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Entropy of the universe

  1. Dec 20, 2011 #1
    Hi. This maybe stupid but I cant get my head around this: if at the early stages the universe was mostly radiation and a soup of sub-atomic particles and now it has gases and stars and planets then doesn't that mean that the entropy has decreased when it should be increasing? does this mean that the universe is not an isolated system? :s why doesn't the second law take the forces of nature into account? Please help!
  2. jcsd
  3. Dec 20, 2011 #2
    Given the early universe was homogenious and gravity was important (pre inflation) then the entropy of the early universe would be low. As the universe expands the energy density drops so in an ever expanding universe the energy density drops so low that the universe becomes "non gravitational" and with a uniform heat distribution no work will be possible. The overall entropy of the uiverse is increasing beacuse it expanding is my my understanding. Seeing local gravitional order is simply local order. There are vast swathes of emptyness with uniform heat distribution not forgeting the super massive blackholes at the centre of most if not all galaxies.

    At least this is my understanding.
  4. Dec 21, 2011 #3


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    A clumpy, low-temperature universe has much higher entropy than an extremely smooth, high-temperature universe.

    To put it really simply, gravity throws a lot of what we normally think about with regards to entropy on its head.
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