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A Model Railroad That Computes
tri44id writes "Several blogs have noted an Austrian team that has built a model train set that is a primitive computer. I have to point out, though, that it's actually only a Finite State Machine, like a pocket calculator, not a general-purpose device. Their plan for a general purpose layout is for an infinite-state machine, not a FSM+tape that Turing envisioned in his original paper. Turing took the concept a further step, by presenting a Universal Turing Machine that embodies a special set of states and transitions that allows its tape to be programmable to emulate any other TM. Do Slashdot readers know of any mechanical implementations of a truly Universal Turing Machine? (Danny Hillis' famous tinkertoy tic-tac-toe machine has neither infinite tape nor programmability, and is thus yet another FSM. It shouldn't be hard to elaborate the Austrian model train FSM to use a series of cars carrying movable magnets to represent Turing's tape cells writable with different symbols, and thus become a true TM or even UTM."
Could they use it to control another digitally controlled model railroad once they build the more advanced system?
Life is just nature's way of keeping meat fresh.
It's interesting to note that almost everything we find weird and wonderful about computers, and about the culture that builds, modifies and programs computers for the sheer love of intellectual challenge, stems from the MIT Model Railroad Club.
The hackers who loved switches, relays, automation systems and doing beyond-tomorrow stuff with all of it irritated the hell out of the guys who liked collecting little models of trains, and eventually went on to be the Midnight Hackers of fame.
SoupIsGood Food
Finite State Machines, however, are useless as models of computation when you're treating them in that way. True, you can theoretically model any physical computation device with an FSM (albeit one with billions of states, even for the most simple systems which allow arbitrary computation), there is a difference between being a simple regular language acceptor and being Turing Complete.
AFAIK the only truly universal turing machine must be implemented with reversible logic and be based on quantum mechanics. http://www.holbornbooks.co.uk/details.aspx?sn=3917 4This book explains it fairly well.
There is an online demonstration of an Alan Turing Machine. http://abacus.sourceforge.net/alanturingmachine/ab acus.php
It is basically an idea of a primitive computer with 2 main components. The components include a Tape to hold the data and a Finite State Machine to contain the instructions to process it. This is like the Processor and Memory relationship. The Tape in the demonstration is finite though.
No need to be a jerk. The poster's meaning was clear enough. "Has anyone built a mechanical (non-electronic) computer which has the capacity to deal with an arbitrary amount of simulated tape and therefore run arbitrary computer programs up to the limits of the tape available at any particular time." If we all spent our times being as literal as you are, computer science would be quite impoverished. "No need to discuss Turing machines in CS class because Turing machines and computers are totally different things: one depends on infinite tape and the other on finite hard disks. Computer languages can therefore never be Turing-complete." It's a pet peeeve of mine and a way for pedants to try to sound "profound and knowledgable."
The question is not vacuous and in fact someone has created a mechanical Turing machine.
Kind of interesting to see that a Chicken can be trained to play a perfect game of Tic-Tac-Toe.
try { do() || do_not(); } catch (JediException err) { yoda(err); }
Linear-bounded automata are not as powerful as Turing Machines, but are still quite powerful.
William Gibson and Bruce Sterling co-wrote a book on Babbage and his proto-computer, wherein the course of history is refigured due to the success of Babbage's invention (i.e. a working computer more than a half-century early). It's called The Difference Engine, for anyone who cares.
You were right the first time. Desmond Bagley wrote "The Enemy" and it featured a model railway that computed genetic manipulations.
It was bought by the main character at an auction, for 31000 pounds. When his boss heard that he had bought a train set for such an ungodly amount of money he said "You expect me to be able to clear that through Expenses?" To which the character replied "Call it by its real name, a computing device."
'Twas a fine yarn that story. Nearly as good as Running Blind.
By far the coolest implementation of a turing machine is the one at the University of Washington. It's steam powered!