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Q & A: M theory

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Most recent answer: 10/22/2007
Q:
Qu’est ce que la théorie M ET quel est sa relation avec la théorie des super cordes? Pourquoi doit on nécessairement développer des théories a 9...10... ou 11 dimentions qui ne semblent avoir qu’un sens mathématique pour pouvoir unifié les forces fondamentales connues de l’univers physique. MERCI
- Jean Yves (age 50)
Quebec Canada
A:
The distinction between M theory and the various string theories is beyond our expertise. M theory is said to be a more general theory from which the various string theories emerge as limits in certain parameter regimes.

The number of dimensions is set by the requirement that the theories be renormalizable. That means that there has to be a way to set parameters so that calculations do not all blow up to infinity when one sums all of the effects. This constarint is even trickier in quantum gravity than in other quantum theories. Any energetic event deforms space time, which creates more events, further deformning spacetime etc. Unless special conditions are met allowing cancellations of most of the terms, the resulting infinite sequences of effects cannot be made to converge. In 10 dimensions (time + 9 spatial ones) string theories can converge. In M theories, which include higher-dimensional constituents than strings, the number of dimensions needed goes up by one.

Here I'm just passing along things I've heard, not things I understand.

Mike W.

(published on 10/22/2007)

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