A Causal Source Which Mimics Inflation

How unique are the inflationary predictions for the cosmic microwave anisotropy pattern? In this paper, it is asked whether an arbitrary causal source for perturbations in the standard hot big bang could effectively mimic the predictions of the simplest inflationary models. A surprisingly simple example of a scaling causal source is found to closely reproduce the inflationary predictions. This Letter extends the work of a previous paper N. Turok, Phys. Rev. D 54, 3686 (1996) to a full computation of the anisotropy pattern, including the Sachs-Wolfe integral. I speculate on the possible physics behind such a source.