*Gravity and Inertia in General Relativity DOI: http://dx.doi.org/10.5772/intechopen.99760*

Carl Brans and his then graduate advisor Robert Dicke created scalar-tensor theory to redress this perceived failing of general relativity. A clear indicator of the importance of the spectator matter argument. The eventual failure of scalar-tensor gravity has left the question of the nature of inertia in a limbo that remains unresolved. Nonetheless, the spectator matter argument still stands as the key issue in the development of general relativity in the past century as it requires that any theory of inertia must satisfy the Equivalence Principle. A test that has not yet been met for any theory of gravity, general relativity included if Brans' argument is accepted as completely correct.
