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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
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.