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M O ATA Z E M A M
S U N Y C O R T L A N D
OUTLINE
Classical v Quantum Fundamental Physics
The Standard Model
Gravity
The problems of fundamental physics
Superstring Theory as a solution
Supergravity Theory as a Classical version
A bit about the work I do
Can you help?
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CLASSICAL PHYSICS
Forces are represented by Vector Fields (Faraday) of attraction or
repulsion
The fields live and propagate in space and time
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CLASSICAL PHYSICS
Consider two similarly charged particles in motion
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QUANTUM FIELDS
Forces between objects are represented by particle exchange
Particles exchange other particles that didn’t exist before, quantum
weirdness!!
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QUANTUM FIELDS
“Quantum” momentum
conservation
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THE STANDARD MODEL
Is a collection of “particle exchange field theories” a.k.a quantum field
theories
Includes:
The electromagnetic field
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JFd
dF~~0
THE STANDARD MODEL
Is a collection of “particle exchange field theories” a.k.a quantum field
theories
Includes:
The strong nuclear force
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THE STANDARD MODEL
Is a collection of “particle exchange field theories” a.k.a quantum field
theories
Includes:
The weak nuclear force
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THE STANDARD MODEL
The matter particles
The force or field particles
(the ones that get exchanged)
All the forces of nature,
except one!
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GRAVITY
Gravity is still a classical theory, no definite quantum version
There are attempts, string theory is one of them
The main problem is experimental verification
Gravity is very weak, its quantum version would be very hard to detect
So what is the classical form of gravity?
Recall that the other three fields live and propagate in space and time
Gravity is space and time
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TgG
GRAVITY
Space and time work together, a single spacetime “fabric”
Energy and mass bend and warp spacetime
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TgG
GRAVITY
Space and time work together, a single spacetime “fabric”
Energy and mass bend and warp spacetime
Bent and warped time control the flow of energy and mass
Objects follow the shortest possible distance in warped space, like a bar
of soap in a sink
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TgG
GRAVITY
The ordinary fields in space and time are easily quantized to the
exchange particle model
Gravity is space and time (spacetime) how do you quantize that?
Futile attempts for many decades
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TgG
OTHER PROBLEMS
Quantizing gravity is not the only problem
Why do the particles have the masses they do?
Why are certain forces much stronger than others?
Divergences appearing in certain calculations, a sign of further structure
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0
dq
And the solution to all these problems is ….
Drumroll please ….
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SUPERSTRING THEORY
Is a model that unifies all of the four forces of
nature
Including Gravity
Explains a lot of problems in the old quantum
model
Consistent and elegant (doesn’t mean easy)
All particles, matter and force, are simply one
entity: the SUPERSTRING
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SUPERSTRING THEORY
So how does that work?
All particles are made of tiny tiny tiny
strings that oscillate differently
Oscillations = particles
Ps: We do not ask what is the string itself
is made of. That’s blasphemy!
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The string scale is roughly ~ 10-35m. This is called the
Planck Scale. Attached Homework: Calculate that number
SUPERSTRING THEORY
Remember this:
In string theory it is not really an
exchange, just a deformation of the
same superstring showing different
particles!
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“SUPER” IS FOR SUPERSYMMETRY (SUSY)
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Bosonic (force) side Fermionic (matter)
side
Photon Photino
Gluon Gluino
W Wino
Z Zino
Selectron Electron
Squark Quark
Graviton Gravitino
STRING THEORY IS A TOE
A THEORY OF EVERYTHING
AN OLD DREAM …
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MEDICINE
BIOLOGY
CHEMISTRY
PHYSICS
TOE
… etc.
THE MAIN ACHIEVEMENTS
All fields, including gravity, arise naturally (it’s a TOE)
Mathematical subtleties explained (The infinities are gone)
Unifies all fields and matter particles in one type of “string” that just
vibrates differently (total unification)
Explains the hierarchy problem, the masses of particles etc
All nice and fine, right?
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THE PROBLEMS OF SUPERSTRING THEORY
What is the string made of? Shhh!
Predicts unobserved particles (a lot more than the supersymmetric ones
we already discussed)
No experimental or observational verification as of yet
And the big one …
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SUPERSTRING THEORY
The theory predicts higher dimensions, all the way to ten extra spatial
dimensions
We live in three dimensions x, y, z (+ 1 of time “t”)
ST requires 10 (+ time) !!!!
(And you thought you were having trouble with 3d physics in class!!)
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THE EXTRA DIMENSIONS
Are either very small, wrapped around tiny six or seven dimensional
shapes, so every point in space is not just a point
Or they are unobserved because we are constrained to live in 3D and
the strings are not allowed to propagate into the higher dimensional
space (known as “the Bulk”)
Or a combination of both
In recent years, these models are explored
using “SUGRA”
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SUPERGRAVITY (SUGRA)
SUPERSTRING THEORY’S CLASSICAL FORM
If we look at the superstrings from a slightly larger scale, we don’t see the
strings any more, but before we zoom out all the way to ordinary physics,
we see something else:
Supergravity
A supersymmetric version of Einstein’s general theory of relativity
So we get curved spacetime with a boost
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SUGRA
The strings are represented by classical fields, not quite the same ones
we are used to, they are also higher dimensional
Those stringy fields propagate in curved spacetime
Supersymmetric versions exist in each SUGRA theory (yes there is
more than one)
Easier to work with, and in a sense more exact
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SUGRA
In both superstring theory and supergravity theory solutions known as
p-Branes (pun intended) emerge
Short for memBranes
They are multi-dimensional fundamental objects, so
0-brane: a point (particle)
1-brane: a string
2-brane: a membrane
3-brane: a volume-like object
>4-brane: no names
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BRANE THEORY (SOMETIMES: M-THEORY)
It is no longer just strings, we’ve got BRAAAANES
What are they?
Elementary objects like strings, charged
May have applications
Our universe could be just a 3-brane
floating into the bulk
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BRANE WORLDS
If our universe is a brane this explains
why we don’t see the higher dimensions
Our strings (matter and fields) are constrained
to live on one brane
Only the gravitonic string can propagate into the
bulk
There is some recent evidence of other brane-
worlds “touching” ours (maybe)
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BRANES IN SUGRA
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In SUGRA, branes can be thought
Of as charged objects, and the fields
Are stringy, not particles
WHAT AM I DOING?
Focus on the gravitational part using SUGRA (lots of general
relativity – lots of “branes” and stringy fields)
Eleven, five and four dimensions
Examples to follow
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HOW DOES ONE BECOME A STRING
THEORIST?
Study every physics and math course there is (at least it will feel like
you did)
Do research with someone until you learn to do it on your own
Must own a “perpetual coffee machine”
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HOW CAN YOU DO RESEARCH IN ST?
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Read popular books on physics (over the summer?) Teaches you the big picture without mathematics
Study: Special relativity (MUST)
General relativity (gravity) (MUST)
Topics in classical and/or quantum Field theory (MAYBE)
Differential geometry and some topology (MAYBE)
Practice with previously known results
Start your own problem
You may also learn : Computer programming with C/C++, Mathematica. Writing papers with LaTeX … etc
The end result will depend on how much time you are willing to give. No guarantee you will get to see your name on a paper.
CHARLES CANESTARO (CLASS OF 2013)
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JESSE CHANDLER (CLASS OF 2014)
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ANTHONY D’ACCOLTI (CLASS OF 2016)
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Ongoing project (almost done)
Studying elliptically symmetric solutions in four dimensional
spacetime
Static non-vacuum and time dependent vacuum solutions
May have applications in higher dimensions with stringy fields
QUESTIONS?
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