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(Conservation of ?) Energy

  1. Feb 9, 2009 #1
    Hey there, i have a problem and i'm going to try to explain it

    Well I know that due to gravity, everything with mass (invariant & reletavistic) is attracted / attracts everything else, however my problem is, where does this energy come from?

    I've been told all the time since i've taken science that energy cannot be created or destroyed, only converted from one type to another etcetera, well if you place two large things in a huge vacuum they attract -- and move towards one another, correct?

    Well where does this energy come from? I have a slight idea for some of your answers and i'd like to pose questions in advance of them;

    Perhaps something along the lines of "gravitational potential energy", however, how is this gravitational potential energy transferred from that form into kinetic energy, also, how was that gravitation potential energy put there in the first place, or was it always there? Also, wouldn't this then mean that if i as a person have X amount of gravitational potential energy attracting everything around me, why is this not included in e = mc^2 and other relevant formulas.

    Related to this, i do understand the very very very basics of general relativity, and i think i understand that everything DOES act like this, but where is the energy from? :XX

    To sum up, i don't see where the attraction comes from in terms of energy, as far as i can see, the attraction just creates energy?! Which obviously is wrong!

    Thanks in advance, i have a bad suspicion that the answer will be like, yeah you're right but it's basically 0 :P.
  2. jcsd
  3. Feb 9, 2009 #2
    As you said, it's basically 'potential energy'. Not sure we actually know or understand so much more than that about it, maybe someone more knowledgeable have an idea.

    Speculation on where it came from originally: I suppose it would have to be created during the big bang, since at that stage there was likely no potential gravitational energy since everything was at the same place, yet when the explosion occured everything was pushed outward, charging up the potential energy.

    On a more local scale we create gravitational potential energy by simply lifting objects up from the ground.
  4. Feb 9, 2009 #3
    I understand the latter part of course, however i understand that as you put in kinetic energy lifting it up, which is then converted into GP energy, but as far as two things in a vacuum etc are concerned, i can't really see where the energy is coming from.
  5. Feb 9, 2009 #4
    You seem to be assuming that it requires some expenditure of energy to create an attraction, as if, say, an electron and a proton must exert some effort to be attracted to each other. In fact, though, an electron and proton do not lose or expend anything in being attracted. It is simply a property of those two kinds of particles that they are attracted to each other. That being the case, they do not have to expend any energy to attract each other any more than they have to expend any energy to continue existing. It is more logical to assume that staying apart is the condition that would require some expenditure of energy, and attraction represents them assuming a state of least effort, so to speak.

    By the same logic, the attraction of gravitation, or any attraction, must represent some state of least effort, or path of least resistance, rather than a thing that requires expenditure of energy to maintain.
  6. Feb 10, 2009 #5
    I see what you're driving at, however again i find it a bit difficult to accept and I have a problem;

    If you have a new universe or something similar to that, and you have 1000 suns/relatively large planets/stars in a solar system all separate, i find it very hard to accept that in that state, and after you 'let go' of them and they accelerate towards one another creating huge amount of kinetic energy etc and you take it the moment before impact (say, ideally they all meet at one point in the middle) and compare that to how they were before?

    I sort of see what you're driving at, but is this still true? Because for an example like this, insanely huge amounts of momentum from what I can see to be no direct loss of energy, if you say it's the energy needed to exist, that has not increased at all over the time of the experiment, I guess i'd like to avoid an answer involving the graviton if at all possible.

  7. Feb 10, 2009 #6
    Try this idea. Wherever the universe originally came from, presumably the Big Bang, the universe was left in the "initial condition" where you don't have everything in the same place, piled on top of everything else, but instead you have things being "uphill" from other things, so that they can fall down. The agency that created the universe did the work to put them "up there" -- that's where all the potential energy originally came from. Even since then, for billions of years, things have been in the process of falling back down.
  8. Feb 10, 2009 #7
    That thought did occur to me, and it's a nice anology you gave thanks =P, but would that mean that we have a huge amount of gravitational potential energy aswell that's not counted in e=mc^2 etc?

    edit; maybe it's in the e² formula? if you take our momentum relative to everything else? lol
    Last edited: Feb 10, 2009
  9. Feb 10, 2009 #8

    Assumption in above logic: Energy is associated only with tasks needing resistance. When things attract (or in the process of attaining a state of least resistance) "energy" is not involved.
    This is invalid. When the masses attract each other, the stored potential energy gets converted to kinetic energy. Now zoobyshoe's query stands - where this potential energy comes from. The ans, logically, is due to their relative positions in the space. Ques> how did they assume this position in the space? Ans> By some previous inter conversion of energy to attain to this state. >Continuing like this, we invariably encounter - The BIG BANG: assumed to be the initial imparter of energy to everything when that atom - explodes (assumed to be previously spinning at VERY HIGH speeds). And my logic cannot see beyond - Ultimately boiling down to the single query - Where did that atom ab initio cam in the beginning possessing that much roatational energy (assuming big bang as THE start)
  10. Feb 10, 2009 #9
    Well in turn, wouldn't this gravitational potential energy account for a HUUUUUGE amount of energy in the universe?
  11. Feb 11, 2009 #10
    Shameless bump
  12. Feb 11, 2009 #11
    A little out of my field, but try this: Gravitational attraction is due to the warping of space. Things roll "downhill" toward objects with mass. The mass of the rolling things adds to the steepness of the well sides (warping of space).

    The potential energy of an object changes relative to its position on the well side. The steeper the well side, the greater the potential energy, the greater the acceleration of the object toward the center (bottom) of the well. This is different from, say, gravity on earth. On earth the farther an object is from the center the greater the potential energy.
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