I'm not a physicist, so I'm asking a question. How much of this "we have no information loss in this universe" prinicple are we simply assuming at the outset? I know that a lot of it is unverified theory, like in the case of Stephen Hawking's black hole vs. no black hole from infinity argument, etc. For instance, are we simply assuming, by the sacred laws of thermodynamics, that in the quantum background there is always an antiparticle for each particle in order to annihilate each other? Or could it be that particles and antiparticles appear and disappear asymmetrically on their own, under our observational radar, even though that wouldn't be elegant? Perhaps all these undetectable asymmetries add up to cancel out any observable asymmetries. Weirder things have happened in quantum physics. Are we assuming by elegance that there is no information loss? You can just tell me to go back to my math if you want.
Tom > > Saibal Mitra wrote: > > How would an observer know he is living in a universe in which information > > is lost? Information loss means that time evolution can map two different > > initial states to the same final state. The observer in the final state > > thus > > cannot know that information really has been lost. > > If the universe allows two different states to evolve into the same final > state, the second law of thermodynamics wouldn't hold, and we would be able > to (in principle) contruct perpetual motion machines. > > I don't know why you say this can't be detected by an observer. In theory > all we have to do is prepare two systems in two different states, and then > observe that they have evolved into the same final state. Of course in > practice the problem is "which two different states?" And as I suggest > earlier, it may be that for anthropic reasons one or both of these states is > very difficult to access. > Yes, in principle you could observe such a thing. But it may be that generic models exhibiting information loss look like model that don't have information loss to internal observers. 't Hooft's deterministic models are an example of this. I'm also skeptical about observers being able to make more efficient machines. The problem with that, as I see it (I haven't read Lloyd's book yet) is as follows. Consider first a model without information loss, like our own universe. What is preventing us from converting heat into work with 100% efficiency is lack of information. If we had access to all the information that is present then you could make an effective Maxwell's Daemon. Lacking such information, Maxwell's Deamon has to make measurements, which it has to act on. But eventually it has to clear it's memory, and that makes it ineffective. To get rid of this problem Maxwell's Daemon would have to be able to reset its memory without changing the state of the rest of the universe. This could possibly be done in an universe with information loss, but that could only work if the Daemon has control over the information loss process. If information loss interferes with the actions of the Daemon, then it isn't much use. You could also think of the possiblity of some ''physical process'' which would be sort of a ''passive Maxwell's Deamon'' that could reduce the entropy in such universe. Using that you could create a temperature difference between two objects. To extract work you now need to let heat flow between the two objects. So, at that stage you need an entropy to increase again. So, to me this doesn't seem to be a generic world in which you have information loss, rather a world in which it is preserved but where it can be overruled at will. The benefits come from that magical power. Saibal ------------------------------------------------- Defeat Spammers by launching DDoS attacks on Spam-Websites: http://www.hillscapital.com/antispam/ --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "Everything List" group. To post to this group, send email to everything-list@googlegroups.com To unsubscribe from this group, send email to [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/everything-list -~----------~----~----~----~------~----~------~--~---
