This page written by
Oberlin College Physics Department;
last updated 8 June 1999.
Chapter 1: Introduction
Classical mechanics describes how ordinary-sized things behave. Quantum mechanics describes how atomic-sized things behave.
Chapter 2: Classical Magnetic Needles
In classical mechanics, a compass needle behaves like a "magnetic arrow" that obeys certain rules.
Chapter 3: The Stern-Gerlach Experiment
Experiments show that atomic-sized magnetic needles do not behave exactly like arrows.
Chapter 4: The Conundrum of Projections; Repeated Measurements
In fact, atomic-sized magnetic needles can't behave like arrows at all! Repeated measurement experiments suggest that only probabilities, not certainties, can be predicted in quantum mechanics.
Chapter 5: Probability
An understanding of probability is necessary for quantum mechanics and important for day-to-day life.
Chapter 6: The Einstein-Podolsky-Rosen Paradox
The probabilistic character of quantum mechanics, suggested previously, is here proved.
Chapter 7: Variations on a Theme by Einstein
Two more proofs, intellectual descendents of the Einstein-Podolsky-Rosen argument.
(This chapter is optional.)
Chapter 8: Optical Interference
Atomic-sized things don't behave in the familiar classical way. But how do they behave? Light provides a clue, in that light from two sources can add up to produce--not more light--but darkness.
Chapter 9: Quantal Interference
We design an apparatus with two routes through which an atom may pass from the input to the output. If the atom must pass through one route, then the probability of passage is 1/4. If it must pass through the other route, then the probability of passage is 1/4. But if it may pass through either route, then the probability of passage is . . . zero!
Chapter 10: Amplitudes
Quantal interference is described using an abstract entity called "amplitude".
Chapter 11: Working with Amplitudes
Amplitude is represented mathematically by an arrow in a plane. Amplitude is associated with a process, not with a particle.
Chapter 12: Two-Slit Inventions
Variations on the quantal interference experiment drive home the point that "the atom takes both routes".
Chapter 13: Quantum Cryptography
Quantum mechanics invites deep thought about the nature of reality and the character of science. But on the practical level, it also allows the construction of an unbreakable code.
(This chapter is optional.)
Chapter 14: Quantum Mechanics of a Bouncing Ball
The quantal rules for amplitudes, when applied to a an ordinary-sized ball moving through space, give the same common-sense result as classical mechanics -- unless we trick the ball!
Chapter 15: The Wavefunction
How does an atom behave when it has no position? How can humans visualize this behavior?
Appendix A: A Brief History of Quantum Mechanics
Appendix B: Putting Weirdness to Work
Applications of quantum mechanics: tunneling, starlight, and quantum computers.
Appendix C: Sources
Appendix D: General Questions
Appendix E: Bibliography
Appendix F: Skeleton Answers for Selected Problems