This is the bit that irks me. Quantum mechanics, the real QM that physicists actually use, involves collapse of the wavefunction. This is absolutely time-asymmetric. But in all these discussions of "why is time one-way?" this never seems to be mentioned. Apparently QM is not a real theory, and just a placeholder until we can work something out properly. Irk!
If you could run an experiment where you account for the interaction between the apparatus and the observer, a meta experiment if you will, you would not see the wave function collapse that the observer thinks they observed.
The basic problem with your suggestion is that it does not explain how anything actually "happens". Unitary evolution is a theory where nothing changes. People seem to think that they can evoke decoherence, or similar, and these issues disappear. But they do not.
Anyway, I'm not positing any solution, I am just saying that it irks me that all these ideas are dismissed whenever it comes to the problem of the asymmetry of time. It just seems bizarre to me.
<u|U^\dag U|v> = <u|v>.
OTOH, I can understand the argument that nothing ever happens. One reasonable requirement for something to happen is that it should not be able to "unhappen," which is why some are looking for the possibility of irreversible decoherence.
This is not unitary. Quantum theory has two parts: unitary evolution, and measurement processes. That's it.
Let u and v be qubits. Apply a Hadamard gate to u while leaving v unchanged. Then they have evolved independently (but unitarily): u according to H, and v according to I.
I don't think so.
> "piles of words"
I definitely agree about the piles. Maybe ordinary language is just to feeble for this stuff.
There is no QM theory. There are interpretations (like the Copenhagen interpretation). We don't know the truth as of yet. (which is exactly what Hawking has been trying: creating a unified physics between QM and General relativity).