# 11 Dimensional M - Theory

#### PhanthomJay

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Aside from the math behind the theory, what's the numerical significance of the 11 dimensions in this Universe? I'm not talking about the mathematical solution, but rather, what are the properties of the Universe that limit this number to 11? Or is it as significant or insignificant as the properties of the Universe that limits lightspeed or the dimensionless constants to certain numbers? Could other Universes have more, or less, dimensions? Or even an infinite number? I don't see why there should be a finite limit.

And as I recall, String theory used to say 10 dimensions, or perhaps 21 dimensions; apparently, the math worked out for both numbers. What happened to the 21?

Related Beyond the Standard Model News on Phys.org

#### PhanthomJay

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This articles concern the idea of extra-dimensions (modular functions, number of dimensions, compactifications...):
Thanks for the links! Pretty much beyond my comprehension, though. I guess I'll just have to accept it; however, at some point in time years ago, a renowned physicist (I forget her name) claimed that some of the extra dimensions may not be curled up small, but might instead be large, something , I suspect, like another Universe hidden beyond the 4D 'observable' spacetime dimensions. Do you know anything about this?

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#### Kevin_Axion

It's fine, I don't plan on reading it. I'm sticking with my Carl Sagan, Roger Penrose and Feynman stash.

#### lpetrich

As to why 11 dimensions maximum, that's from the details of supergravity theories. If one tries to construct a supergravity theory with more than 11 space-time dimensions, one finds multiple gravitons and particles with spins more than 2, both of which are troublesome.

11D supergravity has a rather simple set of particles:

A graviton (space-time)
A gravitino (vector-spinor)
An antisymmetric 3-tensor

#### PhanthomJay

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It's fine, I don't plan on reading it. I'm sticking with my Carl Sagan, Roger Penrose and Feynman stash.
Hawking refers to Feynman's work frequently. Soon, I think, I will have better understanding of the hows and whys of the Universes's behavior.

You don't want to miss reading this book!

#### Kevin_Axion

I'm not sure, I'm not really into the whole String Landscape/Anthropic Principle idea.

#### PhanthomJay

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I'm not sure, I'm not really into the whole String Landscape/Anthropic Principle idea.
Nonetheless, M-Theory seems like it will dominate (my opinion) the scientific literature over the next several decades. String Theory originated oh i don't know somewhere around the 50's, but no one paid too much attention to it and it sort of faded away until the more encompassing M-Theory came into fashion a decade or 2 ago. And the Anthropic Principles have moved to the forefront again. If You like Feynman's works, you'll like this book, since much of it is based on his insights.

#### PhanthomJay

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Nonetheless, M-Theory seems like it will dominate (my opinion) the scientific literature over the next several decades. String Theory originated oh i don't know somewhere around the 50's, but no one paid too much attention to it and it sort of faded away until the more encompassing M-Theory came into fashion a decade or 2 ago. And the Anthropic Principles have moved to the forefront again. If You like Feynman's works, you'll like this book, since much of it is based on his insights.
Hawking concluded that M-theory is the ONLY theory that may lead to the Theory of Everything....if such a Theory may ever be found. I still have several questions that I'll be asking on the Cosmology Forum.

#### dimensional

You should pick up Brian Greene's The Elegant Universe. This book will offer a great amount of layman's insight in String/M-Theory research up until 2004 or 2005 of course.

I didn't think the Grand Design was all that impressive. Maybe I've read too many of the popular books and watched all the documentaries.. but this book is just more of the same. I mean, it's just.. too popular.

I would love to have something between wiki articles and popular books so I could know about the slightly more technical aspects of things like M-theory and the whole shabang.

#### Protonium

i'm sorry because asking this : could our space have more than 11 -D which has been predict by string theory ? there are some kinds of bosonic string require 26-D

#### arivero

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I'm not talking about the mathematical solution, but rather, what are the properties of the Universe that limit this number to 11? Or is it as significant or insignificant as the properties of the Universe that limits lightspeed or the dimensionless constants to certain numbers?
Basically, D=10 for superstrings and D=26 (not 21) for bosonic strings, can be said to come from c and h, as they are implied by quantisation and Lorentz invariance.

D=<11 in supergravity can be said to be implied by quantisation as maximum dimension to avoid spin greatear than two, as said before. But you need to put supersymmetry in the recipe.

If you put susy but not strings (nor many-particle field theory???), then the valid dimensions are D=3,4,6,10. This is really more mathematical than physical input, except perhaps if you look at it as an study of the properties of spinors (which is a lot of maths in any case). When you look at the way to get these solutions and you go to extended bodies, then the 2-brane is related to dimension 11 again.

#### eloheim

You should pick up Brian Greene's The Elegant Universe. This book will offer a great amount of layman's insight in String/M-Theory research up until 2004 or 2005 of course.
I really loved that book too. It was a little dissapointed later to discover a slightly less optimistic opinion of M-theory in the greater community of physicists. Then again when you read about 50++ years of history in a month, real-life time seems soo much slower...

P

#### PhilKravitz

Why do we say 10 space dimensions instead of 3 space dimensions and 7 other degrees of freedom?

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