Introduction to Mtheory
String theory 

Fundamental objects 
Perturbative theory 
Nonperturbative results 
Phenomenology 
Mathematics 
Theorists

In nontechnical terms, Mtheory presents an idea about the basic substance of the universe.
Contents
 Background 1
 Status 2
 See also 3
 References 4
 Further reading 5
 External links 6
Background
In the early years of the 20th century, the atom – long believed to be the smallest buildingblock of matter – was proven to consist of even smaller components called protons, neutrons and electrons, which are known as subatomic particles. Beginning in the 1960s, other subatomic particles were discovered. In the 1970s, it was discovered that protons and neutrons (and other hadrons) are themselves made up of smaller particles called quarks. Quantum theory is the set of rules that describes the interactions of these particles.
In the 1980s, a new mathematical model of theoretical physics called string theory emerged. It showed how all the particles, and all of the forms of energy in the universe, could be constructed by hypothetical onedimensional "strings", infinitesimal buildingblocks that have only the dimension of length, but not height nor width. Further, string theory suggested that the universe is made up of multiple dimensions. Height, width, and length constitute threedimensional space, and time gives a total of four observable dimensions; however, string theories supported the possibility of ten dimensions – the remaining six of which we cannot detect directly. This was later increased to 11 dimensions based on various interpretations of the 10dimensional theory that led to five partial theories as described below. Supergravity theory also played a significant part in establishing the necessity of the 11th dimension.
These "strings" vibrate in multiple dimensions, and depending on how they vibrate, they might be seen in threedimensional space as matter, light, or gravity. It is the vibration of the string which determines whether it appears to be matter or energy, and every form of matter or energy is the result of the vibration of strings.
String theory, as mentioned above, ran into a problem: another version of the equations was discovered, then another, and then another. Eventually, there were five major string theories. The main differences between each theory were principally the number of dimensions in which the strings developed, and their characteristics (some were open loops, some were closed loops, etc.). Furthermore, all these theories appeared to be correct. Scientists were not comfortable with five seemingly contradictory sets of equations to describe the same thing.
In 1994, Edward Witten of the Institute for Advanced Study and other researchers suggested that the five different versions of string theory might be describing the same thing seen from different perspectives. They proposed a unifying theory called "Mtheory", in which the "M" is not specifically defined, but is generally understood to stand for "membrane". The words "matrix", "master", "mother", "monster", "mystery", "magic" have also been claimed. Mtheory brought all of the string theories together. It did this by asserting that strings are really onedimensional slices of a twodimensional membrane vibrating in 11dimensional space.
Status
Mtheory is not 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.
Some cosmologists are drawn to Mtheory because of its mathematical elegance and relative simplicity. Physicist and author Michio Kaku has remarked that Mtheory may present us with a "Theory of Everything" which is so concise that its underlying formula would fit on a Tshirt.^{[1]} Stephen Hawking originally believed that Mtheory may be the ultimate theory but later suggested that the search for understanding of mathematics and physics will never be complete.^{[2]} However, Hawking later changed his mind and stated, "Mtheory is the only candidate for a complete theory of the universe."^{[3]}
Hawking and Leonard Mlodinow, in the popularscience book The Grand Design, take a philosophical position to support a view of the universe as a multiverse, and define it in the book as modeldependent realism which along with a sumoverhistories approach (see Path integral formulation of Quantum mechanics) to the universe as a whole, is used to claim that Mtheory is the only candidate for a complete theory of the universe.
See also
References
 ^
 ^
 ^
Further reading
External links
 The Elegant Universe  A ThreeHour miniseries with Brian Greene by NOVA (original PBS Broadcast Dates: October 28, 810 p.m. and November 4, 89 p.m., 2003). Various images, texts, videos and animations explaining string theory and Mtheory.
 Superstringtheory.com  The "Official String Theory Web Site", created by Patricia Schwarz. Excellent references on string theory and Mtheory for the layperson and expert.