On 5/9/2013 12:40 PM, Jason Resch wrote:
On Thu, May 9, 2013 at 2:08 PM, meekerdb <[email protected]
<mailto:[email protected]>> wrote:
On 5/9/2013 11:28 AM, Jason Resch wrote:
On Thu, May 9, 2013 at 1:11 PM, meekerdb <[email protected]
<mailto:[email protected]>> wrote:
On 5/9/2013 10:02 AM, Jason Resch wrote:
Von Neumann thought the extra baggage was required to make the model
match our
observations, but Everett later showed that step was unnecessary. The
model
(free of additional baggage) predicts the same observations as the
model with it.
He showed that IF the wave function separates into orthogonal
components (an
irreversible process) then FPI explains the observations. But the
model says
it never does that; it only approximates that, in certain bases.
Could you explain this? I don't understand in what sense the Schrodinger
equation
can only approximate itself?
If you include the observer and the system observed then when the observer
interacts
with system in superposition the observers state becomes a superposition
I follow you so far. To confirm we are on the same page, so you think observers are
special in any physical way from any other "non observer" in a physical system?
in the same basis. The cross-terms in the superposition are not zero.
Do they need to be, what if they are not zero? How does a single-universe
interpretation avoid this issue?
They can be shown to become approximately zero if you include interaction
with an
environment that has a large number of degrees of freedom and you trace
over the
environment variables. But that last step isn't part of the Schrodinger
equation,
it's a separate assumption comparable to Boltzmann's assumption of
molecular chaos.
Earlier you said it can be shown, so how is it an assumption? Or do you mean it is an
assumption that the environment has a large number of degrees of freedom?
That and that the interaction is such that it diagonalizes in the variable(s)
of interest.
Decoherence theory tries to fill in the process by which this occurs
give a
statistical mechanics type account of irreversibility.
It gives an account of the appearance of an "irreversible wave-function
collapse"
without their having to be one. It is derived entirely from the theory of
QM and
is not an extra postulate.
It depends on the choice of basis. In general there's other some basis in
which
state is pure. Decoherence says the density of the subsystem is
approximately
diagonal in a particular basis. This involves assumptions about the
environment and
is not part of the wave function.
It doesn't matter which/whose basis you use though, does it?
It's not "whose" but "which". Most measurements are modeled as position measurements but
you can invent ones that are measurements in momentum space too. But in general you can't
create a measurement to determine the pure state which includes the environment.
But you could also take the epistemological interpretation of Peres and
Fuchs
instead of inventing other worlds just to save the determinism of an
equation.
The other worlds are a required element of the theory, unless you deny the
reality
of superposition. I think Everett's thought experiment explains the
situation the
best:
Imagine a box with an observe in it who will be measuring the state of a
particle
and writing the result in a notebook. This box is entirely sealed off from
the
external world such that the internal result of the experiment remains in a
superposition until it is opened. Now a second, external observer models
the
entire evolution of this box over time, including before and after the
observer
inside measures the state of the particle and records the result in a
notebook. He
determines the superposition of all the possible handwritings of all the
possible
results in the notebook. Is the internal observer not conscious in each of
the
various superpositions resulting from the measurement?
Depends on what you mean by THE internal observer. There is a superposition
of
states that represents the external observers theory of the internal
observer.
Okay, then from the view point of the external observers, shouldn't the various internal
observers who remain in a super position, include observers each with a memories of
recording one of the results in the log book, and in their brain? What happens to these
memories (and presumably the experiences) when the external observer opens the room and
collapses the superposition? Are we to believe all the memories and experiences that
internal observer had are retroactively erased from existence and in fact, never
happened at all?
No, we believe the external observer needs to update the wave function he's using to
describe the internal observer, based on his new information.
Epistemological interpretations seem to deny there is any fundamental
reality at
all, aside from what we can see and learn, which to me seems like a dead
end in the
search for truth.
Shifting the truth off to undetectable realms doesn't help much.
They are implied by the model of reality.
They are implied by ONE model of reality.
Just like the galaxies beyond the cosmological horizon are implied by some models of
inflation. Why contort a perfectly good and simple theory to make it match our (known)
limited perceptive capacities? To me, single universe theories are as silly as any
theory of inflation which said: "Once a galaxy crosses beyond our cosmological horizon,
it ceases to exist, and any life forms that might have been in those galaxies cease to be."
Except there are no galaxies that are observed to cross the Hubble sphere.
I like MWI and Bruno's FPI idea, but without some testable prediction
(not
retrodiction) I don't find them compelling.
Why do you find compelling about the idea that all other superpositions
(except for
one) vanish?
It comports with experiment.
What experiment even hints that other superpositions vanish?
"Vanish" = no longer seen.
What do you find compelling about the idea that the unity of your
consciousness is
an illusion.
Is this the real source of your resistance to MWI, that you do not feel yourself split
when your intuition suggests you should feel it?
No. It's that it makes no testable predictions. It's just metaphysics to satisfy a
demand for determinism - unless it can predict something.
Don't worry, you don't need to condemn your copies to a superposition with 0 amplitude
to explain why you (in this branch), do not have access to the memories/experiences of
the other yous (in other branches).
This is the same error presentism makes: believing we must make all other points in time
non-real to explain why we feel ourselves to be in this single point in time.
So to answer your question, what I find compelling is not contorting a theory to solve
imagined problems.
I think of non-determinism as an imagined problem.
Brent
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