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Eternalism (philosophy of time)

Eternalism is a philosophical approach to the ontological nature of time. It builds on the standard method of modeling time as a dimension in physics, to give time a similar ontology to that of space. This would mean that time is just another dimension, that future events are "already there", and that there is no objective flow of time. It is sometimes referred to as the "Block Time" or "Block Universe" theory due to its description of space-time as an unchanging four-dimensional "block", as opposed to the common-sense view of the world as a three-dimensional space modulated by the passage of time.

Issues with the flow of time

Conventionally, time is divided into three distinct regions; the "past", the "present", and the "future". Using that representational model, the past is generally seen as being immutably fixed, and the future as undefined and nebulous. As time passes, the moment that was once the present becomes part of the past; and part of the future, in turn, becomes the new present. In this way time is said to pass, with a distinct present moment "moving" forward into the future and leaving the past behind.

This conventional model presents a number of difficult philosophical problems, and is difficult to reconcile with currently accepted scientific theories such as the theory of relativity.

Simultaneity

Special relativity has shown that the concept of simultaneity is not universal: observers in different frames of reference will have different perceptions of which events are in the future and which are in the past -- there is no way to definitively identify a particular point in universal time as "the present". However, each observer could have an individual flow of time, rather than there being a universal present moment.

Uniqueness of the present

There is no fundamental reason why a particular "present" should be more valid than any other; observers at any point in time will always consider themselves to be in the present. However, every moment of time has a "turn" at being the present moment in flow-of-time theories, so the situation ends up symmetrical.

Rate of flow

The concept of "time passing" can be considered to be internally inconsistent, by asking "how fast does time pass?" However, the question could be no different from "how long is a meter?" — all measurements being equally arbitrary. There is a sense in which relativity allows time to flow at different rates, but it refers to measurements made by one of observer of clocks in a different reference frame. Each observer measures their own clock to be running at the same rate.

McTaggart's argument

In The Unreality of Time, J. M. E. McTaggart divided time into an A-series and a B-series, with the A-series describing events in absolute tensed terms (past, present, and future) and the B-series describing events in terms of untensed temporal relations (before and after). He went on to argue that the A-series was logically incoherent and should be discarded, and that the B-series was insufficient for a proper understanding of time. But while McTaggart's conclusion was that time was therefore unreal, various philosophers and physicists have held that the remaining B-series is all that is needed for a complete theory of time, sometimes referred to as the B-Theory of time.

The Eternalist alternative

Eternalism addresses these various difficulties by considering all points in time to be equally valid frames of reference—or equally "real", if one prefers. It does not do away with the concept of past and future, but instead considers them as directions rather than as a state of being; whether some point in time is in the future or past is entirely dependent on which frame of reference you are using as a basis for observing it.

Since an observer at any given point in time can only remember events that are in the past relative to him, and not events that are in the future relative to him, the subjective illusion of the passage of time is maintained. The asymmetry of remembering past events but not future ones, as well as other irreversible events that progress in only one temporal direction (such as the increase in entropy) gives rise to the arrow of time. In the view suggested by Eternalism, there is no passage of time; the ticking of a clock measures durations between events much as the marks on a measuring tape measures distances between places.

Eternalism has implications for the concept of free will, in that it proposes that future events are as immutably fixed and impossible to change as past events (see determinism).

Eternalism makes two assumptions, which are separable. One is that time is a full-fledged real dimension. The other is immutability. The latter is not a necessary consequence of the first. A universe in which random changes are possible may be indistinguishable from the many-worlds interpretation of quantum mechanics in which there are multiple "block times."

Augustine of Hippo wrote that God is outside of time—that time exists only within the created universe. Many theologians (especially Catholics) agree. On this view, God would perceive something like a block universe, while time might appear differently to us finite beings.

Philosophical objections

Philosophers such as Lucas argue that "The Block universe gives a deeply inadequate view of time. It fails to account for the passage of time, the pre-eminence of the present, the directedness of time and the difference between the future and the past

The comment summarizes the main problem areas. In more detail, they are:

Subjective sense of flow

Whilst the idea that there is some objective sense in which time is flowing can be denied, the fact that humans feel as though it is in some sense flowing cannot be. However, if the flow of time didn't have an objective existence, then we'd simultaneously experience all moments in our lives.

Apparent differences between past, present and future

Many of our common-sense attitudes treat the past, present and future differently.

We apparently fear death because we believe that we will no longer exist after we die. But if Eternalism is correct, death is just one of our temporal borders, and should be no more worrisome than birth.
You are about to go to the dentist, or you have already been. Commonsense says you should prefer to have been. But if Eternalism is correct, it shouldn't matter which situation you're in.
When some unpleasant experience is behind us, we feel glad that it is over. But if the Eternalism is correct, there is no such property as being over or no longer happening now—it continues to exist timelessly.

Status of conscious observers

Eternalists often appeal to the idea that the flow of time (and other features inconvenient for the theory) are subjective illusions. However, Eternalism takes its inspiration from physics and needs to give a physical account of observers. One could, for instance, portray conscious observers as moving through the block universe, in some physically inexplicable way, in order to account for the subjective sense of a flow of time. However, their opponents could equally claim that the time-flow itself, as an objective phenomenon, is physically inexplicable, and that physics is simply misrepresenting time in treating it as a dimension.

Determinism and indeterminism

Previously, it was noted that people tend to have very different attitudes towards the past and the future. This might be explained by an underlying attitude that the future is not fixed, but can be changed, and is therefore worth worrying about. If that is correct, the flow of time is perhaps less important to our intuitions than an open, undetermined, future. In other words, a flow-of-time theory with a strictly determined future (which nonetheless does not exist at the present) would not satisfy common-sense intuitions about time. If indeterminism can be removed from flow-of-time theories, can it be added to Eternalist theories? Surprisingly, the answer is a qualified "yes" in the form of multiverse theories, where multiple alternate futures exist in a fixed framework, but individual observers have no way of knowing which alternative, or "branch" they will end up in.

Objections from physics

Eternalism takes its inspiration from physics, especially the Rietdijk-Putnam argument, in which the relativity of simultaneity is used to show that each point in the universe can have a different set of events that are in its present moment. According to Presentism this is impossible because there is only one present moment that is instantaneous and encompasses the entire universe.

Some philosophers also appeal to a specific theory which is "timeless" in a more radical sense than the rest of physics, the theory of quantum gravity. This theory is used, for instance, in Julian Barbour's theory of timelessness. On the other hand, George Ellis argues that time is absent in cosmological theories because of the details they leave out.

Footnotes and references

External links

Biswas, Shaw, Modak - Time in Quantum Gravity
Davies, Paul (2002). "That Mysterious Flow". Scientific American 287 (3): 40–45.
Dorato,Mauro - Kant, Godel and Relativity
Markosian, Ned Time: 8. The 3D/4D Controversy. Stanford Encyclopedia of Philosophy. (2002). Retrieved on 2006-12-20..
Petkov, Vesselin Is There an Alternative to the Block Universe View?. PhilSci Archive. (2005). Retrieved on 2006-12-20..
http://www.timephysics.com [What is time? What is cause of time?]