In

theoretical physicsTheoretical physics is a branch of physics which employs mathematical models and abstractions of physics to rationalize, explain and predict natural phenomena...

, a membrane, brane, or p-brane is a spatially extended mathematical concept that appears in

string theoryString theory is an active research framework in particle physics that attempts to reconcile quantum mechanics and general relativity. It is a contender for a theory of everything , a manner of describing the known fundamental forces and matter in a mathematically complete system...

and related theories (e.g.

M-theoryIn theoretical physics, M-theory is an extension of string theory in which 11 dimensions are identified. Because the dimensionality exceeds that of superstring theories in 10 dimensions, proponents believe that the 11-dimensional theory unites all five string theories...

and

brane cosmologyBrane cosmology refers to several theories in particle physics and cosmology motivated by, but not exclusively derived from, superstring theory and M-theory.-Brane and bulk:...

). The membrane exists in a static number of dimensions.

String theorists like

Neil TurokNeil Geoffrey Turok is the Director of Perimeter Institute for Theoretical Physics. He is the son of Mary and Ben Turok, activists in the anti-apartheid movement and the African National Congress.-Career:...

,

Burt OvrutBurt Ovrut is an American Theoretical Physicist most famous for his work on heterotic string theory. He is currently Professor of Theoretical High Energy Physics at the University of Pennsylvania....

and

Paul SteinhardtPaul J. Steinhardt is the Albert Einstein Professor of Science at Princeton University and a professor of theoretical physics. He received his B.S. at the California Institute of Technology and his Ph.D. in Physics at Harvard University...

discuss the idea that there are no more or less than 11 dimensions. These structures, membranes, exist across all these dimensions. Presumably, the one dimension of time and other ten dimensions of spaces have always existed. The physicists suggest that our universe may have formed when two extra-dimensional membranes collided. On this conception, our universe may not be so special, since membrane collisions could cause big bangs all the time. The result is a sort of

multiverseThe multiverse is the hypothetical set of multiple possible universes that together comprise all of reality.Multiverse may also refer to:-In fiction:* Multiverse , the fictional multiverse used by DC Comics...

- with universes acting like bubbles that generally cannot interact with one another. These ideas have implications for

CosmogonyCosmogony, or cosmogeny, is any scientific theory concerning the coming into existence or origin of the universe, or about how reality came to be. The word comes from the Greek κοσμογονία , from κόσμος "cosmos, the world", and the root of γίνομαι / γέγονα "to be born, come about"...

.

The variable p refers to the number of spatial

dimensionsDimensions is a French project that makes educational movies about mathematics, focusing on spatial geometry. It uses POV-Ray to render some of the animations, and the films are release under a Creative Commons licence....

of the brane. That is, a 0-brane is a zero-dimensional pointlike particle, a 1-brane is a string, that can either be open or closed, a 2-brane is a "membrane", etc. Every p-brane sweeps out a (p+1)-dimensional

world volumeIn physics, the world line of an object is the unique path of that object as it travels through 4-dimensional spacetime. The concept of "world line" is distinguished from the concept of "orbit" or "trajectory" by the time dimension, and typically encompasses a large area of spacetime wherein...

as it propagates through

spacetimeIn physics, spacetime is any mathematical model that combines space and time into a single continuum. Spacetime is usually interpreted with space as being three-dimensional and time playing the role of a fourth dimension that is of a different sort from the spatial dimensions...

.

## Description

Originally string theory was a theory of 1-branes called

stringA string is a hypothetical vibrating one-dimensional sub-atomic structure and one of the main objects of study in string theory, a branch of theoretical physics. There are different string theories, many of which are unified by M-theory. A string is an object with a one-dimensional spatial extent,...

s. By the mid-1990s it became apparent that the theory could be extended to also include higher dimensional objects. Typically these objects are non-perturbative features of the theory (meaning they do not appear in

perturbation theoryIn quantum mechanics, perturbation theory is a set of approximation schemes directly related to mathematical perturbation for describing a complicated quantum system in terms of a simpler one. The idea is to start with a simple system for which a mathematical solution is known, and add an...

).

Besides the fundamental string (or F-string) of string theory and its magnetic dual, the

NS5-braneIn theoretical physics, the NS5-brane is a five-dimensional object in string theory that carries a magnetic charge under the B-field, the field under which the fundamental string is electrically charged....

, the most important type of branes that appear are the

D-braneIn string theory, D-branes are a class of extended objects upon which open strings can end with Dirichlet boundary conditions, after which they are named. D-branes were discovered by Dai, Leigh and Polchinski, and independently by Hořava in 1989...

s. Different types of D-branes appear in different theories. Dn-branes with even n appear in type IIA string theory whereas the odd Dp-branes appear in type IIB string theory.

With the development of

M-theoryIn theoretical physics, M-theory is an extension of string theory in which 11 dimensions are identified. Because the dimensionality exceeds that of superstring theories in 10 dimensions, proponents believe that the 11-dimensional theory unites all five string theories...

, an extra dimension appeared and the fundamental string of string theory became a 2-dimensional membrane called an M2-brane (or supermembrane). Its magnetic dual is an M5-brane. The various branes of string theory are thought to be related to these higher dimensional M5-branes wrapped on various cycles.

The M-theory states that strings of energy could grow into larger membranes or branes even up to the size of the universe.

It also goes on to state that these strings need to vibrate in more than three dimensions (six) plus another dimension –

timeTime is a part of the measuring system used to sequence events, to compare the durations of events and the intervals between them, and to quantify rates of change such as the motions of objects....

.

## See also

- Black brane
In general relativity, a black brane is a solution of the equations that generalizes a black hole solution but it is also extended —and translationally symmetric— in p additional spatial dimensions...

- Brane cosmology
Brane cosmology refers to several theories in particle physics and cosmology motivated by, but not exclusively derived from, superstring theory and M-theory.-Brane and bulk:...

- Cyclic Universe Theory
- D-brane
In string theory, D-branes are a class of extended objects upon which open strings can end with Dirichlet boundary conditions, after which they are named. D-branes were discovered by Dai, Leigh and Polchinski, and independently by Hořava in 1989...

- S-brane
In string theory, an S-brane is a hypothetical and controversial counterpart of a D-brane, which, unlike a D-brane, is localized in time. Depending on the context the "S" stands for "Strominger", "Sen", or "Space-like". The S-brane was originally proposed by Andrew Strominger in his speculative...

- Multiverse
The multiverse is the hypothetical set of multiple possible universes that together comprise all of reality.Multiverse may also refer to:-In fiction:* Multiverse , the fictional multiverse used by DC Comics...