Hi Bruno and Friends,
I have some comments and questions interleaved below.
----- Original Message -----
From: Bruno Marchal
To: everything-list.domain.name.hidden
Sent: Friday, December 19, 2008 2:56 PM
Subject: Re: Time
Hi Abram,
I agree mostly with Brent's reply. Other precision should appear in my explanation of the UDA to Kim, and in my answer to Ronald (Sunday).
I will just add general remarks to Brent's reply.
Le 19-déc.-08, à 00:18, Abram Demski a écrit :
[Sorry if this is a duplicate, I think that I did not send correctly the first time.]
Bruno, everyone,
I've decided that it will be more productive/entertaining to post my various concerns as a new topic.
What is time?
Third person sharable time could be an illusion. It seems to me that QM + General Relativity could lead to the idea that there is no real "physical time". With MEC this is a direct consequence of the UDA.
[SPK]
Is this conclusion following ideas like those of Julian Barbour? Lee Smolin in several papers thas shown quite convinsingly that Barbour's theory has some serious problems. For instance see:
http://arxiv.org/PS_cache/gr-qc/pdf/0104/0104097v1.pdf
snip
If there is a physical universe, then is there some sort of basic physical connection behind time?
Open and difficult problem for the physics you can extract from comp. Of course, if there is a primary physical universe, we have to resolve the problem of marrying QM and GR before being able to answer your question. Very difficult question.
[SPK]
How are we sure that GR needs to be "quantized" at all? We have, with QM, a very good theory covering all notions of "interactions" in terms of their energy, charge, spin, etc; why is it necessary to "quantize" geometry? What is geometry is a derivative quantity and not a primitive? After all, In Bruno's model our observed universe is derived from NUMBERS...
If the universe is mathematical in nature, then what is the mathematical connection between moments? What sort of mathematical connection counts as time?
I would say that it is logic-mathematical connections. With MEC those relations eventually originates with the natural number successor relation.
I will say a bit more sunday in my answer to Ronaheld. The problem is that it is hard not being a bit technical here. You have to understand the mathematical concept of computation, and then to understand that those computations exists in arithmetic, and indeed are accessible through proof in a very tiny part of arithmetic: the theorems of Robinson Arithmetic (RA). RA is Peano Arithmetic *without* the induction axioms.
PA is the lobian machine. And RA generated all the histories which notably contain all the Lobian machines. RA simulates PA like I can simulate Einstein's brain, or a Chinese brain. This is a subtle point where people do sometimes the Error of Searle with his Chinese Room.
[SPK]
Here is where I have a serious difficulty with Bruno's idea (all the while I must admit that I am in awe of its elegance) it is the fact that all notions of "observable" quantities in QM are coded in terms of complex numbers (
http://en.wikipedia.org/wiki/Complex_number ) as "amplitutes" (
http://en.wikipedia.org/wiki/Amplitude)- which have no notion of a unique successor relation - until after a particular notion of a physical world in introduced to allow for the operation of "reduction of the wavefunction" or what ever equivalent procedure implements the Born's rule:
http://en.wikipedia.org/wiki/Born_Rule
Thus QM tells us that the Universe is Complex valued and thus we have a severe problem in that there is no unique and a priori ordering of events from which to derive a first person notion of time or a "flow of events".
If (as was recently suggested, in connection with relativity) time cannot really be divided into individual moments, then what is it?
It is an ordering on machine knowledge states, and/or observation states. It is a very complex ordered structure (should be isomorphic to the lattice of open sets in a complex topological space and/or Hilbert Space). I approach the math of those spaces with the modal logic of self-reference and their intensional variants.
[SPK]
Does not this property of being " isomorphic to the lattice of open sets in a complex topological space and/or Hilbert Space" make my point that there does not exist a unique ordering?! A simple and visualizable proof of this is seen in that a 2 dimensional Euclidian Plane does not have a unique line or subset that would seperate one portion of the Plane from another; or in English: there does not exist a unique way to cut a piece of paper into two pieces.
Why do we experience time passing?
Each of our knowledge state are relative state generated by "a most probable computation" (generated by the UD, or living in arithmetic). Mainly by ignorance, we feel our knowledge being divided into a sort of past-certainty, and sort of future-uncertainty. Those things can be described by modal logic. I argue all those modal logic arise from self-reference in arithmetic.
[SPK]
But substituting an Asymetry between events for 1st person time does nothing to further our questions. Unless there is a means to derive a notion of a measure or an ordering from primitive arithmatic (that is not that of Natural numbers!) we are still where we started on this excursion. :(
Is it legitimate to think as if the next moment we experience will be chosen randomly in some sense?
Yes. I believe everyone in this list agree with this, but differ on the distribution law, the relative or absolute nature of the probabilities, and about the nature of the events on which the probability bears on.
In the case of comp, I argue (through UDA+AUDA) that our next experience is chosen randomly on the set of all computations going through our actual state which have been generated by the UD, or are "living" in that tiny arithmetic.
There are 2^aleph_0 histories. The measure should be non constructive (thus physics cannot be entirely described by a program or machine)
[SPK]
Given all of that, does there not still remain the need for a measure with which to "order" the histories? It almost seems that the nature of the isomorphism elaborated upon above leadws dirrectly to a "NoGo" theorem here... Since no unique ordering can exist on a complex
Does probability or randomness have a role to play in the flow of time?
I would say yes, given that once a universal machine observes itself it separates a growing "past" from a growing "future".
There is a sort of self-diffraction: the better a machine observes itself, the bigger is the set of possible futures (consistent continuations of computations) she gets.
[SPK]
Does this "self-diffraction" not relie in some way on some from of measure? If the measure is arbitrary and not derived, all we have, AFAIK, is an example of a random walk...
In connection with UDA: what is the meaning of a first-person
probability due to uncertainty of the future?
I will explain this soon to Kim. I suggest you ask in the case this remains unclear, or if you have objection. It is not possible to explain this shortly.
Is there any sense in which such estimates can be more or less accurate if all possible next moments do in fact occur?
All what we have to do consists in finding discrepancies between the theory and the observations. I bet QM is correct, so I tend to bet that the comp estimation of the possible moments will give the same estimation than QM. This would explain where QM comes from. This remains to be seen of course, but formally, preliminary modest results are going in that direction. Bits and Qubits comes from each other.
Hope this short answer to difficult questions can help. I will say more to Ronald Sunday, and I invite you to follow the KIM thread where I explain UDA. And perhaps then I can explain AUDA with the amount of technical details demanded.
Bruno
http://iridia.ulb.ac.be/~marchal/
[SPK]
I will continue to read the posts. ;)
Kindest regards,
Stephen
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Received on Fri Dec 19 2008 - 21:46:11 PST