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Why don't we see quantum weirdness in everyday world?

  1. Jan 1, 2014 #1
    Since, we and everything else in our real world are made up of electrons, protons, and electrons, protons, and atoms show quantum weirdness, why don't we ever see such things to happen in real world? Such as, why don't we see part of an apple suddenly disappearing into thin air? Why do classical mechanics never fail to predict motion of things bigger than atoms?
     
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  3. Jan 1, 2014 #2

    phinds

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    Quantum weirdness happens at the quantum level. An apple is lots bigger than a quantum object. If all the quantum objects on one side of an apple ALL had quantum weirdness at the same time, you would see quantum weirdness in the apple. Theory says that if you wait until about the time when all the black holes in the universe have evaporated, you might actually see this happen.
     
  4. Jan 1, 2014 #3
  5. Jan 1, 2014 #4
    Thank you very much for answering.

    I was thinking, say, I have a bag full of helium atoms. Say, the mass of the bag is 1 kg. Now, if I keep monitoring the weight of the bag, wouldn't there be significant chance of reduction of the mass of the bad suddenly by, say, 1%, in an hour, even if for a short instance? Wouldn't the mass be fluctuating?
     
  6. Jan 1, 2014 #5
  7. Jan 1, 2014 #6

    vanhees71

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    There is no quantum weirdness ;-)). The very fact that we live in an environment where we observe stable matter is a quantum effect that is everything else than weird but a basic constraint for us to exist.

    Perhaps, what you mean by "quantum weirdness" are interference effects of particles at double slits, entanglement (a la Aspect, Zeilinger, et al "teleportation"), etc. That we observe such things never without carefully setting up simple (few-body) quantum systems that are isolated from disturbances from the "environment" is due to what's called decoherence.

    A many-body system like everyday matter, as a quasi continuous energy spectrum on the microscopic level, and thus the slightest interaction which something in its neighborhood mixes a lot of microstates up that for our everyday observations of the macroscopic state make no difference. In other words our everyday experience is based on coarse grained (averaged) observables over a large set of microstates that are mixed up by tiny disturbances with the environment.

    A nice website about these issues can be found here:

    http://motls.blogspot.de/2009/09/schrodinger-virus-and-decoherence.html
     
  8. Jan 1, 2014 #7

    ZapperZ

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    From C.A. Mead, PNAS v.94, p.6013 (1997):

    There are other examples of such things nowadays where macroscopic phenomena are actually manifestation of quantum mechanical properties (solid state diodes and transistors, anyone?). Many people just don't realize it.

    Zz.
     
  9. Jan 1, 2014 #8

    vanhees71

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    Well, the very profane observation that matter around us is pretty stable, already is a quantum effect, as is the fact that we can't simply walk through walls although it's "pretty empty" as are the atoms making it up (Pauli principle).
     
  10. Jan 1, 2014 #9

    Vanadium 50

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    Why would we? We don't see electrons disappearing into thin air.

    Because classical mechanics is quantum mechanics, in the large n limit - i.e. the limit of everyday-sized objects.
     
  11. Jan 1, 2014 #10

    atyy

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    Decoherence is not enough to explain why we don't see quantum weirdness. It has to be coupled with some additional assumptions, called "interpretations of quantum mechanics". Some interpretations are:

    (1) textbook (eg. Landau & Lifshitz, Peres): quantum mechanics as a theory always requires the division of the universe into classical and quantum. We only see classical results, which by definition are irreversible, definite marks. In this view quantum mechanics may be incomplete.

    (2) Bohmian mechanics (eg. http://arxiv.org/abs/quant-ph/0308039) is an example of a theory or interpretation that completes non-relativistic quantum mechanics by postulating hidden variables. In this interpretation, there are truly particles with definite positions, but there is a randomness in their positions called quantum equilibrium, analogous to the randomness of particles in thermodynamic equilibrium.

    (3) Many-worlds in which all definite outcomes occur, and the universe splits into distinct realities. If this interpretation works, then it is a logical possibility that quantum mechanics is complete. It is not yet clear if this definitely works, but an account that seems very convincing is in Wallace's The Emergent Multiverse.
     
    Last edited: Jan 1, 2014
  12. Jan 1, 2014 #11

    Vanadium 50

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    It's not decoherence, and it's certainly not interpretations (which is something people do). If you ask what quantum mechanics predicts for a block down an inclined plane problem, the answer is "exactly what Newtonian mechanics predicts". (Only with a lot more work - one can get from Minneapolis to St. Paul via Shanghai, but it's more work than is necessary)

    Quantum mechanics governs the behavior of everything, and classical mechanics is just a very, very good approximation (~30 decimal places for typical classical systems). This is not only true, but is a more useful way of looking at things than the ever-popular "the world is classical, but at some small scale, quantum weirdness is pasted on".
     
  13. Jan 1, 2014 #12
    Thank you very much.

    I was doing a thought-experiment. I was thinking, say, I have a bag full of helium atoms. Say, the mass of the bag is 1 kg. Now, for the sake of argument, say, there are a billion atoms in the bag. Now, each helium atom contains 2 protons. Now, a proton can either be at the centre of the atom, or NOT, but elsewhere ( or can it? Would the neutrons hold them too strongly? If neutrons do indeed, you might replace the experiment with just protons instead of Helium atoms. ) If the proton is outside the bag at any given moment, the bag will lose the mass of that proton.

    Now, would it be too much to think that at a given moment, maybe 1% of the 2 trillions of protons are outside the bag? And we'll find that mass of that bag decreased by 1%?

    Or is it too much to hope for indeed? May it be that even if the protons are about to disappear from the centre of the Helium, chances are more that the protons will remain nearby, and chances are almost zero that they'll ever be outside the bag?

    What would happen if I do another experiment? I have a bag large enough to pack just 1 kilogram of protons ( say, N number of protons weigh 1 kilogram, and I have a bag of which the volume is N times the volume of a proton ) and nothing else. Now, suppose the time a proton takes to disappear from its place, and my unit of time is T. Now, at any point of time, a proton can either be at its place or outside the bag. They wouldn't be able to remain inside the bag, because it was full of protons the moment I found them to weigh 1 kg. Now the chances are that only half of them can stay inside the bag at any given point of time. Wouldn't we expect to almost always see the mass to be that of half a kilo protons?
     
  14. Jan 1, 2014 #13

    ZapperZ

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    Can you explain what this has anything to do with the original question you asked in this thread?

    Is the question on whether one can't observe quantum effect at the macroscopic scale is still up there? After all the examples you were given, is this still something that you want to know? Or has that question been answered already and you are now turning this thread into a completely different topic?

    Zz.
     
  15. Jan 1, 2014 #14

    phinds

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    Yes, it would be WAYYYYY too much to expect. VERY unlikely that in one hour even a single proton would leave.
     
  16. Jan 1, 2014 #15

    atyy

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    It is true that classical mechanics is a limit of quantum mechanics. However, there must still be a mechanism or postulate for definite results from the wave function. As Landau and Lifshitz say, quantum mechanics requires classical mechanics for its formulation, and classical mechanics is also a limit of quantum mechanics. If one omits the postulate that classical mechanics is required in the formulation of quantum mechanics, and postulates that quantum mechanics applies to everything, then one needs an interpretation such as many-worlds to obtain definite results. So yes, an interpretation is required, whether it be textbook or many-worlds.
     
  17. Jan 1, 2014 #16
    Sorry, I did not explain. I read somewhere ( a long time ago, maybe in Hawking's The grand design ) an electron in my coffee mug can at any point of time disappear and pop up in, say, a distant planet. I thought if that's reality, that subatomic particles keep disappearing, it's very much likely that at least a significant percentage of all the electrons and protons that make up the visual centre of my brain or eyes will not be in my body, and I will go see darkness occasionally. I didn't know that even though the protons can pop up elsewhere in the universe once in a while, it's not very likely. And I said so before phinds said it's way unlikely indeed.

    Since I thought both quantum mechanics and my understanding of it can't be right, I made up a thought experiment to see if there are any flaws in my way of thinking about quantum mechanics. Since quantum mechanics has always been proved right, I thought I might tell you what/ how I think about quantum mechanics, and you would help me by pointing out the errors in my reasoning/ understanding/ conception about quantum mechanics.

    However, you already helped me a lot. Thank you very much for that.
     
  18. Jan 1, 2014 #17
    Thank you very much, again. I didn't know that.
     
  19. Jan 1, 2014 #18
    Thank you very much.
     
  20. Jan 1, 2014 #19
    It's clear that a definite outcome occurs from a superposition upon observation. A superposition of a quantum object is not that its in position A and position B at the same time (as it exists in those two places at the same time) - rather its in a potentiality so doesn't exist in either position until observation. So why we don't see nothing rather than something is because observation (by whatever cause [its unclear what causes a definite outcome]) has taken place.

    If you're talking about why we don't see quantum tunneling of macroscopic objects, or the sudden disappearance and reappearance of objects at another point in space at the same time, I guess its because such a possibility has a low probability. That doesn't mean it can't happen - it may happen in the future.
     
  21. Jan 1, 2014 #20
    Thank you very much.

    About that apple argument. I thought if protons/ electrons disappeared, they wouldn't be the same atoms any more, and hence the atoms that make up apple won't be there, and there wouldn't be a complete apple any more as well.

    And thanks a lot for letting me know that quantum mechanics is actually classical mechanics. I was wrong to think that the reason scientists can't unite quantum theory and general relativity is because quantum theory works for small objects, and general relativity works for larger objects; and the only difference between those subatomic particles and larger matter I could think of is quantum weirdness vs classical ( = predictable ) observation.
     
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