The laws of physics are mostly time-symmetric. Yet time clearly points one way. Films of billiard balls colliding run plausibly forwards and backwards. Films of glasses shattering run only plausibly forwards. The standard explanation - entropy increases in the forward direction - is correct but incomplete. Why was entropy low in the past?
BFUT Paper 22 identifies a substrate-level mechanism for irreversibility that complements thermodynamic entropy.
Outward Propagation Is Irreversible
Every physical interaction involves a substrate coupling event - a local reorganisation of the Spaticle field that propagates outward from the interaction site at speed c. This propagation is physically irreversible: once a substrate reorganisation has propagated outward beyond the interaction site, it cannot be recalled without sending a signal back - which requires further propagation in the same forward direction.
The past is the region of the substrate already written by prior propagation events. The future is the region still being written. This is not a statistical statement about entropy - it is a physical statement about the one-way propagation of causal substrate reorganisations.
The Arrow of Time
In BFUT, the arrow of time is the direction of outward substrate propagation from interaction events. The future is the direction in which substrate reorganisations propagate. The distinction between past and future is not purely statistical - the past is physically fixed by prior propagation events whose effects have already spread through the substrate. The future is physically open - not yet determined by substrate propagation.
Relationship to Thermodynamics
Thermodynamic irreversibility (entropy increase) and substrate propagation irreversibility are not independent. The accumulation of propagated substrate modifications produces increasing structural disorder in the substrate state - which is what thermodynamics measures as entropy. The thermodynamic arrow and the substrate propagation arrow point in the same direction because one is the macroscopic statistical description of the other. The substrate propagation picture provides the physical mechanism that thermodynamics describes statistically.
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