Illusions of general relativity in Brans–Dicke gravity

Contrary to common belief, the standard tenet of Brans–Dicke theory reducing to general relativity in the ω → ∞ limit is false when the trace of the matter energy–momentum tensor vanishes. The issue is clarified in a new approach using conformal transformations. The otherwise unaccountable limiting behavior of Brans–Dicke gravity is easily understood in terms of the conformal invariance of the theory when the sources of gravity have radiation–like properties. The rigorous computation of the asymptotic behavior of the Brans–Dicke scalar field is straightforward in this new approach. To appear in Phys. Rev. D