What is String Theory and how is it used?
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String theory is a model of fundamental physics whose building blocks are one-dimensional extended objects (strings) rather than the zero-dimensional points (particles) that are the basis of the Standard Model of particle physics. For this reason, string theories are able to avoid problems associated with the presence of pointlike particles in a physical theory. Studies of string theories have revealed that they require not just strings but also higher-dimensional objects.
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Besides the classic standard model of quantum mechanics, there's the superspace version where all possibilities happen in alternate universes.  Then there's string theory and its higher dimensional cousin m-theory.  As far as I know, that last is most current.  Recent Nobel prize for it at Institute of Theoretical Physics at UC Santa Barbara.  But see link as well.
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Oh my, have you opened up a can of nightmarish confusion.\n\nYou are referring to String Theory, and it is way too complicated to describe here.  Here is an exerpt from an article on wikipedia of String Theory that describes these extra dimensions:\n\nOne intriguing feature of string theory is that it predicts the number of dimensions which the universe should possess. Nothing in Maxwell's theory of electromagnetism or Einstein's theory of relativity makes this kind of prediction; these theories require physicists to insert the number of dimensions "by hand". The first person to add a fifth dimension to Einstein's four was the German mathematician Theodor Kaluza in 1919. The reason for the unobservability of the fifth dimension (its compactness) was suggested by the Swedish physicist Oskar Klein in 1926.\n\nInstead, string theory allows one to compute the number of spacetime dimensions from first principles. Technically, this happens because for a different number of dimensions, the theory has a gauge anomaly. This can be understood by noting that in a consistent theory which includes a photon (technically, a particle carring a force related to an unbroken gauge symmetry), it must be massless. The mass of the photon which is predicted by string theory depends on the energy of the string mode which represents the photon. This energy includes a contribution from Casimir effect, namely from quantum fluctuations in the string. The size of this contribution depends on the number of dimensions since for a larger number of dimensions, there are more possible fluctuations in the string position. Therefor, the photon will be massless - and the theory consistent - only for a particular number of dimensions.\n\nThe only problem is that when the calculation is done, the universe's dimensionality is not four as one may expect (three axes of space and one of time), but twenty-six. More precisely, bosonic string theories are 26-dimensional, while superstring and M-theories turn out to involve 10 or 11 dimensions. In bosonic string theories, the 26 dimensions come from the Polyakov equation (see technical details in the preprint "Quantum Geometry of Bosonic Strings - Revisited"). However, these results appear to contradict the observed four dimensional space-time.\n\n \nCalabi-Yau manifold (3D projection)Two different ways have been proposed to solve this apparent contradiction. The first is to compactify the extra dimensions; i.e., the 6 or 7 extra dimensions are so small as to be undetectable in our phenomenal experience. The 6-dimensional model's resolution is achieved with Calabi-Yau spaces. In 7 dimensions, they are termed G2 manifolds. Essentially these extra dimensions are compactified by causing them to loop back upon themselves.\n\nA standard analogy for this is to consider multidimensional space as a garden hose. If the hose is viewed from a sufficient distance, it appears to have only one dimension, its length. Indeed, think of a ball small enough to enter the hose but not too small. Throwing such a ball inside the hose, the ball would move more or less in one dimension; in any experiment we make by throwing such balls in the hose, the only important movement will be one-dimensional, that is, along the hose. However, as one approaches the hose, one discovers that it contains a second dimension, its circumference. Thus, a ant crawling inside it would move in two dimensions (and a fly flying in it would move in three dimensions). This "extra dimension" is only visible within a relatively close range to the hose, or if one "throws in" small enough objects. Similarly, the extra compact dimensions are only visible at extremely small distances, or by experimenting with particles with extremely small wave lengths (of the order of the compact dimension's radius), which in quantum mechanics means very high energies (see wave-particle duality).\n\nAnother possibility is that we
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first of all 4 dimentions is true because there are 3 spacial dimentions and the 4th is time.\n\nand we dont know if superstring theory is true, it's still just an idea, and hasn't been proven, nor has any evidence been shown for it, we just like it because it can be used to explain certain things if it were true.  in string theory, there are 11 dimentions, its not crap, why dont you read "the elegant universe" by brian greene, or at least do some type of reading on it before you call it crap.  the dimentions are interwoven in our own universe, just like the 4 that are already proven.
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actually, physicists are still looking for the law of everything that connects the different theories of things and stuff.  String theory is pretty interesting although it doesnt provide definitive answers, it gets closer.  You seem interested in this stuff, you should read "The Elegent Universe" by Brian Greene.  It will explain a lot and help with your understanding.  Be warned though, you might find it too interesting and get too curious like me and end up being a physics major just to get some questions answered, and more do get answered the farther you go in physics haha. Read that book though, it will blow your mind.
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STRING THEORY, is one of the theories of modern sciences where it states that every thing in this universe is made of strings. The visual and other evidence of differences in objects is how the strings are. For example, longer strings mean more red color (this is a hypothetical example.) \nString Theory was predicted to give solutions to lot of problems in modern Physics. It has not ben proved yet, thus is not a complete true science yet.
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String theory is a model of fundamental physics whose building blocks are one-dimensional extended objects (strings) rather than the zero-dimensional points (particles) that are the basis of the Standard Model of particle physics. For this reason, string theories are able to avoid problems associated with the presence of pointlike particles in a physical theory. Studies of string theories have revealed that they require not just strings, but also higher-dimensional objects.
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Well, if you want to break it down even more, the universe only consists of minscule, vibrating strings.  At least, that's the most widely accepted theory in fundamental physics right now.\n\nThe beauty of it all is how much complexity can arise from such simple fundamentals.
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Life would remain simpler with no strings attached.  However, string theory deals with a universe with more that the dimensions we know day-to-day.  For example, you can calculate the diagonal of a square or a cube and the result has physical significance you can deal with.  The forth demension is time but what is meant by the diagonal of that figure no longer a plane or a solid?  What do we know of even greater dimensions, especially if they describe the very small that we can never see?  Certain of the equations that have been produced have enoumous numbers of solutions and it is difficult to find the correct solution and how to test it.  And that is only scratching the surface of a subject that has attracted some of the best brainpower on the globe.  Good luck.
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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. \n 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. \n 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.
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According to string theory, the strings are the universe's \nelemental material. They vibrate in different ways and can\njoin and break apart to form different elemental particles\nthat make up the universe. The strings exist in 11\ndimensions: time, which physicists consider a dimension, and\n10 spatial dimensions. Four of those dimensions are the ones\nwe are familiar with, three spatial dimensions plus time.\nThe other dimensions may be so small they're invisible to\ncurrent detection equipment and are only known to exist because they leave a "footprint" of where they have been.
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In all honesty you can't. String theory is so mathematically complex that you basically need a PhD in string theory to understand it, in fact most PhD physicists who are not string theorists don't understand it, nor do the want to (and a lot of them are opposed to it).\n\nString theory is a very dangerous endeavor. Some of the stuff it suggests (like time travel) are fun to think about, but it has yet yielded an experiment that could be used to test its validity. There has never been anything observed, no measurement taken, that could prove sting theory true or false. So far, it is only a set of very complicated mathematical expressions that may or may not describe the world we live in. \n\nI think its great that your cousin has taken an interest in physics. But I think it would be best if you steer him away from books on string theory. There are many fascinating physical phenomena that have been observed that have nothing to do with strings. I would suggest that he read "1 2 3 ... infinity" by Gamow.
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String theory is the idea that everything in the universe is made out of tiny, vibrating loops of string that are far smaller than the size of an atom.\n\nIn string theory, there are currently believed to be ten dimensions (plus one for time).  A dimension is essentually just a direction:  Left-Right, Up-Down, Forward-Back.  Originally, all the dimensions were very small with little rooom for movement.\n\nAt the time of the Big Bang, the three dimensions I mentioned expanded rapidly to create the enormous universe we see today.  The other seven dimensions are still tiny.  There is not enough room in them for us to detect them directly, but they do influence the behavior of strings on very small scales.\n\nAn example of symmetry is that the rules of physics where you live are exactly the same as the rules of physics where I live.  In other words, the rules of physics are location symmetric.\n\nAnother example is that (by using the rules of general relativity developed by Einstein) the rules are symmetric for all observers, even if they are accelerating in opposite directions.  An interesting result of this symmetry is that gravity warps the fabric of space itself.\n\nSuper-symmetry is another example, like the two I just mentioned.  The details involve more math though, so I won't go into it.  It hasn't really been confirmed by experiment yet, by physicists have been using it to make predictions for years.\n\nCalculations show that the tiny strings of string theory follow the rules of super-symmetry.  That is one reason string theory is widely accepted.  Together, the two ideas predict that all particles we currently know (electrons, muons, quarks, etc.) have a matching super-symmetric particle.\n\nSince none of these have yet been found, they are thought to have much larger masses than the particles who know of.  With the next generation of particle accelerators (such as the Large Hadron Collider scheduled to start operation next year in Europe), it may be possible to test the existence of the matching super-symmetric particles.  That is one of the current ideas for providing evidence for or against string theory.
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At the moment no one knows.\n\nString theories are one attempts to combine Quantum Mechanics and General Relativity, which is what a unified theory is. Thus far no complete theory and no testable predictions have emerged. Perhaps they will in time, or from some of the alternatives like loop gravity.
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In the Standard Model, quarks, electrons and the like are considered to be pointlike. This gives problems at short distances where for instance the electromagnetic force between two of them becomes infinite.\n\nThe basic idea of stringtheory is that the fundamental constituents of matter are strings of a length of order of 10^35 m which vibrate at specific frequencies. However, the simplest string theories give more problems then they solve and consistent theories requires more then four dimensions. \n\nMembranes take the idea even further.  The particles are represented by vibrating surfaces and higher dimensional objects.
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There are two basic types of string theories: those with closed string loops that can break into open strings,  and those with closed string loops that can't break into open strings
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It is a theory that looks at physics differently to try and combine General Relativity with Quantum Mechanics, something the Standard Model (the most widely accepted theory of how the universe work) has not been able to do.  Instead of using zero dimentional point particles, it uses one dimentional strings which cleans out some of the complications with the Standard Model.  However, most of its predictions have yet to be verified, so its not as widely accepted or as successful as the Standard Model.  The amazing thing about String Theory (actually, it is a whole bunch of theories) is that it predicts Gravitons, something the Standard Model has been trying to do for very long but hasn't been able to.