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Conservation of Energy Question

  1. May 30, 2014 #1
    Okay, so as I understand it, matter and energy can't be created nor destroyed, only converted from one form to another. So the question I have is, does that mean the total amount of energy in the universe is always the same? Presumably it is energy that is driving the accelerated expansion of the universe throughout the course time, so am I right in assuming that this energy will never be consumed no matter how long time goes on for?
  2. jcsd
  3. May 30, 2014 #2


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    Conservation of energy applies to any closed system.
    Now some people seem to have certain understandings of the word "universe" but to me, "universe" is synonymous with "(all of) existence"

    If by "the universe" you mean "existence" then, we can't know that. It may be philosophized, it may be suspected, it may even be theorized, but at the end of the day conservation of energy is derived from various closed systems within a bigger system, so we can't truly know if it applies to "the entire system"

    P.S. I am not a scientist, (maybe in 10 years,) so this is not a "scientific" answer. It's simply my perspective of "conservation of energy"
    (Various perspectives are good to have, as long as you don't think that I'm trying to say that my answer is the truth.)
  4. May 30, 2014 #3


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    The simple answer is that it is not known if energy is conserved on the universal scale, because it is not easy to define the energy associated with the expansion of space and gravitational energy in general relativity. This is probably because our theories just aren't good enough yet.

    Energy is conserved in systems where you can neglect the effects of gravity and space expansion.
  5. May 30, 2014 #4
    I see, thanks. I had an idea in my head of blowing a ping pong ball across a table with a straw. As I blow the ball I am using up oxygen (energy) which will eventually run out and stop the ball rolling, however in order for the supply of oxygen to remain constant enough to keep the ball in motion the ball must give up some of its mass and reintroduce some of that mass back into my lungs. So eventually the ball will deteriorate yet will continue to roll across the table as it gives up part of its own mass to maintain momentum and will accelerate as its reduced size experiences less and less friction. I have no idea how relevant it is to the discussion, but I saw it as a kind of analogy for the expansion of the universe and is what sparked my queries in the first place, as I wasn't sure how energy was being distributed and how it was being conserved over all as it transforms into mass and vice versa.
    Last edited: May 30, 2014
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