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
8 - Optical Interference
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
Overview
We have uncovered the first central principle of quantum mechanics, which is that the outcome of an experiment cannot, in general, be predicted exactly; only the probabilities of the various outcomes can be found. In particular, for the magnetic arrow of a silver atom, we know:
If mz has a definite value, then mx doesn't have a value. If you measure mx, then of course you find some value, but no one (not even the atom itself!) can say with certainty what that value will be — only the probabilities of measuring the various values can be calculated.
How do you like it? Do you feel liberated from the shackles of classical determinism? Or do you feel like Matthew Arnold, who wrote in Dover Beach that
… the world, which seems
To lie before us like a land of dreams,
So various, so beautiful, so new,
Hath really neither joy, nor love, nor light,
Nor certitude, nor peace, nor help from pain;
And we are here as on a darkling plain
Swept with confused alarms of struggle and flight,
Where ignorant armies clash by night.
Regardless of your personal reaction, it is our job as scientists to describe nature, not to dictate to it!
In particular, we know that the model of a magnetic needle as an arrow, so carefully developed in chapter 2 and so correct within the domain of classical mechanics, must be wrong.
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- Chapter
- Information
- The Strange World of Quantum Mechanics , pp. 57 - 63Publisher: Cambridge University PressPrint publication year: 2000