What does a local non-realistic theory look like?

[stevendaryl]

We have all sorts of interpretations - real ones, many minds, many worlds, many interacting worlds, I have read about all sorts. QM is pretty ambivalent to whatever view you want to take

Except that the most straightforward, intuitive view--that (1) the universe is at each moment in some state or other, and (2) one part of the universe is only affected by events in the backward light cone, and (3) measurements just reveal local information about the pre-existing state of the universe--is apparently ruled out by QM.

 

[jk22]

Except that the most straightforward, intuitive view--that (1) the universe is at each moment in some state or other, and (2) one part of the universe is only affected by events in the backward light cone, and (3) measurements just reveal local information about the pre-existing state of the universe--is apparently ruled out by QM.

For 3 we can escape with the fact that the local values has to interact with the apparatus hence when the knowledge of the preexisting element lambda and the measurement setting theta does Not determine the outcome. Indeed a probabilistic theory would violate Bell's inequality but the problem is that quantum mechanics does not allow all values that such a theory would give and hence there are global conditions

 

[stevendaryl]

Indeed a probabilistic theory would violate Bell's inequality but the problem is that quantum mechanics does not allow all values that such a theory would give and hence there are global conditions

What do you mean by saying a probabilistic theory would violate Bell's inequality? If by "probabilistic theory" you mean a local, stochastic theory, then I don't believe that's true.

 

[zonde]

Except that the most straightforward, intuitive view--that (1) the universe is at each moment in some state or other, and (2) one part of the universe is only affected by events in the backward light cone, and (3) measurements just reveal local information about the pre-existing state of the universe--is apparently ruled out by QM.

And here you contradict realism. QM can't rule out some particular view of reality. Only experiments and observations can do that.
Probably you wanted to say that experiments almost rule out these options.

 

[stevendaryl]

And here you contradict realism. QM can't rule out some particular view of reality. Only experiments and observations can do that. Probably you wanted to say that experiments almost rule out these options.

No, I don't think so. QM is a theory, and that theory is inconsistent with a particular view of the universe.

 

[RUTA]

This paper looks relevant http://arxiv.org/pdf/1207.5103.pdf.

 

[zonde]

No, I don't think so. QM is a theory, and that theory is inconsistent with a particular view of the universe.

I see, you was talking about interpretations of QM.

 

[jk22]

It is a theory but experimental results favor it towards other descriptions of the universe : Chsh is experimentally bigger than 2.

 

[DrChinese]

I think "realism" means several different things as well. I don't quite understand Dr. Chinese' claim that retrocausality (back-in-time influences) violate realism. But the two meanings that occur to me are: (1) The mathematical objects in the theory assumed to describe the state of an objective, observer-independent world ...

I often interchange the "observer-independent" description you provide and "realism". That goes back to EPR, which specifically gives an "out" to their conclusion if observer independence is not assumed. They use commentary a la "no reasonable description of reality can allow this." I.e. they essentially equate "observer independence" and "non-realism" (or what might be called "unreasonable realism").

If the future actions of an observer (choice of measurement basis) are to be a factor in the outcome, then you have observer dependence and thus the (future) observer shapes reality (in the present). Thus reality would be subjective (and not objectively independent), and thus not realistic in the EPR sense. Such is to be expected in any time-symmetric interpretation, as the past and the future each contribute to outcomes "now".

 

[stevendaryl]

If the future actions of an observer (choice of measurement basis) are to be a factor in the outcome, then you have observer dependence and thus the (future) observer shapes reality (in the present).

Well, I guess that's another subtlety of terminology that needs to be cleared up. I was using "observer-independence" to mean something like "reality is the same for all observers". So an observer affecting reality wouldn't violate observer-independence if those effects affect everyone.

 

[DrChinese]

Well, I guess that's another subtlety of terminology that needs to be cleared up. I was using "observer-independence" to mean something like "reality is the same for all observers". So an observer affecting reality wouldn't violate observer-independence if those effects affect everyone.

I don't believe that is observer independence in the EPR sense. (Sometimes the words are hopeless!)

"This makes the reality of P and Q depend on the process of measurement carried out [by Alice] on the first system, which does not disturb the second system [Bob's] in any way. No reasonable definition of reality could be expected to permit this."

If Alice makes her decision on measurement basis after Bob has observed his results, and you accept Bell, then retrocausality of some type certainly seems a possibility worth considering.

 

[zonde]

1. Time symmetric class includes the retro-causal, transactional, relational blockworld and a few others.

http://arxiv.org/abs/0908.4348
http://arxiv.org/abs/0706.1232
http://www.npl.washington.edu/npl/int_rep/gat_80/

In the above, there is never any influence that propagates in excess of c. Each constituent interaction is local. However, because time direction is allowed to go either way, the net effect can appear non-local.

I do not know if this was discussed before but it seems worth asking anyways.
In these models where time goes both ways, past determines future and future determines past. So there seems to be a need for some dynamical process that determines Now and it then requires some sort of metatime. Do you know about discussion of that sort of question?

 

[RUTA]

I do not know if this was discussed before but it seems worth asking anyways.
In these models where time goes both ways, past determines future and future determines past. So there seems to be a need for some dynamical process that determines Now and it then requires some sort of metatime. Do you know about discussion of that sort of question?

That complaint is close to what we have voiced concerning "retrocausality" in our most recent paper http://www.ijqf.org/archives/2087. Specifically, given that the future is as "real" as the present, then all events are already "there," so in what sense is anything "moving" in either temporal direction, unless you have a metatime? That's why we didn't consider RBW to be a retrocausal interpretation until recent conversations with Wharton revealed a more God's eye view of what retrocausality can mean. So, our adynamical global constraint qualifies as retrocausal not in a metatime or temporal sense, but in a simple methodological sense -- future boundary conditions are needed in the computational process (path integral in our case).

 

[TrickyDicky]

That complaint is close to what we have voiced concerning "retrocausality" in our most recent paper http://www.ijqf.org/archives/2087. Specifically, given that the future is as "real" as the present, then all events are already "there," so in what sense is anything "moving" in either temporal direction, unless you have a metatime? That's why we didn't consider RBW to be a retrocausal interpretation until recent conversations with Wharton revealed a more God's eye view of what retrocausality can mean. So, our adynamical global constraint qualifies as retrocausal not in a metatime or temporal sense, but in a simple methodological sense -- future boundary conditions are needed in the computational process (path integral in our case).

How does RBW deal with the second law?

 

[DrChinese]

How does RBW deal with the second law?

I wouldn't want to tackle that specific question. However, I will voice the opinion (and not all will agree): Whenever entropy is measured, you have a value I refer to as a "local minimum". Entropy increases in *both* time directions from that local minimum.

 

[RUTA]

How does RBW deal with the second law?

Since RBW is not germane to this thread in general, you should send this question to my account as a Conversation. Thanks for your interest :-)

 

[vanhees71]

This discussion, which I've not completely followed to be honest, is a bright example strengthening my prejudice against philosophy. You have a bunch of vaguely defined notions and fight over this indefiniteness forever. I have no clue, what a rigorous definition of "realism" should be, let alone what EPR meant. Further to my understanding an "observer-independent physics" is a contradictio on adjecto, because physics is about observable, reproducible facts about phenomena in nature. You might now start fighting about the question, whether cosmology is part of physics or not ;-)).

There's one notion in this debate, which has a well-defined meaning, which is "locality". A (quantum) field theory is local by definition, if it is derived from a action, whose Lagrange density is a polynomial of the fields and their first derivatives. Besides this constraint for a successful relativistic QT (at least, I've never heard about any other kind of relativistic QT that is (semi-)consistent in the physicists' sense ;-)) should also be microcausal, i.e., at least the Hamiltonian density should commute when its arguments are separated by a spacelike space-time interval, because this is at least a sufficient condition for the unitarity and Poincare covariance of the S-matrix elements which in turn give the observable quantities like decay widths (lifetimes) of unstable particles and cross sections for scattering processes.

 

[atyy]

This discussion, which I've not completely followed to be honest, is a bright example strengthening my prejudice against philosophy. You have a bunch of vaguely defined notions and fight over this indefiniteness forever. I have no clue, what a rigorous definition of "realism" should be, let alone what EPR meant. Further to my understanding an "observer-independent physics" is a contradictio on adjecto, because physics is about observable, reproducible facts about phenomena in nature. You might now start fighting about the question, whether cosmology is part of physics or not ;-)).

Well, whenever it is complained that relativity or quantum mechanics are "counterintuitive", a standard rebuttal is "nature does not care what we think"! Do you think that is wrong?

 

[stevendaryl]

I wouldn't want to tackle that specific question. However, I will voice the opinion (and not all will agree): Whenever entropy is measured, you have a value I refer to as a "local minimum". Entropy increases in *both* time directions from that local minimum.

How is that consistent with the evolution of the universe: Originally (or soon after the Big Bang), there is mostly hydrogen, and a 10 or 20 billion years later, the hydrogen has turned into helium, nitrogen, carbon, oxygen, iron, and all the rest of the elements? In thermodynamic terms, that is a huge increase in entropy. How is that compatible with entropy increasing in both directions?

 

[RUTA]

How is that consistent with the evolution of the universe: Originally (or soon after the Big Bang), there is mostly hydrogen, and a 10 or 20 billion years later, the hydrogen has turned into helium, nitrogen, carbon, oxygen, iron, and all the rest of the elements? In thermodynamic terms, that is a huge increase in entropy. How is that compatible with entropy increasing in both directions?

Isn't there a problem defining universal entropy increase in GR since there is no unambiguous global definition of energy in general?

 

[zonde]

That complaint is close to what we have voiced concerning "retrocausality" in our most recent paper http://www.ijqf.org/archives/2087. Specifically, given that the future is as "real" as the present, then all events are already "there," so in what sense is anything "moving" in either temporal direction, unless you have a metatime? That's why we didn't consider RBW to be a retrocausal interpretation until recent conversations with Wharton revealed a more God's eye view of what retrocausality can mean. So, our adynamical global constraint qualifies as retrocausal not in a metatime or temporal sense, but in a simple methodological sense -- future boundary conditions are needed in the computational process (path integral in our case).

But it's hardly satisfactory that you simply declare that such and such is not there and anything that can lead to it from infinite past and distance or where/when ever is not allowed. No?

 

[DrChinese]

How is that consistent with the evolution of the universe: Originally (or soon after the Big Bang), there is mostly hydrogen, and a 10 or 20 billion years later, the hydrogen has turned into helium, nitrogen, carbon, oxygen, iron, and all the rest of the elements? In thermodynamic terms, that is a huge increase in entropy. How is that compatible with entropy increasing in both directions?

(First, not trying to make any big statement - hopefully nothing controversial here. The only reason for the comment was to indirectly address the thermodynamic arrow of time for non-realistic interpretations which feature a time-symmetric component.)

I would say that if you calculated the number of possible microstates of any closed system at T=0, then the number of possible microstates of that system that could have led to that (say at T=-1 in the past) will be greater. Ditto for T=1 in the future. So entropy increases in both time directions by my measure, and I would think that any quantum level view would support that. What are the histories of any single particle with a specific position at T=0, and what are its future paths?

The reason that it doesn't look that way is that we usually start measuring a specially prepared system at T=0 and never consider how we got there (because the system was not closed in the past).

 

[RUTA]

But it's hardly satisfactory that you simply declare that such and such is not there and anything that can lead to it from infinite past and distance or where/when ever is not allowed. No?

Sorry, I'm not following you. Would you elaborate?

 

[zonde]

Sorry, I'm not following you. Would you elaborate?

Of course. What I said reflected my intuitive understanding of "adynamical global constraint", sorry if it's inaccurate.

 

[stevendaryl]

The reason that it doesn't look that way is that we usually start measuring a specially prepared system at T=0 and never consider how we got there (because the system was not closed in the past).

I know that you're talking about entropy for microscopic evolution, rather than the universe as a whole, but it seems to me that they have to be connected, don't they?

Assuming a Big Crunch at the end of the universe (just because that makes the gross history look a little more time-symmetric), we have one end of history where matter is mostly hydrogen, and we have another end where matter is everything under the sun. So the two ends look very different. (I think the only way that things could be approximately time-symmetric is if the age of the universe, from Big Bang to Big Crunch, were comparable to the Poincare recurrence time for the universe, which is so huge that saying "astronomically huge" is an astronomically huge understatement). So the issue, for a time-symmetric physics, it seems to me, is how to explain why there is (or seems to be--maybe it's an illusion produced by "coarse-graining" somehow, or by the anthropic principle, or whatever) the cosmological arrow of time is aligned with the thermodynamic arrow of time.

If the arrow of time were somehow an illusion, or is a local effect, it's hard to see why vastly separated sections of the universe would have their arrows of time aligned. The argument that every time you measure entropy, you're at a local minimum of entropy, doesn't sound like it would explain why distant stars have their arrows of time aligned, or why they all have their arrows of time aligned with the cosmological arrow of time.

 

[stevendaryl]

Isn't there a problem defining universal entropy increase in GR since there is no unambiguous global definition of energy in general?

I agree, there might not be a well-defined notion of entropy for the universe as a whole. But if you take a subsystem, such as a star, there is definitely a well-defined "arrow of time" for that subsystem: Initially, the star is mostly hydrogen, and then much later the hydrogen is gone, transmuted into heavier elements. The fact to be explained is why the arrows of time for distant stars are pointing in the same direction. That's independent of subtleties of how you define "entropy" for the universe as a whole.

 

[RUTA]

I agree, there might not be a well-defined notion of entropy for the universe as a whole. But if you take a subsystem, such as a star, there is definitely a well-defined "arrow of time" for that subsystem: Initially, the star is mostly hydrogen, and then much later the hydrogen is gone, transmuted into heavier elements. The fact to be explained is why the arrows of time for distant stars are pointing in the same direction. That's independent of subtleties of how you define "entropy" for the universe as a whole.

Right, that sense of an arrow of time is clear.

 

[RUTA]

Of course. What I said reflected my intuitive understanding of "adynamical global constraint", sorry if it's inaccurate.

Another example of an adynamical global constraint is the least action principle applied to the path of a refracted light ray. To use that principle you need to input the emission spacetime event and the future boundary condition (point in spacetime where you want the light ray to terminate). The path in spacetime that obtains is the one that minimizes the total time from emission to termination. In the God's eye perspective (spacetime view), nothing is moving, nothing is happening. The path of extremal action exists "all at once" in spacetime. Now, you can in this case (and in other least action solutions for classical physics) demand the integrand of the action represent a continual process in space as a function of time that is extremal for each infinitesimal forward time lapse. This leads to the corresponding dynamical equation of motion with its view of light moving through space according to the conditions in its immediate spatial vicinity. In this dynamical view, the termination point in spacetime follows inevitably from the properties inherent in the moving object that determine its local interactions as it moves through space (forward in time). These local interactions then dictate where it goes instant by instant. You could change the nature of the interactions along the path and the termination point will change. There's no sense in which the termination point is dictating the path, but rather the converse. There is a problem with this dynamical view in EPR-Bell phenomena (which is the topic of this thread). To overcome this problem, retrocausal accounts say the "termination point/future boundary conditions" (detector settings and outcomes) *must* be input, i.e., there is no forward-time-evolved solution alone (as in classical dynamics) that accounts for the outcomes. If you want a time-evolved solution for EPR-Bell phenomena, you need both forward-time and backward-time evolved components. Did I answer your question?

 

[Jilang]

If the entropy of the system changes do you still have the backwards evolved time component?

 

[julcab12]

If the entropy of the system changes do you still have the backwards evolved time component?

Time is not well defined in QM. We can only assume trajectories moving forward and backward -- retrodiction. If we interpret Time to have that property then the natural and direct consequence is that will be having mixed realities -- time moving forward which we are in and time moving backward that is hidden from us. But we can't say much about it.

http://www.dailymail.co.uk/sciencet...m-experiment-suggests-time-run-backwards.html