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

[bhobba]

Answer: Undefined state.

No - the answer is interpretation dependant.

Who was right? Bohr or Einstein. Their debates were magnificent - but actually both were wrong:
http://www.fisica.ufmg.br/~dsoares/cosmos/10/weinberg-einsteinsmistakes.pdf

Thanks
Bill

 

[Hornbein]

No - the answer is interpretation dependant.

Who was right? Bohr or Einstein. Their debates were magnificent - but actually both were wrong:
http://www.fisica.ufmg.br/~dsoares/cosmos/10/weinberg-einsteinsmistakes.pdf

Thanks
Bill

That is so. They were both wrong. But Einstein was more wrong.

 

[bhobba]

That is so. They were both wrong. But Einstein was more wrong.

I don't look at it that way - they both had issues. I think Dirac was right with his basically shut-up an calculate view - but that's just me. Note - although often attributed to Dirac and/or Feynman they didn't really say it but it does reflect both their views.

Thanks
Bill

 

[Hornbein]

I don't look at it that way - they both had issues. I think Dirac was right with his basically shut-up an calculate view - but that's just me.

Thanks
Bill

Well, the "I-have-no-model" view is logically unassailable. But it ain't no fun.

 

[adfreeman]

There's something I don't understand regarding the subject we've been discussing.

I heard quite a few times that if instant communication was possible using entangled particles, then this would also mean that we would able to send messages backwards in time. I don't understand how, so imagine for a moment that we could use entangled particles for communications; how would this messages to the past work?

 

[bhobba]

I heard quite a few times that if instant communication was possible using entangled particles, then this would also mean that we would able to send messages backwards in time.

This is way off topic - but - yes - you would be able to violate causality eg you could create a device that sends a signal back in time to destroy it.

You can find the detail in Rindler:
https://www.amazon.com/dp/0198539525/?tag=pfamazon01-20

If you want to pursue it start a thread in the SR sub-form.

Thanks
Bill

 

[naima]

it smells like an upcoming closure?

 

[Nugatory]

I heard quite a few times that if instant communication was possible using entangled particles, then this would also mean that we would able to send messages backwards in time. I don't understand how,

Any faster than light signal transmission will do the trick, and "instantaneous" is of course faster than light. Google for "tachyonic anti-telephone" to see how it works, and if you want more start a thread over in the relativity forum - the people there are who you should be asking.

 

[naima]

I have a problem with DrChinese entangled particles.
If the system is in the state (|u>|d> + |d>|u>)/2 the density matrix of the left particle is Id/2 so there is no interference behind the slits.
If alice apply a local rotation of 45° in the u/d plane the systeme is no more entangled and interferences can be seen behind the slits. So Bob could know that Alice applied the rotation. There is obviouly a problem. Where is it?

 

[stevendaryl]

There's something I don't understand regarding the subject we've been discussing.

I heard quite a few times that if instant communication was possible using entangled particles, then this would also mean that we would able to send messages backwards in time. I don't understand how, so imagine for a moment that we could use entangled particles for communications; how would this messages to the past work?

That's got nothing to do with quantum mechanics. It's just pure relativity: if a signal is instantaneous in one frame, then it is back-in-time in a different frame. To use this fact to communicate with your own past requires that the instantaneous signal can be sent relative to any frame. If there is only one frame that allows instantaneous signals (that is, if there is a preferred rest frame), then back-in-time communication would not be possible; it would only seem back-in-time to some observers, but not to others.

 

[DrChinese]

I have a problem with DrChinese entangled particles.
If the system is in the state (|u>|d> + |d>|u>)/2 the density matrix of the left particle is Id/2 so there is no interference behind the slits.
If alice apply a local rotation of 45° in the u/d plane the systeme is no more entangled and interferences can be seen behind the slits. So Bob could know that Alice applied the rotation. There is obviouly a problem. Where is it?

I will repeat my comment (with reference) in #29: entangled particles do not produce interference. Breaking Alice's entanglement - by a measurement - does NOT suddenly cause any detectable change in Bob. And vice versa.

When Alice breaks entanglement with Bob's photon, further (non-commuting) measurements of her photon will not be correlated to any of Bob's measurements.

So the "problem" is that your view of entangled particle behavior needs a minor adjustment.

PS a rotation of Alice (say by a quarter wave plate) will not break entanglement.

 

[naima]

I know that alice cannot change what Bob sees. When she breaks the entanglement i think that the global state changes. Could you give an example where Alice breaks it to see interferences and Bob's density matrix does not change?

 

[entropy1]

I am wondering what the term "instantaneous" means in this context: simultaneity is relative in RT! You can only observe that the correlations are measured space-like separated by Alice and Bob. Information does not exist 'in between' two space-like separated events. The correlation can only be established by slower-than-light communication, as we all know. So IMHO "instantaneity" is not a term that covers the notion of FTL. If you do, you will have to refer to time 'between' the events, and that can only be done in terms of lightcones. The term 'space-like separated correlation' suits better, IMHO.

 

[stevendaryl]

I am wondering what the term "instantaneous" means in this context: simultaneity is relative in RT! You can only observe that the correlations are measured space-like separated by Alice and Bob. Information does not exist 'in between' two space-like separated events. The correlation can only be established by slower-than-light communication, as we all know. So IMHO "instantaneity" is not a term that covers the notion of FTL. If you do, you will have to refer to time 'between' the events, and that can only be done in terms of lightcones. The term 'space-like separated correlation' suits better, IMHO.

Well, the collapse interpretation of QM would seem to require a preferred rest frame. But the odd thing is that it doesn't actually matter which frame you pick--there are no detectable consequences of the choice.

 

[naima]

I read in the Zeilinger paper that Alice can observe interferences after erasement and coincidence countings. Is it always the same trick with intricated particles?

 

[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.