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> The obvious answer in a classical universe is ... Since there is an obvious answer in classical physics, it's a bit disingenuous to claim that this solves a
by shasta 13y ago
> The obvious answer in a classical universe is ...
Since there is an obvious answer in classical physics, it's a bit disingenuous to claim that this solves a long-standing problem in classical physics, no?
> With entanglement and de-coherence however, such reversal becomes impossible even in principle [...] So it does look like a better candidate for the arrow of time.
That would be true if you could demonstrate by experiment that a broken egg springing back up onto the table and reforming is physically impossible instead of just unfathomably unlikely. Can you demonstrate that?
- gameshot911 13y agoI'm on it. I've placed a broken egg on my table. I'll let you know the results.
- ars 12y agoIt's been 6 days - how's your egg doing? :)
- gameshot911 12y agoAt one point a breeze did blow two pieces of shell closer to one another, but beyond that entropy has appeared to increase quite a bit. At this point my highest hopes are that the mold growing on it will evolve into an intelligent species capable of manually reconstructing the egg.
- SoftwareMaven 13y agoIsn't that exactly what the paper this article references is stating a proof of: that the reforming is physically impossible?
- loup-vaillant 13y agoYou do not understand. Let me rephrase. You go on a space ship, on your way to the edges of the universe. Your buddy goes on a space ship, on his way to the other side of the universe. You will soon be outside each other's observable universe. Now, if you drop something in your ship (it spins, so you have gravity), you can "reverse time", and pull it back up. Can you do the same to you buddy's ship, should something ever fall there? The simple answer is no. You can't. He's on his own. Now there _is_ a way I haven't spoken of: non-causal interaction. You and your buddy could agree on some things before you depart. For instance, you could agree to pull back up whatever falls. With Everett branches, it's even easier: you pre-commit to reversing your own Everett branch, whatever it is, so all your selves do it. If successful, the worlds should merge back together, at least locally. Just one catch: all your other selves must successfully reverse time locally. It only takes one failure for the plan to fail. But if you want to reverse time after the fact, say because you happen to be in an Everett branch you don't like (you lost a bet about which way the photon will go), you won't be able to reverse time here, because your other self certainly will not (he won the bet, so…). Maybe, just maybe, you could use the vanishingly small entanglement left with the other Everett Branch to directly communicate with your other self. I'm not even sure it can be done in principle. For practical purposes, it should be forever beyond reach, even if you have a super-intelligent AI to help you.
- shasta 13y ago> Maybe, just maybe, you could use the vanishingly small entanglement left with the other Everett Branch to directly communicate with your other self. I'm not even sure it can be done in principle. My understanding is that this would violate a physical law that we still believe to hold. You're right though, that I don't understand. At least I thought I understood your last post. With this one, I don't follow the connection to the OP.
- loup-vaillant 13y agoOops, I didn't intent to obscure my meaning. I was replying mainly to mbq: https://news.ycombinator.com/item?id=7602812 https://news.ycombinator.com/item?id=7602812 My understanding is, with QM, is is even harder or even impossible to reverse time, even with perfect knowledge of your reachable surroundings. In a classical universe however, it looks much easier, so in such a universe, the explanation for time is less satisfactory.