Linking the Four Distinct Time-Arrows: On Cosmological Black Holes and the Direction of Time

Linking the Four Distinct Time-Arrows: On Cosmological Black Holes and the Direction of Time Abstract Macroscopic irreversible processes emerge from fundamental physical laws of reversible character. The source of the local irreversibility seems to be not in the laws themselves but in the initial and boundary conditions of the equations that represent the laws. In this work we propose that the screening of currents by black hole event horizons determines, locally, a preferred direction for the flux of electromagnetic energy. We study the growth of black hole event horizons due to the cosmological expansion and accretion of cosmic microwave background radiation, for different cosmological models. We propose generalized McVittie co-moving metrics
and integrate the rate of accretion of cosmic microwave background radiation onto
a supermassive black hole over cosmic time. We find that for flat, open, and closed
Friedmann cosmological models, the ratio of the total area of the black hole event
horizons with respect to the area of a radial co-moving space-like hypersurface always
increases. Since accretion of cosmic radiation sets an absolute lower limit to
the total matter accreted by black holes, this implies that the causal past and future
are not mirror symmetric for any spacetime event. The asymmetry causes a net Poynting
flux in the global future direction; the latter is in turn related to the ever increasing
thermodynamic entropy. Thus, we expose a connection between four different “time
arrows”: cosmological, electromagnetic, gravitational, and thermodynamic.