1. Introduction to QED Quantum Electrodynamics

2. Introduction Created in 1929 by a number of scientists to describe the interaction of light and matter Melding of Maxwell’s theory and quantum mechanics Attempts to describe behavior of electrons Paul Dirac made relativistic adjustments 1948 – Richard Feynman, Julian Schwinger and Sin-Itiro Tomonaga calculated the correction due to light

3. Significance Describes all phenomenon but gravity and radioactivity QED is the theory behind chemistry and governs properties of chemicals Has survived over 50 years of testing

4. Basics Describes what happens, not why Light behaves like particles, not waves Only probability can be calculated Little arrows (“probability amplitudes”)

5. General Principle of Quantum Theory The probability that a particular event occurs is the square of a final arrow (probability amplitude) that is found by drawing an arrow for each way the event could happen, and then combining (adding) the arrows

6. Glass Thickness

7. Arrow Lengths

8. Adding Arrows

9. Determining Direction

10. Partial Reflection

11. As the glass gets thicker…

12. Extremes

13. For varying frequencies:

14. Light Propagation A photon has nearly equal chances of going on any path. Therefore, all the arrows are nearly the same length. This difference is negligible.

15. Mirrors and Angle of Incidence

16. Equal Chances

17. Arrows have equal lengths, but different directions.

18. The middle contributes more.

19. Where the time is least is also where the time for the nearby paths is nearly the same; that’s where the little arrows point in nearly the same direction and add up to a substantial length; that’s where the probability of a photon reflecting off a mirror is determined. And that’s why, in approximation, we can get away with the crude picture of the world that says light only goes where the time is least. -Richard Feynman. Time is least where the angle of incidence equals the angle of reflection.

20. The Edges of the Mirror

21. Cutting out Pieces

22. Diffraction Grating

23. Light through Multiple Media

24. The Lifeguard

25. Mirage

26. Light travels in straight lines?

27. Light does not move in a straight path, but rather uses a core of nearby space. (neighboring paths)

28. Restricting the Paths (Single Slit Diffraction)

29. Uncertainty Principle? If the paths are too restricted, the light spreads out. There is no need for the uncertainty principle.

30. Light traveling through many paths.

31. The Focusing Lens

32. Diagrams: Feynman, Richard P. QED: The Strange Theory of Light and Matter. Princeton University Press. Princeton, NJ, 1988.

33. Questions?