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Where does the GPE go?

  1. Nov 10, 2011 #1
    A strange thought has occurred to me this morning. Each piece of matter has a huge amount of gravitional potential energy stored in the universe. My thought is that during nuclear reactions the large amounts of energy that are released would be tiny compared to the loss of gravitational potential out there. Where does the energy go? I've done a little reading and from what I can gather the changes in mass aren't exactly 'real' in the regular sense. I find this concept a little hard to grasp though. So I guess the question is during a nuclear reaction does the change in mass affect the gravitational force exerted by the matter?
  2. jcsd
  3. Nov 10, 2011 #2


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    Staff: Mentor

    Yes. As the sun loses energy through radiation and solar wind, it's mass and gravitational force is reduced. But this is only because the energy is being transfered from the sun to somewhere else. Energy is neither created nor destroyed anywhere.
  4. Nov 10, 2011 #3


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    Staff Emeritus
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    Hey Juiced101,

    Gravity is actually the weakest of the four forces in Nature. Consider the Sun -- it has enormous mass and suffers enormous forces that should make it collapse, but it does not. The energy liberated in the nuclear reactions in its core is sufficient to push the material outwards, balancing the inwards pull of gravity.

    Nuclear reactions really do change the masses of the particles involved. When the Sun combines hydrogen nuclei into a helium nucleus, the helium nucleus weighs less than the sum of its parts. The "missing" mass is turned into energy, mostly in the form of high-energy photons.

    - Warren
  5. Nov 13, 2011 #4
    Thanks warren for clarifying the loss of mass. What I'm asking is if the energy that these high energy photons contain has the equivalent gravitational force that the hydrogen had before fission. If the photons don't have a gravitational force where does the gravitational potential energy that the portion of mass that the hydrogen atoms had go?

    If it isn't clear what I'm asking say imagine a tennis ball made of radioactive material a meter off the surface of the earth. If this decays and releases energy it has a lower mass than before and thus has lower gravitational potential energy. Where does that gravitational potential energy go? Do the high energy photons have a gravitational force?

    Regards, Jason
  6. Nov 14, 2011 #5


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