I know that looks like a disagreement, but it's actually not. Note that I said the odds of observing a reversed entanglement is exactly zero, not that the odds of it actually happening were exactly zero. The odds of it happening are comparable to the odds of thermodynamic reversal. The difference is that if a thermodynamic reversal were to happen, it could be observed. If a quantum reversal were to "happen" (I put "happen" in scare quotes because the whole concept of something "happening" becomes a little murky here) it could not possibly be observed, because any attempt to observe it would "prevent" it from "happening."
lisper, you're obviously a pretty smart guy or gal. But your nit-picking here over 'observing' vs 'happening' is so far from your original very bold claim that the arrow of time is not thermodynamic but quantum. You even went so far to say the original article was 'misleading' because of this.
I had to call you on this. Bold claims require strong confirmation. And even the arxiv paper you linked to makes the same statement that I defended - that irreversibility of purely quantum processes is still due to the macroscopic (ie large) system size, which immediately implies the same broad thermodynamic (and statistical ensemble) considerations we've been assuming for the past century.
We may just have to agree to disagree on this. IMHO the difference between the arrow of time being due to entanglement and the arrow of time being due to the 2nd law is analogous to the difference between gravity being a force and it being an artifact of the curvature of spacetime. Not a big difference as a practical matter but it's a huge difference conceptually. And in an article entitled "The quantum mechanics of fate" this difference matters.
Also, this is HN comments, not Physics Review A. Not everything that gets said here needs to pass the highest standards of peer review.
