Is causality challenged by quantum theory's reliance on indeterminacy?

[Borean]

Hello all.

I am merely an inquirer into physics; not even an amateur.

The question that has puzzled me with regard to quantum theory/physics/mechanics, is the status of causality.

What is the status of causality in quantum theory?

I would be grateful if anyone could explain this to me.

Borean

 

[Bob_for_short]

Everything is OK with it: the wave function equation is causal, its solution is determined with the initial conditions, just like in classical mechanics.

Another thing is a probabilistic outcome of the measurement process. The measurement "points" are spread out (remember an interference picture). But it is an intrinsic property of quantum world. The average (inclusive) things are well predicted with the wave function.

 

[Borean]

My question is more specifically if quantum theory is acausal.

I read in another discussion that John Bells experiments and Bells theorem means that we are forced to abandon causality. Here is the discussion: http://www.physicspost.com/physicsforums/topic.asp-ARCHIVE=&TOPIC_ID=1602.htm

 

[alexepascual]

Quantum theory has two components. There is the wave function (or state vector) which is assumed to evolve in a causal way before it collapses, and then there is the collapse process which is not causal.
There is a standard mathematical machinery that describes these processes and which has been proven to work in all attempted experiments. This mathematical formulation gives good predictions but the results are of a probabilistic nature.
While the mathematical formulation is usually not challenged due to its proven success, its interpretation remains ope to debate.
You can use the math to predict (to the extent allowed by the theory) the results of the experiments. But when you start asking: What does this really mean? you'll get mainly two different answers:
(1) You should not ask this question. Just keep using the math (because it works).
(2) It is valid and potentially useful to try to gain a better understanding of how the different elements in the mathematical apparatus of quantum mechanics correspond (or not) to elements of reality.

 

[Bob_for_short]

I read in another discussion that John Bells experiments and Bells theorem means that we are forced to abandon causality. Here is the discussion: http://www.physicspost.com/physicsforums/topic.asp-ARCHIVE=&TOPIC_ID=1602.htm

It only means that quantum world is different from classical one.

The main thing - the wave function evolution - is causal.

 

[Borean]

Quantum theory has two components. There is the wave function (or state vector) which is assumed to evolve in a causal way before it collapses, and then there is the collapse process which is not causal.
There is a standard mathematical machinery that describes these processes and which has been proven to work in all attempted experiments. This mathematical formulation gives good predictions but the results are of a probabilistic nature.
While the mathematical formulation is usually not challenged due to its proven success, its interpretation remains ope to debate.
You can use the math to predict (to the extent allowed by the theory) the results of the experiments. But when you start asking: What does this really mean? you'll get mainly two different answers:
(1) You should not ask this question. Just keep using the math (because it works).
(2) It is valid and potentially useful to try to gain a better understanding of how the different elements in the mathematical apparatus of quantum mechanics correspond (or not) to elements of reality.

So that means that the math, in itself, is neutral to whether or not there is causality or not behind our observations?

Or does the math specifically force us to abandon causality?

Since we can still predict this supposedly "acausal" wave collapse process probabilistically, wouldn't it be incorrect to say that it is "acausal", and more correct to say that it is not fully determinable?

Causality really just means one thing depending on another, even if we don't know what depends on what, and even if we can't explain every causative event causally, and even if we don't have the observational abillity to give a causative account of everything in the universe.

That is, causality is not = determinism.

 

[Bob_for_short]

There is no wave function collapse while measurement as there is no probability collapse. The notion of probability belongs (covers) all (big amount of) measurements.

 

[Borean]

There is no wave function collapse while measurement as there is no probability collapse. The notion of probability belongs (covers) all (big amount of) measurements.

Yes.

But is the "wave function collapse" (or anything else in quantum theory) explicitly acausal or is it simply undeterminable what it's "cause" is?

 

[Bob_for_short]

But is the "wave function collapse" (or anything else in quantum theory) explicitly acausal or is it simply undeterminable what it's "cause" is?

The cause is an interaction with a measurement device. If we speak of photon absorption by a photographic plate, it cannot be predicted because the plate consists of many atoms whose sizes are much smaller than the photon wave-length. Who knows which one is the most ready to absorb a photon? So such events are not predictable but only their sum.

 

[Borean]

The cause is an interaction with a measurement device. If we speak of photon absorption by a photographic plate, it cannot be predicted because the plate consists of many atoms whose sizes are much smaller than the photon wave-length. Who knows which one is the most ready to absorb a photon? So such events are not predictable but only their sum.

Ah, I see.

So there are some limitations as to our observatory power.

But my question still remains; are there any explicitly acausal things in the universe, according to quantum theory? Can things happen without causes?

And remember, indeterminacy does not mean acausality. If things happen without us knowing the cause, that does not mean they have none. What I am asking is rather if quantum theory positively affirms acausality as such.

 

[Bob_for_short]

No, as far as I know, there is no such an affirmation. There is just huge difference in classical mechanical and quantum mechanical causalities, but there is no acausality in QM.

I would say that the classical mechanical determinism emerges from the inclusive QM picture when many-many events are added together and averaged. The average value is unique.

 

[Borean]

No, as far as I know, there is no such an affirmation. There is just huge difference in classical mechanical and quantum mechanical causalities, but there is no acausality in QM.

I would say that the classical mechanical determinism emerges from the inclusive QM picture when many-many events are added together and averaged. The average value is unique.

Interesting. What about something like atom/nuclear decay? Isn't that acausal?

The discussion I linked earlier says that it is.

Let me quote:

Question: Is it true that quantum mechanics allows/requires certain processes to occur without cause?

Answer: Yes, in a probablistic fashion. For example, if there are two possible decay paths for an unstable particle--it can decay into x+ and y- or into s0 and t0, then there is nothing--nothing--that causes it to take one path or the other. The path taken by the decay is acausal. Likewise, we can say that the mean life of a free neutron is only 15 minutes, but one particular neutron may decay in 14 minutes and another in 16 minutes, and there is no causality connected with the difference in specific decay times. An electron may have a 12% chance of tunnelling across a gap (like a tunnel diode) in .01 seconds, but nothing causes any particular electron to tunnel or fail to tunnel.

It's important to note that physicists are as certain as they can be that there are no hidden variables which control these acausalities, "behind the scenes" as it were. John Bell proposed an experiment which would, according to his analysis, reveal whether or not any such set of variables could be influencing quantum uncertainty. When performed, the experiments indicate that there is no set of hidden variables that are linked to quantum events: the quantum incorporates an element of genuine, irreducible uncertainty, or acausality in the sense described above.

It's very interesting that current best theory says that the entire universe once occupied a region comparable to the Planck size, and thus the entire universe would have been subject to quantum uncertainty.

--Don

But I suspect what he really means is that it is indeterminable, to us.

Can anyone clarify this?

 

[Bob_for_short]

Interesting. What about something like atom/nuclear decay? Isn't that acausal?...But I suspect what he really means is that it is indeterminable, to us.
Can anyone clarify this?

It is the same song. One cannot predict any single quantum event, it is a nature feature. But you can:

1) predict whether it will happen or not. The radioactive decay law says it will happen for sure.

2) predict the average number of decayed or remaining nuclei N(t) in a sample of many-many atoms.

Any single event, taken separately (observed only one time), does not even say what has happened. You need statistics to create notions, language of phenomenon description.

The radioactive decay has a clear cause - the potential barrier transparency (for simplicity).

 

[Borean]

It is the same song. One cannot predict any single quantum event, it is a nature feature. But you can:

1) predict whether it will happen or not. The radioactive decay law says it will happen for sure.

2) predict the average number of decayed or remaining nuclei N(t) in a sample of many-many atoms.

Any single event, taken separately (observed only one time), does not even say what has happened. You need statistics to create notions, language of phenomenon description.

The radioactive decay has a clear cause - the potential barrier transparency (for simplicity).

So does that mean that single quantum events don't have any cause -are acausal- or simply that they are indeterminable/unpredictable in isolation but still have a cause?

 

[Bob_for_short]

So does that mean that single quantum events don't have any cause -are acausal- or simply that they are indeterminable/unpredictable in isolation?

They are are indeterminable/unpredictable but have a certain cause to happen.

Look at the determinism as at an average (unique) picture obtained from many spread, occasional points.

 

[gel]

QM is acausal, as explained by the following experiments.

Shine light through a polarizing filter. Some fraction will pass through it, which will then be polarized.
Now place a second polarizing filter after the first, and aligned with it. Most of the light which gets through the first filter will also pass through the second (100% in theory, but polarizers are not perfect).
Rotate the second polarizer to that it is aligned at 90 deg to the first. Then, none of the light will get through it.
Now align the polarization of the second filter at 45 deg to the first and about 1/2 the light will get through.
However, you can reduce the intensity of light so far that there is only a single photon passing through the apparatus at anyone time. Given that the photon passes through the first filter, it is not possible for "half the photon" to pass through the second. Instead, QM says that the photon either passes through the second filter or it doesn't. The outcome is random, with each possibility happening with a probability of 50%.

When it is said that the wavefunction is deterministic, this means that we can calculate the 50% probability precisely (the probabilities themselves are deterministic), but the outcome of the experiment is still random.

According to the standard interpretation of QM, the outcome is fundamentally random and it is theoretically impossible to predict the outcome.
Of course, you can always suggest that maybe there is some more fundamental theory than QM with additional underlying variables, the knowledge of which would allow you to accurately predict the outcome of such experiments. However, there are good reasons for believing that this is not the case (e.g., Bell's theorem), although it doesn't convince absolutely everyone.

 

[alexepascual]

QM is causal only to the extent that the wave function can accurately predict probabilities. But that is not what we normally understand as strict causality. Let's say we have a wave packet that represents a particle. We can predict how the shape and the position of the wave packet is going to evolve. But when we try to find the location of the particle, we can't say with certainty were we are going to find it. In this respect QM is acausal.
You can send a photon through a half-silvered mirror and it'll have 50% chance of being reflected and 50% chance of being transmitted. You can put detectors that will find out if it was reflected or transmitted. There is no element in the theory that allows you to know beforehand which outcome you are going to get. This is acausal.
There have been discusions about the possibility of some hidden variable determining the outcome of apparently random events. I think it was determined that if there were hidden variables they could not be local.
Nobody has ever been able to exploit the concept of a hidden variable to predict the result of an otherwise random event.
The idea of random (probabilistic) events does not need to be that unacceptable. When you travel through space, you cas find objects scattered around without any "causal" relationship to the adjacent objects. By looking at a region of space you can't predict what you'll find in adjacent regions. Why can't it be the same with time?.
If you believe that there is "one world" (that is one past, one present and one future) you could picture this world as represented in a strip of film. You will find some connection between adjacent frames in the film. Usually you'll see that objects "move" smoothly, etc. But it doesn't necessarily have to be that way. You could imagine a film where a particle is at a totally random location in each frame. In this case you would be assuming that the particle does have a particular location which is unpredictable. But I think there are experiments that show that even assuming that the particle moves in an acausal way is not enough. You have to assume that it does not have a particular location until you measure it.
Other way of looking at it is to say that the particle is in all places at once (a superposition). How you think of this would depend on your particular interpretation of quantum mechanics.

 

[Borean]

According to the standard interpretation of QM, the outcome is fundamentally random and it is theoretically impossible to predict the outcome.

It's random, but that does not mean acausal.

We need to distinguish between determinacy and causality.

Indeterminacy does not mean acausality; it means indeterminacy.

If our ancestors millennia ago had no idea why the sun rose, no matter how hard they tried explaining it, that would not imply that the universe is acausal, but simply indeterminable.

Even if we couldn't determine why the sun rises today, we would still not have come to the conclusion of acausality; still only indeterminacy.

Of course, you can always suggest that maybe there is some more fundamental theory than QM with additional underlying variables, the knowledge of which would allow you to accurately predict the outcome of such experiments.

That is not necessary to affirm indeterminacy of isolated events in the universe.

Simply because, there is nothing that says any theory which has anything less than total information about the universe will ever be able to predict/determine the total amount of events in the universe, in isolation.

However, there are good reasons for believing that this is not the case (e.g., Bell's theorem), although it doesn't convince absolutely everyone.

But Bells theorem does nothing to suggest acausality over a fundamental indeterminacy.

 

[Borean]

QM is causal only to the extent that the wave function can accurately predict probabilities. But that is not what we normally understand as strict causality. Let's say we have a wave packet that represents a particle. We can predict how the shape and the position of the wave packet is going to evolve. But when we try to find the location of the particle, we can't say with certainty were we are going to find it. In this respect QM is acausal.

Again, that is indeterminacy, not acausality.

 

[Bob_for_short]

QM is acausal, as explained by the following experiments.

As soon as QM works with probabilities, it is clear that the events are occasional, spread, with non-trivial distributions. The physics task is to catch this property of nature and QM does it. The laws of ensembles (distributions) are described well, without hidden parameters.

 

[gel]

Indeterminacy does not mean acausality; it means indeterminacy.

Ok, I'm not really sure about the definitions here. Yes, QM is random. Is this the same thing as acausal? What caused the photon to pass through the polarizers rather than be absorbed? I don't know - QM just says that it is just a random event with given probabilities. If you consider that to be enough to constitute a cause, then it is causal.

 

[Bob_for_short]

Ok, I'm not really sure about the definitions here. Yes, QM is random. Is this the same thing as acausal? What caused the photon to pass through the polarizers rather than be absorbed? I don't know - QM just says that it is just a random event with given probabilities. If you consider that to be enough to constitute a cause, then it is causal.

The polariser presence means introducing an interaction (absorption). Any interaction has many channels, choices, paths, etc. No wonder sometimes photons are absorbed, sometimes not.

 

[gel]

I think Borean's only disagreement with my post was over the meaning of the word acausal, and that we agree about what QM is saying. Which is fine by me.

And I think Bob_for_short is agreeing with my post, but I'm not sure. QM tells us the probabilities for each outcome. If that is really the best that can be done (and I expect that it is), then we can't really expect anything more of it.

 

[gel]

The polariser presence means introducing an interaction (absorption). Any interaction has many channels, choices, paths, etc. No wonder sometimes photons are absorbed, sometimes not.

If the polariser is working properly, then
- a photon with polarization aligned with the polariser axis will pass through it.
- a photon with polarization at 90 deg to it will be absorbed.
That's all you need to be able to conclude that the probability is 50% in my experiment, regardless of how the photon actually interacts with the polarizer. Furthermore, it allows you to say that the probability is cos²(a) for an angle a between the polariser axes.

 

[Borean]

Can anyone tell me what is the cause of the phenomenon known as quantum tunnelling?

And additionally, the cause of the phenomenon of vacuum fluctuations or virtual particles?

 

[gel]

If our ancestors millennia ago had no idea why the sun rose, no matter how hard they tried explaining it, that would not imply that the universe is acausal, but simply indeterminable.

This doesn't seem right though. With QM we say that we don't know what the outcome of an experiment will be, not simply because we have no idea what is happening, but rather that it is believed to be impossible to do better than give a probability.
On the other hand, our ancestors had a pretty good idea of whether the sun would rise in the morning. It always did. They just were clueless as to why, and invented some rather fanciful explanations.

 

[Borean]

This doesn't seem right though. With QM we say that we don't know what the outcome of an experiment will be, not simply because we have no idea what is happening, but rather that it is believed to be impossible to do better than give a probability.
On the other hand, our ancestors had a pretty good idea of whether the sun would rise in the morning. It always did. They just were clueless as to why, and invented some rather fanciful explanations.

That wasn't my point really. My point was that even if we don't know or can't know the cause of a given thing, that in no way means there is no cause for given thing.

 

[gel]

That wasn't my point really. My point was that even if we don't know or can't know the cause of a given thing, that in no way means there is no cause for given thing.

We're in agreement then. We don't know whether the photon will pass through the polariser until after it has already passed through or been absorbed. Furthermore, I don't think we will ever be able to predict such things. That doesn't mean that there is no cause. I accept that there could be one, but if it can never be known then it is outside of what can be described by physics.

 

[Borean]

We're in agreement then. We don't know whether the photon will pass through the polariser until after it has already passed through or been absorbed. Furthermore, I don't think we will ever be able to predict such things. That doesn't mean that there is no cause. I accept that there could be one, but if it can never be known then it is outside of what can be described by physics.

Of course. My only point is that the indeterminacy need not be an inherent attribute of the observed thing, that is, "acausality"; it may as well lie in the observer.

Being a skeptic, I find it much more likely that the indeterminism is in the epistemic realm, not the natural realm. If we project it onto the natural realm, we are pretending to some kind of omniscience. Perverse, I say.

 

[gel]

Of course. My only point is that the indeterminacy need not be an inherent attribute of the observed thing, that is, "acausality"; it may as well lie in the observer.

I think that there is a difference between saying that the physics is causal/acausal and saying the same of the universe.
If there is a cause for the photon to pass through the polariser, then it is not included within standard QM. So, we can say that QM is acausal. There may or may not be a cause, but it isn't described by QM.
There are other models, such as the Bohmian interpretation for which there is a cause, and full knowledge of the initial state would allow you to decide the outcome beforehand. The problem with this is that it is generally assumed to satisfy a "quantum equilibrium" hypothesis, in which case the initial state can never be known exactly and you still can't predict the outcome any better than standard quantum mechanics. For this reason, it is often considered to be an interpretation rather than a new model. I personally wouldn't recommend the Bohmian interpretation, I mention it here just as an example.

 

[Borean]

I think that there is a difference between saying that the physics is causal/acausal and saying the same of the universe.
If there is a cause for the photon to pass through the polariser, then it is not included within standard QM. So, we can say that QM is acausal. There may or may not be a cause, but it isn't described by QM.

What do you mean? The Bohmian model isn't QM?

There are other models, such as the Bohmian interpretation for which there is a cause, and full knowledge of the initial state would allow you to decide the outcome beforehand. The problem with this is that it is generally assumed to satisfy a "quantum equilibrium" hypothesis, in which case the initial state can never be known exactly and you still can't predict the outcome any better than standard quantum mechanics. For this reason, it is often considered to be an interpretation rather than a new model. I personally wouldn't recommend the Bohmian interpretation, I mention it here just as an example.

It sounds like the Bohmian model exactly admits to agnosticism/indeterminacy in the human epistemic realm. A more likely explanation, in my opinion.

 

[Dale]

QM is not acausal. A causal system has a state which depends only on past or present values. An acausal system depends at least on some future values and possibly on past or present values. An anticausal system depends only on future values.

There is nothing in standard QM that implies any dependence on future values, so QM is causal. The randomness does not imply acausality unless it somehow depends on future values of the state.

 

[Borean]

Can anyone tell me what is the cause of the phenomenon known as quantum tunnelling?

And additionally, the cause of the phenomenon of vacuum fluctuations or virtual particles?

Could anyone answer this?

 

[Borean]

QM is not acausal. A causal system has a state which depends only on past or present values. An acausal system depends at least on some future values and possibly on past or present values. An anticausal system depends only on future values.

There is nothing in standard QM that implies any dependence on future values, so QM is causal. The randomness does not imply acausality unless it somehow depends on future values of the state.

Interesting insight.

 

[Pio2001]

Hello,
Here is the current state of affairs to my knowledge.

Let's use the definitions given by Borean : indeterminacy means that there are some events whose cause we don't know, and acausality that there are some events that have no cause at all.

It's been common practice to name "hidden variable" an unknown cause that would give birth to the values that quantum mechanics doesn't predict in the measurment process. So if hidden variables doesn't exist, then the universe is acausal.

In 1964, Bell proves that quantum mechanics is in contradiction with local hidden variables (hidden variables whose effect travels slower or at the speed of light).
In 1967, Kochen and Specker prove that no hidden variables can be carried by the measured system and bear all prédictions about their possible measured properties. If hidden variable exist, local or not, they depend at least party, on the measurment setup. They are contextual.
In 1969, Bell's theorem was generalized by Clauser, Horne, Shimony and Holt to contextual hidden variables.

In 1982, Alain Aspect's experiment shows that quantum mechanics predictions in Bell and CHSH theorems are fullfilled. Therefore if the universe is causal, then it is non-local.

The Kochen-Specker theorem have been tested too. The results of a recent experiment by Roos, Blatt et al have just been published in Nature. It confirms the inexistence of non-contextual hidden variables with great accuracy.

Another recent experiment by Gröblacher et al ruled out a whole class of non-local hidden variable interpretations : http://www.arxiv.org/PS_cache/arxiv/pdf/0704/0704.2529v1.pdf
I'm not sure which class exactly, but it seems to me that they are interpretations without entanglement.

So we're left with some philosophiocal problems. Experiments give us the choice between
-Leaving out causality : some events occur without any cause.
-Leaving out locality : the cause of an event can lie in its future.
-Leaving out realism : there is no reality. There is just information gathered by observers.

The Copenhagen interpretation makes both the first and third choices, as well as Rovelli's relational interpretation.
Cramer's transactional interpretation makes the second choice. As did Böhm-De Broglie's pilot wave interpretation (but they didn't know it before Bell's theorem).
Everett many-world's interpretations are usually not developped enough to get a precise position in this choice. JesseM, in this forum, used to describe an extension of Everett's interpretation that would get rid of these three problems ( but introducing the existence of many worlds of course) : https://www.physicsforums.com/showthread.php?t=206291#11

 

[Borean]

Hello,
Here is the current state of affairs to my knowledge.

Let's use the definitions given by Borean : indeterminacy means that there are some events whose cause we don't know, and acausality that there are some events that have no cause at all.

It's been common practice to name "hidden variable" an unknown cause that would give birth to the values that quantum mechanics doesn't predict in the measurment process. So if hidden variables doesn't exist, then the universe is acausal.

In 1964, Bell proves that quantum mechanics is in contradiction with local hidden variables (hidden variables whose effect travels slower or at the speed of light).
In 1967, Kochen and Specker prove that no hidden variables can be carried by the measured system and bear all prédictions about their possible measured properties. If hidden variable exist, local or not, they depend at least party, on the measurment setup. They are contextual.
In 1969, Bell's theorem was generalized by Clauser, Horne, Shimony and Holt to contextual hidden variables.

In 1982, Alain Aspect's experiment shows that quantum mechanics predictions in Bell and CHSH theorems are fullfilled. Therefore if the universe is causal, then it is non-local.

The Kochen-Specker theorem have been tested too. The results of a recent experiment by Roos, Blatt et al have just been published in Nature. It confirms the inexistence of non-contextual hidden variables with great accuracy.

Another recent experiment by Gröblacher et al ruled out a whole class of non-local hidden variable interpretations : http://www.arxiv.org/PS_cache/arxiv/pdf/0704/0704.2529v1.pdf
I'm not sure which class exactly, but it seems to me that they are interpretations without entanglement.

So we're left with some philosophiocal problems. Experiments give us the choice between
-Leaving out causality : some events occur without any cause.
-Leaving out locality : the cause of an event can lie in its future.
-Leaving out realism : there is no reality. There is just information gathered by observers.

The Copenhagen interpretation makes both the first and third choices, as well as Rovelli's relational interpretation.
Cramer's transactional interpretation makes the second choice. As did Böhm-De Broglie's pilot wave interpretation (but they didn't know it before Bell's theorem).
Everett many-world's interpretations are usually not developped enough to get a precise position in this choice. JesseM, in this forum, used to describe an extension of Everett's interpretation that would get rid of these three problems ( but introducing the existence of many worlds of course) : https://www.physicsforums.com/showthread.php?t=206291#11

It seems you don't agree with each other.

I can only guess, then, that there is no consensus?

To the causalists who said that causality is preserved in quantum theory: how do you answer the above post?

 

[DrChinese]

My point was that even if we don't know or can't know the cause of a given thing, that in no way means there is no cause for given thing.

That is accurate. I believe that it is generally accepted that we do not know which of these is true. In other words, there could be a hidden (and non-local) cause - i.e. Bohmian/pilot wave interpretations. There could also be retro-causality. Or there could be no cause at all.

Clearly, we may discover these causes at a later date. However, it is telling that regardless of whether we are talking about photon spin or radioactive decay, there is not the slightest hint that there exists an underlying cause.

 

[Dale]

It seems you don't agree with each other.
...
To the causalists who said that causality is preserved in quantum theory: how do you answer the above post?

It appears to be a semantic argument. The disagreement is on the definition of "acausal". Pio2001 (and you?) are using a non-standard definition, so it is not surprising that there is disagreement. Semantic arguments usually degenerate like that.

 

[Borean]

It appears to be a semantic argument. The disagreement is on the definition of "acausal". Pio2001 (and you?) are using a non-standard definition, so it is not surprising that there is disagreement. Semantic arguments usually degenerate like that.

Inded it seems that "causal" and "acausal" tends to be used as an exaggeration of, very simply "unpredictable" or "indeterminable".

Physicists may be good at doing physics, but they are very bad at being sensitive about the metaphysics and philosophy implicit in their own statements.

 

[ueit]

Tthere could be a hidden (and non-local) cause - i.e. Bohmian/pilot wave interpretations. There could also be retro-causality. Or there could be no cause at all.

There could also be a hidden and local cause.

Clearly, we may discover these causes at a later date. However, it is telling that regardless of whether we are talking about photon spin or radioactive decay, there is not the slightest hint that there exists an underlying cause.

To have a "hint" you need a theory that proposes a hidden variable. Just by looking at a bunch of atoms popping out would not give you any hint, one way or another. If you accept Bohm's theory, you have your "hint".

On the other hand, EPR experiments prove IMO that there must be a cause (local or non-local) behind the individual experimental results. If there were no cause there could be no correlation, just statistical noise.

 

[Fra]

In a sense I'm quite pragmatic on this issue.

What difference is it to the context, between "there is a cause but I don't know about it", and there is no cause?

Unless these causal relations are known, business as usual is what we have, and our actions reflect that fact they we know of no cause. Which means we act just as if there is no particular cause.

In my preferred interpretation of QM, the action of a system is in accordance to it's state of information about it's environment. The systems action is indifference to any hidden causal rules. Most papers on the EPR jumps from no information, to a ergodic hypothesis with a choice of microstructure partition with equiprobably microstates the unknown. This is also (ergodic) information, that is added without physical motivation.

The pragmatic standpoind I have here is, what affects the action of a given system or observer? There is a kind of locality here in information space, that the action of a system is indifferent to information that it doesn't have. It respons to information at hand, and causal laws at hand. The fact that in the future, new laws of causation might be found doesn't impact present actions.

I think this is the key to make sense out of QM weirdness. It does away with a great deal of realism in the sense that a systems action really doesn't depend on "what is REALLY out there", it depends only upon what information the system has about what is possibly out there. It is momentarlity irrelevant wether this information is "right" or "wrong", however information that isn't consistent with the environment will imply a backreaction, which imples physical forces on the system causing it to "revise it's state", and simply "revise it's opinon in the light of new inforamtion".

To ask if we can predict when unexpected new information arrives is a silly question. By construction we can't. That's the undecidability all frogs are destined to live with.

/Fredrik

 

[ueit]

In a sense I'm quite pragmatic on this issue.

What difference is it to the context, between "there is a cause but I don't know about it", and there is no cause?

There is a big difference. You can have evidence for a cause without being able to point it. In fact, I think there is a confusion here between causality and determinism. Any quantum process has a cause and this cause has to do with the energy balance. That's why some nuclei are unstable while others not. So, the cause of radioactivity is the fact that the system after decay has less energy than the initial system.

I think this is the key to make sense out of QM weirdness. It does away with a great deal of realism in the sense that a systems action really doesn't depend on "what is REALLY out there", it depends only upon what information the system has about what is possibly out there. It is momentarlity irrelevant wether this information is "right" or "wrong", however information that isn't consistent with the environment will imply a backreaction, which imples physical forces on the system causing it to "revise it's state", and simply "revise it's opinon in the light of new inforamtion".

How can the information be "wrong"? What do you mean by that?

To ask if we can predict when unexpected new information arrives is a silly question. By construction we can't. That's the undecidability all frogs are destined to live with.

I have no idea what you are talking about.

 

[Fra]

There is a big difference. You can have evidence for a cause without being able to point it.

If we have physical evidence that can be quantified then I have no objection. A cause need not be determinisic. It can be probabilistic or fuzzy. just like there are deductive and inductive inferences.

But sometimes, people tend to impose "possible causations" from some realist minded reasoning, that is not really backed up by physical evidence. That's all I objected to.

How can the information be "wrong"? What do you mean by that?

This may be a nonstandard phrasing indeed. But I elaborated my view on this in this thread "The role of false info in the Copenhagen Int"
https://www.physicsforums.com/showthread.php?t=301893

I borrowed the notion "false info" from that thread.

I have no idea what you are talking about.

This was just a general comment on the common objection to the information interpretation that the wave collapse is nothing but an information update.

/Fredrik

 

[ueit]

This may be a nonstandard phrasing indeed. But I elaborated my view on this in this thread "The role of false info in the Copenhagen Int"
https://www.physicsforums.com/showthread.php?t=301893

I borrowed the notion "false info" from that thread.

I've looked into that thread. Do you imply that an atom can lie? What would an atom lie about?

 

[Fra]

I've looked into that thread. Do you imply that an atom can lie? What would an atom lie about?

I would never put it like that but what I do imply is something along the line that an atoms information about it's environment, can be destabilising itself. A stable atom is an atom whose state is in equilibrium, or in consistency with it's environment.

The "right" state from the point of view of the atom, would be the state in which it's stable.

One can imagine the analogy of an atom beeing wrong, as one beeing prepared in a different environment and then suddently thrown in a new environment. Then, it will still act as if it is in the former environement until the atom has interacted in the new environment in and received reactions. the result of this is either breakdown or destabilisation of the atom, or just an internal state revision.

So my point in that other thread is that in my "interpretation", which is nto strict copenhagen as I pointed out, the role of false information is just a state that is contradiction or not in equilibrium with the LOCAL environment. There are no global measures on correctness.

So if we would put it like a atom can lie, then yes it can lie in the above sense, but it is highly improbable to maintain the lie in a given environment. A lie isn't stable, since the lie is in my by an inconsisntecy that translates into a tension and a physical force.

You can have an ice cube in boiling water, it is not a contradiction per see, but it won't last very long. It's transient only.

/Fredrik

 

[Borean]

Or there could be no cause at all.

The problem I have with this proposition is that, if we define "causality" is the "principle that events need certain necessary and sufficient conditions to come into existence" and we define "cause" or the effect of that cause as the actuality of living up to any necessary and sufficient conditions, then, if you abandon this principle, you are saying that "events need not to live up to any conditions to occur; any conditions are sufficient for the events actuality and no conditions are more necessary for the actuality of any event than any other condition".

And if that is true, then indeed even probablistic causation/prediction would be impossible. Then even quantum mechanics would be false.

If that was the case, the universe would behave very differently, even on the microphysical/quantum level, because EVERY condition would then be affirmed as sufficient for the actuality of EVERY event, and that would mean that every event IS actual no matter what conditions there are and actually so at any point in time and space.

It seems meaningless to make such affirmations when we know that is NOT the case.

 

[DrChinese]

The problem I have with this proposition is that, if we define "causality" is the "principle that events need certain necessary and sufficient conditions to come into existence" and we define "cause" or the effect of that cause as the actuality of living up to any necessary and sufficient conditions, then, if you abandon this principle, you are saying that "events need not to live up to any conditions to occur; any conditions are sufficient for the events actuality and no conditions are more necessary for the actuality of any event than any other condition".

And if that is true, then indeed even probablistic causation/prediction would be impossible. Then even quantum mechanics would be false.

If that was the case, the universe would behave very differently, even on the microphysical/quantum level, because EVERY condition would then be affirmed as sufficient for the actuality of EVERY event, and that would mean that every event IS actual no matter what conditions there are and actually so at any point in time and space.

It seems meaningless to make such affirmations when we know that is NOT the case.

I am not asserting that there is no cause to probablistic behavior, but that may easily be the case.

But I disagree with your statements above. There are theoretical reasons to believe that all possibilities do occur (MWI interpretation is one example). Also, it is pretty clear that the probability waves do act as if they are real. Collapse is then somewhat like the ball randomly landing in the roulette slot - without any specific precipitating cause at all.

 

[Borean]

There are theoretical reasons to believe that all possibilities do occur (MWI interpretation is one example).

That is not a "reason". There are theoretical claims that all possibilities occur. But per Occams Razor, I would think there are much simpler and more minimalistic explanations for the same empirical data.

But anyway, the many-worlds interpretation doesn't live up to abandoning the causal principle I mentioned. It doesn't live up to the claim that "EVERY condition is sufficient for the actuality of EVERY event, and that every event IS actual no matter what conditions there are and therefore actual always and everywhere". Because that clearly doesn't apply in the one world we know - this one, and therefore, they have to invoke the separation of worlds, and those worlds clearly don't live up to this claim individually, either.

It is a completely different way in which "all possibilities occur", which doesn't live up to abandoning that there are certain constraints for necessary and sufficient conditions for events to be actual and take place.

 

[DrChinese]

That is not a "reason". There are theoretical claims that all possibilities occur. But per Occams Razor, I would think there are much simpler and more minimalistic explanations for the same empirical data.
...

Well, it would be a good hint (in favor of causality) if you could set up the same scenario and get the same result every time. That is a typical indication that cause and effect is at work. But that just doesn't happen much - that old uncertainty thing gets in the way. So I really don't think you have your finger on Occam here: you are assuming more, not less.

Besides, per Bell, you end up back at non-local interpretations if you want determinism/hidden variables/causality/etc. So is that minimalistic in your book?

 

[Borean]

Well, it would be a good hint (in favor of causality) if you could set up the same scenario and get the same result every time.

That assumes that you can ever set up two identical scenario, just because you are dealing with the same kind of particle or event. I don't assume this. To the contrary, you can never set up the same scenario, because scenario will always be separated either in time or space.

Besides, per Bell, you end up back at non-local interpretations if you want determinism/hidden variables/causality/etc. So is that minimalistic in your book?

I don't know. Are you saying that the copenhagen interpretation denies non-locality? As far as I know, phenomena such as quantum entanglement are rather widely held.

In any case, we don't need nonlocality for causality if we discount our basic ability to replicate the same scenario (and therefore make valid causal predictions). In that case, all we need to stop assuming is determinacy.

As far as I've discerned, there will always be different energy balances in different quantum particles and events, and in the quantum vacuum. It surprises me no one has considered the vacuum.

We already have good reasons to assume it isn't empty, with the discovery of things such as dark energy, dark matter, gravitational fields, and other entities we aren't aware about. So how could we say that particles erupt spontaneously from the vacuum "without any cause" and receiving their energy from "nowhere", or particles decay for "no reason", when clearly the vacuum is filled with energy and disturbing forces which could causally explain this without our determinacy?