Since a deadly virus appears to be spreading across the globe, I thought it would be useful to explore how this spread is modeled mathematically, and make some predictions about how quickly this can grow.
The simplest model of disease spreading starts by breaking a population up into compartments:
S (Susceptible) I (Infected) R (Removed️) Then, the model describes the flow between these compartments.
NOTE: This version of the model works over short periods and ignores births and natural deaths.
There are some ideas that are obvious to a few mathematicians, scientists and economists, but which are not widely understood or appreciated. One of the big important ones is compound growth.
“Once you start thinking about growth, it’s hard to think about anything else.”
– Robert Lucas, Nobel prize-winning economist
Before launching into an explanation, I want to start with a question: “Would you rather be 1000 times richer today, or become 2% richer each day for a whole year?
The world is changing fast, the last 100 years saw the creation of a global network of airplanes, computers, the internet, nuclear energy, and the discovery, sequencing and editing of the genome. The tendency of politics is to focus on the next election (at least in democracies). The tendency of business is to focus on the next quarter. The engines of our fast-changing modern world tend to focus our attention on the narrow world of right now.