Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Why doesn't the electron fall into the nucleus?

  1. May 1, 2009 #1
    why doesn't the electron fall into the nucleus!?

    yes I know this question must have been asked before right? tried looking for it on here but I couldn't find it. the only answer I have gotten to this was just that particles are quantized... yes yes, fine... but WHY? for instance, why does an electron and a positron collide so readily? but an electron and a proton don't? someone explain please and thanks.

    P.S.

    I have heard an argument that deals with the uncertainty relation but it doesn't make any distinction between a proton and a positron... i don't think... any HELP!?
     
  2. jcsd
  3. May 1, 2009 #2

    ZapperZ

    User Avatar
    Staff Emeritus
    Science Advisor
    Education Advisor
    2016 Award

    Re: why doesn't the electron fall into the nucleus!?

    Please read an entry in the FAQ thread in the General Physics forum.

    Zz.
     
  4. May 1, 2009 #3
    Re: why doesn't the electron fall into the nucleus!?

    The proton itself is not important. The important thing is its charge, that will create an electrical field in which the electron can feel and it must do work to gain its potential energy.
     
  5. May 1, 2009 #4
    Re: why doesn't the electron fall into the nucleus!?

    Thanks ZapperZ... checked it out. Makes sense, but it seems like i could make that same argument with an electron and positron, yet they annihilate quite readily no? Or am I mistaken?
     
  6. May 1, 2009 #5

    jtbell

    User Avatar

    Staff: Mentor

    Re: why doesn't the electron fall into the nucleus!?

    Electrons sometimes do "crash into the nucleus," because an atomic electron's Schrödinger wave function and probability density are generally not zero at the nucleus. In fact, for the lowest energy state (1s), the probability density is maximum at the nucleus! In certain types of nuclei, this causes a decay mode called "electron capture," in which the electron is "converted" to a neutrino, and a proton is converted to a neutron, via the weak interaction.

    But the weak interaction is a lot weaker than the electromagnetic interaction which causes positron-electron annihilation, so it doesn't happen very often, relatively speaking.
     
    Last edited: May 1, 2009
  7. May 2, 2009 #6

    alxm

    User Avatar
    Science Advisor

    Last edited by a moderator: Apr 24, 2017
  8. May 2, 2009 #7
    Re: why doesn't the electron fall into the nucleus!?

    If it makes sense to you, can you explain "why doesn't the electron fall into the nucleus!?" in simple term?
     
    Last edited: May 2, 2009
  9. May 2, 2009 #8

    malawi_glenn

    User Avatar
    Science Advisor
    Homework Helper

    Re: why doesn't the electron fall into the nucleus!?

    what simple terms means is subjective ;-)
     
  10. May 2, 2009 #9
    Re: why doesn't the electron fall into the nucleus!?

    Richard P. Feynman: If you can't explain it to a high school student you probably don't understand it.
     
  11. May 2, 2009 #10

    malawi_glenn

    User Avatar
    Science Advisor
    Homework Helper

    Re: why doesn't the electron fall into the nucleus!?

    here we go again, haven't we told you that it is not applicable? R. Feynman also said "shut up and calculate".

    If I can't explain Baker-Cambell-Hausdroff formula for a high-school student, then I have not understood it? What authority is Feynman when it comes to epistemology??!!

    The language of physics is not intuitive daily language, but math math math...

    The terms "fall into the nucleus" is not even well defined in quantum mechanics, it is not even a stringent mathematical formulated statement.
     
  12. May 2, 2009 #11

    malawi_glenn

    User Avatar
    Science Advisor
    Homework Helper

    Re: why doesn't the electron fall into the nucleus!?

    You have to differ the bound states and interactions in general.

    Electrons and protons will interact if you shoot electrons against proton target (i.e free scattering)

    Electrons and protons will form bound state with a certain probabilty (scattering lenght is negative).

    Same with positrons, there are bound states of electrons and positrons too, with a certain 'lifetime'.

    Everything is clear and free from "paradoxes" if one does the real calculations, now i just stated the results for you.
     
  13. May 2, 2009 #12
    Re: why doesn't the electron fall into the nucleus!?

    Why some annihilation or creation processes occur and others do not? I think the easiest answer: because of conservation laws (momentum, energy, lepton number, baryon number, charge). If they are respected, annihilation or creation processes can happen.

    Positron and electron are antiparticles, so obviously they can annihilate and become an photon.

    I do not know exactly what you get when you crash an electron and proton at very high energies
    (pions), but they will then annihilate. High energy because E=mc².
     
  14. May 2, 2009 #13

    malawi_glenn

    User Avatar
    Science Advisor
    Homework Helper

    Re: why doesn't the electron fall into the nucleus!?

    I just gave the answer, one has to distinguish from scattering and scattering which leads to bound states.
     
  15. May 2, 2009 #14
    Re: why doesn't the electron fall into the nucleus!?

    No one can answer this question correctly.

    Quantum mechanics has given up explainig the motion of electrons clearly, as Pauli and Dirac do since 1920's.
     
  16. May 2, 2009 #15
    Re: why doesn't the electron fall into the nucleus!?

    what are you talking about ever heard of quantum electrodynamics?
     
  17. May 3, 2009 #16

    alxm

    User Avatar
    Science Advisor

    Re: why doesn't the electron fall into the nucleus!?

    What a load of nonsense. Quantum physics does an excellent job of explaining the motion of electrons.
    The proof of that is sitting right in front of you in the form of lasers, semiconductors and other bits of technology that directly followed from quantum theory of atoms, molecules and solids.

    Not to mention providing a theory that reproduced and explained all of chemistry.
     
  18. May 3, 2009 #17
    Re: why doesn't the electron fall into the nucleus!?


    The simple answer is that if the electron stay too far away from the the nucleus, the potential energy will increase, if it stay too close to the nucleus, the kinetic energy will increase. So it will stay where the sum of potential and kinetic energy is minimum.
    Feynman gave his explanation in his famous book, "Feynman lecture on physics", volume 3, section 2-4, <The size of an atom>, He used the argument that deals with uncertainty relation.
     
  19. May 3, 2009 #18
    Re: why doesn't the electron fall into the nucleus!?

    The electron actually has a nonzero probability to be inside the nucleus. When you think of something falling in classical physics, then what you implicitely assume is that when the macroscopic object hits the target (say the ground), it loses energy and then doesn't bounce back up.

    It is this dissipation of energy that doesn't happen in quantum physics for the electron in the ground state. The electron does interact with the nucleus, not only via the Coulomb interaction but also via short range interactions (some QED corrections can be modelled approximately as a Dirac delta potential).
     
  20. May 3, 2009 #19
    Re: why doesn't the electron fall into the nucleus!?

    What happen when the electron is inside the nucleus? Will they stick together or not, due to the attraction of their opposite charges?
     
    Last edited: May 3, 2009
  21. May 3, 2009 #20
    Re: why doesn't the electron fall into the nucleus!?

    "Sticking together" corresponds to electron capture. Then an electron merges with proton, producing a neutron and a neutrino. But if this is energetically not possible such a transition cannot happen. Then the ground state is stable.

    An electron in the ground state should be interpreted as a superposition of the electron being in all possible position (with appropriate amplitudes). These possible positions include the region inside the nucleus.

    So, it isn't like the electron moving into the nucleus from the ground state, rather the electron in the ground state is, in a certain sense, always partially inside the nucleus.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook