> The Einstein field equations are non-linear, so gravitational energy is itself a source of gravity.
Non sequitur? I mean, non-linearity is not the same as feedback. Linear system can exhibit feedback (and still stay linear), and non-linear systems do not have to exhibit feedback.
The equations describing a field theory contain terms which are the product the field, the thing it couples to (could be another field) and the strength of the interaction. When a field couples to itself, there are terms non-linear in the field. So the non-linearity of GR indicates that the gravitational field couples to itself, i.e. that gravity gravitates.
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> The Einstein field equations are non-linear, so gravitational energy is itself a source of gravity.
Non sequitur? I mean, non-linearity is not the same as feedback. Linear system can exhibit feedback (and still stay linear), and non-linear systems do not have to exhibit feedback.
The equations describing a field theory contain terms which are the product the field, the thing it couples to (could be another field) and the strength of the interaction. When a field couples to itself, there are terms non-linear in the field. So the non-linearity of GR indicates that the gravitational field couples to itself, i.e. that gravity gravitates.