Re: Errata (for "the origin of physical laws)

From: Hal Ruhl <>
Date: Fri, 24 Sep 2004 13:58:32 -0400

I once saw a quote attributed to Niels Bohr to the effect that an expert is
a person who has made all the mistakes its possible to make in a narrow
field of endeavor.


At 07:11 AM 9/24/2004, you wrote:
>The curious and amusing thing is that in FU, Smullyan
>call that error the "beginners error" (page 46).
>It consists in believing that the formula (a-> -b) & (a -> b) is
>a contradiction, where actually the formula is true in case a is false.
>A simpler example is (p-> -p). This is true for p false.
>What is curious and amusing is that Smullyan made that very error
>page 42 (of the first edition, and it is wrongly corrected in the second
>edition). Can you see it.
>Morality: consistent machines *can* be inconsistent,
>as any Loebian machine believes (-Bf -> -B- Bf).
>Well; that is neither a justification nor a consolation ...
>At 12:26 23/09/04 +0200, Bruno Marchal wrote:
>>In the second paragraph of the "physics and sensations" section
>>of my paper "the origin of physical laws and sensations" I made
>>a rather stupid error (what a shame!).
>>Indeed I say "Note that neither G nor G* does prove it
>>[where it is for Bp -> -B-p]". This is ridiculous, because
>>G* proves Bp->p, for any p, and thus G* proves B-p -> -p,
>>and thus (by contraposition) G* proves p->-B-p, and by
>>propositional calculus Bp->-B-p.
>>Worst, my justification was that Bf->B-f (where f = false).
>>This is correct, but I infer from that that Bf->-B-f is not provable by G*.
>>But G* proves both Bf->B-f and Bf->-B-f, that is Bf->f.
>>The error has no consequences for the rest of the paper, but
>>still, why did I wrote that???
>>Please, don't hesitate to ask ANY questions, so that perhaps
>>other errors will be single out.
>>You can also propose more general
>>critics. Don't be shy. (You can also ask questions about FU).
Received on Fri Sep 24 2004 - 19:05:28 PDT

This archive was generated by hypermail 2.3.0 : Fri Feb 16 2018 - 13:20:10 PST