This collection can be taken as the analog of the bibliographic references of a normal textbook on physics printed on paper. Since we think, that the collection is big enough; it can also be taken as some kind of encyclopedia of physics, but an animated one.

Some topics appear more frequently than other. This could be because these are more important than other. However, one should be careful in assigning great importance only to the topics with the most numerous links.

Actually there are very many values, which cannot be measured at all!