Re: Decision theory

From: Jacques M Mallah <>
Date: Sun, 3 Jan 1999 16:40:19 -0500

On Fri, 1 Jan 1999, Wei Dai wrote:
> I agree with many of the points you made, but the fact remains
> that we still have no formal decision theory that is compatible with a
> physical theory with no free parameters. There are many possible
> approaches to try to solve this problem, and I hope you agree now that
> there is really a problem to be solved. The impossibility of self-modeling
> is one possible approach, but I'm not sure how to formalize it in
> the context of a decision theory either.

        No, I do not see a problem.
        In the usual case, to make a decision I consider different
scenarios, which I can model using a physical theory and treating the
decision to be made as a free parameter.
        Even if I believe in a theory with no free parameters, there will
never be any reason I can't use that algorithm.
        The only difference is that the scenarios not chosen are
unphysical for a different reason than before: due to the laws and not
just the actual parameters. Despite that, no matter how much physics I
know or how much calculation I do, there is no danger that I can tell a
priori which ones are inconsistent until I make the decision.
        This means that I must be using approximations, but that is also
guaranteed to be so even in a theory with free parameters.

> Why do you not believe in a theory with no free parameters?
> (And what do you mean by "not believe in"? You don't think such a
> theory can be self-consistent, or you don't believe such a theory can
> be true?) What about the theory I proposed?

        As I explained before, I don't see how a theory that includes 'all
possible structures' can have no free parameters.
        One reason theories with no free parameters are of interest is
that quantum gravity may turn out to be such a theory. It would however
be strange if other mathematical structures don't also exist.
        In part, the definition of a free parameter is arbritrary. Any
theory can be viewed as a special case of some set of theories. The
important thing is really the information content of a theory, and I don't
think it can be zero.
        As for your proposal, from what I recall of it - and you may want
to redescribe it under a seperate thread subject - it did not seem that
plausible to me, possibly because I did not get the impression that it
dealt with programs actually being implemented instead of just sitting

                         - - - - - - -
              Jacques Mallah (
       Graduate Student / Many Worlder / Devil's Advocate
"I know what no one else knows" - 'Runaway Train', Soul Asylum
            My URL:
Received on Sun Jan 03 1999 - 13:45:26 PST

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