Ontology of an electron passing through a Stern-Gerlach magnet

[entropy1]

So, as far as I think I understand, an electron that passes through a Stern-Gerlach magnet, will not have a value for its spin until that spin is measured? Does that mean the electron has no position (as given by the SGM) until measured, or that the electron does not even exist until measured?

 

[Vanadium 50]

What is happening when we are not measuring it is a question that cannot be answered by the scientific method.

 

[entropy1]

What is happening when we are not measuring it is a question that cannot be answered by the scientific method.

Does that mean that if we fire an electron or a photon and measure it at a detector, that we can't say we know that it has traveled to the detector or that it is even the same particle?

 

[bayakiv]

The spin of an electron before measurement is a random value, which after measurement becomes a reliable value. This answer is the essence of the scientific method.

 

[Vanadium 50]

Does that mean

What is happening when we are not measuring it is a question that cannot be answered by the scientific method.

 

[EPR]

Ontology is a neat classical notion that has no counterpart in the quantum world.

 

[entropy1]

So does that mean we try to predict the probability that X or Y will happen? Can we ever predict that Z will happen with probability 1? For example, some atom decays, and if we know know the particles it has generated, we know what is has decayed into?

 

[bayakiv]

However, dialectics - in nature, there is a constant struggle between the accidental and the causal, therefore one should not expect probability 1.

 

[haushofer]

Ontology is a neat classical notion that has no counterpart in the quantum world.

Well,no, ontology is that aspect of physics which prevents it from becoming mere bookkeeping.

Of course QM also has an ontology. The many interpretations already prove that your statement is categorically wrong.

 

[haushofer]

So does that mean we try to predict the probability that X or Y will happen? Can we ever predict that Z will happen with probability 1? For example, some atom decays, and if we know know the particles it has generated, we know what is has decayed into?

Yes, sometimes probabilities turn out to be 1.

Measure a particle's spin projection. Say, it's +1. If you "immediately" perform a second measurement, you're guaranteed to obtain the same value.

 

[haushofer]

What is happening when we are not measuring it is a question that cannot be answered by the scientific method.

I don't agree. That depends on your ontology.

 

[Vanadium 50]

I don't agree. That depends on your ontology.

Please describe an experiment that tests what something is doing when we aren't measuring it.

 

[haushofer]

Please describe an experiment that tests what something is doing when we aren't measuring it.

Shoot a cannonball away. The ontology of classical mechanics tells us the trajectory of the ball, regardless of measurements. We can say the ball has a position x at time t, regardless of measurements.

That's the difference with QM; QM (in its standard interpretations) tells you what to expect in a measurement, classical mechanics gives you a trajectory.

That's also the appealing part of Bohmian mechanics.

But maybe we differ in the definition of "the scientific method".

 

[EPR]

Well,no, ontology is that aspect of physics which prevents it from becoming mere bookkeeping.

Of course QM also has an ontology. The many interpretations already prove that your statement is categorically wrong.

What is THE ontology of QM specifically?

 

[Vanadium 50]

classical mechanics tells us the trajectory of the ball, regardless of measurements.

And how do you test that scientifically? i.e. comparing with experiments?

I maintain that science cannot answer the question "what is this system doing when we are not looking at it".

 

[haushofer]

And how do you test that scientifically? i.e. comparing with experiments?

I maintain that science cannot answer the question "what is this system doing when we are not looking at it".

Well, ten we disagree about what the scientific method entails. In my view this method is more than "comparing with experiments". It also includes ontology.

It's similar to the famous "does a falling tree make a sound if nobody is there listening?" From a classical point of view the answer is clear: classical mechanics prdicts that pressure waves will be formed, regardless if there is an observer observing it. If I throw a dice under a cup, classical mechanics tells me that one side is up, whether I look or not. This form of ontology is calledd"realism".

So, yes, of course science can answer those questions. In QM it becomes more subtle of course.

 

[haushofer]

What is THE ontology of QM specifically?

That depends on your "interpretation".

 

[haushofer]

Another example: if a rock falls from a hill on an exoplanet light years from us, we cannot observe it. But that doesn't mean the scientific method can't answer the question what will happen, given some parameters of the planet.

 

[Vanadium 50]

If you are going to decide between two models with identical experimental predictions based on other factors, that's up to you. In my view, though, this is not a scientific decision.

 

[EPR]

That depends on your "interpretation".

Then it's not that QM has an ontology. But me. Since it's me who has to decide it.

 

[haushofer]

Then it's not that QM has an ontology. But me. Since it's me who has to decide it.

Then you seem to believe that there are theories out there without ontology.

Again, a physical theory is more than just a pile of equations.

 

[haushofer]

If you are going to decide between two models with identical experimental predictions based on other factors, that's up to you. In my view, though, this is not a scientific decision.

Well, than we differ about what this scientific method entails.

E.g., I think it's "scientific" to use Occam's razor if one obtains similar empirical results.

 

[martinbn]

What is happening when we are not measuring it is a question that cannot be answered by the scientific method.

Why not? For example clasical mechanics, signle particle. The theory says that the particle will move along the curve determined by the initial conditions and the equations of motion, whether it is measured or not. It can be tested by trying to find it somewhere else. This way the statement is falsifyable, and if it is never found anywhere else, you have tested the theory without measuring it (the particle).

 

[martinbn]

What is THE ontology of QM specifically?

That the particles/fields exist, in this example the electron.

 

[entropy1]

Then it's not that QM has an ontology. But me. Since it's me who has to decide it.

It occurs to me that perhaps the "correct" ontology is so counterintuitive, that we don't accept it as ontology. For instance, particle-wave duality perhaps just means just that: particles are waves and vice-versa.

 

[martinbn]

It occurs to me that perhaps the "correct" ontology is so counterintuitive, that we don't accept it as ontology. For instance, particle-wave duality perhaps just means just that: particles are waves and vice-versa.

It definitely doesn't mean that.

 

[entropy1]

It definitely doesn't mean that.

Well, then, to speak with Christopher Hitchens: "I guess that's progress of a kind"

 

[Demystifier]

So, as far as I think I understand, an electron that passes through a Stern-Gerlach magnet, will not have a value for its spin until that spin is measured? Does that mean the electron has no position (as given by the SGM) until measured, or that the electron does not even exist until measured?

It depends on the interpretation. In the Bohmian interpretation it means that electron, as a pointlike particle, always has a position and never has a spin. When we measure spin, we don't really measure a property of the electron alone, but a property that can be attributed to the electron and the apparatus together.

 

[bayakiv]

It occurs to me that perhaps the "correct" ontology is so counterintuitive, that we don't accept it as ontology. For instance, particle-wave duality perhaps just means just that: particles are waves and vice-versa.

In this regard, let me ask you how intuitive the concept of ether and the concept of a closed world are. I am asking this question because it is directly related to the ontology of quantum mechanics.

 

[entropy1]

In this regard, let me ask you how intuitive the concept of ether and the concept of a closed world are. I am asking this question because it is directly related to the ontology of quantum mechanics.

How do you see that?