Wolfram's 2,3 Turing Machine Not Universal

Fishbat writes "In a cutting message to the Foundations of Mathematics mailing list, Stanford's Vaughan Pratt has pointed out an elementary mistake in the recently announced proof that Wolfram's (2,3) machine is universal." Update: 10/30 04:18 GMT by KD : Ed Pegg Jr. from Wolfram Research points to this response to Dr. Pratt's note, which has been submitted to the FoM mailing list but has not yet appeared there due to moderation.

Comments

The Filter

[eldavojohn]

The author of this e-mail, which is incredibly insightful and articulate asked:

How did an argument containing such an elementary fallacy get through the filter? To be fair, I don't consider this that elementary a fallacy but when you break it down to if x + y = infinity then both x & y are infinity it does sound like a rather obvious pitfall. And, in response to his comment on catching it, it had not yet been through "the filter" as the original story stated:

Smith's proof will be published in the journal Complex Systems. Meaning it had not yet been peer reviewed. But I agree with the author however abrasive he came off (although this is far higher than an elementary mistake) when he said:

Had I pushed my luck my second question would have been, who has verified this proof that has taught an automata theory course at a suitably accredited institution? I can forgive an undergrad prof for missing this, his response was probably just to look at it and encourage the kid to submit it. Afterall, what motive would a professor have to read it?

But what should really be noted is what Wolfram himself is quoted as saying from the initial publishing of this proof:

"I had no idea how long it would take for the prize to be won," said Stephen Wolfram. "It could have taken a year, a decade, or a century. I'm thrilled it was so quick. It's an impressive piece of work." Alright, that last sentence there is pretty damning. I have heard time and time again on Slashdot that Wolfram just took other people's work, that he had people working underneath him & that he didn't actually know what he was talking about in his book. This is some corroborating evidence, in my opinion.

I don't know a lot about finite automata but this whole display has shown that Alex Smith is talented but not the winner of the prize, it's best to accept and seek out all criticisms from your community before publishing & Wolfram is not the genius he makes himself out to be. I don't believe I will ever read "A New Kind of Science" as I have many other books in front of that one on my list.

Sounds like just another step in the learning process for Alex--too bad about the cash but he is only 20 and from the looks of it has a bright and promising future. Quite the embarrassment for Wolfram, however.

The real kicker would be if Wolfram had asked his staff to review the proof and they knew it had an elementary mistake and had told him it was golden. Now that would be poetic justice.

Vaughn Pratt is confused

[evgalois]

No, Vaughn Pratt is confused. There is a post from on the FOM mailing list that explains the confusion. There are subtle issues concerning the nature of computational universality in the presence of infinite initial conditions. Vaughn Pratt is probably remembering work from the 1950s on computational universality, which does not address these issues. There are different definitions that could be given for computational universality with infinite initial conditions. Alex Smith's proof was verified with a particular, natural, definition that was chosen for the prize. So all is well. The 2,3 Turing machine's universality has not been toppled with one email and the personal opinion of Vaughn Pratt. What has happened, though, is that questions that have not been discussed since the 1950s are (this week) back in vogue again.

Re:Vaughn Pratt is confused

[evgalois]

Here is the explanation about the suposed "flaw", which of course it is not: http://forum.wolframscience.com/showthread.php?s=&threadid=1472 And my comments on the guy that thinks that the universality definition was changed for the prize benefit (I am surprised about how many people write about this without knowing a bit of the subject and trying to sound technical talking about "AND gates" completely nonsense): Concerning the definition of universality, a halting state or halting instruction wasn't a requirement. This is a common usage nowadays in the field of small universal Turing machines, which is a generalization of previous definitions. If there is no clear definition is because there is no clear-cut, established procedure to determine when an initial condition is computationally simple enough to be acceptable. Some would wish universal computation stick to a finite initial condition with an unbounded tape filled with "blanks", because that's the only case where the theory is entirely clear. However, others accept generalizations such as periodic "blank" words as long as they remain computationally simple enough (possibly generated in the same fashion as an unbounded "blank" tape). So Alex Smith's use of a non-periodic but still sufficiently computationally simple background is a natural generalization of this sort. The key point is that the background can be set up without doing universal computation, so the 2,3 machine itself actually carries out the computation. We are glad that this is making a contribution to the discussion on universality. We expect that others will further clarify what Alex Smith has done. We particularly hope that his methods can be extended to other similar proofs.

Give Wolfram some credit

[Starky]

I have heard time and time again on Slashdot that Wolfram just took other people's work, that he had people working underneath him & that he didn't actually know what he was talking about in his book. This is some corroborating evidence, in my opinion.

Hardly. Wolfram disappeared for a decade to produce A New Kind of Science. Was he picking his toes while his team of crack Mathematica techies were developing the ideas for the book? I find that hard to believe. In fact, the way I heard it, he did all of his own editing on the book, much to the dismay of some who found it in need of editing.

He probably did have staffers assisting in running simulations (and with his bankroll, I would certainly entertain that notion myself), but name me one prominent professor who hasn't stood on the shoulders of graduate students.

Whether you consider him a genius or a crackpot (and he certainly gives reason to entertain both opinions), Wolfram is undoubtedly brilliant and seems to be dedicated to the advancement of mathematical ideas that he considers to be important. It hardly seems that a lack of academic integrity would be consistent with his actions to date.

Whether history will ultimately judge him a genius or a crackpot, I would guess that he has done more to advance mathematics than all the posters to this article combined, myself included. So give the man some credit.

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