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Black Holes and Thermodynamics

  1. Jun 8, 2005 #1

    Simple question.

    When matter falls into a black hole, I guess it leaves our known "Universe", although I think there is not a concrete proof of that.(we simply do not know what happens once matter reaches the singularity).
    Anyway, when matter falls into the black hole is the First Law of Thermodynamics becomes invalid ? :confused:
    Since energy is absorbed by the black hole and not given back , how is the same amount of energy replenished in order to keep the quantity of energy constant in our Universe? :confused:

    Universe is considered a close system as far as I can say.

  2. jcsd
  3. Jun 8, 2005 #2


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    No, the first law:

    And actually, it is anywhere inside the event horizon that we don't know what's going on, not just at the singularity. That is for those who still believe in a singularity as a point-source, which I don't.

    But, as for your question, since matter and energy are the same thing, any matter falling into the BH would increase its mass and, most likely, the angular momentum so nothing is "lost". a mass-to-mass equivalent would be apparent, and any mass-to-energy change would show up in the angular momentum change. There are several other processes to consider but they would still result in conforming with law #1.
  4. Jun 10, 2005 #3


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    Correct, whatever falls into the black hole does not leave the universe*....it increases the mass of the black hole...which increases the gravitational influence of the BH on this universe.

    * athough it is now inaccessible to the universe except as noted above
  5. Jun 14, 2005 #4
    This is a little off topic but what would happen if the object being sucked into the black hole was bigger than the black hole itself. Imagine putting a tennis ball in your bath tub and then unplugging the drain and seeing it being drawn towards the drain until it just clogs it up. Would the black hole find a way to get the supermassive matter into it? You know what replace the tennis ball with a soccer ball then what would happen?
  6. Jun 14, 2005 #5
    When something falls into a black hole , it becoms part of the dense black hole and further increases its strength.

    Certainly not , the object does not leave the universe ,infact black holes are a part of universe , (...I am anti-those-who-believe-black-holes are gateway to -other-universes..) ...Consider a system ,Let the system be the Universe and black holes are part of the system , when an object (which is a part of the universe..) goes into a black hole ( still remains the part of the universe..) ...Everything remains conserved ..nothing is violated...

    Considering black hole not part of the universe is your assumption which leads your own created problems.

    Even if Black holes were a gateway to some other universe , the same object that Black holes sucks in ....will be spitted out by the time-inverse of the black hole ..that is the white-hole. Though the white-hole concept is just mathematical , therefore if other universes exist , white-holes must...Energy which leaves one universe will appear in some other universe ...As a whole system of two universes energy remains conserved.
    Last edited: Jun 14, 2005
  7. Jun 14, 2005 #6


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    Tidal forces pulverize everything that approaches the event horizon.
  8. Jun 17, 2005 #7
    Second Law of Thermodynamics

    So, since we have covered the First Law, What of the Second?

    I'm just curious to see if anyone knows.

    By adding that mass, the Entropy goes down. Second law says that Entropy wants to always go up. How do Black Holes keep from violating the Second Law of Thermodynamics?
  9. Jun 17, 2005 #8


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    It takes a bit of reading, but the following sites cover the subject fairly well:

    http://relativity.livingreviews.org/open?pubNo=lrr-2001-6&page=node7.html [Broken]


    http://arxiv.org/PS_cache/gr-qc/pdf/9912/9912119.pdf (pg.17)

    http://odarragh.astro.utoronto.ca/GR-II_presentations/Jonathan.Hillel.pdf [Broken]
    Last edited by a moderator: May 2, 2017
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