Dual arrows of time: SMM/DTT and Eternalism and the block universe

01The question behind the comparison

An arrow of time is an asymmetry with a specified meaning. A causal arrow concerns permitted influence; a thermodynamic arrow concerns typical entropy change; a psychological arrow concerns memory and anticipation. SMM/DTT adds a proposed generative orientation: production is organized toward completion, after which a result can participate in later records. These orientations can support one another, but their agreement is an explanatory question. A growing archive by itself says nothing about the entropy of the entire universe, and a time-symmetric microscopic law can still support asymmetric records when supplied with asymmetric conditions.

The phrase dual arrows is most useful when it names the relation between inner completion and outer succession. The inner orientation is functional: unfinished and finished configurations have different roles. The outer orientation is historical: a retained result can constrain later access. They need not be opposite vectors drawn on a plane. Drawing two arrows can obscure the real issue if no criterion identifies what reverses when an arrow is reversed. For example, reversing a movie reverses the displayed order, whereas unmaking its records would also require reversing changes in the storage device and environment.

The six nested levels locate completion inside a structured process. Nesting can explain why some operations depend on earlier achievements, but nesting alone does not establish irreversible dynamics. A perfectly reversible circuit also contains dependencies. A physical arrow can arise when a subsystem loses access to correlations, when a boundary state selects one orientation, or when a genuine noninvertible law is posited. These alternatives have different implications for energy, probability conservation and the possibility of recovering a previous state. DTT becomes sharper when it chooses between them in a particular model.

02The single-source and nested-time proposal

SMM begins with one nonspatial generative source. DTT distinguishes its inner production from the outer order in which completed results become accessible. The six inner levels are nested functional dependencies within that production; the seventh denotes outer completion. They are not six independent clocks, six spatial directions, or six simultaneously occupied temporal axes. This distinction makes the framework more specific than a general claim that everything changes: it asks how a world of persistent relations can be generated before its spatial representation is taken for granted. ^[2]

03The comparator’s explanatory structure

Eternalism treats events at different times as equally real. A block representation displays a history as a spacetime whole. Relativistic geometry provides powerful reasons to be careful about a universal present, but it does not by itself prove every metaphysical claim associated with eternalism. An eternalist can describe local causal processes, change and the internal experience of time without supposing that objects are motionless within each event.

A complete trajectory is a relation among positions and clock readings. Representing all its points together does not eliminate the difference between walking and standing: the trajectories remain different. The relevant issue for DTT is whether generation adds a physically consequential relation that a complete history omits, or instead offers an explanation of how such a history is constituted. A block description can contain all the records an observer ever accesses. It need not contain an additional moving spotlight. This makes completion, rather than the mere presence of change, the sharp point of comparison. ^[1]

04The precise agreement and difference

Eternalism does not require a thermodynamically symmetric universe. A four-dimensional history can have low-entropy conditions toward one end and records pointing in the corresponding direction. DTT’s two arrows therefore do not refute a block description simply by explaining why observers remember one direction. What they can add is an account of why the record-producing structure has that orientation.

The sharper disagreement concerns whether the direction toward completion is fully represented among the block’s relations. If it is, DTT can be understood as a generative explanation of an asymmetric block. If it is not, the missing structure must be specified: for example, an ontological distinction between uncompleted possibilities and completed events. A physical test would still concern differences in accessible correlations, not the bare assertion that the block exists as a whole. This comparison makes room for a substantial DTT contribution while avoiding the familiar mistake of equating eternalism with absence of change, absence of causes or absence of an arrow of memory. ^[1]

05Worked example: what follows and what does not

Take a memory initially in a known state 0 and a fair bit X. A reversible copy maps (X,0) to (X,X). Before copying, the two devices are uncorrelated; afterwards they share one bit of mutual information. No information has been erased in this ideal operation. The record points toward the earlier value because of the initially blank memory and the chosen interaction. Restoring only the memory to 0 is a different operation, with a thermodynamic cost under the usual erasure assumptions. This simple distinction shows how a record arrow can depend on preparation without proving a fundamental violation of time-reversal symmetry. It also shows why a source-memory budget belongs inside any physical completion model.

06What this comparison contributes

The promising connection is a derivation of aligned orientations from a shared source law and admissible boundary conditions. An inner stage count would then acquire meaning through its relation to records and entropy production, not through the appearance of an arrow in a diagram. The conceptual gain is already useful: it prevents the familiar experience of passage, the ordering of causes and the irreversible loss of accessible information from being silently treated as the same phenomenon.

THE SAME QUESTION, DIFFERENT STARTING POINTS

The comparison at a glance

Continue on SMONAD

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