> if a sound is made, does the universe permanently keep a record of it? I would imagine the waves would die down, until at a certain quantum level, they will stop entirely.
> Or, if two particles annihilate each other, is it possible from the resulting particles/energy produced to know which particles were involved?
These are really great questions! The facile answer is that all known physical processes are reversible in principle, but the actual truth is more complicated than that. For starters, quantum measurement may or may not be reversible depending on which interpretation of QM you subscribe to. On the currently-most-popular account, the Copenhagen interpretation, measurement is by assumption irreversible. There are many reasons to believe that this is not the case, that measurements are in fact reversible (in principle, not in practice) but no one really knows, and no one can know because the process of reversing a measurement is indistinguishable form the normal state of affairs. It might actually be happening all the time. There is no way to know.
> Or, if two particles annihilate each other, is it possible from the resulting particles/energy produced to know which particles were involved?
These are really great questions! The facile answer is that all known physical processes are reversible in principle, but the actual truth is more complicated than that. For starters, quantum measurement may or may not be reversible depending on which interpretation of QM you subscribe to. On the currently-most-popular account, the Copenhagen interpretation, measurement is by assumption irreversible. There are many reasons to believe that this is not the case, that measurements are in fact reversible (in principle, not in practice) but no one really knows, and no one can know because the process of reversing a measurement is indistinguishable form the normal state of affairs. It might actually be happening all the time. There is no way to know.
For more info see:
http://blog.rongarret.info/2014/10/parallel-universes-and-ar...
(And its prequel: http://blog.rongarret.info/2014/09/are-parallel-universes-re...)
If you want a deeper understanding of all this stuff I recommend:
https://www.amazon.com/Philosophy-Physics-Princeton-Foundati...
https://www.amazon.com/Quantum-Mechanics-Experience-David-Al...