(November 18, 2021 at 6:37 pm)Jehanne Wrote:

He's comeback to have Poly school him all over again 

(November 18, 2021 at 6:19 pm)Klorophyll Wrote:

(November 5, 2021 at 7:15 pm)polymath257 Wrote:  In point of fact, I don't think there is asuch a thing as synthetic a priori knowledge. 

I suspect that you have a self-refuting sentence here (I might be wrong). The assertion : "there is no synthetic a priori knowledge" is either synthetic a priori or not. If it is, it refutes your own claim. If it isn't, we can dismiss your claim as a baseless a posteriori assertion.

On the contrary, it is an example of extrapolation from known cases and is thereby an example of analytic knowledge. All claims I have found for a statement being synthetic a priori have been easily seen to be wrong.

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(November 5, 2021 at 7:15 pm)polymath257 Wrote: And the fact that QM is a supreme example of a scientific theory AND is acausal is enough to show that causality isn't required to do science. Just repeatability and testability.

I don't think it's fair to say that QM is acausal. It surely changes our commonsense picture of causality, but there is always a kernel of causal order that underlies any physical theory.
And if we define a cause as an explanation of an effect, then it's wrong to say QM is acausal, since its main goal is to explain the behavior of atoms/ subatomic particles.

Nope. It *describes* the behavior. it does NOT explain specific instances of the behavior. For example, there is no explanation of why any particular nucleus decays at one time as opposed to another. it does describe the probability of decay, though.

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(November 5, 2021 at 7:15 pm)polymath257 Wrote: Exactly. Special relativity is a non-quantum theory. It is a classical theory. When quantum mechanics is added on, we get quantum field theories. So, in the classical theory, all influences remain in the light cone. In the quantum version, the correlations outside of the light cone are zero.

A good reference is Peskin and Schroeder, 'An Introduction to Quantum Field Theory'. The relevant section is even labeled 'Causality', pp 27-29. Here' the description of causality is that no measurement can affect any other measurement outside of the light cone. How is this achieved? By having the commutator of the fields be zero (no correlation) for events outside of each others light cones.  In order for this to happen, anti-particles must have the same mass as the ordinary particles. this discussion of causality comes up in the determination of the propagator.

Or, if you prefer Nachtman's book 'Elementary Particle Physics', the relevant equations are 3.50, once again describing the commutator of events outside of each others light cones and requiring the commutator be zero. Once again, this means no correlation.

Or, if you prefer Kaku's book, 'Quantum Field Theory', the description of microcausality in section 3.4 once again hinges on the nature of the commutators and thereby the correlations between events separated in a way that light could not travel between them.

Or, if you prefer Weinberg's book, The Quantum Theory of Fields (Vol 1), you can find the same discussion in section 3.5.

In ALL of these, the term 'causality' is used precisely when the events outside of each others light cones have vanishing commutators. In other words, they are uncorrelated.

Are those valid enough sources for you? All are standard texts for graduate physics in this subject (although Kaku's book is pretty poor, frankly).

Now, I don't believe for a second you have actually read/understood anything about quantum field theories that goes beyond the popular treatments. I have. And the notion of causality used in quantum mechanics isn't the type of causality you require for your program. It is a matter of probabilities and correlations and NOT of what is 'necessary' for other events to happen. And yes, it has to do with vanishing commutators outside of light cones, just as I said.

Physics isn't my field of expertise, my studies in physics stopped a while ago at some basic applications in QM of Schrödinger's equation, in addition to other undergraduate level courses in newtonian mechanics, electromagnetism, thermodynamics, etc. Is there some accessible interpretation of the "vanishing commutators outside of light cones" ? And does it allow for violating causal order? 

Since you have not defined what 'causal order' means aside from temporal order and since nothing other than temporal order is ever used in physics, the question itself is irrelevant.

As for your education, you are at least above many people. I have done the PhD qualifying exams in physics, as well as having a PhD in mathematics.

I doubt that there is an 'accessible' interpretation of what vanishing commutators implies that actually deals with the substance of the concept. That is because it is a technical property involving the operators that describe the quantum fields at any point. If you don't know what the commutator of two operators is and how it affects the quantum mechanics (through an uncertainty principle), then you can't grasp the impact.

But I'll try. A non-zero commutator means the quantities involved show an uncertainty principle, like position and momentum, or time duration and energy uncertainty. Measurements of one cannot be done without affecting the probabilities of the other. For events outside of the light cones, the opposite happens: the measurements are guaranteed not to affect the other. In other words, the results are independent.

But, the essence is that events outside of the light cones have zero correlation.

Quote:After doing a bit of research I again found what seems to contradict your assertions above:

Quote: "For a quantum field theory the equal time commutation relations are the equivalent of the initial conditions on classical field equations. It is a requirement on the dynamical equations that the property of commutation between two local observables is extended to all pairs of points with spacelike separation. This is the equivalent of the requirement of causal propagation in a (well-behaved) classical field theory."

Source: https://www.researchgate.net/post/What_i...eld_theory

In other words, there is still a requirement of causality even in quantum field theory.

Yes, it is the 'equivalent' in the same way that Schrodinger's equation is the equivalent of F=ma in the classical setting.

In this context, the *meaning* of causality is that the non-zero commutators are limited to the forward light cone. it does NOT mean what philosophers would like it to mean.

Good luck Poly. He needs this to be true for his god to exist. At the end of the day, he'll insist that a fact is wrong rather than concede he got a fact wrong.

Sort of like trying to explain biology to an ider. When you've gone through and explained all the things they'd been misinformed about, rather than go, huh...cool..they think "well, this is dumb, biology is dumb, i didn't happen that way".

(November 19, 2021 at 8:08 am)The Grand Nudger Wrote: Good luck Poly.  He needs this to be true for his god to exist.  At the end of the day, he'll insist that a fact is wrong rather than concede he got a fact wrong.

Sort of like trying to explain biology to an ider.  When you've gone through and explained all the things they'd been misinformed about, rather than go, huh...cool..they think "well, this is dumb, biology is dumb, i didn't happen that way".

In defense of Kloro, I think he has asked Poly questions in good faith.  Most wouldn't even bother to look up the points Poly makes.

There is a problem with terminology when discussing physics terms with non-physicists.  Quantum Mechanics is causal, but not deterministic (but quantum causality doesn't mean what many think it means).  By that I mean that individual events are random, but their probabilities are calculable with knowledge of the local state, or by knowledge of past state within the light cone.

I wouldn't explain commutators the same way Poly did (though it may make sense that way in Quantum Field Theory, which I haven't studied. I'd have to see the actual math). A commutator measures uncertainty between two observable properties (i.e. the knowledge of one causes uncertainty in the other), not causality. It is true that a zero commutator means no correlation (and therefore no causal connection) between two observables (where at the same place, or separated), but a non-zero commutator at two points does not mean causation directly between those points. Causation is about information (proven by freely setting one state and seeing correlations with another). We all know the idea of "spooky" action at a distance, where two separated particles can have entangled observables and they would be correlated. However, one is not free to "set" one state.

Macroscopic reality forms when single states get so entangled with the environment that their Hamiltonian becomes diagonal or "classical", or when many random events (owing to the law of probabilities) create what we think of as classical laws (F=ma, thermodynamics, etc.).

(November 19, 2021 at 6:17 pm)HappySkeptic Wrote: Macroscopic reality forms when single states get so entangled with the environment that their Hamiltonian becomes diagonal or "classical", or when many random events (owing to the law of probabilities) create what we think of as classical laws (F=ma, thermodynamics, etc.).

In other words, the Correspondence Principle:

Wikipedia -- Correspondence principle

(November 19, 2021 at 6:17 pm)HappySkeptic Wrote:

(November 19, 2021 at 8:08 am)The Grand Nudger Wrote: Good luck Poly.  He needs this to be true for his god to exist.  At the end of the day, he'll insist that a fact is wrong rather than concede he got a fact wrong.

Sort of like trying to explain biology to an ider.  When you've gone through and explained all the things they'd been misinformed about, rather than go, huh...cool..they think "well, this is dumb, biology is dumb, i didn't happen that way".

In defense of Kloro, I think he has asked Poly questions in good faith.  Most wouldn't even bother to look up the points Poly makes.

There is a problem with terminology when discussing physics terms with non-physicists.  Quantum Mechanics is causal, but not deterministic (but quantum causality doesn't mean what many think it means).  By that I mean that individual events are random, but their probabilities are calculable with knowledge of the local state, or by knowledge of past state within the light cone.

I wouldn't explain commutators the same way Poly did (though it may make sense that way in Quantum Field Theory, which I haven't studied.  I'd have to see the actual math).  A commutator measures uncertainty between two observable properties (i.e. the knowledge of one causes uncertainty in the other), not causality.  It is true that a zero commutator means no correlation (and therefore no causal connection) between two observables (where at the same place, or separated), but a non-zero commutator at two points does not mean causation directly between those points.  Causation is about information (proven by freely setting one state and seeing correlations with another).  We all know the idea of "spooky" action at a distance, where two separated particles can have entangled observables and they would be correlated.  However, one is not free to "set" one state.

Macroscopic reality forms when single states get so entangled with the environment that their Hamiltonian becomes diagonal or "classical", or when many random events (owing to the law of probabilities) create what we think of as classical laws (F=ma, thermodynamics, etc.).

What is typically described as 'causality' in books on quantum field theory is precisely that commutators outside of each others light cones are zero. Commutators inside the light cone can be non-zero, but do not have to be. That can depend on the specifics of the interaction.

So, once again, it is a difference in terminology as much as anything else. What the word 'causality' means in QFT is not the same, or even close, to what it means in  philosophy or theology.

(November 19, 2021 at 6:17 pm)HappySkeptic Wrote:

(November 19, 2021 at 8:08 am)The Grand Nudger Wrote: Good luck Poly.  He needs this to be true for his god to exist.  At the end of the day, he'll insist that a fact is wrong rather than concede he got a fact wrong.

Sort of like trying to explain biology to an ider.  When you've gone through and explained all the things they'd been misinformed about, rather than go, huh...cool..they think "well, this is dumb, biology is dumb, i didn't happen that way".

In defense of Kloro, I think he has asked Poly questions in good faith.  Most wouldn't even bother to look up the points Poly makes.

Neither did Kloro. Had he looked it up, he wouldn't be pushing a doomed argument.

(November 19, 2021 at 8:08 am)The Grand Nudger Wrote: He needs this to be true for his god to exist.  At the end of the day, he'll insist that a fact is wrong rather than concede he got a fact wrong.

As I said before, I think you're confusing necessity with sufficiency. When was the last time you did some mathematics..? 

Let's break it down again, if there is a valid argument that proves x exists given causality. This means that causality is a sufficient condition for x to exist, if causality turns out to be invalid, this doesn't mean x doesn't exist.

Your commentary above shows that you think sufficient conditions are also necessary conditions, i.e. that causality being wrong means that the assertion "x exists" is wrong. This is a basic logical mistake. 

https://en.wikipedia.org/wiki/Necessity_and_sufficiency

(November 18, 2021 at 8:14 pm)polymath257 Wrote: On the contrary, it is an example of extrapolation from known cases and is thereby an example of analytic knowledge. All claims I have found for a statement being synthetic a priori have been easily seen to be wrong.

If your assertion is an extrapolation from known causes, then it is based on empirical data, and thus is a posterori by definition, and definitely not analytic. Your assertion "there is no synthetic a priori" is therefore self-refuting. 

Also, if there were synthetic a priori statements that turned out to be wrong, this doesn't mean that all synthetic a priori statements are wrong. Black swan fallacy..

(November 18, 2021 at 8:14 pm)polymath257 Wrote: Nope. It *describes* the behavior. it does NOT explain specific instances of the behavior. For example, there is no explanation of why any particular nucleus decays at one time as opposed to another. it does describe the probability of decay, though.

I agree that QM is descriptive like any physical theory. But you are asserting here that QM is acausal without providing reliable sources for this claim.

From wiki, we learn that the label "acausal" that is sometimes used in some interpretations of QM is, actually, misleading.

Quote:"Confusion between causality and determinism is particularly acute in quantum mechanics, this theory being acausal in the sense that it is unable in many cases to identify the causes of actually observed effects or to predict the effects of identical causes, but arguably deterministic in some interpretations (e.g. if the wave function is presumed not to actually collapse as in the many-worlds interpretation, or if its collapse is due to hidden variables, or simply redefining determinism as meaning that probabilities rather than specific effects are determined)."

Source: https://en.wikipedia.org/wiki/Causality_(physics)

In other words, QM being acausal doesn't really mean that, under some hypothetical scenario, you can precede your mother's existence, as Nudger thinks, it just means our physical theories about the world are inherently limited and can't identify the causes of observed effects at the quantum level, we can merely assign probabilities. To state it differently, saying that there are effects without causes at the subatomic level is an appeal to ignorance, an appeal to the limitations of scientific investigation. 

The only thing these recent advancements in physics prove is that we should be less ambitious about what we can ever know about reality.

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As HappySkeptic said above, one can't impose some state in QM. Atheists seem to forget that the theory exposes the inherent limitations of our knowledge. The skirmishing about causality at the subatomic level arises merely because we just can't point out a cause to such and such effects, not because we actually observe things popping into existence. QM undermining causality is maybe to be expected in pop sci magazines, our observations/measurements are inherently limited forever as per the uncertainly principle, and thus we can't really observe a violation of causality (in its classical sense) to begin with......

The door is wide open for the theist to interpret these permanent gaps of knowledge in his worldview. It's true that many god-of-the-gaps arguments are weak because they appeal to ignorance. But thanks to QM, there really is inherent and permanent ignorance about what happens at the subatomic level.

I’m not confusing anything with any other. You, and no one but you, has decided that the world must be a particular way for your god to exist. That makes your mistake, about the way the world is according to physics, a necessary component of your beliefs.

Carry on.

(November 19, 2021 at 6:17 pm)HappySkeptic Wrote: By that I mean that individual events are random, 

You probably should've mentioned that this is only one possible interpretation of quantum mechanics. John Bell showed that, in theory, there can be hidden determinism behind the curtains, that sets up how things should play out, giving room to manoeuvre for the theist. It's only when the hidden variables are local that they conflict with the predictions of QM.

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(November 20, 2021 at 3:05 pm)The Grand Nudger Wrote: I’m not confusing anything with any other.  You, and no one but you, has decided that the world must be a particular way for your god to exist.  That makes your mistake, about the way the world is according to physics, a necessary component of your beliefs.

Carry on.

You're doing it again. I am only saying that the world can be sufficient to make an agument for God, not that it must be in some particular way.

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(November 19, 2021 at 8:02 pm)Jehanne Wrote: In other words, the Correspondence Principle:

And if, according to this principle, causality is preserved at the macroscopic level (relativistic causality), doesn't this mean that the apparent violation of causality in quantum field theory is just that, apparent...?

Correct me if I'm wrong: We know that any observation or measurement in QM is limited because of the uncertainty principle, and because of that, we can't observe the underlying causal structure that governs the behavior of subatomic particles.