# Causality in QM?

• I
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

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.

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.

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bhobba
Mentor
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 lets take BM - in what way isn't it classical. Its simply a field theory like EM.

Thanks
Bill

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bhobba
Mentor
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
Mentor
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

Gold Member
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
Mentor
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

Gold Member
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
Mentor
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

So, if there is no realism, a particle may not even exist if not measured? What does the qualification 'local' mean in this context?
That is a good question. Adopting a no realism/epistemic interpretation does appear to avoid ontic, non-local causal influences (and maintain a fully relativistic account of physical goings-on). But, at the same time, it's not clear that a non-realist interpretation actually saves locality because in adopting that kind of interpretation, the distinction between 'local' and 'non-local' would not even appear to apply.

entropy1
Gold Member
That is a good question. Adopting a no realism/epistemic interpretation does appear to avoid ontic, non-local causal influences (and maintain a fully relativistic account of physical goings-on). But, at the same time, it's not clear that a non-realist interpretation actually saves locality because in adopting that kind of interpretation, the distinction between 'local' and 'non-local' would not even appear to apply.
Thank you. It seems to me that, if you don't measure the event, there is at least no 'informational' connection established between the observer and the event - concerning a measurement. (?)

DrClaude
Mentor
The initial question has been answered a long time ago. Yes, QM is causal.

Time to close the thread.

bhobba