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Galaxies beyond the horizon

  1. Dec 6, 2014 #1
    Are galaxies that exist beyond the horizon of the visible universe in a superposition of many different states relative to us?
    A related question: If we take a laboratory with some scientists inside and put them all in a big box that's perfectly isolated from the rest of the universe, then the scientists will be in a superposition of several different states. But does that also mean that from the point of view of those scientists the rest of the universe is in a superposition?
     
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  3. Dec 6, 2014 #2
    This bumps firmly up against the measurement problem and hence gets into interpretations of quantum mechanics—what exactly one believes the wave function represents. However regardless of interpretation we can say that they are certainly not in any kind of coherent superposition if they're in any superposition at all. Macroscopic objects cannot be isolated for any significant period of time and so are subject to decoherence which turns quantum superpositions into classical mixtures. So to whatever extent its meaningful to talk about things outside the observable universe, our ignorance would be represented by classical probabilities not quantum amplitudes.

    Same question, really, and with essentially the same answer, with the caveat that "perfectly isolated" isn't really a meaningful assumption. You might as well be talking about two separate universes in that case. Though in this phrasing, it's very similar to a classic extension of the "Schrödinger's cat" thought experiment called "Wigner's friend" that you might enjoy reading about.
     
  4. Dec 6, 2014 #3

    Nugatory

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    No more so than galaxies that are within the observable universe. Galaxies don't care whether we can see them or not.

    Let's go back to Schrodinger's cat for a moment. Schrodinger was not suggesting that the cat was both and alive at the same time; the point of his thought experiment was that quantum mechanics in 1930 didn't explain why the cat had to be one or the other but not a superposition of both. In the intervening decades the discovery of decoherence has gone a long ways towards answering this question, and there's no longer any reason to think that we have to look at something to make a superposition go away. Instead, complex systems like cats and galaxies naturally settle into unsuperimposed states, just as random collections of gas molecules naturally evolve in ways that conform to the ideal gas laws.

    No, for the reasons above.
     
  5. Dec 7, 2014 #4
    But how am I to interpret this experiment then?
    http://www.nature.com/news/2010/100317/full/news.2010.130.html
    According to that article they managed to put a macroscopic object into a superposition of different states.
    So what would happen if a whole building (with a laboratory inside) were to be put into the same kind of superposition? What would the people inside see if they tried to measure the state of the outside world? Using the same kind of measurement techniques that were employed in that article I linked to?
    Wigner's friend is indeed interesting but it doesn't tell me what would actually be measured in an experiment.
     
  6. Dec 7, 2014 #5

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    It is possible, just barely and and then only with heroic efforts, to get an object that it is visible to the naked eye to remain in superposition for a short time when it subjected to a limited set of observations. Note in particular that they had to cool the object to cryogenic temperatures; otherwise the interactions between the atoms that made up the object itself would have been enough of an interaction to cause decoherence even in the absence of any observation. Quantum effects can also be observed in macroscopic volumes of liquid helium (I had a lot of fun with this years ago when I was in college), but again cryogenic temperatures are required.


    It can't be done. The first thing you would have to do is cool the entire lab, scientists and all, to nearly absolute zero - this will put something of a crimp in their ability to observe or do much of anything else. And even without that obstacle, extrapolating from the current macroscopic superposition results to anything as complex as an ant, far less Schrodinger's cat, a lab full of scientists, or the entire galaxies that this thread is about is an unrealistic stretch. It's like observing that surface tension will support a speck of dust on the surface of a bowl of water so in principle it should be possible to float a bulldozer on a lake - it would be if you could get the mass to surface area ratio right, but it's not going to happen.

    (However, I do have to mention that the impossibility here is of a statistical nature. There's no reason in principle why the air molecules randomly bouncing around underneath the chair I'm sitting in might not, just by random chance, happen to be all be moving upwards at the same moment - and then I would be smashed against the ceiling with lethal force. That's not likely, but it is unimaginably more likely than the probability that an entire lab full of scientists could be maintained in a superposition in any basis for any measurable amount of time).
     
    Last edited: Dec 7, 2014
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