Book contents
- Frontmatter
- Dedication
- Epigraph
- Contents
- Preface
- 1 Introduction
- 2 Classical Magnetic Needles
- 3 The Stern–Gerlach Experiment
- 4 The Conundrum of Projections; Repeated Measurements
- 5 Probability
- 6 The Einstein–Podolsky–Rosen Paradox
- 7 Variations on a Theme by Einstein
- 8 Optical Interference
- 9 Quantal Interference
- 10 Amplitudes
- 11 Working with Amplitudes
- 12 Two-Slit Inventions
- 13 Quantum Cryptography
- 14 Quantum Mechanics of a Bouncing Ball
- 15 The Wavefunction
- Appendix A A Brief History of Quantum Mechanics
- Appendix B Putting Weirdness to Work
- Appendix C Sources
- Appendix D General Questions
- Appendix E Bibliography
- Appendix F Skeleton Answers for Selected Problems
- Index
2 - Classical Magnetic Needles
Published online by Cambridge University Press: 05 August 2014
- Frontmatter
- Dedication
- Epigraph
- Contents
- Preface
- 1 Introduction
- 2 Classical Magnetic Needles
- 3 The Stern–Gerlach Experiment
- 4 The Conundrum of Projections; Repeated Measurements
- 5 Probability
- 6 The Einstein–Podolsky–Rosen Paradox
- 7 Variations on a Theme by Einstein
- 8 Optical Interference
- 9 Quantal Interference
- 10 Amplitudes
- 11 Working with Amplitudes
- 12 Two-Slit Inventions
- 13 Quantum Cryptography
- 14 Quantum Mechanics of a Bouncing Ball
- 15 The Wavefunction
- Appendix A A Brief History of Quantum Mechanics
- Appendix B Putting Weirdness to Work
- Appendix C Sources
- Appendix D General Questions
- Appendix E Bibliography
- Appendix F Skeleton Answers for Selected Problems
- Index
Summary
How shall we approach the principles of quantum mechanics? One way is simply to write them down. In fact I have already done that (in the first paragraph of the Preface), but to do so I had to use words and concepts that you don't yet understand. To develop the necessary understanding I will use a particular physical system as a vehicle to propel our exploration of quantum mechanics. Which system? An obvious choice is the motion of a tossed ball. Unfortunately this system, while simple and familiar in classical mechanics, is a complicated one in quantum mechanics. We will eventually get to the quantum mechanics of a tossed ball (in chapter 14, “Quantum mechanics of a bouncing ball”, page 103), but as the vehicle for developing quantum mechanics I will instead use a system that is simple in quantum mechanics but that is, unfortunately, less familiar in daily life. That system is the magnetic needle in a magnetic field. This chapter describes the classical motion of a magnetic needle so that we will be able to see how its classical and quantal behaviors differ.
Magnetic needle in a magnetic field
A magnetic needle — like the one found in any woodsman's compass — has a “north pole” and a “south pole”. I will symbolize the magnetic needle by an arrow pointing from its south pole to its north pole.
- Type
- Chapter
- Information
- The Strange World of Quantum Mechanics , pp. 5 - 12Publisher: Cambridge University PressPrint publication year: 2000