String Theory

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String Theory

• Brian Bertrand

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What is Theoretical Physics?

• Theoretical physics is the use of math to
  describe certain aspects of nature. The first
  Theoretical Physicist was Sir Isaac Newton.
  Newton invented Calculus so that problems
  involving moving objects could be solved.

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Why Use Theoretical Physics?

• Theoretical physics is useful in that you can use
  it to very accurately predict what would happen
  if you performed certain experiments. Theorists
  are usually exploring areas that are so advanced
  that modern technology would not allow you to
  conduct an experiment on the theoretical topic.

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From Newton to Strings

• There have been many theories throughout the
  world.
• Newtons Calculus developed into Classical Field
  Theory due to studies in electromagnetism.
• When the electron was discovered Quantum
  Mechanics was formed.
• Later Einstein came up with the Special Theory of
  Relativity
• Relativity was combined with Quantum Mechanics to
  form the Relativistic Quantum Field Theory which
  was used to describe subatomic particle behavior.
• Einstein then encompassed Newtons laws into
  Relativity and formed the General Theory of
  Relativity.

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Why Strings?

• String Theory was conceived because all the other
  theories had weak spots. Quantum Theory only
  works when gravity is neglected and General
  Relativity works only if we neglect Quantum
  Theory and assume that the universe is purely
  classical. Early String Theory combined these
  two and was considered a theory of Quantum
  Gravity.

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What is String Theory?

• String Theory is basically the idea that strings
  located in spacetime that vibrate and create
  particles. The Strings size is around Plancks
  Length, which is about 10-33 cm. String Theories
  are classified on whether or not the strings are
  required to be in a closed loop.

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Supersymmetry

• Supersymmetry is a special type of symmetry in
  which every boson, a particle that transmits a
  force, there is a corresponding fermion, a
  particle that makes up matter. Supersymmetry is
  required for String Theory to be correct.

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Spacetime Dimensions

• According to String Theory there is either 26 or
  10 dimensions, 10 being the most widely accepted.
  After the big bang the 10 dimensions separated
  and 4 of them length, width, height, and time,
  grew in size while the other 6 dimensions shrunk
  to around Plancks Length.

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The Many String Theories
Type Spacetime Dimensions Details
Bosonic 26 Deals with just bosons and open and closed strings. Major flaw has a particle with imaginary mass called a tachyon
I 10 Supersymmetry between forces and matter. Open and closed strings.
IIA 10 Supersymmetry. Closed strings only. Fermions spin both ways.
IIB 10 Supersymmetry. Closed strings only. Fermions spin only one way.
HO 10 Supersymmetry. Closed strings only. Right moving and left moving strings differ. SO(32) group symmetry.
HE 10 Supersymmetry. Closed strings only. Right moving and left moving strings differ. E8 x E8 group symmetry.