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

[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.