peterdjones wrote:
 > Georges Quenot wrote:
 >> peterdjones wrote:
 >>> Georges Quénot wrote:
 >>>> 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) ?
 >> For various historical and practical reasons and because
 >> identity is still a conjecture/speculation. Just like we
 >> used to consider "inertial mass" and "gravitational mass".
 > So you meant "there might not be any difference",not "there cannot
 > possibly be any difference".

I meant "the idea is that it is possible that there is no
difference ...".

 >> it would be a
 >> "mathematical monism" in which one and only one particulat
 >> "mathematical object" would exist. This seems logically
 >> difficult and then: why just this one?
 > Why only mathematical objects and not any other kind ?

We were talking of mathematical objects and I asked why only
one of them would be "given" "physical existence" (as *you*

The question of whether there could be other type of objects
than mathematical is a different one. I can figure what could
mathematical objects and that they can exist (though I am
afraid I cannot easily transmit that feeling). It is harder
for me to imagine what non mathematical objects could be and
how/why they happened to come to existence. Did some God pull
them out of nothingness?

 >>> 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).
 >> Whether HP universes require or not a more complex set
 >> of laws is a very good question but it seems unlikely
 >> that it can be easily answered. For some physicists,
 >> the currently known (or freseeable) set of rules and
 >> equations for our universe *is* compatible with "HP
 >> events".
 > Physical MWI is more constrained than mathematical
 > multiverse theories, so there is not so much Harry-Potterness.

This is just an opinion. It must refer to prejudices about
what physical MWI and mathematical multiverse theories could
or could not be.

 > Moreover,
 > physical MWIs have measure and can at least predict the HP
 > universes will be rare  (or faint, or something).

This question of measure is difficult but I see no reason
why this should differ between physical MWI and mathematical
multiverse theories.

 >> Such events might appear in other portions of
 >> our universe. For others, it is just the opposite, it
 >> might well be that there do not exist any set of rules
 >> and equations that would correspond to a "HP universe".
 > There cannot fail to be. The HP game my nephew
 > plays on is a mathematical simulation -- what else
 > could it be?

I am not sure that what your nephew plays with is a rich
enough mathematical description so that, even if it was
"turned physical" by some God or magician, it would contain
conscious beings. Furthermore, most of this HP universe is
in the brain of your nephew. What is in the game would be
almost nothing without your nephew's imagination to fill
the (huge) gaps.

 >>> However, we are bound to end up with
 >>> physical laws being "just so".
 >> Not really. What is "just so" is that a conscious being
 >> has to live in only one universe at once just as he has
 >> to live in only one place and in only one period of time
 >> at once.
 > That does not follow form the mathematical
 > hypothesis. If I am a set, I am a subset of any
 > number of other sets. If I am a digit-string, I a m a
 > substring of any number of other substrings.

This is where we have a different intuition about what
mathematical objects can be and what a mathematical object
containing (description of) conscious beings might be. For
me this is just like you have to live here and now and not
in Egypt 3500 years ago. What "aspect" of a mathematical
object I could be is not so clear to me but it is unlikely
to be as trivial as a digit string.

 >> It is no more mysterious that I do not live
 >> Harry Potter's life that I do not live Akenaton's life.
 > From the common-sense POV, yes. From the MM POV, no.

Maybe there is more than one MM POV. MM does not really
have POV. You and I have POV on what MM can or cannot be.
And they do differ.

 >> And lots of "HP-like" events have also been reported in
 >> *this* world.
 > Nowhere near enough! (compared to what MM predicts).

MM does not predict. You do and I do from our respective
interpretations of what MM could or should be (or not).

 >>>>>> 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, rather than the "territory" sense. Switching to
 >>> a maths-only metaphysics can only make the Hard Problem harder.
 >> As I perceive it, this is the hard problem even starting
 >> with a (classical) physical context. A I perceive it also
 >> placing it in a mathematical context doesn't make it harder
 >> or easier. But this is just from my viewpoint indeed.
 > You didn't say why it doesn't change anything.

I mean that whatever there might be in particles to make
them real is irrelevant to the question since (this is a
conjecture) all that is needed to determine the behavior
of particles is the set of rules and equation they have
to follow. What they are made of (if any) has no influence
on that.

 > I think
 > that having a richer ontology automatically makes it easier
 > to solve metaphysical problems, since you can say that X , Y or Z
 > is intrinsic to the universe and therefore not to be "explained away"
 > as something else. Of course, this manoeuvre should be used sparingly.
 > An intrinsic theory of heat would have been dead wrong.

As long as what is inside particle has no effect on the
particle behavior I do not see how it can help to understand
how sets of interacting particles (this is an image) can
produce consciousness.

 >>> "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).
 >> Well, if "every competent mathematician gets the same answer
 >> to a given problem", "competent mathematicians" do not have
 >> much freedom about what they might find as an answer to some
 >> given problems. So there must "exist" "something" that
 >> "constrain" them.
 > Yes: rules, the principle of non-contradiction.

So. These exist for you too? Are they physical objects?

 >> And "this" might even exist in the absence
 >> of "competent mathematician".
 >>> isomorphism is **not** identity!
 >> This is obviously untrue: it might well be that not all
 >> isomorphisms are identity
 > then isomorphism is not identity,

I said "not all". I did not said "none of".

 > since identity is not mere overlap.

Identity is: "f(x) = x".
Isomorphism is: "f(a R b) = f(a) R f(b)".
I am sure you can make it.

 >> but, indeed, identity is always
 >> an isomorphism and, hence, at least *some* isomorphisms
 >> *can* be the identity.
 > can be, yes,

Yes. You finally got it. It *can* be.

 > but more is needed for MM than Tegmark's hypothesis.

This is a question of viewpoint. I would rather say that more
than Tegmark's hypothesis is needed for *something else* (or
something more) than MM.

Tegmark's hypothesis is indeed necessary. It might be that is
is not sufficient but is it necessary to postulate something
more? What can we explain better with something more? Apart
from just saying that "it must be richer, we should get more
out of it"?

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