Right now we’ve had more than 5,000 cases of Ebola and at least 2,600 people have died.

Some scientists, like Alessandro Vespignani at Northeastern University in Boston, are taking numbers like that and putting them into computer models to see where this epidemic is going.

“You know, for instance, in our modeling, by mid-October, we’re already between 10,000 to 25,000 cases,” he says.

Five thousand cases of Ebola is bad; 10,000 to 25,000 is crazy. And that’s where the exponential curve comes into play.

“Well, an exponential curve is a curve that doubles every certain amount of time,” Vespignani says. And with outbreak, cases are doubling every three to four weeks.