As I said, there must be another part of the analysis that we are missing.

The explanation I gave works for a static shell, but we live in an expanding universe. If the shell is expanding uniformly, and assuming the gravitational force is mediated by gravitons that travel at the speed of light, the nearby part of the shell would be moving away less rapidly that the opposite side, which would lead to the effect described.

David, Burt, Scruffy, or others well-versed in this, am I on the right track here?

Fred Bortz -- Science and technology books for young readers (www.fredbortz.com) and Science book reviews (www.scienceshelf.com)