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".
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).
Brent
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