### This Week’s Finds in Mathematical Physics (Week 290)

#### Posted by John Baez

In week290 of This Week’s Finds, ponder the number of seconds in a week — and the number of inches in a mile. Read about categorification in analysis. Learn more about analogies between different kinds of physical systems, and meet the five most popular 1-ports: resistances, capacitances, inertances, effort sources and flow sources. And take stock of where we stand in our tour of rational homotopy theory!

Posted at January 16, 2010 2:14 AM UTC
## Re: This Week’s Finds in Mathematical Physics (Week 290)

“A careful study of where these numbers came from would lead us down some very tangled paths, just like the question why there are 63360 inches in a mile.”

Wasn’t Grothendieck said to be obsessed with this question at some point? (“What is the definition of a meter?”)