6. Quantum matter

When vast numbers of particles cluster together, they can, under special conditions, display coherent quantum behaviour at the macroscopic level. ‘Quantum matter’ explains how this produces some of the most exotic matter of which we know: superfluids, in which a quantum fluid suddenly loses all its viscosity, and superconductors, where all electrical resistance is lost. The results are dramatic and spectacular. These phenomena have led to the development of measurement devices that allow the basic unit of mass, the kilogram, to be defined in terms of the fundamental constants of nature to an unprecedented degree of precision.

4. Energy, mass, and light

By the beginning of the twentieth century, our understanding of matter was completely transformed by the great discoveries of electromagnetism and relativity. ‘Energy, mass, and light’ outlines Einstein’s special theory of relativity of 1905, which describes what happens when objects move at speeds close to the speed of light. The theory transformed our understanding of the nature of space and time, and matter through the equivalence of mass and energy. In 1916, Einstein extended the theory to include gravity in the general theory of relativity, which revealed that matter affects space by curving space around it.

3. Forms of matter

Solids, liquids, and gases are the great states of matter; a solid has a shape and a volume, a liquid has a volume but no shape, and a gas has neither shape nor volume. ‘Forms of matter’ explains how these different states arise from a competition between opposites: thermal motion driving particles apart and the attractive forces between atoms pulling them together, repulsion and attraction. The ‘glue’ that holds electrons to atoms, brings atoms together to form molecules, and draws molecules together to make solids and liquids, is electricity. Chemical bonds, crystals, intermediate states, and plasma—the fourth state of matter—are discussed.

9. Dark matter and dark energy

‘Dark matter and dark energy’ reveals that the familiar everyday matter that we experience around us—the atoms and molecules—constitutes only 5% of all the matter that is ‘out there’ in the universe. The remainder appears to consist of two mysterious invisible substances: dark energy (70%), and dark matter (25%). We know almost nothing about what these substances are. Dark matter is needed to prevent the galaxies from flying apart, and dark energy has a strange ‘antigravity’ effect, pushing space and the galaxies apart. The evidence for the existence of these dark substances is outlined, and the possibilities for what they might be are described.

8. Where do the elements come from?

To understand where the chemical elements came from, we look at the earliest moments of the universe. ‘Where do the elements come from?’ traces the evolution of all the matter and energy in the universe, starting from a fraction of a second after its birth in the ‘Big Bang’, 13.8 billion years ago. The light elements, for example the hydrogen atoms in your body, were made in the Big Bang. The middleweight elements, such as carbon and oxygen, were (and still are being) forged deep inside stars, while the heavyweight elements, like gold and platinum, were produced in violent stellar explosions. The life cycles of stars, including supernovae, neutron stars, and pulsars is outlined.

7. Fundamental particles

‘Fundamental particles’ introduces the ultimate building blocks of matter, which include antimatter, and describes how the world can be understood in terms of around twenty different quantum fields. Most of the mass of normal matter can be explained by the energy in these quantum fields. Only a handful of elementary particles make up the world: quarks, leptons, and the force particles, which appear in the Standard Model of Particle Physics. The elementary particles get their masses by interacting with the all-pervasive Higgs field, but the dominant source of the mass of ordinary matter comes from the energy of the quark and gluon fields inside nucleons. The Standard Model is a towering achievement of science, but it is not complete.

2. Atoms

‘Atoms’ describes how humans discovered that the world is composed of atoms, even though they are invisible to the unaided eye. Starting with the prescient ideas of the Ancient Greeks 2,500 years ago there were, by the time of the Enlightenment, three ideas for a definition of matter: all matter is made of atoms, atoms take up space, and atoms have mass. The concept of atoms became more firmly rooted with the chemical experiments of the 19th century, but it was not until Albert Einstein’s interpretation of Brownian motion (the random jiggling of tiny dust particles) in 1905, that any last objections to the atomic hypothesis were finally quashed.

5. The quantum world of the atom

‘The quantum world of the atom’ considers the profound discoveries of the early twentieth century that exposed the inner structure of the atom and the revolutionary new physics of quantum mechanics—the behaviour of matter on very small scales. At the microscopic level, ‘particles’ of matter resemble waves, a feature that enables us to understand the structure, stability, and properties of atoms. Key discoveries and concepts are described: the fundamental constant of nature, Planck’s constant; Heisenberg’s uncertainty principle; the Schrödinger equation; quantum tunnelling; the wavelike characteristics of microscopic particles; and the two types of particles, fermions and bosons.

1. What is matter?

Matter is the stuff from which everything in the world is made. ‘What is matter?’ explains that all things are made of atoms. Inside every atom is a tiny nucleus, and, surrounding the nucleus, a cloud of electrons. The nucleus is made out of protons and neutrons, and, inside, there are smaller particles, quarks. As far as we know, electrons and quarks are not made from anything smaller and so they are fundamental particles. Matter exists in forms of immense variety and complexity; there are ninety-two naturally occurring chemical elements, which can form billions of different molecules. The scale of matter is also described.