inverse function
in [Lisp]
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From: Tim Bradshaw on 22 Feb 2010 06:26 On 2010-02-19 17:26:32 +0000, Pascal J. Bourguignon said: > The law of physics that are inversible are incomplete (ie they don't > apply to open systems). If I parse this correctly, this is mostly a tautology - if you're allowed to throw stuff into some non-considered bit of the system (which is what "open" means), then you can throw information away, because you can throw it there. I don't mean this to say I disagree with you or I think your comment is wrong/stupid - I don't at all, I just want to make sure I understand what you're saying. > > The universe constantly throws information away too. Or rather afar. > Therefore any system smaller than the universe loses information Yes, that's right, or rather I think: any system which interacts with the universe may throw information away (typically as heat), because the universe provides this vast sink for information. I think this all very related to measurement in QM. > (even > the black holes, that should tell you something!). The whole "no hair" thing is very interesting I think, especially when combined with Hawking radiation - because black holes *do* throw information away of course: you can throw completely arbitrary stuff into a black hole, and it will then give it back to you as black-body-spectrum radiation, having forgottoen everything but mass, charge and angular momentum. So much for reversibility... I am no longer sure (if I ever was sure, it is now a long time since I had pretensions to be a physicist) if the loss of information is due to the event horizon or the singularity: I think that the event horizon provides some kind of partitioning, but the ultimate loss of information (as opposed to it merely sitting in some inaccessible bit of the state space) must be the singularity. And this makes me feel a bit better because singularities are so obviously bogus things in some way that there has to be some new physics in there which will avoid them. Anyway, this is kind of off-topic now.
From: Pascal J. Bourguignon on 22 Feb 2010 06:37 Tim Bradshaw <tfb(a)tfeb.org> writes: > On 2010-02-19 17:26:32 +0000, Pascal J. Bourguignon said: > >> The law of physics that are inversible are incomplete (ie they don't >> apply to open systems). > > If I parse this correctly, this is mostly a tautology - if you're > allowed to throw stuff into some non-considered bit of the system > (which is what "open" means), then you can throw information away, > because you can throw it there. > > I don't mean this to say I disagree with you or I think your comment > is wrong/stupid - I don't at all, I just want to make sure I > understand what you're saying. Yes, you understood correctly. Too often people forget the pre-conditions of the theorems (or "laws"). >> The universe constantly throws information away too. Or rather afar. >> Therefore any system smaller than the universe loses information > > Yes, that's right, or rather I think: any system which interacts with > the universe may throw information away (typically as heat), because > the universe provides this vast sink for information. > > I think this all very related to measurement in QM. > >> (even >> the black holes, that should tell you something!). > > The whole "no hair" thing is very interesting I think, especially when > combined with Hawking radiation - because black holes *do* throw > information away of course: you can throw completely arbitrary stuff > into a black hole, and it will then give it back to you as > black-body-spectrum radiation, having forgottoen everything but mass, > charge and angular momentum. So much for reversibility... > > I am no longer sure (if I ever was sure, it is now a long time since I > had pretensions to be a physicist) if the loss of information is due > to the event horizon or the singularity: I think that the event > horizon provides some kind of partitioning, but the ultimate loss of > information (as opposed to it merely sitting in some inaccessible bit > of the state space) must be the singularity. And this makes me feel a > bit better because singularities are so obviously bogus things in some > way that there has to be some new physics in there which will avoid > them. > > Anyway, this is kind of off-topic now. Well, not if you believe the universe is simulation in a computer, what's more, written in Lisp! :-) (Even if some believe it's hacked in perl). -- __Pascal Bourguignon__
From: Tim Bradshaw on 22 Feb 2010 07:08 On 2010-02-22 11:37:01 +0000, Pascal J. Bourguignon said: > Well, not if you believe the universe is simulation in a computer, > what's more, written in Lisp! :-) This depends on who you ask I think. Mathemeticians probably think it's written in some pure functional language. Theoretical physicists think it is written in Common Lisp (specifically not any other Lisp dialect). Expermintal physicists think it is FORTRAN (specificlly FORTRAN 66) Biologists think it is Perl using some statistics package Chemists COBOL --tim
From: Espen Vestre on 22 Feb 2010 07:14 Tim Bradshaw <tfb(a)tfeb.org> writes: > Biologists think it is Perl using some statistics package And I thought they would suggest APL. -- (espen)
From: Tim Bradshaw on 22 Feb 2010 07:29
On 2010-02-22 12:14:08 +0000, Espen Vestre said: > And I thought they would suggest APL. That's better: biologists APL and chemists Perl (or maybe the other way around, but I can never tell biologists and chemists apart: they both spend their time manfacturing illicit drugs in their garage don't they?). Polititians COBOL, which explains a lot. |