The deepest equations of physics, like the Wheeler–DeWitt equation, contain no time. Past and future are scrambled within them, like frames on a film reel with no arrow indicating which way to play it. This symmetry is not a flaw but a feature.
Thus, in quantum gravity (for instance, in the work of Rovelli), the flow of time is born spontaneously. No tweaking of the laws: an internal metronome turns chaos into the arrow of time. This also explains how time could have started after the Big Bang. And most astonishingly, any sufficiently large object, even a spinning galaxy, can act as such a clock, selecting a future from a fan of possibilities.
Paradox: time doesn’t flow on its own: it requires an ‘observer’ in the form of a physical clock. Without one, all moments exist at once, like frames on a frozen film reel.
Just like in ‘Tenet’, where reversed entropy turns time backward, the new work shows that at a fundamental level, motion in either direction is equally valid — until a clock intervenes.