Hi Bruno and Friends,
I have some comments and questions interleaved below.
----- Original Message -----
From: Bruno Marchal
To: [email protected]
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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