David,

You caught my inadvertent slip, and it is now repaired. I also edited the piece to use blockquotes, which I had removed during the first go round, when I saw they were working again.

Anonymous, I think you're onto something. But how could Science News and Physical Review Letters have missed that? There must be something else. I'll have to look into it.

For those who are not tuned into such things, if the spherical shell is truly uniform, the net gravitational field at all points inside is zero. If you don't think things through, it is easy to jump to the incorrect conclusion that a test mass will be attracted gravitationally to the closest point on the shell. But if you draw a pair of lines through that point and rotate them to scribe out circles on the spherical shell, there is more mass within the opposite side circle than within the near side circle. Given the inverse square nature of the force, you find that the masses opposite each other differ by the same factor as the inverse square of their distances from the point in question. Hence, no net gravitational pull.

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

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