# Help regarding strings and m-theory

1. Aug 19, 2004

### aekanshchumber

To everyone,

Being new to string theory (m-theory) this theory is not completely clear to me. I'd be like if some one please help me in understanding it.

Thanks Aekansh

Last edited: Aug 19, 2004
2. Aug 20, 2004

### sol2

Hope this helps, as I am sure it will. Kaku is very heplful as well. Some do not appreciate this link?

Brane Cosmology

Last edited: Aug 20, 2004
3. Aug 29, 2004

### Tom McCurdy

www.quantumninja.com/toe

is a site that I am trying to work on building to help people first starting studying string theory, please tell me in what areas you would like to know more information about.

4. Aug 29, 2004

### PRodQuanta

You will find, and everybody will probably agree, that all of us at PF are asking that same question.

5. Aug 29, 2004

### Tom McCurdy

Well ask a specific Question and lets see what we can do

6. Aug 30, 2004

### aekanshchumber

how did the idea of 11 dimension universe came?what made the theorist tothink that the universe might exist in 11 dimensions. it could be more or less. and what does these extra dimensions tell or represent like 3-dimenssional spce let us move.
thanks

7. Aug 30, 2004

### sol2

If this is a expansitory mode, from where did it originate?

Here is (x,y,z,t)+six=Ten The Bubble encapsulating all of it, is eleven? M stands for Membrane.

From a one dimensional string, how would we get there? I had been looking for geometrical consistancy, so looking at model constructions, how does a sphere originate?

If from a point, where is this? If the gravitational collapse takes place in the blackhole, we quickly come to recognzie where this point would emerge from becuase as this blackhole collapses, tremendous heat is generated, and at planck length energy s looked at quite differently. Expansitory modes must orignate from some place.

So particle reductionism has been applied to energy considerations. They had no choice. They have run out of room(energy) and needed a different place to look at this. So cosmologically we understand then how particle reductionism has now changed our view of the cosmo?

http://superstringtheory.com/experm/exper5a.html

Last edited: Aug 30, 2004
8. Aug 30, 2004

### Tom McCurdy

why 11 dimensions

http://www-th.phys.rug.nl/~schaar/htmlreport/node12.html

Well added dimensions wasn't something completly unique to string theory it actually started with Kaluza Klein theory in 1919 which postulated the existance of an extra spacial dimension that was currled up. You see mathmatically you have a lot more freedom than you do in what you view as reality. For example lets say you calculate the volume of a 4-d object, it would simply be $$length1 * length2 * length 3 * length4 = volume$$ So dimensions were added because it allows more freedom mathmatically and allowed the physicsts do do additonal calculations to unify EM with GR. It went from there to 10 dimensions with string theory. The strings needed the extra degrees of freedom to viberate. Since the particular viberation of a string determines what properties it has it needed to be able to viberate in more than just 3 extended dimensions, so again mathmatically they added the dimensions. (here is a good link on history of dimensions in relation to string theory http://www.pbs.org/wgbh/nova/elegant/dimensions.html )

Now if you get why there needs to be extra dimensions (to allow for more freedom for strings) it becomes apparent that the extra dimensions must be in very specific shapes to get particular viberations. This is where the term calabi yau manifold comes from. It is the predicted shape of the curled up dimensions. However there are thousands of calabi yau shapes so they must be limited down further based on how they would create viberations. And I believe currently we need a calabi yau manifold with 3 holes which allows for the extended dimensions we are familar with today.

However the 10 dimensional model of string theory caused a problem for most people becaue it produced 5 different string theories which a man named Ed Witten was able to combine into one theory known as M-theory which basically said the old theories were merely reflections of each other. (Also keep in mind string theory math is approximate at this stage which is why they added a dimension when they learned it needed an extra one)

So they basically came up with the idea for extra dimensions by mathmatically recoginzeing what they could do with extra dimensions in accordance with a particular theory.

9. Aug 30, 2004

### sol2

good explanation Tom

With this link here, we will understand better what was being relayed in post above Tom's.

10. Aug 30, 2004

### Tom McCurdy

thanks sol

11. Aug 30, 2004

### aekanshchumber

Thanks to all of you for the posts,
But i still can not understand that how did the basic four forces are told as the ripples in the higher dimensions. once, i read an article by Michio Kaku in which he said that the forces are the ripples in the higher dimensions which we can't see but feel that they are there.

Awaiting replies
Aekansh

12. Aug 30, 2004

### sol2

Hyperspace, by Michio Kaku Pg 9

What is the true Vacuum?

https://www.physicsforums.com/showpost.php?p=298300&postcount=12

13. Sep 27, 2004

### aekanshchumber

I think i have started learning a little bit about it. Recently i read a book in which these things were explained. But now a new problem arrived Hiegher dimensional mathematics.In the book it was said that when the basic laws of nature are tried to solve in hiegher dimensions the are much simplified. Like a tiger in its natural habitat but in our three dimensional world these forces are little it destorted like the tiger in capitivity.
Now will any body please tell me some thing about the Hiegher Dimensional mathematics.

Thanks