On 10/03/11 14:10, Bruno Marchal wrote:

On 10 Mar 2011, at 13:47, Andrew Soltau wrote:

All the moments exist, and as Deutsch points out, as you summarise, 'The appearance of change is already explained by the fact that there are different frames that have an implicit sequence and in which the observers state is different', but for change to actually happen, the magic finger must move. Otherwise reality would be like a movie film sitting in the can in storage.

The change in the "working program" is brought by the "universal machine" which interprets it.
Yes, but you still require an explanation of how the machine actually runs. All possible states of the machine exist 'already' in an arithmetical universe.
All you need is an initial universal "machine". It happens that addition and multiplication, with first order logic is enough to define such an initial universal system, and the UDA+MGA shows that the laws of mind, including the laws of matter, does not depend on the choice of the initial universal system.

So elementary arithmetic does emulate, in the mathematical sense, computations.
Naturally. But you still require an explanation of how such arithmetic, or how such computations, are carried out. This is where you need an 'external' time.
Arithmetic does not just describe all those computations: it literally emulate them. This is not trivial to show, although computer science gives the insight. Computations in arithmetic are not like movie, they are like a observer line universe in a block universe.
Ok. And you still require an explanation of how something moves along the line. This is what is missing from physics. It is inherently absent in any concept of straightforward existence.

To add an external time reintroduces a mystery where it is not needed.
Provided you can explain how we come to be experiencing change, in other words, how it comes to be that the computation is running, as opposed to simply existing.
That use of time is like the use of "God" as gap explanation by the pseudo-religious (authoritative) people. You will end up with a primitive time, a primitive matter, and why not a primitive "god" responsible for all this.

That is, in my opinion, the correct insight of Deutsch.
In which case you have to accept that the passage of time is an illusion. In this case, you are not a being which witnesses change. You are simply, at each moment in time, that which exists at that moment in time, and has the illusion, at that moment in time, that you have existed at other moments in time. Objectively this is unassailable. Subjectively I personally, for one, consider that it does not account for my experience.

I don't really think that there is a lot more one can say about it.
Except that he mentions an "implicit sequence", which is typically made explicit by the universal machine which emulates, albeit statically or arithmetically-realistically, the computation. All computations in that setting are ultimately based on the explicit sequence 0, s(0), s(s(0)), ... (or the equivalent in the combinators, etc.).
How the sequence is defined, and whether it is fundamentally physical or arithmetical, is of no consequence to this - admittedly highly philosophical - point.



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