jwl@ernie.Berkeley.EDU (James Wilbur Lewis) (09/20/88)
In article <7059@aw.sei.cmu.edu> firth@bd.sei.cmu.edu (Robert Firth) writes: >In article <388@quintus.UUCP> ok@quintus.UUCP (Richard A. O'Keefe) writes: > >>But is there any reason to suppose that the universe _is_ a Turing machine? > >None whatever. The conjecture is almost instantly disprovable: no Turing >machine can output a true random number, but a physical system can. Since >a function is surely "computable" if a physical system can be constructed >that computes it, the existence of true random-number generators directly >disproves the Church-Turing conjecture. Two comments. First, I think "deterministic automaton" is a more apt (putative) metaphor for the universe than a Turing machine. Turing machines have infinite tapes, symbols, read/write heads, etc.; it is a model of computation, and bandying it about as an analogy for the workings of the universe in this sort of discussion is sloppy, and bound to make theorists wince. ;-) Regarding "true randomness": randomness, in a theoretical sense, is more closely related to predictability than determinism. Turing machines are certainly capable of outputting highly unpredictable sequences which would satisfy any statistical criteria of randomness you care to invent. If, by "random", you mean to imply nondeterministic behaviour, the existence of "true", physically realizable random number generators is contingent upon the Copenhagen interpretation of quantum mechanics (no hidden variables). Can you supply a proof that God does indeed play dice with the universe? -- Jim Lewis U.C. Berkeley
cik@l.cc.purdue.edu (Herman Rubin) (09/21/88)
In article <26154@ucbvax.BERKELEY.EDU>, jwl@ernie.Berkeley.EDU (James Wilbur Lewis) writes: > In article <7059@aw.sei.cmu.edu> firth@bd.sei.cmu.edu (Robert Firth) writes: > >In article <388@quintus.UUCP> ok@quintus.UUCP (Richard A. O'Keefe) writes: .................. > Regarding "true randomness": randomness, in a theoretical sense, is more > closely related to predictability than determinism. Turing machines are > certainly capable of outputting highly unpredictable sequences which would > satisfy any statistical criteria of randomness you care to invent. If, by > "random", you mean to imply nondeterministic behaviour, the existence of > "true", physically realizable random number generators is contingent upon > the Copenhagen interpretation of quantum mechanics (no hidden variables). > Can you supply a proof that God does indeed play dice with the universe? A deterministic universe implies that all our actions, including this posting, are determined. The philosophical implications of this should be obvious. Quantum mechanics is even worse than randomness. The observations have proper- ties which observe probabilistic rules, but what happens between observations is worse (from a mathematical point of view. No value judgments here :-)). I have no difficulty with probability as a property of the universe, with its behavior included in the description of the physical laws. This has nothing to do with unpredictibility, but with indeterminism. Then there is free will. -- Herman Rubin, Dept. of Statistics, Purdue Univ., West Lafayette IN47907 Phone: (317)494-6054 hrubin@l.cc.purdue.edu (Internet, bitnet, UUCP)
mesard@bbn.com (Wayne Mesard) (09/21/88)
From article <936@l.cc.purdue.edu>, by cik@l.cc.purdue.edu (Herman Rubin): > A deterministic universe implies that all our actions, including this posting, > are determined. The philosophical implications of this should be obvious. I knew you were gonna say that ;-) But seriously, why does it seem so counter-intuitive. If you put a dozen balls in a box and shake it, the resulting trajectories will seem--to the uninformed eye--random and unpredictable. But given the proper information [note I don't say observational powers and thus avoid the Uncertainty Principle], one can exactly predict the paths that the ball will take. Now scale that model up by many thousand orders of magnitude. Instead of balls, we have subatomic particles and more subtle forces at work, but the principle is still the same. We may never haveenough information to exactly predict events in the universe, or even a reasonable subregion thereof. But the inability to make the exact calculation doesn't mean that the universe isn't exactly, completely deterministic. -- unsigned *Wayne_Mesard(); The last thing one knows in constructing MESARD@BBN.COM a work is what to put first. BBN, Cambridge, MA -- Blaise Pascal
gbn474@leah.Albany.Edu (Gregory Newby) (09/21/88)
In article <936@l.cc.purdue.edu>, cik@l.cc.purdue.edu (Herman Rubin) writes: > Then there is free will. > > Herman Rubin, Dept. of Statistics, Purdue Univ., West Lafayette IN47907 No, No. Please, not free will again. It's been debated to death on comp.ai, with no result (except of course insult). I picked up a book by Karl Popper (_Of Clouds and Clocks_, actually a lecture) which reminded me of the discussion that went on here. He, as it happens, supports the notion of free will, but must conclude in the end that he has no way to test the theory. And if it ain't testable, it ain't science (ref: your introductory methods textbook from ___101). --newbs ( gbnewby@rodan.acs.syr.edu gbn474@leah.albany.edu ) ps: i *had* to say that.
cdfk@otter.hple.hp.com (Caroline Knight) (09/21/88)
> >Now scale that model up by many thousand orders of magnitude. Instead >of balls, we have subatomic particles and more subtle forces at work, >but the principle is still the same. We may never haveenough >information to exactly predict events in the universe, or even a >reasonable subregion thereof. But the inability to make the exact >calculation doesn't mean that the universe isn't exactly, completely >deterministic. > >-- >unsigned *Wayne_Mesard(); The last thing one knows in constructing >MESARD@BBN.COM a work is what to put first. >BBN, Cambridge, MA -- Blaise Pascal >---------- Balls are only models of atoms - if the "real" (whatever that means!) form of atoms is different then this argument has no substance. All you have said is: If one can model atoms by something purely deterministic like balls then they are purely deterministic Sounds tautological to me. Caroline Knight HPLabs, Bristol, UK
dorn@fabscal.UUCP (Alan Dorn Hetzel) (09/21/88)
If you remain convinced that the universe is deterministic, and awaits only adequate observational and computational resources to be modeled, I have some bad news for you... I don't want to make this a mega-message, so I'll just put it this way; Check out a few books on Quantum Physics / Chaos Theory. Dorn gatech.edu!fabscal!dorn p.s. FOLLOWUPS to sci.physics PLEASE>
smryan@garth.UUCP (Steven Ryan) (09/22/88)
>must conclude in the end that he has no way to test the theory. > And if it ain't testable, it ain't science (ref: your introductory methods >textbook from ___101). Does this mean we're back to belief systems again? -------------------------------------------------- Of course, `what is the answer to this question' has another answer: Shut up.
mike@ists.yorku.ca (Mike Clarkson) (09/22/88)
In article <29891@bbn.COM>, mesard@bbn.com (Wayne Mesard) writes: > But seriously, why does it seem so counter-intuitive. If you put a > dozen balls in a box and shake it, the resulting trajectories will > seem--to the uninformed eye--random and unpredictable. But given the > proper information [note I don't say observational powers and thus avoid > the Uncertainty Principle], one can exactly predict the paths that the > ball will take. > Now scale that model up by many thousand orders of magnitude. Instead > of balls, we have subatomic particles and more subtle forces at work, > but the principle is still the same. We may never haveenough > information to exactly predict events in the universe, or even a > reasonable subregion thereof. But the inability to make the exact > calculation doesn't mean that the universe isn't exactly, completely > deterministic. This Laplacian view of the Universe died out a long time ago, both in quantum mechanics, and non-equilibrium statistical thermodynamics. Amongst other things, the Laplacian view depends on both locality, and linearity of the equations involved, neither of which holds true in either of these cases. For a good introduction to this, see I. Prigogine's books, such as "Being to Becoming" (Freeman). The implications for large AI systems are quite apparent. Mike Clarkson mike@ists.UUCP Institute for Space and Terrestrial Science mike@ists.yorku.ca York University, North York, Ontario, uunet!mnetor!yunexus!ists!mike CANADA M3J 1P3 +1 (416) 736-5611
gilbert@cs.glasgow.ac.uk (Gilbert Cockton) (09/23/88)
In article <1024@leah.Albany.Edu> gbn474@leah.Albany.Edu (Gregory Newby) writes: > And if it ain't testable, it ain't science (ref: your introductory methods >textbook from ___101). and if it is tested, it may still be uncertain (ref: any proper discussion of hypothetico-deductive methods) >ps: i *had* to say that. Me too -- Gilbert Cockton, Department of Computing Science, The University, Glasgow gilbert@uk.ac.glasgow.cs <europe>!ukc!glasgow!gilbert
bwk@mitre-bedford.ARPA (Barry W. Kort) (10/04/88)
For an interesting report on the subject of predictability vs. chaos, see the current issue of Scientific American. According to recent studies, an infinitesimal perturbation in the initial conditions of the orbit of Pluto leads to exponentially divergent solutions. After 30 million years, the two solutions can place Pluto on opposite sides of its orbit about the Sun. And if the orbit of Pluto is chaotic, then the whole Solar System is chaotic as well. [The article can be found the the Science and the Citizen column, and is titled "God takes a nap".] --Barry Kort
usenet@cps3xx.UUCP (Usenet file owner) (10/07/88)
To Mr. Juergen Cronau: University of Dortmund, Department of Computer Science, W-Germany UUCP: cronau@exunido I'm also interested in logic programming and deductive databases. Can you send me information about your selected papers? Thanks in advance. Kuan, Yih-pyng Computer Science Department Michigan State University kuan@cpsvax.msu.edu