Review of John Moffat's "Reinventing Gravity"

In the second half of the twentieth century, a disparate collection of observations on the galactic scale and beyond: the speed of rotation of stars in the discs of spiral galaxies, the velocities of galaxies in galactic clusters, gravitational lensing of distant objects by foreground galaxy clusters, the apparent acceleration of the expansion of the universe, and the power spectrum of the anisotropies in the cosmic background radiation, have yielded results grossly at variance with the predictions of General Relativity. The only way to make the results fit the theory is to assume that everything we observe in the cosmos makes up less than 5% of its total mass, and that the balance is “dark matter” and “dark energy”, neither of which has yet been observed or detected apart from their imputed gravitational effects. Sound familiar? ...

The author recounts his quest for such a theory, and eventual development of Modified Gravity (MOG), a scalar/tensor/vector field theory which reduces to Einstein's General Relativity when the scalar and vector fields are set to zero.

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The book is fascinating, but in a way unsatisfying. The mathematical essence of the theory is never explained: you'll have to read the author's professional publications to find it. There are no equations, not even in the end notes ...

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However, once the gravitating power of virtual particles inside the vacuum is recognized, it may be that Einstein's gravity need not be reinvented. However, it is too soon to decide which path is the one to take.