reasons why, see below) in Newton's inverse square law for gravity at small distances. There ongoing investigations looking for such modification, but, so far, none have been detected.Ratzinger said:

I, too, have a question. If evidence for either supersymmetry or extra spatial dimensions is found, string theorists will jump all over the results and claim vindication. But, since (as far as i know) they are not sufficient conditions, will either of these results really be enough?

It seems that superstring theory implies supersymmetry and superstring theory implies extra spatial dimensions, but how likely is that these necessary conditions can be "true" without symmetry being true? Scientific theories are often "verified" (note the scare inverted commas) for a certain domain of validity by a finding a number of necessary conditions. In this case, how much is enough?

For what it's worth, finding *both* supersymmetry and extra spatial dimensions would go a long way towards bringing me around.

Now, why do extra dimensions modify Newton's inverse square law? First, a somewhat wordy motivation for the inverse square force in three spatial dimensions. Consider gravitational lines of force coming from a point mass. Consider two (massless) imaginary balls with radii R and r that both have the point mass at their centres. The lines of force cross the surfaces (boundaries) of the balls at points. The (relative) strength of gravity at these surfaces will be proportional to the number of crossing point per unit area. Since the same lines of force pierce both surfaces, the number of crossing points is the same for the two surfaces. However, the surface areas scale as radius squared, and thus the strength of gravity (number of points per unit area scales inversely to radius squared.

Now consider gravitational lines of for from a point mass in a universe that has four spatial dimensions. A ball now is a 4-dimensional spatia volumel, and the boundary ("surface") of a ball is a 3-dimensional object. Consequently, the number of crossing points per unit "surface area", i.e., the gravitational force, now scales inversely to radius cubed.

In practice, the extra spatial dimensions, if they exist, are probably folded up in a complicated manner, so the precise deviation from Newton's inverse square law is probably impossible to calculate.

Regards,

George

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marcus

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compliments on the prose style, which is as concentrated and salty as a boullion cube. if you hadna been a math/physicist you could have been a writer about science.selfAdjoint said:No experimental evidence in favor of SST. Theoretical discovery of huge number, maybe infinite number, of inequivalent vacua causes dismay among some SST physicists and circle-the-wagons psychology in others. Revisions to estimated mass of top quark (experimental, from Tevatron) tighten the window for Higgs mass and may force supersymmetry theorists into unwanted fine tuning.

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George Jones

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Oops, I meant to say "... how likely isGeorge Jones said:It seems that superstring theory implies supersymmetry and superstring theory implies extra spatial dimensions, but how likely is that these necessary conditions can be "true" without symmetry being true?

Opinion, anyone?

Regards,

George

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selfAdjoint

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Haelfix

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Incidentally there is a lot more wiggling room in the higgs sector for the SuSy/GUT models w.r.t the recent top quark revisions than there is in just the standard model.

I will say this, finetuning to one or two orders of magnitude doesnt really bother me, I mean there could in principle be all sorts of other physics going on at very high energies that has been neglected and influencing those numbers. Otoh, more than that starts becoming damn disturbing.

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The problem, and the declining optimism doesn't just come from the experimental developments. Equally important, string theorists are finding it much harder than anticipated to derive theoretical predictions from the models. If you theory can't make concrete predictions, no amount of experiment does you any good.Ratzinger said:

One of the big virtues of the Loop Quantum Gravity program is that it has, a least, started to get to the point where it can say something about what the theory says about real life.

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