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Thread: Why does the electron orbit the nucleus?

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    Why does the electron orbit the nucleus?

    I know the short answer is the electromagnetic force, but that of course just begs the question of how the electromagnetic force actually accomplishes this feat. Are electrons and protons in a simple hydrogen atom throwing off a bunch of photons to each other?

    I suppose the same thing could be asked of the sun and earth with respect to gravity.

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    The answer will depend on how deep down the physics rabbit holes you want to go.

    The Bohr model has the electron “orbit” like a planet around the star due to the electric potential, but this isn’t actually a good model.

    The QM model fixed Bohr’s problems by having the electron have a wave function with quantized states within the nucleus’ electronic potential. The word “orbit” doesn’t really make much sense anymore.

    I don’t know too much about quantum field theory so all the virtual particle mediation of forces is a bit beyond my understanding.

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    Quote Originally Posted by Shadowy Man View Post
    The answer will depend on how deep down the physics rabbit holes you want to go.
    That's what tends to happen when you ask why about most anything in physics. It's rabbit holes inside rabbit holes until you either reach your limits, or his the limits of human knowledge.

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    the baby-eater
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    Quote Originally Posted by SLD View Post
    I know the short answer is the electromagnetic force, but that of course just begs the question of how the electromagnetic force actually accomplishes this feat. Are electrons and protons in a simple hydrogen atom throwing off a bunch of photons to each other?

    I suppose the same thing could be asked of the sun and earth with respect to gravity.
    In quantum mechanics, electromagnetic interactions, including the attraction of electrons to photons, is modelled by the ongoing exchange of virtual photons. These are different than real photons in that they don't actually have any energy. Plus, electrons don't orbit the nucleus like a planet orbits a star. Instead, electrons move around the nucleus in an unpredictable manner.

    The motion of the Sun and Earth is best modelled by relativity. Massive objects cause spacetime to curve, and the motion of objects follows that curvature.

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    Quote Originally Posted by bigfield View Post
    Quote Originally Posted by SLD View Post
    I know the short answer is the electromagnetic force, but that of course just begs the question of how the electromagnetic force actually accomplishes this feat. Are electrons and protons in a simple hydrogen atom throwing off a bunch of photons to each other?

    I suppose the same thing could be asked of the sun and earth with respect to gravity.
    In quantum mechanics, electromagnetic interactions, including the attraction of electrons to photons, is modelled by the ongoing exchange of virtual photons. These are different than real photons in that they don't actually have any energy. Plus, electrons don't orbit the nucleus like a planet orbits a star. Instead, electrons move around the nucleus in an unpredictable manner.

    The motion of the Sun and Earth is best modelled by relativity. Massive objects cause spacetime to curve, and the motion of objects follows that curvature.
    The problem is, as Shadow points out, is that each of these explanations are just question begging. And one must delve into the intricacies of QED. Which requires a graduate level education to understand.

    But another question arises as well. How does the electron orbit the nucleus? Not in the sense of the exchange of virtual particles, but what kinds of paths does it actually take, and what determines that path? Orbit is a poor word of course. Obviously it’s random and is the result of quantum fluctuations, but it never just stops in mid space and reverse itself, right? So it’s not 100% random. There are physical limits like conservation of momentum, and other constraints. Are we even able to determine the paths?

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    Quote Originally Posted by SLD View Post
    The problem is, as Shadow points out, is that each of these explanations are just question begging. And one must delve into the intricacies of QED. Which requires a graduate level education to understand.
    Science will never arrive at a complete answer. Every time scientists answer a question, it just provokes another one. Scientists will be delving forever.

    Quote Originally Posted by SLD View Post
    But another question arises as well. How does the electron orbit the nucleus? Not in the sense of the exchange of virtual particles, but what kinds of paths does it actually take, and what determines that path? Orbit is a poor word of course. Obviously it’s random and is the result of quantum fluctuations, but it never just stops in mid space and reverse itself, right? So it’s not 100% random. There are physical limits like conservation of momentum, and other constraints. Are we even able to determine the paths?
    Quantum mechanics says we can't predict either the exact location or momentum of an electron, which means that we can't predict which path an electron follows, let alone figure out what determines that path, or whether it even follows a continuous path in the first place. On top of that, the double slit experiment shows that electrons exhibit wave-like properties, which means that electrons are not simply little specks zipping around outside the nucleus.

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    In QM “path” is not a meaningful word. The electron has a probability distribution. You only know where it could be. To say it follows a path is extra formalism that doesn’t add predictive value to the theory.


    I’ll admit it’s been a while since my last Quantum class, so maybe I’m wrong.

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    As I recall from my college physics courses 35 years ago, the electron orbit was described as a "probability cloud".

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    http://web.physics.ucsb.edu/~phys128...l-AP-8210A.pdf

    An updated version of the oil drop experiment.

    Milikan's apparatus was more primitive and took him years to gather all his data working nights. Not as well known, he was up there wit Einstein and others.

    There were competing theories to explain electric current. His won out.

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    It doesn't.

    Electrons have a higher probability of being found in an area close to their associated atomic nucleus than they do of being found anywhere else; But their probability of being found vastly further away is non-zero. Their exact position cannot be known at the same time as their exact momentum, so any kind of orbital motion is impossible - or at least, impossible to ever observe, which is a distinction best left for philosophers to argue over.

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