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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."
It may be because it's 4:11 am, but I didn't understand ANY of that. :( Anybody smarter care to fill me (and hopefully others) in?
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I haven't been fortunate enough to find a computer that was more powerful than a sufficiently large finite-state machine.
Dyslexics have more fnu.
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.
I just wasted about half a day compiling and recompiling my linux kernel to get it "just right".
But still, I feel even I have the authority to say that some people just have too much time.
That is really awesome! The idea of a model railroad being a computer is not new though. I read a book by Desmond Bagley (or was is Alistair Maclean) many years ago where a scientist who wanted his work to remain secret built a model railroad/computer. His dying act is to give his model railroad timetables to the main character. The main character later realises that the timetables are actually code for this unique computer.
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.
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I have to point out, though, that it's actually only a Finite State Machine, like a pocket calculator, not a general-purpose device
Yes, and your desktop computer is also another example of a finite state machine. Granted, all those little silicon switches have an enomorous number of possible states, but rest assured, the total number is indeed finite.
Would a UTM Railroad be a train of thought?
Is this not a Choo-Chooring machine?
Given the requirement for an infinitely long tape, I suspect the answer to this question might be no.
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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.
Do Slashdot readers know of any mechanical implementations of a truly Universal Turing Machine?
Of course not. A truly Universal Turing Machine needs an infinite amount of tape. Or RAM. Or HDD. Or Spaghetti. Or any other infinite amount of storage device. Hell, the submitter makes this clear in their spiel, just after they ask the vacuous question above. I guess they should read what they write a little closer; or stop prancing around like a tit, trying to sound profound and knowledgable.
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I'm currently at work, graveyard, and this thing just blew my mind. Someone said this thing is terribly slow, (I doubt they meant it as an insult) but if you wanted to solve that problem you could make a three dimentional roller coaster version. That would be MUCH faster.
Don't you mean.. BIZZARO!
I bet they still don't run on time.
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Thomas the tank engine has been solving problems for ages now, and in multi task more he keeps the kids amused while he does it.
Do not try to read the dupe, thats impossible. Instead, only try to realize the truth
What truth?
There is no dupe
There was a 70s adventure novel - I believe by Hammond Innes although the title eludes my memory) in which a bomb-scientist who had promised to do no further research when he left government service is kidnapped
Investigators found that he had a large model railway which was controlled by a computer and the answers to calculations were reported by numbered wagons being arranged in certain orders and locations.....
It wasn't a very good book, actually.
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Do Slashdot readers know of any mechanical implementations of a truly Universal Turing Machine?
No, but I have an infinite tape lying around in my shed, so if you know how to do the logic stuff, we can team up.
sudo ergo sum
Of course not.
I'm sure there must be some... they'll be in a backroom somewhere, stacked next to the perpetual motion machines and the random noise compression algorithms.
A 'proper' Turing machine is supposed to be able to take on infinitely many states, OK?
That means that if you want to build one, before you get into how you are going to have the thing operate, you at least have to find a way of coding infinitely many discrete states using some finite amount of matter. Which is not possible: even if you could manipulate matter to the point of using every individual subatomic particle to store a bit of data, there are only finitely many particles and you will have a finite state machine.
Per the Heisenberg uncertainty principle, you cannot try to encode your state as an infinite-precision real which is (part of) the position or whatever of an object either, if you want to build a machine which is always contained in a finite space.
You could build a machine which will extend up to physical limits: stick a radar reflector in space, well away from any gravitational influence (which might be a problem, but...), and build a rocket ship which keeps track of how far away the radar reflector is, in the obvious way, keeps it an exact multiple of 1 metre, and runs a universal program (can do this in silicon logic on board) with that distance as the register. Assume that somehow it is possible to fuel the ship. With a bit of care, you can program things such that this program goes wrong with very low probability (you can allow for relativity, you can't rule out quantum effects deciding to move things suddenly by >0.5m, but it is very very unlikely). That will function as a universal Turing machine whenver you put in a program that does not require you to store any really large numbers. But when you are required to store large numbers you may run up against a physical limit in that you may well find there is an upper limit on the length of a geodesic in space-time, and you will be unable to store bigger numbers.
After reading this article and the article on the tinkertoy "computer", it surprises me what people consider to be a computer. Did anyone else notice the fact that the train "computer" is just pushing digits around? It computes in *unary*, which is the most inane operation one can think of. We're supposed to be impressed if someone can get a machine to take the input, 11011101 (Meaning 2+3+1) and produce the output, 11111100 (meaning 6)? I'd rather use my much more powerful hands... I mean... autobiological computers.
If they didn't have the model train, they wouldn't have gotten the idea for the big trains
"I have to point out, though, that it's actually only a Finite State Machine, like a pocket calculator, not a general-purpose device."
So, does that means it runs Windows? Perhaps it is a special version Windows: Windows RR (as opposed to Windows 958MeNTXP2000CE). Of course, unlike other versions of Windows, it does not crash--it derails.
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You're trying to be clever but I hope you do know that having a "finite number of states" is not in and of itself a definition of a FSM. He wasn't trying to be clever, just accurate. Your computer is a finite state machine; It is not a Turing machine. We tend to think of them as Turing machines only because they have an enormous number of states; thus they seem to act like Turing machines as long as we don't do anything that requires more states than the computer has. However, when you run out of ram and/or disk space, you've just recognized the limitation of your desktop FSM. It is demonstrably the case that a finite state machine cannot be programmed to run a JVM or a Python interpreter. That is incorrect. Every computer program is a FSM.
At least it beats a lot of dead horse...
... nevermind.
Except in Soviet Russia, where the dead horse beats
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He was probably using a steam locomotive model train. You were probably using one of the bullet train model railways.
The bullet trains are much better at hard tasks like compiling kernels, but watch out if they derail. Gives new meaning to the term "system crash".
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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); }
This layout is horrible! Get some trees in there! Some buildings? This guy made up the computer idea to hide the fact that he couldn't use plaster-of-Paris.
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Turing showed that such a train can never compute whether it will stop at a given station.
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Linear-bounded automata are not as powerful as Turing Machines, but are still quite powerful.
Amtrak?
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Imagine, a search engine (perhaps a small diesel) looking for those missing op codes. I suppose that there would be more likelihood of crashes too, especially if there are too many wet leaves on the tracks.
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.
The resulting computers are nondeterministic. They are computers in the sense that, given a Turing machine and a given input, you can construct a corresponding sliding-block puzzle that is solvable if and only if the Turing machine would eventually print YES. The catch is that this only works when the Turing machine is allowed to use only an amount of tape polynomial in its input size (but then, the same is effectively true of real computers). Technically, this means that sliding-block puzzles are PSPACE-complete - that's the next complexity class up from NP-complete.
Anyway, the construction does involve building logic gates out of sliding-block components, so the things are rather like actual computers. The constructions are based on the earlier result that you can build computers out of Rush Hour puzzles.
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By far the coolest implementation of a turing machine is the one at the University of Washington. It's steam powered!
You're missing the point here -- a modern computer is not a closed device. Its ability to interact with the outside world via I/O of various kinds gives it the full range of a TM's power. A computer is not just its RAM and CPU and hard drive.