Georges Quénot wrote:
> peterdjones wrote:
> >
> > Georges Quénot wrote:
> >> peterdjones wrote:
> >>> [...]
> >>> (To put it another way: the point is to explain
> >>> experience. Physicalism explains non-experience
> >>> of HP universes by saying they don't exist. MM appeals
> >>> to ad-hoc hypotheses about non-interaction. All explanations
> >>> have to end somewhere. The question is how many
> >>> unexplained assumptions there are).
> >> I would like to understand your view. How do *you* solve
> >> the "HP universe" problem? In your view of things, amongst
> >> all the mathematical objects to which a universe could be
> >> isomorphic to, *what* does make only one (or a few) "exist"
> >> or "be real" or "be physical" or "be instanciated" and all
> >> others not?
> >
> > In your view, what means that only mathematical objects exist ?
> I can try to answer to this but I do not see how it helps
> to answer my question. It is hard to explain what it means
> to someone that resist the idea (that must be like trying
> to explain a mystic experience to a non believer).
> It is just the idea that there could be no difference between
> mathematical existence and physical existence.

Then why do we use two different words (mathematical and physical)  ?

> I would say
> that it

"it" meaning mathematical existence IS different to physical existence.

> makes sense only in the case in which the three other
> mentionned conjectures also make sense and could be true.

I don't see why the mathematical realism needs to be true.
The difference between mathematical existence and physical
existence could consist in physical things exisitng, and mathematical
objects not exisiting.

> I believe that we have a diffculty here because we have very
> different intuitions about what mathematical objects can be
> and about what a mathematical object corresponding to a
> universe hosting conscious beings could look like. I already
> mentionned three possibilities to deal with the HP universe
> "problem" in this context. I understood that it did not make
> it for you because of this difference between our intuitions.
> > All explanations stop somewhere. The question is whether they
> > succeed in explaining experience.
> Do you mean that it is "just so" that the "mathematical
> object" that is isomorph to our universe is "instantiated"
> and that the "mathematical objects" that would be isomorph
> to HP universes are not?

We can go some way to explaining the non-existence
of HP universes by their requiring a more complex
set of laws ( where "we" are believers in physical
realism). However, we are bound to end up with
physical laws being "just so". However -- so every
other explanation ends up with a "just so". In physical
MWI it is just so that the SWE delimits the range of possible
universes. In Barbour's theory it is just so that Platonia
consists of every possible 3-dimensional configuration of
matter, not every 7dimensional one, or n-dimensional one.
In Mathematical Monism, it is just so that , while very mathematical
object exists, no non-mathematical object exists.

> Isn't that a bit ad'hoc? Does it explain anything at all?
> >> Also, you reject "mathematical monism" as not making sense
> >> for you but what about the ohter conjectures I mentionned?
> >> Do you find that "physical monism" ("mind emerges from
> >> matter activity"), "mathematical realism" ("mathematical
> >> objects exist by themselves") and "Tegmark's hypothesis"
> >> ("our universe is isomorphic to a mathematical object",
> >> though Tegmark might no be the first to propose the idea)
> >> make sense? Have some chance of being true?
> >
> >> Do you find that "physical monism" ("mind emerges from
> > matter activity"),
> >
> > All the evidence points to this.
> OK. So in your view this makes sense and is likeky to be true.

Those are two different claim: it is likely to be true,
but seeing *how* it is true, making sense of it is the Hard Problem.
IMO the hardest part of the hard problem is seeing how mind
emerges from mathematical description -- from physics in the
"map" sense, rathert than the "territory" sense. Switching to
a maths-only metaphysics can only make the Hard Problem harder.

> Evidence is also that a lot of people resist physical monism
> just as you resist mathematical monism.

Under my analysis the problem with physical monism is
reification (confusion of map with territory) of the maths!

> >> "mathematical realism" ("mathematical objects exist by themselves")
> >
> > Not supported by empirical evidence; not needed to explain
> > the epistemic objectivity of mathematics.
> That could be a language problem. In my view, what I was
> thinking of is likely to be equivalent to the "epistemic
> objectivity of mathematics" in your view.

"Epistemic objectivity of maths" means "every competent mathematician
gets the same answer to a given problem". It doesn't say anything about
the existence of anything (except possibly mathematicians).

> >> and "Tegmark's hypothesis"
> >> ("our universe is isomorphic to a mathematical object",
> >
> > Must be at least partially true, or physics would not work,
> Partially is not of much help in this context. Th question is
> whether it can/could be *fully/absolutely* true.

Even if it is *fully* true, isomorphism is **not** identity!

> Georges.

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