Nature Physics on quantum foundations

[physika]

Quantum theory describes experiments, but does not provide explanations

Right, Just describes.

No more.

 

[bhobba]

Right, Just describes.

All mathematical models just describe reality (whatever that is). The map is not the territory. We do not discuss philosophy here but for your own personal interest you may wish to investigate if we, as human beings, only ever have deceptions of reality. But here is not the place to do it, except to note that is what theories in physics are.

Thanks
Bill

 

[Demystifier]

All mathematical models just describe reality (whatever that is).

Most scientific theories offer explanations (whatever that is). Quantum theory is perhaps the only scientific theory for which a large fraction of scientists say that it should only be used for quantitative predictions, not for qualitative explanations.

 

[martinbn]

Most scientific theories offer explanations (whatever that is). Quantum theory is perhaps the only scientific theory for which a large fraction of scientists say that it should only be used for quantitative predictions, not for qualitative explanations.

I don't see the difference between QM and any other. Can you give an example?

 

[physika]

Most scientific theories offer explanations (whatever that is). Quantum theory is perhaps the only scientific theory for which a large fraction of scientists say that it should only be used for quantitative predictions, not for qualitative explanations.

I don't see the difference between QM and any other. Can you give an example?

Physiology.

 

[Fra]

I don't see the difference between QM and any other. Can you give an example?

You can probably make a comment on this complicated but how about this:

In classical mechanics we have an understanding of causal mechanism in terms that systems are are affected either deductively or probabilistically by local objective facts, such as other local objects in spatial contact, or by local fields that are given a similar ontology. This is understandable. So when combining such "mechanisms" to build the hamiltonian of a system, we at least thinkg we have a decent explanation.

In QM, we simply do not understand the causal mechanism. It SEEMS that things (actions, dynamics) are more affected by expectations, rather than actual matters. And expectations that are moreover not objective facts. But what kind of explanation or understanding does this offer us? It's very different from the causality in classical physics. (That said, even in classical physics we can not "explain" everything, but that is not the main point)

Understanding causality is to understand the details of interactions. Classical mechanics is understood "mechanistically", if you by "objects" include "classical fields". Quantum mechanics is mainly understood in terms of information - but what does that really mean, for the causality?

(I think rejecting these questions to philosohpy is a way of avoiding difficult questions that theoretical physicists should figure out! I feel more symphaty for people that acknowledge this, even if they have a different opinion of the solution that me, than those that consistently try to play this question down. As to what a potential insight may lead to should be obvious, because we still do not have a unified theory of all interactions, but perhaps that is also a philosophical fantasy)

/Fredrik

 

[martinbn]

You can probably make a comment on this complicated but how about this:
...

/Fredrik

@Demystifier said that only in QM there are scientists that say that QM is just for quantitative predictions and not for qualitative explanations. What is an example of an explanation in non-quantum physics that is different from what one has in QM?

 

[Fra]

@Demystifier said that only in QM there are scientists that say that QM is just for quantitative predictions and not for qualitative explanations. What is an example of an explanation in non-quantum physics that is different from what one has in QM?

I find the best explanatory power in classical physics to be found in statistical mechanics. But its based on an underlying ontology where simply infer macroscopic dynamics using ignorance classical probability theory.

I agree CM does not "explain" everything. QM IMO also (due to its measurement/observer focus) comes with an expectation higher explanatory standard of inference. But which it doesnt live up to yet. So my expectations on QM (or what we wait for) is much higher than on CM.

/Fredrik

 

[bhobba]

I

@Demystifier said that only in QM there are scientists that say that QM is just for quantitative predictions and not for qualitative explanations. What is an example of an explanation in non-quantum physics that is different from what one has in QM?

Just heuristically. In Newtonian physics, you can use your everyday experience to help solve problems like blocks sliding down inclined planes. You draw diagrams and arrows for things like the reaction force of the block on the plane. You can't, at least at our current level of technology (that may change in the future), do that in QM. You develop intuition in QM by solving problems, often solving differential equations. In fact, in the partial differential equation course I did, a number of examples were taken from QM eg solving Schrödinger's equation for the hydrogen atom, even though many were just math students and didn't know any QM - we were just told this is the equation you get. It was a standard example of the separation of variables method. This lack of contact with everyday experience leads some to differ in positions about QM. They are neither right nor wrong - my position is the simplest of all - there is no essential difference. Others prefer something like the pilot wave theory.

Thanks
Bill

 

[Fra]

I feel like I repeat myself but what I think is the missing understanding of "causality in QM" as opposed to causality in CM (which essentially would suggest a HV mechanism, as per Bell, it sort of follows from the ontological concepts of CM, but which we know does not work!). So the old causality principle does not work, but what do we have instead? This is open but some hints into alterantives that is a little more elaborate than intuition gained from playing with the equations of QM (I am convinced we can do better than that)....

Information causality as a physical principle​

"...We suggest that information causality—a generalization of the no-signalling condition—might be one of the foundational properties of nature."
-- https://www.nature.com/articles/nature08400

As for other intuition see also this...

Connection between Bell nonlocality and Bayesian game theory​

"In 1964, Bell discovered that quantum mechanics is a nonlocal theory. Three years later, in a seemingly unconnected development, Harsanyi introduced the concept of Bayesian games. Here we show that, in fact, there is a deep connection between Bell nonlocality and Bayesian games, and that the same concepts appear in both fields. This link offers interesting possibilities for Bayesian games, namely of allowing the players to receive advice in the form of nonlocal correlations, for instance using entangled quantum particles or more general no-signalling boxes. This will lead to novel joint strategies, impossible to achieve classically. We characterize games for which nonlocal resources offer a genuine advantage over classical ones. Moreover, some of these strategies represent equilibrium points, leading to the notion of quantum/no-signalling Nash equilibrium. Finally, we describe new types of question in the study of nonlocality, namely the consideration of nonlocal advantage given a set of Bell expressions."
-- https://www.nature.com/articles/ncomms3057

Anyone can imagine, actual games of expectation, it's all around us. But in forms of higher order interactions in social systems or economic systems, and I argue that you can understand this (ie. not just by playing to equations), and what if this isomorphism between QM and bayesian games are not just a conicindence? I think it can't be. What is the "causal mechanism" in a game of expectation? Think about that, and perhaps QM is not really that strange after all? Is it just strange beceause we think wrong?

/Fredrik

 

[physika]

. But in forms of higher order interactions in social systems or economic systems,

Right, a short sighted vision of casuality.

Example; an effect can become a cause.