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Why am I so dumb?

  1. Dec 3, 2012 #1
    I like to think that I have a moderately complete education in science and liberal arts, recently
    though the popular physics shows I used to love leave me completely bewildered.For example
    Lawrence Krauss says that two + two equals five for sufficiently large values of two. Epistimologically this is utter nonsense, WTF is he talking about? Another example, If dark matter can't be detected it makes no sense to me to talk about fields in empty space since logically you cant differentiate between truly empty space and space permeated by dark matter. I assume dark matter cant be distributed equally throughout the cosmos because the overall gravitational effects would be null. So how can anyone talk about the properties of empty space? One more, Schroedingers cat! Why does the cat not count as an observer,surely it must know at least that it is not dead. Would you get the same results(both is and is not) if a scientist were locked in a box instead of a cat? What if the the cat were in a box and the observer w/box were trapped in a bank vault till monday morning? would the cat be dead till we could observe the observer? Please dumb down your answers for me wherever possible. Feel free to tell me its too hard for easy answers.
    sincerely
     
  2. jcsd
  3. Dec 3, 2012 #2
    It's a joke, usually uttered as a humorous response to the claim that 2+2 is not equal to 5. One is supposed to be reminded of phrases like "x+x is greater than five for sufficiently large values of x." Like so much humor that relies on subverting expectations, the joke is funny because it implicitly treats the constant 2 as if it were a variable.

    Dark matter can be detected (indirectly) via its gravitational effects. That's how we know it exists in the first place. We can even map out the distribution of dark matter based on how it pulls on things with its gravity.

    The term "observer" in quantum mechanics does not mean "conscious being" or "human" or something like that. It's a technical term. This is a major stumbling block to popular presentations of QM. It may help to mentally replace "observer" with "measuring apparatus" whenever you see the term in the context of QM. This may remove some of the mystery.

    Yes.

    If the observer opens the box while inside the vault, the contents of the bank vault would be in a superposition of "observer has seen a dead cat" and "observer has seen a live cat" until we open up the vault.

    (Note that the Schrodinger's cat experiment requires a very special kind of box (or bank vault) which allows absolutely no interaction between the contents of the box and the outside of the box. In practice, no existing boxes or bank vaults are anywhere close to achieving this, and you need to construct specialized experiments in physics labs to actually create superpositions).
     
  4. Dec 3, 2012 #3
    I'd trust The_Duck's answers more than mine in this case, but my view on this is that we're thinking of the experiment from the point of view of the scientist performing the experiment, not the cat's. From the cat's point of view (or anyone else inside the box, for that matter,) it's likely going to be either dead or alive. From the scientist's point of view, until the box is opened and observations about the contents are made, the cat's in a superposition of being dead and alive.

    After a little research, this seems to be specifically Relational Quantum Mechanics' explanation, most other interpretations might offer a different story.

    (Interpretations of Quantum Mechanics are basically just different ways of intuitively explaining the math behind Quantum Mechanics. For the time being, there's really no way to "prove" any of them, all of them should lead to the same results of any experiment.)
     
  5. Dec 3, 2012 #4

    bapowell

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    The cat was meant to be a humorous stand-in for "quantum state", which is not considered part of the observational apparatus. Instead of cat, think electron.

    Schroedinger's cat was not meant to be a reasonable proposal for an experiment, it was intended to be an illustration of the absurdity that follows when you extend quantum physics to the macroscopic realm. And I think Jim has pointed out precisely why it fails in this regard.
     
  6. Dec 3, 2012 #5
    The joke about 2 + 2 = 5 could be understood from an experimentalist's perspective. We always have some error in our measurements, so without specifically writing the error intervals, 2 might mean anything in the range [1.5,2.5). So, large values of 2 are stuff like 2.4. 2.4 + 2.4 = 4.8 which can be rounded to 5.

    Schrodinger's cat really showcases a conundrum in quantum mechanics which we don't really understand (the observer problem/explanation of the collapse of the wavefunction/what is quantum reality) and there is no consensus on. Various interpretations of quantum mechanics have sprung up which provide different viewpoints on the phenomenon.

    One interpretation is that reality itself is relative to the observer. It's only in the observer's reality that the cat is both dead and alive. The cat doesn't experience this state. If you put the scientist in the box, then the scientist can be both dead and alive to another observer outside the box, but not to the scientist in the box. There are many more interpretations. We don't know which is correct and whether this can be answered scientifically.
     
  7. Dec 4, 2012 #6
    Thank You all for your considerate responses. I didn't know what to expect in terms of the answers I'd recieve but I appreciate your courtesy. Whatever I may think about theoretical physics I know the physicists are gentlemen!
    Sincerely
     
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