1. Introduction to QED Quantum Electrodynamics Part II

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

3. 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.

4. Compound Events Events that can be broken down into a series of steps, or events that consist of a number of things happening independently Multiplication of probability amplitudes “turning and shrinking”

5. Partial Reflection of Multiple Surfaces

6. Multiplying Arrows Expressed as a transformation of the unit line

7. Successive Transformations Transformations can be applied in succession Work just like the rules for numbers

8. Successive Transformations

9. Reflection by a Single Surface

10. Transmission by a Single Surface

11. Reflection from the Back Surface

12. Reflection by Two Surfaces Average of 8% (4% each for front and back surfaces) Fluctuates between 0% and 16%, depending on the thickness of the glass The rest are transmitted

13. Transmission by Two Surfaces

14. Making the Sum Probabilities 100% When reflection is 0%, sum is 92% When reflection is 16%, sum is 108% Compensate by considering all possibilities

15. Other Possibilities

16. 100% Probability

17. More Reflection Possibilities

18. Independent Events If one of the ways a particular event can happen depends on a number of things happening independently, the amplitude for this way is calculated by multiplying the arrows of the independent things.

19. Simultaneous Transmission and Absorption

20. Another Possibility

21. Coming Soon… Electron interactions Feynman Diagrams

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

23. Questions?