For and Against Eternalism

In our study of time, we compare four leading theories: Presentism, Eternalism, Growing Block Theory, and Branching Tree Theory. We aim to show in a future post that a metaphysics of time anchored in the work of Thomas Aquinas is superior. Here’s how Eternalism stacks up.

In Favor of Eternalism. Eternalists, such as Ted Sider[1] argue that all moments in time are equally real, forming a 4-dimensional “block” universe where events are fixed. Objects, such as galaxies or people, persist (or perdure) as “worldlines”—paths tracing their existence through spacetime, like worms extending through the block.[2]  A person is the sum of their temporal parts, like snapshots in a film. Time coordinates record events, which are determined and unchanging, with no preferred direction or flow. This aligns with special relativity’s tenseless spacetime and the universe’s expansion from a low-entropy Big Bang, marked by the Cosmic Microwave Background (CMB), detectable as a universal time reference 380,000 years after the Big Bang.[3]

Against Eternalism. E.J. Lowe[4] rejects perdurantism. He argues that objects are not temporal parts but enduring substances with changing attributes or modes, challenging the static block model. 19^th-century psychologist, Henri Bergson[5] rejects the determinist view as inconsistent with the experience of time. His work pre-dates McTaggart. He admits two views of time, one associated with timelines and instrumentation, and the other associated with human consciousness. We perceive time as a flow or duration (durée), not as an instant, and therefore operate within time, enabling free will. Although it is possible, Bergson claims, to accurately predict the mechanistic motion of planets, it is not possible to infallibly predict the actions of voluntary agents. A timeline applies to past action, but the future is open to possibilities. This is because our consciousness endures. “I change because, I endure.” Consciousness is not a collection or association of feelings or states, but a seamless whole that experiences the flow of time. Conscious agents willfully act in time’s flow. They are not pulled along with its current into a predetermined future.

Counterarguments. Bergson contrasts the predictability of celestial mechanics with the  voluntary choices of human agents. But unlike the Laplacian orrery Newtonian mechanics expects, planetary motion comprises a dynamical system whose motion is chaotic. Short term predictions, like the time of the next eclipse, are possible, but small perturbations in initial estimates can dramatically effect predictions over millions of years. Bergson’s work also predates the development of quantum mechanics and its associated indeterminacy.

To Bergson’s point on willful action, Bertolero and Basset argue that: “one’s present brain, and so one’s mental state, can be thought of as a compilation of past states that can be used to predict the future. A neuroscientist who knew all the principles of brain function and everything about someone’s brain could predict that person’s mental conditions—the future, as well as the past, would be present inside the person’s mind.”[6]

Counter-counterarguments. Independent counterarguments to the components of Bergson’s theory conflict with each other. How can relatively simple planetary motion be unpredictable, and complex brain states be fully predictable? On the one hand, Laskar et al. note that despite chaotic variation of inner-planet motion over million-year timescales, integrated statistical analysis reveals remarkable stability over billion-year timescales that constrains chaotic dynamics.[7] On the other hand, many neuroscientists argue that the mind is not the brain.[8] If it were, then truth claims from abstract reasoning would be the untrustworthy result of chemical reactions.[9] Furthermore, if quantum mechanics applies at a neuronal level, then its characteristic indeterminacy may affect the decision-making process.[10]

Summing it up. Eternalism aligns well with the geometry of spacetime, but the static block theory lacks many answers, including the beginning and end of time, the irreversibility of time, human consciousness, and free will. Time’s beginning and structured geometry (spacetime) points to a cause for this ordered beginning and also implies a purpose and end associated with this causation. Einstein’s theory of relativity is reversible with respect to time, as is the Standard Model of quantum mechanics, yet cosmologists know that the universe had a highly-ordered beginning (low entropy) and is expanding (entropy is increasing). Finally, geometric descriptions do not explain how human agents experience or interact with time. A comprehensive philosophy of time based on Thomas Aquinas aims to address all these topics.

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