A electron can exist in everywhere ?

[ZapperZ]

Honestly, I haven't heard of them. And I don't know what you mean by being "adamant", everyone is convinced of what they believe in until they aren't. And quite frankly, what you're defending is not exactly a widespread view (even if it might be correct), in fact if I google "Delft/Stony Brook SQUID experiments", the first hit I get is to a blog of yours and then to threads in these forums where you posted that stuff. And no one's ever heard or read everything there's to hear or read, so you can't really hold that against me.

Wait, it isn't widespread? In where?

Superposition is a central tenet of QM! How not widespread is this? In fact, it is the whole reason that quantum entanglement exists and is so strange! Without quantum entanglement, this is nothing more than a simple conservation of angular momentum problem that we find trivial in classical mechanics!

And if you look at those links I posted, the Delft/Stony Brook experiments were widely covered in science media when they appeared! And the publicity isn't even about superposition. It is about the SIZE of superposition! In other words, we have already accept superposition at the small scale, and now we are seeing it at the 10^11 particle scale! That's massive! That is what made the news!

Moreover, I didn't even say superposition isn't real ("adamant in your argument that it isn't real because you obviously don't know enough do so"), and it didn't really make any arguments for it. And I know that effects of superposition are visible, it's just I was never convinced that meant it was something real. And I'm sorry if I was wrong about, jeez...

So if you want to say something say it, but get off your high horse because no one likes arrogance.

And I will fully admit that I slapped you around a bit, because I'm seeing all of these arguments that are not supported by evidence. This is not science, and this is certainly not how physics is done. You cannot simply argue things based on tastes, or "beliefs". This isn't politics. If you do not know stuff well enough, then ASK! That is the strength of this forum, that we have such experts in many different fields. Learn from them! But if you start spewing all of these nonsense about a subject that some of us have had years of work in, then you are not only being insulting to us to think that you know enough to make such definite statements, but you are also being annoying!

So yes, from my point of view, you not only need to have some physics lessons of what we already know, but also an attitude adjustment on how you participate in this forum.

Zz.

 

[Amok]

And I will fully admit that I slapped you around a bit, because I'm seeing all of these arguments that are not supported by evidence. This is not science, and this is certainly not how physics is done. You cannot simply argue things based on tastes, or "beliefs". This isn't politics. If you do not know stuff well enough, then ASK!

How am I supposed to know I don't know my stuff well enough before someone shows it to me? What I learned is that when a system is in a superposition of states and you make a measurement on it, then it collapses into some eigenstate as we make our measurement (the textbook stuff). How is it possible to directly observe superposition in that case (and not just its effects, like interference patterns and such)? Can you concisely explain why you can (please, I am truly interested)?

That is the strength of this forum, that we have such experts in many different fields. Learn from them! But if you start spewing all of these nonsense about a subject that some of us have had years of work in, then you are not only being insulting to us to think that you know enough to make such definite statements, but you are also being annoying!

I didn't know you were an expert in this, I couldn't have known it, and I even if I did, argument for authority isn't the best. I didn't insult anyone directly or personally, I didn't mean to be insulting. If you felt insulted then you take these things way too personally, and that's really your problem, not mine.

but also an attitude adjustment on how you participate in this forum.

I have no problem admitting I was wrong, but no one needs to be arrogant or condescending about being right ("your assertions are silly", "you obviously haven't read enough to talk, but I have", "I'm an expert and I've made several posts about this already", "spewing all this nonsense", "this is not how science is done"). So if you think I'm wrong, just say it, and say why and that's it. Because if you really know all you say you do, you should be able to argue your position easily. If you don't feel like it, then refrain from posting.

And really, try not to take the things that I say that are wrong (or that you perceive as being wrong) as a personal insult against you. That really doesn't help a debate.

 

[Neandethal00]

I'm not sure, it sounds like some of the posters are saying
Wavefunctions are physical entities.
If yes, would anyone shine a little light on its physical nature?
I have been thinking all along wavefuntions are mathematical
models of 'environment' surrounding a particle.

 

[DrChinese]

I'm not sure, it sounds like some of the posters are saying
Wavefunctions are physical entities.
If yes, would anyone shine a little light on its physical nature?
I have been thinking all along wavefuntions are mathematical
models of 'environment' surrounding a particle.

The probability waves act AS IF they are real in and of themselves until collapse (whatever that actually is) occurs. So they can be manipulated (even split and recombined). That is in fact what happens with the double slit experiment.

So what starts off as a mathematical device also appears to have an element of reality itself. As ZapperZ and Drakkith have said, you see as "real" that which you set up the experiment to see.

 

[Drakkith]

Thanks Doc. You explain Quantums much better than I do!

 

[bohm2]

And if you look at those links I posted, the Delft/Stony Brook experiments were widely covered in science media when they appeared! And the publicity isn't even about superposition. It is about the SIZE of superposition!

I'm trying to understand this and I'm having some difficulty but is the superposition of macroscopic stuff like superconductivity analogous to quantum superposition on the microlevel? I'm asking because of this post by xepma and some other posts/links by deMystefier in this thread. Then again, I might be misunderstanding their arguments particularly because I haven't read the papers, yet:

The Psi in superconductivity is an order parameter of the system -- it's not the wavefunction of the electrons itself, even though it's frequently called that way. It's pretty easy to see that it can't be a wavefunction, since it has only one coordinate (hence it's not the wavefunction of a many-body system). The order parameter can be interpreted as the object responsible for breaking the U(1) symmetry. It therefore represents the charge density of the system (the absolute value of Psi) and the velocity field of the current (the phase term). The fact that charge is conserved automatically leads to the current equation you mentioned.

There is no reference to individual electrons.

The Ginzburg-Landau equation is an expression for the free energy of the system. The order parameter is treated as a classical object, and the non-linear Schrodinger equation follows from minimizing the free energy -- it is not based on the quantum-mechanical Schrodinger equation for the wavefunction (although you can derive it, strating from BCS theory).
In a Ginzburg-Landau approach there is absolute no reference to the underlying degrees of freedom carried by the electrons, i.e. the microscopics. It is solely phenomenological. You can derive this effective theory by starting from a quantum-mechanical treatment. A book such as Tinkham has treatments on that.

https://www.physicsforums.com/showthread.php?t=448366

Comparison of the Ahronov-Bohm effects in the two-slit interference experiment and in superconductor ring reveals fundamental difference between the Schrodinger wave function and the wave function describing macroscopic quantum phenomena.

http://xxx.lanl.gov/pdf/0812.4118v1.pdf

 

[Jazzdude]

I feel like he's trolling us. Repeating stuff he read somewhere else without understanding it.

Be careful with such statements. For what it's worth that statement would hold for you and others in this thread too. I've rarely read so many questionable and wrong statements stated with this much authority. And I'm not talking about the OP.

 

[tris_d]

No, all physical laws should describe the world we observe. If they describe differently, then either the laws are wrong or the world we observe isn't quite the idea we have of it.

We would like to describe the world we observe with certainty, but some of it we can not, so we use mathematical concepts that embed this uncertainty in the description. And this description is practical in a sense that it is useful, but it's not to be interpreted literally. While wave-particle duality is rather real, wave function is just abstract mathematical concept. Or so I would think.

 

[ZapperZ]

I'm trying to understand this and I'm having some difficulty but is the superposition of macroscopic stuff like superconductivity analogous to quantum superposition on the microlevel? I'm asking because of this post by xepma and some other posts/links by deMystefier in this thread. Then again, I might be misunderstanding their arguments particularly because I haven't read the papers, yet:

https://www.physicsforums.com/showthread.php?t=448366

http://xxx.lanl.gov/pdf/0812.4118v1.pdf

I would point out to you the Tony Leggett paper that I've referenced several times, and will reference here again:

A.J. Leggett "Testing the limits of quantum mechanics: motivation, state of play, prospects", J. Phys. Condens. Matt., v.14, p.415 (2002).

Note that no mater how you describe the supercurrent, there is a strong consensus that the entire supercurrent is describe by a single wavefunction, the same way 2 entangled particles are describe via one inseparable wavefunction. So this is ONE coherent entity even though it comprises of huge number of electrons. And that is all we need, and what is why Carver Mead stated that superconductivity is the clearest manifestation of quantum mechanics.

Zz.

 

[bhobba]

'doesn't address the issue of whether particles and reality exist at all times and esp. before detection.

QM does not answer that issue. What its wave nature is is waves of the representation of the system state when expanded in terms of position so its square gives the probability of being in that location if you observe it. A system state is the codification of what the outcome would be if you were to observe a quantum system, but what it is 'doing' or 'existing' when it is not being observed the theory is silent about. Different interpretations have a different take on it but since no experiment can tell the difference between them it is of little use in answering your question in any definite way. This is one of the essential aspects of QM that is responsible for much of its weirdness as well as misunderstandings. It is important though to understand what the issue really is rather than the (to use 'nice' language - if we were face to face I would say something more colorful) the half truths of some popular accounts.

Thanks
Bill

 

[bhobba]

The probability waves act AS IF they are real in and of themselves until collapse (whatever that actually is) occurs. So they can be manipulated (even split and recombined). That is in fact what happens with the double slit experiment.

So what starts off as a mathematical device also appears to have an element of reality itself. As ZapperZ and Drakkith have said, you see as "real" that which you set up the experiment to see.

I think 'appears' is a key word here - exactly as you indicate by 'AS IF'. I can find zero definite evidence it is any more than a codification of the knowledge about what the probability of the outcome of observations would be. This is the view of Ballentine in his book on QM. I know his ensemble interpretation is not everyone's but as far as I know no refutation of it exists.

Thank
Bill

 

[big_bounce]

Superposition waves just occur in a medium ?
Can two photons make a super position in vacuum ?

 

[bhobba]

Superposition waves just occur in a medium ?
Can two photons make a super position in vacuum ?

I have zero idea where you would get that from. The principle of superposition is a general principle having nothing to do with a medium:
http://en.wikipedia.org/wiki/Quantum_superposition

It actually follows from the definition of a state being a positive operator of unit trace but that's for a more advanced exposure to QM - the article above is a good start.

Thanks
Bill

 

[ZapperZ]

I think 'appears' is a key word here - exactly as you indicate by 'AS IF'. I can find zero definite evidence it is any more than a codification of the knowledge about what the probability of the outcome of observations would be. This is the view of Ballentine in his book on QM. I know his ensemble interpretation is not everyone's but as far as I know no refutation of it exists.

Thank
Bill

Then I suggest that you read this:

http://arxiv.org/abs/1111.3328

Zz.

 

[bhobba]

The hypothesis it is trying to refute 'is that the quantum state is a state of knowledge, representing uncertainty about the real physical state of the system'.

It is a state of knowledge all right but IMHO it does not represent 'uncertainy about the real physical state of the statem' because you first need to show it has a real physical state to be uncertain about. Got a proof for that?

Indeed the paper recognizes this: 'Nonetheless, this assumption, or some part of it, would be denied by instrumentalist approaches to quantum theory, wherein the quantum state is merely a calculational tool for making predictions concerning macroscopic measurement outcomes'.

This is precisely the view I take. A state can be viewed exactly as the ensemble interpretation espoused by Ballentine interprets it as - simply as a way of predicting the outcome of observations - the reality being the system and observational apparatus combined. Outside that, other than predicting the probabilities of what an observation would yield, a state, just like assigning probabilities to a coin, has no meaning. Probabilities do not represent elements of reality of something out there - neither do states - at least you can view it that way.

Thanks
Bill

 

[ZapperZ]

The hypothesis it is trying to refute 'is that the quantum state is a state of knowledge, representing uncertainty about the real physical state of the system'.

It is a state of knowledge all right but IMHO it does not represent 'uncertainy about the real physical state of the statem' because you first need to show it has a real physical state to be uncertain about. Got a proof for that?

Er... you missed the point here. They are starting with the premise that has been argued that says that a quantum state is DIFFERENT from a real physical state, that a quantum state merely contains the state of our knowledge of the system (see Ref. 1-8, which is the "proof"). It is from this that they proceed to show that if this is true, then such an assumption will produce a result that contradicts quantum mechanics.

Indeed the paper recognizes this: 'Nonetheless, this assumption, or some part of it, would be denied by instrumentalist approaches to quantum theory, wherein the quantum state is merely a calculational tool for making predictions concerning macroscopic measurement outcomes'.

And again, isn't that what they were tackling?

This is precisely the view I take. A state can be viewed exactly as the ensemble interpretation espoused by Ballentine interprets it as - simply as a way of predicting the outcome of observations - the reality being the system and observational apparatus combined. Outside that, other than predicting the probabilities of what an observation would yield, a state, just like assigning probabilities to a coin, has no meaning. Probabilities do not represent elements of reality of something out there - neither do states - at least you can view it that way.

But is this what you meant by the quantum state being nothing more than a "codification of the knowledge" of the system? This is what I was addressing when I produced such a reference, to show that if one were to argue that a quantum system is nothing more than a reflection of our knowledge and CAN be different than the physical system, then one CAN arrive at a TEST to differentiate between the two! They can be distinguished from one another! And I will include the reference on the test of quantum contextuality that I cited earlier as added evidence.

On the other hand, if that is not what you meant, and you think there is a third way to look at this, then this doesn't apply to you, because that is not what is being addressed here.

Zz.

 

[bhobba]

But is this what you meant by the quantum state being nothing more than a "codification of the knowledge" of the system?

I am scratching my head a bit here. I thought I was pretty clear. What I wrote previously was: 'A system state is the codification of what the outcome would be if you were to observe a quantum system, but what it is 'doing' or 'existing' when it is not being observed the theory is silent about'.

Again from the paper you linked to:
'The argument depends on few assumptions. One is that a system has a 'real physical state' not necessarily completely described by quantum theory, but objective and independent of the observer. This assumption only needs to hold for systems that are isolated, and not entangled with other systems. Nonetheless, this assumption, or some part of it, would be denied by instrumentalist approaches to quantum theory, wherein the quantum state is merely a calculational tool for making predictions concerning macroscopic measurement outcomes.'

My position is precisely this denial - namely it is an instrumentalist view with the reality being the system and observational apparatus - the state merely codifies the result of what would happen, statistically, if you were to observe it. The state is not 'real and physical' any more than the probabilities assigned to a the sides of a coin are real and physical - it does not exist in any real sense, simply as a tool to predict the outcomes of observations. This is the view of Ballentine etc in the Ensemble interpretation, although I personally incorporate decoherence into it but that is another issue.

Thanks
Bill

 

[ZapperZ]

I am scratching my head a bit here. I thought I was pretty clear. What I wrote previously was: 'A system state is the codification of what the outcome would be if you were to observe a quantum system, but what it is 'doing' or 'existing' when it is not being observed the theory is silent about'.

Again from the paper you linked to:
'The argument depends on few assumptions. One is that a system has a 'real physical state' not necessarily completely described by quantum theory, but objective and independent of the observer. This assumption only needs to hold for systems that are isolated, and not entangled with other systems. Nonetheless, this assumption, or some part of it, would be denied by instrumentalist approaches to quantum theory, wherein the quantum statebis merely a calculational tool for making predictions concerning macroscopic measurement outcomes.'

My position is precisely this denial - namely it is an instrumentalist view with the reality being the system and observational apparatus - the state merely codifies the result of what would happen, statistically, if you were to observe it. The state is not 'real and physical' any more than the probabilities assigned to a the sides of a coin are real and physical - it does not exist in any real sense, simply as a tool to predict the outcomes of observations. This is the view of Ballentine etc in the Ensemble interpretation, although I personally incorporate decoherence into it but that is another issue.

Thanks
Bill

Well I'm scratching my head as well, because it appears that you're straddling both sides of the fence.

Let's be clear here. If the sides of the coin is the way that this paper has described, then we now have a way to test it. This is very much what Bell did with a test for local interaction as stated in EPR. His test moved it from being merely a matter of philosophy to actual physics that can be tested.

This paper, with the caveat of its assumption, is doing just that, and proposed for the first time a test to distinguish one from the other. It may not be the final form of such test, the same way Bell test has evolved into stricter and more stringent tests, but it is at least a start that will drag this debate from philosophy into physics.

Now, if your world view is different than from either of these, and presumably from your arguments, you can't distinguish one from the other, then you are back into the philosophy realm where we are going to argue based on a matter of taste! That may be what you wish to do, but that isn't the point of this discussion.

Zz.

 

[bhobba]

Let's be clear here. If the sides of the coin is the way that this paper has described, then we now have a way to test it..

I am equally bemused by your position. My view is the system state is not like the sides of the coin which have a real physical existence - it is like the probabilities we assign to the sides of a coin that codifies knowledge of the long term outcomes of flipping the coin. It is not a 'real physical state' of the coin - but a codification of knowledge about the coin. To be specific I reject that the system must a priori be described by a real physical state - what we call the state simply tells us about long term statistical outcomes of observations. It, or something similar it depends on, may be real - but a priori does not have to be.

The issue is not philosophical - I am generally a bit anti philosophy - but a simple bit of common sense. Knowledge of something real and physical like the expected outcome of observations on a system is not the same as the outcomes themselves. The outcomes are real and physical - no denying it - but knowledge of what the expected value of those outcomes are over a long sequence of observations is not a 'real physical state' to use the words of the paper you linked to.

Balentine states the second axiom of QM as follows (although I personally prefer deriving it from the assumption of additivity of expectation values as was done by Von Neumann long ago - or even by Gleasons Theorem - but that is another issue) - if R is an observable then there exists a positive operator p of unit trace, called the state of the system, such that the expected value of R E(R) = Tr(pR).

Since the expected value of the outcome of many observations is simply knowledge about the system precisely why do you consider the state p a 'real physical state' or indeed that the system must depend on some such? Do you also consider the probabilities assigned to each side of the coin real and not just a calculational device to predict the proportion of long term outcomes? Do they in turn must depend on something real and physical (of course in this case it depends on all all sorts of other things like how hard the coin is flipped but in principle it does not have to - this is my key point)? Of course I can't prove you wrong and indeed there could be a long drawn out philosophical discussion on what exactly real is that IMHO would be pointless (just like I believe a lot of philosophical stuff is - which is why I am a bit anti philosophy) but to me this is pretty much common sense.

I suppose after thinking about it a bit you for some reason believe a quantum system must be described by something that exists external to us and exists in a real physical sense - I do not agree that is a priori so. It is very easy to be fooled by something like the coin flipping of the classical world. If we knew all the details of how it was flipped then in principle we could predict the outcome and so think the probabilities we assign to it depend in some imperfect way on something real - which in that case it does. But the quantum world a priori does not have to be like that.

Regarding issues of taste - isn't that exactly what a choice of QM interpretation amounts to? And the point of answering a question like the OP posted is that the answer depends on interpretation?

Thanks
Bill

 

[bohm2]

My view is the system state is not like the sides of the coin which have a real physical existence - it is like the probabilities we assign to the sides of a coin that codifies knowledge of the long term outcomes of flipping the coin. It is not a 'real physical state' of the coin - but a codification of knowledge about the coin.

The PBR no-go theorem rules out a ψ-epistemic interpretations (see links).

1. If one assumes that there is some reality that underlies the quantum state (probability distributions over the ontic states)it is ruled out.
2. If one assumes that there is no deeper underlying reality, then PBR has no effect.

Does Ballentine's ensemble approach you favour subscribe to position 1 or 2?

Can the quantum state be interpreted statistically?
http://mattleifer.info/2011/11/20/can-the-quantum-state-be-interpreted-statistically/

https://www.physicsforums.com/showthread.php?t=551554

 

[San K]

Hello all .
In quantum physics there are any theory that says a electron or Partial of electron exist in everywhere in universe ?
Means a electron in other side me can exist Partial of it in 300000 light year ?

if probability (wave-function) is quantized, then the electron probability cloud has a limited boundary

beyond a certain range (of time-space) the probability of finding an electron will drop to zero

interestingly (per some assumptions/hypothesis) even quantum entanglement would then have a limit/range

 

[bhobba]

Does Ballentine's ensemble approach you favour subscribe to position 1 or 2?

It is silent on it, and deliberately so. You can choose either. Einstein favored the Ensemble interpretation because it whispered the first alternative in your ear (and it most certainly does) but whispering and being so are two different things.

In discussing issues of principle I personally choose position 2 because a lot of the philosophical waffle goes out the door - but that does not mean I rule position 1 out - I simply hold that view until we know something more definite from experiment. To me its easier that way - but what is one persons easier is another's I can't stand it.

By philosophical waffle I mean issues such as what position does an electron have when not observing it, and how does it instantaneously change to another state when you observe it - they become non issues.

Thanks
Bill

 

[bohm2]

Then, I'm guessing that PBR not only rules out Einstein's ensemble interpretation but also Lee Smolin "real ensemble interpretation":

A real ensemble interpretation of quantum mechanics
http://arxiv.org/pdf/1104.2822v1.pdf

 

[bhobba]

Then, I'm guessing that PBR not only rules out Einstein's ensemble interpretation but also Lee Smolin "real ensemble interpretation":

A real ensemble interpretation of quantum mechanics
http://arxiv.org/pdf/1104.2822v1.pdf

No it doesn't. Einstein would have loved the PBR because it pointed to a deeper reality that the ensemble was an approximation to ie the out here is QM was not complete so the underlying theory that is really in charge is different from QM hence PBR does not apply. In Smolin's theory the ensembles are literally real so the state is real anyway.

Thanks
Bill

 

[bohm2]

No it doesn't. Einstein would have loved the PBR because it pointed to a deeper reality that the ensemble was an approximation to ie the out here is QM was not complete so the underlying theory that is really in charge is different from QM hence PBR does not apply. In Smolin's theory the ensembles are literally real so the state is real anyway.

If you read the papers linked above, Leifer argues that PBR rules out an option favoured by Einstein:

Wavefunctions are epistemic and there is some underlying ontic state. Quantum mechanics is the statistical theory of these ontic states in analogy with Liouville mechanics.

It is argued in this paper that this is the view Einstein endorsed:

The historical significance of this result becomes evident when one recognizes that the same reasoning is present in Einstein’s preferred argument for incompleteness, which dates back to 1935. This fact suggests that Einstein was seeking not just any completion of quantum theory, but one wherein quantum states are solely representative of our knowledge.

Einstein, incompleteness, and the epistemic view of quantum states
http://arxiv.org/pdf/0706.2661v1.pdf

Such a model is ruled out by PBR.

 

[bhobba]

If you read the papers linked above, Leifer argues that PBR rules out an option favoured by Einstein:

I have read what Leifer says and think he is correct but is drawing the wrong conclusion - or rather just because it is sick does not mean the theory (under that interpretation) still can not be used.

The PBR theorem only applies to standard QM - not to some hypothetical theory that QM may be the approximation of like classical thermodynamics is the approximation of quantum thermodynamics. This was Einsteins belief - QM was not incorrect - just incomplete and he would have thought the PBR theorem is simply a symptom of that incompleteness. Classical thermodynamics has problems such as the black-body radiation problem quantum theory fixes up. There are similar issues with Electrodynamics such as the infinite self energy of the field and acasual runaway solutions in some circumstances. But again it is not an issue because it is only an approximation to QED that resolves the problems (but of course has others) - in virtually all practical situations classical Electrodynamics is applied to no problems arise - but to be sure it is in fact a sick theory. Einstein would be smiling merrily and looking over to Bohr who really couldn't care less because like me he thought the state, although fundamental, was simply knowledge about the system and not something real and physical.

In fact one version of the Ensemble interpretation accepts Einsteins take and that when you make an observation it selects a pre existing outcome despite Kochen-Sprecker. It invokes some as yet unknown theory to resolve it. Conceptually actually a very neat solution. It has but one problem - what is this theory it is an approximation to - damn that pesky detail.

Funny how nothing really has changed on the QM interpretation front - each side simply retreats to their impregnable positions - hmmm - I seem to recall posting that before.

Thanks
Bill

 

[bohm2]

I think Bohr would have been happier with the PBR theorem than Einstein. The reason, being that PBR leaves anti-realist approaches unscathed whereas it eliminates certain ontic models where ψ is epistemic/probabilistic. Not that there are any theorems that are likely to eliminate anti-realistic approaches. Having said that, there are other models that are also not affected by PBR or Bell's: superdeterministic ones.

 

[bhobba]

Yea Bohr may have liked PBR.

But really its this 'realist' view of the world that is the issue - for some of us its just so deeply ingrained its hard to shake and why I think there will always be disagreement.

Early on I was in the realist camp but after a while its baggage became too much and I jumped ship - long before PBR BTW.

Thanks
Bill