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String theoryexplanation needed

by ant0
Tags: string, theoryexplanation
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Feb22-04, 07:53 AM
P: 6
Basically i need educating here!! What are the basic concepts, etc of string theory? I heard that it is something to do with explaining how protons act, etc instead of explaining with quarks? Any help will be appreciated, cheers
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Feb22-04, 08:09 AM
PF Gold
P: 8,147
No, strings do not replace the quark model. Quarks are part of the present day successful theory called the Standard Model. And string theory does not propose to replace that but to explain it. The basic idea is that the quarks, and other elementary particles, are actuallly vibration modes of tiny, very very tiny strings, or other things called branes.

To give you an idea of what a vibration is, a note, such as middle C, is a vibration mode of a string in a piano. That same string has other modes, overtones of C, and each one of those tones is a vibration mode of that string.

So the tiny strings (BTW, string theory doesn't say what they are made of) vibrate in different modes, which are moreover quantized so the modes don't vary smoothly among themselves but come at separate energies, these quantized modes in some way constitute the particles. The way they do that has not really been fully explained by the string theorists, but they insist they are making progress and will be able to explain it real soon now.

So bottom line the quarks would still be used, just as Maxwell's equations of electromagnetism are still used in spite of the development of quantum electrodynamics, but another level of understanding would have been added.
Feb22-04, 10:33 AM
P: 6
bump, any more simple in a nutshell explanatons of string theory?

Feb24-04, 11:00 AM
P: 6
String theoryexplanation needed

another questoin i have: What was the original super gravity theory(s) that were replaced in the mid 1980s by string theory? Can anyone explain them? Was it to do with infinities of energy or something??? I'm a tad confused here
Feb24-04, 12:56 PM
Sci Advisor
HW Helper
P: 2,537
I thought that string theory was called string theory because the elemetary sping 1/2 particles could be described by equations that are similar to the equations that describe the motions of n dimensional strings or membranes.

This leads to a natural terminology for these elementary particles including a string as an elementary particle, and qualities such as tension or length which are not actually length or tension in a physical sense, but instead correspond to positions in the equations that describe the particles.

Since the inception of string theory, there have been developments of several string theories, which model elementary particles as behaving like different strings - for example as closed loops or allowing for open strings instead.

String theory has also been expanded to include particles with integer spin. These expanded theories are referred to as superstring theory.

The existance and variety of string theories has led theoretical physicists to consider the possibility that they are all aspects of a larger theory that includes them. This larger theory is referred to as M theory.
Feb24-04, 03:01 PM
PF Gold
P: 8,147
Nate, there are some misunderstandings in your account.

First, spin 1/2 particles (fermions) could only be incorporated into string theory by employing supersymmetry, in which each boson has a corresponding fermion and vice versa. This superstring theory quickly broke into five theories based on different gauge groups. Eventually the discoverey of dualisms unified them again in the 11-dimensional M-theory, of which Matrix theory is the currently most active representative.

In all of this, the actual representation of low energy particles as we understand them, in the standard model, has been an ever receding foxfire. The only particle that the theory has really had any success with is the graviton. Unless you want to count the tachyon.

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