Time, being so essential to the nature of all our experience, is a difficult concept to explore. Attempts to model time in terms of something else are especially challenging due to the fact that people will inevitably have to interpret the model in a temporal sort of way in order to understand it. Presentism, the claim that only the present exists, represents a rejection of the project of explaining time. For a presentist, no explanation is needed because the temporal nature of how we subjectively experience things is held to be the absolute objective nature of time. No further exploration is allowed, there is only the present experience, which has an irreducible property of change. Opposed to presentism is the block universe theory, a model which presentists reject as failing to properly explain subjective intuitions. For the presentist, the only way to explain what tenses naturally mean to us is through asserting that "now" is the only existing time, with the past being gone and the future being simply the form which the now will change into... all talk of an objective time containing the totality of all moments in history or future is from their perspective a blatant mistake. A better understanding of the block universe not only demonstrates that it explains subjective reality just as much as any objective theory should be expected to, it also illustrates the underlying objective simplicity of the block universe compared to the presentist universe.

The belief that tensed facts must be treated as absolutely tensed, and cannot be given any relative (untensed) interpretation, is an essential part of presentism. Non-presentists have, however, offered ways to analyze tensed facts as untensed in space-time. "The execution of Socrates already happened" can be expressed as being equivalent in meaning to the untensed expression "the execution of Socrates is earlier relative to this utterance." This makes use of token reflexivity, defining the meaning of earlier and later relative to the spatio-temporal (four dimensional) location of the utterance. The utterance is the reference frame relative to which the concepts of earlier and later are given meaning. The presentist brings the charge that if there's no objective tense then none of our regular tensed talk would make sense; it can be responded that our normal talk does indeed make objective sense and have objective true/false values as you'd expect, once you translate it from the subjective onto the objective scheme in this manner. A.N. Prior is skeptical and believes that these revised versions still have tense, since they're expressed in the present tense "is." [1] Prior is correct in that the English language lacks an ability to write about something existing without tense, so the present tense is indeed the linguistic form in a literal sense. If the words of our language don't properly allow talking without tense, this is natural, because tenses are subjectively real (that fact not being debated here, the objective necessity being the question at hand). What Prior seems unable to recognize is that the tense is not in any way essential or important to the statements after translation, it adds no information to them, and this is why they can be called untensed.

Against the untensed interpretation, Ian Hinckfuss brings the further objection that being able to refer to earlier and later isn't sufficient to account for the fact that future and past are not interchangeable. [2] To say something is past is not equivalent to saying it's future, the distinction is more than arbitrary, and so he argues tenseless language is inadequate. In order to respond to this objection, it's necessary to delve deeper into the nature of the block universe by considering the nature of a person as a being inside a four dimensional world, observing from this inside as a part of it. A person, as a tiny creature in the middle of space-time with the odd ability to sense objects, creates eight directions with his or her perimeters: right, left, ahead, behind, above, below, earlier, and later. (Note, these come in pairs with two for each of the four dimensions.) Objectively these eight may seem interchangeable, but it would be a mistake to suppose their subjective differences don't have objective causes. To begin our conceptual exploration, grant the presentists their status as being serious about tense and see how it could in theory apply to left and right -- in this way we can begin to see the objective connection of these eight directions as well as the objective causes of their subjective differences. Suppose a person has such an ego that they cannot conceive of "left" except as it is for them. For an object to be "to the left" has to mean it's on their left, and other people who disagree about what's to the left are simply confused and should be ignored. For this person, as he slowly turns around , objects in the world flow from right to left. Suppose, for the sake of argument, that he were born on a slowly rotating platform incapable of movement, lived his whole life there, and died before it completed a full revolution. It would appear to this person that objects have a natural flow: objects always go from the right to left. For this person, right and left appear much like our earlier and later. The concept that right and left could be arbitrarily defined would seem absurd -- obviously right has an entirely different sort of nature from left. If someone claims that a particular object is to the right which this person sees as being to the left would be not only blatantly false but illogical -- yet for us, it would seem perfectly reasonable. It's perhaps easier to imagine this situation in terms of ahead and behind (a person on a moving platform such that things flow from ahead to behind), but it can apply to any of the pairs of directions. Above and below provide perhaps the closest analogy to time in how they've subjectively worked for us. The clouds have traditionally been resting places of the gods, the location of heaven... to imagine the clouds as "below" may once have been absurd, for it seemed clear that they were objectively above and this made them the proper place for the gods. The earth, in contrast, seemed to be the objective "below" or at least the objective "down." Gravity is a constant force capable of creating this illusion -- to the ancients, it seemed that gravity obviously pulled things downward and thus established the objective scheme of aboveness and belowness. Suggest to an ancient the idea of an outer space in which the entire planet can change from being above or below with a simple twist of the body, and tell them there's no objective direction of gravitational pull to establish the correct down and up independent of a person's subjective intuitions (and that gravity is only a relationship between masses), and it's wise to expect heavy resistance followed by outright rejection. Concepts which seem reasonable to us can seem counterintuitive to someone with more limited experience, and in turn our limited experience makes other concepts seem counterintuitive to us.

With the scene set, we make our way at last to the concepts of earlier and later. We can note that in our world, we have a limited degree of spatial freedom -- but however limited our movement may be relative to the size of the universe, we do have the ability to rotate left or right and to look up and down, despite any confusions that may have crept into the minds of the ancients regarding gravity. We lack this sort freedom with respect to earlier and later. We do not sense earlier and later in the way we sense other directions -- they do not come to us directly through sensation, even if sensations may aid us in getting a subjective sense of them. Unlike space, time exists in the mind. We don't encounter time as we encounter space, rather we are (in an untensed sense) objectively a series of points in time which each have introspective senses of a relation to other time as well as sensory impressions of a relation to space. For a being to observe and interact with the universe, it must exist across one dimension as well as sensing the others -- anything which sensed all dimensions could not be said to think or act, because it would not have any dimension for thoughts to take place in (thoughts being sequences of brain states, and sequences automatically requiring a dimension to exist in just as multiple points makes a line). Here we can see that despite a lack of objective distinction between the four dimensions, any subjectively existing being (a thinker) must encounter one of those dimensions subjectively in the form of time. Time is that dimension in which thoughts are sequenced. Simply existence of thought across time, however, has not yet explained the cause of the distinction between earlier and later; to do that we must bring memory into the picture. Memory for us is like the slow turntable is for the person whose world flows right to left: memory unfailingly directs us from earlier to later. Memory is the key to this because it contains representations of points from one of the eight directions -- the fact that this is memory causes us to call the subjective result of the representations the direction of "earlier" relative to the thought which is considering the memory. The objective direction of the eight which memory builds from is unimportant (actually indefinable), because the objective senses of the directions are indistinct and entirely interchangeable. What is important is that whichever direction it is that memories are causally connected from, this automatically becomes the past and its opposite automatically becomes the future, by definition. We've escaped Hinckfuss's objection by showing how the subjective difference between earlier and later arises from objective indifference, and we've also illustrated how the block universe model can offer detailed explanations of what objective conditions bring about our familiar subjective realities.

One of A.N. Prior's major misconceptions regarding the block universe theory is that it has the past and future existing now. This leads to his labeling of it as the "tapestry" view, and to his claim that it implies determinism. His insistence on past and future being now is clearly a refusal to step outside of presentist dogma, a refusal which makes it impossible for him to give a proper criticism of what the view actually claims. Space-time theories are not making a tensed statement about the current existence of the past and future, as Prior implicitly takes them to be doing, and so do not imply the irrational concept of the past and future exiting in the present and do not imply one way or the other on the issue of determinism. As J.J.C. Smart explains, "when we say that future events exist we do not mean that they exist now (present tense). The view of the world as a four-dimensional manifold does not therefore imply that, as some people seem to have thought, the future is already 'laid up.'" [3]

The block universe relegates tenses to the subjective realm, and a large part of the problem with misinterpretations of the model is that each person who contemplates it must do so from their own subjective perspective where there are indeed tenses. The block model is limited by the fact that it is only a model, and that as a model it must be a publicly accessible representation. (As objectively accurate as it might be, a model which cannot be drawn will not be effective.) The block universe model does not actually intend to imply that space-time is block-shaped, because there is no such observer to look at it and give it that shape. There is no tapestry because to suppose a tapestry is to suppose that it's coherent to imagine standing outside looking in at space-time... it's simply a false intuition generated by imagining what it would be like to view such a situation when in fact the idea of viewing it is logically incoherent. We imagine the block universe as like a slide show, or like or frames in a film, but these analogies inevitably impose temporal notions on it -- still pictures are a notion of a preserved present-time -- which don't belong in the properly objective theory. There is something or other which can be plotted in a reasonably representative sort of fashion as a block, but this provides no sense of determination and implies no sense of temporal coexistence of distinct times. All that the block universe asserts is that time slices are related to each other, as are space slices, so that it's possible to plot them and learn something from such a graph (Minkowski diagram). Thus the assertion that temporal events have relationships in no way implies any sort of deterministic relationship -- any sort of relationship works so long as it allows the notion of there being locations in time to be coherent based on the relations between space-time points. As Smart properly concludes, "the view of the world as a space-time manifold no more implies determinism than it does the fatalistic view that the future 'is already laid up.'" The block universe makes no attempt whatsoever to answer the question of if the universe is deterministic or indeterministic, remaining as Smart says "compatible both with determinism and indeterminsim." Determinsim is a thesis about the precise manner in which slices in the "later" direction are related to slices in the "earlier" direction along the time axis, and the block universe model makes no attempt to influence a decision on that in either way.

This inability to imagine the objective reality of the situation the block universe theory proposes is something presentists will point to as a problem. Actually, however, it's quite reasonable. Considering that to seek objectivity is to seek a perspective independent of the nature of the self, there's no reason to expect that objective reality be something which it would be possible to stand outside and observe. We're on the inside and there is no outside, so any images we have of what it looks like falsely suppose that observation of it is a logically coherent possibility. Any theory which makes objective reality look like it's observable should be treated with severe skepticism, since it fails to account for what exactly such observation would be done in. A properly objective theory seeks to explain what conditions make our observations possible, but does not use something observable in the explanation -- to make the explanation of observation be itself dependent on the idea of observation would imply a Homuncular regress. Presentism, of course, posits a 3D universe with "change" or "becoming" but refuses to explain what the change is becoming within... it's left as a brute fact of the theory, a traditional but rather inelegant ad hoc way to save an idea without explaining anything. Presentism is a subjective intuition which stands in need of objective explanation, but which offers only the notion of absoluteness -- arbitrary ontological complexity in order to avoid having to explain.

Again appealing to subjective intuition, Prior attempts to hold up the expression "thank goodness it's over" as something not explainable by his block model opponents. Once more his claim rests on the belief that the subjective nature of the experience denies the objective context of space-time, while the space-time universe is actually just a widening and explaining of that subjective reality. His suggested analysis of "thank goodness its over" as "thank goodness the latest part of that is earlier than this utterance" does indeed lack some of the intended subjective meaning just as he suggests, but that does not mean it can't be accounted for as much as is objectively needed with a minor exploration of what sort of objective reality corresponds to the subjectively intended meaning. The expression does indeed mean that the event is over, and this is not as simple as "earlier". The additional meaning of "over" implied by the relief expressed is related to the event receding in memory. As memory builds from time slice to time slice in the causal arrow it defines from earlier to later, giving information to later brain states which represents earlier brain states, the connection which the particular time slice of the event has to the time slice of later consciousness tends to weaken. This is what we subjectively recognize as memories fading over time. "Thank goodness it's over" is an expression of appreciation for the fact that the memory collection near the surface illustrates less and less dominance of thoughts about that particular event in the "later" and thus more dominant parts of the memory. The time slice region of consciousness which expresses the sentence "thank goodness it's over" recognizes the trend and sees the subjective progression of memory towards not involving thoughts of that event anymore... from the subjective perspective this is naturally considered a good thing worthy of thanks. Four dimensional space-time in no way contradicts the subjective meaning -- rather, it gives some fuller explanation of it as a piece of an objective context. It's true that objective explanations seem dry and emotionless simply because they have little to do with the self, and this doesn't mean that they can't imply/contain localized subjective interpretations which have the emotional content. The sentence "this food is sweet" might be more objectively analyzed as "the chemical composition of this structure has features x, y and z, and the tongue of the person consuming it has properties p, q and r"... yet that does not mean the more objective analysis captures the truest intent of the speaker, only that it explains the objective validity of it. W should expect no more. The objective nature of "thank goodness it's over" is properly captured by a four dimensional model, even if the subjective interpretation of it is rather more important to us.

The presentist response to the theory of relativity is another area where their criticisms lack force. While presentists such as Prior can claim that Einstein's relativity theory is mistaken and that it doesn't deal with the "true" space-time, it seems quite odd that a theory can so perfectly account for all of the Earthly low-relative-velocity experiences we have of time and yet suddenly become mistaken when it comes to things we have no experience with. These circumstances Prior says the theory is wrong about are those where we surely haven't had the exposure in order to form proper subjective intuitions of how time should be. The theory fully explains why all of Prior's experience would lead him to believe in absolute reference frames, while also explaining why this isn't actually the case in the wider context. Prior's response is no more than an ad hoc discussion that since the theory disagrees with him it must be wrong no matter how much supporting evidence and no matter how well the theory accounts for why he has the subjective intuitions living on a planet where relative velocities are similar for all people. By Prior's method of argument, time could very well be caused by billions of invisible and imperceptible three foot tall demons stirring things up to create change with their pitchforks -- two in each hand. Unfortunately there's no way to observe the demons since they "are systematically concealed from us", as he says the "true" space-time is, but we can rest assured that they're there. It seems more reasonable however, given no reason to expect subjective intuitions must hold objectively true and given an objective explanation for why the subjective intuition would exist, to conclude the presentists are the guilty party rather than Einstein's relativity theory.

Proponents of presentism accept change as a brute fact of the world -- a giant unexplained absolute which should simply be placed into our ontology and forgotten about. Their commitment to this absolute leaves them both unable and unwilling to explain what causes time... instead, they attempt to criticize the idea that time can have an explanation. If we can judge that their arguments against the block universe theory are ineffective, however, Occam's razor demands that we reject presentism in favor of the ontologically and metaphysically simpler theory. The model which accounts for the observed nature of time completely with less ontological commitment is via Occam the correct model to follow. If there's one lesson to learn from presentism, it's that subjective intuitions need not imply objective realities.



End Notes

1: Prior, A.N. "Some Free Thinking About Time".
2: Hinckfuss, Ian. "Topis, Soris, Noris". The Existence of Space and Time. Oxford: Oxford Universtity Press, 1975
3: Smart, J.J.C. "The Space-Time World." Philosophy and Scientific Realism. London: Routledge, 1963