4 ms·

> In the presence of gravity, systems tend to go towards lower entropy, just see how a planetary system can form out of a gas cloud. This isn't correct: the en

> In the presence of gravity, systems tend to go towards lower entropy, just see how a planetary system can form out of a gas cloud. This isn't correct: the entropy (and energy) of the gas cloud goes decreases as it collapses, but the entropy of its surroundings increases faster as it radiates.

credit_guy 3y ago
Is that a fact? Or just a hypothetical way that could save the second principle?
- consilient 3y ago
  It's a fact. See for instance https://arxiv.org/pdf/0907.0659.pdf https://arxiv.org/pdf/0907.0659.pdf
  - credit_guy 3y ago
    It's more like an opinion. Of one particular guy who has a Ph.D. in Physics. But there are many, and there is no consensus overall. Here's the relevant quote from wikipedia [1] Recent work has cast some doubt on the heat death hypothesis and the applicability of any simple thermodynamic model to the universe in general. Although entropy does increase in the model of an expanding universe, the maximum possible entropy rises much more rapidly, moving the universe further from the heat death with time, not closer. This results in an "entropy gap" pushing the system further away from the posited heat death equilibrium. Other complicating factors, such as the energy density of the vacuum and macroscopic quantum effects, are difficult to reconcile with thermodynamical models, making any predictions of large-scale thermodynamics extremely difficult. [1] https://en.wikipedia.org/wiki/Entropy#Cosmology https://en.wikipedia.org/wiki/Entropy#Cosmology
    - consilient 3y ago
      That's discussing the effects of metric expansion, which are not relevant for gravitationally bound systems. It also doesn't claim the second law of thermodynamics fails. On the contrary, > entropy does increase in the model of an expanding universe
    - kergonath 3y ago
      This is quite different from what you were saying about gravity reducing entropy, though. And I know quite well that having a PhD in Physics does not make someone right, but then quoting Wikipedia in such an argument is really not great.

credit_guy 3y ago

Is that a fact? Or just a hypothetical way that could save the second principle?

consilient 3y ago
It's a fact. See for instance https://arxiv.org/pdf/0907.0659.pdf https://arxiv.org/pdf/0907.0659.pdf
- credit_guy 3y ago
  It's more like an opinion. Of one particular guy who has a Ph.D. in Physics. But there are many, and there is no consensus overall. Here's the relevant quote from wikipedia [1] Recent work has cast some doubt on the heat death hypothesis and the applicability of any simple thermodynamic model to the universe in general. Although entropy does increase in the model of an expanding universe, the maximum possible entropy rises much more rapidly, moving the universe further from the heat death with time, not closer. This results in an "entropy gap" pushing the system further away from the posited heat death equilibrium. Other complicating factors, such as the energy density of the vacuum and macroscopic quantum effects, are difficult to reconcile with thermodynamical models, making any predictions of large-scale thermodynamics extremely difficult. [1] https://en.wikipedia.org/wiki/Entropy#Cosmology https://en.wikipedia.org/wiki/Entropy#Cosmology
  - consilient 3y ago
    That's discussing the effects of metric expansion, which are not relevant for gravitationally bound systems. It also doesn't claim the second law of thermodynamics fails. On the contrary, > entropy does increase in the model of an expanding universe
  - kergonath 3y ago
    This is quite different from what you were saying about gravity reducing entropy, though. And I know quite well that having a PhD in Physics does not make someone right, but then quoting Wikipedia in such an argument is really not great.