String Theory Brian Bertrand

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.

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.

From Newton to Strings There have been many theories throughout the world. Newton’s 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 Newton’s laws into Relativity and formed the General Theory of Relativity.

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.

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 Planck’s 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.

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.

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 Planck’s Length.

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 Supersymmetry. Closed strings only. Fermions spin both ways. IIB Supersymmetry. Closed strings only. Fermions spin only one way. HO Supersymmetry. Closed strings only. Right moving and left moving strings differ. SO(32) group symmetry. HE Supersymmetry. Closed strings only. Right moving and left moving strings differ. E8 x E8 group symmetry.