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Is it possible to make the quantum coherent?

  1. Aug 20, 2004 #1
    It just crossed my mind, some wierd idea I've got. There's a great deal of chance and probability involved in quantum physics, I was thinking is it possible to make particles, instead of making it most likely to have a particular momentum or position, why not make it more "classical", as in a particle with unique momentum and trajectory.

    Since the observer participates in the experiment as well in quantum physics, is it possible to find out how the observer changes the readings and outcome of the experiment and somehow take that into consideration when interpreting results. Just like adjusting zero error on a micrometer screw gauge or something. Is it possible to do that? Or is my understanding of uncertainty flawed?
  2. jcsd
  3. Aug 20, 2004 #2
    in Layman terms only (the only way I can explain)

    Actually, no, it is not possible. You may wish to browse around in some of the other threads for deeper explanations, but it goes a little something like this: QM is full of probabilities, etc., not by choice but by experimentally verified theory. It's not that our measurements are so imprecise that we can't see this stuff, it's that it is logically and physically impossible to measure a quantity like position without disturbing another quantity like momentum (or velocity). We can't just "give" a particle a definite trajectory because it simply doesn't have one (double-slit experiment).

    It is not possible to measure the effect of the observer for the following reason: without an observer you can't observe. The "observer" doesn't have to be conscious; it can be a machine, but if no measurements are taken of anything (to find the baseline) then you have no information.

    Let me clarify this further: To find the effect of an observer, you'd (hypothetically) need two measurements: the initial state of the system, and the final state of the system after the influence of the observer. But, to find the initial state, you have to "look" at it. Looking at it changes it.
    So you still don't know what the initial conditions actually were, just where you're saying they are at the moment of observation. Then, say, you observe it again, and it changes again. Even if you do this thousands of times, and measure the difference each time, and try, then, to "average" the result, you still end up with never having the actual initial conditions. So the most "damage" to the system has already been done and you have no way of recording it.

    And that's only one example of observer-participation.

    For an example of position/momentum uncertainty, here goes. Once again, I must stress that these equations have nothing to do with technological prowess. So say you want to measure the position of an electron. You put it in a small tube with a magnetic field (otherwise it'll just charge the tube). Now you know where it is--it's in the tube. Now it's momentum is different, because it can't go where it wants to. So you say, "that's fine. I'll let it go, and, since I know the force from the magnetic field acting on it, I know (classically) how fast it will shoot out of the tube. But we're not talking about a bullet, which is at rest before it is propelled out of the gun. We're talking about an electron, which zips around in crazy directions all of the time. So you go to let the electron out, and either:
    a)it's not there. Now you don't know its position *or* its momentum.
    b) it is still there, and you "shoot" it out of the tube. But you never knew it's intitial velocity, because you changed it when you put it in the tube. As soon as you let it out, you can't find it anymore. Why? Because it didn't just take *one* path to where it landed on the detecting screen, it took them *all*. It interfered with itself on the way there.

    I know this doesn't make much sense, but it really is this way. There are a slew of books just on this, and you may want to "google" the "double-slit experiement", interpretations of Quantum Mechanics, and interpretations of the Uncertainty principle. Also, check out the threads of predictable unpredictables
    Is Uncertainty principle Unbeatable?

    I hope this helps more than hurts. Sometimes I confuse myself.
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