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The Metric As The Field

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Posted by pmb on February 24, 2000 13:12:00 UTC

One has to be careful when using the term "mass" when speaking about light. The gravitational field created by light is (while more complicated than a particle) produces twice the acceleration on particles that would normally be expected from m = E/c2. Light, when acting as a source of gravity, is said to posses an active gravitational mass (i.e. the mass that acts like the source of gravity). When light is responding to gravity then that property is called the passive gravitational mass.

The statement In GR mass almost always means the m in : m2c2 = gmnPmPn. is incorrect. If the mass refers to the source and is not otherwise qualified then they mean mass-energy (i.e. integral of T00) [See the definition for "M" in MTW page 452 Eq. 19.14]. If the mass refers to the mass of an object moving in the field then they mean rest mass (however they usually quality it at least once).

re = Otherwise for extended bodies, "system mass" is useless. - Not if it's the source of gravity. - MTW page 452.

re - If we restrict ourselves to using ordinary three component vectors in a SR revision of Newtonian mechanics it turns out the equation F = ma doesn't hold true anymore. ---


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