string theory

[space noob]

It's said that there are only 6 categories of different string theories and around over 600 known different models, what's yours?

[ajb]

It's said that there are only 6 categories of different string theories....

 

You mean perturbatively defined string theories?

 

1. Bosonic
   
2. I
   
3. IIA
   
4. IIB
   
5. HO
   
6. HE
   

 

By models, do you mean the string vacua?

[MigL]

I thought Witten had shown that all FIVE string theories were part of a whole, ie subtheories of the ONE theory.

 

Five, because Bosonic was not a true string theory but a failed attempt by Veneziano ( ? ) to model the strong interaction which QCD did much better.

[space noob]

You mean perturbatively defined string theories?

 

1. Bosonic
   
2. I
   
3. IIA
   
4. IIB
   
5. HO
   
6. HE
   

 

By models, do you mean the string vacua?

 

No I meant categories and I meant models, that is why they are the words I chose

 

I'm sorry I've just re-release over a book now, in a part it says 600 theories and in another part he states that there are ten 10 to the power of 500 he says each one is distinct in there own way, which can't be true, he says ask the string theories fit into 6 groups, some places say there are four, others say five, then others say there are five with a new emerging string theory,

Anyway i've just done a bit of looking into the guy himself and it seems like he is a great physicist but he thinks we should reject the string theory itself, it would appear my head has been filed with his opinions

[Arch2008]

Well the Large Hadron Collider has found no evidence of fundamental building blocks smaller than a quark, nor extra dimensions. This is not a head shot for string theory in general, but some of the string “sub-theories” are in trouble.

[MigL]

Not a big surprise Arch, since the LHC isn't capable of the energies needed to investigate Planck scale particles and events. Nor compacted extra dimensions, also of the same scale. A much bigger collider is needed for Plank scales and the only one we know of is called the Big Bang.

[ajb]

No I meant categories and I meant models, that is why they are the words I chose

 

I'm sorry I've just re-release over a book now, in a part it says 600 theories and in another part he states that there are ten 10 to the power of 500 he says each one is distinct in there own way, which can't be true, he says ask the string theories fit into 6 groups, some places say there are four, others say five, then others say there are five with a new emerging string theory,

Anyway i've just done a bit of looking into the guy himself and it seems like he is a great physicist but he thinks we should reject the string theory itself, it would appear my head has been filed with his opinions

 

You will need to be clearer on categories and models, they can mean very specific things to mathematicians.

 

10^500 is an estimate on the number of solutions in superstring theory, each one of these vacua represents a different choice in the details of the universe.

 

Via dualities we can relate the different perturbative superstring theories. More than this, each specific string theory is believed to be different limits of an 11 dimensional theory called M-theory. There is also an 11 dimensional supergravity as another limit.

 

So, these are the perturbative string theories, in between these there are many other string theories "sat inside" M-theory.

 

I should also point out that the bosonic string theory is an odd ball and does not fit into M-theory as far as we know.

Edited May 17, 2012 by ajb

[Arch2008]

MigL, the LHC can still do this:

http://www.wired.com/wiredscience/2010/12/lhc-black-holes-string-theory/

and this:

http://arxiv.org/abs/1008.2461

[MigL]

Arch2008, the first link describes a specific version of string theorywhere gravity is postulated to fall off with r^9 instead of r^2. This is because gravity falls off with r^(n-1) where n is the number of dimensions. The fact that M-theory is 10 spatial dimensioned, and that in certain versions of M-theory gravitons are the only bosons whose 'string' is not attached at either end to a brane, means that they can pass through all 10 dimensions, leading to a force of gravity which is very much stronger at extremely small distances than the currently accepted theory.

To investigate actual Planck scales a collider the size of the galaxy would be needed. I don't think they'll get funding for it anytime soon.

 

I don't understand the significance of the second link.

Edited May 20, 2012 by MigL