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I Gravitating particles and entropy

  1. Oct 2, 2016 #1

    Student100

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    <Moderator's note: this is a spin-off from another thread>

    Matter isn't spreading out because of gravitational attractions between matter. If you took a bunch of gravitating particles and sealed them in container, the highest state of entropy is one where all the particles coalesce, which would be counter to the highest state being spread out. If that's what you mean, but I'm not sure I fully understand your argument.

    You still have the opportunity, assuming you don't get banned for spamming this thread in the other forum. You do need solid references when discussing something "basic" when counter to what's currently accepted.
     
    Last edited by a moderator: Oct 2, 2016
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  3. Oct 2, 2016 #2

    DaveC426913

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    I think this is exactly backwards.
     
  4. Oct 2, 2016 #3

    Student100

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    Hrmm, I don't believe so. I02-35-entropy2.jpg

    But, I certainty could be wrong.
     
  5. Oct 2, 2016 #4

    DaveC426913

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    a) shows that a dispersed gas is highest entropy.
     
  6. Oct 2, 2016 #5

    Student100

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    I think you missed the gravitating particles before the quote. =)
     
  7. Oct 2, 2016 #6

    DaveC426913

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    I didn't.
    I think you are reading too much into the graph.

    I see the entropy timeline applying to the top series, but not the bottom series. Without explanatory context, the interpretation is ambiguous (for all I know the bottom series is a personal pet theory of the author's,)

    But I'd be interested in clarifying the intended meaning of the diagram, and then its provenance and veracity.

    Here's a PF thread describing the ultimate increase in entropy.

    https://www.physicsforums.com/threads/can-gravity-decrease-entropy.224800/#post-1875395

    Maybe this should be split off. It's off-topic.
     
  8. Oct 2, 2016 #7

    Student100

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    http://math.ucr.edu/home/baez/entropy.html

    Is a pretty good discussion on the topic. It's a lot more complicated than what I said above or the figure, but as far as I understand it, it's physically sound.

    Edit: I see you already linked to a topic here, that links to the link above as well.
     
  9. Oct 2, 2016 #8

    DaveC426913

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    It seems to suggest the gravity only temporarily and locally reduces entropy (like energy from the sun does for Earth.) but that, ultimately, the entropy of the universe goes up.
     
  10. Oct 2, 2016 #9
    I appreciate this discussion point, however I wasnt referring to entropy of gravitating particles or matter. I was referring to for example, a single particle which somehow contains a large sum of energy without exploding. That its energy should spread out with the intensity of an atomic blast, should it be released from these bounds. That somehow energy from the big bang could somehow be restrained to form a particle in the first instance, but then also to persist for billions of years, longer.... I enjoy these conversations and learn through them, but this thread is going to be locked soon or deleted. So what a grand waste of time this place is
     
  11. Oct 2, 2016 #10
    The tread that spun this off has been closed as well. This place is stifling. This forum is in a battle against entropy, in a bid to keep things tidy tidy. Sterile more like.

    I like you people, but stop talking to me plz. I'm trying to leave
     
  12. Oct 2, 2016 #11

    Student100

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    I think that would be a correct way to look it. The net entropy change due to coalescing gravitating particles is positive, irreversible due to inelastic collisions and the radiation of energy away from the local system, but can be viewed locally as a decrease in entropy since we're ignoring the transfer of information away from the local system.

    In the figure above the particles coalesce into a black hole, in which the entropy would be related to the surface area of the event horizon. If the other set of particles also collapsed and those two black holes merged, the resulting surface area would have to be larger than either of the originals, and entropy would increase. Eventually, they would decay and the system would obtain equilibrium.

    Maybe the easiest way to view this would be to look at the uniformity of the CMB I think. Neglecting gravity, the universe was already basically in the maximum state of entropy. However, with gravity, the gravitational entropy of the system was low.

    It's not the easiest physics concepts to understand, and I don't understand it very well myself. It's also very easy to fall into misconceptions, like I think the other guy who spurred this thread did???? Or that I'm probably doing.

    I'm still going through the previous linked post and the links from @atyy. It's getting late and I should probably try to sleep. Hopefully someone with more knowledge on this sort of thing will reply. o_O
     
  13. Oct 2, 2016 #12
    No, I didnt misconceive. I spoke on such a simple circumstance of entropy, not much room for confusion. Not like that whole black hole event horizon entropy tossed bs
     
  14. Oct 2, 2016 #13

    phinds

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    You keep SAYING that. I didn't realize it was so difficult.
     
  15. Oct 2, 2016 #14

    Vanadium 50

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    And yet you are still here. This is dragging on like a death scene from Bugs Bunny.
     
  16. Oct 2, 2016 #15

    phinds

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    :biggrin:
     
  17. Oct 2, 2016 #16
    Haha still here. I tried to delete my account but apparently can't. Disabled email notifications
     
  18. Oct 2, 2016 #17

    Bystander

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