Author's comments: The following article appeared in novembre, 2007 in the popular scientific review, Pour la Science, but in a version slightly revised by the editors and their consultants for expository purposes and with diagrams added. I am sure the revised form is indeed easier for a layman to understand, but some assessments were added that are not mine. Rather than interfere with the editors' difficult task of turning arcane material into something meaningful to their readers, I let the revised version stand. I wished, nevertheless, to make my own version available as well. There are many imaginative diagrams in the version published and I urge the curious reader to look at it if possible. Unfortunately, it does not seem to be available on line.
I am grateful to Claude Levesque for a close, critical reading of the article.