Eternalism vs. Presentism

There are three main ways to think about what exists in time. Presentism says only the present exists. The growing block says the past and present exist, but the future does not. Eternalism says past, present and future all exist.

Presentism matches ordinary intuition. When you mourn a past event, it feels as if it is gone. When you wait for a future event, it feels as if it has not yet arrived. Eternalism asks us to treat those feelings as a perspective from inside time rather than as a guide to what exists.

The growing block theory is an attempt to keep the past real while preserving a privileged present. It inherits the intuitive cost of presentism — what is so special about the edge of the block? — and the metaphysical cost of eternalism — it admits that the future is no less determinate than the past, it simply denies it exists.

The strongest pressure on presentism comes from special relativity. In relativity, whether two distant events happen at the same time depends on how the observer is moving. Two observers passing each other disagree about what is happening 'now' on a distant planet.

If only present things exist, and the two observers disagree about which distant things are present, then they disagree about what exists. But they are standing in the same place, looking at the same world. The only difference is their velocity. Existence should not depend on how fast you are walking.

The Rietdijk–Putnam argument makes this precise. It says that if simultaneity is relative and existence is tied to simultaneity, then existence is relative. The natural way to avoid this is to deny that a single present slice is the fundamental unit of reality. Take the whole block instead.

Eternalism does not deny that time feels like it flows. It denies that the flow is a feature of the universe as a whole. Inside the block, each moment contains records of earlier moments and no records of later moments. This asymmetry is enough to produce the experience of passage.

The direction of that passage is explained by entropy, causation, and memory, not by a metaphysical spotlight moving from past to future. The block is static, but minds embedded in the block are not. They accumulate experience in one direction because that is the direction in which information flows.

Some philosophers find this unsatisfying. They want the present to be objectively real in a way that the past and future are not. Eternalism replies that this desire is a residue of the way we are located, not evidence of the way things are.

Presentism has the burden of reconciling its privileged present with the relativity of simultaneity. It can try to define a preferred frame of reference, but it has to do so without contradicting the physics. The task is not impossible, but it is hard enough that many philosophers of physics regard it as a costly repair.

Eternalism has the burden of making sense of our experience of passage. It has to explain why the block feels like a river from the inside. The usual answer is that it feels that way because the block is full of locally time-asymmetric processes: memory, entropy, causation, perception.

Worldline Identity Theory is not a physics argument. It is a metaphysical account of what a person is, given eternalism. If the block view is correct, then you are a four-dimensional object, and the question of what makes you the same person over time becomes a question about the structure of that object.