Is Causality Preserved in Quantum Mechanics?

[entropy1]

Do these particular events lie outside past/future light cones or can they also lie in the future light cone?

If someone feels ok with answering this, I would probably be helped a whole lot!

 

[DrChinese]

Discussing retrocausality implies an interpretation of QM. Personally, I believe there are a lot of reasons to consider retrocausal interpretations, I think they are given less consideration than they are due. However, an interpretation is still an interpretation and there are none that are currently "scientifically" preferred (as long as they are not local realistic).

So I think I should point out that none of the generally accepted interpretations are "causal" or "deterministic" in any normal fashion. The Bohmian is the closest. MWI and retrocausal (time symmetric) and the others cannot predict the evolution of all elements from any state to any other state. The Heisenberg Uncertainty Principle is always operating to blur the values of non-commuting observables. Know one, you still know nothing of the other. No interpretation fixes this, even the Bohmian doesn't really solve this (even though they try to claim they do). So saying a state evolves deterministically is exactly fair. The values of many observables cannot be explained at all.

So the term "retrocausal" may be a bit misleading, as will similarly be the notion that Bohmian Mechanics is "deterministic". BM inherently cannot provide the answer to a key variable which would need to be known to make it causal in the normal sense of the word.

 

[atyy]

Do these particular events lie outside past/future light cones or can they also lie in the future light cone?

See DrChinese's reply. Retrocausation is a loophole that allows local realism. (Hmmm, I realize DrChinese wrote that local realism excludes retrocausation ... Might be a terminology difference?)

 

[entropy1]

How is 'realism' compatible with 'probabilism'? I mean, in the sense that probabilism is not concerned with 'pre-existing values'? (Unless you take the state as a value)

 

[bhobba]

How is 'realism' compatible with 'probabilism'? I

Flip a coin. The heads and tails are real - the outcome is simply unknown.

Thanks
Bill

 

[entropy1]

Then (and I know I am going a littlebit off topic here, but it is relevant in this context), I guess I don't really understand what 'local realism' is. Can someone explain that in a relatively simple way to me?

 

[bhobba]

Then (and I know I am going a littlebit off topic here, but it is relevant in this context), I guess I don't really understand what 'local realism' is. Can someone explain that in a relatively simple way to me?

See:
http://www.johnboccio.com/research/quantum/notes/paper.pdf

Thanks
Bill

 

[entropy1]

See:
http://www.johnboccio.com/research/quantum/notes/paper.pdf

Thanks
Bill

Let us define a “counterfactual” theory [10, 11] as one whose experiments uncover properties that are pre-existing. In other words, in a counterfactual theory it is meaningful to assign a property to a system (e.g. the position of an electron) independently of whether the measurement of such property 2 is carried out.

So, if there is no realism, a particle may not even exist if not measured? What does the qualification 'local' mean in this context? And why should a specific particle exist when not measured?

 

[bhobba]

So, if there is no realism, a particle may not even exist if not measured?

Yes.

What does the qualification 'local' mean in this context?

Its independent of that concept.

And why should a specific particle exist when not measured?

Why not?

Those types of questions belong to philosophy and that discipline never reaches any conclusions. That's one reason science and mathematics divorced itself from it many many moons ago (another was great philosophers like Kant claimed all sorts of things that others like Gauss showed were rubbish using not philosophy but math and science). Don't worry about them.

Thanks
Bill

 

[entropy1]

Those types of questions belong to philosophy and that discipline never reaches any conclusions. That's one reason science and mathematics divorced itself from it many many moons ago (another was great philosophers like Kant claimed all sorts of things that others like Gauss showed were rubbish using not philosophy but math and science). Don't worry about them.

I think that physicists that want to endorse local realism are already operating in de philosophical discipline.

 

[bhobba]

I think that physicists that want to endorse local realism are already operating in de philosophical discipline.

That's exactly what they haven't done because, as you can see in the link I gave, they carefully defined their terms.

Thanks
Bill

 

[entropy1]

That's exactly what they haven't done because, as you can see in the link I gave, they carefully defined their terms.

Thanks
Bill

I haven't read it yet, but I scanned the document for 'local realism' and found nothing...?? I guess I have to read it in its entirety...

 

[bhobba]

I haven't read it yet, but I searched the document for 'local realism' and found nothing...??

That's because it uses counterfactual definiteness which has an exact definition - realism is much more vague.

Thanks
Bill

 

[entropy1]

I see now. Thanks! I'm going to study the paper.

 

[Bruno81]

I think that physicists that want to endorse local realism are already operating in de philosophical discipline.

I don't know of any, there may be none. Unless some superdeterminism wacko types. If you've come to that, one can consider the basics - we always refract the outside world(whatever that is) through a brain. That brain always perceives a classical reality and, as far as we know, it originated in an entirely quantum world. We know from other fields of science that we perceive reality as we are structured, not as it fundamentally is(subject to constant debate). Reality as is known today is basically is like this -> quantum reality - brain - classical world. Why nature chose to be like this no one knows, but we surely got to know better than trust naïve realism and its variety local realism.

 

[Edward Hunia]

If initial conditions determine final conditions its causal.
Bil

Thats determinism.

By virtue of superposition, which is more realistically representing a natural system, there is cause.

I think things can be causal, which we should understand as constraints, yet be non deterministic by virtue of computational limits... which paradoxically is a constraint.
What do I mean by causal as a parametric constraint? because that's how math works. at its primary function, a formula is just a constraint that allows the determination of some result. nature follows natural constraints.

The big question, does future constrain the past? lol I'm going to say yes... because the computational limit is a human thing, not a natural one. But I'm also going to say no, because the computational limit is a human thing, and a natural one.

 

[bhobba]

Thats determinism.

Causal - one thing causing another. Initial conditions cause final conditions.

By virtue of superposition, which is more realistically representing a natural system, there is cause.

I think you need to learn what superposition in QM is. Its got nothing to do, except perhaps very indirectly, with causality or determinism, it simply expresses the vector space structure of pure states.

because that's how math works. at its primary function, a formula is just a constraint that allows the determination of some result. nature follows natural constraints.

That's not what a formula is nor is it how math works, or rather it would be a very unusual view of logic - most would not classify consequences from the rules of logic as constraints. You might like to become acquainted with, for example, Topos theory.

Thanks
Bill

 

[bhobba]

we always refract the outside world(whatever that is) through a brain.

Observations in QM exists independent of brains except for some very fringe interpretations of QM .

Why people want go down brains, conciousness etc being involved has me beat. It leads to an unnecessarily weird view of the world.

Thanks
Bill

 

[Bruno81]

Observations in QM exists independent of brains except for some very fringe interpretations of QM .

Why people want go down brains, conciousness etc being involved has me beat. It leads to an unnecessarily weird view of the world.

Thanks
Bill

That 'weird' view of the world is a non-Newtonian worldview. The Newtonian worldview is dead wrong and a worldview of the 18 century. Oh wait, we don't have an established scientific worldview today :). No, seriously, I shared this post to provoke thinking, we really need to examine the basics in light of the modern developments.

 

[bhobba]

That 'weird' view of the world is a non-Newtonian worldview. The Newtonian worldview is dead wrong and a worldview of the 18 century.

That's incorrect. The modern non Newtonian world view has nothing to do with conciousness, brains etc etc except in very fringe interpretations

Beyond that there are interpretations of both QM and even relativity that are Newtonian in spirit.

Whether that is the correct way to proceed is purely a matter of taste. I don't believe it is - I believe symmetry, mathematical beauty and simplicity is the way to proceed - but that means diddley squat.

The truth of theories lies in the formalism and its correspondence with experiment - not what people want to read into it or philosophical waffle associated with such.

Thanks
Bill

 

[Edward Hunia]

Thats determinism. I think things can be causal, which we should understand as constraints, yet be non deterministic by virtue of computational limits... which paradoxically is a constraint.
What do I mean by causal as a parametric constraint? because that's how math works. at its primary function, a formula is just a constraint that allows the determination of some result. nature follows natural constraints.

The big question, does future constrain the past? lol I'm going to say yes... because the computational limit is a human thing, not a natural one. But I'm also going to say no, because the computational limit is a human thing, and a natural one.

Causal - one thing causing another. Initial conditions cause final conditions.
I think you need to learn what superposition in QM is. Its got nothing to do, except perhaps very indirectly, with causality or determinism, it simply expresses the vector space structure of pure states.
That's not what a formula is nor is it how math works, or rather it would be a very unusual view of logic - most would not classify consequences from the rules of logic as constraints. You might like to become acquainted with, for example, Topos theory.

Thanks
Bill

 

[Edward Hunia]

Causal - one thing causing another. Initial conditions cause final conditions.
I think you need to learn what superposition in QM is. Its got nothing to do, except perhaps very indirectly, with causality or determinism, it simply expresses the vector space structure of pure states.
That's not what a formula is nor is it how math works, or rather it would be a very unusual view of logic - most would not classify consequences from the rules of logic as constraints. You might like to become acquainted with, for example, Topos theory.

Thanks
Bill

Its a fact that two waves can add, which have a result. the result can, in principle. be retraced to their cause. The result is a superposition.

I guess I chose my words poorly, I make the distinction here that computational limits make determinism unlikely. I totally agree that final result from initials, but make the distinction that cause need not lead to a fully determined solutions.

I disagree, one can indeed look at math as a simply constraint... and do well that approach. this is because there is a precise result and definitions that are constrained to their solutions. I brought up the view point because some were loosing sight of the reality of natural system, and it allows people to see that determinism can be and I think should be viewed as distinct from cause in that cause leads to indeterminate solutions. I don't disregard the normal view of probable system being indeterminate, I'm just pointing out a deep philosophical idea.

 

[Bruno81]

That's incorrect. The modern non Newtonian world view has nothing to do with conciousness, brains etc etc except in very fringe interpretations
Bill

Please read again, it's in English:

"That 'weird' view of the world is А(one) non-Newtonian worldview"

If further clarification is needed, let me know.

Beyond that there are interpretations of both QM and even relativity that are Newtonian in spirit.

You should stop spreading misinformation. The Newtonian universe is a misconception of the past and no, it is not a matter of taste. It can't be something else and Newtonian(just in spirit) because it's not Newtonian. The Newtonian universe would have been true if the universe was made of solid balls of matter as Newton envisioned and the speed of light wasn't constant across frames of reference(among many other things). Please read and follow the rules to which you agreed upon signing up. But this is all offtopic and if you like to argue for a Newtonian universe, just start a separate thread.

 

[bhobba]

You should stop spreading misinformation. The Newtonian universe is a misconception of the past and no, it is not a matter of taste.

Before accusing people of spreading misinformation it might be wise to learn the facts. You should become acquainted with Bohmian Mechanics:
http://arxiv.org/pdf/quant-ph/0611032v1.pdf

And its not the only one eg see the following on Primary State Diffusion:
http://arxiv.org/pdf/quant-ph/9508021.pdf

Both are classical interpretations fully in the Newtonian spirit.

If you agree with them is another matter - but as interpretations they are valid.

For the sake of discussion let's take BM - in what way isn't it classical. Its simply a field theory like EM.

Thanks
Bill

 

[bhobba]

Thats determinism. I think things can be causal, which we should understand as constraints, yet be non deterministic

That makes no sense.

A differential equation from its initial conditions uniquely determines what happens at any time t - that's from the theory of differential equations. That's pretty much the definition of cause.

Physics generally isn't concerned with semantics.

Thanks
Bill

 

[bhobba]

Its a fact that two waves can add, which have a result. the result can, in principle. be retraced to their cause. The result is a superposition.

Sure waves can add and that's a superposition but such analogies in QM are rather misleading. Its really got nothing to do with waves - eg waves are not complex nor does multiplying such by complex number not make a difference as it does in QM

I disagree, one can indeed look at math as a simply constraint... and do well that approach.

My background is not physics, but applied math. Math is not constraints. A mathematical model is expressing a problem in mathematical language and working out the logical consequences. How that is a 'constraint' has me beat, it really does.

Thanks
Bill

 

[entropy1]

That makes no sense.

A differential equation from its initial conditions uniquely determines what happens at any time t - that's from the theory of differential equations. That's pretty much the definition of cause.

Isn't determinism only a forward-in-time causality? That is, given the state of the system at t, its state at t+dt can in principle be 'calculated' (determined)?

Suppose the state at t does not only (partly) gives the state at t+dt, but also vice-versa, the state at t+dt (partly) gives the state at t (retrocausality, which is a kind of causality). We get causal loops. Is the (total) system state still calculable?

 

[bhobba]

IWe get causal loops. Is the (total) system state still calculable?

That makes no sense at all - at least as far as I can see. Differential equations in general aren't reversible because you have phenomena like strange attractors when different starting values wind up in the same place. But even if it was there is no loops involved.

T%hanks
Bill

 

[entropy1]

That makes no sense at all - at least as far as I can see. Differential equations in general aren't reversible because you have phenomena like strange attractors when different starting values wind up in the same place. But even if it was there is no loops involved.

T%hanks
Bill

I don't understand this, but that is my problem. Don't bother.

 

[bhobba]

I don't understand this, but that is my bad. Don't bother.

Do a search on strange attractors - you likely will find it interesting.

Thanks
Bill