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.

As humans we are confronted with devices which are supposed to work and often do not. Just think of all the domestic appliances you have at home. Do all of them work? I am sure that you can remember the time when the toaster gave up the ghost or the torch in the garden shed did not work. We have a notion of device and we have an expectation that it will work. But when we say a device does not work, what do we mean? Generally, we mean that it does not perform the function we expect of it. If you put sliced bread into the toaster and press down the lever at the side and nothing happens you utter a sigh of frustration because the device is not working.

What might exobeings really be like? To begin answering this question consider the deep history of our own evolution. Would the evolution of exobeings show the same key turning points we find in our own evolution? Would they develop complex multicellular life forms at an early stage and then move on to become vertebrates with a central nervous system controlled by a brain, allowing them to move around freely in their surroundings?1 Indeed, to what extent would what appear to us as preconditions, vertebrae and a skeleton to stabilise an animal’s body, be necessary on an exoplanet?

The degree of variability on an exoplanet could be similar to that found on Earth, with a certain range for cognitive ability (types of intelligence), personality, aspects of physical appearance such as size, eye and hair colour or shape of skeleton (observable in body build, hands, feet, arms, legs, etc.).

A key question that is often posed is, ‘Are we alone in the universe?’ If the answer to this question were simply ‘Yes’ or ‘No’, this book would probably not have been written. But what looks like a simple question is actually a complex and multifaceted set of issues which can hopefully be elucidated by discussing the many aspects involved.

First, by ‘the universe’ we can only mean the small corner of the galaxy which we inhabit, say within about a 100-light-year or, at maximum, 1,000-light-year radius. This is a tiny fraction of our Milky Way galaxy (at least 100,000 light years in diameter) and we cannot even see half of the galaxy which is beyond the central bulge of the disk on the other side. The Milky Way is an infinitesimally small part of the entire universe.

Normally the final section of a book on language matters would simply be labelled ‘Conclusion’, where the author reviews the main arguments in the book, draws the threads together and presents the results and insights in summary form. However, with this book there can be no definitive conclusion as the subject matter is speculative. But what one can do is summarise the possibilities of exolanguage as a series of questions with tentative answers. Admittedly, the following may be regarded by some readers as unduly anthropocentric, too heavily reliant on what we humans are like. However, in keeping with the principle applied throughout this book, the speculative sections begin with what we know from our existence on our Earth and then move in careful steps to consider what might be the case for exobeings on an exoplanet.