The philosophy of time

Questions to think about for 20.04.2015 (Week 2)

1. Fatalism

  1. Markosian says that the Open Future response entails what he calls "the tensed view of semantics", but he does not spell out why. Can you?

    Suppose a sentence like "It rains on 2 June, 2016" lacks a truth-value since it is about the future. (Admittedly this is a strange "future-tensed" sentence since its main verb is present-tensed, but we can't use a more natural example like "It will rain (e.g. tomorrow)" since we wouldn't get the entailment Markosian wants.) When 2 June comes to pass, the sentence will then receive a truth-value, whence (iii) is true: it is possible for a proposition to receive different truth-values at different times. Also (i) clearly follows: propositions have truth-values relative to times, and not simpliciter. Given the example statement in question, we can see that there is no way to fill in the proposition so that it is true/false simpliciter, so (ii) must follow: "p is true/false at time t" is the fundamental semantical locution.

2. Reductionism and Platonism with respect to time

  1. Can you say why reductionism with respect to time presupposes that the relevant properties with respect to which change is defined are non-temporal? What of reductionism if one can change with respect to their temporal properties?

    Suppose something can change with respect to its temporal properties, like "presently existing at time t". Then clearly time cannot pass without anything changing if anything whatsoever exists. For that thing will have the property of presently existing at one time t but fail to have it at another time when t ceases to be present. One could deny that there is a privileged time called "the present", but then reductionism presupposes the falsity of a number of plausible views about time (like presentism and the growing universe/block), which is likely not what Markosian had in mind. In any case, we can use the property "being exactly n in age", for n some real number of the smallest unit of time, which something will have at exactly one moment and no other.

  2. How could one deny both time without change and Platonism with respect to time?

    One could be a presentist and hold that only the present is real. Then a thing's temporal properties will always be changing (consider properties of the form "presently existing at t", so that if there's time, there's change, and yet they still might identify times with events (or sums of events or sums of individuals that exist at those events).

3. The topology of time

  1. What would it mean for time to have the topology or structure of (i) a straight line, and (ii) a tree, branching out toward the future?

    To have the structure of a straight line means that the future is determinate, and to have a tree-like structure means that the future is indeterminate, with many possible continuantions from at least some given moments.

  2. What would it mean for time to branch backward toward the past?

    If time branches backwards, then contrary to intuition and our phenomenology, the past is indeterminate. Something could happen today so that it is true e.g. that it is sunny, and yet tomorrow it becomes indeterminate that yesterday it was sunny.

4. McTaggart's argument

  1. Which of the series (A or B) distinguishes a privileged moment called the present? What does this say for Markosian's parenthetical remark concerning the two series being identical?

    Only the A-series distinguishes a privileged moment called the present. This means that the structure of the two series is different, but only in virtue of this small but important detail. (I am assuming a mathematical representation of a structure, such as a set consisting of a domain of objects and a relation on those objects, possibly with the addition of a distinguished element. Thus while the B-series looks like this, {D, <}, the A-series looks like this, {D, <, t}, where D is a set of moments, and < is a temporal ordering on D.)

5. The A-theory and the B-theory

  1. What are some worries the A Theory faces?

    The main one is that it stands in tension with the special theory of relativity (SR), a well-received empirical theory. According to SR, there is no absolute simultaneity; whether two distant events take places at the same time is relative to an observer. From this it follows, e.g., that no time can be called the present simpliciter, and no event can be said to be taking place at present simpliciter. The argument is very simple and very powerful because none of the solutions to the problem (which are not really discussed in the text) look in the least appealing.

    Another worry is that the notion of times passing seems problematic. If time passes then it makes sense to ask at what rate. Yet there seems to be no sensible answer to that question.

  2. What are some worries the B Theory faces?

    One is that it makes a mockery of the common sense notion of time according to which some time is present and the rest are not, time passes, and so on.

6. Presentism, eternalism, and the growing universe theory

  1. What is presentism, and what is non-presentism and its two main varieties?

    Presentism is the view that everything is present or that "only present objects exist". Non-presentism is the negation. Two main non-presentist views are eternalism, according to which past, present, and future things exist, and the Growing Universe Theory, according to which only past and present things exist. There are some other views that Markosian does not list, such as the moving spotlight, and Storrs McCall's view where the branches of the tree of time fall off as time passes.

  2. What are some problems facing presentism?

    First, what do we refer to by 'Socrates' when we say e.g. that Socrates was wise? Second, how do we make sense of cross-temporal relations--that is, relations holding between things of different times? Don't the relata need to exist in order for it to be true that x and y are so related? Third, if every truth has a truthmaker, what is the truthmaker for past-tensed sentences like 'Socrates was wise'? It can't be Socrates!

7. Time travel

  1. Besides the one mentioned in the text, can you think of any other "paradoxes" of time travel?

    Here is an admittedly weak but cute one, not deserving of the 'paradox' title. If time travel were really possible, why haven't we yet met any time travelers?

8. The 3D/4D controversy

  1. What are three- and four-dimensionalism?

    Three-dimensionalism is the view that things "wholly exist" at the times at which they exist; I wholly exist now and wholly existed yesterday. Four-dimensionalism is the view that things are spread out across time, so that they exist only partly at any time at which they exist, and they--the worm!--exist wholly only over the entire course of their existence, which spans a duration of time. Think of a block with worms in it--the block is time and the worms are us. Not a pretty picture!

  2. According to 3D and 4D, is it true that things have properties (like being red) only relative to a time?

    For 3D yes, for 4D, yes and no. Consider a car that was once red but is later painted blue. The car is red only relative to a time, the times at which its red temporal parts exist. But the parts themselves are not red only relative to a time. They are red simpliciter. So while some things have certain properties only relative to times, such as continuants (persisting things), other things may have their properties simpliciter.