Strong CP Non-Solving

The strong CP problem is the observation that quantum chromodynamics permits a CP-violating term in the Lagrangian — the theta term proportional to the topological charge density F̃F — yet the experimentally measured electric dipole moment of the neutron constrains theta to be less than 10⁻¹⁰, an extraordinarily small value with no explanation within the Standard Model. The Peccei-Quinn mechanism postulates a new global U(1) symmetry whose spontaneous breaking produces the axion — a pseudoscalar particle that dynamically relaxes theta to zero — but no axion has been detected despite extensive searches. The strong CP problem therefore represents a fine-tuning puzzle: why is theta so small if there is no symmetry reason for it to vanish? ΛCDM cosmology does not address this question at all, leaving it as an unresolved fine-tuning in the fundamental theory.

Successive Collision Theory does not introduce new particles or fields to address the strong CP problem, but it does change the cosmological context in which the problem must be evaluated. In SCT, our observable universe is embedded within eternal infinite spacetime where infinitely many prior collision events have occurred. The effective theta parameter experienced in any given collision debris patch is not a freely tunable initial condition set at a single moment of creation but is inherited from the pre-existing matter in the two colliding pockets. Those pockets themselves emerged from prior collision events, and their theta values were set by the same inheritance chain extending arbitrarily far back through the eternal collision history. If the QCD vacuum structure relaxes theta toward small values over the timescales between successive collision events — as the topological susceptibility of the QCD vacuum permits through thermal fluctuations and vacuum tunneling in the high-temperature plasma between collisions — then the pre-existing pockets would naturally arrive with small theta values, which are then inherited by the debris field of each subsequent collision.

This SCT perspective reframes the strong CP problem from a fine-tuning question into an evolutionary question: given eternal infinite spacetime with repeated collision cycles, is theta naturally driven toward small values over cosmological timescales in the high-temperature environments between collision epochs? The QCD phase transition and the behavior of topological charge in hot dense matter suggest that theta does relax in high-temperature QCD plasmas, and the eternal universe provides unlimited time for this relaxation to operate between collision cycles. SCT therefore predicts that small theta is the natural attractor state of the eternal universe's QCD vacuum, inherited sequentially through collision generations rather than requiring a dynamical axion mechanism within any single universe patch. This is a conceptually distinct resolution that emerges solely from the eternal-universe framework without introducing new particles.