The Atlas of Reality
Page 70
Here is an apparently possible scenario that is more difficult for us to dismiss:
Suppose that, before the Big Bang, there was a single, infinitely extended process of locomotion, by which two membranes were continuously moving close to each other. As we look farther into the past, we see the membranes farther and farther apart, with no limit. When the membranes collided, they produced the Big Bang, the beginning of complex time.
This scenario would be a problem for Aristotelian Finitists (although not for Temporal Discretists), since Aristotelian Finitists admit that locomotion can involve the covering of distance by means of a continuous, undivided process. However, they could question whether the imagined scenario is really possible, on the grounds that nothing in it licenses us to speak of measurable spatial distances before the collision. This is because distance, like temporal duration, derives its measure from finite processes, bounded at both their beginning and their end. Without real spatial distances, real locomotion would also be impossible. Once again, there is a dilemma. Either space is self-measuring or it is not. If it is self-measuring, then every region of space has an infinity of actual parts, and every process of locomotion through that region has a correspondingly dense infinity of temporal parts. Again, this contradicts the conclusion of the Grim Reaper paradox. If space is not self-measuring, then the imagined scenario is impossible.
19.4 Conclusion
If temporally extended intervals and processes are fundamental, this fact will have a profound effect on our understanding of change and motion, questions that we will take up again in Chapter 24. It may also provide insight into the problem of persistence or identity through time, as we will see in Chapter 24 as well. There is a natural affinity between Intervalism about time and the fundamentality of persisting things, including people and other organisms. In contrast, if Instantism is true, then we have good reason to adopt the At/At Theory (24.5A.1T) of motion and change, reducing facts about motion and change to facts about what properties or locations things have at one instant or another. This leads naturally to the view that all fundamental entities are instantaneous or durationless, and so that all persisting things are mere logical constructions. That, in turn, has profound ethical and legal consequences when applied to persons.
20
Time's Passage
Time is, of course, an important part of life. We are always experiencing time and its passage. As the saying goes, change itself is the only constant. So time is the sort of thing that seems unproblematic, at least until one begins to think about it (as St. Augustine of Hippo noted in Book 11 of his Confessions). Some philosophers have questioned whether there is such a thing as time at all:
20.1T Temporalism. There are moments of time.
20.1A Atemporalism. There are no moments of time.
J.M.E. McTaggart is the most famous proponent of Atemporalism. In addition, some of the historic proponents of Monism (11.2A), specifically, Parmenides and F.H. Bradley, took their Monism to entail the unreality of time. Since we've already discussed Monism, we will focus here on McTaggart's challenge to Temporalism (McTaggart 1908).
McTaggart distinguished three “series” of moments: the A, B, and C series. The A series compares moments in relation to the present, dividing time into past, present, and future. The B series consists of relations of earlier-than and later-than, and the C series is limited to the relation of betweenness, without any temporal direction.
Let's suppose that the first manned mission to Mars occurs at some point in the late twenty-first century. Compare these three propositions:
(1) The Civil War occurred over one hundred years in the past, while the first manned mission to Mars is still in the future.
(2) The Civil War occurred at least two hundred years earlier than the first manned mission to Mars.
(3) The election of Barack Obama occurred between the Civil War and the first manned mission to Mars.
(1) locates the Civil War and the Mars mission in the A series, relating them to the present moment. (2) concerns these events' locations in the B series. (1) was false in 1850 and will be false again in 2100. (2), in contrast, will remain true forever and arguably has been true throughout all the past. Positions in the B series never change: they are eternal. (3) relates three events in the C series. Like (2), (3) is eternally true. The difference is that (3) implies nothing about the direction of time. (3) could be true, even if we thought that our experience of before and after were a mere illusion.
McTaggart's argument for the unreality of time proceeds in several steps:
Time is real only if the B series is real.
The B series is real only if change is real.
Change is real only if the A series is real.
The A series is contradictory and hence unreal.
Therefore, time is unreal.
McTaggart argues that the reality of the C series alone is not sufficient to make time real. If time is unreal, then there are no moments of time. Relations of before and after are essential to time. If these relations are unreal, then what we call “time” is really a dimension of reality without any intrinsic direction, like space.
In step 2, McTaggart connects the reality of temporal direction with the reality of change. If nothing changed, then there would be no sense to talking about the passage of time, and no way to distinguish earlier from later.
Next, McTaggart claims that the reality of change depends on the reality of the A series. He rejects Bertrand Russell's notion that real change is possible so long as objects have different properties at different times. Consider an iron poker that “changes” from being cold at one time to being hot at a later time. McTaggart argued that without the A series this case is no different from a case of an iron poker that is cold on one end and hot on the other. In neither case is there real change, unless the events involved are themselves changing in their position in time. If only the B and C series were real, then events would never change, since an event's B and C relations to other events are all unchanging. The only way that an event can change is to pass from being future to being present or from being present to being past. These changes involve the A series.
Finally, in step 4, McTaggart argues that we cannot coherently conceive of the A series. His argument for this has become known as “McTaggart's paradox”. We will take up McTaggart's paradox in Section 21.5.
There is another sort of challenge to the reality of time to consider. McTaggart accepts that there are many moments but argues that these are not moments of time because they cannot really stand in a temporal order. We could instead consider a challenge to the existence of more than one moment of time. This would be like George Santayana's Solipsism of the Present Moment (13.1T.1), discussed in Chapter 13.
20.1T.1T Temporal Pluralism. There are, have been, and will be more moments of time than one.
20.1T.1A Solipsism of the Present Moment. There are, have been, and will be only one moment of time (the present).
The argument for Solipsism of the Present Moment involves an appeal to Ockham's Razor (PMeth 1): don't multiply entities needlessly. If we suppose all of our beliefs about the past and future to be simply false, then we could make do with only the present moment.
However, there are powerful arguments for the existence of past and future moments.
Memory. We have apparent acquaintance with past moments. And given the Reliable Perception Presumption (PEpist 4), this gives us good reason to believe that those moments are real.
The specious present. Sensory perception and introspection present us with an apparently moving and changing world, entailing the existence of multiple times.
Intelligibility of language and of complex thoughts. If Solipsism of the Present Moment were true, then we would have good grounds for doubting that we really understand any language, since language learning takes time. If we do not understand the sentences of what we take to be our native language, then we do not understand most of our complex thoughts, which take lingu
istic form. This includes all of our philosophical thoughts. Thus, if Solipsism of the Present Moment were true, we could not understand or believe it, or even consider it as a possibility. Therefore, by engaging in philosophical discourse, we tacitly presuppose the falsity of Solipsism of the Present Moment. More generally, Solipsism of the Present Moment runs afoul the following principle of epistemology:
PEpist 2.2.1 Presumption of Philosophical Discourse. It is prima facie plausible to presume the truth of all of the pragmatic presuppositions of philosophical discourse.
20.1 Tensers and Anti-Tensers
As we have seen, McTaggart introduced into philosophy the distinction between the A and B series of moments. Later philosophers of time have extended McTaggart's labels to theories of time. In particular, many philosophers talk about the dispute between the ‘A-Theory’ and ‘B-Theory’ of time. We say this is the debate between ‘Tensers’ (A-Theorists) and ‘Anti-Tensers’ (B-Theorists).
20.2T Tensism (A-Theory). Some tensed truths are metaphysically fundamental.
20.2A Anti-Tensism (B-Theory). There are no metaphysically fundamental tensed truths.
A tensed truth is a proposition whose content contains a tense (past, present or future) or that predicates a tensed property. Tensed properties include the property of being past, being present, and being future. By virtue of containing some reference to the pastness, presentness, or futurity of some time, tensed propositions can be true at some times and false at others. They do not have fixed truth-values.
Def D20.1 Tensed Proposition. A tensed proposition is a proposition that can have different truth-values (true or false) at different times.
Tensers maintain that some true tensed propositions are fundamentally true: that is, that their truth is not conceptually grounded in the truth of untensed propositions. Anti-Tensers think that no tensed proposition is fundamental in this sense.
Anti-Tensers come in two varieties: Eliminative and Reductive:
20.2A.1T Eliminative Anti-Tensism. There are no tensed truths.
20.2A.1A Reductive Anti-Tensism. There are tensed truths, but all tensed truths are wholly grounded in tensed truths.
Eliminative Anti-Tensers either deny that there are any tensed propositions at all, though they may acknowledge that there are tensed statements, or insist that all tensed propositions are false, thereby committing to an error theory of our common sense judgments about tensed propositions. Reductive Anti-Tensers concede that there are true tensed propositions but insist that they are all made true by tenseless propositions. Either way, there are no fundamental tensed truths.
McTaggart argues that Eliminative Anti-Tensism is false, since the lack of tensed truths entails Atemporalism. For McTaggart, it is obviously true that if event 1 is earlier than event 2, then it was once, is now or will be true that event 1 is present and event 2 future, and it was once, is now or will be true that event 2 is present and event 1 past. Hence, if there are never any tensed truths, there can be no temporal order whatsoever.
The other apparent drawback to Eliminative Anti-Tensism is that it forces us to reject as false many sentences that we are all naturally inclined to accept as true. We can appeal to common sense and the viewpoint embedded in our ordinary linguistic practices to support the claim that many tensed sentences or sentences predicating tensed properties (such as pastness, presentness, and futurity) are sometimes true.
Eliminative Anti-Tensers have a response to this objection, however. They can suppose that each sentence that seems to express a tensed truth does not really do so. Instead, it expresses a tenseless truth, but a different one at different times. In other words, Eliminative Anti-Tensers can suppose that one and the same sentence-type can express different propositions at different times. Consider the following sentence-type:
(4) It is now 9 a.m. 10 July 2010.
This sentence seems to express the tensed truth of the presence of a particular date and time. However, Eliminative Anti-Tensers could suppose instead that utterances of (4) express different untensed propositions at different times. When (4) is expressed at time t, then it predicates the property of being identical to t to the time and date (of 9 a.m. 10 July 2010). For each time t, the property that is predicated of 9 a.m. 10 July 2010 is a B-property.
Reductive Anti-Tensers must also account for the truth of statement (4). If we can ground the truth of such statements in truths about the B series, it will be easy to ground the truth of propositions about what is past and future, since the past is obviously earlier than the present, and the future later.
There is a strong argument for thinking that any such reduction of tensed to untensed truths must fail, since untensed truths are true permanently, while tensed truths are (by definition) true only temporarily. How can what is true temporarily be derived from what is true permanently? If a truth p is grounded in another truth q, we have assumed that the truth of q must entail the truth of p. If q is permanently true, and the truth of p is grounded in the truth of q, then p must be permanently true as well. So, it is impossible to ground temporary truths in permanent truths, and Reductive Anti-Tensism must be false.
In order to give Reductive Anti-Tensism a chance, we must relax somewhat our standards for what counts as grounding one truth in another (in the sense of the logical or conceptual grounding discussed in Section 3.4). Reductive Anti-Tensers must argue that predications of tensed properties are not true absolutely or simpliciter. Instead, they are true or false relative to this or that time. Reductive Anti-Tensers can then argue that the truth of some tensed proposition p at time t is grounded in the permanent truth of some untensed proposition q, and the falsity of p at some other time t2 is grounded in the permanent falsity of some untensed proposition q2. Consider, for example, the relation of (4) to (5) and (6):
(5) 9 a.m. 10 July 2010 is the same time as 9 a.m. 10 July 2010.
(6) 9:01 a.m. 10 July 2010 is the same time as 9 a.m. 10 July 2010.
(4) is true at 9 a.m. and false at 9:01 a.m. We could say that its truth at 9 a.m. is grounded in the trivial truth of the identity (5), and that its falsity at 9:01 a.m. is grounded in the trivial falsity of the identity (6).
We can clarify Reductive Anti-Tensism further if we assume Classical Truthmaker Theory (2.1T). Reductive Anti-Tensers propose that the only truthmakers for tensed truths are facts about B-relations, like fixed earlier-than and later-than relations among events. What is it that makes (4) true at 9 a.m.? Nothing except the truthmaker of (5), that is, nothing but the self-identity of the relevant moment of time. What makes (4) false at 9 a.m.? Nothing but the absence of a truthmaker for proposition (6), that is, nothing but the distinction between the two times 9 a.m. and 9:01 a.m. Consequently, one way of bringing out the difference between Reductive Anti-Tensers and Tensers is this: for Tensers, statements like (4) are true simpliciter, while for Reductive Anti-Tensers, they are true only at some time or another.
Here's another way of capturing the difference between Tensers and Reductive Anti-Tensers. Tensers believe that there is a unique present that is constantly in motion. There is always a unique point in time that is present, but different moments have been present in the past and will be present in the future. For Tensers, this movement of the property of presentness is one of the fundamental facts of the world.
In contrast, Anti-Tensers deny the existence of any such pure flow of time. Of course, they do not deny the obvious truth that there is a unique present moment, nor the obvious truth that what time counts as present is different at different times. Anti-Tensers will give an account of the truth of the propositions expressing the flow of time that grounds their truth in eternal truths, making use of a kind of conceptual grounding (in the sense described in Section 3.4). Consequently, Anti-Tensers can consistently deny that the flow of time is real. Consider (7) and (8):
(7) There is exactly one moment that is present, but in the past other moments were uniquely present.
(8) There is exactly one moment that is identical to 9 a
.m. 10 July 2010, but there are earlier times, each of which is distinct from 9 a.m. 10 July 2010, and each of which is uniquely identical to itself.
Tensers believe that (7) is true, and that the truth of (7) is in no sense grounded in the truth of (8). The presentness of the present moment has nothing to do with its being identical to itself, and the fact that earlier moments were once uniquely present is not grounded merely in the fact that those moments stand in the earlier-than relation to the moment that happens to be present. In fact, Tensers might argue that the truth of (8) is grounded in that of (7): what makes certain times earlier than the present is the fact that they once were but are no longer uniquely present.
For Anti-Tensers, in contrast, the priority between (7) and (8) runs the other way. When (7) was expressed at 9a.m. on 10 July 2010, the truth it expressed was exactly the truth expressed by (8) and no other. (7) was true then because (8) was then, and still is, true.
We can see this difference in explanatory direction in other cases. Consider the following pairs of statements:
(9a) The Civil War ended 145 years ago.
(9b) The Civil War ended in 1865.
(10a) The Civil War has already ended, and human beings will but have not yet colonized Mars.
(10b) The Civil War ended before human beings colonized Mars.
Assuming that the Civil War did indeed end in 1865, that human beings will colonize Mars in some year after 2010, and that all four statements were made in 2010, all four statements were true at their time of utterance. Tensers take (9a) and (10a) to be fundamental, with the truth of (9b) and (10b) to be explained in terms of them. Anti-Tensers take (9b) and (10b) to be fundamental, with (9a) and (10a) being merely ways of expressing the very same truths in a way that exploits facts about when the statements are being made.