Book contents
- Frontmatter
- Contents
- Preface
- 1 Motion on Earth and in the Heavens
- 2 Energy, Heat and Chance
- 3 Electricity and Magnetism
- 4 Light
- 5 Space and Time
- 6 Least Action
- 7 Gravitation and Curved Spacetime
- 8 The Quantum Revolution
- 9 Quantum Theory with Special Relativity
- 10 Order Breaks Symmetry
- 11 Quarks and What Holds Them Together
- 12 Unifying Weak Forces with QED
- 13 Gravitation Plus Quantum Theory – Stars and Black Holes
- 14 Particles, Symmetries and the Universe
- 15 Queries
- APPENDIX A The Inverse-Square Law
- APPENDIX B Vectors and Complex Numbers
- APPENDIX C Brownian Motion
- APPENDIX D Units
- Glossary
- Bibliography
- Index
11 - Quarks and What Holds Them Together
Published online by Cambridge University Press: 20 January 2010
- Frontmatter
- Contents
- Preface
- 1 Motion on Earth and in the Heavens
- 2 Energy, Heat and Chance
- 3 Electricity and Magnetism
- 4 Light
- 5 Space and Time
- 6 Least Action
- 7 Gravitation and Curved Spacetime
- 8 The Quantum Revolution
- 9 Quantum Theory with Special Relativity
- 10 Order Breaks Symmetry
- 11 Quarks and What Holds Them Together
- 12 Unifying Weak Forces with QED
- 13 Gravitation Plus Quantum Theory – Stars and Black Holes
- 14 Particles, Symmetries and the Universe
- 15 Queries
- APPENDIX A The Inverse-Square Law
- APPENDIX B Vectors and Complex Numbers
- APPENDIX C Brownian Motion
- APPENDIX D Units
- Glossary
- Bibliography
- Index
Summary
How protons and neutrons and other baryons are made of quarks, bound together by a subtle generalization of electromagnetism.
Seeing the Very Small
Lenses were used for microscopic purposes in the second half of the seventeenth century. The Dutch microscopist, van Leeuwenhoek identified blood capillaries, red blood cells, spermatazoa and bacteria. In the nineteenth century, the cell structure of plants and animals was established.
But optical microscopes, using light of wavelength about four to eight times 10-7 metre, cannot resolve smaller distances than these and certainly cannot be used to study atoms or even large molecules. To do better, one must use electromagnetic radiation of shorter wavelength, like X-rays, or beams of particles that have, according to quantum theory, wave functions with wavelengths determined by the momenta of the particles. X-rays were discovered by Röntgen in Würzburg in 1895. Their ability to penetrate opaque bodies, like hands, was of course the initial cause of excitement, but it is not our concern here. In 1912, von Laue in Berlin showed that X-rays incident on a crystal produce (on a photographic plate) a pattern of spots. The spots (that is, positions of maximum intensity) appear where the waves scattered by individual atoms add up constructively (where there phases are equal). This is the phenomenon of interference described in Section 4.6. It works because the wavelength of X-rays is comparable to the atomic separation in crystals.
From the X-ray “diffraction patterns” (of spots), it is possible to deduce the arrangement of atomic positions in the crystal. The Braggs, father and son (William and Lawrence), developed these methods.
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- Information
- Hidden Unity in Nature's Laws , pp. 309 - 323Publisher: Cambridge University PressPrint publication year: 2001