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Quantum Measurements and Macroscopic Objects

  1. Aug 19, 2009 #1
    In the beginning there were only probabilities. The
    universe could only come into existence if someone
    observed it. It does not matter that the observers
    turned up several billion years later. The universe
    exists because we are aware of it.
    — Martin Rees Professor of Cosmology and Astrophysics and Master of Trinity College at the University of Cambridge.

    As far as I understand, In Schrödiger's cat experiment, The Copenhagen Interpretation claims that at the moment that you open the box after one hour, it is in that moment that the past of the cat (either whether it is death or alive) is decided. basically as I understand it the past is being created in the act of opening the box by a conscious observer.

    If this is true what are the implications for macroscopic objects? For instance if im with a geiger counter and if a particle decays, is it the fact of me watching and being aware that a
    particle decayed what makes it come into existens?

    If this is true , what would happen if my geiger counter registers a particle decaying and keep the record of it but I don check the geiger counter until one year later? would I be making that particle to come into existens one year after the geiger counter detected it?

    Extending this to the early universe, and to the remanecesce of particles in the early unvierse perhaps from the Cosmic microwave background radiation or some other remanecesce of particles in the early universe, could they have been created in some way by the fact that conscious observers exists in the universe.

    Finally could the big bang have been created because of consciouss observers inhabiting the universe? is this the logic the one that Martin Rees used when he said the above mentioned quote?
  2. jcsd
  3. Aug 19, 2009 #2
    Your quote is misleading. It holds the inconsistent view that reality only exists during observation and that reality existed before being observed. In its typical interpretation, CI does not claim that an objective history is created through the act of observation. It claims that there is no objective history, because there is no distinct (separable) objective reality. Reality is best described, at its basic level, in relation to our experience of it.

    The cat being alive is as real as the cat having the color black. Is a cat black when it isn't being perceived as such? Our old notions of intrinsic and extrinsic properties would say no... color is not a property of objects; it only exists in our perception. CI simply recognizes that the spatiotemporal properties we thought were intrinsic aren't actually that way. There is no intrinsic / extrinsic. There is only extrinsic. We should therefore say that the cat is black and the cat is dead, even while acknowledging that there is no such thing as a real objective cat.
    Last edited: Aug 19, 2009
  4. Aug 19, 2009 #3
    In that case perhaps the quote was meant to be allegorical in some way. I have read many books written by physicists about the subject and they mention that an objective history was "created" just as the act of looking at a particle "creates" it, I guess it is easy to make that kind of wrong assumption.
  5. Aug 20, 2009 #4
    There are certainly people who have made that claim, but it is not consistent with Niels Bohr's thoughts at least, and it doesn't appear to me to be logically consistent (absent an intentionally inconsistent use of language). How you interpret QM depends on your assumptions, and nothing about QM itself dictates which assumptions must be made. It is rare for someone presenting a view to actually outline their assumptions and to qualify the validity of their interpretation by those assumptions, and such complete descriptions don't make for very good quotes or headlines. It is especially rare to have consistent assumptions stated if the presenter doesn't agree with a view and is trying to show its absurdity.

    QM is certainly very paradoxical. No matter what assumptions are made, we can't have a world that is, at its basic level, (separably) objective, deterministic, and located in space-time. QM is paradoxical enough without the need to violate logic though, so you are definitely right to ask questions when it appears that a contradiction is being made.
  6. Aug 23, 2009 #5
    I guess the fact that we cant have a spaciotemporal objective reality shouldnt come as a surprise though because of special relativity and quantum entanglement. It is great to see that although QM seems utter paradoxical it dosent necesarily violates logic.

    Though a paradox arises about the roll of multiple consciouss beings which are at the same time part of an objective reality and their roll in reality. I think Heidegger had a philosohpical argument about this issue though.

    It is intersting though that modern philosophy and some schools such as phenomenology, existensialsm already adressed subjective ways of approaching reality as well.
    Last edited: Aug 23, 2009
  7. Aug 24, 2009 #6
    I think the most common view today is that Schodringer's cat is definitely dead or alive well before you open the door. Macroscopic objects the size of a cat don't show superpositions such as a cat alive/dead or being at two places at the same time.
    The process of decoheerence describes how something that is originally in a superposition assumes a more definite state after interaction with the environment.
    There are still paradoxes and certain things that are not explained by deoherence, but it does enhance our understanding o the transition from quantum to classsical.
  8. Aug 24, 2009 #7
    The process of decoherence describes how the two states in superposition cease to overlap after a short amount of time, not that one of them ceases to exist. This does not explain the Schroedinger cat thing, not even slightly.

    As far as I know, you can only do that by

    (1) just saying that one of the branches ceases to exist, i.e. the wave function 'collapses' (conveniently stops obeying the Schroedinger equation for a while to avoid you getting frustrated), or

    (2) saying that the wave function is not all there is. i.e. that there are particles as well (guided by the waves). 'Things' are made of particles, and these just deterministically end up in one of the branches with the appropriate probability [Bohm interpretation].
  9. Aug 25, 2009 #8
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