Re: Superposed observers (was No new Einstein)

Charles Francis <charles@xxxxxxxxxxxxxxxx> writes:

>In message <df4ijj$1eip$1@xxxxxxxxxxxxxxxxxxxx>, rof@xxxxxxxxxxxx writes
>>
>>My problem is that I don't see what relationalism, in the
>>Cartesian-Leibnizian sense, has to do with quantum mechanics.

>>>From what I understand, the idea of relational quantum
>>mechanics is merely to say "relational" and "quantum mechanics"
>>in the same sentence. When I ask what's so great about that,
>>I'm told that Leibnizian space is a better idea than Newtonian
>>space. I agree, but I still don't see any connection to
>>quantum mechanics.

>This surprises me, because I find it strongly intuitive that there is a
>connection.

I would probably be inclined to think there was a connection if I
thought that relationalism was a new and deep insight, but
it doesn't seem that deep to me at all. On that subject, I
have a question which might be related to the teleparallelism
business: Leibniz says that space is not something which exists
and which has objects within it, but rather that objects have
determinate relations to one another which we might call relative
positions.

Now, in a curved spacetime, if I have two extended objects (say
two pencils, for example), the separation between them can't be
considered as a vector, but instead I have to specify a path
joining one pencil to the other. Whether the two pencils will
be parallel when I bring them together depends on the path
taken and the holonomy of the manifold.

Leibniz would appear to be in trouble in that case, since the two
pencils don't have a simple relation of relative position any more,
and certainly they don't have a well-defined relative orientation,
since one must first specify a path before one can say whether they
are parallel. Space, considered as a set of relations between objects,
doesn't seem like such a good idea any more, since the relations
between distant objects depends on the specification of a path
joining them. The existence of gravitational waves is another
indicator that space isn't simply a set of relations between
objects.

Rovelli has abandoned Leibniz's theory of space at this
point, by reintroducing space as an entity with its own existence,
independent of the existence of the objects inside it. Of course,
he calls it a gravitational field instead of space, but that's
essentially what he's doing, when he says that things stand
in determinate relations "to the gravitational field", rather
than to each other.

So the question is: Is your adoption of teleparallelism intended
as a way to retain the idea that objects have a relative
position, and hence a relative orientation, and hence a way
to save Leibniz's theory of space, even in the presence
of gravitational effects?

>The difficult thing is expressing it clearly and
>demonstrating the wave equation, as Heisenberg found when he withdrew
>the microscope paper.

I wasn't aware that Heisenberg withdrew a microscope paper. Can
you tell me more about it?

>>Incidentally, there have been insights since then. In particular,
>>Kantian space is better than Leibnizian space, but people don't
>>read it because it can't be understood without years of hard work.

>I am generally impressed with Kant, but I confess I haven't absorbed all
>the details of who said what. I realised when I started this avenue that
>actually one should be guided by reason, and that if one tried to get on
>top of everything everyone else has said one would merely put one's
>brain cells into overload.

There's only one thing to read - the Critique (the Guyer and Wood
translation of it, more specifically). Nobody else said anything
of any importance. The problem with the Critique is that you
have to read it a hundred times before it makes sense.

>>>I think the trouble is you are looking at the wrong problem. The cat is
>>>alive or dead, no issue, no relative clause needed. The issue starts
>>>when you ask the position of a particle.
>>
>>In the Stanford article, Rovelli says:
>> Consider for instance a two-state system
>> O (say, a light-emitting diode, or l.e.d., which can be on
>> or off) interacting with a two-state system S (say, the
>> spin of an electron, which can be up or down). Assume the
>> interaction is such that if the spin is up (down) the l.e.d.
>> goes on (off). To start with, the electron can be in a
>> superposition of its two states. In the account of the state
>> of the electron that we can associate with the l.e.d., a
>> quantum event happens in the interaction, the wave function
>> of the electron collapses to one of two states, and the
>> l.e.d. is then either on or off. But we can also consider
>> the l.e.d./electron composite system as a quantum system
>> and study the interactions of this composite system with
>> another system O'. In the account associated to O', there is
>> no event and no collapse at the time of the interaction,
>> and the composite system is still in the superposition of
>> the two states [spin up/l.e.d. on] and [spin down/l.e.d.
>> off] after the interaction.
>>
>>This seems to be Rovelli saying that it's not just position which
>>is relative, but the actual states of systems, for example
>>whether an LED is on or off, or whether a cat is alive or dead.
>>
>>It may be that your interpretation of relationalism differs
>>from Rovelli's, as Italo's does. But if there's such a multiplicity
>>of interpretations out there, which differ on such crucial
>>points as whether a cat's being alive is a relational property,
>>then it would seem to me that there isn't a well-defined
>>concept of relationalism at all.

>That is a problem with any pre-scientific theory. I am sure you have
>read Kuhn.

I read "The Structure of Scientific Revolutions" to see what the
fuss was about. It was better than I had expected it to be, but
all of his paradigm talk sounds to me like exactly the kind of
thing he would refer to as a paradigm.

>But there is a deeper problem here, not just in how one thinks of qm,
>but also how one thinks of language and reality. I say the cat is alive
>or dead as an objective ontological property. But what an observer is
>able to say about whether the cat is alive or dead is relative to the
>observer. And I follow Von Neumann in that qm describes what we can say
>about measurements. Another philosopher might claim that what we can say
>is reality.

He might, but I don't agree with those relativists who say that there
is no absolute right and everybody's right in his own way. In a
post some time ago you mentioned the idea that somebody can be regarded
as sane if his beliefs are shared by those around him. I replied
(several times) but the post never appeared so I gave up. The gist
of my reply was that there is another way to decide what is right
or sane rather than appealing to the verdict of the local peasantry.

The other way is to examine whether a person's method of deciding
what statements are to be considered true adheres to the rules of
rational enquiry. For example, if a person claims that a particular
mathematical statement is true, we would check to see if he has
a proof, rather than asking the people in the village square to
vote on it.

The same holds of philosophy. There are clear rules of rational
enquiry, which should be adhered to. It isn't the case that
one philosopher's view is as good as any other's. Unfortunately,
most modern philosophers (including Russell, Popper and so on),
seem to consider that the way to do philosophy is to begin
by stating your assumptions and end by stating your opinions.

>>.... Rovelli's proposal would appear to be that when somebody
>>doesn't know something about a system, then we should say that that
>>system is "in a superposition relative to" that person. But this
>>would merely be a suggestion about what words we should use, and
>>would hardly qualify as an insight into quantum mechanics.
>>
>>For these reasons, it appears to me that Rovelli's relational
>>quantum mechanics is incoherent.

>I'm not convinced Rovelli would say otherwise. I felt he put forward a
>view on how interpretational issues might be resolved, not a complete
>resolution.

But it still appears to me that all that's being said is "I like
relativism and I'm interested in quantum mechanics, therefore
quantum mechanics is about relativism."

>>>I was trying to be too polite to say so. They get very upset if you tell
>>>them such things.
>>
>>I think I'm becoming less polite as I age. Arnold stormed off when
>>I told him he had a mental disease.

>He got pretty upset with me when I told him he needed to study the
>content of a first year course in analysis. But then he had just told me
>that analysis legitimised use of infinity. Weierstrass would turn in his
>grave.

Weierstrauss could do with a turn once a century or so.

>>>>>Plus of course, there are some really nasty
>>>>>mathematical problems which make them think qft can't be built on qm.
>>>>
>>>>Do you mean Haag's theorem? Or do you mean the problems with
>>>>making path integrals rigorous? Or finding an actual example
>>>>of an interacting field theory? Or something to do with
>>>>renormalization?
>>
>>>All of those. But the worst is the Landau Pole, I think.
>>
>>I think the usual response given to the Landau pole is that QED is
>>only an effective low-energy theory, so we're entitled to use
>>a cutoff. Unification at high energies will give us a theory
>>without a Landau pole, we're told.

>This is true, of course. The minimal discrete unit of time which I use
>to demonstrate Schwarzschild regularises loop integrals and also
>eliminates the Landau pole. They will also argue that a discrete model
>cannot be covariant, but if measurement is relative we have to redefine
>covariance. And if field operators act on the non-interacting space and
>are used to describe interactions then the idea that one has to
>construct an interacting field is a red herring.

Most of this doesn't make sense to me right now. I have to look at
it a bit more. I'll have some questions for you soon.

R.

.

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