Dark energy and entropy

Discussion in 'Physics & Math' started by Magical Realist, May 19, 2023.

  1. exchemist Valued Senior Member

    Messages:
    12,513
    I've described - a bit loosely, I admit - what thermodynamic entropy is, earlier in the thread. It is not about what a given observer can see. It is about the distribution of energy among the microstates of the system. https://en.wikipedia.org/wiki/Microstate_(statistical_mechanics)

    Boltzman's formula for entropy is S=k lnW, in which W is the number of states available.

    The Hawking quotation you give in post 20 (for which you have not given a source - it would be useful if you could do that) is consistent with this.
     
    Last edited: May 22, 2023
  2. Google AdSense Guest Advertisement



    to hide all adverts.
  3. Guestfornow Registered Member

    Messages:
    63
    The Hawking quote says the black hole entropy is: "a measure of the amount of information about the initial state which was lost in the formation of the black hole." So are you saying the distribution of energy among the thermodynamic states is the same entropy?
    The observer is who sees this loss of information, if they see a black hole form.

    So like I say, particles are hidden and so are their states.
     
  4. Google AdSense Guest Advertisement



    to hide all adverts.
  5. exchemist Valued Senior Member

    Messages:
    12,513
    Loss of information is equated with increase in entropy, in Shannon's concept of information entropy.

    The connection between information entropy and thermodynamic entropy is subtle and I do not pretend, as a chemist, to understand it all thoroughly. Hawking no doubt did. If you can post the source of the extract you quoted, it may shed more light on how we should interpret it.

    I have been speaking about thermodynamic entropy, which is what the thread was originally about, since it was related to energy: dS = dQ/T.
     
    DaveC426913 likes this.
  6. Google AdSense Guest Advertisement



    to hide all adverts.
  7. Guestfornow Registered Member

    Messages:
    63
    Here's a link to the article: https://www.mdpi.com/1099-4300/22/1/17
    I can recommend the Wikipedia article on entropy, it lists various kinds of them and discusses the differences between them, or where the apparently different kinds lead to the same results. It also discusses complexity a little, but you might find John Baez a bit easier to understand on the connections between entropy and complexity.

    Also it's important to understand when the ideas are largely theoretical, such as in AdS/CFT or holographic theories. Entropy is a very useful item in theory. The caveat is it's a work in progress and there's a lot that isn't understood yet. Such is physics.

    Which is why, on a personal note, I don't agree that anyone can say they know what something physical is. They can claim to have the answer but on inspection they seem to have some kind of personal preference.
    So someone saying they know what black hole entropy is, is probably wrong. Nobody does yet.

    Steven Hawking was making an educated guess, along with some equations that at face value, appeared to describe something. You may know that the case of Hawking radiation is still waiting for the jury to return.
    Which of course, doesn't stop the theorists.
     
    Last edited: May 22, 2023
  8. DaveC426913 Valued Senior Member

    Messages:
    18,959
    It kind of feels like you are dragging this off-topic. The OP is not about information entropy or various other flavors - that is not what we signed up for. It is about entropy and the thermodynamics of an expanding universe.
     
    Pinball1970 likes this.
  9. Guestfornow Registered Member

    Messages:
    63
    Are you hoping that, if so restricted, the discussion will hasten towards a conclusion?
    That would be great, but don't hold your breath. Ok?
     
  10. exchemist Valued Senior Member

    Messages:
    12,513
    This is not the Hawking article but another one that quotes the passage in question. So it doesn’t do a great deal to help us understand the context of what Hawking was saying. But I note the authors of this article treat Boltzmann entropy and Shannon entropy as effectively the same thing in this context, and they relate it to S=k lnW.

    There is no reference in that formula to observers, and no suggestion that being hidden somehow alters the entropy.

    This thread is not about black holes. If you would like to pursue that subject I suggest you start your own thread in Astronomy and Cosmology. That will also have the advantage that Janus, who is a professional astronomer, may see it if he swings by. He will know far more about this than I do.
     
    Last edited: May 22, 2023
  11. Guestfornow Registered Member

    Messages:
    63
    But the 1976 paper Hawking published is available if you look for it.
    Do you think that's significant? Maybe it's just a coincidence.
    If you hide particles, however you do it, there is loss of information.
    I'm glad for you, that you've been able to partition the universe into one with black holes, and the one you want to consider, without them.

    Carry on then. Don't mind me.
     
  12. exchemist Valued Senior Member

    Messages:
    12,513
    OK but if you hijack this thread I’ll report you, because that is bad behaviour.

    OK?

    Please Register or Log in to view the hidden image!

     
  13. Guestfornow Registered Member

    Messages:
    63
    I feel suitably admonished.
     
  14. DaveC426913 Valued Senior Member

    Messages:
    18,959
    "Hiding particles" is a poorly-defined hand-waving term.
     
  15. DaveC426913 Valued Senior Member

    Messages:
    18,959
    "Restricted"? To addressing the question asked? That's pretty gaslighty.

    The thing to do would be to start a new thread. That way, the title, the opening post, the subsequent discussion and member interest are all aligned.
     
  16. DaveC426913 Valued Senior Member

    Messages:
    18,959
    Yeah. These were the comments that led to my suspicion that GFN was a sock, and why I reported him as such.

     
  17. exchemist Valued Senior Member

    Messages:
    12,513
    Well done. I was trying hard not to allow myself to jump at shadows, but I had suspicions of something familiar at that point. However the black holes schtick made me initially think along the lines of one of those argumentative Indians, The God or someone like that.
     
  18. Pinball1970 Valued Senior Member

    Messages:
    1,035
    Check the maths, what these things actually are. You have not mentioned enthalpy so I am guessing you have a popsci interest?
     
  19. exchemist Valued Senior Member

    Messages:
    12,513
    This was a sock of former member arfa brane, who seems to have gone a bit senile and has a preoccupation with information theory (I think he may have been a communications engineer or something, back in the day). He got banned for abusive language a while back.

    In fact, the connection between Shannon entropy and thermodynamic entropy would be a topic worth discussing, if we had someone who was really au fait with it, which I do not pretend to be.
     
  20. Pinball1970 Valued Senior Member

    Messages:
    1,035
    Unfortunately the OP was based on a complete misconception.
    Scientific words like, Energy especially "Dark energy," Entropy, Entanglement, Infinity, superposition, singularity, strings, virtual particles and Quantum have pervaded modern lingo and popsci has not helped with that.
    You CAN learn some science I think using popsci but not physics or very little.
    Mathematics?
    There is a fantastic little book called "Fermat's last Theorem" by Simon Singh.
    It is the story of a problem and one can get a flavour of the history. Zero insights into the mathematics really.
    Same with "The Poincaré conjecture," an amazing book. The players and deep history from Euclid to Euler, Gauss, Riemann, Poincaré himself and through to Perelman who finally solved it.
    Could a reader even begin to understand differential geometry and topology from a read?
    The concept of "i?"
    I learned the hard way, UG, units in QM (basics) Chemistry as part of a life Sciences course I can learn about deep concepts in maths and physics on my own right? Just go to the library and get some books out.
    What's the issue!
     
  21. DaveC426913 Valued Senior Member

    Messages:
    18,959
    I think I was a spry young lad of 40 when I read that.
     
    Pinball1970 likes this.
  22. exchemist Valued Senior Member

    Messages:
    12,513
    The issue, I think, is that it is hard to learn highly abstract and mathematical subjects from books, on your own. You need to talk to people, ask questions about things you don't understand etc. So it's fair enough to come to a science forum to fill in gaps, or get a few pointers, on an unfamiliar topic. The OP was barking up the wrong tree, but that's fine. Then our friend shows up and tries to wrench the thread onto black holes and information theory. Which is less fine, esp. when he's a sock of a banned individual.
     
    Pinball1970 likes this.

Share This Page