## Monday, September 25, 2006

### Why strings?

There are considerable amounts of blogs which attack string theory.

Some of the argued reasons against it are things like: "they require additional non-observed dimensions", "they don’t make predictions and so they are not refutable", et, etc, you can see the "not even wrong" blog to find many of them.

I particularly have a problem with string theory far before all these questions even appear in the theoretical development. For me the problems begin at the very idea of an string as a basic object.

I mean, in the macroscopic world you can have an string. We know that we can describe it in terms of component (atoms) which keep joined themselves by means of their electronic interactions.

But, what about "fundamental" strings? What keeps them joined? I mean, we can think that we have some one-dimensional region of space witch shares some common features which differ from the ones of their environment and that is what we can call an string. The question is , why does it remains joined under time evolution?

I find that it would be natural to expect that their component point evolve in a manner that makes them to separate and we end up without an string any more.

Of course you can simply postulate that the string keeps joined. But for me it is an unsatisfactory situation. How could we circumvent it?

Well, let’s look at what we know. Where else do we have strings?

Well, there are another kind of strings apart from the one made of atoms. The cosmic strings. They appear as topological defects when a phase transition occurred. Similar topological defects happen in condensed matter physic. Could we think of a preliminary sate of the universe which went under some phase transition leaving as a result topological defects such as strings and branes?

Recently loop quantum gravity physic has presented some ideas which I thought could hold some light in these directions. I am referring to a paper by Friendklin (i will edit these later to put the arxiv) in which they claim that beginning from an spin foam model of pure gravity they obtain one-dimensional topological defects which behaves as particles. At least that is the promise. Until now it is a 2+1 spin foam model. And it is well known that gravity in that dimension is a pure topological theory (that is, not local degrees of freedom, only global ones). It is expected soon a new paper where the result is extended to 3+1 dimensions.

My problem with that article is that in some point it is introduced some hint that seems a lagrangian of a point particle which status is greatly an-explained and wich is the basic of the rest of the article. I am waiting for the next 3+1 article before doing a harder effort to understand these theory.

Anyway, is there another reason why string could keep joined under evolution? Maybe, the key word here is "evolution". I´ll do a separate post about these possibilities sometime later.

But of course you always can accept that strings (or branes) keep joined as a postulate, as seemingly everybody does without even worrying about how bizarre these notion could be and keep doing formalism. If you adopt these viewpoint the goodness of string theory relays in their good mathematical properties and ultimately in experimental confirmation.

P.S. Latex:

$c=\sqrt{a^2+b^2}$

### The first three seconds of the blogverse

These is intended as a blog mainly centered in diferent aproachs to quantum gravity, that is, string theory and loop quantum gravity and maybe others. Also it will paid some atention to the historical development of the subject.

I don´t claim to be an expert in none of them. That makes me feel freeand to not be tied to any of the contending theories.