What Is Time?

Presumably, ecologists are in agreement in assuming that time exists, that it flows, and that this flow has a definite and predictable direction. But perhaps we ecologists are also allied in wondering, at least on occasion, what time really is. It seems worthwhile, therefore, before proceeding under potentially false assumptions, that we address three questions related to the nature of time. First, does it in fact exist? Second, if so, does it flow or pass? And third, if it does flow, is it absolute and therefore gone when it passes, or does it recur? These questions will be essential in deciding whether time really can be considered a resource and a limited one at that.

PHILOSOPHICAL VIEWS OF TIME: IDEALISM, RELATIONISM, AND REALISM

The discipline of the philosophy of time offers insightful perspectives on the reality and nature of time, and this chapter will draw extensively on notable works in this field. Why should we review philosophical theories of time? Such treatments of time have been mostly anthropocentric, concerned with the reality and nature of time from human perspective. But if time is real, and represents a resource, then we must subsequently examine the nature of it from nonhuman perspective as well. Hence, examining what fields of study outside ecology have to say about the nature of time will aid us in developing a clearer understanding of the nature of time in ecology. As will be suggested in chapter 3, for instance, notions of the directionality of time may, in ecology, differ from the typical human experience.

Among philosophies of time, idealism denies the existence of time on the basis that change, an intuitive and apparently observable feature of time, is an illusion (Bardon 2013). A key feature of this perspective is the so-called paradox of movement: for an object to travel from one point to another, it must cross an infinite series of halfway points, which can never be achieved. Therefore, temporal idealism concludes that apparent movement, and change in general, is the misperception of an object occupying a space equal exactly to its own dimensions at any given instant. Furthermore, idealism contends that only the present is real. Any notion of past or future cannot be supported logically because neither is observable in the present, and if past and future do not exist, then the present cannot develop from the future or become the past, further refuting the reality of change. Relationism counters this by arguing that we should not conflate time and change because time is not a process but rather something independent of the process that merely allows us to measure it. In relationism, time consists fundamentally of events arranged according to their overlap, order, or rank with other events (figure 1.1) (Meyer 2013).

This view of time has relevance to the concept of the phenological community (chapter 3). It defines time according to subsets of events and their overlap or lack thereof, a notion that will be demonstrated in subsequent chapters as central to the interactions of individuals and species in time. Realism, last, simply represents the view that time is indeed real (Bardon 2013). Temporal realism has its most formal roots in Newtonian physics. Newton argued that the interdependence of time and space necessitates that time must be considered in absolute terms if we also consider motion in absolute terms (Newton 1687). This suggests that time exists independently of change, and that change occurs in time rather than as a result of the passage of time (Bardon 2013). This latter perspective is perhaps best represented by the cosmological or astrophysical view of time discussed later in this chapter.

A-SERIES, B-SERIES, AND THE FLOW OF TIME

If we accept that time does indeed exist, then we must next address whether time "flows" or "passes" and, if so, whether it does so unidirectionally and continuously (Callender 2011). This exercise is not simply esoteric or superfluous, but rather, for the purposes of developing an ecological framework for time, entirely necessary. The process of allocating time to biological maintenance, growth, and offspring production would, for instance, be very different if time were static or recurrent, and therefore unlimited, compared to such a process if time were in limited supply because of its unidirectional passage. Similarly, continuous passage of time might select for strategies relating to the allocation of time to maintenance, growth, and reproduction that could be expected to differ from strategies selected for under conditions of discontinuous passage of time. Ecology applies two different types of mathematical models in describing processes occurring in discrete time steps, such as population dynamics in species with nonoverlapping generations, and those occurring continuously, such as population dynamics in species with overlapping generations. However, ecology does not focus on the nature of time itself. Chapter 3will suggest that there are different forms of time of relevance in ecological systems, but in all of these the assumption is that time itself is continuous. Nonetheless, we might regard one of these forms of time, relative ecological time (about which more will be said in chapter 3) as more continuous in largely aseasonal environments such as the tropics than it is in highly seasonal environments such as the Arctic.

Furthermore, if time does pass and if it does so unidirectionally, then in which direction does it flow? Our innate perception may be that the future lies ahead of us while the past lies behind us, but does this mean we move forward through time and thus that time washes backward over us? Causality, for instance, appears temporally asymmetrical: any action or decision in the present influences at least to some extent actions in the future but not those in the past, imbuing time with a sense of directionality (Callender 2011). Philosophers of time offer insights into such questions through the opposing theories of dynamic, or A-series, and static, or Bseries, time. It may be tempting to dismiss philosophical theories of time as irrelevant to the role of time in ecology because the former appear concerned mainly with human perception of time while the latter should operate universally and independently of human awareness. But astrophysics gives consideration to such questions as well, and does so from a perspective that is decidedly nonanthropocentric. Hence, there is no inherent reason for ecology to avoid such questions.

The A-series, or dynamic, theory of time assigns nonstationary temporal values to events. According to this theory, events move from being...