# What are branes in string theory?

## What are branes in string theory?

Brane, an object extended in one or more spatial dimensions, which arises in string theory and other proposed unified theories of quantum mechanics and general relativity.

In string theory, D-branes, short for Dirichlet membrane, 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.

What does a brane look like?

Your brain is the size of a large grapefruit, but it looks like a large pinkish-gray walnut. There are many folds and creases and it feels soft and squishy. It weighs about 1 pound at birth, 2 pounds at elementary age, and 3 pounds as an adult.

### How many branes are there in string theory?

String Theory. String theory has 9 space dimensions, so a brane can have anywhere from 0 to 9 dimensions. Branes were hypothesized as part of string theory in the late 1980s. In 1995, Joe Polchinski realized that Edward Witten’s proposed M-Theory required the existence of branes.

Why do open strings end on D-branes?

Back to the perturbative realm. The condition that open strings can end on D-branes – and nowhere else – means that there exists a particular spectrum of open strings stretched between such D-branes. By quantizing these open strings, we obtain all the fields that propagate along (and in between) such D-branes.

Which is an example of the arrangement of D-branes?

The arrangement of D-branes constricts the types of string states which can exist in a system. For example, if we have two parallel D2-branes, we can easily imagine strings stretching from brane 1 to brane 2 or vice versa. (In most theories, strings are oriented objects: each one carries an “arrow” defining a direction along its length.)

## How are D branes related to the M theory?

In 1995, Polchinski identified D-branes with black p-brane solutions of supergravity, a discovery that triggered the Second Superstring Revolution and led to both holographic and M-theory dualities. D-branes are typically classified by their spatial dimension, which is indicated by a number written after the D.