Thread: can anyone explain to me m theory and the singularity

thank you =P

Well lets start with my post in the thread on string theory and see if you have more specific questions.

Originally Posted by mitchellmckain

Well one simple way of looking at string theory is that point particles and the interaction between particles at a point in quantum field theory tended to make the equations blow up as in singularities, like when you look at the function f(x)=1/x when x approaches zero. Therefore making the fundamental elements of existence extended strings rather than point particles made a lot of these mathematical problems go away.

Now for a while the biggest problem with string theory was that it was theories not theory. There were too many string theories. So a more recent breakthrough (called M-theory) was the realization that all these different string theories could made into different derivations of a single theory (and therefore equivalent) that treats the fundamental elements of existence as extended object of any number of dimensions, called branes. So for example a string would be called a 1-brane, that is a one dimensional brane, while a point particle would be a 0-brane. Now as I understand it, the inclusion of the 0-brane does not re-introduce the problem with singularities because of a principle of dualism, which makes a p dimensional brane in an n dimensional space equivalent (under some transformation of the field equations) to a n-p dimensional brane.

inst singularity is when the universe begin ?
and how many dimention are in the string theories?

first its called dimensions
second there is 11 dimensions
universe started in a singularity, but accordint to string theory there is no singularity that the universe started in.

y is there so many dimension? do they even use all of them? are even all the dimention actually exist?

why? becuase the physics and string require 11 dimensions to work there.
they do, whats the point else haivng them?
the dimenSions may exist, but there is only 4 visible and acting in ordinary life

11?? i though they were only 6..

11?? i though they were only 6..

11?? i though they were only 6..

11?? i though they are only 6..

11?? i though they are only 6..

11?? i though they are only 6..

No, 6 is the number of times you made the same post.

started with 10, then became 11

Originally Posted by Zelos

started with 10, then became 11

NO NO NO NO NO!!!!!

I thought I explained this to you before, Zelos!!!!

11 dimension was tried in a theory called Supergravity. It has since been proven that 11 dimensions is impossible. In any case string theory has never, ever, ever used 11 dimensions. For a long time it was either 10 or 26 dimensions depending on which string theory. But the unification of string theory under M-theory has made 10 dimensions the only option!

The point is that the vibrational modes of the string in enough dimension can corespond to the known types of elementary particles. And the number of dimensions that makes this work is 10 = 1 dimension of time, 3 large dimensions of space and 6 dimension much smaller than a proton.

Originally Posted by iLOVEscience

inst singularity is when the universe begin ?

A singularity is a mathematical term and it refers to mathematical functions like f(x)=1/x which gets bigger and bigger the closer x is to zero. Since the theories of physics are mathematical theories, there can be singularities in theories. Two such singularities in General relativity are black holes and when the universe began. But many singularities appear when you attempt to make a quantum theory of gravity, and the history of the development of unified field theories is the successful elimination of these singularities. Supersymmetry was one such success which led to the theory of Supergravity, but string theory (which also uses supersymmetry) successfully eliminates much more of these singularities than Supergravity.

For the most part scientists assume that when there are singularities in a theory of physics it means that the theory is wrong, breaks down, or at least unusable. For most things in the real world to do not go to infinity. So for example physicist will say that General relativity breaks down at the center of a black whole and at the beginning of the universe because of these singularities in the theory.

NO NO NO. i thought you saw pbs nova "The elegent universe" and read it on wikipedia
http://en.wikipedia.org/wiki/String_theory

In the 1990s, Edward Witten and others found strong evidence that the different superstring theories were different limits of a new 11-dimensional theory called M-theory. These discoveries sparked the second superstring revolution.

Dont question me when i am right MOHAHAHAHA

i suggest you dl the elegant universe and watch it, m theory is 11, its the old string theories that WERE 10

i heard that m theory and the string theories have been corrupted

by what?

idk and zelos thz for the sugestion on the elegant universe i found it interesting :-D

I am unclear on how a dimension can be smaller than a proton (or, more generally, how a dimension can have a size).

they are simply curled up so small nothing can be in them exept the strings

Originally Posted by Zelos

m theory is 11, its the old string theories that WERE 10

Originally Posted by M. J. Duff Int.J.Mod.Phys. A11 (1996) 5623-5642

Superunification underwent a major paradigm shift in 1984 when eleven-dimensional supergravity was knocked off its pedestal by ten-dimensional superstrings. This last year has witnessed a new shift of equal proportions: perturbative ten-dimensional superstrings have in their turn been superseded by a new non-perturbative theory called M-theory, which describes supermembranes and superfivebranes, which subsumes all five consistent string theories and whose low energy limit is, ironically, eleven-dimensional supergravity.

You are right. I have been caught in one of those ironic twists in the development of physics. None of the seminars I attended at the university when this M-theory was presented (as it was first coming out) mentioned this low energy limit going to 11-d Supergravity. My guess is that no one mentioned it at the time, where I was, because no one really believed it yet. I wonder, however, what happened to that proof that 11-dimensions could not work, that I read about. Maybe it had to do with high energy calculations which require a compactification of M theory in order to be useful (which they didn't know how to do yet). Hmmmm....

This article by Michio Kaku is really great, which I will quote from

Originally Posted by http://www.fortunecity.com/emachines/e11/86/dimens.html

at last physicists know where superstrings come from : they originate in the 11th dimension from M-theory.
...
But there are many loose ends. For example, what precisely is M-theory? So far, we only know fragments of the theory (the low-energy part). We are still waiting for someone to come up with a full description of M-theory Last year, Vafa shocked physicists by announcing that there may be a 12-dimensional theory lurking out there, which he called "F-theory" (F for father).
...
So will the final theory be in 10, 11 or 12 dimensions? According to Schwarz, the answer may be none of these. He feels that the true theory may not have a fixed dimensionality, and that 11 dimensions only emerge once we try to solve it. Townsend takes a similar view, saying, " The whole notion of dimensionality is an approximate one that only emerges in some semiclassical context."

So does this means that the end is in sight-that some day soon we will be able to work out the Standard Model from first principles? When I put this question to some leading physicists in this field they were still cautious. Townsend likened our present state of knowledge to the old quantum era of the Bohr atom, just before the full elucidation of quantum mechanics. "We have some fruitful pictures and some rules," he says. "But it's also clear that we don't have a complete theory."

I cannot say that I understand this idea of no fixed dimensionality....

Since the universe is beyond our understanding at this point, saying that it has only 11 dimensions could be 100000000000000th of the actual number. But this statement is obvious, and only a sidenote of the discussion at hand.