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In this MTW Ex 21.16, MTW refers to box 14.5 in which the Riemann curvature scalar contains a second derivative of the scale factor a for the same Friedmann metric.

Now using the equation suggested by MTW, i.e. eq 21.77, the value of tr(K)^{2}- tr(K^{2}) would be zero since K is multiple of the unit tensor.

This is said, what remains of Eq 21.77 is simply :

-G^{0}_{0}= 1/2R^{0}_{0}

but this would not yield the equation to be proved since we still have a second derivative of a.

I'm confused.

Note: In Landau's section 107 however, the value of the G^{0}_{0}found will give the equation to be proved despite the difference of the values of the curvature tensors.

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# MTW Exercise 21.16

Can you offer guidance or do you also need help?

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