I Is quantum weirdness really weird?

[OmCheeto]

The following popped up in my Facebook feed this morning:

Why quantum mechanics might need an overhaul [ sciencenews.org ]
Nobel laureate Steven Weinberg says current debates suggest need for new approach to comprehend reality
BY TOM SIEGFRIED 3:37PM, NOVEMBER 4, 2016

"...
But quantum theory’s explanatory power has come at a substantial price: the need to accept counterintuitive weirdness about reality that many physicists, including such pioneers as Einstein and Schrödinger, refused to accept.
...
Einstein objected, saying God does not play dice. He further objected to another weird aspect of quantum mechanics, involving its description of pairs of particles separated at birth. Two photons emerging from a single atom, for instance, could fly very far apart yet share a single quantum description; making a measurement on one can reveal something about the other, no matter how far away it is."​

I wasn't sure if the author was quoting professor Weinberg, so I tracked down the speech.

[4:40] [refs: videos @ casw.org & youtube ]
Steven Weinberg; "...today I'm going to talk about precisely what is weird and counterintuitive about quantum mechanics, how it has been that way from the very beginning, ..."

Anyways, I found the entire lecture delightful, and Quantum Mechanics, a bit less weird.

----------------------------------------
Steven Weinberg

... an American theoretical physicist and Nobel laureate in Physics for his contributions ... to the unification of the weak force and electromagnetic interaction between elementary particles.
[ref: wiki ]​

Tom Siegfried

managing editor of Science News...
In addition to Science News, his work has appeared in Science, Nature, Astronomy, New Scientist and Smithsonian...
He earned an undergraduate degree... with majors in journalism, chemistry and history, and has a master of arts with a major in journalism and a minor in physics...
[ref: sciencenews.org ]​

 

[ProfessorLogical]

isn't indeterminism weird? the fact that something that can in essence be known yet cannot actually be determined even when all possible information is available. but I'm not sure if i am saying that right.

what i actually want to post is... can there be anything that is weird period?... by anyone's definition.
if there is, then doesn't QM underpin it? if we drill down into that weirdness we get to the QM level, if we find an explanation there then weirdness goes away. if not then QM is weird. if QM is not weird then there actually is no such concept as weird, it is only a lack of understanding that makes it seem weird.

how QM gives rise to classical physics is weird. how when we use QM to determine the past state of a system it leads us to a point when QM breaks down is weird. the existence of reality is weird and thus QM is weird. how fields can be superimposed upon one another, occupying the same location at the same time is weird. how infinity can be expanding is weird. lines of force which apparently emanate from a particle and extend out infinitesimally...charge...is weird.

how QM is in fact concerned with measurement is weird...we are QM and we are concerned with measurement.

how a system can give rise to something that can question the system is weird.

we are the universe questioning itself...that is fact not philosophy and that is very weird.

 

[houlahound]

the fact that something that can in essence be known yet cannot actually be determined even when all possible information is available.

I will try show why this is just word salad that makes no sense;

can you give an example of a "fact" you "know" in "essence" only, and that you simultaneously have full information of even though you have not "actually determined" it.

and no, we are in the universe, we are not the universe.

 

[ProfessorLogical]

I will try show why this is just word salad that makes no sense;

can you give an example of a "fact" you "know" in "essence" only, and that you simultaneously have full information of even though you have not "actually determined" it.

you left out the part "i'm not sure if i am saying that right"

we can know facts can be known in essence by knowing the information after the fact.

like we know in essence we can know where an electron is...but only after we have looked for it and found it. so we know for a fact there are electrons to be found and where to find them, but yet we cannot determine where they are with all the information possible in our possession until we add ourselves to the equation.

and no, we are in the universe, we are not the universe.

we are products of the universe, products of the system we call the universe, we are not separate from it. please tell me is the universe one thing and everything in it another? or are we just using phrases like "in the universe" just as a way of being less confusing when we talk about the universe in general?

what material is the universe made of that everything else is not?

 

[houlahound]

we are products of the universe, products of the system we call the universe, we are not separate from it.

the set of all mothers is not a mother.

we can know facts can be known in essence by knowing the information after the fact.

what exactly does known in essence even mean?

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

like we know in essence we can know where an electron is...but only after we have looked for it and found it. so we know for a fact there are electrons to be found and where to find them, but yet we cannot determine where they are with all the information possible in our possession until we add ourselves to the equation.

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.

 

[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.