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Gravitational mass vs inertial mass

  1. Oct 3, 2009 #1
    In Sean Carroll's lecture book is written:

    "... if gravitation did not couple to itself, a "gravitation atom" (two particles bounded by their mutual gravitational attraction) would have a different intertial mass (due to negative binding energy) than gravitational mass..."

    Would you please clarify why? or which mass would be bigger ?
  2. jcsd
  3. Oct 3, 2009 #2
    "Without self-coupling", the gravitational mass of the whole would be only the sum of the gravitational masses of the components (which is exactly how charge works in electrodynamics). However, it is obvious (since it would take work to overcome the gravitational binding) that the energy of the whole is not just the sum of the quantities of energy that the components possess separately. Could it be that you're asking why inertial mass is identified with energy?
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