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So is energy relative?

  1. Sep 17, 2008 #1
    Or is it absolute? Ive heard the conservation of energy on a large scale doesn't hold true. How can this be so?
  2. jcsd
  3. Sep 17, 2008 #2


    Staff: Mentor

    Energy is relative, both in Relativity and in Newtonian mechanics. This means that different reference frames will determine different values for the energy of a given object at a given point in space and time. However, the conservation of energy holds in any reference frame. This means that, in a single reference frame the total energy (KE + PE) will be constant over time.

    This is the difference between the concepts of "invariant" and "conserved". Energy is conserved, but not invariant.
  4. Sep 17, 2008 #3


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    Science Advisor

    In General relativity, for technical reasons, the conserved quantity is called the stress-energy pseudotensor, rather than the stress-energy tensor. This is why you may have heard that energy is not globally conserved. As DaleSpam indicated, the stress-energy pseudotensor is globally conserved, but it is coordinate dependent.

    Edmund Bertshinger's notes:
    Last edited by a moderator: Apr 23, 2017
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