Three Chronic Errors: Some Misconceptions Concerning the Direction of Time

1 Three Chronic Errors: Some Misconceptions concerning the Direction of Time In a subject in which differing opinions are rife, it is difficult to discern anything like a consensus on what constitutes the direction of time. Physicists routinely identify it with the direction of increasing entropy, and then part company over whether this is in turn founded on such esoterica as the expansion of the universe (Gold), the no-boundary condition + weak anthropic principle (Hawking), a broken time-symmetry at the microscopic level (Prigogine), or the surfeit of entropy produced by a massive inflation of spacetime in the first –35 10 seconds of the universe’s existence (Guth, Davies).1 Philosophers, on the other hand, have been skeptical of attempts to define time’s direction in terms of entropy considerations, at least since the failure of Reichenbach’s efforts in mid-century.2 Grünbaum has abandoned the idea of a ‘direction’ in favor of an anisotropy between the two possible directions of time3; Earman doubts the relevance of entropy4; and Mehlberg, Horwich and Price see time as intrinsically symmetric.5 There is, nevertheless, an orthodoxy of sorts. For, despite their differences over the origin or relevance of the Second Law of Thermodynamics, all these authors (save Prigogine) agree on the following premises as their point of departure: the direction of time is not the direction in which events “come to be”, since temporal becoming is a mere facet of 1 Thomas Gold, “Cosmic Processes and the Nature of Time”, in Mind and Cosmos, ed. Robert G. Colodny (Pittsburgh: University of Pittsburgh Press, 1966), 311-329; Stephen Hawking, “The No- Boundary Condition and the Arrow of Time”, in The Physical Origins of Time Asymmetry ed. J. J. Halliwell, J. Perez-Mercader and W. H. Zurek (Cambridge: Cambridge University Press, 1994), pp. 346-57; and Ilya Prigogine, From Being to Becoming (San Francisco: W. H. Freeman, 1980), ch. 8; Paul Davies, “The Inflationary Universe: Was the cosmos born in a fleck of foam?”, The Sciences 23, 2, 32-37. 2 Hans Reichenbach, The Direction of Time (Berkeley/Los Angeles: University of California Press, 1956). 3 Adolf Grünbaum, “The Meaning of Time,” in Basic Issues in the Philosophy of Time , ed. Eugene Freeman and Wilfrid Sellars (La Salle, Ill., Open Court, 1971), pp. 196-227. 4 John Earman, “Irreversibility and Temporal Asymmetry”, Journal of Philosophy, LXIV, 18, 543- 549, 1967 5 Henryk Mehlberg, “Philosophical Aspects of Physical Time”, in Basic Issues, ed. Freeman and Sellars (1971); pp. 16-60; Paul Horwich, Asymmetries in Time (Cambridge, MA: MIT Press, 1987), ch. 3; and Huw Price, Time’s Arrow and Archimedes’ Point (New York: Oxford University Press, 1996). 1 2 subjective experience. That is, the laws of physics do not distinguish between past and future; events simply “are” in spacetime; they do not “become” in serial fashion.6 As Grünbaum expresses it, there is nothing more to temporal change than the (“tenseless”) occurrence of events or states at different times. Thus, although his point of view denies “that physical events themselves happen in the tensed sense of coming into being apart from anyone’s awareness of them”, it nevertheless asserts that they “do happen independently of any mind in the tenseless sense of merely occurring at certain clock times in the context of objective relations of earlier and later”.7 Given these premises it is easy enough to see how the direction of time becomes a “problem”. For if all events simply lie in a relation of temporal succession to other events in the four-dimensional spacetime manifold, yet do not actually come to be out of those that preceded them, then we can equally well read the order in either direction. This then raises the question, how does our conception of time’s direction arise? Why is it that we experience events as coming to be in one direction only? Why are so many facets of our experience temporally asymmetric? The standard answer to these questions has been to explain all of these facts as arising from the existence of irreversible processes. If there were no such processes, it is claimed, then time would be intrinsically symmetric. It would be just like one of the spatial dimensions, on which we can conventionally order objects asymmetrically, for instance from left to right. But this corresponds to no preferred direction of the line itself, and to no feature of the objects lying on the line: it is merely imposed by us. Irreversible processes, however, are thought (by most) to spoil this symmetry. There is all the difference in the world between the kinds of processes one sees in a typical video, and the impossible processes one sees when the video is played backwards, such as spilled coffee and shards of china miraculously composing into a cup of coffee leaping up in a graceful parabola onto some nearby table. The process of a cup of coffee falling off the table and smashing is irreversible, 6 Cf. Hermann Weyl’s famous remark: “The objective world simply is, it does not happen”, Philosophy of Mathematics and Natural Science ( ), p. 116; and Adolf Grünbaum, “Time, Irreversible Processes and the Physical Status of Becoming”, in J. J. C. Smart, Problems of Space and Time (New York: Macmillan, 1964), pp. 397-425: “the relativistic picture of the world … conceives of events not as ‘coming into existence’ but as simply being and thus allowing us to ‘come across’ them” (417). 2 3 and knowing that its time-reverse is impossible allows us to determine which way time is “flowing” for the processes filmed in the video. Processes go from a state of low entropy to a state of high entropy (at least in isolated systems, over a sufficiently long time). Thus entropy can be used to fix the “arrow of time”. Or, on Grünbaum’s more considered version of this view, the existence of irreversible processes allows us to single out one of the directions along the time axis as preferred, and enables us to fix the direction of increasing entropy as that from earlier to later.8 Now I do not at all accept this consensus, and this is because I do not accept the premise on which it is based: the denial of the reality of becoming and process. I shall not argue directly for the reality of becoming here;9 my intention is rather to show how its denial has led to certain deep-going errors in discussions of the direction of time–the “chronic errors” of my title. (By the way, in calling the errors “chronic” I do not mean to suggest they are “egregious”, to use Grünbaum’s favourite term for bemoaning his critics’ errors; I only call them this because they run deep and have been around for some time; and, of course, because I couldn’t resist the pun). And since I do not believe a coherent account of the direction of time is possible which does not in some way presuppose becoming or lapse into incoherency, then to the extent that my critique of orthodoxy is successful it should constitute an indirect argument for my view. Let me be more explicit about what my view is. I maintain that temporal becoming is an objective fact; and this is entirely sufficient to explain the direction of time neatly and without residue. That is, each and every event or happening comes into existence out of earlier events and conditions; a sequence of such events ordered by the relation of “comes to be out of” or “is later than” is what we call a process; and the direction in which this becoming occurs is what we call the direction of time. Otherwise stated, the order of 7 Grünbaum, “Meaning” (1971), p. 213-14. 8 Grünbaum, “Meaning” (1971), p. 210? Even those who reject the explanation of time's direction in terms of entropy (with the notable exception of Earman) agree that time has two possible directions, and that if they cannot be distinguished from one another by means of irreversible processes or some other such criterion, then time is intrinsically symmetric. See Mehlberg, Price. 3 4 temporal succession is intrinsically asymmetric, and this is what constitutes the time- orientedness of every natural process. Stated so baldly, this will so far seem not much more than a contradiction of some of the main tenets of the orthodox position, such as the distinction between time asymmetry and time direction or anisotropy. Worse, it seems to assert as a physical fact what the usual theories set about trying to explain, the origin of time asymmetry. Compared to the sophistication of the attempts to ground time asymmetry on an asymmetry in boundary conditions, or on a broken time-symmetry at the microscopic level, or on the surfeit of entropy produced by a massive inflation of spacetime in the first 10-35 seconds of the universe’s existence, a mere assertion of intrinsic asymmetry is bound to appear prosaic. I acknowledge these objections; but I cannot do anything to assuage them, since I am persuaded that the attempts to found time asymmetry in something more basic are ultimately incoherent. I shall argue that the existence of irreversible processes is one thing, the violation of the symmetry of time reversal invariance another, and the asymmetry of time another, and that the conflation of these matters is a cause of much of the difficulty in this subject. The Three Errors But I believe three errors in particular have bedevilled discussion of the direction of time. Let me begin by outlining them. I have already mentioned that many leading philosophers of science have expressed skepticism about the viability of defining the direction of time on the basis of the second law of thermodynamics.

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