Preface to the First Edition
- Is space an ingredient of reality in its own right, or simply nothingness? What does the passage of time amount to? Is only the present real, or is the past real as well? and what of the future? Are space and time finite or infinite? For anyone with an interest in the large-scale composition of the cosmos, no questions are more pressing than these; likewise for those concerned to understand the framework within which we live our lives. But few questions are more challenging. Trying to think clearly about space is not easy. How does one go about thinking about nothing? But time is harder still. While it may seem clear that the past is real in a way the future is not, it also seems clear that the present is real in a way the past is not, so what sort of reality does the past possess? It may seem obvious that time passes, that the present is steadily advancing into the future, but just what does the passage of time involve? These are simple questions about the most fundamental features of our world, yet no obvious answers spring to mind.
- Answers to all these questions have been proposed; many of them are fascinating, and many far from obvious. The philosophical literature, both ancient and modern, is both large and wide-ranging, embracing as it does topics as diverse as semantics, causation1, modality2 and phenomenology. The relevant scientific and mathematical literature is no less vast, and the relevant theories are diverse and difficult: the physics of motion; the nature of the continuum; the geometry of flat and curved spaces; relativity theory; and quantum mechanics. This range and diversity make the study of space and time uniquely rewarding. Few other subjects introduce as many unfamiliar and exotic ideas, and perhaps no other subject stretches the imagination so far. But it also makes the subject unusually difficult for anyone approaching it for the first time. The aim of this book is to make this task easier.
- I have tried to provide an introduction to the contemporary philosophical debate that presupposes little or nothing by way of prior exposure to the subject, but that will also take the interested and determined reader quite a long way. Anyone completing the book should be in a position to make a start on some of the more advanced philosophical work, as well as coming away with a reasonable (if elementary) understanding of the current state of play in physics. The book is intended primarily for students of philosophy doing courses in metaphysics or philosophy of science (second year and above), but most of it should be intelligible to the interested reader who is new to philosophy: philosophical jargon is used, but sparingly, and often explained en route; a good many other terms can be found in the Glossary. Since they will already be familiar with many of the basic themes, avid consumers of popular science should have little difficulty with most of the book, especially those whose appetite for mind-bending ideas from the frontiers of physics is temporarily sated, and who are starting to wonder what the implications of these ideas might be. Much contemporary philosophy of space and time is devoted to precisely this question.
- Given the complexity of the subject matter, I have narrowed my focus and concentrated on just two key questions:
Since these questions cannot be addressed in isolation a good many other topics are discussed as well, but there are some that are not treated at all (e.g. Zeno's paradoxes3). These omissions are regrettable, but a more comprehensive treatment would necessarily have been more superficial, and ultimately less interesting, so I had no qualms about making them. There are three interconnected parts to the book. The first of these, taking up Chapters 2-8, is devoted exclusively to time. Although a good deal of the analytic philosophy of time over the past half century has been devoted to linguistic and semantic issues, I decided not to give prominence to these. The significance of these intricate debates is far from obvious to the uninitiated, and their interest has diminished as the prospect of their having any decisive metaphysical impact has receded. More recently, thanks to the appearance of works such as Michael Tooley's Time, Tense and Causation4 (1997) and Huw Price's Time's Arrow and Archimedes' Point (1996), the climate has changed as metaphysical and scientific issues have come more to the fore. I have tried to reflect this development in my treatment here.
- Does time pass?
- Does space exist?
- Although my approach to time is largely ahistorical, I begin with McTaggart's paradox (1908), which has exerted a significant influence on recent discussions. Although some believe that J. M. E. McTaggart's argument (properly interpreted) reveals the untenability of all dynamic conceptions of time, I argue for a more moderate verdict: some dynamic conceptions perish, but others survive intact. The surviving dynamic conceptions are examined in Chapters 5 and 6 (the latter includes discussions of the "growing universe" model advocated by C. D. Broad and Tooley, and "Presentism", the doctrine that only what is present is real). Before this, in Chapters 3 and 4, the alternative "Block" (or eternalist) conception of time is considered: the (initially astonishing) doctrine that time is essentially like space, in that it does not pass. Of especial concern here is saving the appearances: why is it that time seems to pass if in reality it doesn't? This topic is taken up again in Chapter 7, which is entirely devoted to the phenomenology of time; how time is manifest in our streams of consciousness. This puzzling and important issue is too often treated very superficially or not at all. To round off this opening stage, the possibility (or otherwise) of time travel5 is examined in Chapter 8.
- My approach to space follows a different kind of trajectory. After a general overview in Chapter 9, we take a step back into the past and look in some detail at the sixteenth- and seventeenth-century debates concerning space and motion, the main protagonists being Descartes, Galileo, Leibniz and Newton (with the latter pair having starring roles). This historical detour provides a change of atmosphere after the largely a priori investigation into time, but is also justified on other grounds. Since purely metaphysical investigations into the nature of space do not carry one very far, empirical considerations have to be introduced at an earlier stage, and the Leibniz-Newton controversy provides a useful point at which to start, not to mention the fact that this controversy is still being discussed in the contemporary literature.
- Chapter 12 takes the debate about motion and dynamics a step further by examining how the transition to neo-Newtonian spacetime affects the Leibniz-Newton controversy. The move towards the present day is continued in Chapters 13 and 14, where the impact of non-Euclidean geometries is considered, together with Kant’s "hand" argument and Poincare's conventionalism. Chapter 15 is purely metaphysical: the topic is Foster's powerful but complex argument for adopting an anti-realist stance to physical space.
- The final part of the book is devoted entirely to contemporary scientific theories and their interpretation. I provide an informal introduction to Einstein's special theory of relativity and Minkowski spacetime in Chapter 18, and consider their metaphysical implications in Chapter 19. It is sometimes assumed that the special theory by virtue of the way it relativizes simultaneity (and hence the present) establishes the Block view of time beyond all doubt, but this is not so. There are dynamic models that are compatible with the special theory, and while these models have some counterintuitive consequences, so, too, does the Block conception, not to mention the special theory itself. Some of the rudiments of Einstein's general theory are expounded in Chapter 20, and its metaphysical implications (mainly concerning substantivalism) are examined in Chapter 21. I close by briefly considering some of the more speculative developments in recent physics.
- The book's three parts could be seen as being devoted to time, space and spacetime respectively - for a while I considered separating and labelling them as such - but this would have been misleading. The "Block universe" considered in Chapters 3 and 4 is a four-dimensional spacetime continuum, and spacetime returns again (albeit in neo-Newtonian guise) in Chapter 12. On reflection it seemed better to acknowledge the interrelated character of the issues by not imposing a formal division into parts.
- A problem facing any book such as this concerns the balance between philosophy and science. How much science should be included? How advanced should it be? Where should it go? Needless to say, there is no perfect solution. I have opted for a policy of progressive integration: as the story unfolds the balance tilts from "philosophy + a little physics" to "physics + philosophy of physics", but the latter stage is reached only in the last few chapters, and the level of exposition remains elementary. A more difficult choice was what physics to include, and here, too, hard choices had to be made: there is no separate or systematic treatment of quantum theory. This is a deficiency, for it may well be that developments in this area will have a decisive impact in years to come, when quantum gravity theory comes into its own. But we are not there yet, and given the plethora of competing interpretations of quantum theory in its current guise, it is impossible to know what impact it will eventually have. Hence I came to the conclusion that the omission was justifiable; remedying it would have made a long work even longer, and sacrificing relativity was never an option. Quantum theory does, however, make an occasional unsystematic appearance: in §8.6, in the context of backward causation6, and in §19.4, where the focus is on the tension between quantum entanglement and special relativity.
- Throughout the book I am less concerned with reaching final conclusions than with revealing interconnections. Given the number of important questions in physics and cosmology that have yet to be answered, such conclusions would be premature at best. But, as we shall see, if our understanding of space and time is to improve, progress also needs to be made on certain philosophical problems. Some doubt this is possible, but I am more optimistic. Progress in metaphysics is not impossible, but it does not come easily. When it comes it often involves uncovering patterns of dependency, connections between doctrines not previously suspected, or at least not obvious. By revealing what must stand or fall together, these patterns shed new light on what the coherent metaphysical options might be. I have tried to bring some of these patterns into clearer view.
- In fact, these are now covered in the Second Edition – Chapters 16 & 17.
- Dainton has kindly updated the Chapter numbers in this Preface to accommodate these two interloping Chapters.
Text Colour Conventions (see disclaimer)
- Blue: Text by me; © Theo Todman, 2018
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