Is quantum weirdness really weird?

[bhobba]

isn't indeterminism weird?

Maybe yes - maybe no. There are a number of words with philosophical overtones that no one can reach agreement on - what is God, are we just illusion - the number is endless and I want to add a totally legitimate intellectual inquiry. Its just not what we generally discuss around here - we occasionally end up discussing such if its unavoidable, but the mods, correctly, keep a tight reign on it.

This is one if those things - is in-determinism weird, is QM weird, is QM in-deterministic to begin with - all these are really philosophy and not of relevance to this forum except in a superficial way.

Thanks
Bill

 

[ProfessorLogical]

the set of all mothers is not a mother.
what exactly does known in essence even mean?

a fact is only a fact once it is known to be a fact.

the way i used it is to mean without the physicality that would accompany the thing...like i know in essence an apple is red, without actually having the apple to show it. we know there are apples for a fact, therefore when we discuss them without them being present we are talking about them in essence.

why are you so hung up on my phrasing? this is striking me as pedantic...if it makes it better i concede i could have used better phrasing.

knowing you can know a fact and actually knowing a specific fact is a cheap equivocation on knowing, logical fallacy right there.

yes we know for a fact there are electrons because we have defined their properties and experimentally confirmed their existence.

ok whatever. your issue is phraseology? i'll try to be more precise in the future. the uncertainly principle is weird. is that better?

and the uncertainty principle shows we are part of the whole system. the mother of sets is not a mother? ok so? "mother" is a function, not a thing, it spawns things...what is this mother made of? whatever it is that is what it's offspring are reducible to. if mother is a number, whatever it produces is in "essence" a number even if it looks like a ham sandwich.

you are not your mother. but both of you are humans...or to be more precise, you are both subatomic particles.

whatever the universe is at it's root, down at it's immutable level, that is what in essence all things are even if they "look" different.

 

[ProfessorLogical]

Maybe yes - maybe no. There are a number of words with philosophical overtones that no one can reach agreement on - what is God, are we just illusion - the number is endless and I want to add a totally legitimate intellectual inquiry. Its just not what we generally discuss around here - we occasionally end up discussing such if its unavoidable, but the mods, correctly, keep a tight reign on it.

This is one if those things - is in-determinism weird, is QM weird, is QM in-deterministic to begin with - all these are really philosophy and not of relevance to this forum except in a superficial way.

Thanks
Bill

i hear you. i was just following the subject of the thread. but there is science in this as well.

 

[Igael]

Apart EPR, the double slit experiment and the delayed choice quantum eraser, what are the main "weird" observations ?

 

[stevendaryl]

Apart EPR, the double slit experiment and the delayed choice quantum eraser, what are the main "weird" observations ?

I think that EPR pretty much illustrates everything weird about quantum mechanics. Why do you want more?

 

[Igael]

to identify what may be weird.

These 3 experiments aren't while some of their interpretations are. The student may ignore them unless he is learning how to speak to donators.

 

[vanhees71]

There's nothing weird with EPR. Quantum theory describes it perfectly well ;-).

 

[stevendaryl]

There's nothing weird with EPR. Quantum theory describes it perfectly well ;-).

I would say that it doesn't. To me, there is a distinction between a theory and a recipe. There is a recipe for getting answers, but it isn't a theory, because it relies on a distinction, between a measurement and other interactions, which is not described by the theory. There is a rule of thumb for when a measurement has been made, but not an actual definition in terms of the theory.

 

[OmCheeto]

This is now making it difficult for me to watch the "Sixty Symbols" videos, as every time a professor at Nottingham says "weird", I scream; "Ah ha! Even the smarty pantsers say it's weird!"

[2:20] "And in this weird, quantum mechanical world..."

[ref: Quantum Cheshire Cat]

 

[Zafa Pi]

It's not wise to mix "realism" into discussion as it can be understood differently in general contexts and Quantum physics contexts.
Having said that why do you find "counterfactual definiteness" questionable? Let's say you use some model to make prediction about possible measurement. This is type of counterfactual reasoning. So what's wrong with that?

You are constantly questioning "counterfactual definiteness" in your posts. Why don't you make separate thread for that question?

I was responding to georgir's version of the Bell inequality which requires counterfactual definiteness (which if you accept locality) must be false in general.
Why do you think the Bell inequality is false?

 

[zonde]

Why do you think the Bell inequality is false?

Do you mean, why Bell inequality is violated?

 

[vanhees71]

Quantum theory predicts Bell's inequality to be violated. That's the important point of Bell's ingenious idea, how to test whether a local deterministic hidden-variable theory or quantum theory describes nature. Experiments of amazing accuracy prove quantum theory right, which solves this question satisfactory. In my opinion it's the last word on "interpretation". There's no weirdness left.

The really interesting fundamental question concerning quantum theory in our days is, in my opinion, how to find a consistent quantum theory of the gravitational interaction, maybe solving the problem with the cosmological constant in our universe.

 

[zonde]

Quantum theory predicts Bell's inequality to be violated. That's the important point of Bell's ingenious idea, how to test whether a local deterministic hidden-variable theory or quantum theory describes nature. Experiments of amazing accuracy prove quantum theory right, which solves this question satisfactory. In my opinion it's the last word on "interpretation". There's no weirdness left.

Quantum theory gives only statistical predictions for measurements. If we want to speculate about physics behind individual "clicks" in detectors we have to resort to interpretations.

 

[vanhees71]

Quantum theory tells you that nature is indeterministic and thus you can only have probabilities for the outcome of measurements given the state of the system, even if this knowledge is complete in the sense that you know the exact pure state of the system. This is only weird if you believe that Nature must behave as described by classical physics, but classical physics is based on observations on macroscopic systems, where we don't and usually can't resolve the full microscopic details. We only have (and for any practical purposes also only need) a "coarse-grained description" of some "relevant macroscopic observables", and these almost always behave with high accuracy the classical laws of physics. The apparent determinism of classical physics only applies to this coarse-grained picture but not to the microscopic details of macroscopic matter, and that's why our worldview is quite deterministic from our everyday experience. In other words QT shows that this determinism is only "on average".

On the other hand applying the classical worldview to microscopic physics leads to "weirdness", i.e., predictions crossly disproved by everyday experience: The matter around us is pretty stable, which is a prerequisite of our very existence of course. According to classical physics together with the finding that this matter consists of atomic nuclei surrounded by electrons forming atoms, molecules, and all kinds of condensed matter around us, leads to the conclusion that this matter is unstable since the electrons should move around the atomic nuclei in a kind of miniature solar system with the electromagnetic rather than gravitational force holding this system bound together, but this implies that the electrons are in accelerated motion, and classical electrodynamics (Maxwell equations) imply that their kinetic energy would be radiated off by electromagnetic radiation in a very short time, and thus the atom would collapse. QT solves this problem elegantly because there are stable solutions of the time-independent Schrödinger equation. So the true weirdness would occur if classical physics would be the entire truth about the microscopic constituents of the matter surround us, and QT solves this weirdness.

The only problem is to get used to the apparently unintuitive implications of QT, i.e., you have to readjust your intuition given the empirical fact that QT is the by far better description of nature's behavior!

 

[A. Neumaier]

If we want to speculate about physics behind individual "clicks" in detectors we have to resort to interpretations.

But then it is speculation, not physics.

 

[zonde]

But then it is speculation, not physics.

It's physics. We just have to call this speculation a hypothesis.
Look here: https://en.wikipedia.org/wiki/Scientific_method#Elements_of_the_scientific_method
Don't know if you like Feynman but anyways. Look at the very start of this video about first step in the process of getting new law:


The problem with interpretations of QM is rather about turning them into something more than interpretation and getting unique predictions ... and maybe getting rid of unacceptable interpretations (interpretations that will newer be anything more than an interpretation).

 

[A. Neumaier]

It's physics. We just have to call this speculation a hypothesis.

This view is certainly fringe, as it would turn everything into physics: flat earth, hollow earth, cold fusion, perpetuum mobiles...

 

[zonde]

Quantum theory tells you that nature is indeterministic and thus you can only have probabilities for the outcome of measurements given the state of the system, even if this knowledge is complete in the sense that you know the exact pure state of the system.

This is not Quantum theory by itself, it's Copenhagen interpretation (wave function is complete description of every quantum system in ensemble).

 

[vanhees71]

The predictions of QT are very well defined within the minimal interpretation, and there's no contradiction so far with any experiment/observation. Everything going beyond the minimal interpretation, leading to the same (probabilistic) predictions of QT are by definition just speculation although not in contradiction to QT, and you can follow these interpretations, but it's not of anything beyond standard QT.

 

[zonde]

This view is certainly fringe, as it would turn everything into physics: flat earth, hollow earth, cold fusion, perpetuum mobiles...

Ah, but therefore you have other steps in scientific method so that you can drop false and unscientific hypotheses.

 

[vanhees71]

This is not Quantum theory by itself, it's Copenhagen interpretation (wave function is complete description of every quantum system in ensemble).

Well, as long as there's no disprove of QT, I don't see any reason in believing otherwise. That's indeed part of standard quantum theory in the minimal interpretation. I'm not sure whether you can call the minimal interpretation a flavor of Copenhagen interpretation. Note that the Copenhagen interpretation consists of at least as many physicists having worked together with Bohr in Copenhagen ;-)). Even Heisenberg's and Bohr's point of view are slightly different although I think one could say that Heisenberg was most closely working together with Bohr on the philosophy of QT, called "interpretation" ;-).

 

[rubi]

Violation of counterfactual definiteness isn't a matter of interpretations of quantum mechanics. It's an experimentally tested fact that must be included in every physical theory that describes every aspect of nature. We can't blame quantum mechanics for this.

 

[zonde]

That's indeed part of standard quantum theory in the minimal interpretation. I'm not sure whether you can call the minimal interpretation a flavor of Copenhagen interpretation.

Some would say that minimal interpretation is Ballentine's statistical interpretation. And Ballentine makes clear distinction between his interpretation and Copenhagen.

 

[stevendaryl]

Quantum theory tells you that nature is indeterministic and thus you can only have probabilities for the outcome of measurements given the state of the system, even if this knowledge is complete in the sense that you know the exact pure state of the system.

I think that the indeterminism is NOT the weird part of quantum mechanics, to me. The weird part is that the Rules of Quantum Mechanics are in terms of results of measurements, when measurements are just complicated interactions. It's weird to describe what goes on microscopically, at the level of individual particles, in terms of something that is macroscopic and very human-centered--measurement. If there is nothing weird going on in the measurement process--it's just the working out of ordinary physics (including QM) on the macroscopic scale, it seems to me that there should be a formulation of QM that doesn't mention measurements, or observations. If measurements are ordinary interactions (just macroscopic), then what happens when you perform a measurement should be derivable from the laws of physics, it shouldn't be postulated.

 

[A. Neumaier]

The weird part is that the Rules of Quantum Mechanics are in terms of results of measurements

Only the textbook rules, not the rules that are actually used, which are much more flexible and more along my thermal interpretation.

 

[A. Neumaier]

what happens when you perform a measurement should be derivable from the laws of physics, it shouldn't be postulated.

And it is derivable. When creating a high performance measurement one uses a lot of QM to ensure that the measurement results are good! There is a whole industry of quantum measurement, with only 0.1% of it being covered by the textbook account.

 

[stevendaryl]

And it is derivable.

In that case, there should be a formulation of quantum mechanics that doesn't mention measurement (in particular, the rule that the result of a measurement is an eigenvalue). Deriving facts about measurements from postulates that already assume facts about measurements seems a little circular. (Although a circular derivation is comforting, to a certain extent, because it shows that at least the whole story hangs together, and doesn't contradict itself.)

 

[rubi]

In that case, there should be a formulation of quantum mechanics that doesn't mention measurement

There is already such a formulation (consistent histories) and it doesn't even require any shift in perspective, just a little more precise use of language.

(in particular, the rule that the result of a measurement is an eigenvalue).

I don't know whether you wanted to put the emphasis on the word "measurement" or on "eigenvalue", but if the latter concerns you, then I don't understand the problem. It's just specifying the set of physically allowed values of an observable, similar to classical mechanics, where the physically allowed values of observables are also restricted (for example, the energy $H=p^2+x^2$ of a harmonic oscillator can only be positive).

 

[stevendaryl]

There is already such a formulation (consistent histories) and it doesn't even require any shift in perspective, just a little more precise use of language.

Whether this is accurate or not, I think of consistent histories as a variant of the Everett Many-Worlds. I actually think that something along those lines might be the right way to think about it. I was mostly complaining about the so-called "minimal interpretation". If "measurement" is mentioned in the formulation, then it's not really very minimal, since measurement is a complicated thing.

 

[rubi]

Whether this is accurate or not, I think of consistent histories as a variant of the Everett Many-Worlds.

Yes, a fair statement would be to say that consistent histories is Everett Many-Worlds with only one world, although that is also not completely accurate.

I was mostly complaining about the so-called "minimal interpretation". If "measurement" is mentioned in the formulation, then it's not really very minimal, since measurement is a complicated thing.

I agree that measurement should not have the status of a fundational concept.

 

[vanhees71]

Well, but physics is about what we can objectively observe (and measurements are just accurate quantitative observations) nature and about regular patterns ("natural laws") of such observtions. So any physics more or less explicitly includes ideas on more or less complicated measurements of quantitatively observable phenomena. Already measuring the width of my table uses a lot of assumptions and physics (sufficient accuracy of the validity of Euclidean geometry for example) although you wouldn't think about this very much as it seems very natural to you, but if you think about it, it's already not so simple. We are just used to it from elementary school on. That QT compared to classical physics seems so "weird" to us is simply because we are not very used to quantum phenomena like interference of probabilities, entanglement etc.

 

[A. Neumaier]

In that case, there should be a formulation of quantum mechanics that doesn't mention measurement (in particular, the rule that the result of a measurement is an eigenvalue). Deriving facts about measurements from postulates that already assume facts about measurements seems a little circular. (Although a circular derivation is comforting, to a certain extent, because it shows that at least the whole story hangs together, and doesn't contradict itself.)

Relativistic quantum field theory (the true foundation of quantum mechanics) is usually developed from scratch without the slightest reference to measurement. The latter comes much later in when interpreting the S-matrix, but that is done mainly to establish contact to tradition rather than to justify the foundations. Moreover, the S-matrix also appears in the derivation of the Boltzmann equation, where it gets a measurement-free interpretation that shows that nothing in the foundations depends on a notion of measurement.

 

[stevendaryl]

Well, but physics is about what we can objectively observe (and measurements are just accurate quantitative observations) nature and about regular patterns ("natural laws") of such observtions. So any physics more or less explicitly includes ideas on more or less complicated measurements of quantitatively observable phenomena.

I would disagree completely. Newtonian physics is about the motions of particles under the influence of forces. It is not about measurements. Of course, you have to do measurements to test Newtonian mechanics, but it isn't about measurements.

 

[madness]

If one interprets "weird" as meaning "defies the common sense expectations we've acquired from a lifetime lived in a classical world", as is the rest of your post does, the quantum mechanics is indisputably weird.

By that definition, classical physics is also "weird". For example, the fact that if I move my hand it will cause the moon to move. Or even more basically, the fact that things will continue at a constant speed unless acted upon by something - that went completely against common sense and took a very long time to be realized or accepted.

 

[Nugatory]

By that definition, classical physics is also "weird".

A point that serves to reinforce the general futility of trying to characterize a discipline as "weird" or "not weird"...