In this chapter we will consider in what way the big bang model needs to be modified. Recall from the previous chapter that there are a number of shortcomings with the model, in particular, with the uniformity of the cosmic radiation. Let us reconsider this cosmic radiation further. Its uniform temperature is problematic because the model predicts that the horizon distance grows faster than the separation between two points in space.

Our assumption that the horizon distance grows more rapidly than the expansion of space may not always be correct in the environment of the very early universe. It is quite possible that space itself might have expanded faster than the horizon for a brief interval some time before the decoupling of radiation and matter took place. Suppose, for the moment that this had indeed been the case. How would it affect our conclusions regarding the cosmic radiation?

We could begin with a region of the universe that was much smaller than the horizon. Physical processes could have operated within this region to establish thermal equilibrium, and any temperature differences that might have existed could in principle be eliminated. If this region then grew at a faster rate than did the horizon, it would eventually come to exceed it.

The final result would correspond to Figure 8.3a when we identify the boundary of the initial region with the lines A and B.