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.
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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