Is Causality in Quantum Mechanics as Clear-Cut as in Classical Mechanics?

[Bob_for_short]

Ah, I get it now. The field supplies the "causes", but then the field just adds that many MORE variables (which presumably are random anyway). So the electron itself does not contain the "hidden variable", it is external and many.
...And you have it in the virtual ("dressed") field.

If you mean me personally, then yes. Each charge comes with its own quantized EMF ("dressed" field). In this sense the QEMF represents the "internal" degrees of freedom of a compound system. I would not call them "external" like vacuum fluctuations in vacuum. Rather, they are internal degrees of freedom belonging to a real charge, capable of radiation wherever it is. So each electron (or charge) carries its own "dressing" with it. The charge in such a system is quantum mechanically smeared, not point-like. And as soon as there is no threshold for exciting soft modes, one cannot prepare the system in its ground state.

I do not think that in an empty space (classical vacuum) there are independent field fluctuations. They always come with charges and are a charge feature, in my humble opinion. Thinking so prevents me from paradoxes like how to harness/extract vacuum energy from empty space (with vacuum cleaner?).

 

[italiano vero]

the fact that fairies have not been documented is not proof that there are no fairies.

yeah, but there is a foundamental difference between fairies and causes: at the macroscopic level there is causality. how can it be, if quantum world is random? The quantum causality must exist to explain the classical one. Also the brownian motion was thought at the beginning as random, only because no causes were observed. But this is in opposition with Classic causality: how can they coexist? They cannot. I know the difference between the brownian motion and the quantum one, but the example is pertinent.


If we cannot know if there are or not the causes, we can introduce them to explain Classic causality.

Earthquakes are unpredictable but caused. Who can predict a single quake? Is it random only for this?

 

[DrChinese]

yeah, but there is a foundamental difference between fairies and causes: at the macroscopic level there is causality. how can it be, if quantum world is random? The quantum causality must exist to explain the classical one.

Sorry, that is circular reasoning! You are assuming classical causality (which may or may not exist - this is quite debatable, especially if you have free will) to justify micro causality.

Regardless, there is no physical requirement that macro causality require micro causality anyway. What do you have to compare it to? How can you prove this? Just asking "how can it be, if quantum world is random?" is not a convincing argument; how can ANY physical phenomena (entanglement, HUP, Pauli exclusion principle, general relativity, etc.) be?

My point was that it is NOT possible to disprove micro causality, but it MIGHT be possible to prove it. Of course, I doubt that, but I understand that others might not agree. But if you are asking me to DISPROVE causality, I can't and never will. But lack of evidence FOR causality does not constitute evidence FOR, it definitely tends to the AGAINST side given the investigation done so far.

If you take a photon polarized at 0 degrees and run it through a polarizing filter at 45 degrees, what causes the result? That is the specific question at hand. Theory and experiment agree: there is no known cause.

 

[Bob_for_short]

If you take a photon polarized at 0 degrees and run it through a polarizing filter at 45 degrees, what causes the result? That is the specific question at hand. Theory and experiment agree: there is no known cause.

The result is always a radiated by the filter medium photon, not the incident one. So it is the medium who brings uncertainty in this particular case due to interaction with the incident photon.

 

[italiano vero]

Sorry, that is circular reasoning!

oh, yeah, it is. For centuries thinkers debated on the causes of the events. Hume said that there is no connection between an event and another: causes doesn't exist, the motion of billiard balls is random and not causal. We will indeed not solve this problem here.

there is no physical requirement that macro causality require micro causality anyway. How can you prove this?

How can I prove that classical mechanics cannot be based on randomness? ... This is evident! Hume asks to the other philosophers to prove the existence of gravity. So they hit an object and this one fall down. The answer of Hume was "This is not a proof: how can you say that this is not random? How can you know that one day one object will not fall?" This is twisted. If the classical phisic laws are valid in the macroscopical context, regularity and causality must exist.

The existence of a single valid law proves the existence of causality: laws cannot exist in anarchy, in randomness, because randomness is lack of laws.

The causality exists and this is proved by the existence of any phisic law, and causality cannot be based on randomness. This is my position. Of course is criticizable, like any other position.

there is no known cause.

yes, no KNOWN cause.

 

[DrChinese]

...The causality exists and this is proved by the existence of any phisic law, and causality cannot be based on randomness...

This is, as I said, circular. So is this conversation, as apparently you are not familar with the laws of quantum physics. You might want to learn more about these before you make statements like this. QM is probabilistic and yet has fairly rigid rules.

 

[dmtr]

If you take a photon polarized at 0 degrees and run it through a polarizing filter at 45 degrees, what causes the result? That is the specific question at hand. Theory and experiment agree: there is no known cause.

What makes you think, that the observer who've seen the photon any less real in comparison to the observer who have not?

-- Dmtr

 

[DrChinese]

What makes you think, that the observer who've seen the photon any less real in comparison to the observer who have not?

-- Dmtr

I don't understand your question. I didn't intend to draw the observer into the equation so much as say: a photon's polarization value at a specifc angle has no known cause that has as yet been demonstrated.

 

[dmtr]

I don't understand your question. I didn't intend to draw the observer into the equation so much as say: a photon's polarization value at a specifc angle has no known cause that has as yet been demonstrated.

I thought you did. You've said "if you take a photon polarized at 0 degrees", that assumes an observer correlated (entangled) with a photon at the certain state.

-- Dmtr

 

[DrChinese]

I thought you did. You've said "if you take a photon polarized at 0 degrees", that assumes an observer correlated (entangled) with a photon at the certain state.

-- Dmtr

OK, so how does that relate to what "causes" the subsequent polarization value?

 

[dmtr]

OK, so how does that relate to what "causes" the subsequent polarization value?

You need the "subsequent polarization value" first, before you are talking about what is "causing" it. The subsequent polarization value is just an another entanglement in between the observer and the photon. What you would get as a result is an observer in the superposition of two states. Now it would be up to an observer in some certain state to interpret his own state, and there is no problem with that. So there is no such thing, as the "defined subsequent polarization value", and there is no point of talking on what causes it.

-- Dmtr

 

[Bob_for_short]

Dmtr, you should call this concept Dr^tm.

 

[DrChinese]

You need the "subsequent polarization value" first, before you are talking about what is "causing" it. The subsequent polarization value is just an another entanglement in between the observer and the photon. What you would get as a result is an observer in the superposition of two states. Now it would be up to an observer in some certain state to interpret his own state, and there is no problem with that. So there is no such thing, as the "defined subsequent polarization value", and there is no point of talking on what causes it.

-- Dmtr

I have no clue to what you are talking about, but apparently we agree that there is no cause for the result.

 

[Descartz2000]

It is my understanding that in classical mechanics, cause and effect are universally accepted.

Is it the same in QM? Is causality sound in QM?

It seems obvious that the role of determinism is not consistent with QM, but it too seems that all events (micro and macro) must have sufficient causes. A lack of causality argues for spontaneous emergence or the event being a first cause. It seems to me that all events will default back to available variables (sufficient causes). Otherwise, an event is based on nothingness or a lack of something, something without conditions or configurations or parameters. This seems to argue that acausality is based on nothing. Logically speaking, this makes no sense, an event then is either its own first cause (self causation), or it is based on available variables (causality of a larger system). I think some logic should be used in our interpretations.

 

[italiano vero]

all events (micro and macro) must have sufficient causes. A lack of causality argues for spontaneous emergence or the event being a first cause.
Logically speaking, this makes no sense, an event then is either its own first cause (self causation), or it is based on available variables (causality of a larger system). I think some logic should be used in our interpretations.

Exactly. This is my position. However, there's no reason to think that logic can understand all the characteristic of reality. But there's no reason also to think the contrary. So we can only say that an event that seems random could be caused or not. But, in my opinion, we can't explain macroscopical causality without the assumption of microscopical causality for the reason that Descartz2000 has explained.

However, as DrChinese has underlined, this assumption is more phylosophical than purely mathematical/physical.

"Ai posteri l'ardua sentenza." (Manzoni, 5 Maggio)