# String theory

1. Feb 19, 2010

### clm321

in string theory is it that each quark of an atom has one string or is it made up of millions?

i know this is a kinda silly question

2. Feb 19, 2010

### Frame Dragger

All of the particles of The Standard Model are explained as the behaviour of one string, usually in a loop.

3. Feb 19, 2010

### humanino

There is a popular construction where quarks are open strings ending on two different stacks of branes. The topology of the stacks is supposed to build geometrically the gauge groups. It's cute.
http://arxiv.org/abs/hep-th/0502005v2

4. Feb 19, 2010

### humanino

That does not really answer the first question by the way...

Already in the standard model, there are two ways to think of the quarks. The fundamental quarks (with current, small, masses) are directly in correspondence with the strings in different models as above. But there are also the quarks we probe in experiment, let me say phenomenological, or dressed quarks. They have a running mass which depends on the scale. Those are made up of more quarks and gluons if you look at them closer, just as strings are made up of more strings if you look at them closer. From this point of view, the question is far from trivial. In order to make contact with experiments dealing with quarks, you can not stay at the tree level, you need at least one, maybe two loops. So you need renormalization in QFT.

5. Feb 19, 2010

### clm321

ok but in m theory there are not only looped strings but open strings right?

6. Feb 19, 2010

### Frame Dragger

I believe so, but definitely not loose; that would be type I I think.

7. Feb 19, 2010

### Galap

In string theory, what is the key difference between bosons, fermions, and leptons?

Edit: let me rephrase. What is the difference in the strings that explains the observable differences?

Last edited: Feb 19, 2010
8. Feb 19, 2010

### Naty1

In string theories, closed loops are gravitons which are free to go off in extra dimensions; open strings are bound on each end to a brane which we inhabit...

the detailed pattern of vibration executed by a string produces a specific mass, electric charge, spin and so forth. heavy particles vibrate faster, with more energy, than light ones.
spin 1 particles are messenger, spin 1/2 are matter particles.

9. Feb 20, 2010

### Naty1

Am not sure what "loose" means, but closed loops, gravitons, are not affixed to branes.

I am not sure if all the constitutent string theories associated with M theory have branes...and if they do which types, p and/or d....I just did a quick Wikipedia check....it says there are different types of d branes in different string theories...
http://en.wikipedia.org/wiki/Branes

Methinks we have too many theories, not enough experimental evidence so far...

10. Feb 20, 2010

### Frame Dragger

You're correct; not all STs rely on brane cosmology, and 'loose' means that they're not bound in a loop, but are under tension bound to at least one brane (I have no idea how this works for a theoretical entity with no basis in reality other than clever math).

String Theory is fascinating, but it's an intellectual exercise and a dart thrown at a VERY large board. As for how many... There's... 5 sub-types of string theory including M-Theory... I think. Some are obsolete or have parts that are now part of other string theories.

11. Feb 21, 2010

### Dav333

So is it safe to assume that ST will never be proved or disproved?

12. Feb 21, 2010

### Frame Dragger

I think if you could make money betting that, you might stand to become rich. That said, it's never really safe to assume that a theory can't be proven or falsified (unless it's insane to begin with, and that is merely confirmed), but I can't imagine how String/M theory could be examined.

We're already unlikely to be able to observe a lone quark (undressed), but I would imagine that happening before anything like confirmation of strings, or fuzzballs inside BH event horizons. The theory itself doesn't really allow for much by the way of confirmation it seems.

I'm no expert however, that's just my opinion.