Re: Definiteness of Meaning (was: A superposition in QM is just due to a choice of basis?)
On 18 Sep, 22:20, "Stephen P. King" wrote:
> Hi Peter and Friends,
>
> -Original Message-
> From: everything-list@googlegroups.com
>
> [mailto:everything-l...@googlegroups.com] On Behalf Of 1Z
> Sent: Friday, September 17, 2010 8:16 AM
> To: Everything List
> Subject: Re: A superposition in QM is just due to a choice of basis?
>
> On 28 Aug, 20:29, "Stephen P. King" wrote:
> > Hi Bret,
>
> > Could you elaborate on this point and/or point me to a
> > good discussion of it? From what I have studied so far there is no
> > solution to the measurement problem so far in terms of an explanation
> > of the way that the choice is made in each successive event, world or
> > whatever. Even decoherence does not help things from what I can tell,
> > but this business that "What's a superposition in one basis is still
> > an eigenfunction in some basis." is new to me.
>
> It is a much overlooked point. It pretty completely disposes of the version
> of MWI that says the objectively decomposes into N classical universes.
> I believe the relativity of superposition is best handled by the relational
> interpretation
>
> http://en.wikipedia.org/wiki/Relational_quantum_mechanics
> ***
>
> I would like to quote from this web article reference by 1Z and
> make a comment:
>
> "Observer-dependence of state
> According to O, at t2, the system S is in a determinate state, namely spin
> up. And, if quantum mechanics is complete, then so is his description. But,
> for O', S is not uniquely determinate, but is rather entangled with the
> state of O — note that his description of the situation at t2 is not
> factorisable no matter what basis chosen. But, if quantum mechanics is
> complete, then the description that O' gives is also complete.
> Thus the standard mathematical formulation of quantum mechanics allows
> different observers to give different accounts of the same sequence of
> events. There are many ways to overcome this perceived difficulty. It could
> be described as an epistemic limitation — observers with a full knowledge of
> the system, we might say, could give a complete and equivalent description
> of the state of affairs, but that obtaining this knowledge is impossible in
> practice. But whom? What makes O's description better than that of O', or
> vice versa? Alternatively, we could claim that quantum mechanics is not a
> complete theory, and that by adding more structure we could arrive at a
> universal description — the much vilified, and some would even say
> discredited, hidden variables approach. Yet another option is to give a
> preferred status to a particular observer or type of observer, and assign
> the epithet of correctness to their description alone. This has the
> disadvantage of being ad hoc, since there are no clearly defined or
> physically intuitive criteria by which this super-observer ("who can observe
> all possible sets of observations by all observers over the entire
> universe"[8]) ought to be chosen.
> RQM, however, takes the point illustrated by this problem at face value.
> Instead of trying to modify quantum mechanics to make it fit with prior
> assumptions that we might have about the world, Rovelli says that we should
> modify our view of the world to conform to what amounts to our best physical
> theory of motion.[9] Just as forsaking the notion of absolute simultaneity
> helped clear up the problems associated with the interpretation of the
> Lorentz transformations, so many of the conundra associated with quantum
> mechanics dissolve, provided that the state of a system is assumed to be
> observer-dependent — like simultaneity in Special Relativity. This insight
> follows logically from the two main hypotheses which inform this
> interpretation:
> Hypothesis 1: the equivalence of systems. There is no a priori distinction
> that should be drawn between quantum and macroscopic systems. All systems
> are, fundamentally, quantum systems.
> Hypothesis 2: the completeness of quantum mechanics. There are no hidden
> variables or other factors which may be appropriately added to quantum
> mechanics, in light of current experimental evidence.
> Thus, if a state is to be observer-dependent, then a description of a system
> would follow the form "system S is in state x with reference to observer O"
> or similar constructions, much like in relativity theory. In RQM it is
> meaningless to refer to the absolute, observer-independent state of any
> system."
>
> It is this notion that "it is meaningless to refer to the absolute,
> observer independent state of any system" what has deep implications when
> applied to the Universe itself. In effect, it argues that there is no such
> thing as a "view from nowhere" ala Nagle IF and only IF we are thinking that
> that a state can have any sort of property definiteness associated to it as
> an independent entity. This seems to undermine the traditional idea of an
> objective universe existing with a definite set of
RE: Definiteness of Meaning (was: A superposition in QM is just due to a choice of basis?)
Hi Peter and Friends,
-Original Message-
From: everything-list@googlegroups.com
[mailto:everything-l...@googlegroups.com] On Behalf Of 1Z
Sent: Friday, September 17, 2010 8:16 AM
To: Everything List
Subject: Re: A superposition in QM is just due to a choice of basis?
On 28 Aug, 20:29, "Stephen P. King" wrote:
> Hi Bret,
>
> Could you elaborate on this point and/or point me to a
> good discussion of it? From what I have studied so far there is no
> solution to the measurement problem so far in terms of an explanation
> of the way that the choice is made in each successive event, world or
> whatever. Even decoherence does not help things from what I can tell,
> but this business that "What's a superposition in one basis is still
> an eigenfunction in some basis." is new to me.
It is a much overlooked point. It pretty completely disposes of the version
of MWI that says the objectively decomposes into N classical universes.
I believe the relativity of superposition is best handled by the relational
interpretation
http://en.wikipedia.org/wiki/Relational_quantum_mechanics
***
I would like to quote from this web article reference by 1Z and
make a comment:
"Observer-dependence of state
According to O, at t2, the system S is in a determinate state, namely spin
up. And, if quantum mechanics is complete, then so is his description. But,
for O', S is not uniquely determinate, but is rather entangled with the
state of O — note that his description of the situation at t2 is not
factorisable no matter what basis chosen. But, if quantum mechanics is
complete, then the description that O' gives is also complete.
Thus the standard mathematical formulation of quantum mechanics allows
different observers to give different accounts of the same sequence of
events. There are many ways to overcome this perceived difficulty. It could
be described as an epistemic limitation — observers with a full knowledge of
the system, we might say, could give a complete and equivalent description
of the state of affairs, but that obtaining this knowledge is impossible in
practice. But whom? What makes O's description better than that of O', or
vice versa? Alternatively, we could claim that quantum mechanics is not a
complete theory, and that by adding more structure we could arrive at a
universal description — the much vilified, and some would even say
discredited, hidden variables approach. Yet another option is to give a
preferred status to a particular observer or type of observer, and assign
the epithet of correctness to their description alone. This has the
disadvantage of being ad hoc, since there are no clearly defined or
physically intuitive criteria by which this super-observer ("who can observe
all possible sets of observations by all observers over the entire
universe"[8]) ought to be chosen.
RQM, however, takes the point illustrated by this problem at face value.
Instead of trying to modify quantum mechanics to make it fit with prior
assumptions that we might have about the world, Rovelli says that we should
modify our view of the world to conform to what amounts to our best physical
theory of motion.[9] Just as forsaking the notion of absolute simultaneity
helped clear up the problems associated with the interpretation of the
Lorentz transformations, so many of the conundra associated with quantum
mechanics dissolve, provided that the state of a system is assumed to be
observer-dependent — like simultaneity in Special Relativity. This insight
follows logically from the two main hypotheses which inform this
interpretation:
Hypothesis 1: the equivalence of systems. There is no a priori distinction
that should be drawn between quantum and macroscopic systems. All systems
are, fundamentally, quantum systems.
Hypothesis 2: the completeness of quantum mechanics. There are no hidden
variables or other factors which may be appropriately added to quantum
mechanics, in light of current experimental evidence.
Thus, if a state is to be observer-dependent, then a description of a system
would follow the form "system S is in state x with reference to observer O"
or similar constructions, much like in relativity theory. In RQM it is
meaningless to refer to the absolute, observer-independent state of any
system."
It is this notion that "it is meaningless to refer to the absolute,
observer independent state of any system" what has deep implications when
applied to the Universe itself. In effect, it argues that there is no such
thing as a "view from nowhere" ala Nagle IF and only IF we are thinking that
that a state can have any sort of property definiteness associated to it as
an independent entity. This seems to undermine the traditional idea of an
objective universe existing with a definite set of properties absent the
notion of interactions of systems with each other. OTOH, we could take this
as a positive and propose that definiteness emerges from interactions
between subsets of the Universe.
