Melvyn Bragg and his guests discuss the photon, one of the most enigmatic objects in the Universe. Generations of scientists have struggled to understand the nature of light. In the late nineteenth century it seemed clear that light was an electromagnetic wave. But the work of physicists including Planck and Einstein shed doubt on this theory. Today scientists accept that light can behave both as a wave and a particle, the latter known as the photon. Understanding light in terms of photons has enabled the development of some of the most important technology of the last fifty years.With:Frank Close Professor Emeritus of Physics at the University of OxfordWendy Flavell Professor of Surface Physics at the University of ManchesterSusan Cartwright Senior Lecturer in Physics and Astronomy at the University of Sheffield.Producer: Thomas Morris.

Melvyn Bragg and guests discuss Behavioural Ecology, the scientific study of animal behaviour.What factors influence where and what an animal chooses to eat? Why do some animals mate for life whilst others are promiscuous? Behavioural ecologists approach questions like these using Darwin's theory of natural selection, along with ideas drawn from game theory and the economics of consumer choice.Scientists had always been interested in why animals behave as they do, but before behavioural ecology this area of zoology never got much beyond a collection of interesting anecdotes. Behavioural ecology gave researchers techniques for constructing rigorous mathematical models of how animals act under different circumstances, and for predicting how they will react if circumstances change. Behavioural ecology emerged as a branch of zoology in the second half of the 20th century and proponents say it revolutionized our understanding of animals in their environments.GUESTSSteve Jones, Emeritus Professor of Genetics at University College LondonRebecca Kilner, Professor of Evolutionary Biology at the University of CambridgeJohn Krebs, Principal of Jesus College at the University of OxfordProducer: Luke Mulhall.

Melvyn Bragg and guests discuss Isambard Kingdom Brunel, the Victorian engineer responsible for bridges, tunnels and railways still in use today more than 150 years after they were built. Brunel represented the cutting edge of technological innovation in Victorian Britain, and his life gives us a window onto the social changes that accompanied the Industrial Revolution. Yet his work was not always successful, and his innovative approach to engineering projects was often greeted with suspicion from investors. Guests:Julia Elton, former President of the Newcomen Society for the History of Engineering and TechnologyBen Marsden, Senior Lecturer in the School of Divinity, History and Philosophy at the University of AberdeenCrosbie Smith, Professor of the History of Science at the University of KentProducer: Luke Mulhall.

Melvyn Bragg and his guests discuss nuclear fusion, the process that powers stars. In the 1920s physicists predicted that it might be possible to generate huge amounts of energy by fusing atomic nuclei together, a reaction requiring enormous temperatures and pressures. Today we know that this complex reaction is what keeps the Sun shining. Scientists have achieved fusion in the laboratory and in nuclear weapons; today it is seen as a likely future source of limitless and clean energy.Guests:Philippa Browning, Professor of Astrophysics at the University of ManchesterSteve Cowley, Chief Executive of the United Kingdom Atomic Energy AuthorityJustin Wark, Professor of Physics and fellow of Trinity College at the University of OxfordProducer: Thomas Morris.

Melvyn Bragg and his guests discuss Euler's number, also known as e. First discovered in the seventeenth century by the Swiss mathematician Jacob Bernoulli when he was studying compound interest, e is now recognised as one of the most important and interesting numbers in mathematics. Roughly equal to 2.718, e is useful in studying many everyday situations, from personal savings to epidemics. It also features in Euler's Identity, sometimes described as the most beautiful equation ever written. With:Colva Roney-Dougal Reader in Pure Mathematics at the University of St AndrewsJune Barrow-Green Senior Lecturer in the History of Maths at the Open UniversityVicky Neale Whitehead Lecturer at the Mathematical Institute and Balliol College at the University of OxfordProducer: Thomas Morris.

Melvyn Bragg and his guests discuss the Sun. The object that gives the Earth its light and heat is a massive ball of gas and plasma 93 million miles away. Thanks to the nuclear fusion reactions taking place at its core, the Sun has been shining for four and a half billion years. Its structure, and the processes that keep it burning, have fascinated astronomers for centuries. After the invention of the telescope it became apparent that the Sun is not a placid, steadily shining body but is subject to periodic changes in its appearance and eruptions of dramatic violence, some of which can affect us here on Earth. Recent space missions have revealed fascinating new insights into our nearest star.With:Carolin Crawford Gresham Professor of Astronomy and Fellow of Emmanuel College, CambridgeYvonne Elsworth Poynting Professor of Physics at the University of BirminghamLouise Harra Professor of Solar Physics at UCL Mullard Space Science LaboratoryProducer: Thomas Morris.

Melvyn Bragg and his guests discuss the life and work of Robert Boyle, a pioneering scientist and a founder member of the Royal Society. Born in Ireland in 1627, Boyle was one of the first natural philosophers to conduct rigorous experiments, laid the foundations of modern chemistry and derived Boyle's Law, describing the physical properties of gases. In addition to his experimental work he left a substantial body of writings about philosophy and religion; his piety was one of the most important factors in his intellectual activities, prompting a celebrated dispute with his contemporary Thomas Hobbes.With:Simon Schaffer Professor of the History of Science at the University of CambridgeMichael Hunter Emeritus Professor of History at Birkbeck College, University of LondonAnna Marie Roos Senior Lecturer in the History of Science and Medicine at the University of LincolnProducer: Thomas Morris.

Melvyn Bragg and his guests discuss photosynthesis, the process by which green plants and many other organisms use sunlight to synthesise organic molecules. Photosynthesis arose very early in evolutionary history and has been a crucial driver of life on Earth. In addition to providing most of the food consumed by organisms on the planet, it is also responsible for maintaining atmospheric oxygen levels, and is thus almost certainly the most important chemical process ever discovered.With:Nick Lane Reader in Evolutionary Biochemistry at University College LondonSandra Knapp Botanist at the Natural History MuseumJohn Allen Professor of Biochemistry at Queen Mary, University of London.Producer: Thomas Morris

Melvyn Bragg and his guests discuss the science of matter and the states in which it can exist. Most people are familiar with the idea that a substance like water can exist in solid, liquid and gaseous forms. But as much as 99% of the matter in the universe is now believed to exist in a fourth state, plasma. Today scientists recognise a number of other exotic states or phases, such as glasses, gels and liquid crystals - many of them with useful properties that can be exploited.With:Andrea Sella Professor of Chemistry at University College LondonAthene Donald Professor of Experimental Physics at the University of CambridgeJustin Wark Professor of Physics and Fellow of Trinity College at the University of OxfordProducer: Thomas Morris.

Melvyn Bragg and his guests discuss the eye. Humans have been attempting to understand the workings and significance of the organ for at least 2500 years. Some ancient philosophers believed that the eye enabled creatures to see by emitting its own light. The function and structures of the eye became an area of particular interest to doctors in the Islamic Golden Age. In Renaissance Europe the work of thinkers including Kepler and Descartes revolutionised thinking about how the organ worked, but it took several hundred years for the eye to be thoroughly understood. Eyes have long attracted more than purely scientific interest, known even today as the 'windows on the soul'.With:Patricia Fara Senior Tutor of Clare College, University of CambridgeWilliam Ayliffe Gresham Professor of Physic at Gresham CollegeRobert Iliffe Professor of Intellectual History and History of Science at the University of SussexProducer: Thomas Morris.