One fun thing math lets us do is measure difficult-to-measure things. Like fame.

We all have an instinct for what fame is, and the more we put it into words, the more we’ll find we can translate fully into math. So what let’s us know if someone is famous? Well, famous people are well known. We tend to know them, and they don’t know us. In fact, we could say that people become famous when more people know them than they know.

As soon as we’re dealing with quantities, we have something that’s pretty easy to describe mathematically. Let *U = the number of people you know* and *M = the number of people who know you*. Then we could define the *fame quotient *as *U/M*, the ratio between the number of people who you know and the number of people you know.

Happily, we can get good estimates on these numbers from twitter. I’m not a huge user, with 154 followers and 93 people I’m following. But I can still calculate my fame quotient as 154/93, or about 1.66. That feels about right… I’m not particularly famous.

Let’s try some more famous people.

Obama has 41.3 million followers and 654 thousand he’s following, so his Fame Quotient is 41,300,000/654,000 = ~63

Justin Bieber has 49.4 million followers and 124 thousand he’s following, so his Fame Quotient is 49,400,000/124,000 = ~400

*Who’s more famous: President Obama or Justin Bieber?*

With a fame quotient of close to 400, Bieber is about 6.5 times as famous as the president.

**Here’s the challenge: who is the most famous living person in the world?**

Remember, I’m using our twitter-based version of fame here. It might not match other intuitions or definitions of fame. In fact, we’ll probably have to fix it as we go. But it’s a start.