2. What physics covers and what it doesn’t

Physics can be defined as the study of matter, energy, and the interaction between them. This is concise and seemingly clear, but physics is a sprawling and dynamic science and this basic definition needs to be amplified to truly reflect what physics is all about. ‘What physics covers and what it doesn’t’ considers the different meanings of matter and energy; and also explains how physics can be defined and described by scale, and how it deals with different aspects of the universe by their size. From quarks to atoms to galaxies, the components of the universe span many orders of magnitude in size. The different sub-divisions of physics are also considered.

6. Future physics: unanswered questions

Today, physics can look back at recent breakthroughs at all scales, small to large, and in all its usages, pure to applied, such as the discovery of the predicted Higgs boson and the surprise discovery of dark energy; successes in exploring space and finding exoplanets, and in examining our own planet; achievements in novel electronic and photonic technology; and in biological physics with new tools to probe living systems and ourselves. These results show that physics continues to deepen our understanding of nature and affect how we live our lives, and raises new questions while addressing old ones. ‘Future physics: unanswered questions’ examines the questions that physicists are currently asking, and considers where physics will go next.

5. A force in society

Physics is intellectually significant for humanity because of its success in explaining nature, and practically significant because it powerfully affects the wider world outside the laboratory. Physicists recognize this important interaction. ‘A force in society’ looks at the range of impacts that physics has had on the world: from the devastating effects of nuclear weaponry that started with the Manhattan Project in World War II, to the more positive applications in areas such as solar energy, digital electronics, and medicine. These events and inventions have appeared within the last century, but the societal influence of physics goes much further back and comes from pure as well as applied physics.

1. It all began with the Greeks

From consumer devices to research at the edge of the unknown, physics is woven into our daily activities, our civilization, and our highest aspirations. It is a foundational science that is massively supported by society and underpins other science and technology. ‘It all began with the Greeks’ considers the history of physics from the minds of early Greek thinkers who wanted to understand the world around them to today’s intricate theories and apparatus. It discusses how through processes of observation, recording, experimentation, and analysis over millennia in different nations and cultures, modern physics has evolved, and highlights some of the key stages of that evolution.

4. Physics applied and extended

‘Physics applied and extended’ considers how foundational physical concepts and theories apply broadly across science and serve as a basis for technology and its industrial use. Instruments and processes that use physical methods, or were created or discovered in physics labs, have wide uses outside them such as the range of imaging techniques that have revolutionized medical practice. Physical theories can also provide tools or conceptual frameworks that support other sciences or technology: quantum theory is necessary for applications of light and lasers and for nanotechnology; the complex theory that describes the motion of liquids and gases underpins meteorological forecasting and climate modelling; and quantum computation has implications for national security.

3. How physics works

Today, physics is firmly grounded in classical physics, which accurately describes much of our immediate and relatively nearby world, the mid-range scale of the cosmos; and in modern physics, quantum mechanics and relativity, which describe much of the small and large scales of the universe that lie far beyond direct human reach. However, physics is not stagnant, it still lacks important answers because of unexplained phenomena, because of new research tools, and because its aspirations, especially the quest for a Theory of Everything, have grown. ‘How physics works’ considers how physicists choose which experiments to perform, how to develop theories, and how these two halves of the physics equation come together.