On Fri, Oct 9, 2015 at 3:22 PM, John Clark <johnkcl...@gmail.com> wrote:
> On Fri, Oct 9, 2015 at 7:12 AM, Bruno Marchal <marc...@ulb.ac.be> wrote: > > >> > >> In Turing minds, the potentially infinite tape is just modeling >> > > Exactly, A Turing machine is just a model, a model of something real, > it's a toy, a analogy, > > a > parable > , a tool to aid in understanding, but is not supposed to be taken > literally. When physicists say electrons are in shells outside the nucleus > they don't mean there are tiny mollusks at the center of atoms that excrete > layers of calcium carbonate. > > > >> the papers and ink that a human can use when doing a computation by hand. > > > And the ink and papers and the human hand that moves them around and that > human brain that directs the hand are all made of matter that obeys the > laws of physics. > > > >> >>> There is no evidence a Turing machine, or any abstract entity for that >>> matter, has a memory at all; >> >> >> > >> That is false. It has the tape >> > > Show me the Turing Machine's tape! > > > >> > >> where it can store previous calculation result. >> > > Store the entire contents of Wikipedia on the tape of your Turing > machine and then retrieve that information or explain to me why you are > unable to do so. > If you believe Pi contains wikipedia, you should also believe there are Turing machines whose execution outputs Wikipedia to its tape. Neither Pi, nor this Turing's machine tape will spontaneously appear on your computer screen. For that to happen, you need to rig up a bunch of atoms to behave in the same way as a Turing machine that computes Pi, or a Turing machine that outputs wikipedia. Mathematical objects, like other physical universes, don't affect the evolution of physics in this universe, at least not unless we choose to simulate those mathematical objects/other universes to learn how they behave and then lift up the result out of the simulation. > > >> > >> the tape is not a physical thing though. >> > > Bingo! The tape is an analogy, a simple idea that helps humans understand > how real and far more complex physical computers work. > > > >> >> >>> its memory is not infinite and it's not unlimited either but is in fact >>> very limited indeed, limited by zero . A Turing machine has ZERO memory. >> >> >> > >> That is false. It has a potentially unlimited memory (but no actual >> infinite memory). >> > > A Turing machine has no memory of any sort. But it would be easy to > prove me wrong, all you need to do is store the entire contents of > Wikipedia on your Turing machine and then retrieve it and put all the disk > drive manufacturers out of business. How hard can that be? And after that I > will concede defeat and thank you for correcting my errors. > > >> You can make a physical Turing machine with toilet paper and pebble, or >> ropes and strings. >> > > Yes that is true, a physical Turing machine would be VERY slow but you > could actually make calculations in that way, it won't work nearly as well > as a silicon microchip but at least it would work; but then toilet paper > and pebbles and ropes and strings are all made of matter that obeys the > laws of physics. > > Purely abstract things like analogies or parables > or stories have no need to conform with the laws of physics, even > Turing machines don't need to do that but unlike abstract things in > general Turing machines do conform with the laws of logic, and that's why > they help us understand. > I have a feeling you might learn a lot more if you weren't always so certain that you are right. Jason -- You received this message because you are subscribed to the Google Groups "Everything List" group. To unsubscribe from this group and stop receiving emails from it, send an email to everything-list+unsubscr...@googlegroups.com. To post to this group, send email to everything-list@googlegroups.com. Visit this group at http://groups.google.com/group/everything-list. For more options, visit https://groups.google.com/d/optout.
