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A question

  1. Sep 6, 2004 #1


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    I've recently read about a phenomenem which i believe is called "action at a distance" (or sometimes "spookey action at a distance"??) and it confuses me. Specifically I am talking about fact, which has apparently been proved, that if a particle and it's sister particle are fired off in different directions and you interfere with one of those particles the other immediately "knows" about this interference (sorry if the language is a bit loose here but I'm not a physist - barely even an amatuer if truch be known!!) It seems to me that this violates the speed of light limit set bt relativity. My question is this: is there anything in current thoery that may explain this? If not, does anyone have any suggestions as to why this may be?
  2. jcsd
  3. Sep 6, 2004 #2
    Welcome alf !
    there has already been many discussions here, and you could benefit from reading those. Try to search "entaglement" for instance, you will see many threads.
    For instance Aspect's experiment

    I give you a short answer : it does not violate relativity, since no energy is transfered. Quantum mechanics say that the particles are initially in a superposition of states (like a door being close and open. I know, this is surprising at first :surprised), and the measurement destroys this superposition : there is a collapse of the wavefunction, that is all the possibilities have been reduced to one.
  4. Sep 7, 2004 #3


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    Thanks for the thread Humanino. I figured it had probably been discussed somewhere, but being new here I didn't know where to look!
  5. Sep 7, 2004 #4
    You can search PF in the upper toolbox. This site is really neat !
  6. Sep 7, 2004 #5


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    Thanks again for the help. I've spent the last 4 hours reading about entanglement and I think I'm starting to get it, but my head hurts too much to continue! I guess the counter-intuitive nature of the quantum world just takes a while to wrap your head around!
  7. Sep 7, 2004 #6
    You bet ! QM has been around since almost a century now, and nobody still gets it :wink:

    Seriously, I don't remember who said :
    The guy was french, so I slightly modified the quotation...
  8. Sep 7, 2004 #7
    More like trying to work out an Alien language for which we don't yet have a dictionary.
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