On 07-10-2015 12:52, Bruno Marchal wrote:
On 07 Oct 2015, at 05:11, smitra wrote:
On 07-10-2015 02:04, Brent Meeker wrote:
On 10/6/2015 4:35 PM, smitra wrote:
On 07-10-2015 00:06, Bruce Kellett wrote:
On 7/10/2015 7:51 am, Brent Meeker wrote:
On 10/6/2015 1:18 PM, Stathis Papaioannou wrote:
I'm not sure I understand what you are getting at. I meant that
if the normal sequence of brain states is s1-s2-s3 with
corresponding mental states m1-m2-m3 and s2 is omitted, there is
nothing in m3 to give any indication of the discontinuity. Of
course, normally s2 is necessary in order to generate s1, but
that doesn't change the argument.
But I think that's wrong. Brains are not like ideal von Neumann
computers or Turing machines that have "brain states"
corresponding to "mental states". If you simulated a brain
using a computer you would find that an enormous number of "brain
states" were required to instantiate a single conscious thought
and furthermore the brains states necessary for one thought
overlapped with those necessary for the next thought. So this
overlap at the low level is part of the physical continuity
needed for consciousness. The fact that the physics can be
simulated by discrete computation doesn't imply that the
conscious states are discrete.
I think that is an important insight, Brent. One thing that it
means
is that two brains can, by chance, be in the same physical state at
one instant, but those two brains might be supporting quite
different
thought processes. The consequence is that there is one person per
brain -- the same person can't be spread over several brains.
Bruce
That's impossible, two identical physical states within an isolated
system will yield the same (statistical) results when measured. So,
if one person would be experiencing something different compared to
the other person at that very instant then, by definition, they
were not in the same physical state at that very moment, because
that's how we define physical states to begin with.
No, the contention is that a physical state, a state that obtains at
a
single moment (Planck time?), does not instantiate a thought or an
experience. A thought or experience requires a sequence many
physical
states and having two sequences share some subsequence of states is
not enough to make the two experiences the same. Consider an
airport:
the fact that two runways cross doesn't make them the same runway.
Brent
Yes, this is the "observer moment problem" discussed a long time ago
in this list, but the requirement of needing a sequence of states is
also problematic, because at any given time I'm a conscious being.
This paradox is related to the well known paradox where one argues
that you can map the states of the brain of a person as it evolves in
time to that of a clock and then ask why the clock isn't conscious.
Of course, the clock doesn't perform any computations, but to see
this you have to consider the counterfactual inputs and the
corresponding counterfactual outputs. Then as I've argued here one
or two years ago, a much better solution is to invoke the MWI. Given
your conscious experience, your brain can still be in an
astronomically large number of states. So, instead of identifying
yourself with the single branch, you should consider the very large
bundle branches that contain the same macroscopic information.
The superposition of these states describes a person that is
entangled with the environment. This entanglement contains the
counterfactuals that you need to define what computation is performed
at any given moment.
But invoking the environment makes this a messy way out, a better way
i.m.o. is to include one computational step, you identify the
operator:
O = sum over inputs i of |output(i)><i|
as your observer moment . The summation is over states that fall
within your resolution, and this then partially defines a computation.
Physical computations?
You don't need physical counterfactuals to define what is a
computation. You do need the right logic of the counterfactual to have
a notion of first person sharable matter. But that exists in
arithmetic, using the standard, non physical, notion of computations
by Church, Turing, ...
But any observer that arises from such a deeper theory will presumably
find himself in what looks to him a physical world free of paradoxes...
Saibal
Bruno
Saibal
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