B Bohr vs Einstein: is the Moon there when we are not looking?

[DrChinese]

I read in the Zeilinger paper that Alice can observe interferences after erasement and coincidence countings.

Yes, that is true. Note that again, there is nothing specific changing that you see without sending classical communication.

 

[Robert100]

We need to be very careful about this question. The moon, as is currently understood and explored by modern science and lunar landers, absolutely most certainly is there, even when it is not being observed by any form of life on Earth.

To claim otherwise is equivalent anti-Science, postmodernist social deconstructionism.

No same physicists believes that recent human observations of the Moon called it into existence. If any part of these babbling philosophical physics papers were true, then the moon as explored by Chinese scientists would likely have vastly different properties than the moon has, as explored by Russian or American scientists.

Yet no matter who the observer is, American, Russian, or Chinese, and no matter the year in which we make the observation, the results about what the moon is, where it is, and what it is made of, are always the same.

Yes, there are some serious issues in understanding QM. We obviously have a lot to learn about the fundamental nature of reality itself. Perhaps are three dimensional universe, as is now fashionable to believe, maybe a three-dimensional projection of a different dimensional space. Maybe there are wonderful and weird explanations for the non-local connections between particles that we have measured in EPR experiments

But the planets and moons do exist independently of our observations. At this point one might ask what the nature of reality is, but not whether or not some form reality exists.

 

[DrChinese]

The moon, as is currently understood and explored by modern science and lunar landers, absolutely most certainly is there, even when it is not being observed by any form of life on Earth.

To claim otherwise is equivalent anti-Science, postmodernist social deconstructionism.

...

I don't know what "postmodernist social deconstructionism" is, but it sounds like fun.

The actual context of the "moon" reference in the OP makes it clear that there is no question as to whether the moon itself exists when not being observed. The quote is attributed to Einstein, and states:

"I think that a particle must have a separate reality independent of the measurements. That is: an electron has spin, location and so forth even when it is not being measured. I like to think that the moon is there even if I am not looking at it."

So the actual question is whether or not quantum objects, such as an electron, have simultaneous non-commuting observables independent of the act of observation. Most physicists, but not all, would disagree with Einstein on this point. Of course, we have the great advantage of being aware of Bell's Theorem and the other no-go theorems and experiments.

So Einstein's comment really has nothing to do with the existence of the moon, and everything to do with his view of quantum reality. Referencing the existence of the moon is simply a shorthand for this.

 

[eltodesukane]

"is the Moon there when we are not looking?"
Just like an old Pokémon game I used to play.
When I get to some part of the map, nurse Joy is looking at me from the hospital's window.
If I walk just a bit so that the hospital is no longer visible on the 2D screen, is nurse Joy still looking at me?

 

[naima]

You discovered the displacement of the Heisenberg's cut. congratulations.

 

[naima]

A last question about the Zeilinger paper. If the first detector is in the focal plane of the lens, the which way information is lost and there is an interference pattern for photons correlated to those passing thru the slits.
Could you give me the state of the global system dor coinciding particles. By two tracing out, we should have a pure reduced density matrix in the focal plane and Id/2 at the slits?

 

[DrChinese]

A last question about the Zeilinger paper.

Which paper? It sounds like you are thinking of a quantum eraser setup but am not sure.

 

[mikeyork]

The moon is still there because the rest of the universe is "observing" (interacting with) it even when we are not looking. And those observations can be communicated to us so that, in effect, we are always observing it. This is simple logic based on the principle that our observations of nature (or at least our interpretations of those observations) must be self-consistent.. Now I grant that at the microscopic level things are more subtle, but the non-contradictory requirement of our observations still holds. If some "observer" in the universe knows that an electron is in a specific state and that electron remains isolated in that state, then any subsequent "observer" capable of communicating with the previous "observer" must record that same state.

 

[bhobba]

So Einstein's comment really has nothing to do with the existence of the moon, and everything to do with his view of quantum reality. Referencing the existence of the moon is simply a shorthand for this.

Very nice.



Einstein to his dying day believed QM incomplete. Ever since a famous attack Einstein bought against QM that Bohr defeated he believed it correct - but that there was something else behind it. That was his beef with Bohr and the Copenhagenists - they believed there view of QM was complete. He even had his own interpretation - the Ensemble interpretation. But his version was not as developed as the version now espoused by Ballentine - it was really a hidden variable theory in disguise. Indeed Ballentine's famous 1970 review article had exactly the same issue - but his book now has a more subtle view. We are really still having the same arguments today.

Thanks
Bill

 

[naima]

Dr chinese,
the question is about your link:
skip to the erasing in the focal plane of Heisenberg lens.
Bob sees no interference but he can get an interference pattern from coinciding particles. I wonder what is the pure state for these pairs in the global Hilbert space.

That is correct; there is no interference UNLESS you first make the light coherent by diffracting it through a pinhole or similar. Entangled photons are not coherent. It makes sense when you think about it, but I never did until someone pointed this out to me. See an enlightening article by Anton Zeilinger, p. 290, Figure 2.

Experiment and the foundations of quantum physics ...

 

[Jon Richfield]

The moon is still there because the rest of the universe is "observing" (interacting with) it even when we are not looking. And those observations can be communicated to us so that, in effect, we are always observing it. This is simple logic based on the principle that our observations of nature (or at least our interpretations of those observations) must be self-consistent.. Now I grant that at the microscopic level things are more subtle, but the non-contradictory requirement of our observations still holds. If some "observer" in the universe knows that an electron is in a specific state and that electron remains isolated in that state, then any subsequent "observer" capable of communicating with the previous "observer" must record that same state.

I came in on this discussion very late, and skimming the foregoing postings I kept wondering when something like Mike's point would come up. I am no physicist, but all my adult life it has seemed to me that the widespread habit of speaking of an "observer" as though it meant someone with a microscope and a measuroo spotting an item or an event, made no sense. They often speak as though if his microscope were pointing somewhere else, then the subject under discussion doesn't exist or cannot be said to be in anyone of conceivably alternative states. It even seemed that they thought that if no one was watching the measuroo (ie no "observer") then there would be no observer-initiated collapse of alternative states.
To me it seemed obvious from waaay back, both
that the rest of the universe (lightspeed delayed of course) had to amount to an observer of any object (though I remain agnostic about event horizons etc)
and more particularly
that for large articles such as moons and cats in boxes
that other parts of the system under consideration, amount to distant observers. For example, the tip of the cat's ear is an altogether adequate observer of whether the cat's tail (well over a light-nanosecond away) has been dead for a nanosecond or so, and hence that the atom HAS decayed, no matter whether anyone outside the box knows it, and so does the broken glass vial of cyanide "observe" it.
And the meteor that hits the moon "observes" the moon and the moon's core "observes" the moon's crust.
It takes very, very little of the universe to observe in such a sense. Only while a (more or less macroscopic) system is unaffected by the outcome of a quantum event, is it possible to maintain the uncollapsed state.

Could anyone finally tell me where I am wrong here?
Please?

 

[naima]

In special cases one thing can happen and be observed by one "observer" and another "observer will observe that nothing happened. Take the Unruh effect.
accelerated observers see thermal radiation in the universe. Non accelerated observers do not see these radiations. What is real for one is virtual for the other.

 

[Jon Richfield]

In special cases one thing can happen and be observed by one "observer" and another "observer will observe that nothing happened. Take the Unruh effect.
accelerated observers see thermal radiation in the universe. Non accelerated observers do not see these radiations. What is real for one is virtual for the other.

That is a sharp one naima. However, I do not see it as invalidating the question I posed, any more than "proper acceleration" that one observer experiences is "virtual" acceleration to an inertial observer measuring his acceleration from outside. They both observe different measurements of the event, but both agree on the event.
Accordingly, I disagree that "What is real for one is virtual for the other". Each measures the thermal radiation, and sure, one gets a numerical reading of zero, and the other a reading of (whatever is implied by his proper acceleration), and if they communicate, they can reconcile their respective proper accelerations with their respective thermal radiation readings. Just like any other RT frames of reference.
Nothing virtual, just different readings, not so?

 

[naima]

How can they agree if one observe an ice cube and the other boiling water?

 

[DrChinese]

...I am no physicist, but all my adult life it has seemed to me that the widespread habit of speaking of an "observer" as though it meant someone with a microscope and a measuroo spotting an item or an event, made no sense.

... And the meteor that hits the moon "observes" the moon and the moon's core "observes" the moon's crust.

...

As I mentioned earlier, I don't think the moon reference is related to whether collapse is occurring or not (with or without human observers). It is not related to whether the moon exists when it is not being observed. The question at hand is Einstein's (and many others') concept that quantum observables exist without regard to how an observation is made.

On the other hand, with Bell and related experiments: you pretty much have to abandon the idea that there is independence of observation. The choice of observation "here" somehow changes the results "there", or vice versa. (This is also true across the time dimension: The choice of observation "now" somehow changes the results "then", or vice versa.

 

[votingmachine]

For some time now I’ve been intrigued by the famous argument between Bohr and Einstein, and which was apparently settled when Bell’s inequality was tested in various experiments carried out by Alain Aspect. After going around and around the whole issue for a while, I don’t think I’m convinced Bohr won; at least not because of Bell’s inequality and Aspect’s test.
...

I think it is incorrect to say that Bohr was conclusively correct in his response to the EPR paper. The EPR paper tried to show an experimental process for determining the underlying reality at a level that the Heisenberg uncertainty principle prevents in a single particle ... by using a matched set of particles. Bohr more or less said it is unproductive to try to visualize quantum mechanics in the terms of reality we are comfortable using in models. When we use a baseball as a metaphorical model for a electron, we are likely to be misled, more than informed.

Einstein was arguing FOR a model of quantum things in classical modeling terms ... a complete description of reality that conforms to the way we see things at a classical physics level. Bohr was unable to refute that the proposed thought experiment was a method of getting to the underlying reality ... that required experiments. He did continuously hold forth that attempting to map quantum things into classical physics models was unlikely to work.

EPR argued that there is an underlying reality that can be modeled completely. The use of two identical things with an expectation that they behave independently, and both can be measured for an individual property precisely, implies that they both have inherent properties defined, and that the quantum model is incomplete. Bohr argued that Einstein was already applying a classical physics model of reality, and that such models generally were not useful.

As I read the history, it was regarded that Einstein's reasoning was the more sound of the two. But that it was not a question that could be pursued. And meanwhile QM was useful, even if you agreed with the EPR position that it was incomplete.

 

[Jon Richfield]

How can they agree if one observe an ice cube and the other boiling water?

With difficulty I reckon, but before I can take the question seriously, you will have to suggest how such an eventuality could (in principle at any rate) arise. As things stand, I do not see how the question relates to the topic.

 

[Jon Richfield]

As I mentioned earlier, I don't think the moon reference is related to whether collapse is occurring or not (with or without human observers). It is not related to whether the moon exists when it is not being observed. The question at hand is Einstein's (and many others') concept that quantum observables exist without regard to how an observation is made.

On the other hand, with Bell and related experiments: you pretty much have to abandon the idea that there is independence of observation. The choice of observation "here" somehow changes the results "there", or vice versa. (This is also true across the time dimension: The choice of observation "now" somehow changes the results "then", or vice versa.

Thanks DrChinese, but my question dealt with the nature of an observer or observation in quantum theory, not with Bell or collapse in particular. It had more to do with Schroedinger and cats or the moon when we look away, rather than entanglement. The suggestion that Einstein might really have meant a quantum entity when he said "moon" might well be valid or even correct, but then it is not relevant to that problem. There are other considerations that I didn't mention, such as how MANY observations it takes to collapse a state, but the question as it stands should suffice, and until someone can lay it, I think that a large slice of discussion and traditional argy-bargy about QT remains meaningless.

 

[naima]

I (and DrChinese will say if he agrees) think that reality is never intrinsic. Events only exist through relations (a flow of relations). The existence of something is not a yes/no question which will have a proof later when observed. It looks like philosophy but physics is not far away.

 

[Jon Richfield]

I (and DrChinese will say if he agrees) think that reality is never intrinsic. Events only exist through relations (a flow of relations). The existence of something is not a yes/no question which will have a proof later when observed. It looks like philosophy but physics is not far away.

That sounds good as long as we are looking at single photons, single leptons, single hadrons, single molecules, and lately even single molecules of buckminsterfullerene, but single cats? Single moons? By that time I get the idea that we are getting into handwaving territory.

 

[DrChinese]

That sounds good as long as we are looking at single photons, single leptons, single hadrons, single molecules, and lately even single molecules of buckminsterfullerene, but single cats? Single moons? By that time I get the idea that we are getting into handwaving territory.

At the very least, we would be in cat-waving territory.

 

[votingmachine]

I came in on this discussion very late, and skimming the foregoing postings I kept wondering when something like Mike's point would come up. I am no physicist, but all my adult life it has seemed to me that the widespread habit of speaking of an "observer" as though it meant someone with a microscope and a measuroo spotting an item or an event, made no sense. They often speak as though if his microscope were pointing somewhere else, then the subject under discussion doesn't exist or cannot be said to be in anyone of conceivably alternative states. It even seemed that they thought that if no one was watching the measuroo (ie no "observer") then there would be no observer-initiated collapse of alternative states.
To me it seemed obvious from waaay back, both
that the rest of the universe (lightspeed delayed of course) had to amount to an observer of any object (though I remain agnostic about event horizons etc)
and more particularly
that for large articles such as moons and cats in boxes
that other parts of the system under consideration, amount to distant observers. For example, the tip of the cat's ear is an altogether adequate observer of whether the cat's tail (well over a light-nanosecond away) has been dead for a nanosecond or so, and hence that the atom HAS decayed, no matter whether anyone outside the box knows it, and so does the broken glass vial of cyanide "observe" it.
And the meteor that hits the moon "observes" the moon and the moon's core "observes" the moon's crust.
It takes very, very little of the universe to observe in such a sense. Only while a (more or less macroscopic) system is unaffected by the outcome of a quantum event, is it possible to maintain the uncollapsed state.

Could anyone finally tell me where I am wrong here?
Please?

I think the common denominator in this and your subsequent posts are that there is an underlying fundamental reality, that exists, and we observe it. So things that are unknown are like a flipped coin, covered by a hand. It is merely unknown. It already exists as a head or a tails. We can apply probability, just as in QM, and determine the odds for the possible outcomes. But anyone with common sense expects that the coin exists with a head or a tail side up already.

The problem that the experiments that confirm Bell's inequality show is that the quantum equivalent of that coin flip is not just unknown. It does not exist. The coin flip is a poor analogy, but the reasoning in the Bell experiments is that if there exist particles with a set of properties, then the probabilities of observational outcomes must have a certain distribution. Since the observational outcomes do not have that distribution, there DO NOT EXIST particles WITH A SET OF PROPERTIES.

It is a subtle difference between saying a thing has properties that exist but are unknown, and a thing has properties that do not exist, but probabilities of their existence are known.

I am in the group that hopes eventually the connection between the linked particles is understood to be part of some model that makes more sense than this, but it is not necessary that the rules of the universe should be ones that I find most pleasing.

I will add that I have never found Schroedinger's cat to be anything but an example of a thing that is determined, but unknown. If I put an automatic coin flipper in the box, and it was set to go off for heads, I seem to get the same unknown box contents. Perhaps that is a mistake, but it just seems contrived.

 

[naima]

At the very least, we would be in cat-waving territory.

We have to think that the cat is lucky.
http://www.mychinesestudy.com/blog/2012/what-is-the-chinese-waving-cat.html

 

[bhobba]

Thanks DrChinese, but my question dealt with the nature of an observer or observation in quantum theory, not with Bell or collapse in particular.

The modern situation is this. QM is a theory about observations where you are a bit vague on exactly what an observation at the beginning. It's not a human being observing it or anything like that - a mark here in the macro world is a reasonable starting point. This is similar if you study probability where event is a bit vague to start with. As the theory develops you come across this phenomena called decoherence which without going into the details explains apparent collapse. So what is now done is an observation is defined to be just after decoherence. This leads to a purely quantum definition of observer and observation without being vague. It means you no longer assume the existence of a macro world observations appear in so there is no circularity in explaining the macro world using just QM which as a minor blemish with the Copenhagen interpretation.

Why is the moon there when we are not looking? Its never not observed - its being observed by environment all the time. This means both Einstein an Bohr were wrong. But that is not to belittle those two giants. Their debates were magnificent, invaluable in arriving at our present understanding, and well worth anyone's attention. Its just things have moved considerably since then - but interestingly, and this is quite possibly the main value of those debates, certain key issues they grappled with are still with us.

Thanks
Bill

 

[baruch60610]

Is the Moon there when we are not looking?

The question cannot be answered through experiment. Anything we did to determine its existence would be tantamount to looking at it.

As a result, the question falls outside of scientific investigation, into the realm of philosophy or metaphysics.

 

[stevendaryl]

Is the Moon there when we are not looking?

The question cannot be answered through experiment. Anything we did to determine its existence would be tantamount to looking at it.

As a result, the question falls outside of scientific investigation, into the realm of philosophy or metaphysics.

I beg to differ. Progress in science happens when people treat the world as something that actually exists, as opposed to random stimulations of our senses. I suppose there is a sense in which you could say that we don't need to care about anything other than predicting future sensory information based on past sensory information, but the hypothesis that there is an external world independent of our senses is an extremely useful one in developing our theories.

 

[StevieTNZ]

Is the Moon there when we are not looking?

The question cannot be answered through experiment. Anything we did to determine its existence would be tantamount to looking at it.

As a result, the question falls outside of scientific investigation, into the realm of philosophy or metaphysics.

An experiment test of the Leggett-Garg inequality may help answer that.

 

[naima]

Entangled photons do not produce interference in a double slit setup. Entanglement must be broken first before that is possible.

Another question:

When we have which path information the interference pattern is destroyed. is there the same notion with the internal degrees of freedom of the particles?Is the interference destroyed in the Young setup?
Suppose that the hilbert space of one particle is the tensor product of a space for positions end momenta, another for internal properties (color, spin ...).
With a pair of particles we tensor two copies of these spaces.
Internal degrees of freedom may be correlated while the others are not.
What about interferences? Stern and Gerlach setups measure spins, i don't know what Young's setup measures. Is entanglement => no interference always valid?

 

[DrChinese]

Internal degrees of freedom may be correlated while the others are not. ... Is entanglement => no interference always valid?

A pair of particles can be entangled on one or more bases. If a pair were not entangled on spin/momentum/position but perhaps some other basis, interference might still be possible (in a double slit setup, for example).

I can't think of a physical example of that, but then I'm not very imaginative.

 

[naima]

So after entanglement the Von Neumann's entropy can exceed one bit.
Is there a limit to the quantity of information stored in an elementary particle?

 

[Tollendal]

It would be better if we speak about Physics, not metaphysics. Kant is three hundred years in thew past!

 

[Zayl]

So bells theorem says that there are no local hidden variables. Quantum mechanics obviously tells us that cause and effect occurs at non local levels as well. It only tells us something about the ontological structure of the universe. Thus the randomness needs not be fundamental either.

 

[Nugatory]

We've diverged from the initial topic enough that the thread should be closed.