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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" (they all have the same ontological status), as opposed to the presentist idea that only the present is real. This would mean that future events are "already there", and that there is no objective flow of time. Modern advocates often take inspiration from the theory of relativity, with some such as Rietdijk and Putnam invoking relativity of simultaneity, which says that the question of whether two events occur at the same time is not absolute, but depends on the observer's reference frame. Some also take inspiration from the way that the mathematical formulation of relativity treats time as a single dimension in a four-dimensional spacetime. However, the philosophical proposal 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. Eternalism, defined as the view that there are no ontological differences between past, present and future, is also known as the "block universe" theory (the term "block time" is also used, with some authors treating it as interchangeable with "block universe", and some defining it specifically as the temporal dimension of the block universe) due to its description of space-time as an unchanging four-dimensional "block" (the name is inspired by the depiction of spacetime in the Minkowski diagrams used in special relativity),Cite error: A <ref> tag is missing the closing </ref> (see the help page).

The comment summarizes the main objections. 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 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.

Apparent differences between past, present and future

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

1. 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.
2. 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.
3. 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 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.

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.

Relation to 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.

Relation to Eastern body of thought

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. See: Śūnyatā, section "Eternalism"

In fiction

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."

See also

• Introduction to special relativity
• Eternity of the world

Footnotes and references

1. Kuipers, Theo A.F. (2007). General Philosophy of Science: Focal Issues. North Holland. p. 326. ISBN 978-0-444-51548-3.
2. Peterson, Daniel; Silberstein, Michael (2009), "Relativity of Simultaneity and Eternalism: In Defense of the Block Universe", in Petkov, Vesselin (ed.), Space, Time, and Spacetime: Physical and Philosophical Implications of Minkowski's Unification of Space and Time, p. 208
3. Dowden, Bradley (2001). "Time [Internet Encyclopedia of Philosophy]". Retrieved 25 July 2012. The third and more popular theory is that there are no significant ontological differences among present, past, and future because the differences are merely subjective. This view is called "the block universe theory" or "eternalism."
4. ^ Dowden, Bradley (2009). The Metaphysics of Time: A Dialogue. New Dialogues in Philosophy. Rowman & Littlefield. p. 149. ISBN 9780742560314. LCCN 2009021319. Block universe theory: Metaphysical theory that implies all of the past, present, and future is real. The name derives from the fact that a Minkowski diagram would represent events as points in a block if space and time were to be finite in all directions. Also called "eternalism."
5. Dieks, Dennis (2008). The Ontology of Spacetime II. p. 229. It is commonly held that relativity favors the "block universe" view (known also as "eternalism"), according to which all events enjoy the same ontological status regardless of their location
6. Rea, Michael (2009). Arguing About Metaphysics. p. 223. It does not help, either, that there is a tendency to conflate eternalism — the four-dimensional "block universe" view — with causal determinism.
7. Carroll, S.M. (2010). From Eternity to Here: The Quest for the Ultimate Theory of Time. Dutton. p. 39. ISBN 9780525951339. LCCN 2009023828. In the philosophic literature, this is sometimes called the "block time" or "block universe" perspective, thinking of all space and time as a single existing block of spacetime. For our present purposes, the important point is that we can think about time in this way. Rather than carrying a picture in the back of our minds in which times is a substance that flows around us or through which we move, we can think of an ordered sequence of correlated events, together constituting the entire universe. Time is then something we reconstruct from the correlations in these events.
8. Mooij, J.J.A. (2005). Time and Mind: The History of a Philosophical Problem. Brill Academic Pub. p. 224. ISBN 9789004141520. This four-dimensional manifold was assigned the name 'block universe'. Its temporal dimension, block time, was the objective counterpart of the ongoing and passing time that people experience internally.
9. "Block" here refers to the idea of spacetime as something fixed and unchanging, like a solid block, and not to the actual geometric shape of space or spacetime.
10. "Platonia", Julian Barbour's time-skeptical website
11. Ellis (2006). "Physics in the Real Universe: Time and Spacetime". Gen.Rel.Grav. 38 (12): 1797–1824. arXiv:gr-qc/0605049. doi:10.1007/s10714-006-0332-z.

External links

• Biswas; Shaw; Modak (1999). "Time in Quantum Gravity". Int.J.Mod.Phys. D. 10 (4): 595. arXiv:gr-qc/9906010. doi:10.1142/S0218271801001384.
• Davies, Paul (2002). "That Mysterious Flow". Scientific American. 287 (3): 40–45. doi:10.1038/scientificamerican0902-40. {{cite journal}}: Unknown parameter |month= ignored (help)
• Dorato,Mauro - Kant, Godel and Relativity
• Markosian, Ned (2002). "Time: 8. The 3D/4D Controversy". Stanford Encyclopedia of Philosophy. Retrieved 2006-12-20.
• Nikolic, Hrvoje. "Block time: Why many physicists still don't accept it?" (PDF).
• Petkov, Vesselin (2005). "Is There an Alternative to the Block Universe View?" (PDF). PhilSci Archive. Retrieved 2006-12-20.
• Duda, J (2009). "Four-dimensional understanding of quantum mechanics". arXiv:0910.2724/. {{cite arXiv}}: Check |arxiv= value (help)

• Time
• Philosophy of time
• Metaphysical theories