Phantom-Divide Crossing Test for the Spin Fluid: Where the Effective Equation of State Would Cross Minus One

An effective dark-energy equation of state crosses the phantom divide when a negative contribution grows to rival the positive constant term. Adding the negative, steeply scaling spin correction to a cosmological constant produces exactly that structure, so the crossing redshift is a well-defined calculation in this frame. Normalised at the bounce, the crossing occurs at a redshift of order ten to the fourteenth power, deep in the pre-nucleosynthesis universe and far outside any observable window. Within the entire range probed by supernovae, baryon acoustic oscillations, and the microwave background, the effective equation of state departs from minus one by less than one part in ten to the eightieth. Reports of phantom crossing at low redshift, if sustained, would therefore falsify this combination rather than confirm it. Headline values are: z cross = 1.410e+14, log10 z cross = 1.415e+01, deviation at z1 = 1.630e-83, rho tor today kg m3 = 7.431e-112. This study is simulated and computed from stated assumptions; it is not a measurement.