On 25 May 2015, at 03:27, meekerdb wrote:
On 5/24/2015 5:05 AM, Pierz wrote:
On Sunday, May 24, 2015 at 4:02:42 PM UTC+10, Brent wrote:
On 5/23/2015 9:58 PM, Pierz wrote:
On Saturday, May 23, 2015 at 8:36:40 PM UTC+10, Liz R wrote:
I'm not sure why comp would predict that physical laws are
invariant for all observers. I can see that it would lead to a
sort of super-anthropic-selection effect, but surely all possible
observers should exist somewhere in arithmetic, including ones who
observe different physics (that is compatible with their
existence) ?
I really must dig up the old thread! But I'm not saying comp does
entail invariant physics for all observers, just that if there are
different physics, the substitution level must be very low indeed.
Think of the original scenario in the UDA: a person
in Washington is suddenly annihilated, and then
duplicated in Helsinki and Moscow (or whatever). That operation
creates a 50% probability of finding oneself in Helsinki or
Moscow. But the ultimate point of the UDA is that one's actual
probability of finding oneself in Helsinki or Washington depends
on the total measure of all virtual environments within which that
observer is instantiated in an environment that looks like one of
those cities. One can't isolate a particular virtual system from
the trace of the UD. So you can't create an arbitrary physics in
an environment that looks like either city (or anywhere). Well you
can, but any observer will always find their own physics to be the
measure of *all* their continuations in arithmetic. So there can't
be an environment that is like Helsinki or Moscow at some point
but that has different physical laws. Carry this logic over to the
scenario of a person standing in an empty room - the physics the
person experiences will be the measure of all
such identical persons standing in empty rooms.
"Experiencing physics" I think needs some explication. If
experiencing only refers to consciously thinking propositions, then
one may not be experiencing much physics: the world seems 3D with
colors, there's a mild temperature, air smells OK,... One doesn't
directly, consciously experience the 2nd law, or the Born rule.
The "laws of physics" are human inventions to describe and predict
events. They're not out there in Nature; which is why we have to
revise them from time to time as we find more comprehensive, more
accurate "laws".
OK, but it doesn't seem relevant to the argument. We experience a
world predictable and stable in certain ways that, now we're so
sophisticated, we formalise into the science of physics. Bruno's
claim is that these regularities are not intrinsic properties of
some primary stuff, but emergent from the computational properties
of observers - namely how often various continuations of those
observers crop up relatively to one another in the abstract space
of all possible continuations. I'm trying to make an admittedly
difficult point about whether or not observers in different places
can experience different physics within this paradigm, and if so,
how that relates to "substitution level". If you're worried about
people "experiencing physics" let's just concentrate on observers
who go to the trouble of doing physics experiments. It really
doesn't matter.
My point was that most people's conscious experience most of the
time could be accommodated within a large range of physics. For
example Newtonian physics seems intuitive while quantum mechanics
isn't; but we think QM is the better theory. But Bruno claims that
his theory implies QM and not Newtonian mechanics. So if people
consciously experienced a Newtonian universe (which they once
thought they did) would that falsify comp or would it just imply
that the UD can instantiate Newtonian universes.
Which it can't. So, a Newtonian universe would have refute comp, and
indeed even locality as the Newtonian universe is not local. But of
course, a computationalist could say, that the "newtonian character is
illusory, and that by looking closer we will discover ... something
like QM.
Without Everett, I am not sure I would dare to defend the plausibility
of the comp's consequences, especially with the quantum logic provided
by the Theaetetus' definitions. Booleanity is not recovered in any
points of view, but truth and proofs. All the material and
"psychological" hypostases are non boolean.
Bruno
Brent
The question here is what constitutes the observer? How detailed
would a simulation of me have to be before it became a subjective
duplicate of me, its continuations my continuations? If there is a
person A somewhere in the UD who is experiencing an empty room
with physics A, and another identically configured person B
somewhere else experiencing physics B, what is stopping the
continuations of A mixing with the continuations of B, so that the
measures combine into a merged physics? There has to be something
in both observers' computational states that distinguishes them
sufficiently that their experiences cannot interfere with one
another - the comp equivalent of decoherence. (In fact if QM
effects are the manifestation of UD observer measures, the
threshold at which these effects start to kick in should probably
give us a strong clue about how low the substitution level is!)
Observers and their experiences, including physical laws, can't be
kept apart by physical or temporal space, but only by differences
in the computational states that define them. Physics is emergent
from the computational properties of observers, and therefore any
difference in physics experienced by different observers is a
function of their mathematical configuration. If we find that
there are observers in other universes who experience different
physics, then it must be the case that the substitution level for
those observers includes their entire universe.
That said, if I recall our previous discussion correctly, Bruno
disfavoured the idea of different physics for different observers.
He seems to believe it should indeed be invariant.
That position appears to me to be at odds with the direction of
modern cosmology.
That would seem to depend on how different. Modern cosmology
naturally builds on quantum field theory, so it starts with the
hypothesis the QFT applies, but possibly with different values of
those parameters we attribute to symmetry breaking (i.e. random).
Yeah. I mean the ultimate underlying unity and coherence of reality
is surely a given, so go deep enough and of course there is only
one law that applies to all observers. But at issue is whether
quite different apparent physics (say, the elements and their
properties, or the masses of particles) is possible without the
substitution level being super-duper low. It seems to me not, and I
believe Bruno agreed, though I may have misunderstood. No-one seems
to be addressing that question.
Brent
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