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# String theory

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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

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### String theory

1. 1. String Theory is Retarded:  An Objective Analysis Jared Snyder Scott Goodrow Raphael Balke PHYS43 Modern Physics, SRJC Section 5756 Instructor: Dr. Younes Ataiiyan Modern Physics Project
2. 2. Fundamental Forces • There are four forces. • Each is associated with force-carrying particles: ➢ Strong force: gluon ➢ Weak force: W boson, Z boson ➢ Electromagnetic force: photon ➢ Gravitational force: graviton (maybe) • The Standard Model describes all of them except the gravitational force.
3. 3. The Standard Model and Gravity • The Standard Model uses the discrete fields of Quantum Mechanics, as required by Heisenberg’s Uncertainty Principle. www.nasa.gov •Gravity is best described by Einstein’s Relativity, which requires continuous fields. •When you try and put them together, you get a mess!
4. 4. The Problem • The Standard Model and Relativity can be used to describe some fundamental forces, but there is no theory which can describes all fundamental forces. “Just because things get a little dingy at the subatomic level doesn't mean all bets are off.” –Murray Gell-Mann
5. 5. 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!
6. 6. 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. http://superstringtheory.com/basics/basic5.html
7. 7. 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://en.wikipedia.org/wiki/Image:Calabi-Yau.png
8. 8. http://members.wri.com/jeffb/visualization/calabi-grid.gif   Calabi-Yau Shapes on a Surface
9. 9. A Brief History of String Theory:  The String Idea • 1968: Gabriele Veneziano, struggling to make sense of various experiments at CERN, discovered Euler’s beta-function: • The beta-function surprisingly seemed to describe features of the strong force. • What was the physics behind this description? http://en.wikipedia.org/wiki/Beta_function
10. 10. The Next Step • 1970: Yoichiro Nambu, Holger Nielsen and Leonard Susskin came up with the idea to model elementary particles as strings. • Based on the beta function, it seemed they had discovered a pleasing theory for the strong force.
11. 11. String Theory Initially Dismissed • 1970: The same year, improved experiments showed inconsistencies in the theory. • The success of the point-particle quantum field theory of quantum chromo-dynamics resulted in the first dismissal of string theory. • John Schwarz continues to work on it. “The mathematical structure of string theory was so beautiful and had so many miraculous properties that it had to be pointing toward something deep.” -John Schwarz
12. 12. • 1971: Supersymmetry is discovered in both the Standard Model and string theory. • 1974: John Schwarz and Joel Scherk discovered that string theory had failed because its scope was constrained. • String theory not only described quantum effects, but also the graviton, thus the idea developed that string theory might be the key to the grand unified theory. Greene, Brian. The Elegant Universe String Theory and the Graviton
13. 13. The First String Revolution • 1976: Supersymmetry is added to gravity, resulting in SUPERGRAVITY. • 1980: SUPERSTRINGS discovered. • 1984: John Schwarz and Michael Green published their 12 years of work in a paper on string theory, resolving many conflicts of quantum mechanics. • The “First String Theory Revolution” began, resulting in thousands of research papers being published on the topic between 1984 and 1986.
14. 14. The Second String Revolution • 1995: Edward Witten introduced M-theory, combining the five different conflicting theories, beginning the “Second String Theory Revolution”. • What does the “M” stand for? Nobody knows, but there are many suggestions: – master, mathematical, mother, mystery, membrane, magic, matrix theory, or is jut an upside down W? • Today: M-Theory remains incomplete, and even after long years of intense research string theory has incredibly limited predictive power.
15. 15. String Theory and Science “I have deep faith that the principle of the universe will be beautiful and simple.” -Albert Einstein While these romantic attributes of the universe satisfy us, does satisfaction alone make them a valid basis for constructing a theory of the Universe? String Theorists say yes. We say… maybe not. String Theory attempts to solve a number of the issues of the Standard Model. It does so based on the attributes of: 1. Beauty 2. Elegance 3. Oneness http://www.wellingtongrey.net/miscellanea/archive/2007-01-15%20--%20science%20vs%20faith.png
16. 16. Is String Theory Scientific “In so far as a scientific statement speaks about reality,it must be falsifiable; and in so far as it is not falsifiable, it does not speak about reality.” -Karl Popper Some argue that this is a limitation of our technology and the observer. Many claim that String Theory is not science because… 1. It is not corroborated empirically 2. It makes no testable predictions 3. It is not falsifiable by nature But are these arguments valid? If they are, String Theory should fit the guidelines of the scientific method. http://www.wellingtongrey.net/miscellanea/archive/2007-01-15%20--%20science%20vs%20faith.png
17. 17. “For every fact there is an infinity of hypotheses.” -Robert Pirsig As a mathematical representation of both particle physics and relativistic physics, String Theory is a mathematical approach to unifying the two aspects the Universe: the very big and the very small. Get an idea? Is String Theory Scientific http://www.wellingtongrey.net/miscellanea/archive/2007-01-15%20--%20science%20vs%20faith.png
18. 18. “The strongest arguments prove nothing so long as the conclusions are not verified by experience.” -Roger Bacon It is commonly believed that to test the theory experimentally would require energetic feats on the solar-system scale. Hence, while methods of experimental verification have been suggested, they are all too conveniently out of reach. Perform an Experiment? Is String Theory Scientific http://www.wellingtongrey.net/miscellanea/archive/2007-01-15%20--%20science%20vs%20faith.png
19. 19. Qualities of myth include: •Explains the Universe •Elegantly describes nature •Fundamentally unfalsifiable •Extends beyond observable world Science or Mythology? Qualities of science include: •Explains the Universe •Requires peer review before belief •Describes nature as nature is to be described •Fundamentally falsifiable Verdict: Myth http://www.mlahanas.de/Greeks/Mythology/RM/ZeusThunderbolt.jpg http://www.phy.cuhk.edu.hk/phyworld/iq/lightning/return_stroke_e.jpg
20. 20. How Did We Get Stuck Here? The Culmination of Science: In only 400 years, science and philosophy discovered… •Newtonian Mechanics •Electricity •Maxwell’s Equations •The Atom •General Relativity •Nuclear Physics •Schrodinger’s Wave Equation •Quantum Mechanics •The Standard Model …and then science grew silent. Because of this progress, theoretical particle physics has become a victim of its own success for the past quarter century. Theories have emerged that are based on no evidence, such as String Theory. http://imgs.xkcd.com/comics/string_theory.png
21. 21. Where Do We Go From Here? Before we get hooked into another charade, we must remember to work One step at a time. May 2008: The Search for Evidence Continues at the LHC! •Where are the elusive Higgs bosons? •Are more precise quark masses consistent with the Standard Model? •Are particles locked in supersymmetry? •What is the nature of dark matter and dark energy? •Why is gravity so comparatively weak? There are solutions to be found, but as Sherlock Holmes once said, “It is a capital mistake to theorize before one has data. Insensibly one begins to twist facts to suit theories instead of theories to suit facts.” Quotations gathered from: http://www.lhup.edu/~dsimanek/sciquote.htm