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String Theory
• String theory suggests that the elementary particles are
one-dimensional strings as opposed to zero-dimensional
point particles.
• All known elementary particles are made up of one
building block: the string.
• The resonance of each string determines the properties
(mass, charge, spin, etc.) of the particle, thus different
resonant frequencies correspond to different particles.
• Strings are on the order of the Planck length (10-35 m),
or 1020 times smaller than the diameter of an atomic
nucleus!
The Five Main String Theories
• Type I: Supersymmetry between forces and matter, open and closed
strings; group symmetry is SO(32)
• Type IIA: Supersymmetry between forces and matter, closed strings, open
strings bound to D-branes, massless fermions spin both ways (achiral).
• Type IIB: Supersymmetry between forces and matter, closed strings, open
strings bound to D-branes; massless fermions only spin one way
(chiral).
• Type HO: Supersymmetry between forces and matter, closed strings,
heterotic (right moving and left moving strings differ), group symmetry is
SO(32).
• Type HE: Supersymmetry between forces and matter, closed strings,
heterotic (right moving and left moving strings differ), group symmetry is
E8×E8.
Predictions of String Theory
• The five main theories suggest an 11-dimensional
universe, composed of 3 space dimensions, 1 time
dimension and 6 (or 7) spatially coiled dimensions!
• These coiled dimensions form the Calabi-Yau manifolds.
http://superstringtheory.com/basics/basic5.html