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Quantum enigma

  1. Dec 13, 2012 #1
    So the laser test with the slits is as followed as far as I understand.

    When observed, electrons act as particles.
    When not observed, electrons act as waves.

    How can electrons know if your eyes are open or closed? Unless your eyes give off some wort of radiation that it can pick up on.

    Also when the electrons are not observed and go through the slits, than are observed on the other end. They instantly change, how can they go back and time and change? Because they instantly change at the point of the gun.
  2. jcsd
  3. Dec 13, 2012 #2


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    You cannot say this. Well, taken literally, you can, but it is not right.

    Interactions with the electrons (to observe it) can influence the electron and change how it behaves. Expressed like that, it sounds trivial, right?

    There is no need to go back in time.

  4. Dec 13, 2012 #3

    How do scientists know they act like waves? Wouldn't they have to observe the electron acting as a wave for this to be true, but that contradicts the face that, when they are observed they turn to particles.

    When scientists look on the other side of the slit, the electrons instantly turn to particles. They go back in time, meaning the electrons that have already left the gun instantly turn to particles when observed. If they have already left the gun as a wave, how could it change to particle?
  5. Dec 13, 2012 #4


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    The way the experiment works, we can use an electron source so weak that it only emits electrons one at a time. An electron leaves the source and eventually hits the screen, where it leaves a tiny dot. Every time we see another dot appear, we know that another electron has been emitted. There's no wave-like behavior going on here; each electron leaves a single dot where it hits just as if it were a tiny rifle bullet.

    But.... If we run the experiment long enough to build up a pattern of thousands of those little dots we don't see two spots, one behind each slit, as we would with particles acting like little bullets. We see the interference pattern that would be produced by waves passing through the two slits, with many electron dots at the points where the peaks of the waves line up, and few where a peak and a trough cancel each other.

    This is how we see wave-like behavior without trying to observe and measure each electron.
  6. Dec 13, 2012 #5
    Thanks a lot that really clears it up a bit more.
  7. Dec 14, 2012 #6
  8. Dec 15, 2012 #7
    What about quantum entanglement? Does this mean, there is something that can travel over the speed of light?
  9. Dec 15, 2012 #8


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    I would not call it "something". In particular, you cannot transmit any information via entangled particles. You can show that theories have to be non-local (=> objects can influence other objects (in a specific way) faster than the speed of light) if you want them to satisfy some other conditions at the same time.
  10. Dec 15, 2012 #9
    DeepSpace, in my interpretation the nonlocal influences are at the level of possibility. They are physically real, but not contained in spacetime.
  11. Dec 16, 2012 #10
    Space can expand faster than the speed of light. The speed of light is only for particles like photons, etc... Seems that "information" or empty space can do whatever the heck they want to.
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