# Layman's understanding of interactions in string theory

Recently I have read some non-technical publication and books on strings (ex. The elegant universe by B. Greene). Greene says that the string theory unifies all interactions and explains their nature.

In fact I haven’t found any explanation why do particles / strings interact. I mean – why do two electrons repel or why do 2 quarks attract strongly? Or why do all particles attract gravitationally?

Does the string theory realy clarify the nature of interactions or is it only the mathematical tool for calculations as the quantum mechanics is?

tom.stoer
String theory as of today is not able to predict the particle content of the standard model. So it cannot predict their interactions, either.

ooh i loved that book; for your first series of question no one knows all work in particle physics basically describes how particles interact with bosons without telling why; for your second question it does clarify interactions in a nonmathmatical way: as the book says, particles interact through the fundamental forces via bosons or particle carriers of the particular force. according to string theory, when an electron(arbitrary particle) emits a photon, a piece of the electron's string breaks off and becomes the photon which can then be absorbed by whatever particle it's interacting with

String theory as of today is not able to predict the particle content of the standard model. So it cannot predict their interactions, either.
That it is not able to predict is true. But that it can calculate the interactions without any further assumption is one of its greatest appeal. We are used to having to somehow "choose" the interactions once the free theory is defined. String interactions however are already in the "free" lagrangian, they just happen to be topological. For instance in
http://xxx.soton.ac.uk/abs/hep-ph/0001166 [Broken]
you will find explicit string corrections to the standard model.

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tom.stoer
You should add the remark that these corrections are derived under the assumption that the extra dimensions are large. So it's not ST, it's "ST +large extra dimensions".

Again, it's one of many possible ST-inspired models, so there's no prediction from first principles.

Let's wait for the first LHC results ...

ooh i loved that book; for your first series of question no one knows all work in particle physics basically describes how particles interact with bosons without telling why; for your second question it does clarify interactions in a nonmathmatical way: as the book says, particles interact through the fundamental forces via bosons or particle carriers of the particular force. according to string theory, when an electron(arbitrary particle) emits a photon, a piece of the electron's string breaks off and becomes the photon which can then be absorbed by whatever particle it's interacting with

I'm still confused the by these matters. I used to think that what is described above was the accepted way an electron would emmit a photon ie by the string breaking in two. But ive also heard that an electron is the ossilation at the end of an open string and the photon is the vibration onlong the string between the end points.

In this sense one should understand particles as possible modes of vibration on a string. There is only one type of string(or one for each type of string theory). Certainly it seems that gauge particles can be viewed in a stringy picture as vibration modes on a string. But quite how one should view quarks and leptons im not sure.

I don't claim to know what im talking about...this is just what i pick up from conversations with string theorists and from laymans books.

well i'm not much of an expert but i've never heard of this and it seems counterintuitive; for instance, if an electron is at the end of the open string and the bosons are along it, where is the particle the electron is interacting with?

well i'm not much of an expert but i've never heard of this and it seems counterintuitive; for instance, if an electron is at the end of the open string and the bosons are along it, where is the particle the electron is interacting with?

The other end of the string! Yeah it seems a bit weird. But i think the idea goes back to the original idea of strings describing the strong force. The string could be understood as a field line between the two particles. So one is quantizing the field lines or the flux as supposed to the field.