The cyclic model is a brane cosmology model of the creation of the universe, derived from the earlier ekpyrotic model. It was proposed in 2001 by Paul Steinhardt and Neil Turok. Cyclic model - The model. In the cyclic model, two parallel orbifold planes or M-branes collide periodically in a higher dimensional space. The visible four-dimensional universe lies on one of these branes. The collisions correspond to a reversal from contraction to expansion, or a big crunch followed immediately by a big ba ...

Including:

• Cyclic model - The model

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The term 'string theory' properly refers to both the 26-dimensional bosonic string theories and to the 10-dimensional superstring theories created by adding supersymmetry. Nowadays, 'string theory' usually refers to the supersymmetric variant while the earlier is given its full name, 'bosonic string theory'. While understanding the details of string and superstring theories requires considerable mathematical sophistication, some qualitative properties of quantum strings can be understood in a fairly intuitive fashion. For example, qua ...

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String theory, String theory - History, String theory - Basic properties, String theory - Dualities, String theory - Extra dimensions, String theory - Problems, String theory - References and further reading, String theory - Footnote, String theory - Popular books and articles, String theory - Textbooks, String theory - External links

Read more here: » String theory: Encyclopedia II - String theory - Basic properties

Our physical space is observed to have only four large dimensions, and a physical theory must take this into account, but nothing prevents a theory from involving more than 4 dimensions, per se. In the case of string theory, consistency requires spacetime to have 10, 11 or 26 dimensions. The conflict between observation and theory is resolved by making the unobserved dimensions compact dimensions. Our minds have difficulty visualizing higher dimensions because we can only move in three spatial dimensions. Even then, we only see in 2+1 ...

See also:

Superstring theory, Superstring theory - Number of dimensions, Superstring theory - Number of superstring theories

Read more here: » Superstring theory: Encyclopedia II - Superstring theory - Number of dimensions

String physics - Closed and open strings. Strings can be either open or closed. A closed string is a string that has no end-points, and therefore is topologically equivalent to a circle. An open string, on the otherhand, has two end-points and is topologically equivalent to a line interval. Not all string theories contain both open and closed strings. However, any theory which contains open strings must also contain closed strings as interactions betwee ...

See also:

String physics, String physics - Types of strings, String physics - Closed and open strings, String physics - Orientation

Read more here: » String physics: Encyclopedia II - String physics - Types of strings

The term 'string theory' properly refers to both the 26-dimensional bosonic string theories and to the 10-dimensional superstring theories created by adding supersymmetry. Nowadays, 'string theory' usually refers to the supersymmetric variant while the earlier is given its full name, 'bosonic string theory'. While understanding the details of string and superstring theories requires considerable mathematical sophistication, some qualitative properties of quantum strings can be understood in a fairly intuitive fashion. For example, qua ...

See also:

String theory, String theory - History, String theory - Basic properties, String theory - Dualities, String theory - Extra dimensions, String theory - Problems, String theory - Popular culture, String theory - References and further reading, String theory - Footnote, String theory - Popular books and articles, String theory - Textbooks, String theory - External links

Read more here: » String theory: Encyclopedia II - String theory - Basic properties

Our physical space is observed to have only four large dimensions, and a physical theory must take this into account, but nothing prevents a theory from involving more than 4 dimensions, per se. In the case of string theory, consistency requires spacetime to have 10, 11 or 26 dimensions. The conflict between observation and theory is resolved by making the unobserved dimensions compact dimensions. Our minds have difficulty visualizing higher dimensions because we can only move in three spatial dimensions. Even then, we only see in 2+1 ...

See also:

Superstring theory, Superstring theory - Extra dimensions, Superstring theory - Number of superstring theories

Read more here: » Superstring theory: Encyclopedia II - Superstring theory - Extra dimensions

It was believed before 1995 that there were exactly five consistent superstring theories, which are called, respectively, the Type I string theory, the Type IIA string theory, the Type IIB string theory, the heterotic SO(32) (the HO string) theory, and the heterotic E8×E8 (the HE string) theory. As the names suggest, some of these string theories are related to each other. In the early 1990s, string theorists discovered that these relations were so strong that they could be thought of as an identification ...

See also:

M-theory, M-theory - Background, M-theory - Basics, M-theory - Naming conventions or What does M stand for?, M-theory - M-theory in various backgrounds, M-theory - Membranes, M-theory - Matrix Theory, M-theory - The Anti-deSitter/Conformal Field Theory Correspondence

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Brane cosmology assumes that the visible universe lies on a four-dimensional brane which moves in higher dimensional space. Our brane may be one of innumerable others moving through these extra dimensions. The ekpyrotic scenario was proposed by Khoury, Ovrut, Steinhardt and Turok in 2001. It suggests that the visible universe was empty and contracting in the distant past. At some time, our brane collided with another, parallel "hidden" brane, which caused the contracting universe to reverse and begin expanding. Hot matter and radiation was c ...

See also:

Ekpyrotic, Ekpyrotic - Introduction, Ekpyrotic - Outstanding problems, Ekpyrotic - Popular reception

Read more here: » Ekpyrotic: Encyclopedia II - Ekpyrotic - Introduction

Modern particle physics research is focused on subatomic particles, which have less structure than atoms. These include atomic constituents such as electrons, protons, and neutrons (protons and neutrons are actually composite particles, made up of quarks), particles produced by radiative and scattering processes, such as photons, neutrinos, and muons, as well as a wide range of exotic particles. Strictly speaking, the term particle is something of a misnomer. The objects studied by particle physics obey the principles of quantu ...

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Particle physics, Particle physics - Subatomic particles, Particle physics - History of particle physics, Particle physics - The Standard Model of particle physics, Particle physics - Experimental particle physics, Particle physics - Theoretical particle physics, Particle physics - Particle physics and reductionism, Particle physics - Public policy and particle physics, Particle physics - The future of particle physics

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While the classical theory (i.e. the tree diagrams) and semiclassical corrections (one-loop diagrams) behaved as expected, the Feynman diagrams with two (or more) loops led to ultraviolet divergences - i.e. infinite results that could not be removed because the quantized general relativity was not renormalizable, unlike Quantum electrodynamics. In popular terms, the discreteness of quantum theory is not compatible with the smoothness of Einstein's general relativity. These problems, together with some conceptual puzzles, led many physicists ...

See also:

Graviton, Graviton - Gravitons and models of quantum gravity, Graviton - Gravitons and experiments, Graviton - Problems with the Graviton

Read more here: » Graviton: Encyclopedia II - Graviton - Gravitons and models of quantum gravity

String theory was originally invented to explain peculiarities of hadron (subatomic particle which experiences the strong nuclear force) behavior. In particle-accelerator experiments, physicists observed that the spin of a hadron is never larger than a certain multiple of the square of its energy. No simple model of the hadron, such as picturing it as a set of smaller particles held together by spring-like forces, was able to explain these relationships. In 1968, theoretical physicist Gabriele Veneziano was trying to understand the strong nu ...

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String theory, String theory - History, String theory - Basic properties, String theory - Dualities, String theory - Extra dimensions, String theory - Problems, String theory - Popular culture, String theory - References and further reading, String theory - Footnote, String theory - Popular books and articles, String theory - Textbooks, String theory - External links

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Detecting a graviton, if it exists, would prove rather problematic. Because the gravitational force is so incredibly weak, as of today, physicists are not even able to directly verify the existence of gravitational waves, as predicted by general relativity. (Many people are surprised to learn that gravity is the weakest force. A simple experiment will demonstrate this, however: an ordinary refrigerator magnet can generate enough force to lift a mass against ...

See also:

Graviton, Graviton - Gravitons and models of quantum gravity, Graviton - Gravitons and experiments, Graviton - Problems with the Graviton

Read more here: » Graviton: Encyclopedia II - Graviton - Gravitons and experiments

Detecting a graviton, if it exists, would prove rather problematic. Because the gravitational force is so incredibly weak, as of today, physicists were not even able to directly verify the existence of gravitational waves, as predicted by general relativity. (Many people are surprised to learn that gravity is the weakest force. A simple experiment will demonstrate this, however: an ordinary refrigerator magnet can generate enough force to lift a mass against ...

See also:

Graviton, Graviton - Gravitons and models of quantum gravity, Graviton - Gravitons and experiments, Graviton - Problems with the Graviton

Read more here: » Graviton: Encyclopedia II - Graviton - Gravitons and experiments

String theory remains to be verified. No version of string theory has yet made a prediction which differs from those made by other theories—at least, not in a way that could be checked by a currently feasible experiment. In this sense, string theory is still in a "larval stage": it possesses many features of mathematical interest, and it may yet become supremely important in our understanding of the universe, but it requires further developments before it is accepted or falsified. Since string theory may not be tested in the foreseeable fu ...

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String theory, String theory - History, String theory - Basic properties, String theory - Dualities, String theory - Extra dimensions, String theory - Problems, String theory - Popular culture, String theory - References and further reading, String theory - Footnote, String theory - Popular books and articles, String theory - Textbooks, String theory - External links

Read more here: » String theory: Encyclopedia II - String theory - Problems

Theoretical physicists were troubled by the existence of five separate superstring theories. This has been solved by the second superstring revolution in the 1990s during which the five superstring theories were discovered to be different limits of a single underlying theory: M-theory. The five consistent superstring theories are: The type I string has one supersymmetry in the ten-dimensional sense (16 supercharges). This theory is special in the sense that it is based on unoriented open and closed strings, while the rest ...

See also:

Superstring theory, Superstring theory - Extra dimensions, Superstring theory - Number of superstring theories

Read more here: » Superstring theory: Encyclopedia II - Superstring theory - Number of superstring theories

The book The Elegant Universe by Brian Greene was adapted into a three-hour documentary for Nova. String theory is also a series of books based in the Star Trek: Voyager universe. ...

See also:

String theory, String theory - History, String theory - Basic properties, String theory - Dualities, String theory - Extra dimensions, String theory - Problems, String theory - Popular culture, String theory - References and further reading, String theory - Footnote, String theory - Popular books and articles, String theory - Textbooks, String theory - External links

Read more here: » String theory: Encyclopedia II - String theory - Popular culture

String theory remains to be verified. No version of string theory has yet made a prediction which differs from those made by other theories—at least, not in a way that could be checked by a currently feasible experiment. In this sense, string theory is still in a "larval stage": it possesses many features of mathematical interest, and it may yet become supremely important in our understanding of the Universe, but it requires further developments before it is accepted or falsified. Since string theory may not be tested in the foreseeable fu ...

See also:

String theory, String theory - History, String theory - Basic properties, String theory - Dualities, String theory - Extra dimensions, String theory - Problems, String theory - References and further reading, String theory - Footnote, String theory - Popular books and articles, String theory - Textbooks, String theory - External links

Read more here: » String theory: Encyclopedia II - String theory - Problems

The idea that matter is composed of elementary particles dates to at least the 6th century BC. The philosophical doctrine of "atomism" was studied by ancient Greek philosophers such as Leucippus, Democritus, and Epicurus. Although Isaac Newton in the 17th century thought that matter was made up of particles, it was John Dalton who formally stated in 1802 that everything is made from tiny atoms. Dmitri Mendeleev's first periodic table in 1869 helped cement the view, prevalent throughout the 19th century, that matter was made of atoms. ...

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Particle physics, Particle physics - Subatomic particles, Particle physics - History of particle physics, Particle physics - The Standard Model of particle physics, Particle physics - Experimental particle physics, Particle physics - Theoretical particle physics, Particle physics - Particle physics and reductionism, Particle physics - Public policy and particle physics, Particle physics - The future of particle physics

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Theoretical particle physics attempts to develop the models, theoretical framework, and mathematical tools to understand current experiments and make predictions for future experiments. See also theoretical physics. There are several major efforts in theoretical particle physics today and each includes a range of different activities. The efforts in each area are interrelated. One of the major activities in theoretical particle physics is the attempt to better understand the standard model and its tests. By extracting the param ...

See also:

Particle physics, Particle physics - Subatomic particles, Particle physics - History of particle physics, Particle physics - The Standard Model of particle physics, Particle physics - Experimental particle physics, Particle physics - Theoretical particle physics, Particle physics - Particle physics and reductionism, Particle physics - Public policy and particle physics, Particle physics - The future of particle physics

Read more here: » Particle physics: Encyclopedia II - Particle physics - Theoretical particle physics

Particle physicists internationally agree on the most important goals of particle physics research in the near and intermediate future. The overarching goal, which is pursued in several distinct ways, is to find and understand what physics may lie beyond the standard model. There are several powerful experimental reasons to expect new physics, including dark matter and neutrino mass. There are also theoretical hints that this new physics should be found at accessible energy scales. Most importantly, though, there may be unexpected and unpredicted surpr ...

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Particle physics, Particle physics - Subatomic particles, Particle physics - History of particle physics, Particle physics - The Standard Model of particle physics, Particle physics - Experimental particle physics, Particle physics - Theoretical particle physics, Particle physics - Particle physics and reductionism, Particle physics - Public policy and particle physics, Particle physics - The future of particle physics

Read more here: » Particle physics: Encyclopedia II - Particle physics - The future of particle physics