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Bohr and solipsism

  1. May 4, 2010 #1
    I wonder if Bohr QM point of view could be labeled as "solipsism" or even "Metaphysical solipsism". Any hint would be appreciated.

    I may be wrong at some point, so I would be glad to hear other opinions or corrections.

    According to Bohr (subjective Copenhagen interpretation of Quantum theory) "there is no underlying reality".

    I have also heard another softer version: "we are unable to describe reality between measurements", but that would be to say that QM is unable to describe reality and that would be equivalent to say that QM is incomplete (Einstein's point of view). I would be very surprised to discover that Bohr stated such a thing!

    So, I think only hard version "there is no underlying reality" could be really Bohr's world view. Right?

    If that is true, can we say that Bohr was a solipsist? According to Wikipedia, Metaphysical solipsism is an idealism based on the argument that no reality exists other than one's own mind. I think that is quite the same as to say that "there is no underlying reality", isn't it?

    Thanks in advance for any other point of view.
  2. jcsd
  3. May 4, 2010 #2
    Good question, but Bohr was definitely not a solipsist :tongue:. Bohr has often been misinterpreted through the various versions of the "Copenhagen Interpretation" over many years. I recommend reading http://plato.stanford.edu/entries/qm-copenhagen/. From the article:
    I also highly recommend reading Bohr's "Atomic Theory and the Description of Nature." Don't trust second hand sources when it comes to historic QM interpretation (But Jan Faye of the SEP article is good). Original Bohr is very readable.

    To get more into your question... Bohr definitely believed that QM was complete, while also believing that we can't describe reality between measurements. But asking what happens between measurements didn't make sense for Bohr. From ATDN:
    Any underlying "real essence" for Bohr is and has always been outside of the scope of physics or descriptive language. He argues for this conclusion from relativity:
    So Bohr isn't a solipsist and he isn't denying that anything exists. He's saying that we had the wrong idea all along. It was never about an objective description of things "out there." What are measurements or any events except for interactions? And how do you have interactions without your observee and observer - how do you have any events at all with no context for them to occur in?

    It relates to the "If a tree falls in a forest..." question. Bohr would say that a tree falling in a forest does not make a sound if no one is there to hear it. Sound is not a thing that exists independently of ears. It takes both a falling tree and a working set of ears with a brain attached for sound to exist. It also requires proper experimental conditions - the tree cannot be in a vacuum etc. But without ears, a falling tree only creates vibrations in the air.

    All phenomena, for Bohr, require a measurement context to exist. Everything, in this sense, is subjective. But this is not something new to QM. This is a simple epistemological fact. That is why Bohr can say that QM is complete. There is no way around the problem, quantum uncertainty or not, so the best thing we can do is accept it and move on.
    Last edited: May 4, 2010
  4. May 4, 2010 #3


    I'd say he was.

    "Everything we call real is made of things that cannot be regarded as real."

    -Niels Bohr
  5. May 4, 2010 #4
    Let's apply some logic to that: if a complete theory can't describe reality between measurements then reality becomes indescribable there, right?

    So, reality is indescribable. If you say something is indescribable, isn't that describing it? Reductio ad absurdum.

    If you find anything wrong in this reasoning, please tell me.

    Thanks again.
  6. May 4, 2010 #5
    No, that is not a description, any more than x is a description for 3.14...

    Its merely a placeholder.

    The word 'nothing' is similar. Linguistically, nothing, is a noun, which as you may know, is a person, place or thing.

    The word 'nothing' is really just a negation of 'thing', as in 'no-thing', but since language is abstract, and can treat concepts as things, the lack of a thing can be treated as a thing.

    Language is flexible... and in a lot of cases it is the nature of language that has caused a lot of confusion in philosophy.

    And no, Bohr is not a solipsist. But people use the word 'reality' to describe different things.
  7. May 5, 2010 #6


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    If you know there to be actually something, then already you are describing "something", even if the details are sparse. So claiming something to be literally indescribable is simply self-contradictory here.

    And as for the gaps between measurements, again you know there to be gaps that are "really there". QM gives you a description of what can fill those gaps - even if the sum over histories allows an exact degree of uncertainty.

    The quantum zeno effect would be relevant here. Making the gaps between measurements smaller has an interesting result on reality.

  8. May 5, 2010 #7
    Solipsism can never be proved or disproved. Since Bohr never openly advocated solipsism, your question really is:

    Can Bohr's theory be consistent with a rejection of solipsism.


    1. Assume the existence of minds other than your own; Alice and Bob.

    2. Alice and Bob prepare identical classical apparatus to measure spin or something. They record and plot their results. Their individual results will be different but they will (within experimental error) both be representable by the same probability distribution.

    3. That the probability distributions are the same is evidence of an underlying objective quantum reality even though the properties of individual quantum "particles" do not have pre-existing values (i.e. are not real).

    Therefore rejection of solipsism is consistent with Bohr's theory.

    "There is no underlying reality." does not imply that there is no reality. It means that quantum mechanics does not pretend to be any kind of theory which describes the sub-microscopic world. It is a (possibly complete and presently the best) theory of how our interactions with the sub-microscopic world will work out.

  9. May 5, 2010 #8
    Philosophically, what does it mean for a quantum system to have NO objective existence prior to observation/measurement, as that was Bohr's insistence? Bohr claimed that 'particles' do not possess properties when they are not being observed.

    What is the ontology that is consistent with this premise, but solipsism?
  10. May 5, 2010 #9

    This is wrong. Bohr led a 30-year debate(possibly the longest in science) that QM was a complete theory. The completeness of QM was the central point of the debate between Einsten and Bohr.
  11. May 5, 2010 #10
    Ontological solipsism denies the existense of 'other minds', but affirms the existense of the conscious self.

    Observation/measurement, in terms of QM, doesn't even require one mind.
    In QM, observation, is all about 'interaction'.

    Consider what happens when you crumble a piece of paper, it begins interacting with itself, in a way it does not when it is flattened out. Solipsism gives primacy to one really crinkly bit of the paper and defines the rest of the piece from that perspective. QM doesn't, all crinkles are treated equally.

    But flatten it out again, and the crinkles disappear. The paper is not reality, because there is no way to describe a lack of interaction. Physics only appears with the friction of paper against paper, the crinkles.
  12. May 5, 2010 #11

    This is a bold statement. The problem is that it is based on an assumption that there exists a mind-independent reality that does not require a mind. I am perfectly aware that Bohr never made such a statement and we are discussing Bohr's ontological propositions for reality.

    Bohr explicitly said that unmeasured phenomena are not real. What he made of that ontologically is not clear to me, but it looks like solipsism. I am not even sure an ontology is even possible on the proposition that unmeasured events are not real.

    We are not talking of QM in general, where there is still NO agreement on what the theory means, though you very strongly imply and believe it is otherwise. We are talking of the QM of Niels Bohr. Niels Bohr assessment was that "unmeasured/unobserved entities are not real". Bohr insisted that his QM was complete which means that that is how reality is.

    I contend that "unmeasured/unobserved entities are not real" is a form of solipsism. I see no reason to believe that someone who denies the objective reality of objects with fixed properties in time and space will believe in the existence of other minds. What would drive such a belief?

    This discussion requires that i remind of his famous quote:

    “If quantum mechanics hasn't profoundly shocked you, you haven't understood it yet.”

    Or let's re-run the argument as it was in 1935:

    Einstein: - Do you really believe the Moon is not there when nobody is looking?
    Bohr: -Yes, it's not there when nobody is looking.

    What is this if not a form of solipsism?
    Last edited: May 5, 2010
  13. May 5, 2010 #12
    Not really, if reality is defined as (observed) interaction.
    Correct. I don't see a problem, unless you limit the idea of 'measurement' to 'measured by a conscious' entity, as opposed to 'measured' being equivalent to 'interaction'.

    When two atoms bounce off each other, energy is converted.... that would be a form of measurement... a very basic observation. Just like the detectors used in the LHC, for instance.
    I never said I agreed with any of this. The question was:
    Answer: Reality is interaction. Whether Bohr would agree with me, I don't know. Never met the man, but I see no reason to believe Bohr was ontologically solipsist. I think you're getting hung up on the word 'reality'.
    Still not seeing where solipsism comes in. I don't think he was implying that if Niels Bohr didn't observe something, then it doesn't exist. Is this what you mean? That would be solipsism. But QM doesn't require an conscious human 'observer'. I'm thinking Bohr knew that. Do you have a quote that contradicts this?
    I contend you are wrong.
    I don't think he was doing that. After all if you observe an object existing in time and space.... then according to Bohr, it is real.
    Interaction with other minds?
  14. May 5, 2010 #13

    And how does the above statement lead to the conclusion:

    except by assuming that reality exists even without a mind?

    Bohr's position was that unmeasured entities were not real. My position DOES NOT matter at all as that is not the subject of the thread.

    But you did state:

    This is your belief and you made it into a strong statement.

    We do not know what reality is, or even how it is. The formalism of QM does not address these issues. They are philosophical and when Bohr was being philosophical he stated:

    ""Everything we call real is made of things that cannot be regarded as real."

    He also states that wavefuncions are not real and unobserved entities, e.g. the Moon when nobody is looking does not exist.

    Go teach Einstein and tell he didn't understand Bohr's points correctly. You need to reread the EPR.

    Who said anything about the current trends in QM? We are at QM as it was "understood" around 1935.

    Yes, according to Bohr, quantum systems do not have definite properties prior to observation/measurement. And this is very widely known as the CI of Niels Bohr(that Einstein argued against). Or are you saying it is possible to exist and be real without having definite properties? That would be absurd.

    How did you prove that unreal(according to Bohr's view) superposition of states actually exist(according to Bohr's view)? You did not.

    So reality is real because it is real? Ha, great way of arguing but that was not Bohr's point at all.

    Let's re-run the argument as it was in 1935:

    Einstein: - Do you really believe the Moon is not there when nobody is looking?
    Bohr: -Yes, it's not there when nobody is looking.

    What is this if not a form of solipsism?

    If Bohr is right, i'd be cautious with that belief.

    The EPR argument between Bohr and Einstein was because of Einstein's concerns for Realism after the arrival of the Copenhagen Interpretation of Niels Bohr. Einstein believed as you do, that objects have properties whether anyone chooses to measure them or not at all times. Niels Bohr was of the opposite opinion and this is closer to solipsism than any other ontology i can think of.
    Last edited: May 5, 2010
  15. May 5, 2010 #14
    Maybe I am missing something, and it is possible that I am, but why haven't we considered Bohr's position as idealist? I believe it is consistent with all of the statements attributed to him (the ones in this thread at least, I am by no means familiar with his statements regarding reality as described by quantum theory), and for me, solipsism is too large a jump to ascribe to Bohr
  16. May 5, 2010 #15
    My 2 cents... the entire point of "complementarity" is to make room for the possibility of a classical spacetime theory that is capable of accounting for the essence of Nature, as she is immediately experienced (i.e. "measured"). So, Bohr's stance, in my view, was much more philosophically sympathetic towards the two competing tendencies of mankind to 1) be certain of some fact and to 2) understand how that fact is at all possible.

    But the new generation of theorists (e.g. Heisenberg, Pauli, etc.) saw fit to stop trying to understand empirical reality, in its possibility--and simply held fast to varying forms of ontological skepticism or outright denial (not atheism, but aontism?). And it was for this reason that Einstein dedicated his entire post-relativity career to keeping alive the hope that a "complete" theory of physical reality could indeed, in time, be found.
  17. May 5, 2010 #16

    It could be of course. The question is how does one remain idealist for long? If someone believed that all of reality is just in the mind, wouldn't that lead him/her to doubt the existence of other minds? What justification would an idealist have for the belief of the existence of other minds(provided they didn't believe in the realness of experienced reality)?
  18. May 5, 2010 #17
    True, that is a valid question that possibly the more philosophically informed could reply to. I would guess that it is all about not proceeding beyond from what is directly "empicrically" available to us through our senses, and the conception that there exists an external material reality does not follow from what we experience as "sense-data". Yet our interacting with other minds makes the existence of other minds seem more plausible. But at that point I suppose it would be right to say that denying external reality due to it not following could also be said of other minds, though that is more radical. I would be interested to see how an idealist would discuss that issue.
  19. May 5, 2010 #18
    If physics describes interactions between things, and physics describes reality, then only things that interact with other things are part of reality. In fact, it would be nonsensical to even talk about 'something' if it didn't interact with something else. Something that doesn't interact with anything in our reality, is not part of our reality.

    What Bohr actually thought, is anyone's guess. I'm not a mind reader. But Bohr's position does not imply solipsism. If Bohr was a solipsist, then the moon, and Einstein, would only exist.... when Bohr was looking at it. That does not appear to be his position.
    LOL. Ok, well I guess that ends that.
    There are two aspects to QM. We have the theory, and we have the observation.
    The theory, seems to work mathematically, but very few people, if any, understand what the math is doing. However, the math does allow us to predict what we will observe on the quantum scale. In fact, Einstein objected very strenuously to 'spooky action at a distance', something the theory predicted, and was then observed to occur. Einstein was wrong.

    No, I don't understand quantum theory. All I know, is that it seems to work. What can be said about it, is that it describes interactions on the quantum level. These quantum interactions can occur even when 'a mind' is not directly invovled in the observation, but until some form of measurement is done, there is a serious question as to what if anything is actually there.

    If quantum reality is the sum of quantum interaction, then reality can be said to equivalent to interaction. Whether this is actually true or not, I don't know, but seeing as you can't measure something you can't interact with, you'd be hard pressed to show that something is real.
    He is not part of this reality anymore.... so I can't interact with him.
    No, we're at... how one man understood it.
    You know, you don't seem the least bit interested in a discussion, you're not even arguing with me anymore... you're just throwing up straw men.
  20. May 6, 2010 #19

    This isn't a settled issue what physics is describing. And that is even a mild statement :surprised. Nor is it settled how wavefunctions become single states(e.g. the reality of our observations). Moreover, the assumption of causality is under question, as well that of realism and locality. There are interpretations that do away with causality, and there are others that do away with the whole 'particle' thing, e.g. MWI. What are we to make of this mess? Well, if Feyman is to be the authority, you should "shut up and calculate" and "do not ask these questions, if you can possibly avoid it. Nobody has...". So the above statement is more of a belief, than fact(as would be any other statement on how reality works).

    In the standard form, QM is just a statistical theory and causality takes a secondary role. Same goes for interactions. Oly when you add up near infinite measurements can we begin to talk of causality and interactions. They do not play the fundamental role that we find at out level of existence. Why are certain outcomes favored by Nature? Hmmm, i'd like to know this too.

    Sure you are not, nor is anybody else. The point is the CI is a non realist interpretation, and back in the days when arguments between Einstein and Bohr erupted, it was thought by Bohr that quantum mechanics was a complete description of how nature is. A non realist interpretation in the physics sense(denying realism) means that objects do not have properties prior to the vague notion of 'collapse'(whatever that means). It's only after the observation has been made that we can talk about physical objects. This to me is closer to idealism and solipsism than any other ontology.

    I am certain that Bohr didn't think Einstein was there all the time. Even when nobody was looking. Hell, he was even accused of brain-washing a whole generation of scientists that his interpretation was the only possible. This has changed but the fact remains that at that time this is how it was thought reality was.

    Nobody understands quantum theory :wink:. This is certain.

    There are a bunch of interpretations that don't agree with that statement - the Relational, the CI(though it's not always clear what is measurement or observer, it could be argued that without my mind - the electricity between the neurons of my brain that constitutes whatever it is i am - there is no measurement, collapse or reality). The many minds interpretations doesn't fit the above statement either. The Von Neumann interpretation wouldn't agree either. What about String theory and the attempts to do away with the concepts of time and space altogether? How does a mind fit the picture of a spacetime that emerges from more basic concepts?
    It is not known yet, if we can do away with the concept of mind from physics, though it's the desire of the majority for very obvious reasons. Even Einstein who was a realist more than yourself, said:

    "It is basic for physics that one assumes a real world existing independently from any act of perception. But this we do not know. We take it only as a program in our scientific endeavors."

    Anyways, someone who declares there is no quantum world, everything that we call real is not made of objects that are real, if you aren't shocked by qm you haven't understood it yet, etc. appears to me to be much more an idealist/solipsist than anything else i can think of.

    And then the whole ordeal about interpreting qm is over, it is going to raise even more philosophical questions when it is settled. Why do we understand reality? Where are those laws that allow such immense mathematical accuracy coming from? The platonic realm? Or are we digging deeper into the Mind of God? For sure, it's going to be a great pre-occupation for the future breed of philosophers.
    Last edited: May 6, 2010
  21. May 6, 2010 #20
    Which would be why I used the word IF
    Of course it is. So what? Again you seem to be having an argument with someone else.
    Idealism maybe, there are many forms of idealism, but IT IS NOT SOLIPSISM.

    Solipsism is not about the interaction of observed and observer collapsing a wavefunction, in solipsism, all there is, is self. Nothing collapses, even statistically.
    Feel free to provide a quote to support this.
    You keep saying this, like its some new toy, you got for your birthday.
    Who has done this??? Not me. And I think you have missed the point he was making because his opinion offends your sensibilities.

    Do you even read what I wrote?
    You realize, you just failed the Turing test.
    Last edited: May 7, 2010
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