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While the basic laws of physics seem time-reversal invariant, ourunderstanding of the apparent irreversibility of the macroscopic world is wellgrounded in the notion of entropy. Because astrophysics deals with the largeststructures in the Universe, one expects evidence there for the most pronouncedentropic arrow of time. However, in recent theoretical astrophysics work itappears possible to identify constructs with time-reversal symmetry, which ispuzzling in the large-scale realm especially because it involves the engines ofpowerful outflows in active galactic nuclei which deal with macroscopicconstituents such as accretion disks, magnetic fields, and black holes.Nonetheless, the underlying theoretical structure from which this accretingblack hole framework emerges displays a time-symmetric harmonic behavior, afeature reminiscent of basic and simple laws of physics. While we may expectsuch behavior for classical black holes due to their simplicity, manifestationsof such symmetry on the scale of galaxies, instead, surprise. In fact, weidentify a parallel between the astrophysical tug-of-war between accretiondisks and jets in this model and the time symmetry-breaking of a simpleoverdamped harmonic oscillator. The validity of these theoretical ideas incombination with this unexpected parallel suggests that black holes are moreinfluential in astrophysics than currently recognized and that black holeastrophysics is a more fundamental discipline.

Symmetry and the arrow of time in theoretical black hole astrophysics