Actor, painter, scientist, or food?

As part of Google’s mind-reading efforts, they have been working on finding connections between search targets: ‘Knowledge Graph‘, as they call it. The idea is partly to group ambiguous search results so you can choose the ones you meant, and partly to suggest other searches that you might be interested in.

For example, if you search for ‘bacon’, you could mean the 16th Century natural philosopher, the 20th century painter, the cured pig product, or actor Kevin Bacon. At the moment, I get the food as the main set of results, with Knowledge Graph side boxes suggesting the two Francis Bacons.  Kevin doesn’t show up until much further down the list.   In partial recompense, Google is advertising Knowledge Graph by providing a Bacon Number calculator, as the Herald tells us.

An actor’s Bacon Number gives their network distance from Kevin Bacon, where each link is a movie collaboration.  The same idea was had first by the mathematicians, who calculate Erdős numbers based on research collaborations with Paul Erdős. Both Bacon and Erdős are notable for the great diversity of their collaborations, not just the sheer number, so most actors and mathematicians have surprisingly small network distances from them . My Erdős number is 45(Scott, Rao, Vijayan, Erdős), and I’m not even a mathematician. Barack Obama has a Bacon Number of 2, and acting is not what he’s most famous for.   The existence of people like Erdős or Bacon makes a huge difference to the structure of a network of contacts — without them, the network tends to come apart into disconnected chunks. Worldwide connectedness is interesting for acting or mathematics, but it is more important in infectious diseases, where a few people can make a big difference to epidemic size.  There’s a nice (if somewhat old) description of some of the research on small-world networks in a magazine from the Santa Fe Institute (in the centerfold)

Back to Google again, the Bacon Number calculator is far from perfect, but the point is that, unlike the definitive Oracle of Bacon, Google gets Bacon Numbers as a by-product of a general approach rather than as a special project. Knowledge Graph also has other failures (for example, it persistently gave the wrong photograph for Australian SF author Greg Egan), but it’s another illustration of Google’s original discovery that links between pages, rather than the contents of the pages, tell you what is important.

[update: I hadn’t realised that my Erdős number decreased from 5 to 4 a few months ago]