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  1. Standard member sonhouse
    Fast and Curious
    19 Aug '13 11:47
    http://scitechdaily.com/photons-traverse-optical-obstacles-as-both-a-wave-and-particle-simultaneously/
  2. 19 Aug '13 11:56
    Originally posted by sonhouse
    http://scitechdaily.com/photons-traverse-optical-obstacles-as-both-a-wave-and-particle-simultaneously/
    The thing is, photons are neither classical particles, nor classical waves. They show wave-like and particle-like behaviours. It is generally a mistake to take the analogies too far and demand that at some moments they are particles and other moments they are waves or sometimes both as the article suggests -they are, and always will be, neither.

    Waves themselves are generally patterns rather than substance. If you see a wave in a football stadium crowd, is it a wave? Does it appear at one position, propagate, then disappear? Or is it a pattern rather than an entity?
    Similarly, in quantum mechanics, the 'wave' is a pattern of behaviour rather than an entity.
  3. 19 Aug '13 12:38
    Originally posted by twhitehead
    The thing is, photons are neither classical particles, nor classical waves. They show wave-like and particle-like behaviours. It is generally a mistake to take the analogies too far and demand that at some moments they are particles and other moments they are waves or sometimes both as the article suggests -they are, and always will be, neither.

    Waves ...[text shortened]...
    Similarly, in quantum mechanics, the 'wave' is a pattern of behaviour rather than an entity.
    What about the wave function of the electron? I read somewhere that the electron wave function is what keeps them from crashing into the nucleus. I always wondered if this was a credible theory and I am still wondering.

    http://chemed.chem.wisc.edu/chempaths/GenChem-Textbook/The-Wave-Nature-of-the-Electron-559.html

    You would think an electron (-) would be attracted to a proton (+) and crash instead of circle around it. Why does this happen? What is the force that keeps the space between them?
  4. 19 Aug '13 12:50
    Originally posted by Metal Brain
    What about the wave function of the electron? I read somewhere that the electron wave function is what keeps them from crashing into the nucleus. I always wondered if this was a credible theory and I am still wondering.

    http://chemed.chem.wisc.edu/chempaths/GenChem-Textbook/The-Wave-Nature-of-the-Electron-559.html

    You would think an electron (-) wo ...[text shortened]... of circle around it. Why does this happen? What is the force that keeps the space between them?
    All quantum particles have wavelike and particle like behaviour. However they are neither waves, nor classical particles. They are quantum particles, which are something altogether different. You simply cannot try to visualize them as classical particles and expect to get it right.
    I don't know how the electrons behaviour is explained, but I am sure it can only be worked out using quantum dynamics equations.
  5. 19 Aug '13 13:29
    Originally posted by Metal Brain
    What about the wave function of the electron? I read somewhere that the electron wave function is what keeps them from crashing into the nucleus. I always wondered if this was a credible theory and I am still wondering.

    http://chemed.chem.wisc.edu/chempaths/GenChem-Textbook/The-Wave-Nature-of-the-Electron-559.html

    You would think an electron (-) wo ...[text shortened]... of circle around it. Why does this happen? What is the force that keeps the space between them?
    An electron on top of the proton would have extremely high kinetic energy. You can solve the hydrogen atom (one proton + one electron) exactly, and the solution will give you the ground state (lowest energy state) of the electron. Usually when solving for the electron wave function, the proton is assumed to be stationary. The proton does, in fact, move about, but since it is so much heavier than the electron this gives only a minor correction to the electron wavefunction. Since the solution is exact, we are pretty sure about it and it can only be wrong if the underlying assumptions (that is, the axioms of quantum mechanics) are wrong.
  6. Standard member sonhouse
    Fast and Curious
    19 Aug '13 14:25
    Originally posted by KazetNagorra
    An electron on top of the proton would have extremely high kinetic energy. You can solve the hydrogen atom (one proton + one electron) exactly, and the solution will give you the ground state (lowest energy state) of the electron. Usually when solving for the electron wave function, the proton is assumed to be stationary. The proton does, in fact, move ...[text shortened]... nly be wrong if the underlying assumptions (that is, the axioms of quantum mechanics) are wrong.
    Does that mean then that if the electron decided to shift its personality from a wave to a particle it would crash into its parent proton?
  7. 19 Aug '13 16:21
    Originally posted by sonhouse
    Does that mean then that if the electron decided to shift its personality from a wave to a particle it would crash into its parent proton?
    I'm not sure what that question means - an electron can't decide to be a wave or particle, it's always just a "wavefunction." You can scatter electrons away from an atom though (e.g. ionize atoms by using light), I suppose that would be "particle-like" behaviour.
  8. 20 Aug '13 00:09
    Originally posted by KazetNagorra
    An electron on top of the proton would have extremely high kinetic energy. You can solve the hydrogen atom (one proton + one electron) exactly, and the solution will give you the ground state (lowest energy state) of the electron. Usually when solving for the electron wave function, the proton is assumed to be stationary. The proton does, in fact, move ...[text shortened]... nly be wrong if the underlying assumptions (that is, the axioms of quantum mechanics) are wrong.
    But what keeps the electron away from the proton? They are always kept a considerable distance away from each other without touching even though they have opposite charges.
  9. Standard member DeepThought
    Losing the Thread
    20 Aug '13 01:47 / 1 edit
    Originally posted by Metal Brain
    But what keeps the electron away from the proton? They are always kept a considerable distance away from each other without touching even though they have opposite charges.
    Given the Bohr radius is of the order of half an angstrom, how considerable a distance do you think a mile is?

    The 1s orbital has a most probable separation of zero. Elementary particles do not "touch" each other and have separations like classical particles. They have wave-functions which can overlap. This means there is some probability of the electron being inside the proton; to go with this there is an amplitude for the electron and proton to merge and become a neutron - this is a process known as K-shell capture and is observed in some (typically large) nuclei.

    An error in the discussion above is that a proton is not an elementary particle, it's a composite consisting of 3 quarks and some glue. This affects the spectrum of hydrogen so that the most precise measurements of spectral lines of atomic hydrogen are used to calculate the radius of the proton.

    We superimpose classical constructs onto elementary particles to make things understandable but, as Kazet said, these analogies fail if you try to take them too far.
  10. 20 Aug '13 03:04 / 1 edit
    Originally posted by DeepThought
    Given the Bohr radius is of the order of half an angstrom, how considerable a distance do you think a mile is?

    The 1s orbital has a most probable separation of zero. Elementary particles do not "touch" each other and have separations like classical particles. They have wave-functions which can overlap. This means there is some probability of the el ings understandable but, as Kazet said, these analogies fail if you try to take them too far.
    I'm not sure I follow everything you stated. I don't understand all the terms you are using. Could you explain it to me like I am a child?

    Is it the wave function that keeps the electron distant from the nucleus like I think I read in a physics book?
    If an atom is cooled to almost absolute zero will the orbital distance be reduced? I am thinking that would explain why a Bose-Einstein Condensate can fit through solid objects that other liquids can't because the atom is reduced in size. Just a theory.
  11. 20 Aug '13 12:48
    Originally posted by Metal Brain
    But what keeps the electron away from the proton? They are always kept a considerable distance away from each other without touching even though they have opposite charges.
    "Touching" is not so well-defined in this context (as mentioned by DeepThought).

    Like I said, it's the kinetic energy which causes the electron to have a finite wavefunction amplitude "far" from the proton. If it was peaked sharply about the proton, the kinetic energy of the electron would be relatively high. There is a sort of "competition" (as physicists like to describe it) between kinetic energy, which tends to make the electron spread out far over space, and electromagnetic energy, which tends to bring the electron and proton close together. The balance between the two results in the electron wavefunction orbitals as they are. You can see this in terms of the Heisenberg uncertainty principle - if the position is well-defined about some specific position, the velocity is not so well-defined, i.e. you have high kinetic energy.
  12. 20 Aug '13 13:43
    Originally posted by KazetNagorra
    "Touching" is not so well-defined in this context (as mentioned by DeepThought).

    Like I said, it's the kinetic energy which causes the electron to have a finite wavefunction amplitude "far" from the proton. If it was peaked sharply about the proton, the kinetic energy of the electron would be relatively high. There is a sort of "competition" (as phys ...[text shortened]... pecific position, the velocity is not so well-defined, i.e. you have high kinetic energy.
    So the wavefunction does keep the electron away from the proton, right?

    If a helium atom is cooled to nearly absolute zero does the electron slow down to lesson the wavefunction enough to allow for the electron to orbit the nucleus at a closer distance?

    Would that explain why some of the atoms of a Bose-Einstein Condensate of helium can fit through the lattice of a solid cup and leak through? Also, can the different wavefunctions cause some to be pushed about by the cup's solid atoms and flow over the top of the cup overcoming gravity?
  13. 20 Aug '13 15:06 / 1 edit
    Originally posted by Metal Brain
    So the wavefunction does keep the electron away from the proton, right?

    If a helium atom is cooled to nearly absolute zero does the electron slow down to lesson the wavefunction enough to allow for the electron to orbit the nucleus at a closer distance?

    Would that explain why some of the atoms of a Bose-Einstein Condensate of helium can fit throug ...[text shortened]... o be pushed about by the cup's solid atoms and flow over the top of the cup overcoming gravity?
    If you cool down things, the "quantum size" actually becomes larger. This is why you get Bose-Einstein condensation below a certain temperature - the size of the constituent atoms becomes so large they they start to overlap and act as if they were just one giant "matter wave". (helium actually does not form a pure BEC at any temperature, although many alkali atoms do)
  14. Standard member DeepThought
    Losing the Thread
    20 Aug '13 15:33
    Originally posted by Metal Brain
    So the wavefunction does keep the electron away from the proton, right?

    If a helium atom is cooled to nearly absolute zero does the electron slow down to lesson the wavefunction enough to allow for the electron to orbit the nucleus at a closer distance?

    Would that explain why some of the atoms of a Bose-Einstein Condensate of helium can fit throug ...[text shortened]... o be pushed about by the cup's solid atoms and flow over the top of the cup overcoming gravity?
    So the wavefunction does keep the electron away from the proton, right?

    You seem to have a picture of an elementary particle as a composite of two things, a particle and a wave-function to tell the particle where to be. This is known as the Pilot Wave Theory which was invented in the 1920s in an attempt to produce an interpretation of quantum mechanics which retained deterministic outcomes. Within the Pilot Wave view of quantum mechanics, yes the wave function keeps the electron away from the proton. However, there are problems with hidden variable theories as they produce predictions that are distinguishable from quantum theory, De Broglie–Bohm theory, the modern version of pilot waves, is immune to this as it is manifestly non-local. It is regarded as identical to Everett's Many-worlds_interpretation by some people (including me), which renders the DeBroglie-Bohm particle redundant.

    The Copenhagen Interpretation is this horrible piece of logical positivism where the purpose of physics is to predict the results of experiments and not try to understand it. It's essentially the standard interpretation, and with a few exceptions, no one is happy with it. In the Copenhagen interpretation the outcome of a measurement of an observable depends on the wave-function alone. There is only a wave-function and there is no particle. The probability of a position measurement returning a result where the particle is in a small box is the square of the wave-function (*) times the volume of the box. So in the Copenhagen interpretation your question makes no sense, the particle is the wave-function. The electron's wave-function overlaps the proton's, so there is a small probability of an experiment to determine the location of the electron finding it within the proton. The probability of the experiment finding it outside the proton is much higher.

    (*) The algebra of quantum-theory has non-relativistic wave-functions as complex objects so the probability density is the modulus squared of the wave-function.

    If a helium atom is cooled to nearly absolute zero does the electron slow down to lesson the wavefunction enough to allow for the electron to orbit the nucleus at a closer distance?

    It's not normal to assign a temperature to a system that small. For helium in it's ground state the expectation value of the result of an experiment to give the orbital radius of the electrons would give a lower value than the result of an experiment on an excited state of helium.

    A problem I have with quantum theory is that a lot of the experiments used to establish the theory are hypothetical. I know of no experiment which can measure the position of anything that small to that precision. To actually "look" at an electron you have to bounce photons (or some other particle) off them and see what happens to the photon. To get a resolution high enough to detect that the electron was inside the nucleus you'd need to use a gamma ray, so the interaction would probably ionize the atom. So the result of the experiment would be to tell you that the electron was inside the nucleus before we whacked it out of the atom all together.

    Where I've put something in bold it means there is a Wikipedia page with that name.
  15. Standard member RJHinds
    The Near Genius
    20 Aug '13 20:42
    Isn't "photon" just a word made up for the unknown something of which light is believed to consist?

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