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  1. Subscriber joe shmo
    Strange Egg
    24 Nov '10 19:53
    How is it that we know that our universe is an isolated system, such that its energy is a conserved quantity. It seems to me if we encapsulate the boundry of our universe in the control volume surely heat and work have the opportunity to be transferred?
  2. 24 Nov '10 20:18
    Originally posted by joe shmo
    How is it that we know that our universe is an isolated system, such that its energy is a conserved quantity. It seems to me if we encapsulate the boundry of our universe in the control volume surely heat and work have the opportunity to be transferred?
    We don't. But you could argue that if it isn't, then it's not our universe - it plus whatever it transfers energy to/from is.

    Richard
  3. Subscriber joe shmo
    Strange Egg
    24 Nov '10 20:40
    Originally posted by Shallow Blue
    We don't. But you could argue that if it isn't, then it's not our universe - it plus whatever it transfers energy to/from is.

    Richard
    ok, so it leads us nowhere via ad infintum logic.
  4. Standard member sonhouse
    Fast and Curious
    25 Nov '10 02:49
    Originally posted by joe shmo
    ok, so it leads us nowhere via ad infintum logic.
    What about the newer theories that propose our universe budded off a much larger universe and our universe buds off other universes like grapes on a vine? The idea is we are the other side of a black hole in another universe and black holes in ours jump starts new ones.

    In that case, what about the conservation of energy? So matter and energy presumably from our universe crunches down to a black hole and that energy/mass is now lost from the scale of what used to be in our universe. How does that jive with conservation of energy?
  5. 25 Nov '10 04:52
    Does the law of conservation of energy even hold for the universe as a whole? Is there any reason to believe it does?
    Surely if the universe is expanding then potential energy is being continuously created. Does this mean that energy in other forms is being used up?
  6. Standard member sonhouse
    Fast and Curious
    25 Nov '10 08:28 / 1 edit
    Originally posted by twhitehead
    Does the law of conservation of energy even hold for the universe as a whole? Is there any reason to believe it does?
    Surely if the universe is expanding then potential energy is being continuously created. Does this mean that energy in other forms is being used up?
    In the case of black holes, they all eventually 'evaporate', becoming a white hole, thus restoring that particular cycle of energy that 'left' the universe and coming back in in the form of radiation. The only thing is, the tiny ones go fast, microseconds for the real small ones but the big ones, if they don't evaporate till eons after the life of the universe is over, what does that say to the laws of conservation of energy? Could the universe die it's whatever it is death, then the black hole is still there with all its energy intact, what now?
  7. 25 Nov '10 10:20
    Originally posted by sonhouse
    In the case of black holes, they all eventually 'evaporate', becoming a white hole, thus restoring that particular cycle of energy that 'left' the universe and coming back in in the form of radiation. The only thing is, the tiny ones go fast, microseconds for the real small ones but the big ones, if they don't evaporate till eons after the life of the unive ...[text shortened]... ever it is death, then the black hole is still there with all its energy intact, what now?
    I see black holes and the energy contained therein as being part of the universe, regardless of whether or not they can communicate directly with us. After all, we can detect their gravity can we not?
    But your response doesn't answer my question as to whether the universe as a whole has any conservation of energy law.

    Space is expanding, and this creates potential energy. Is there any reason to believe that this potential energy is being balanced by a loss of energy somewhere else?

    If we had a rope between us and one of the galaxies that shows redshift due to the expansion of space, we could potentially use the ropes pull to power something.
    It may seem an insignificant issue now, but in the early seconds of the big bang the energy release must have dominated the energy scene at the time.
  8. Standard member flexmore
    Quack Quack Quack !
    25 Nov '10 10:23 / 3 edits
    Originally posted by twhitehead
    Does the law of conservation of energy even hold for the universe as a whole? Is there any reason to believe it does?
    Surely if the universe is expanding then potential energy is being continuously created. Does this mean that energy in other forms is being used up?
    If the universe is expanding then gravitational potential energy is growing; being "created" ... this energy creation can by supplied by using up numerous other forms of energy.
    This type of energy transfer by depletion of one type to create another type happens everywhere we look, all the time.

    But I somehow think you already knew that .. ?!
  9. 25 Nov '10 12:17
    Originally posted by twhitehead
    I see black holes and the energy contained therein as being part of the universe, regardless of whether or not they can communicate directly with us. After all, we can detect their gravity can we not?
    But your response doesn't answer my question as to whether the universe as a whole has any conservation of energy law.

    Space is expanding, and this cre ...[text shortened]... ly seconds of the big bang the energy release must have dominated the energy scene at the time.
    As the universe is expanding, it is also cooling down.

    As for conservation of 4-momentum (the relativistic version of conservation of energy), it's just an axiom AFAIK and can not really be "proven" to hold for the universe as a whole.
  10. 25 Nov '10 21:52
    Originally posted by joe shmo
    ok, so it leads us nowhere via ad infintum logic.
    Yup. Essentially, the question is meaningless.

    Richard
  11. 26 Nov '10 06:46
    Originally posted by flexmore
    If the universe is expanding then gravitational potential energy is growing; being "created" ... this energy creation can by supplied by using up numerous other forms of energy.
    This type of energy transfer by depletion of one type to create another type happens everywhere we look, all the time.

    But I somehow think you already knew that .. ?!
    I knew that conversion of energy happens all the time, what I don't know is whether or not it is happening with regards to the expansion of space. Is there any reason to believe that it is.

    I read somewhere (after posting earlier) that the expansion of space causes a net loss of energy - something about red-shifted radiation having lower energy.

    My question another way:
    The universe is expanding. Is that expansion caused by internal factors and does the expansion itself use energy or create energy? Is there reason to believe that that creation of loss of energy for the expansion of space perfectly matched to a creation of loss of energy that results as a side effect of that expansion?
  12. 26 Nov '10 06:47
    Originally posted by KazetNagorra
    As the universe is expanding, it is also cooling down.

    As for conservation of 4-momentum (the relativistic version of conservation of energy), it's just an axiom AFAIK and can not really be "proven" to hold for the universe as a whole.
    Do you know whether the expansion of the universe is explainable in relativistic terms?
  13. Standard member black beetle
    Black Beastie
    26 Nov '10 10:54
    Originally posted by twhitehead
    Does the law of conservation of energy even hold for the universe as a whole? Is there any reason to believe it does?
    Surely if the universe is expanding then potential energy is being continuously created. Does this mean that energy in other forms is being used up?
    If we assume that spacetime, matter and energy emerged at t=0, then, if our universe contains more than a critical density of matter and energy, its spacetime is infinitely finite and bounded in a shape analogous to a sphere. Since spacetime does not exist beyond this boundary, the conservation of energy can be suspended so that matter and energy may be created from the curved spacetime alone;

    Needless to add that spacetime, matter and energy in our universe expand into an unknown void which is itself empty of space, dimension, time and matter (needless, but I like it)
  14. Standard member sonhouse
    Fast and Curious
    26 Nov '10 11:03
    Originally posted by black beetle
    If we assume that spacetime, matter and energy emerged at t=0, then, if our universe contains more than a critical density of matter and energy, its spacetime is infinitely finite and bounded in a shape analogous to a sphere. Since spacetime does not exist beyond this boundary, the conservation of energy can be suspended so that matter and energy may be ...[text shortened]... own void which is itself empty of space, dimension, time and matter (needless, but I like it)
    Your fundamental assumptions may be faulty. For instance, you say as a fact that spacetime does not exist outside our universe but that is not a given, only a conjecture. T zero may be only a local clock zero if there are other dimensions and the recent work by Penrose analyzing the CMB seeming to show perhaps a connection to a larger universe inherent in the cosmic microwave background with the supposed concentric circles they found in the data. T zero may be only when OUR universe got jump started and our universe may be expanding in a higher dimensional framework which would allow other universes to pop up 'near' ours in a higher dimensional sense leaving open the concept of a truly infinite 'whole' universe outside our ken.
  15. Standard member black beetle
    Black Beastie
    26 Nov '10 13:39
    Originally posted by sonhouse
    Your fundamental assumptions may be faulty. For instance, you say as a fact that spacetime does not exist outside our universe but that is not a given, only a conjecture. T zero may be only a local clock zero if there are other dimensions and the recent work by Penrose analyzing the CMB seeming to show perhaps a connection to a larger universe inherent in t ...[text shortened]... nsional sense leaving open the concept of a truly infinite 'whole' universe outside our ken.
    Oh son I thought I clarified I just offer an assumption -I wrote: “If we assume blah blah”. Of course these BB fundamental assumptions are neither events, not facts; but I still like the theory