Can anyone give a simple(ish) explanation on how String Theory works?

[DQuaN]

Well...?

 

[Famine]

For "simple" explanations, Wikipedia is usually a good source. But, as with other things Universe, if you understand it you don't.

 

[Specialized]

Not having the worlds greatest understanding of string theory i decided to do a little search to see if i could simplify the extremely long definitions i have read about and i found this. Granted its not the shortest or simplist but in comparison to others its just a snippit.

. Think of a guitar string that has been tuned by stretching the string under tension across the guitar. Depending on how the string is plucked and how much tension is in the string, different musical notes will be created by the string. These musical notes could be said to be excitation modes of that guitar string under tension.
. In a similar manner, in string theory, the elementary particles we observe in particle accelerators could be thought of as the "musical notes" or excitation modes of elementary strings.
. In string theory, as in guitar playing, the string must be stretched under tension in order to become excited. However, the strings in string theory are floating in spacetime, they aren't tied down to a guitar. Nonetheless, they have tension. The string tension in string theory is denoted by the quantity 1/(2 p a'), where a' is pronounced "alpha prime"and is equal to the square of the string length scale.
. If string theory is to be a theory of quantum gravity, then the average size of a string should be somewhere near the length scale of quantum gravity, called the Planck length, which is about 10-33 centimeters, or about a millionth of a billionth of a billionth of a billionth of a centimeter. Unfortunately, this means that strings are way too small to see by current or expected particle physics technology (or financing!!) and so string theorists must devise more clever methods to test the theory than just looking for little strings in particle experiments.
. String theories are classified according to whether or not the strings are required to be closed loops, and whether or not the particle spectrum includes fermions. In order to include fermions in string theory, there must be a special kind of symmetry called supersymmetry, which means for every boson (particle that transmits a force) there is a corresponding fermion (particle that makes up matter). So supersymmetry relates the particles that transmit forces to the particles that make up matter.
. Supersymmetric partners to to currently known particles have not been observed in particle experiments, but theorists believe this is because supersymmetric particles are too massive to be detected at current accelerators. Particle accelerators could be on the verge of finding evidence for high energy supersymmetry in the next decade. Evidence for supersymmetry at high energy would be compelling evidence that string theory was a good mathematical model for Nature at the smallest distance scales.

Spec.

 

[Shannon]

I don't get the whole different-vibrations-affect-the-type-of-particle thing.

http://en.wikipedia.org/wiki/String_theory

"The basic idea behind all string theories is that the fundamental constituents of reality are strings of extremely small scale (possibly Planck length, about 10−35 m) which vibrate at specific resonant frequencies.[2] Thus, any particle should be thought of as a tiny vibrating object, rather than as a point. This object can vibrate in different modes (just as a guitar string can produce different notes), with every mode appearing as a different particle (electron, photon etc.)"

So my understanding is that if a string vibrates at X frequency it is an electron, but if it vibrates at Y frequency it is a photon. And according to this, a single string can vibrate at a number of different frequencies. Meaning, one string could go from being an electron to photon simply by vibrating at a different frequency? Surely something can't change its properties (going from a particle responsible for electricity to a particle responsible for light) just by moving faster/slower?

Or maybe my understanding is waaay off.

 

[skip0110]

So my understanding is that if a string vibrates at X frequency it is an electron, but if it vibrates at Y frequency it is a photon. And according to this, a single string can vibrate at a number of different frequencies. Meaning, one string could go from being an electron to photon simply by vibrating at a different frequency? Surely something can't change its properties (going from a particle responsible for electricity to a particle responsible for light) just by moving faster/slower?

A couple things might help clear this up.

1) Remember, the string is just a model to help you understand the electron (or photon, or other fundamental particle). The physicists goal is to make a mathematical model that fits the behavior of the electron. Once the developed a mathematical model (string theory) they realized that the equations that describe the electron are very similar to the set of equations that describe a string vibrating in 9 (or however many it is) dimensions. So, since envisioning a string vibrating is slightly more simple that doing 9-dimensional calculus, they present the model as "strings inside an electron". No one is saying that there actually are tiny strings inside the electron...what they are saying is that you can predict the behavior of the electron if you imagine there are tiny strings inside it. And the true way to predict the behavior is to use the equations, because the strings are not a perfect analogy (consider...a real string has material, weight, etc.).

And, as an addendum to this, people commonly expect physics to present them with a neat, commonly understandable, model like the string. But there is nothing inherent in the practice of physics that says that what goes on at the subatomic level must be able to be modeled by everyday things you see in the macroscopic world...which is one of the reasons people have so much difficulty understanding quantum mechanics.

2) The are referring to the string's natural frequency, which is unique for a given string of a given length. That string can vibrate at any integer multiple of it's natural frequency. A particle is modeled by a string of a certain length...to convert it to another particle, you would need to change the length of the string.

3) But wait! Remember, the strings are just a model. They don't really exist at all, so you can't just "change the length of the string." Something must happen at the subatomic level, which changes numbers in the equations, so that the particle would be modeled by a string of a different length. What kind of thing would that be? Well, you could bombard the electron with some quarks or leptons (or something like that, some fundamental particles), and that would turn it into a proton.

Hope that clarifies more than it confuses!