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In physics , string theory    is a theoretical framework in which the point-like particles of particle physics are replaced by one-dimensional objects called strings. String theory describes how these strings propagate through space and interact with each other. On distance scales larger than the string scale, a string looks just like an ordinary particle, with its mass , charge , and other properties determined by the vibrational state of the string.
In string theory, one of the many vibrational states of the string corresponds to the graviton , a quantum mechanical particle that carries gravitational force. Thus string theory is a theory of quantum gravity. String theory is a broad and varied subject that attempts to address a number of deep questions of fundamental physics. String theory has contributed a number of advances to mathematical physics , which have been applied to a variety of problems in black hole physics, early universe cosmology , nuclear physics , and condensed matter physics , and it has stimulated a number of major developments in pure mathematics.
Because string theory potentially provides a unified description of gravity and particle physics, it is a candidate for a theory of everything , a self-contained mathematical model that describes all fundamental forces and forms of matter. Despite much work on these problems, it is not known to what extent string theory describes the real world or how much freedom the theory allows in the choice of its details.
String theory was first studied in the late s as a theory of the strong nuclear force , before being abandoned in favor of quantum chromodynamics.
Subsequently, it was realized that the very properties that made string theory unsuitable as a theory of nuclear physics made it a promising candidate for a quantum theory of gravity. The earliest version of string theory, bosonic string theory , incorporated only the class of particles known as bosons.
It later developed into superstring theory , which posits a connection called supersymmetry between bosons and the class of particles called fermions. Five consistent versions of superstring theory were developed before it was conjectured in the mids that they were all different limiting cases of a single theory in 11 dimensions known as M-theory. One of the challenges of string theory is that the full theory does not have a satisfactory definition in all circumstances.
Another issue is that the theory is thought to describe an enormous landscape of possible universes, which has complicated efforts to develop theories of particle physics based on string theory. These issues have led some in the community to criticize these approaches to physics, and to question the value of continued research on string theory unification.
In the 20th century, two theoretical frameworks emerged for formulating the laws of physics. The first is Albert Einstein 's general theory of relativity , a theory that explains the force of gravity and the structure of spacetime at the macro-level.
The other is quantum mechanics , a completely different formulation, which uses known probability principles to describe physical phenomena at the micro-level. By the late s, these two frameworks had proven to be sufficient to explain most of the observed features of the universe , from elementary particles to atoms to the evolution of stars and the universe as a whole. In spite of these successes, there are still many problems that remain to be solved. One of the deepest problems in modern physics is the problem of quantum gravity.
A quantum theory of gravity is needed in order to reconcile general relativity with the principles of quantum mechanics, but difficulties arise when one attempts to apply the usual prescriptions of quantum theory to the force of gravity. String theory is a theoretical framework that attempts to address these questions and many others. The starting point for string theory is the idea that the point-like particles of particle physics can also be modeled as one-dimensional objects called strings.
String theory describes how strings propagate through space and interact with each other. In a given version of string theory, there is only one kind of string, which may look like a small loop or segment of ordinary string, and it can vibrate in different ways. On distance scales larger than the string scale, a string will look just like an ordinary particle, with its mass , charge , and other properties determined by the vibrational state of the string.
In this way, all of the different elementary particles may be viewed as vibrating strings. In string theory, one of the vibrational states of the string gives rise to the graviton , a quantum mechanical particle that carries gravitational force.
One of the main developments of the past several decades in string theory was the discovery of certain 'dualities', mathematical transformations that identify one physical theory with another. Physicists studying string theory have discovered a number of these dualities between different versions of string theory, and this has led to the conjecture that all consistent versions of string theory are subsumed in a single framework known as M-theory.
Studies of string theory have also yielded a number of results on the nature of black holes and the gravitational interaction. There are certain paradoxes that arise when one attempts to understand the quantum aspects of black holes, and work on string theory has attempted to clarify these issues. Since string theory incorporates all of the fundamental interactions, including gravity, many physicists hope that it will eventually be developed to the point where it fully describes our universe, making it a theory of everything.
One of the goals of current research in string theory is to find a solution of the theory that reproduces the observed spectrum of elementary particles, with a small cosmological constant , containing dark matter and a plausible mechanism for cosmic inflation.
While there has been progress toward these goals, it is not known to what extent string theory describes the real world or how much freedom the theory allows in the choice of details.
The scattering of strings is most straightforwardly defined using the techniques of perturbation theory , but it is not known in general how to define string theory nonperturbatively. The application of quantum mechanics to physical objects such as the electromagnetic field , which are extended in space and time, is known as quantum field theory.
In particle physics, quantum field theories form the basis for our understanding of elementary particles, which are modeled as excitations in the fundamental fields. In quantum field theory, one typically computes the probabilities of various physical events using the techniques of perturbation theory. Developed by Richard Feynman and others in the first half of the twentieth century, perturbative quantum field theory uses special diagrams called Feynman diagrams to organize computations.
One imagines that these diagrams depict the paths of point-like particles and their interactions. The starting point for string theory is the idea that the point-like particles of quantum field theory can also be modeled as one-dimensional objects called strings.
At the level of Feynman diagrams, this means replacing the one-dimensional diagram representing the path of a point particle by a two-dimensional 2D surface representing the motion of a string. One of the vibrational states of a string corresponds to the graviton, a quantum mechanical particle that carries the gravitational force.
The original version of string theory was bosonic string theory , but this version described only bosons , a class of particles which transmit forces between the matter particles, or fermions. Bosonic string theory was eventually superseded by theories called superstring theories. These theories describe both bosons and fermions, and they incorporate a theoretical idea called supersymmetry. In theories with supersymmetry, each boson has a counterpart which is a fermion, and vice versa.
The different theories allow different types of strings, and the particles that arise at low energies exhibit different symmetries. For example, the type I theory includes both open strings which are segments with endpoints and closed strings which form closed loops , while types IIA, IIB and heterotic include only closed strings. In everyday life, there are three familiar dimensions 3D of space: height, width and length. Einstein's general theory of relativity treats time as a dimension on par with the three spatial dimensions; in general relativity, space and time are not modeled as separate entities but are instead unified to a four-dimensional 4D spacetime.
In this framework, the phenomenon of gravity is viewed as a consequence of the geometry of spacetime. In spite of the fact that the Universe is well described by 4D spacetime, there are several reasons why physicists consider theories in other dimensions. In some cases, by modeling spacetime in a different number of dimensions, a theory becomes more mathematically tractable, and one can perform calculations and gain general insights more easily.
One notable feature of string theories is that these theories require extra dimensions of spacetime for their mathematical consistency. In bosonic string theory, spacetime is dimensional, while in superstring theory it is dimensional, and in M-theory it is dimensional.
In order to describe real physical phenomena using string theory, one must therefore imagine scenarios in which these extra dimensions would not be observed in experiments. Compactification is one way of modifying the number of dimensions in a physical theory. In compactification, some of the extra dimensions are assumed to "close up" on themselves to form circles. A standard analogy for this is to consider a multidimensional object such as a garden hose.
If the hose is viewed from a sufficient distance, it appears to have only one dimension, its length. However, as one approaches the hose, one discovers that it contains a second dimension, its circumference.
Thus, an ant crawling on the surface of the hose would move in two dimensions. Compactification can be used to construct models in which spacetime is effectively four-dimensional. However, not every way of compactifying the extra dimensions produces a model with the right properties to describe nature.
In a viable model of particle physics, the compact extra dimensions must be shaped like a Calabi—Yau manifold. Another approach to reducing the number of dimensions is the so-called brane-world scenario.
In this approach, physicists assume that the observable universe is a four-dimensional subspace of a higher dimensional space. In such models, the force-carrying bosons of particle physics arise from open strings with endpoints attached to the four-dimensional subspace, while gravity arises from closed strings propagating through the larger ambient space. This idea plays an important role in attempts to develop models of real world physics based on string theory, and it provides a natural explanation for the weakness of gravity compared to the other fundamental forces.
A notable fact about string theory is that the different versions of the theory all turn out to be related in highly nontrivial ways. One of the relationships that can exist between different string theories is called S-duality. This is a relationship that says that a collection of strongly interacting particles in one theory can, in some cases, be viewed as a collection of weakly interacting particles in a completely different theory.
Roughly speaking, a collection of particles is said to be strongly interacting if they combine and decay often and weakly interacting if they do so infrequently. Type I string theory turns out to be equivalent by S-duality to the SO 32 heterotic string theory.
Similarly, type IIB string theory is related to itself in a nontrivial way by S-duality. Another relationship between different string theories is T-duality. Here one considers strings propagating around a circular extra dimension. For example, a string has momentum as it propagates around a circle, and it can also wind around the circle one or more times. The number of times the string winds around a circle is called the winding number.
If a string has momentum p and winding number n in one description, it will have momentum n and winding number p in the dual description. For example, type IIA string theory is equivalent to type IIB string theory via T-duality, and the two versions of heterotic string theory are also related by T-duality. In general, the term duality refers to a situation where two seemingly different physical systems turn out to be equivalent in a nontrivial way.
Two theories related by a duality need not be string theories. For example, Montonen—Olive duality is example of an S-duality relationship between quantum field theories. If two theories are related by a duality, it means that one theory can be transformed in some way so that it ends up looking just like the other theory.
The two theories are then said to be dual to one another under the transformation. Put differently, the two theories are mathematically different descriptions of the same phenomena. In string theory and other related theories, a brane is a physical object that generalizes the notion of a point particle to higher dimensions. For instance, a point particle can be viewed as a brane of dimension zero, while a string can be viewed as a brane of dimension one.
It is also possible to consider higher-dimensional branes. In dimension p , these are called p -branes. The word brane comes from the word "membrane" which refers to a two-dimensional brane. Branes are dynamical objects which can propagate through spacetime according to the rules of quantum mechanics.
They have mass and can have other attributes such as charge.
Offers end pm EST. Conceptual progress in fundamental theoretical physics is linked with the search for the suitable mathematical structures that model the physical systems. Quantum field theory QFT has proven to be a rich source of ideas for mathematics for a long time. This book contains a collection of papers highlighting the mathematical foundations of QFT and its relevance to perturbative string theory as well as the deep techniques that have been emerging in the last few years. An introduction, written by the editors, provides an overview of the main underlying themes that bind together the papers in the volume. Graduate students and research mathematicians interested in mathematical aspects of quantum field theory.
Vol 1 ,2,3,4Simon. Dimassi Limit. Reese Harvey. Goldhaber, C. An Introduction. Grosse H.
Recent years have seen noteworthy progress in the mathematical formulation of quantum field theory and perturbative string theory. We give a.
She kicked off her shoes and began to descend the cliff, sliding in the dust, catching her frock against a rock, and all the time cursing Brooke foully with one imprecation after another. Her momentum dragged him down off the rocks and onto the sand. She fell upon him, punching his face.
She kicked off her shoes and began to descend the cliff, sliding in the dust, catching her frock against a rock, and all the time cursing Brooke foully with one imprecation after another. Her momentum dragged him down off the rocks and onto the sand.
Quantum physics is the result of applying the framework of quantum mechanics to di erent physical phenomena. Quantum physics require more pure and basic mathematics system to firm the theory. The first one is: to solve the problem of establishing general quantum number constrained equation, the symmetry transformation mechanism of charge eigenstates for elementary particles is adopted, and the quant. The only real difference is in how the probabilities are calculated. This is a continuation of Fundamentals of Physics, I PHYS , the introductory course on the principles and methods of physics for students who have good preparation in physics and mathematics.
This book contains a collection of papers highlighting the mathematical foundations of QFT and its relevance to perturbative string theory as well as the deep.Eneas F. 04.05.2021 at 17:09
The book is very different from other books devoted to quantum field theory, both in the style of exposition and in the choice of topics.Terrence W. 08.05.2021 at 11:36
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