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Eternalism is a philosophical approach to the ontological nature of time, which takes the view that all points in time are equally "real", as opposed to the presentist idea that only the present is real. Modern advocates often take inspiration from the way time is modeled as a dimension in the theory of relativity, giving time a similar ontology to that of space (although the basic idea dates back at least to McTaggart's B-Theory of time, first published in The Unreality of Time in 1908, only three years after the first paper on relativity). 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 view of the world as a three-dimensional space modulated by the passage 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.
Within this intuitive understanding of time is the philosophy of presentism, which argues that only the present exists. It does not travel forward through an environment of time, moving from a real point in the past and toward a real point in the future. Instead, the present simply changes. The past and future do not exist and are only concepts used to describe the real, isolated, and changing present.
This conventional model presents a number of difficult philosophical problems, and seems difficult to reconcile with currently accepted scientific theories such as the theory of relativity.
Special relativity suggests that the concept of simultaneity is not universal: according to the relativity of simultaneity, observers in different frames of reference can have different perceptions of whether a given pair of events happened at the same time or at different times, with there being no physical basis for preferring one frame's judgments over another's (though in a case where one event A happens in the past light cone of another event B, all frames will agree that A happened in the past of B). So, in special relativity there can be no physical basis for picking out a unique set of events that are all happening simultaneously in "the present".
Many philosophers have argued that relativity implies eternalism. Although he disagrees in a qualified sense, philosopher of science, Dean Rickles, notes that "the consensus among philosophers seems to be that special and general relativity are incompatible with presentism." For example, Christian Wüthrich writes:
Presentists have responded in a variety of ways to the pressure exerted by the Rietdijk-Putnam argument... [A] presentist could deny Naturalism. Such denial could take different forms. One could, as does Jonathan Lowe, claim that SR is not a theory about time but about something else instead. Alternatively, one could retort by accepting that SR speaks to the geometry of space-time but reject that this has any ontological import, as does Dean Zimmerman (2008). Second, a presentist might reject SR-Realism, simply asserting that SR is not approximately true of the world. This could occur simply on a priori grounds... Also, considerations from quantum mechanics can be invoked in an attempt to establish that SR is false or incomplete insofar as it lacks an absolute, privileged frame of reference. This response comes in different flavours: (a) (non-relativistic) collapse dynamics require a preferred frame in which the collapse occurs; (b) Bohmian interpretations are incompatible with SR; and (c) invoke Bell's theorem to argue that some tenets of SR must be given up...
[A] presentist might simply bite the bullet and consequently relativize existence... since what is present is relative to an inertial frame, what exists becomes fragmented in that it depends on the choice of frame...[Another] is to accept that SR offers a perfectly empirically adequate theory, but to insist that absolute simultaneity still exists. It is just that we cannot possibly detect the privileged frame of reference which determines the present. In other words, absolute simultaneity is not empirically accessible... [The] metaphysics fully relies on postulated extra-structure that can't even in principle be observed... It violates Ockham's razor so crassly that the move cannot be justified by putting some post-verificationist philosophy of science on one's flag.—Christian Wüthrich, "No Presentism in Quantum Gravity" in Space, Time, and Spacetime: Physical and Philosophical Implications of Minkowski's Unification of Space and Time
However, there are some, such as Dean Zimmerman, who have argued that it is possible to accept the physical predictions of relativity while adopting an alternative interpretation of the theory (For instance, see Lorentz ether theory) in which there is a single privileged frame whose judgments about length, time and simultaneity are the "true" ones, even though there would be absolutely no empirical way to distinguish this frame from other frames, and no real experience could identify it.
[When] appealing to findings from empirically well-grounded disciplines, philosophers face a strong temptation to overstate their case — especially if their philosophical opponents can be relied on to be relatively innocent of new developments in the relevant science. I fear that some B-theorists have succumbed to the temptation, judging by the relish with which they often pronounce a verdict based on Relativity. They can practically hear the crunch of the lowly metaphysician’s armor giving way, as they bring the full force of incontrovertible physical fact down upon our A-theoretically-addled heads. But what actually hits us, and how hard is the blow? SR is false; GR’s future is highly uncertain; and the presentist’s conflict with either version of Relativity is shallow, since the presentist’s manifold can satisfy the same geometrical description as a B-theorist’s manifold, and afford explanations of all the same phenomena in precisely the same style. In these circumstances, how could appeal to SR or GR justify the frequent announcements that the A-theory–B-theory dispute has been “settled by physics, not philosophy”?—Dean Zimmerman, "Presentism and the Space-Time Manifold" in The Oxford Handbook of Time
While the present is intuitively understood as the object that moves through the environment of time, it is common to also describe time as an object that moves, in the same way that a passenger on a train perceives the environment passing by. This perception of the passage or flow of time can can be confused with the previous idea of the present moving through time, leading to the misunderstanding that time is moving through time, i.e., that it is moving through itself. This illogical premise can lead to circular questions asking how fast time travels per unit of time:
The concept of "time passing" can be considered to be internally inconsistent, by asking "how much time goes by in an hour?" The question "how fast does time pass" seems to have no satisfactory answer, in which answers such as "a second per second" would be, as some would argue, circular and thus false. In addition, even if we do accept the above answer, then the statement "a second per second" can be expressed as a fraction which is always equal to "one". But this "one" has no meaning beyond being a number and is thus also the wrong kind of answer. Therefore, the argument goes, the rate of the passage of time is nonsensical.
There is a major problem though in that the question of time is no different from space. One can similarly ask, "how much space is contained in a meter?" — and face a similar objection.
"Time passing" may be seen as a metaphor for the continuous human experience of some expected future events becoming directly experienced qualia, while experienced qualia becoming just objects of memory.
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 also added the notion of a "C-series", a series that has an order but with no notion of time, like a series of letters. He went on to argue that the A-series was needed for anything deserving the name "time", since he argued that only the A-series can allow for genuine change, and he considered change to be an essential part of any reasonable definition of time. But, he argued, the A-series was logically incoherent, so he concluded that time was unreal, and since he also believed the B-series depended on the A-series, he also concluded that only the C-series could remain as a meaningful ordering. However, various philosophers (sometimes identified as "B theorists") have held that the remaining B-series qualifies as a valid framework for a theory of time, sometimes called the B-Theory of time.
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 directions rather than states 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 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 changes are possible may be indistinguishable from the fully deterministic many-worlds interpretation of quantum mechanics, in which there are multiple "growing block universes".
Philosophers such as John 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 objections. In more detail, they are:
Whilst the idea that there is some objective sense in which time is flowing can be denied, the fact that conscious beings feel as though it is in some sense flowing cannot. However, if the flow of time didn't have an objective existence, then it is argued conscious beings would simultaneously experience all moments in their lives. A response is that since the brain presumably perceives time through information processing of external stimuli, not by extrasensory perception, and obeys the laws of causality, it is hard to see how the flow of time, whether it exists or not, could make any subjective difference: all conscious beings are built to perceive time as a chain of events, whether or not it occurs as such.
Many of our common-sense attitudes treat the past, present and future preferentially.
Eternalists often appeal to the idea that the flow of time is a subjective illusion. 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. But there is no need to do so to explain the subjective flow of time. Their opponents 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.
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? Regarding John G. Cramer’s transactional interpretation, Kastner (2010) "proposed that in order to preserve the elegance and economy of the interpretation, it may be necessary to consider oﬀer and conﬁrmation waves as propagating in a “higher space” of possibilities.
The main topic of our conversation was indeterminism. I tried to persuade him to give up his determinism, which amounted to the view that the world was a four-dimensional Parmenidean block universe in which change was a human illusion, or very nearly so. (He agreed that this had been his view, and while discussing it I called him "Parmenides".) I argued that if men, or other organisms, could experience change and genuine succession in time, then this was real. It could not be explained away by a theory of the successive rising into our consciousness of time slices which in some sense coexist; for this kind of "rising into consciousness" would have precisely the same character as that succession of changes which the theory tries to explain away. I also brought in the somewhat obvious biological arguments: that the evolution of life, and the way organisms behave, especially higher animals, cannot really be understood on the basis of any theory which interprets time as if it were something like another (anisotropic) space coordinate. After all, we do not experience space coordinates. And this is because they are simply nonexistent: we must beware of hypostatizing them; they are constructions which are almost wholly arbitrary. Why should we then experience the time coordinate—to be sure, the one appropriate to our inertial system—not only as real but also as absolute, that is, as unalterable and independent of anything we can do (except changing our state of motion)?
The reality of time and change seemed to me the crux of realism. (I still so regard it, and it has been so regarded by some idealistic opponents of realism, such as Schrödinger and Gödel.)
When I visited Einstein, Schilpp's Einstein volume in The Library of Living Philosophers had just been published; this volume contained a now famous contribution of Gödel's which employed, against the reality of time and change, arguments from Einstein's two relativity theories. Einstein had come out in that volume strongly in favour of realism. And he clearly disagreed with Gödel's idealism: he suggested in his reply that Gödel's solutions of the cosmological equations might have "to be excluded on physical grounds".Now I tried to present to Einstein-Parmenides as strongly as I could my conviction that a clear stand must be made against any idealistic view of time. And I also tried to show that, though the idealistic view was compatible with both determinism and indeterminism, a clear stand should be made in favour of an "open" universe—one in which the future was in no sense contained in the past or the present, even though they do impose severe restrictions on it. I argued that we should not be swayed by our theories to give up realism (for which the strongest arguments were based on common sense), though I think that he was ready to admit, as I was, that we might be forced one day to give it up if very powerful arguments (of Gödel's type, say) were to be brought against it. I therefore argued that with regard to time, and also to indeterminism (that is, the incompleteness of physics), the situation was precisely similar to the situation with regard to realism. Appealing to his own way of expressing things in theological terms, I said: if God had wanted to put everything into the world from the beginning, He would have created a universe without change, without organisms and evolution, and without man and man's experience of change. But He seems to have thought that a live universe with events unexpected even by Himself would be more interesting than a dead one.—Karl Popper, Unended Quest: An Intellectual Autobiography
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.
Augustine of Hippo wrote that God is outside of time—that time exists only within the created universe. Thomas Aquinas took the same view, and many theologians agree. On this view, God would perceive something like a block universe, while time might appear differently to the finite beings contained within it.
The philosopher Katherin A. Rogers argued that Anselm of Canterbury took an eternalist view of time, although the philosopher Brian Leftow argued against this interpretation, suggesting that Anselm instead advocated for a type of presentism. Rogers responded to this paper, defending her original interpretation. Rogers also discusses this issue in her book "Anselm on Freedom", using the term "four-dimensionalism" rather than "eternalism" for the view that "the present moment is not ontologically privileged", and commenting that "Boethius and Augustine do sometimes sound rather four-dimensionalist, but Anselm is apparently the first consistently and explicitly to embrace the position." Taneli Kukkonen argues in the Oxford Handbook of Medieval Philosophy that "what Augustine's and Anselm's mix of eternalist and presentist, tenseless and tensed language tells is that medieval philosophers saw no need to choose sides" in the manner that modern philosophers do.
In Buddhism, a special term Dharmadhatu is translated as 'total field of events and meanings' or 'field of all events and meanings.' Here the 'Block Universe' seems to be encompassing not only every possible event in the physical universe but also having a psychological component.
Dirck Vorenkamp, a professor of religious studies, argued in his paper "B-Series Temporal Order in Dogen's Theory of Time" that the Zen Buddhist teacher Dōgen presented views on time that contained all the main elements of McTaggart's B-series view of time (which denies any objective present), although he noted that some of Dōgen reasoning also contained A-Series notions, which Vorenkamp argued may indicate some inconsistency in Dōgen's thinking.
Eternalism is a major theme in Kurt Vonnegut’s novel, Slaughterhouse-Five. The Tralfamadorians, an alien species in the novel, have a four-dimensional sight and can therefore see all points in time simultaneously. They explain that since all moments exist simultaneously, everyone is always alive. The hero, Billy Pilgrim, lives his life out of sequence, which, among other things, means that his point of death occurs at a random point in his life rather than at the end of it.
Eternalism also appears in the comic book series Watchmen by Alan Moore. In one chapter, Dr. Manhattan explains how he perceives time. Since past, present, and future events all occur at the "same time" for him, he speaks about them all in the present tense. For example, he says "Forty years ago, cogs rain on Brooklyn" referring to an event in his youth when his father throws old watch parts out a window. His last line of the series is "Nothing ends, Adrian. Nothing ever ends."
In his science fantasy novel The Number of the Beast, Robert Heinlein has one of the novel's protagonists, the mathematician and "geometer" Dr. Jacob Burroughs invent a device which can navigate through time as one scalar dimension in a six-dimensional universe. The novel carries its main characters through time as well as countless alternate universes, some of which are fictional worlds, accessible by quantum-wise progression through one of the six axes of the universe Burroughs' invention can access. In this novel, there is not only block time, but a block plenum of many alternate universes, each a quantum step along an axis of space-time.