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Thread: molucular motion at absolute zero

  1. #1 molucular motion at absolute zero 
    Forum Sophomore keeseguy's Avatar
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    I did some looking into my inquiry, and had no luck. As things cool, particularly closer to absolute zero, what happens? I remember learning molecular motion slows, do the electrons in the shells reduce in speed? Or is it just a vibration thing?
    Also, super conductance, is (from my understanding) dependent on cold temperatures, is this correct? Does it perhaps have to do with the slowed motion of electrons? I am looking forward to learning the physics of this.


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  3. #2  
    Bullshit Intolerant PhDemon's Avatar
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    It is vibrational/translational motion that slows (but can never stop - google uncertainty principle). Electrons are not classical particles in atoms and don't have a speed as such, they are described by a wave function the allowed solutions of which gives the probability that they will be found in a particular region of space and have a particular energy (these solutions are atomic/molecular orbitals). At low temperatures they will always be in the atoms/molecules ground state (not the same as zero energy look up zero point energy). It may help you to think about absolute zero in terms of entropy (google third law of thermodynamics). As for superconductivity not my area I'll leave that for someone else...


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  4. #3  
    Forum Sophomore keeseguy's Avatar
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    thanks Demon
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  5. #4  
    Forum Junior AndresKiani's Avatar
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    Absolute zero or near absolute zero the energy that an atom has is so low that the atomic vibration slows down to a point that matter breaks down theoretically. The electron cloud around the atom will not have enough energy to keep up its electromagnetic field therefore matter "theoretically" would fall apart as atoms will crash into atoms. Because, remember atoms are 99.9% open space, without the electromagnetic field it would fall apart.

    I'm not sure if we could actually get to absolute zero, I think its just in theory. Entropy, I believe prevents this from occurring, because organization of matter leads to further chaos in the universe (randomness). That which I think will prevent absolute zero, unless, as physicists describe it, dark matter/energy pulling the universe so far apart (this coincides with the fact that the Universe is accelerating farther and farther apart) in the future that everything will freeze. All matter will be so far apart from each other that eventually we will get to absolute zero and then all matter will "theoretically" crumple.
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  6. #5  
    Bullshit Intolerant PhDemon's Avatar
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    Where did you get this from? It's utter nonsense.
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  7. #6  
    Forum Junior AndresKiani's Avatar
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    Wow I suck, ok I'm not going to make assumptions anymore just going to sit listen and ask questions lol.

    I thought this is what I learned...
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  8. #7  
    exchemist
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    Quote Originally Posted by AndresKiani View Post
    Wow I suck, ok I'm not going to make assumptions anymore just going to sit listen and ask questions lol.

    I thought this is what I learned...
    You seem to have got a bit mixed up. It happens to us all.

    At absolute zero there is no more extractable thermal energy (=heat) in matter. Thermal energy is present in the kinetic energy of the various modes of vibration, rotation and translation (movement from place to place) in atoms and molecules. As PhDemon says, this does not mean these motions completely stop at absolute zero, due to what is called "zero point energy", which is a non-extractable residue of motion that arises due to QM effects. But they very nearly do.

    The "motion" of electrons in atoms is something else entirely and does not contribute to thermal energy. Electrons in atoms have energy of course (a mixture of electrostatic potential energy and kinetic energy), but this is not thermal energy and is intrinsic to the orbital they occupy. It is better to think of it as a different class of energy, "electronic energy", if you like. This is not affected at all by the temperature of matter.

    We can approach absolute zero asymptotically, but since getting to it exactly would rely on extracting all the extractable heat, we cannot quite get there. As mathematicians say, we can get "as close as we like" to it, if we try hard enough.
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  9. #8  
    Bullshit Intolerant PhDemon's Avatar
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    Wow I suck, ok I'm not going to make assumptions anymore just going to sit listen and ask questions lol.

    I thought this is what I learned...
    OK, we all make mistakes and no one knows everything but some people come here to learn. If someone asks a question unless you are really sure of your knowledge check your facts before answering (a lot of the errors in your post could have been corrected with 5 mins of research). It does no one any favours for people to post nonsense with confidence (neither the poster, the members who get frustrated by it or casual readers here to learn about science).
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  10. #9  
    Forum Junior AndresKiani's Avatar
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    Well, has their actually been experimental tests on matter at absolute zero? I thought we couldn't actually get to absolute zero. I honestly thought that the electro potential energy would be affected by lower temp. to absolute zero. But it makes sense that it wouldn't, because chemical bonds do not break at extremely lower temperatures, instead atoms stop moving passed each other, because there is not enough thermodynamic energy to break the intermolecular bonds. This is the case with molecules that have even the weakest intermolecular bonds like gases at room temperature.

    Am I wrong? If I am just let me know, I'm here to learn. I'm not confident in my thinking anymore lol.
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  11. #10  
    Bullshit Intolerant PhDemon's Avatar
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    Read post #2 again and google the terms I suggested, this should answer your questions, if you still have questions after that let us know.
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  12. #11  
    Brassica oleracea Strange's Avatar
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    Quote Originally Posted by keeseguy View Post
    Also, super conductance, is (from my understanding) dependent on cold temperatures, is this correct? Does it perhaps have to do with the slowed motion of electrons? I am looking forward to learning the physics of this.
    Most superconducting materials only become superconductors at very low temperature.(Note that not all metals become superconducting when cooled.) It was first observed at temperatures of a few degrees above 0. Then "high temperature" superconductors were discovered - in this context, "high temperature" means above the temperature of liquid nitrogen (about 77K). Since then, various materials have been found which are superconducting at much higher temperatures (over 100K).

    The mechanism is something to do with electrons forming pairs, which act as bosons. But it is way over my head. (John Bardeen, who was one of the people to come up with the explanation, is the only person to have two Nobel Prizes in physics. So I don't feel too bad about not being able to understand it!)
    ei incumbit probatio qui dicit, non qui negat
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  13. #12  
    AI's Have More Fun Bad Robot's Avatar
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    Quote Originally Posted by exchemist View Post
    Quote Originally Posted by AndresKiani View Post
    Wow I suck, ok I'm not going to make assumptions anymore just going to sit listen and ask questions lol.

    I thought this is what I learned...
    You seem to have got a bit mixed up. It happens to us all.

    At absolute zero there is no more extractable thermal energy (=heat) in matter. Thermal energy is present in the kinetic energy of the various modes of vibration, rotation and translation (movement from place to place) in atoms and molecules. As PhDemon says, this does not mean these motions completely stop at absolute zero, due to what is called "zero point energy", which is a non-extractable residue of motion that arises due to QM effects. But they very nearly do.

    The "motion" of electrons in atoms is something else entirely and does not contribute to thermal energy. Electrons in atoms have energy of course (a mixture of electrostatic potential energy and kinetic energy), but this is not thermal energy and is intrinsic to the orbital they occupy. It is better to think of it as a different class of energy, "electronic energy", if you like. This is not affected at all by the temperature of matter.

    We can approach absolute zero asymptotically, but since getting to it exactly would rely on extracting all the extractable heat, we cannot quite get there. As mathematicians say, we can get "as close as we like" to it, if we try hard enough.
    The link below is pretty close to what you just said.

    Absolute Zero
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  14. #13  
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    Quote Originally Posted by AndresKiani View Post
    Well, has their actually been experimental tests on matter at absolute zero? I thought we couldn't actually get to absolute zero. I honestly thought that the electro potential energy would be affected by lower temp. to absolute zero. But it makes sense that it wouldn't, because chemical bonds do not break at extremely lower temperatures, instead atoms stop moving passed each other, because there is not enough thermodynamic energy to break the intermolecular bonds. This is the case with molecules that have even the weakest intermolecular bonds like gases at room temperature.

    Am I wrong? If I am just let me know, I'm here to learn. I'm not confident in my thinking anymore lol.
    Andres, in my reply to you I explained we can get very close indeed to absolute zero, but not quite there, for the purely practical reason that getting out the last bit of heat gets harder and harder as you approach it. There is no mystery about that and nothing dramatic happens.

    You are now on the right track to realise that chemical bonds stay intact at absolute zero, due to the continued motion of electrons in molecular orbitals. And indeed yes, as you get closer to absolute zero, even very weak intermolecular attractions (due to electrons in motion) can no longer be overcome by the feeble amount of kinetic energy remaining in the atoms or molecules, forcing them into the solid state.

    The lowest amount of energy an electron in an atom or molecule can have is the amount it has in what is called its "ground state". The ground state is the bottom rung of its energy ladder and there is nothing you can do can get it lower. This is in fact one type of "zero point energy", which is the quantum mechanical concept that any quantised system has a bottom energy state which in general is one at which some energy remains in the system.
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  15. #14  
    Brassica oleracea Strange's Avatar
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    Quote Originally Posted by exchemist View Post
    The ground state is the bottom rung of its energy ladder and there is nothing you can do can get it lower. This is in fact one type of "zero point energy", which is the quantum mechanical concept that any quantised system has a bottom energy state which in general is one at which some energy remains in the system.
    Someone pointed out that this is an inevitable consequence of uncertainty. At any given energy level there must be some variation above and below that. As you approach zero, the opportunity for varying below vanishes which means the average energy must always be greater than zero. (Their explanation was a bit more technical, with talk of expectation values, and such, but I think that was the gist of it!)
    ei incumbit probatio qui dicit, non qui negat
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  16. #15  
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    Quote Originally Posted by Strange View Post
    Quote Originally Posted by exchemist View Post
    The ground state is the bottom rung of its energy ladder and there is nothing you can do can get it lower. This is in fact one type of "zero point energy", which is the quantum mechanical concept that any quantised system has a bottom energy state which in general is one at which some energy remains in the system.
    Someone pointed out that this is an inevitable consequence of uncertainty. At any given energy level there must be some variation above and below that. As you approach zero, the opportunity for varying below vanishes which means the average energy must always be greater than zero. (Their explanation was a bit more technical, with talk of expectation values, and such, but I think that was the gist of it!)
    Yes, PhDemon referred to this as well. I decided not to go there, as I've always found the energy.time version of the Uncertainty Principle a bit tricky to get right. As I understand it, the uncertainty in time relates to lifetime of states - hence uncertainty broadening in spectroscopy - so I've never been totally clear about what this really implies for stable states.

    On the other hand, the QM idea of a lowest-energy "fundamental" mode of resonance, for the wave associated with any system involving a constrained particle, seems (to me) easier.

    But if anyone cares to develop how to apply ΔE.Δt >hbar/2 to stable states to account for zero point energy, I'd be interested.
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  17. #16  
    Forum Junior AndresKiani's Avatar
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    I hate that formula, I tried to skip it as much possible.
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  18. #17  
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    Quote Originally Posted by AndresKiani View Post
    I hate that formula, I tried to skip it as much possible.
    I think you should try to learn to love it, though, at any rate the momentum and position version.

    The explanation of that in terms of Fourier series superposition of wavelengths was a real eye-opener for me in my understanding of how the QM world works. Wiki has a nice animation of this, actually: Uncertainty principle - Wikipedia, the free encyclopedia

    I also prefer the term I gather Heisenberg used for it, which is the principle of indeterminacy. That seems to me to convey the real significance of it, in that these two properties are not simultaneously defined, even, i.e. it is not just a matter of simultaneous measurement, it is a matter of existence, i.e. of reality itself. It is quite deep.
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  19. #18  
    Forum Junior AndresKiani's Avatar
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    Quote Originally Posted by exchemist View Post
    Quote Originally Posted by AndresKiani View Post
    Well, has their actually been experimental tests on matter at absolute zero? I thought we couldn't actually get to absolute zero. I honestly thought that the electro potential energy would be affected by lower temp. to absolute zero. But it makes sense that it wouldn't, because chemical bonds do not break at extremely lower temperatures, instead atoms stop moving passed each other, because there is not enough thermodynamic energy to break the intermolecular bonds. This is the case with molecules that have even the weakest intermolecular bonds like gases at room temperature.

    Am I wrong? If I am just let me know, I'm here to learn. I'm not confident in my thinking anymore lol.
    Andres, in my reply to you I explained we can get very close indeed to absolute zero, but not quite there, for the purely practical reason that getting out the last bit of heat gets harder and harder as you approach it. There is no mystery about that and nothing dramatic happens.

    You are now on the right track to realise that chemical bonds stay intact at absolute zero, due to the continued motion of electrons in molecular orbitals. And indeed yes, as you get closer to absolute zero, even very weak intermolecular attractions (due to electrons in motion) can no longer be overcome by the feeble amount of kinetic energy remaining in the atoms or molecules, forcing them into the solid state.

    The lowest amount of energy an electron in an atom or molecule can have is the amount it has in what is called its "ground state". The ground state is the bottom rung of its energy ladder and there is nothing you can do can get it lower. This is in fact one type of "zero point energy", which is the quantum mechanical concept that any quantised system has a bottom energy state which in general is one at which some energy remains in the system.
    Ah, that makes a lot of sense, just put everything into place for me thank you.
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