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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

    Dale

    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

    atyy

    User Avatar
    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:
    http://web.mit.edu/edbert/GR/gr7.pdf
     
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