Newtonian gravity is reviewed and an attempt is made to combine it with special relativity, first by expanding the sources from mass to more general mass-energy, and then by considering relativistic force predictions. The gravito-electro-magnetic field equations are developed by analogy with Maxwell’s equations, and using dynamical source configurations familiar from the study of E&M. In addition to the fields, there are predicted particle interactions, like the bending of light, that go beyong Newtonain gravitational forces. Finally, it is clear that this attempt to combine gravity and special relativity lacks the necessary self-coupling of the gravitational field, which carries energy and therefore acts as its own source.

An introduction to field Lagrangians for scalars, vectors, and the Einstein–Hilbert Lagrangian for gravity provides a venue to think about coupling together different field theories. The natural expression of that coupling comes from an action, and we show how the “Euler–Lagrange” field equations enforce the universal coupling of all physical theories to gravity. As an example, the combined field equations of electricity & magnetism and gravity are solved in the spherically symmetric case to give the Reissner–Nordstrøm spacetime associated with the exterior of charged, massive, spherically symmetric central bodies.

Starting from the definition of tensorial objects by their response to coordinate transformation, this chapter builds the flat space vector calculus machinery needed to understand the role of the metric and its associated geodesic curves in general. The emphasis here is on using tensors to build equations that are “generally covariant,” meaning that their content is independent of the coordinate system used to express them. Motivated by the transformation of gravitational energy sources, the gravitational field should be a second-rank tensor, and given the way in which that tensor must show up in a particle motion Lagrangian, it is natural to interpret that tensor as a metric.

Consciousness is the seamless inner subjective state which accompanies you in every moment of your wakeful life and which no-one else is privy to. It is a non-physical experience, which cannot be observed by examining the brain. In attempting to define consciousness, various scientists have strived to specify its necessary and sufficient properties or at least to narrow these down so as to get a handle on it. This is where the difficulties arise. While we all have consciousness and recognise it as an experience, it is difficult to pinpoint it in the form of a definition.1 And how would one go about doing this? One can give an operational definition: consciousness is when we show awareness and when we react to external stimuli. But it is much more than that, it is our inner world which we experience even when there are no external stimuli. Consciousness is where our thoughts are, where we get our ideas.

If you look at the animal kingdom you will see a bewildering array of life forms, with an even more astounding variety of no longer extant species in the past. Among these life forms we find the class of mammals in which the relation of brain size to body mass is greater than in other groups of animals. This is particularly true for cetaceans (sea mammals like whales and dolphins) and for elephants. However, there is one species which stands out from all others: the genus Homo, specifically the species Homo sapiens, the only surviving species of this genus. We are characterised by our large brains in proportion to our body mass and the prominent cortex (outer layer of the brain), especially at the front of the head.

Our story begins with the formation of our Earth about 4.55 billion years ago from the swirling disk of dust and gas, at the centre of which was the young Sun. The latter was formed from the large concentration of material in the middle of this disk. Other concentrations had begun to emerge outside the centre and these grew with time, attracting increasing amounts of material by their growing gravity. The more matter gathered in these concentrations the greater the gravity they had, this in turn causing some of them to steadily increase in size. These concentrations yielded the eight planets we know in our Solar System, with many smaller fragments forming asteroids in the region between Mars and Jupiter and other objects, far beyond the planets, in the Kuiper Belt and the even more distant Oort Cloud.

The term ‘artificial intelligence’ or just ‘AI’ is a buzz word tossed around at liberty in many publications and on the internet today. It is often used to refer to technologies for very specific tasks where human labour would be expensive, or subject to error due to endless repetition. Such technology has considerable applications in many fields of present-day engineering, in digitally based manufacturing and in important scientific domains such as medical research, diagnosis and treatment. Where the technology is used to replace human operators, as on assembly lines, it is more accurately known as robotics. The basis for such technology lies in high-performance computers,1 which have been programmed to perform precise complex tasks. The programming behind such computers is generally declarative, that is, the computers are given precise instructions about what they are to do.

By cognition is meant mental power, the performance of the brain. This varies among individuals but we can see when considering humans as a whole that there is a certain level which is characteristic of all humans and separates us from other animals. For instance, we can plan for the future, utilise past experiences, teach ourselves a wide variety of skills and engage in myriad activities which have nothing to do with our survival as a species.

Considering the high end of human cognitive achievement for a moment, we recognise that it is represented by our best scientists and among these there are, and have been, a small number of individuals who have furthered our scientific knowledge to an inordinate degree. Just think of the great names from the golden age of physics in the early twentieth century, of which Albert Einstein or Max Planck are among the best known to the general public.

Information, knowledge and understanding are closely related concepts but with clear differences between them. First of all, information refers to single facts and is independent of any human agent. It is a fact that the Sun is just under 150 million kilometres from the Earth; that is a piece of information. An individual may know that. Furthermore, this individual might know many other facts about our Solar System, and so have a coherent and structured amount of astronomical information, in which case one speaks of that person possessing knowledge about astronomy.

The question here is whether the biochemical processes observable on Earth would be replicated on another planet. Take photosynthesis as an example. This is the means by which plants utilise sunlight in the production of adenosine triphosphate (ATP) and glucose as sources of energy. During this process oxygen is given off and carbon dioxide is absorbed, hence the value of photosynthesis for environments on our planet. The actual process is highly complex and involves electrons going through intricate chemical reactions leading at the end to glucose formation. There is also a kind of reverse process, which involves the release of energy through the oxidation of a chemical derived from carbohydrates, fats and proteins. This is known as the citric acid cycle, an essential metabolic pathway used by aerobic organisms.