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Q.E.D. (Quantum Electro Dynamics) Physics 43, SRJC, spring 2008

Richard P. Feynman (the father of Quantum Electro Dynamics). Q.E.D. (Quantum Electro Dynamics) Physics 43, SRJC, spring 2008. Presented by:. Anthony Disbrow Kelly Jewett Scot Spinner. History. The word electrodynamics was originally coined by André-Marie Ampère in 1822.

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Q.E.D. (Quantum Electro Dynamics) Physics 43, SRJC, spring 2008

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  1. Richard P. Feynman (the father of Quantum Electro Dynamics) Q.E.D.(Quantum Electro Dynamics)Physics 43, SRJC, spring 2008

  2. Presented by: • Anthony Disbrow • Kelly Jewett • Scot Spinner

  3. History • The word electrodynamics was originally coined by André-Marie Ampère in 1822. • The phrase "quantum physics" was first employed in Johnston's Planck's Universe in Light of Modern Physics. • Quantum theory began in 1900, when Max Planck assumed that energy is quantized in order to derive a formula predicting the observed frequency dependence of the energy emitted by a black body. • The concept that light energy comes in small “packets” was first explored by Einstein in his paper on the photoelectric effect. http://en.wikipedia.org/wiki/Quantum_electrodynamics

  4. More History... • Feynman's mathematical technique, based on his diagrams, initially seemed very different from the field-theoretic, operator-based approach. • QED served as a role model for quantum chromodynamics • Starting in 1975, physicists showed how the nuclear weak force and QED could be unified into the electro weak force http://en.wikipedia.org/wiki/Quantum_electrodynamics

  5. What is Q.E.D.? • QED mathematically describes all phenomena involving electrons, positrons, the exchange of photons and the electromagnetic field. • QED was the first satisfactory quantum description of a physical field and of the creation and annihilation of quantum particles. http://en.wikipedia.org/wiki/Quantum_electrodynamics http://hyperphysics.phy-astr.gsu.edu/Hbase/forces/qed.html

  6. What is Q.E.D.? Con’t • QED is used to approximate interactions in electrodynamics • Perturbation theory is used to find an approximate solution to a problem or experiment with no exact solution. http://en.wikipedia.org/wiki/Perturbation_theory

  7. Use of Perturbation Theory • Perturbation theory is used to approximate solutions to the Schrödinger equation . Using perturbation theory, we can use the known solutions to simple Hamiltonians such as that of the hydrogen atom, to generate solutions for more complicated systems http://en.wikipedia.org/wiki/Perturbation_theory_(quantum_mechanics)

  8. Accuracy • QED can predict the probability of what will happen in an experiment • It can predict the outcome of an experiment with an error of only 10−12 • QED is one of the most accurate physical theories to date http://www.britannica.com/EBchecked/topic/486203/quantum-electrodynamics

  9. Feynman Diagrams http://hyperphysics.phy-astr.gsu.edu/hbase/particles/imgpar/feynm5.gif

  10. http://www.youtube.com

  11. Mathematical example • Mathematically, QED has the structure of an abelian gauge theory, with the symmetry group U(1) as gauge group. The gauge field which mediates the interaction between the charged spin-1/2 fields is the electromagnetic field. The QED Lagrangian for the interaction of electrons and positrons through photons is • where •   are Dirac matrices. • and its Dirac adjoint are the fields representing electrically charged particles, specifically electron and positron fields represented as Dirac spinors. •                     is the gauge covariant derivative, with   the coupling strength (equal to the elementary charge), •    the covariant four-potential of the electromagnetic field and •                          the electromagnetic field tensor. http://en.wikipedia.org/wiki/Quantum_electrodynamics

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