Introduction to M-theory: Difference between revisions

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In the early years of the 20th century, the [[atom]] – long believed to be the smallest building-block of [[matter]] – was proven to consist of even smaller components called [[protons]], [[neutrons]] and [[electrons]], which are known as [[subatomic particles]]. Other subatomic particles began being discovered in the 1960s. In the 1970s, it was discovered that protons and neutrons (and other [[hadron]]s) are themselves made up of smaller particles called [[quarks]]. The [[Standard Model]] 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 different subatomic particles known to science could be constructed by hypothetical one-dimensional "strings", infinitesimal building-blocks that have only the dimension of length, but not height or width. These "strings" vibrate in multiple dimensions and, depending on how they vibrate, they might be seen in three-dimensional space as matter, light or gravity. It is the vibration of the string that determines whether it appears to be matter or energy, and every form of matter or energy is the result of the vibration of strings.

However, for string theory to be mathematically consistent, the strings must be in a universe of ten [[dimension]]s. This contradicts the experience that our real universe has four dimensions: three space dimensions (height, width, and length) and one time dimension. To "save" their theory, string theorists therefore added the explanation that the additional six dimensions exist but cannot be detected directly;. thisIn wasessence, explainedthe byidea sophisticatedwas mathematicalthat objectsthe calledextra [[Calabi–Yaudimensions manifold]]s.existed, Thebut numberthey ofwere dimensions"curled was later increasedup" to 11be basedso onsmall variousthat interpretationsthey ofcould thenot 10-dimensionalbe theoryobserved. thatThe ledtechnical toterm fivefor partialthis theories, as described below.is ''[[SupergravityCompactification (physics)|compactification]].'' theoryPhysicists alsospeculated playedthat athe significantcompactified partdimensions in establishingtook the necessityshape of themathematical 11thobjects dimensioncalled [[Calabi–Yau manifold]]s.

These "strings" vibrate in multiple dimensions and, depending on how they vibrate, they might be seen in three-dimensional space as matter, light or gravity. It is the vibration of the string that 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 described above ran into a problem: another version of the equations was discovered, then another, and then another. Eventually, five major string theories were developed. The main differences between the theories 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 workable. Scientists were not comfortable with five seemingly contradictory sets of equations to describe the same thing.