Hi Bruno,

I had few questions regarding some of the things said in your post.

On Sat, Nov 19, 2011 at 3:49 AM, Bruno Marchal <marc...@ulb.ac.be> wrote:

> On 19 Nov 2011, at 03:02, Pierz wrote:
>  David Deutsch's idea
>> of a good explanation is one that closely matches the structure of the
>> thing it describes, allowing for little variation. The vast variation
>> in the possible worlds where UDA could be invoked makes it a bad
>> explanation, in those terms.
> You have just not (yet) understood the role of the 1/3 person pov
> distinction in the reasoning. UDA shows that physics is determined by a
> relative measure on computations. If this leads to predict that electron
> weight one ton then mechanism is disproved. UDA shows that physics is
> entirely reduce to computer science/number theory in a very specific and
> unique way (modulo a variation on the arithmetical definition of knowledge).

Couldn't the UD predict various computational histories and different types
laws of physics for different observers?  Of course the electron weighing a
ton might be ruled out from observation if such electrons are incompatible
with life, but I don't see that the UD could ever perfectly derive the laws
of physics if there are multiple computational histories compatible with
observers.  For example, might there be such histories that have observers
but no electrons at all?  I see the UD perhaps being used in the future to
derive a rough estimate of the probabilities for different common universes
observers might expect to find themselves in, but nothing definite.

>> This is not a problem for an Everett -type multiverse, in which the
>> universes are bound together by consistent physical laws which allow
>> one to speak of a proportion of universes in which event x occurs.
>> However, in a mathematical platonia where all possible calculations
>> occur, and nothing outside of them, there can be no such ordering
>> principle.
> If the Everett idea works, and is the solution, (which has not yet been
> completely proved) then the UDA conclusion is that the Everett simultion in
> the UD wins the "measure battle", and we HAVE to justify this from computer
> science alone.
More general physical principals like the Schrodinger equation might be
applicable to all observers if it is truly, as Russell staid, a theory of
observation.  But something like the weight of the electron, the
Gravitational constant are, in my mind, more properly considered local
properties rather than global principals.


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