I am steadily working my way through D'Inverno and have reached Chapter 20. On page 272 there is a problem which goes along the lines of ... here is a Lagrangian ... show that the Einstein tensor can be derived from it. The Lagrangian in question is a 'quadratic' Lagrangian and has four terms along the lines of h(adsbygoogle = window.adsbygoogle || []).push({}); ^{ab}_{,b}h^{c}_{c,a}, ie four products of h with a variety of subscripts and superscript.

So my question is - where the hell does that come from? What is the physical significance of the terms? Is this a case of someone working backwards from the Einstein tensor to produce the equivalent Lagrangian?

Earlier in the book there was a problem relating to the Eddington Lagrangian, again the question is - What motivates the construction of these objects?

Can anyone shed some light?

TerryW

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# Inventing Lagrangians (D'Inverno)

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