String Theory

String theory attempts to unify the four forces in the universe (electromagnetic force, the

strong nuclear force, the weak nuclear force, and gravity) together into one unified

theory.

Electromagnetism - the force that holds a fridge magnet to a refrigerator while

gravity is trying to pull it off towards the earth.

Strong nuclear forces - responsible for holding the central part of atoms (their

nuclei) together, while the weak nuclear force is involved in the decay of these

nuclei.

Weak nuclear forces causes subatomic particles within the nuclei of atoms to

decay or break up into smaller particles and togive off energy as radiation.

Gravity - the force of attraction between all masses in the universe; especially the

attraction of the earth's mass for bodies near its surface.

- String theory attempts to reconcile general relativity (gravity) with quantum mechanics.

General relativity

- Albert Einstein Unified space, time and gravity.

- Waves and curves in space and time are responsible for the force of gravity.

- It explains how gravity in the world of the large works. It tells how and why

planets orbit stars, and how those stars orbit the Milky Way. Relativity makes

predictions which can be seen and verified when you look through a telescope.

Quantum mechanics

- Gravity becomes insignificant because the atomic and subatomic masses are

very small.

- It explains the world of the tiny. It gives us a mathematical description of atoms,

electrons and quarks and how they interact with each other. Unlike the world of

the large, which could be described as serene, smooth and predictable, the

quantum world is incredibly strange, weird and chaotic.

String theory attempts to unite quantum mechanics and general relativity so we

can make sense of the universe on all scales, at any place or time, large or small

without breaking down.

- Uses a model of one-dimensional strings in place of the particles of quantum physics.

These strings, the size of the Planck length (i.e. 10-35 m) vibrate at specific resonant

frequencies. 

- These strings came in two forms — closed strings and open strings. An open string

has ends that don’t touch each other, while a closed string is a loop with no open end. It

was eventually found that these early strings, called Type I strings, could go through five

basic types of interactions.

- The interactions are based on a string’s ability to have ends join and split apart.

Because the ends of open strings can join together to form closed strings, you can’t

construct a string theory without closed strings.

- This proved to be important, because the closed strings have properties that make

physicists believe they might describe gravity. Instead of just being a theory of matter

particles, physicists began to realize that string theory may just be able to explain

gravity and the behavior of particles.

- The strings are free to vibrate at different modes. The different vibrational modes may

represent the different particle types ---- electron, photon or even a graviton.

- Graviton - it is the corresponding force-carrying particle of gravity.

- A new connection (called supersymmetry) exists between two fundamentally different

types of particles, bosons and fermions.

- String theories are classified according to whether or not the strings are required to be

closed loops, and whether or not the particle spectrum includes fermions. In order to

include fermions in string theory, there must be a special kind of symmetry called

supersymmetry, which means for every boson (particle that transmits a force) there is a

corresponding fermion (particle that makes up matter). So supersymmetry relates the

particles that transmit forces to the particles that make up matter.

String Theory

- The theory was originally developed in the 1970s, the filaments of energy in string

theory were considered to be 1-dimensional objects: strings. (One-

dimensional indicates that a string has only one dimension, length, as opposed to say a

square, which has both length and height dimensions.)

- 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.

- In this theory, the different types of observed elementary particles arise from the

different quantum states of these strings.

- In addition to the types of particles postulated by the standard model of particle

physics, string theory naturally incorporates gravity, and is therefore a candidate for a

theory of everything, a self-contained mathematical model that describes all

fundamental forces and forms of matter.

References

http://zidbits.com/2011/03/a-laymans-explanation-for-string-theory/

http://www.dummies.com/how-to/content/string-theory-for-dummies-cheat-

sheet.html

http://www.dummies.com/how-to/content/the-basic-elements-of-string-theory.html

http://www.space.com/17594-string-theory.html

http://hubpages.com/education/String-Superstring-Theory-In-Simple-Terms

http://physics.about.com/od/quantumphysics/f/stringtheory.htm

http://www.crystalinks.com/stringtheory.html