brane

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

Brane cosmology is a protoscience motivated by, but not rigorously derived from, superstring theory and M-theory. The idea is to solve problems in cosmology using speculative particle physics theories and in turn use cosmological observations to motivate ideas in string theory. The central idea is that our visible, four-dimensional universe is entirely restricted to a brane inside a higher-dimensional space, called the bulk. The additional dimensions may be taken to be compact, in which case the observed universe contains the e ...

Read more here: » Brane cosmology: Encyclopedia - Brane cosmology

edit Einstein's general theory of relativity was introduced in 1915. Physicists accepted the theory because it correctly accounted for the precession of the perihelion of Mercury, a phenomenon which had long baffled physicists and because it unified Newton's law of universal gravitation with special relativity in a conceptually simple way. (Einstein has been famously quoted as saying that if his theory was falsified, then he would have felt "sorry for the dear Lord.") Despite Einstein's proposal of three classical te ...

Including:

• Tests of general relativity - Classical tests
• Tests of general relativity - Modern tests
• Tests of general relativity - Post-Newtonian tests of gravity
• Tests of general relativity - The equivalence principle
• Tests of general relativity - Strong field tests
• Tests of general relativity - Cosmological tests

Read more here: » Tests of general relativity: Encyclopedia - Tests of general relativity

Dr. Brian Greene (born February 9, 1963) is a physicist and one of the world's foremost string theorists. Since 2003 he has been a professor at Columbia University. Born in New York City, Greene was a prodigy in mathematics. At the age of five, he could multiply 30-digit numbers. His skill in mathematics was such that by the time he was twelve years old, he was being privately tutored in mathematics by a Columbia University professor because he had surpassed the high-school math level. He entered Harvard in 1980 to major in physics, and with his bachelor's degree, Greene went to ...

Including:

• Brian Greene - Facts
• Brian Greene - Important contributions to physics
• Brian Greene - Publications

Read more here: » Brian Greene: Encyclopedia - Brian Greene

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

The RS1 model attempts to address the hierarchy problem. The warping of the extra dimension is analogous to the warping of spacetime in the vicinity of a massive object, such as a black hole. This warping, or red-shifting, generates a large ratio of energy scales so that the natural energy scale at one end of the extra dimension is much larger than at the other end. where k is some constant and η has -+++ metric signature. This space has boundaries at y=1/k and y=1/Wk, with where k is around the Planck scale and ...

See also:

Randall-Sundrum model, Randall-Sundrum model - The RS1 model, Randall-Sundrum model - The RS2 model

Read more here: » Randall-Sundrum model: Encyclopedia II - Randall-Sundrum model - The RS1 model

The modern era of testing general relativity was ushered in largely at the impetus of Dicke (1959, 1962) and Schiff (1960) who laid out a framework for testing general relativity. They emphasized the importance not only of the classical tests, but of null experiments, testing for effects which in principle could occur in a theory of gravitation, but do not occur in general relativity. Another important theoretical development were the new alternatives to general relativity theory – such as Brans-Dicke theory and other scalar-tensor theorie ...

See also:

Tests of general relativity, Tests of general relativity - Classical tests, Tests of general relativity - Modern tests, Tests of general relativity - Post-Newtonian tests of gravity, Tests of general relativity - The equivalence principle, Tests of general relativity - Strong field tests, Tests of general relativity - Cosmological tests

Read more here: » Tests of general relativity: Encyclopedia II - Tests of general relativity - Modern tests

The RS1 model attempts to address the hierarchy problem. The warping of the extra dimension is analogous to the warping of spacetime in the vicinity of a massive object, such as a black hole. This warping, or red-shifting, generates a large ratio of energy scales so that the natural energy scale at one end of the extra dimension is much larger than at the other end. where k is some constant and η has "−+++" metric signature. This space has boundaries at y = 1/k and y = 1/Wk, w ...

See also:

Randall-Sundrum model, Randall-Sundrum model - The RS1 model, Randall-Sundrum model - The RS2 model

Read more here: » Randall-Sundrum model: Encyclopedia II - Randall-Sundrum model - The RS1 model

Observations of binary pulsars have all demonstrated substantial periapsis precessions that cannot be accounted for classically but can be accounted for by using general relativity. For example, the Hulse-Taylor binary pulsar PSR B1913+16, has an observed precession of over 4o of arc per year. This precession has been used to compute the masses of the components. A binary pulsar discovered in 2003, J0737-3039, has a perihelion precession of 16.88o. Similarly to the way in which atoms and molecules emit electromag ...

See also:

Tests of general relativity, Tests of general relativity - Classical tests, Tests of general relativity - Modern tests, Tests of general relativity - Post-Newtonian tests of gravity, Tests of general relativity - The equivalence principle, Tests of general relativity - Strong field tests, Tests of general relativity - Cosmological tests

Read more here: » Tests of general relativity: Encyclopedia II - Tests of general relativity - Strong field tests

There are major outstanding problems with the ekpyrotic scenario. Foremost among them is that colliding branes are not understood by string theorists, and nobody knows if the scale invariant spectrum will be destroyed by the big crunch, or even what happens when two branes collide. Moreover, like cosmic inflation, while the general character of the forces (in the ekpyrotic scenario, a force between branes) required to create the vacuum fluctuations is known, there is no candidate from particle physics. Moreover, the scenario uses some essent ...

See also:

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

Read more here: » Ekpyrotic: Encyclopedia II - Ekpyrotic - Outstanding problems

In his 1916 paper, Einstein proposed three famous tests of general relativity, now called the classical tests: the gravitational redshift of light the deflection of light by the Sun the precession of the perihelion of Mercury In Newtonian physics, a lone object orbiting a spherical mass would trace out an ellipse with the spherical mass at a focus. The point of closest approach, called the perihelion in the solar system, is fixed. There are a number of solar system effects that cause the pe ...

See also:

Tests of general relativity, Tests of general relativity - Classical tests, Tests of general relativity - Modern tests, Tests of general relativity - Post-Newtonian tests of gravity, Tests of general relativity - The equivalence principle, Tests of general relativity - Strong field tests, Tests of general relativity - Cosmological tests

Read more here: » Tests of general relativity: Encyclopedia II - Tests of general relativity - Classical tests