Is the Moon there when nobody looks at it?

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Please help me with this. Can anyone direct me to the specific mathematics that is interpreted as saying that "the Moon does not exist when nobody looks at it."
Is there any book or discussion of the actual math and physics of this?
What specifically was Einstein reacting to when he said:
"I cannot believe that the Moon exists only because a mouse looks at it." ?
Please feel free to write or send me anything you wish about this subject. I have no axe to grind, and I only would like to understand this better. Thank you.-Ron
 
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To add to the question, what would constitute "looking". Would a video camera that displays the image on a screen in an empty sealed basement that no one can enter be considered "looking?

What if the images were captured digitally and were later destroyed without anyone looking at it?

or perhaps someone does look at it later.

The issue of looking, taping and viewing presents an interesting discussion topic.

Tardis
 
DrChinese
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RonLevy said:
Please help me with this. Can anyone direct me to the specific mathematics that is interpreted as saying that "the Moon does not exist when nobody looks at it."
Is there any book or discussion of the actual math and physics of this?
What specifically was Einstein reacting to when he said:
"I cannot believe that the Moon exists only because a mouse looks at it." ?
Please feel free to write or send me anything you wish about this subject. I have no axe to grind, and I only would like to understand this better. Thank you.-Ron
Welcome to PhysicsForums, Ron!

I keep a page on my site which explains this in more detail:

Bell's Theorem with Easy Math

This is partially based on a paper by N. David Mermin called: "Is the moon there when nobody looks? Reality and the quantum theory" (1985). As you might guess, my page is probably a bit easier to follow for most people, especially as to the math.

The fact is: Einstein (sadly) died before Bell's Theorem appeared. He likely would have changed his opinion had he known about it. Experiments support the ideas of Quantum Mechanics in this area quite solidly.
 
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DrChinese said:
Welcome to PhysicsForums, Ron!

I keep a page on my site which explains this in more detail:

Bell's Theorem with Easy Math

This is partially based on a paper by N. David Mermin called: "Is the moon there when nobody looks? Reality and the quantum theory" (1985). As you might guess, my page is probably a bit easier to follow for most people, especially as to the math.

The fact is: Einstein (sadly) died before Bell's Theorem appeared. He likely would have changed his opinion had he known about it. Experiments support the ideas of Quantum Mechanics in this area quite solidly.
There are some recent:http://www.physics.uq.edu.au/people/andrew/publications/2005/weakvalue.pdf [Broken]

workings on the experimental setup?

I like your pages on the setup principle, though simplistic it has the essence of answering some questions, whilst I must admit it has lead to me asking "more-than" the original question!
 
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The moon is there when nobody is looking at it. You don't have to look at
something for it to exist. QM never said you did.
 
DrChinese
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Antiphon said:
The moon is there when nobody is looking at it. You don't have to look at
something for it to exist. QM never said you did.
No one is actually talking about the moon. At least, I'm not. But if you are saying there are values for particle attributes independent of actual measurement, then I am going to disagree with you.

I believe this position is as consistent with experiment and theory as it is possible to state: the act of observation changes reality, even after the fact.
 
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Hello Tardis, Dr.Chinese, and Spin Network, Thank you for your prompt replies. It is my pleasure to meet you. I downloaded David Mermin's paper, but could not open the file. How is the question of whether the Moon exists when nobody looks at it tied into EPR and Bell's Theorem?
Can you show me the equations that can be interpreted as showing that the Moon(or anything else) does not exist when nobody looks at it. I am familiar with issues about observer-created reality. Is this issue about the Moon a result of scaling up a quantum physics fact to macroscopic sizes, sort of like how this is done with Schrodinger's Cat? If so, what is it specifically that is being scaled up? Thanks, and Best Regards,-Ron
 
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DrChinese said:
No one is actually talking about the moon. At least, I'm not. But if you are saying there are values for particle attributes independent of actual measurement, then I am going to disagree with you.

I believe this position is as consistent with experiment and theory as it is possible to state: the act of observation changes reality, even after the fact.
Why doesn't this statement naturally lead to application with macroscopic bodies, such as the moon. The moon is composed of fundamental particles, is it not?

I have read a little about a particular Copenhagen stance considering macroscopic objects as different entities than fundamental particles. Something about a macroscopic measuring device being able to collapse the wave function, so there is some kind of interplay between the macroscopic world and the microscopic world and both are needed to create the human experience. Is this sort of what you're saying? That since the moon is macroscopic it is capable of having a definite position even when not being measured? It just seems to me that if you take the statement that fundamental particles don't have definite positions unless they're being measured and follow it to its logical conclusion, the moon also can't have a definite position unless it's being observed. ???
 
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DrChinese said:
No one is actually talking about the moon. At least, I'm not. But if you are saying there are values for particle attributes independent of actual measurement, then I am going to disagree with you.

I believe this position is as consistent with experiment and theory as it is possible to state: the act of observation changes reality, even after the fact.
Actually, I was very careful to say that the thing [moon] "exists" and not
that it "is there" implying a particular position. As you know Dr. C, to exist
in QM is to have a unit probability of being somewhere in the universe
without actually being any one place most of the time.

It's a freaky business and (quoting myself from another thread) the person
who figures out the physical basis of quantum superposition will be a rock
star on par with Einstein.

Edit: As far as the macroscopic-composed-of-microscopic goes, Ellipse, to my
way of thinking the best answers so far are given by the folks who say that
a large object perturbs (or observes if you will) itself and this is what gives
rise to the emergence of more classical persistence of position.
 
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DrChinese said:
No one is actually talking about the moon. At least, I'm not. But if you are saying there are values for particle attributes independent of actual measurement, then I am going to disagree with you.

I believe this position is as consistent with experiment and theory as it is possible to state: the act of observation changes reality, even after the fact.
So, if I observe the Moon, does this "effect" the motion of tides here on Earth?

What would such consequences be if everyone that can observe the Moon at the same instance, did so. Would there be a verifyable difference in Tidal action?

What I am asking is the number of observers influential on imparting "effects" to the observed ?
 
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Spin_Network said:
So, if I observe the Moon, does this "effect" the motion of tides here on Earth?

What would such consequences be if everyone that can observe the Moon at the same instance, did so. Would there be a verifyable difference in Tidal action?

No, beacuse the gravity of the moon is there (and is the same) even when you don't look at
it- more evidence that you don't need a human observer to make a thing
manifest in a particular position.
 
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RonLevy said:
Is this issue about the Moon a result of scaling up a quantum physics fact to macroscopic sizes, sort of like how this is done with Schrodinger's Cat? If so, what is it specifically that is being scaled up?
That is a good way of describing it, yes.

What is being scaled up is the idea that particles have definite attributes independent of observation. The Heisenberg Uncertainty Principle (HUP) restricts the "simultaneous reality" of various particle attributes according to its relations. Observation of position affects momentum, for example. QM treats HUP as fundamental; therefore the existence of attributes varies according to the nature of the observation. All known experiments satisfy the HUP.

EPR (Einstein) tried to use measurements on entangled particle pairs as a way to outsmart the HUP. However, the HUP came through as QM would predict, after Bell came along and showed the way. You see, many thought the HUP was simply an experimental limitation; Bell concluded it was fundamental to the nature of reality. Most people do not look at Bell in terms of the HUP, but that is in fact at the base of the debate.

I do not mean to imply that anyone really knows what an observer is - i.e. must it be a conscious mind? I only mean to say that the act of observation is somehow fundamental to the outcome as to what reality becomes.
 
DrChinese
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Antiphon said:
No, beacuse the gravity of the moon is there (and is the same) even when you don't look at
it- more evidence that you don't need a human observer to make a thing
manifest in a particular position.
Talking about the moon confuses the issue greatly, because it is a macroscopic object. The combined uncertainty of the particles composing the moon is not a factor in macroscopic observations. The question is not whether the particles composing the moon exist. It is whether those particles have distinct values independent of individual observation. The answer is that they don't. That does not mean that the particles don't obey gravity - because they do. They also bond into atoms. Etc.

But no individual atom escapes the rules of the HUP. This is fundamental to QM. And this is the debate. People simply talk about the moon as a metaphor. It is not intended to be literal.
 
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RonLevy said:
How is the question of whether the Moon exists when nobody looks at it tied into EPR and Bell's Theorem?
Can you show me the equations that can be interpreted as showing that the Moon(or anything else) does not exist when nobody looks at it.
Referring to my paper:

Einstein said: "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."

If you look at my Table 1, you will see 8 cases ([1]...[8]) listed with all permutations for the hypothetically real polarization attributes at 3 angle settings - 0, 120 and 240 degrees. The existence of these 8 permutations is what is being debated. If there is reality independent of observation, then all 8 exist. But QM/HUP denies this explicitly! In fact, the mere assumption that there are 8 permutations leads to a burdensome requirement that was not previously suspected, and this requirement is called Bell's Inequality. Bell's Inequality cannot be supported experimentally, although the predictions of QM/HUP can. This is Bell's Theorem.
 
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Hi Dr. Chinese, Please help me understand if this Moon-existence issue results from the whole take on the Copenhagen Interpretation, or not. I think I see now how it is related to EPR and Bell's, because the moon-existence thing is related to the question of whether there is or is not a "deep reality" independent of observations. Let me be straight with you: After spending the last 4 months trying to learn The Quantum Theory, (including the Bra-Ket notation), I came across a startling argument for the existence of God, (I am an agnostic.), which is that "If the Moon continues to exist when nobody looks at it, that this is because there is a conscious observer who is continuously observing the moon 24 hours a day." Naturally, I would like to see exactly where this follows logically from the science that yields the notion that "the moon does not exist if it is not observed by anyone."
What do you think about this? If the moon-existence paradox, (MEP), is actually a kind of "non-issue," so that MEP follows from a metaphor that conveys the essence of the Copenhagen Interpretation, then that is one thing. However, if, as you have pointed out, it leads straight back to The Heisenberg Uncertainty Principle, which has never failed an experimental test, that seems a lot stronger. Best regards, Ron
 
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Have finally gotten Mermin's paper to open, and am studying it and Dr. Chinese's discussion on his site. This is deep stuff. Fascinating and amazing stuff. Thanks. If you guys think I'm mixed up or confused, please tell me. I have no axe to grind or point I need to make. I just want to learn it and understand it.
-Ron
 
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DrChinese said:
I believe this position is as consistent with experiment and theory as it is possible to state: the act of observation changes reality, even after the fact.
:smile: If you *really* want to be politically correct, you should say that in quantum theory, the act of observation changes PERCEIVED reality, even after the fact.
The whole discussion (amongst those who accept of course current predictions of QM) resides in what is the underlying reality, and what part of it is perceived. It is only in the case you identify the underlying reality with the perception you have, that you can make such a statement.
In mathematical terms, this comes down to saying that the quantum state represents "reality", and that observation (projection) affects "reality" or that observation only comes down in picking one of the terms as the *perceived* reality.
 
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How can something not exist if it does exist? There are somethings that maths simply fails to explain.

If no one looks at the sun for about 8 minutes 20seconds and when we look back would sun be there or would it not be there?????

If it happenes to moon it will surly happen to sun!
 
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RonLevy said:
I came across a startling argument for the existence of God, (I am an agnostic.), which is that "If the Moon continues to exist when nobody looks at it, that this is because there is a conscious observer who is continuously observing the moon 24 hours a day."
Why are you so certain that the moon must have a definite position when it's not being observed? It *does* exist, as someone pointed out earlier, fundamental particles/waves always exist, they just don't always have a definite position. So why wouldn't quantum theory naturally lead to the fact that if there are no moon observers, there is no definite position for the moon.

However, I have come accross a similar type of argument, that perhaps the one thing that seperates an observer from the quantum world is a soul. I really don't understand why wave functions should ever collapse, but they obviously do when humans are involved, so should that lead to the conclusion that there is something humans possess which isn't built up from the quantum world? Oh well, :tongue:.
 
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vanesch said:
:smile: If you *really* want to be politically correct, you should say that in quantum theory, the act of observation changes PERCEIVED reality, even after the fact.
The whole discussion (amongst those who accept of course current predictions of QM) resides in what is the underlying reality, and what part of it is perceived. It is only in the case you identify the underlying reality with the perception you have, that you can make such a statement.
In mathematical terms, this comes down to saying that the quantum state represents "reality", and that observation (projection) affects "reality" or that observation only comes down in picking one of the terms as the *perceived* reality.
I think the whole point is that QM tells us that percieved reality is the only reality. This also goes right to the question regarding Conscious-mind observer vs. video recorder. Perhaps the statement in the OP could better be expressed as, "YOUR Moon only exists when you are looking at it". If the video camera is looking at the Moon, then the Moon exists for it, but you cannot prove that it exists for you. Of course, if you are not looking at the camera, then I suppose you can't even say that "the Moon exists for the camera", because the question then becomes "what camera?", since the camera also does not exist for you when you're not looking at it, right?

Why are you so certain that the moon must have a definite position when it's not being observed? It *does* exist, as someone pointed out earlier, fundamental particles/waves always exist, they just don't always have a definite position. So why wouldn't quantum theory naturally lead to the fact that if there are no moon observers, there is no definite position for the moon.
But for the Moon to exist as "moon", many articles/waves must be in definite positions. Those that make up the material in the loose dust on the surface must be above those that make up the carbonaceous rocket and magma underneath, with perhaps some others making a tiny metal core at the center. If all of these bits have only "existence" without a particular location, then they cannot be assembled together in their proper places to form a Moon.
However, I have come accross a similar type of argument, that perhaps the one thing that seperates an observer from the quantum world is a soul. I really don't understand why wave functions should ever collapse, but they obviously do when humans are involved, so should that lead to the conclusion that there is something humans possess which isn't built up from the quantum world? Oh well, .
I think that it only looks that way to a human.
 
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If the Moon did not exist when nobody looked at it, then wouldn't the gravitational attraction disappear too? If that happened, the tides would change (at least). Does our experiencing of the gravitational effects of the Moon amount to an indirect way of making a measurement (observing the Moon)?
 
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RonLevy said:
If the Moon did not exist when nobody looked at it, then wouldn't the gravitational attraction disappear too? If that happened, the tides would change (at least). Does our experiencing of the gravitational effects of the Moon amount to an indirect way of making a measurement (observing the Moon)?
There's a serious problem with applying quantum ideas to gravity. It might even be the key to the solution of the riddle. But let's for a moment assume that that is not a difficulty.
The tides would not "change" because by observing those tides, or their effects, you are indirectly observing the moon's position. So in the same way as the moon would maybe "jump around but only appear to be in the right spot when you observe a few photons bounced off its surface", the moon would maybe "jump around but only appear to be in the right spot when you observe a few tidal effects". So as long as you *observe* a consistent set of things, you will not conclude about an anomaly. That doesn't mean that things have to be that way (only), but that means that they have to give rise to consistent observations.
 
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LURCH said:
I think the whole point is that QM tells us that percieved reality is the only reality. This also goes right to the question regarding Conscious-mind observer vs. video recorder. Perhaps the statement in the OP could better be expressed as, "YOUR Moon only exists when you are looking at it". If the video camera is looking at the Moon, then the Moon exists for it, but you cannot prove that it exists for you. Of course, if you are not looking at the camera, then I suppose you can't even say that "the Moon exists for the camera", because the question then becomes "what camera?", since the camera also does not exist for you when you're not looking at it, right?
Yup, that's right, it is a way to look at things (I adhere to that view). Well, no, I adhere to the view that the camera exists in BOTH states (with and without a picture of the moon), but that I only observe ONE of these states.

But for the Moon to exist as "moon", many articles/waves must be in definite positions. Those that make up the material in the loose dust on the surface must be above those that make up the carbonaceous rocket and magma underneath, with perhaps some others making a tiny metal core at the center. If all of these bits have only "existence" without a particular location, then they cannot be assembled together in their proper places to form a Moon.
In fact, for the Moon to exist as moon, many particles must not be in definite positions. There are many quantum states of the overall system that would be a sufficiently accurate description of what we vaguely call "Moon", and there's a whole body of theory (decoherence theory) which tries to demonstrate that the interactions of that system with its environment keep it in those states most of the time.

I think that it only looks that way to a human.
Worse, it only looks that way to YOU. All other humans have a different view, but YOU only see them in their only aspect where they have only seen ONE of the states :rofl:
 
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Dear Vanesch, To see if I understand: You and others are saying that it is not a question of whether or not the moon exists, but instead, by The Heisenberg Uncertainty Principle the question is whether the Moon occupies a specific spot in x,y,z,t space-time if it no one makes an observation? -Ron
 
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This business of "Is the moon there......" is one of the oldest issues known to mankind, and has virtually nothing to do with QM, nor with empirical science. You have your platonic ideals to Hume's extreme skepticism, with which I pretty much agree. As several have pointed out, we observe the moon all the time -- it is, from time-to-time directly visible. When it's not, its gravity has a well defined and well predicted effect on the earth; similarly with the sun, ...... Thus it is prudent to assume that the moon is indeed there all the time. Astronauts have confirmed this to a point; during their time their experience told us all that the moon was solid at the surface, was round, ...
The point is that there are other possible configurations, cf. optics and potential theory, that can provide a model of the moon that accounts for what we know of it -- great homework assignment.

So why do we assume the moon is in fact a solid body, much like other planets and moons in the solar system? Its the best Occam game in town. We work with what we call common sense and intuition and assumption -- all of which have changed radically since Plato's time -- sort of like "It's the economy stupid" a memorable statement of recent political affairs.

If you really think about it, there are a huge number of assumptions required to assert that "A is really there" or "B is not there." The key one, to which virtually all of us subscribe, is that there's something out there that generates the signals which we perceive -- and there's no way to find out whether or not that's true, because we rely totally on our perceptions to live, to understand, to do science, and so forth. Over the centuries we have become highly sophisticated, or so we like to think, and we've adopted a perspective on science, made authoritative via Popper's idea of falsification -- hardly a euphonious word --, with which David Hume would agree. And, of course, to date our common assumption of an external world has survived in admirable form. It boils down to: if you cannot observe or measure something by any means, for a short or long time, then you have no empirical way to assert existence during the time of observation -- this is true of legal evidence and reasoning as well as scientific evidence and reasoning. But the assumption of continuity of existence -- including possible alterations by one means or other -- has served us well. But make no mistake: reality is a human invention, a convenient assumption beyond proof.

Schrodinger's Cat? Perhaps I'll drum myself of the respectable scientific community, but I have never understood "the problem" since I first heard of it many years ago. In no small measure, my take on this matter has been fortified by many years of day-to-day work with statistics and probability, which I've also taught at the undergraduate level. If you don't know, you don't know. Of course I work with the assumption that we have yet to encounter a cat which in, other than some mystical or a specific medical sense, simultaneously is alive and dead. Why in the world would we assume the cat's state in Schrodinger's experiment takes on a wholly different aspect than one we see in the "real" world? Cats, humans, other animals are either alive or dead -- except, perhaps in unusual medical circumstances -- are either alive or dead. There is, certainly, a probability that the cat is either alive or dead, the two allowed states. And the probability is conditioned on the state of the radioactive system, which does or does not decay. To me, standard probability theory does an Occam-like job with Schrodinger's cat.(Not dissimilar to assuming, in an unwatched horse race, that A won, because just before crossing the finishing line B stopped and tried to turn around. Arguably this could happen, but......)

Suppose you did many EPR experiments with detectors at different distances from the source, or many scattering experiments with detectors spanning the space allowed to the scattered particle. (I mean one set of counters per experiment; not multiple scattering configurations.) You, of course, will find events in different configurations, and different places. That is you will map out the density of events in the appropriate configuration space, and thus you will map out the probability of events. This approach is equally valid in the classical and quantum worlds --measure and count. (Recall that the low energy cross section for charged particle scattering, the Rutherford cross section, is equally valid classically and quantum mechanically. Granted, this scattering phenomena occupies a small portion of the space of all possible scattering experiments. Nonetheless it is suggestive that a straightforward application of basic probability to such low energy scattering is quite appropriate.)


Finally, the results discussed above, define perfectly additive measures, as do all spaces of disjoint events -- a single measurement cannot simultaneously give both a spin up and a spin down result. For a basic probability measure to exist, discrete or continuous or mixed, an additive measure is necessary and sufficient. Thus, a global perspective puts QM on a standard probability basis, and therefore allows a "knowledge interpretation", a la Sir Rudolph Peierls.

Regards,
Reilly Atkinson
 

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