QM Incompleteness: Can We Predict Uncertainty?

[atyy]

You mean that QM doesn't describe the observer in the same way as the quantum system. But it does describe him, it insist that he is a classical object.

"Classical" object does not mean a set of well-defined classical laws of physics. "Classical" object means "common sense" object. There is no known theory of a whole universe as a single system of interacting classical and quantum parts.

 

[vanhees71]

The point is that QM is intrinsically incomplete - it is incomplete even before comparison with data.

Why is it incomplete? It would be incomplete if you could show that the world is deterministic, while QM only delivers a probabilistic description, but who (or what) tells you that the world in fact is deterministic?

 

[martinbn]

"Classical" object does not mean a set of well-defined classical laws of physics. "Classical" object means "common sense" object.

Not sure what your point is?

There is no known theory of a whole universe as a single system of interacting classical and quantum parts.

What about QM?

 

[atyy]

Not sure what your point is?

While some parts of classical physics are complete, the classical observer in quantum mechanics is not fully described by classical laws, since he has to interact with a quantum system. Only a theory that describes both the classical observer and the quantum system as a single system with no observer is complete.

What about QM?

QM does not describe the classical observer and the quantum system as a single system with no observer.

 

[atyy]

Why is it incomplete? It would be incomplete if you could show that the world is deterministic, while QM only delivers a probabilistic description, but who (or what) tells you that the world in fact is deterministic?

There is no QM without a classical-quantum cut. Does the universe have a classical-quantum cut as real?

 

[martinbn]

There is no QM without a classical-quantum cut. Does the universe have a classical-quantum cut as real?

This is irrelevant. In your terminology, the question is about internal completeness, not whether the theory can describe the actual universe.

 

[atyy]

To the OP: it is uncontroversial that QM in the Copenhagen is incomplete eg. https://www.amazon.com/dp/3527403914/?tag=pfamazon01-20. One can finesse the statement, but it is essentially correct. To make QM complete, one needs another interpretation eg. MWI or Bohmian Mechanics.

 

[martinbn]

While some parts of classical physics are complete, the classical observer in quantum mechanics is not fully described by classical laws, since he has to interact with a quantum system. Only a theory that describes both the classical observer and the quantum system as a single system with no observer is complete.
QM does not describe the classical observer and the quantum system as a single system with no observer.

What do you mean it doesn't? May be you mean that it doesn't describe them in a way that you expect it should? But there is no such requirement for a theory.

 

[atyy]

This is irrelevant. In your terminology, the question is about internal completeness, not whether the theory can describe the actual universe.

Yes, but internal completeness is not the same as internal coherence. So you miss the point. The point is the classical-quantum cut, which is the definition of incompleteness, unless there is a theory in which classical and quantum objects co-exist and are described by a single set of laws.

 

[atyy]

What do you mean it doesn't? May be you mean that it doesn't describe them in a way that you expect it should? But there is no such requirement for a theory.

QM does not say when a measurement is made.

 

[martinbn]

Yes, but internal completeness is not the same as internal coherence. So you miss the point. The point is the classical-quantum cut, which is the definition of incompleteness, unless there is a theory in which classical and quantum objects co-exist and are described by a single set of laws.

This is a strange definition of incompleteness!

Why should there be a single set of laws? You are imposing arbitrary restrictions on the theory.

 

[martinbn]

QM does not say when a measurement is made.

So?

 

[PeterDonis]

Thread closed for moderation.

 

[fresh_42]

To all who are still interested in the topic, I'd like to recommend our archive (use the search function), which already contains a vast number of threads about quantum theory and this one won't certainly be the last one. So thread remains closed.