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Does gravity gravitate?

  1. Jan 1, 2008 #1
  2. jcsd
  3. Jan 1, 2008 #2
    Hi zankaon,

    Gravity most definitely is believed to gravitate. All forms of mass and energy (with the possible exception of the kinetic energy of movement) are believed to gravitate, regardless of whether they have a zero rest mass. This includes gravity itself, photons, and the strong and weak nuclear forces.

    When a very large star (say, more than 20 solar masses) runs low on fuel to sustain its fusion, its internal pressure drops and it begins to collapse on itself. This causes density to increase, which increases the internal gravitational field, and so on; the process becomes self-reinforcing until the star collapses to a black hole singularity. "Remarkably, as one approaches the singularity, it is this gravitation of gravity, rather than the gravitation of matter, that is the most important effect - or, as it is sometimes said, near a singularity matter doesn't matter."

    The quotation is from the Einstein Online article on Singularities . I recommend that article and two others on Einstein Online for an introduction to this fascinating topic: Gravity of Gravity, and Binding Energy. These articles also explain the nonintuitive concept of "mass defect".

  4. Jan 2, 2008 #3
    Do gravity waves gravitate?

    Do gravity waves gravitate? Yes. In the vicinity of compact object binary, such as for binary double neutron stars, or a double Black Holes, both in tight orbits, gravity waves would be generated. Even though the energy of g.w.s can't be localized, still an average energy can be derived. Such energy would contribute to stress-energy- momentum tensor on the right, and hence to curvature on the left in Einstein eq. http://http://en.wikipedia.org/wiki/Gravitational_radiation
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