On 13 May 2015, at 21:49, meekerdb wrote:
On 5/13/2015 8:49 AM, David Nyman wrote:
On 13 May 2015 at 14:53, Bruno Marchal <marc...@ulb.ac.be> wrote:
I think it is a good summary, yes. Thanks!
Building on that then, would you say that bodies and brains
(including of course our own) fall within the class of embedded
features of the machine's generalised 'physical environment'? Their
particular role being the relation between the 'knower' in platonia
and the environment in general. At a 'low' level, the comp
assumption is that the FPI results in a 'measure battle' yielding
a range of observable transformations (or continuations) consistent
with the Born probabilities (else comp is false). A physics
consistent with QM, in other words. But the expectation is also
that the knower itself maintains its capacity for physical
manifestation in relation to the transformed environment, in each
continuation, in order for the observations to occur.
BTW, Bruce made the point that the expected measure of the class of
such physically-consistent observations, against the background of
UD*, must be very close to zero. ISTM that this isn't really the
point (e.g. the expected measure of readable books in the Library
of Babel must also be close to zero). What seems more relevant is
the presumed lack of 'un-physical' observer -environment relations
(i.e. not only 'why no white rabbits?' but 'why physics?'). From
this perspective, the obvious difference between the Library of
Babel and UD* is that the former must be 'observed' externally
whereas the latter is conceived as yielding a view 'from within'.
Hence what must be justified is why our particular species of
internal observer - i.e. the kind capable of self-manifesting
within consistently 'physical' environments, should predominate.
As they say on TV, "This just in!"
Why Boltzmann Brains Don't Fluctuate Into Existence From the De
Sitter Vacuum
Kimberly K. Boddy, Sean M. Carroll, Jason Pollack
(Submitted on 11 May 2015)
Many modern cosmological scenarios feature large volumes of
spacetime in a de Sitter vacuum phase. Such models are said to be
faced with a "Boltzmann Brain problem" - the overwhelming majority
of observers with fixed local conditions are random fluctuations in
the de Sitter vacuum, rather than arising via thermodynamically
sensible evolution from a low-entropy past. We argue that this worry
can be straightforwardly avoided in the Many-Worlds (Everett)
approach to quantum mechanics, as long as the underlying Hilbert
space is infinite-dimensional. In that case, de Sitter settles into
a truly stationary quantum vacuum state. While there would be a
nonzero probability for observing Boltzmann-Brain-like fluctuations
in such a state, "observation" refers to a specific kind of
dynamical process that does not occur in the vacuum (which is, after
all, time-independent). Observers are necessarily out-of-equilibrium
physical systems, which are absent in the vacuum. Hence, the fact
that projection operators corresponding to states with observers in
them do not annihilate the vacuum does not imply that such observers
actually come into existence. The Boltzmann Brain problem is
therefore much less generic than has been supposed.
Good opportunity to recall the answer of the question asked in the
title of the thread:
What MGA explains is that the computationalist has not that option,
even if the winner will be that infinite but non robust physical
universe (weird but not yet shown comp impossible).
In the sigma_1 complete reality, you don't need to fluctuate to get
all brains, in infinitely many exemplars. Perhaps too much actually,
but that remains to be evaluated.
Note that the "quantum logics" Z1*, X1*, and S4Grz1 suggest infinite
dimensional (quasi-) Hilbert Space, technically.
For a very nice (but a bit technical) intro to quantum logic, see:
http://plato.stanford.edu/entries/qt-quantlog/
Bruno
arXiv:1505.02780v1 [hep-th]
Brent
David
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