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The Uncertainty Principle

  1. Jul 25, 2004 #1
    I've got a few questions about the uncertainty principle and I'm new to more advanced physics. So from what I understand about the uncertainty principle is,

    Ok, I've got a particle. And say, I want to know the exact location of the particle. And the wave amplitude is highest closest at its location. So I get alot readings of this particle's momentum which in turn I can find the amplitudes and wavelengths, and this would guide me to the location of the particle.

    But, in the course of doing so, I actually can't figure out the momentum of the particle because I used tons of readings of the momentum to pinpoint its location. Is this right? But there are still a few questions,

    1. Isn't momentum varaible as in it varies with time right? As time goes by, won't there be external forces acting upon the particle?

    2. Isn't a particle always moving as it has not experienced the absolute zero?

    Or is it in this case we are interested in looking for the momentum and location of a particle at a certain instance? But if so, isn't finding a set of values for momenta enough? And from this, can't we exactly define the particle location and momentum? Do we take the time which these 2 things vary into consideration here?

    Yea, thanks for any help.

    Also, actually I'm more interested in nuclear physics, but do I have to understand quantum physics in order to do nuclear?
  2. jcsd
  3. Jul 25, 2004 #2
    I think you are making things a bit complicated. Heisenberg-principle just states that If you wish to locate a particle, the position is exact or the position-interval where you will find the particle is very very small. Momentum-interval will then be very very high, so from the moment on that you want to see the particle, it will allready be gone, due to this high momentum. hence, you never see the particle when the position is exact. You can conclude from this that position and momentum are uncertain.

    A same relation works for energy-interval and time-interval

    Beware that we are always talking about intervals, not exact values for things like position. The reason for this is, as mentioned, an exact position value corresponds to extremely high momentum-interval. This means that the momentum can take a lot of different values, so you do not really know the momentum.

    2) Particles can be in rest. What do you mean with experiencing the absolute zero ???

    3) Attention, at a certain instance is a frase that is difficult in QM. Time is also uncertain with energy. So if you say for instance, at a specific time or moment, the energy-interval of the particle is infinite. So you cannot speak about the energy of a particle.

    4) In order to study nuklear fysics you will certainly need a profound knowledge of QM. For example the alpha-decay is explained by the concept of potential-wells. The well is created by the potential energy (binding-energy) of the atomic nukleus, that a particle will have to overcome so that the mother-nukleus can become stable.

    beta-decay is explained bij QFT

    Also the rules for describing the interactions of a nukleus with the surrounding elektron-clouds through distortion of the sferical form of the nukleus is explained by QM (think of the dipole-momentum)

    and so on and so on

    conclusion (nuclear fysics) - (quantummechanics) = ?????

    hope to have helped

    nikolaas van der heyden
  4. Jul 25, 2004 #3
    the uncertanty principle is very simple. It is really easy to explain. If you want to see something, you should use waves (ex. electromagnetic) that have a smaller wavelength than the actual object, the samller they are, the more accureate and clear the object looks. Now, in the quantum world, there objects you are trying to see are extremely small, and in some cases they are the same size as the wavelength of light used to observe them, or even smaller. In order to see there objects, a scientist needs to use lower wavelengths (ex.gamma rays). BUT, when the scientist lowers the wavelength of the source used to see the object, he HIGHTENS the energy (E = hf). This increase in energy means the particle used to observe (lets say a photon) has a higher momentum, which in turn makes it harder to bounce off the observer particle without affecting it. This is why you cant have the exact momentum and position of a quantum particle, the more you know about one, the less you know about the other. I hope I've been a help. If you have any confusion, pm me.
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