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Introduction to String Theory - Reverence - 06-20-2011
Particle Properties
In String Theory, Each known particle's (and unknown) smallest constituent is a string. If you take a paper and cut it in half enough times, you will reach the microscopic string. You may ask: "If every particle is a string, the aren't all particles the same?" The answer: No. The explanation: A photon (the electromagnetic force's "messenger" particle) for example, is composed of a string, not just a string, a string that acts as a guitar string, and hence a vibrational string. Every string vibrates in such a unique manner that the result of such a vibration is a specific particle.
Extra Dimensions
The equations of String Theory do not agree if applied to a mundane three dimensional world, instead, String Theory requires not three, not four, not seven, but nine space dimensions plus the time dimension, which equals a total of 10 spacetime dimensions. If the dimensions are extremely small then as predicted they will be shaped as a Calabi-Yau shape, Google is your friend. If that is the case, then EVERY single force of the known four forces (gravitational, electromagnetic, strong nuclear force, weak nuclear force) have access to the extra dimensions. But if the dimensions are larger than we can expect then [it will be discussed later in the thread].
What is a Dimension?
A dimension is not another world. When we speak of three dimensions, we speak of three pieces of information (left-right, back-forth, up-down), and when in two dimensions you only need two pieces of information (up-down, right-left), and so on.
Branes
Yes, there are other types of strings, membranes, branes for short. And they are heavier than strings and can either be three dimensional (3-branes), two dimensional (2-branes), one dimensional (1-branes) or any-number-less-than-11 dimensional (p-branes {not to be confused with brains composed of urine}). P-branes are heavier than strings by a minuscule amount and are rather sticky.
Open Strings
Strings that have loose ends are called "open strings" and these are the strings that tend to stick on a p-brane. Open strings are vital, for they are what compose ALL particles of the three forces. However, "gravitons" (the messenger particles of the gravitational force) are not composed of open strings and therefore they are free to visit other branes.
M-theory, Braneworlds, and Large Dimensions
M-theory, was developed to combine the five types of string theory (again, Google is your friend) and required ten spacial dimensions, equaling a number of eleven spacetime dimensions. Now, the M-theoretic framework explains what the Universe would be like if it was composed of ten large dimensions. Each dimension can serve to be one very large consecutive brane, thus inaccessible by our current dimension, even light can't reach the other branes. However, there is an exception for the gravitational force, and this is where cyclic cosmology comes into play.
Cyclic Cosmology
In such a braneworld scenario, gravity influences the other dimensions to clump together, creating another "bang". And so forth and so forth. The branes will not compress, they will take an increase in size based on the size of the two p-branes.
Conclusion
Thanks for reading, and I hope that you will take some of your time and indulge yourself within this and other similar scientific subjects.