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A Is total Gravitational force quantifiable?

  1. Oct 25, 2017 #1
    I am sure this question includes multiple mistakes, so please bear with me.

    Gravity is force that is capable of doing work (moving objects over a distance). So under some circumstances, force of gravity is a form of energy or potential energy. How much gravitational energy/potential energy exists in the known universe?

    Is the total gravitational energy/potential energy simply a function of the total mass of the universe, or does it depend on the distances between objects?

    How does gravitational energy/potential energy compare to the quantity of other forms of energy (EM radiation, heat, any others?) in the known universe?

    Thanks in advance. Any links or pointers to books/articles would be appreciated.
     
  2. jcsd
  3. Oct 25, 2017 #2
    The potential energy occurs when there is an object that can drop through the gravitational field - so it depends on distances.
    I suppose the amount of this potential energy in the universe would be what you would release if everything merged into a single massive black hole.
    But there are all sorts of problems in determining exactly what that would mean. For one thing, any energy released during that merge process would add mass back into the universe in the form of EM and gravity waves. Would that mean that you had failed to tap all of the potential energy?
     
  4. Oct 26, 2017 #3
    Energy is a very subtle subject in gravitational physics, at least if you consider General Relativity. For example, you can only define a Hamiltonian in the ADM-formalism, i.e. in spacetimes which can be foliated into spacelike hypersurfaces, which is not always true, but e.g. stationary spacetimes provide an example. Unfortunately, the usual cosmological spacetimes violate some asymptotic boundary condition, which in addition is needed to define a conserved energy. Hence, gravitational energy cannot be defined properly in cosmology.

    Take a look at this post at stackexchange: https://physics.stackexchange.com/questions/2838/total-energy-of-the-universe
     
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