Re: A Look at Quantum "Spookiness"
- From: Andreas Most <Andreas.Most@xxxxxxxxx>
- Date: Thu, 01 Dec 2005 14:07:21 +0100
Ilja Schmelzer wrote:
> "Andreas Most" <Andreas.Most@xxxxxxxxx> schrieb
>
>>Ilja Schmelzer wrote:
>>
>>>"Andreas Most" <Andreas.Most@xxxxxxxxx> schrieb
>>>
>>>>Ilja Schmelzer wrote:
>>>>
>>>>>...
>>>>>A box containing some liquid in equilibrium also, in some sense,
>>>>>summarizes the information I have about the liquid. Therefore the
>>>>>box is not a physical object?
>>>>
>>>>This would not tell me anything. You also need to tell me the size
>>>>of the box, temperature, type of liquid, entropy etc.
>
>
>>>All these are properties of the box. Note we are in equilibrium,
>>>moreover the word "only for water" is written on the box, and all
>>>observations up to now have shown that such boxes are used
>>>only for water.
>>
>>You were talking about some liquid, not water.
>
>
> I have specified my toy example after your criticism.
>
>
>>>(Equilibrium is relevant, because from point of Bohmian mechanics
>>>the wave function defines the quantum equilibrium state.)
>>
>>Yes, but you would still need to know the temperature, the pressure,
>>etc.
>
>
> They may be measured by measuring properties of the box.
>
>
>>I think we are not getting to the point with this example. (Nicht alles,
>>was hinkt, ist auch ein Beispiel...)
>
>
> I think for the purpose I have invented it it is already sufficient.
> The box allows to describe most of the properties (if not all)
> of the water in it, similar to the wave function. Nonetheless it is
> a real object. Thus, your argumentation is faulty.
I would consider the box being the electron, not the wave function.
A measurement is perfromed on the physical object. The wave function
is just a mathematical object, that tells me about the possible outcomes
of a mesurement. The electron is not the wave function. The wave
function only describes the electron's behaviour.
It seems as if you are trying to tell me with your example that the
moon's orbit is the moon itself.
>>>>>>In the EPR case no information is transferred between the two
>>>>>>particles
>>>>>>nor is it possible to communicate with such an EPR setup.
>>>
>>>>>That it is not possible to communicate with an EPR device is a proven
>>>>>theorem. But why do you think no information is transferred?
>>>
>>>>If information were transferred there would be a way to communicate in a
>>>>EPR setup. But there is no indication of any information transfer.
>>>
>>>No. There is no reason to assume that some [should be no] hidden
>>>information channel
>>>may be used. And there is a very strong indication - the violation of
>>>Bell's inequality.
>>
>>That is what I said!
>
> Sorry, that was a typo.
>
>>>>Also the quantum mechanical description works perfectly without
>>>>transferring information.
>>>
>>>The quantum mechanical description (in its minimal interpretation)
>>>is not a realistic one in the sense used by Bell. We can easily
>>>transform it into a realistic interpretation, following BM.
>>>In this case we have a real mechanism transferring information.
>>
>>Now I am confused. You just confirmed that there is no hidden
>>information channel, but now you are talking again about information
>>transfer.
>
> Don't be confused, that was just a typo.
>
>>>>>Instead, Bell's theorem proves that, if you insist that no information
>>>>>is transferred, you have to give up realism. But once you give up
>>>>>realism, it makes no sense to say that no information is transferred.
>>>
>>>>It seems as if you have not understood Bell's theorem. Bell proved that
>>>>if hidden variables are involved in measurements in quantum mechanics
>>>>you have to give up locality.
>>>
>>>That's another formulation.
>>>
>>>"Hidden variables" is a bad word for realism, it sounds like it is not
>>>worth to care if we reject them. Moreover, "is involved" sounds like
>>>it is a very strange idea to "involve" them.
>>
>>Calling them "realism" is taking "hidden variables" already for granted.
>
> To decide which word is more appropriate - realism or hidden variables -
> we have to look into the details. Hidden variables implies that we can
> reject all this without much care. Realism implies that we need very strong
> arguments to reject it, or that we would better take it for granted.
The main problem with hidden variables (or "realism" as you call it) is
that it has not led to new insights in physics. It does not provide any
new predictions that go beyond what quantum physics does using the
null hypothesis.
> To be clear, I think we make no error if we take it for granted. It is
> IMHO some sort of extended logic of science.
>
> There are things which we have to take for granted to be able to do
> science. (For example, the law which forbids contradictions. Without
> this, contradictions in our theories are not problems, no problems
> are, therefore, left, and there remains no open scientific problem.
> Note: Whatever the contradictions in empirical evidence, we will
> not reject the logical law that forbids contradictions.)
>
> In a similar reasoning, we can add some other principles. This includes
> IMHO classical logic, classical probability theory and some basic
> principles of realism.
IMHO all interpretations of quantum mechanics try to describe quantum
mechanical behaviour with explanations that fits better into our
world view which is biased by classical physics.
People are rather inventing weird ideas about hidden variables or
multiverses than accepting that quantum behaviour is as natural as is
the behaviour we know from classical physics.
>>>"Locality" is, on the other hand, a very good word for Einstein
>>>causality.
>
>>Ooops, "locality" and "causality" are two different things. Locality is
>>assumed because of causality. However, the inverse conclusion doesn't
>>work.
>
> In the original proof of Bell's inequality the additional requirement is
> Einstein causality. AFAIU, in considerations about Bell's inequality
> locality is used as a sloppy replacement instead of Einstein causality.
When talking about physics one shouldn't be too sloppy.
> If you use another meaning of locality, please explain. If you use it
> in another meaning (say, for example, in such a meaning that a
> theory with limiting speed of 10^20 c is local), then, of course,
> the violation of Bell's equality for space-like separated events
> is compatible with local realism.
>
>>>Sounds like it is very, very bad to give it up. But let's remember that
>>>Newtonian theory is "nonlocal". Thus, nonlocal theories are nothing
>>>very bad.
>>
>>You should know better than this. Newtonian theory is only an
>>approximation for small velocities and weak gravitational fields.
>
> I know. Nonetheless, it is a nonlocal theory, that means, nonlocal
> theories are legitimate part of science. Maybe only as intermediate
> theories until some very big limiting speed will be found.
Yes, but only insofar as we now where the limits of this nonlocality
are.
Are you trying to tell me that we should accept nonlocality for now
and find later a theory that will show that this assumption was only
an approximation?
>>In this context you may safely assume that time is absolute and
>>interactions occur instantaneously. In this approximation the theory
>>is nonlocal. But it is dangerous to conclude that you can generalize
>>this concept as it already doesn't work in general relativity.
>
> General relativity needs only minor modifications to become
> compatible with a preferred frame (named in GR context
> preferred foliation).
Apart from the fact that I don't know why somebody would want to
introduce a "preferred frame", what has this to do with nonlocality?
>>>There remains nonetheless some difference in the formulations. You
>>>have to take a look at the actual proof. It proves that the results of
>>>the measurements cannot be independend of the decisions of the
>>>experimenters at the other end. As a consequence, if the measurements
>>>are space-like separated, Einstein causality is violated.
>>
>>Causality is not violated because it is not possible to exchange
>>information with such a setup. And although experimentor A might
>>already know what B will measure, B must still use a superposed state
>>for the description of his system. There is no contradiction in doing so.
>
> Assume we observe a situation which allows only two explanations:
> Or A gives information to B, or B gives information to A.
This has nothing to do with a EPR setup.
> In this case we can be sure that there exists some information channel.
> But it also follows that we cannot use this hidden channel to transfer
> information. To use it to transfer information from A to B is impossible
> if the correct explanation is that the information was transferred from
> B to A. And reverse.
I can't follow your argumentation here.
> Your argumentation therefore leads to a contradiction. In a situation
> where some hidden channel exists you can show that no such channel
> exists.
Your were starting from a wrong assumption from which you may conclude
anyhing.
>>>"Realistic interpretation" simply means that you have to specify (in
>>>your
>>>interpretation) which objects of your theory are real physical objects.
>>>Correct?
>
>>I did that in the previous posts.
>>The physical reality is what you can measure, i.e. the observables.
>
> In this case, QM does not describe reality, but only allows to
> compute, without explanation, some probability distributions.
What is your definition of reality?
Physicists are interested in describing the world. They are
not interested in describing something that has no impact on what
we observe. Apart from that, there is not necessarily an explanation
for everything. E.g. we take for granted mathematics and the existence
of space, time and matter.
>>The wave function is unobservable. Therefore it makes no sense to
>>consider the wave function as a physical object.
>>And btw, this is not "my" interpretation.
>
> It is the minimal interpretation. Shut up and calculate. What really
> happens, what really leads to the observable probability distributions,
> remains unexplained.
In classical physics you do not question the existence of matter and the
equations of motion. Why do you need an explanation for the equations of
quantum mechanics?
>>>All realistic interpretations I know of use the wave function as a
>>>real object. Feel free to invent another one to justify your claim.
>
>>I cannot see that any of these interpretations can explain anything
>>beyond the interpretation, which considers the wave function solely
>>as a mathematical object.
>
> In BM, the probability distributions of QM are derived from
> the basic equations, which are deterministic.
>
>>>Then, if we assume that the "real objects" which define the behaviour
>>>of the quantum state do not predefine/influence the decisions of the
>>>two experimenters A,B, and that there is no causal influence
>>>A->B or B->A, then Bell's inequality holds.
>>>It is violated, and I conclude A->B or B->A.
>>
>>You are certainly aware of the fact that this conclusion is a
>>direct consequence of your assumptions. Namely, that the wave
>>function is a "real" object. Because of that, I avoid this type
>>of interpretation.
>
> No. It is (part of) Bell's theorem. It does not assume that
> the wave function is real. All it assumes is that
>
> 1.) There exists some set of possible states of "reality" L
> with probability distribution rho(l)
>
> 2.) The results of the measurements m depend on this state
> and the decisions of experimenters a: m=m(l,a)
>
> so that the resulting probability distribution of measurement
> results will be
>
> rho(x,a) = int delta(x-m(l,a)) rho(l) dl
>
> No assumption is made that the wave function is part of l. We
> obtain Bell's inequality if we subdivide the decisions of experimenters
> and the measurement results into two parts
> A=A(l,a,b), B=B(l,a,b) and add as the additional Einstein
> causality assumption A=A(l,a), B=B(l,b) only.
In a GHZ setup you would also have to assume that your measurement
result also depends on the measurement setups of the other experiments
or else you run into a contradiction. That is A=A(l,a) doesn't work.
In a space-like separation of the measurements it is not clear whose
measurement setup is influencing the others measurements. You can
maybe overcome this dilemma by giving up "free will" in that the
experimentors are not free in choosing their setup.
Anyway, this is what I would call "spooky action at a distance".
>>But I will not keep you from continueing this track. Maybe you
>>can find a solution to the so called measurement problem by that.
>
> The measurement problem is solved in standard BM. No
> need to search for a solution.
Maybe, but at which cost?
>
> Ilja
.
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