What is time? Don't ask me, and I know. Ask me, and I don't know. (St. Augustine) This post sketches, without defending, one theory of time.
On the B-Theory of time, real or objective time is exhausted by what J. M. E. McTaggart called the B-series, the series of times, events, and individuals ordered by the B-relations (earlier than, later than, simultaneous with). If the B-theory is correct, then our ordinary sense that events approach us from the future, arrive at the present, and then recede into the past is at best a mind-dependent phenomenon, at worst an illusuion. Either way, not something that really occurs. For on the B-theory, there are no such irreducible monadic A-properties as futurity, presentness and pastness. There is just a manifold of tenselessly existing events ordered by the B-relations. Time does not pass or flow, let alone fly. There is no temporal becoming. My birth is not sinking into the past, becoming ever more past, nor is my death approaching from the future, getting closer and closer. Tempus fugit does not express a truth about reality. At best, it picks out a truth about our experience of reality.
The B-theorist does not deny that there is time. He does not hold that time is an illusion or mere appearance. What he denies is that the sense we all have that time passes or flows is an ingredient in real time. His claim is that real or objective time is exhausted by the B-series and that temporal becoming is at best subjective.
If there is no temporal becoming in reality, then change is not a becoming different or a passing away or a coming into being. When a tomato ripens, it does not become ripe: it simply is unripe at certain times and is ripe at certain later times. And when it ceases to exist, it doesn't pass away: it simply is at certain times and is not at certain later times.
You could say that that the B-theorist has a static view of time that strips way its 'dynamism.'
Employing a political metaphor, one could say that a B-theorist is an egalitarian about times and the events at times: they are all equal in point of reality. Accordingly, my blogging now is no more real (but also no less real) than Socrates' drinking the hemlock millenia ago. Nor is it more real than my death which, needless to say, lies in the future. (But this future event is not approaching or getting closer.) Each time is present at itself, but no time is present, period. And each time (and the events at it) exists relative to itself, but no time exists absolutely.
This is to say that the present moment enjoys no privilege. There is nothing special about it. So you can't say that the present alone exists.
This is not to say that the B-theorist does not have uses for 'past,' 'present,' and 'future.' He can speak with the vulgar while thinking with the learned. Thus a B-theorist can hold that an utterance at time t of 'E is past' expresses the fact that E is earlier than t. An old objection is that this does not capture the meaning of 'E is past.' For the fact that E is earlier than t, if true, is always true; while 'E is past' is true only after E. This difference in truth conditions shows a difference in meaning. The B-theorist can respond by saying that his concern is not with semantics but with ontology. His concern is with the reality, or rather the lack of reality, of tense, and not with the meanings of tensed sentences or sentences featuring A-expressions. The B-theorist can say that, regardless of meaning, what makes it true that E is past at t is that E is earlier than t, and that, in mind-independent reality, nothing else is needed to make 'E is past' uttered at t true.
Compare 'BV is hungry' and 'I am hungry' said by BV. The one is true if and only if the other is. But the two sentences differ in meaning. The first, if true, is true no matter who says it; but the second is true only if asserted by someone who is hungry. Despite the difference in meaning, what makes it true that I am hungry (assertively uttered by BV) is that BV is hungry. In sum, the B-theorist need not be committed to the insupportable contention that A-statements are translatable salva significatione into B-statements.
The B-theorist, then, denies that the present moment enjoys any temporal or existential privilege. Every time is temporally present to itself such that no time is temporally present simpliciter. This temporal egalitarianism entails a decoupling of existence and temporal presentness. There just is no irreducible monadic property of temporal presentness; hence existence cannot be identified with it. To exist is to exist tenselessly. The B-theory excludes presentism according to which there is a genuine, irreducible, property of temporal presentness and existence is either identical or logically equivalent to this property. Presentism implies that only the temporally present is real or existent. If to exist is to exist now, then the past and future do not exist, not just now (which is trivial) but at all.
Please note that the B-theory is incompatible not only with presentism, but with any theory that is committed to irreducible A-properties. Thus the B-theory rules out 'pastism,' the crazy theory that only the past exists and 'futurism,' the crazy view that only the future exists. It also rules out the sane view that only the past and the present exist.
Why be a B-theorist? McTaggart has a famous argument according to which the monadic A-properties lead to contradiction. We should examine that argument in a separate post. The argument is endorsed by Hugh Mellor in his Real Time.
Another consideration is that the physics of Einstein & Co, has no need of temporal becoming. So if physics gets at the world as it is in itself apart from our subjective additions, then real time is exhausted by the B-series.