Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Does Moon exist if you don't look at it?

  1. Jul 5, 2007 #1
    From NewScientists 23 june 2007 "RealityCheck":


    <<What they found(*) is that Leggett's formula is violated as well: even if you allow for instantaneous influences, quantum measurements do not fit with the idea of an objective reality. This is surprising because you might expect that, once any spooky "non-local" action is allowed, you could account for almost any relationship between two particles, and there would be no reason to ditch our concepts of reality. "This is not the case", says Aspelmeyer.

    Although some loopholes remain - not all non-local models have been ruled out - we now have to face the possibility that there is nothing inherently real about the properties of an object that we measure.
    In other words, measuring those properties is what brings them into existence. "Rather than passively observing it, we in fact create reality", says quantum researcher Vlatko Vedral of the university of Leeds, UK.>>

    (*) It refers to an experiment performed by Markus Aspelmeyer e Anton Zeilinger (Nature, vol 446, p 871) to test Leggett's formula (a variant of Bell's inequality, with the additional hypothesis that instantaneous inluences are allowed).
  2. jcsd
  3. Jul 5, 2007 #2
    I would say that yes, the moon very much does 'exist' - since it's made of a vast quantity of matter, each particle of which is interacting with others - and an interaction must have a locus. This counts as a 'measurement' since at that point the particle's attributes are specified and the wavefunctions of - say - two electrons are collapsed by one another.

    At least, that's my interpretation of quantum mechanics. It all sounds very hand-wavy to me.
  4. Jul 5, 2007 #3


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Decoherence nicely solves 'paradoxes' like this. The particles that comprise the Moon are constantly interacting with photons and other particles. Furthermore, the particles constantly interact with each other. This prevents any kind of macroscopic superposition from ever occuring, which means there's no paradox.

    Quantum superposition is a very difficult thing to achieve.

    - Warren
  5. Jul 5, 2007 #4
    Quantum measurements aren't at odds with objective reality. A quantum realm, where photons, electrons, etc. exist as individual objects, is at odds with the reality our sensory experience. So, photons, electrons, etc. exist as sets of mathematical and experimental operations. Theorists and experimenters bring them into existence. They, in effect, create the reality of the quantum realm by how they choose to talk about quantum experimental phenomena.

    Not so for moons and computers and other objects of our sensory experience.

    Quantum phenomena don't exist independent of the operations which define them -- the act of looking at them is the act of producing them. The moon, on the other hand, is always there for anyone to see whether they choose to look or not. So, of course, the moon is there even when nobody is looking at it -- and quantum theory doesn't contradict this belief.

    There have been many good suggestions by the mentors and others on this forum about how to look at quantum theory so as not to get caught up in unnecessary musings such as whether or not objects of our ordinary sensory experience exist when we're not sensing them. :smile:

    One way to think of the physical world is as a hierarchy of various media, and waveforms in those media, interacting in various degrees of complexity. Our sensory experience is at a rather higher (more complex) level than more purely quantum phenomen. Qualitatively, our sensory experience involves interactions across media interfaces and between media. Whereas the more purely quantum realm, it's conjectured, must consist mostly of media whose particulate structures are unknowable as far as we're concerned. And if there is a fundamental medium that is nonparticulate and perfectly seamless and continguous (disturbances in which form the foundations for all other media and hence ultimately our sensible physical reality), then this can never be established empirically.
  6. Jul 5, 2007 #5

    This is an example where logic is being ignored, one of my big beefs with Copenhagen Interp.

    If something does not exist in an ontologically real sense PRIOR to observation, there is no observation. If your logic is correct, we have lost the meaning of the word "observation" and should stop using it at once and instead speak of "creation."

    You can only affect, in a causal sense, something ontologically existing prior to. If it isn't there, then you cannot have any causal relationship to it. You cannot even speak of "producing" them, since that act would place you in a causal relationship with what was produced. But you can only exist in a causal relationship to something ALREADY there. If it isn't there, you can't have a causal influence on it. If it just appears hocus pocus, you or noone or nothing else had any effect on it in a causal sense whatsoever!

    So your logic won't even allow you to say that your observing it produced it.
  7. Jul 5, 2007 #6

    Hans de Vries

    User Avatar
    Science Advisor
    Gold Member

    The article in Nature is here:

    http://www.scribd.com/doc/48376/nature05677 [Broken] and

    The preprint is here:


    Popular coverage (from New Scientist) is here:


    The paper has a pretty far going conclusion:

    Leggett's non local hidden variable model is discussed in appendix 1 of the preprint.

    My personal opinion:

    The Hidden Variable model here which is excluded by this test is,
    like the Bell ones, a model were the Hidden Variables are merely input
    parameters to random processes involving polarizers.

    Two independent uncorrelated random processes at both sides (Bob and
    Alice) can not support the conservation law tested, and therefor must
    fail in experiments testing this conservation law.

    Ruling out such a model is one thing, drawing very far reaching conclusions
    on this is something else, especially if one can expect the failure of the
    model on forehand.

    In my opinion only LHV models which do not involve uncorrelated random
    processes can hope to obey conservation laws.

    Regards, Hans
    Last edited by a moderator: May 3, 2017
  8. Jul 5, 2007 #7
    My question "Does Moon exist if you don't look at it?" was intended to stimulate discussion about the NewScientists article, not in a literal sense (I believed it was obvious, but clearly it wasn't, sorry!)
  9. Jul 5, 2007 #8
    Yeah, I think that if we don't see a thing then can issume it don't exist. but it is valid while we don't sense it's affects and properties. For example don't see the storm but it DESTROYS the other things in its way. Therefore the storm exists. Also in QM Does exists positron? Since we have photon then it is confirmed that positron exists. All of the statements of QM are to this form because of their existance probability and limitations for seeing.

    Mr beh
  10. Jul 5, 2007 #9
    I agree with that. But do you think that the CI is correct really? if you confirm it then we have an idea for agreement the your wrting in the CI: if we don't measure the properties of QM system then they are non-sense. And firs REQUISITE of that is seeing of QM system's components.

    Mr Beh
  11. Jul 5, 2007 #10
    Last edited by a moderator: May 3, 2017
  12. Jul 5, 2007 #11
    And what of the tides?
  13. Jul 5, 2007 #12
    quote: "measuring those properties is what brings them into existence"

    This is a logically nonsensical statement. If the "measuring" brings them into existence, then there is no measuring! There is only creating. Measuring no longer has any meaning. You are now talking about creation.

    In what sense does the word "measure" have any meaning according to the accepted definition of the word in view of this statement?

    To measure something PRESUMES something already existing. To say "it doesn't exist until it's measured" completely violates the logical integrity of the accepted meaning of the word "measured."
  14. Jul 6, 2007 #13
    What you say is very important. Often physicists or others talk about " to measure" as if it was an action on something that already exist. We should talk a bit more on what exactly this actually means, in my opinion.
  15. Jul 6, 2007 #14
    Of course the phrase "Does Moon exist if you don't look at it", was intended in allegoric sense, that is "..if you don't measure it", and didn't refer to the very moon but to microscopic objects, described by QM. My title was intended as a "poetic" reference to the results of that experiment.
    Last edited: Jul 6, 2007
  16. Jul 6, 2007 #15
    Chroot's answer was perfect- observation isn't merely 'looking'- it involves all causal interaction with the observer and his local environment- therefore the state of a complex interacting world will be quite defined except for under very specific conditions where coherence is preserved- so the Moon is always there- but for example your non-interacting junk DNA might be in superposition until someone sequences it
    Last edited: Jul 6, 2007
  17. Jul 6, 2007 #16
    Do I have to assume you didn't even read my post previous to your?
  18. Jul 6, 2007 #17
    What is your purpose from posting of the #15 in this thread?
  19. Jul 7, 2007 #18
    Assuming that the experiment is good (it looks nice, both setup and results) then the possible candidates to question are counterfactual definiteness and absence of actions into the past. Especially the latter - as I think a lot remains to be understood with respect to time in QM.
  20. Jul 7, 2007 #19

    no I didn't- I just glanced at the thread and saw chroot's responnse- then gave it a +1
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook