Re: Is the universe computable

From: Stephen Paul King <>
Date: Tue, 27 Jan 2004 11:57:35 -0500

Dear Bruno,

    Thank you for this post. It gives me a chance to reintroduce one problem that I have with your model. Like you, I am very interested in comments from others, as it could very well be that I am misunderstanding some subtle detail of your thesis.

    You wrote:

"... remembering the comp 1-indeterminacy, that is that if you are duplicate
into an exemplary at Sidney and another at Pekin, your actual
expectation is indeterminate and can be captured by some measure,
let us say P = 1/2, and this (capital point) independently of the time
chosen for any of each reconstitution (at Pekin or Sidney), giving that the
delays of reconstitution cannot be perceived (recorded by the first person))."

    Now my problem is that IF there is any aspect of perception and/or "observers" that involves a quantum mechanical state there will be the need to take the "no-cloning" theorem into account. For example, we find in the following paper a discussion of this theorem and its consequences for teleportation:

    As a possible way to exploit a potential loop hole in this, I point you to the following:

    My main question boils down to this: Does Comp 1-determinacy require this duplication to be exact? Is it sufficient that
approximately similar copies could be generated and not exact duplicates?

    How would this affect your ideas about measures, if at all?

    I understand that you are trying to derive QM from Comp and thus might not see the applicability of my question, but as a reply to this I will again point your to the various papers that have been written showing that it is impossible to embed or describe completely a QM system (and its logics) using only a classical system (and its logics), if that QM system has more that two Hilbert space dimensions associated. Start with the Kochen-Specker theorem...

    I will address Kory's post latter.

Kindest regards,


  ----- Original Message -----
  From: Bruno Marchal
  Sent: Tuesday, January 27, 2004 10:46 AM
  Subject: Re: Is the universe computable

  Hi Kory, Hi Stephen, Hi All,

  I understand Kory very well and believe he argues correctly in this
  post with respect to Stephen.
  But at the same time, I pretend that if we follow Kory's form of
  reasoning we are lead to expect a relation with (quantum) physics.

  This can seem a total miracle, ... but only for someone being both
  computationnalist and physicalist, and that has been showed
  impossible (marchal 88, Maudlin 89, ref in my thesis).

  Let me try to explain shortly.

  The reason is that if the initial CA is universal enough the (and that
  follows for theoretical computer science) "universal CA" will
  dovetail on an infinite number of similar computations passing through
  each possible SAS computational state, and then ...

  ... remembering the comp 1-indeterminacy, that is that if you are duplicate
  into an exemplary at Sidney and another at Pekin, your actual
  expectation is indeterminate and can be captured by some measure,
  let us say P = 1/2, and this (capital point) independently of the time
  chosen for any of each reconstitution (at Pekin or Sidney), giving that the
  delays of
   reconstitution cannot be perceived (recorded by the first person)).

  So if we run an universal dovetailer (implemented in CA, or FORTRAN,
  or even just arithmetical truth), each SAS will have an indeterminate futur
  and his/her/its expectation (from his 1-person pov) will be given by
  a measure on all its computational continuation, runned, or even just defined,
  in the complete procession of the universal CA.

  Now, that measure on those computations must fit the SAS's physical law,
  if not the SAS will correctly infer that comp is false, which, we know,
  must be true (we runned the CA, for exemple).
  So the physical laws must result from a relative (conditional to a state S) measure
  on all computations continuing S. (and actually this looks like Feynman formulation
  of QM).

  OK, I was short, please look at (where UDA = Universal Dovetailer Argument)

  UDA step 1
  UDA step 2-6
  UDA step 7 8
  UDA step 9 10
  UDA last question
  Joel 1-2-3
  Re: UDA...
  Joel's nagging question

  for previous post where I explain the thing step by step;

  or look at

  For a one-post presentation of the argument.

  I would be very interested if you, or anyone in the list (btw apology for
  the minority who would have already see the point), could tell me at which
  step of the reasoning you would disagree (in either presentation).

  Kind Regards,


  At 01:19 27/01/04 -0500, Kory Heath wrote:

    At 1/26/04, Stephen Paul King wrote:

      The modern incarnation of this is the so-called
      4D cube model of the universe. Again, these ideas only work for those who
      are willing to completely ignore the facts of computational complexity and
      the Heisenberg Uncertainty principle.

    I think you and I are living in two completely different argument-universes here. :) I'm not arguing that our universe is computable. I'm not arguing that our universe can definitely be modeled as a 4D cube. I'm not arguing that only integers exist. The only reason why I keep using CA models is that they're extraordinarily easy to picture and understand, *and*, since I believe that SASs can exist even in very simple computable universes like CAs, it makes sense to use CA models when trying to probe certain philosophical questions about SASs, physical existence, and instantiation. Quantum physics and the Heisenberg Uncertainty principle are simply irrelevant to the particular philosophical questions that I'm concerned with.

    Forget about our own (potentially non-computable) universe for a second. Surely you agree that we can imagine some large-but-finite 3+1D CA (it doesn't have to be anything like our own universe) in which the state of each bit is dependent on the states of neighboring bits one tick in the "future" as well as one tick in the "past". Surely you agree that we could search through all the possible 4D cube bit-strings, discarding those that don't follow our rule. (This would take a Vast amount of computation, but that's irrelevant to the particular questions I'm interested in.) Some of the 4D cubes that we're left with will (assuming we've chosen a good rule for our CA) contain patterns that look all the world like SASs, moving through their world, reacting to their environment, having a sense of passing time, etc.

    This simple thought experiment generates some fascinating philosophical questions. Are those SASs actually conscious? If so, at what point did they become conscious? Was it at the moment that our testing algorithm decided that that particular 4D block followed our specified CA rule? Or is it later, when we "animate" portions of the 4D block so that we can watch events unfold in "realtime"? These are not rhetorical questions - I'd really like to hear your answers, because it might help me get a handle on your position. (I'd like to hear other people's answers as well, because I think it's a fascinating problem.)

    Anyway, the point that I'm really trying to make is that, while these thought experiments have a lot of bearing on the question of mathematical existence vs. physical existence, they have nothing at all to do with quantum physics or Heisenberg uncertainty. The fact it seems so to you makes me think that we're not even talking about the same problem.

    -- Kory
Received on Tue Jan 27 2004 - 12:26:52 PST

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