String Theory

What it’s all about

The Basics

• String theory is an attempt at understanding how the universe works: both what it’s made of and how it behaves.

• The very basic idea is that particles aren’t points, but instead stretched strings.

• The strings can either be closed, like a ring, or open.o This along with the way they vibrate give them

their traits, making electrons different from muons, for example.

Why strings?

• One of the reasons why string theory is so popular is that it explains gravity on a quantum level, which isn’t nearly as easy with point particles.

• It’s also a path to connecting the 4 fundamental interactions: gravity, electromagnetic, weak and strong forces

• It also doesn’t seem to have any major discrepancies with what we already know

Why isn’t this in textbooks?

• Since string theory is about particles in high energies, this is all very theoretical – we have no way of experimenting these ideas.

• It’s also very new, and research is on-going.

• String theory is a result of a research program called the S-

matrix theory which was begun by Werner Heisenberg in

1943 and had the support of many theorists. However due to

it not changing things much, it was quickly forgotten.

• The theory itself was that the strongly interacting particles

were in fact extended objects, and because there are

difficulties of principle with extended relativistic particles, he

proposed that the notion of a space-time point broke down at

nuclear scales.• In 1958 Tullio Regge discovered that bound states in

quantum mechanics can be organized into groups with

different angular momentums called Regge trajectories. All

these theories contributed to string theory.

The History of String

Theory

Kaluza-Klein Theory

• The theory of extra dimensions

• Kaluza and Klein made a crucial discovery for inventing string theory between 1921 and 1927: electromagnetism can be derived from gravity if there are four space dimensions

The Birth of String Theory

• Gabriele Veneziano, a researcher at CERN noticed that properties of strong nuclear force have in common with the Euler beta-function in 1968

• Deeper research revealed that the interactions of elementary particles modeled as one–dimensional strings were described thoroughly by the Euler beta-function.

• Later experiments in the 1970s revealed that many of the theory's predictions were noticeable only with experimental data.

• Point-particle theory succeeded and string theory was left behind • The reason for this was that String vibrations produce observable

properties that we see in fundamental particles, for instance, string theory seemed to provide vibrating configurations that corresponded to the properties of gluons

• It also provided other vibrating patterns which were soon shown to correspond with properties of the graviton which were not welcome

The Revolutions of Super String

Theory• Super string theories are string theories including fermionic

vibrations

• The first super string revolution was brought to publicity by Michael Green and John Schwarz in 1984o It resolved the conflict between string theory and quantum

mechanics and also proved that string theory encompasses the fundamental forces and all the matter in existence

• The super string revolution brought physicists around the world to once again research the same theory they had earlier abandoned

• It was thought that the theory was the most promising to unify physical theories

The Revolutions of Super String

Theory• After years, investigations led to the

invention of super symmetry

• The next few years showed that the features of the standard model can be derived from the new string theory but the equations of the new theory were so difficult that the exact form could not be definedo approximations had to be used which were found insufficient,

and string theory was discarded

• This resolved the conflict between string theory and quantum mechanics and also proved that string theory encompasses the fundamental forces and all the matter in existence

The Revolutions of Super String

Theory• The second super string revolution started in 1995 at a

conference called Strings, where Edward Witten suggested moving to further research areas

• He was one of those who found evidence for different superstring theories, like M-theory

• The consequences of his ideas are still being analyzed by theorists seeking the final answers from what they believe will prove to be the “theory of everything”

M-theory

M-theory is not yet complete, but the underlying structure of the

mathematics has been established and is in agreement with all the string theories. Furthermore, it has passed

many tests of internal mathematical consistency... But the final

experimental certification

is either impossible or very

hard with current technology.

Theory of all

Basis:-Five different string theories

-The beginning of everything is “Bosonic String Theory” -Bosonic String Theory is the original version of string theory, developed in

the late 1960s. -That original String Theory only described particles that were bosons, and it

did not describe Fermions at all. So quarks and electrons, for instance, were not included in Bosonic String Theory.

--->

--->-By introducing supersymmetry to Bosonic

String Theory, we can obtain a new theory that describes everything... The forces and the matter which make up the Universe.

-The basic idea of supersymmetry is that every fundamental particle has its own so called “superpartner”. All superpartners have same features as their original particle but they have half-integer spin.

-There are three different superstring theories which make sense, i.e. display no mathematical inconsistencies.

-In two of them strings are closed and from third on open strings are the building blocks.

-Mixing the best features of the bosonic string and the superstring theories, we can create two other consistent theories of strings, Heterotic String Theories.

Dimensions

• The basic assumption is that we obviously have only three dimensions of space and one of time. However, if we assume that six of these dimensions are curled up very tightly, then we may never be aware of their existence. But one of the most remarkable predictions of String Theory is that space-time has ten dimensions!

• Later in 1995 the most well known researcher of string theories Edward Witten with his colleague Paul Townsend found the 11th dimension.

• So now we have five different theories of strings which comprise 10 dimensions.

M-theory

M-theory-New idea was that instead of one there are five different, healthy

theories of strings (three superstrings and two heterotic strings) there is only one theory

-those five different theories are part of one theory, they are only different aspect.

This was called M-theory.

M-theory

• M-theory includes 11 dimensionso four space-time dimensions + seven very very small dimensions

• The first "theory of all“o Explains forces and mattero The first theory which is able to explain BOTH quantum mechanics and general

gravity

• It would also seem to be able to explain black holes

References and sources

• http://www.onemanswonder.com/2011/11/us-versus-us-tied-together-by-string.html

• http://en.wikipedia.org/wiki/String_theory• http://www.superstringtheory.com/history/history4.html• http://www.fractalforums.com/general-discussion-b77/imaginary-n

umbers/• http://responsiveuniverse.wordpress.com/2011/11/30/can-astrophy

sics-prove-that-an-afterlife-exists/• http://www.mozardien.com/halls/2011/12/30/superstring-theory-sol

ved-by-supercomputer/• http://library.thinkquest.org/27930/stringhistory.htm• http://www.damtp.cam.ac.uk/research/gr/public/qg_ss.html• http://superstringtheory.com/