On this day in 1845, mathematician Georg Cantor was born in St. Petersburg, Russia. In the 1870s and 1880s he founded set theory, which mathematicians use today to analyze the properties of collections of numbers or objects. Considering sets of numbers allowed Cantor to clarify the mind-boggling concept of infinity. He showed that infinity is not just some blanket term for unimaginably huge—you could create infinite sets of different sizes.
