| 1. | Greece and Western Asia Minor. |
| 2. | Two-slit interference. |
| 3. | The Michelson-Morley experiment. |
| Source: (a) Albert Abraham Michelson, Michelson interferometer, perspective illustration, 1881. Public domain. |
| 4. | The Lorentz factor γ. |
| 5. | Time dilation aboard a moving train. |
| 6. | The angles of a triangle drawn on a sphere add up to more than 180°. |
| 7. | An object with a large mass-energy, such as the Earth, curves the spacetime around it. |
| 8. | Gravitational waves detected by the LIGO observatory. |
| Source: Adapted from Figure 1 in B.P. Abbot et al. (LIGO Scientific Collaboration and Virgo Collaboration), ‘Observation of Gravitational Waves from a Binary Black Hole Merger’, Phys Rev Lett 116, 061102 (11 February 2016), http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.116.061102. CC-BY-SA-3.0// https://creativecommons.org/licenses/by/3.0/ |
| 9. | All-sky map of temperature variations in the cosmic background radiation derived from data obtained from the Planck satellite. |
| Source: EUROPEAN SPACE AGENCY, the Planck Collaboration/ SCIENCE PHOTO LIBRARY. |
| 10. | Examples of standing wave patterns. |
| 11. | Atomic orbitals for an electron in a hydrogen atom. |
| 12. | Quantum mechanics and the Rutherford–Bohr ‘planetary’ model of the atom. |
| 13. | Electron spin orientations. |
| 14. | If we start out from any point on a Möbius band, we find that we have to travel twice around it to get back where we started. |
| 15. | Two-slit interference with electrons. |
| Source: Reproduced with kind permission of Dr Tonamura. |
| 16. | A Feynman diagram representing the interaction between two electrons as described by quantum electrodynamics. |
| 17. | Feynman diagrams representing the interaction of an electron with a photon from a magnet. |
| Source: Adapted from Richard P. Feyman, QED: The Strange Theory of Light and Matter, Penguin, London, 1985, pp. 115–77. |
| 18. | Continuous vs. discrete symmetry transformations. |
| 19. | Symmetry properties of liquid water and ice. |
| 20. | The Higgs mechanism and the ‘origin’ of mass. |
| 21. | The contrasting behaviours of the electromagnetic and colour forces. |
| 22. | The standard model of particle physics. |
| Source: Adapted from Standard Model of Elementary Particles, by PBS NOVA (1), Fermilab, Office of Science, United States Department of Energy, Particle Data Group/CC-BY-SA-3.0/, https://creativecommons.org/licenses/by/3.0/. |
| 23. | The source of mass in a cube of water ice. |