Quantum physics is our starting to find the mathematical description that does not neglect any possibilities. At first we thought this encompasses only the alive and dead Schrödinger cats in our particular universe, but this immediately includes all the ways a universe may be described to unfold internally as its own Schrödinger box, so it contains anyway all possible universes; everything possibly phenomenal is included in the ultimate description, else it is not the ultimate description by definition. Nota bene: The core insight is not quantum (!); already with classical determinism would an ultimate description contain all possible worlds (including all possible initial conditions and time-like loops). "Many worlds" are tautologically true, already classically. However, quantum interference (entanglement) between alternatives makes not caring about alternatives a lot more difficult.
Quantum physics therefore starts re-describing something that has been understood again and again throughout the ages, an insight that is trivially true but nevertheless only fully admitted by the pathologically rational: The tautologically totalitarian nature of totality. Totality is all that is possible. All possible is possible, that is all. Asking whether alternatives actually also “exist” (absolute rather than relative actualization) makes fundamentally no sense. Via quantum physics, we arrive at a more precise description of what wise people probably knew for thousands of years: Totality is totality is totality. There is nothing that any of your decisions add or subtract. All that is possible is possible; none of the impossible will be made possible. Fundamentally, you cannot ever remove the slightest bit of suffering; you can do nothing that would add a quantum of happiness.
This total determinism* is more scary and unpalatable than the anti-realism that comes with quantum mechanics (which is the uncomfortable result people refuse to face which I usually write about, a quite different topic.)
Why we find totality unpalatable
Evolved reproducers that are conscious and have beginnings of rationality have evolved to rationalize their world in terms of purpose and agency, simply because this out-competes alternatives, thus humans fear such tautological truths, and they are unconsciously driven to fight them with all their powers of rationalization, as contemporary academic philosophy still clearly evidences. This rather more than mathematical difficulties, simply this fear of powerlessness slowed the progress of modern physics especially during the last hundred years and it is the source of the circular regress arguments that are the biggest problem in fundamental science and philosophy. Even most of those who work on relativity or quantum physics refuse the core of these modern forms of physics, which is a form of modal realism – the tautological triviality of that in a fundamental description, all equivalent alternatives (for example other points in time) are equivalent.
There is nothing that your decisions add to totality. None of the possible can be made impossible. Of course, such insights are suppressed by evolved systems, everything else would be inconsistent. We would not be here otherwise, certainly not anywhere near the shape we are in. Your own existence and that of society ensures that such interpretations are taboo. This holds in precisely the same way as that you can only find yourself in a universe in which life can find itself. Such 'relativism' has been likened to a mortal disease, and that analogy is quite correct in a profound sense, however, I will refrain from touching that topic today.
Evolution is a selection process along an apparent time dimension, an emergent causal description. Fundamentally, nothing is selected, totality stays totality. Ultimately, evolution is one aspect of a self-consistent description. Self-consistency ensures that we defend your agency and ridicule modal realism as preposterous nonsense.
My writing happens, my moral outrage is a rhetorical exercise that I find myself doing at times. The desire for a future state that is comfortable with answers and also remembers having been me has dwindled. The mere joy in or better obsession with ruminating remains: What is possible? If quantum physics as we know it today has no corrections from phenomenal consistency, if “terribly inconsistent states” are possible, is there no more to be said than that their low expectation value (~ probability) makes us label those states as madness? Is the answer to these questions to be found via more fundamental physics, via the derivation of Born probabilities from relational quantum mechanics, or is this all no more than resolving the details of Higgs mechanisms and string mathematics, basically a more sophisticated form of chemistry, until one fine day perhaps pure logic grasps the phenomenal redness of red?
*I plan to explain the difference between classical determinism and quantum determinism allowing for apparent in-determinism, since many confuse quantum-in-determinism to mean that quantum physics is somehow not deterministic. Much like with a similar misrepresentation of chaos theory, which is also deterministic, such are misconceptions.