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Proton vibrations

  1. Feb 5, 2014 #1
    Hi all,

    a) Do a proton still vibrate if it isnt bound to its nucleus? I mean, if it is "alone" (no neutron, no electron). Do anybody know if they have done experiments on it? I would like to know if it has been observed/measured in some way.

    b) An electron does not "like" to be still, it moves around the nucleus. But how about a neutron? Do a neutron behave in the same way? If it would be detached from its atom, would it behave like a photon/ would it move even if I am trying to stop it? As if it had some "inner force" (like photons have)?

    Edit: Ive just read that neutrons have kinetic energy. So called "fast neutrons" move in a speed of ~14000 km/s (~ 5% of the speed of light). But do protons also have such kind of kinetic energy? If a proton was "free", would it have a inner force that drives it "forward"/makes it move?

    If I would hold a electron in my hand, it would travel away (lets say it doesnt interact with the protons in my hand). And if I would have a neutron, it would also take of. But would the proton be still?

    Thank you
    Last edited: Feb 5, 2014
  2. jcsd
  3. Feb 5, 2014 #2


    Staff: Mentor

    Protons don't 'vibrate'.

    You may be thinking of the so called wave particle duality.

    However that so called duality is not the way we look at things in modern times:

    The quantum nature of protons however has been experimentally verified many many times.

    There is a fundamental quantum property called the Heisenberg uncertainty principle that says if you know position exactly then its momentum is completely unknown, so yes in your thought experiment an electron, proton or neutron would scoot off elsewhere with an unknown momentum.

  4. Feb 5, 2014 #3
    Antigone, I think you need to rephrase your question. I can't tell if bhobba's interpretation of what you were trying to get at is right or if you are asking about kinetic energy of a proton. I will reply with a few notes.

    1) From part b, photons do not keep going if you try to stop them. I am currently stopping quite a few that are flying at me from my lamp. I am also emitting quite a few. If you mean that the speed of a photon in a vacuum is alway c, then no, protons are not like that. No particle with mass is like that.

    QM is different from Classical Mech. in some ways, but the basic idea that objects can have different energies depending on the environment is the same. The exact way that particles respond is different.

    2) If you hold an electron in your hand (and could somehow measure that it was there) and then checked back a second or so later, it would most likely still be there. Not in the exact same spot, but it is unlikely that it would fly away unless you are near a charged object. The uncertainty principle means that it will probably move, but it isn't likely that it would move too far without a push.
  5. Feb 5, 2014 #4

    First of all I really want to thank you for your answer, because you have understood my question. I am from Sweden, and my English is not the best.

    Now to your answer.

    Yes, you are stopping photons, but these are never motionless. For a while they are in a electron and "slows down", but they dont "stop". Matter can slow photons down, emitt them, reflect them etc. but not stop them. Atleast I Think so. And if a photon is slowed down by matter, as soon as it is free it will soon be moving in the speed of light (if it is moving in vacuum after its interaction with matter).

    Electrons move around the neclues. Nothing is "pushing" it. Yet it moves.

    A neutron, also, moves. From wikipedia: A fast neutron is a free neutron with a kinetic energy level close to 1 MeV (1.6×10−13 J), hence a speed of ~14000 km/s (~ 5% of the speed of light). A free neutron, that is.

    I wonder if a proton also "moves" when it is "free".

    Thank you for your answer
    Last edited: Feb 5, 2014
  6. Feb 5, 2014 #5
    Dear Bill,

    Atoms do vibrate:

    I Think ive Heard that an nucleus vibrates even if it is freezed down. But I am not sure on that one.
  7. Feb 5, 2014 #6


    Staff: Mentor

    The link said:
    The atoms and ions, which are bonded with each other with considerable interatomic forces, are not motionless. Due to the consistent vibrating movements, they are permanently deviating from their equilibrium position. Elastic waves of different lengths, frequencies, and amplitudes run through crystalline solids at all times. The typical order of the atomic vibrations frequencies is 1013 Hz, and that of the amplitudes is 10-11 m.

    That's atoms bonded to other atoms, which was not your query - it was if protons vibrate. They don't - simple as that.

    What you probably heard, and misinterpreted, is again the Heisenberg Uncertainty Pricniple (HUP) or quantum zero point energy which is an effect of Quantum Field Theory (just as an aside it is these fluctuations that are responsible for effects like spontaneous emission). Even when cooled to very low temperatures the nucleus, and the atom in general, cant be still because that would imply its position is known - which the HUP says it will then scoot off elsewhere (in a rough sense). Then there is the energy of the ground state. This is the reason absolute zero is not possible:
    'Absolute zero is the lowest temperature possible. More formally, it is the temperature at which entropy reaches its minimum value, 0. The laws of thermodynamics state that absolute zero cannot be reached using only thermodynamic means, as the temperature of the substance being cooled approaches the temperature of the cooling agent asymptotically. A system at absolute zero still possesses quantum mechanical zero-point energy, the energy of its ground state. The kinetic energy of the ground state cannot be removed.'

  8. Feb 5, 2014 #7


    Staff: Mentor

    Electrons do not move around the nucleus - where you got that idea from I have zero idea.

    They do not have proprieties like momentum or position that can be used to determine if they are moving until they are measured to have those properties - this is the very essence of QM. The reason a fast neutron can be said to move is the one exception to this quantum weirdness - if its in an eigenstate of momentum:

    You do understand that electrons have negative charge and the nucleus is positively charged? If it was like you are thinking the electron would be attracted to the nucleus and spiral into it. The fact it doesn't is what QM is required to explain. The real issue isn't why electrons move - its why they don't. QM's answer is very radical - it doesn't even have the property of movement, position, velocity etc etc until its measured to have it. And if you did measure it all you can predict are probabilities.

    Last edited: Feb 5, 2014
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