On Apr 20, 6:10 pm, Russell Standish <li....domain.name.hidden> wrote:
> On Sun, Apr 20, 2008 at 01:20:21PM -0700, Tom Caylor wrote:
>
> > Except that the evidence seems to support that our past is also
> > recorded in a reality "out there" that seems independent of our
> > brains. For example when we are reminded of something from our past,
> > from looking at old photos, or from someone from our past telling a
> > story about us, which as far as we can tell we would have never
> > remembered without that reminder from outside of our possible streams
> > of consciousness without the reminder.
>
> You have to distinguish between "being reminded of something" - here
> an external event triggers our brain to recall a memory that is really
> there, and "finding out about our past" by performing a
> measurement. The latter entails completely new knowledge. It is no
> different in principle to finding out about the present by performing
> a normal measurement.
>
> I would argue that this implies our past (that which is beyond our
> memories) is a superposition of those histories prior to any
> measurement that might distinguish them, just as it might be in an
> experimental apparatus measure circular polarisation.
>
> The independent "out there" feeling is just the self consistency of
> all our observations - one that is nevertheless quite remarkable, but
> not entailing the existence of something that is out there.
I find this to be a fascinating idea, to relate mutiple possible
histories to quantum superpositions. How does this notion relate to
the idea that mutiple possible histories may degenerate to single
"now"? Information about the past states of the universe being lost is
equivalent to a gain in entropy, such that the state of the universe
at time = t may not uniquely identify the state of the universe at
time < t. Superficially this appears to be symmetrical with the notion
of many possible worlds at time > t springing from a single state at
t, another example of time invariance. However, it would be
impossible, even in principle, to determine which one of these
possible histories is the real one, since it would be meaningless to
claim that only one led to the current state. If more than one history
degenerate in to a particular state, then they are all correct in this
scenario since irreversible steps make recovering one unique history
impossible.
But the meaning of the notion that the outcome an experiment performed
in the past exists in a superposition of outcomes until the moment of
an observation probably does depend greatly on whether one considers
the existence of the world to be observer-dependent or independent. Is
the ensemble merely the set of all possible observer experiences? Or
are there ensembles that are at least as valid that take reality to be
external and observer independent? I intuitively suspect that there is
nothing special about what we call consciousness, and that an
observation is any physical measurement, be it a photon impinging on a
retina or a photodetector or whatever. It does not seem as sensical to
me to claim that a measurement made with instruments does not
constitute an observation until looked at by a conscious observer.
However, I am trying to understand the differences in these two views
-- not the easiest task to do since I am invested in one of them
already.
I hate to tax the patience of those who read this list with yet
another thought experiment, but I think it may be useful to illustrate
this with an example.
Suppose that there is a distant galaxy that has never been observed
from Earth, but only because no one has yet looked it with a
sufficiently powered telescope. When we do decide to point the Hubble
at it, we either will or will not observe the aftermath of a
particularly dramatic supernova whose light would have been visible
from earth centuries ago, assuming that it in fact happened, and
someone had looked at it. If I look at it with the Hubble tomorrow and
I see the results of a powerful supernova, I can safely assume that
the version of me observing it exists within the same reality as one
that experienced that supernova. If I do not see the results of the
supernova (which would have been evident if it had taken place) then
that means that the 'I' who sees the galaxy exists in a branch that
did not experience that supernova. The superposition would be resolved
into actualities by my observation.
Here is the problem: the light from that supernova would have first
reached earth centuries before I made that observation. Hence, I would
not be the first earthbound entity to observe that event. Perhaps the
first conscious entity, but inanimate objects on the Earth also "saw"
the light from that supernova. It would seem that in this case the
superpostion was not one of genuine quantum superposition but only
uncertainty about history from our own ignorance. Suppose that I do
see that a supernova occurred, but unbeknownst to me, an ancient
astronomer had already observed the supernova. Would my observation
that a supernova had occurred still constitute a resolution of a
superposition? or would I simply learn something of which I had
previously been ignorant?
It seems that questions such as what consitutes an observer and the
role of consiousness in observation go directly to the heart of the
meaning of quantum mechanics and how it may be understood/interpreted.
In order to make the schrodinger cat experiment work, an unphysical
object had to be invented, the isolation box in which the cat was
placed. It has been claimed that in fact such a macroscopic level
superposition would be impossible to realize in actuality since it is
impossible to avoid "observations" in the form of the environmental
interactions causing the system to decohere. Of course, preserving
such superpositions in QM systems is a problem that is very
technologically relevant as it is one that must be solved in order to
develop quantum computers.
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Received on Tue Apr 22 2008 - 15:44:41 PDT