Two mathematicians have proved that two different infinities are equal in size, settling a long-standing question. Their proof rests on a surprising link between the sizes of infinities and the complexity of mathematical theories. Our own Professor Emeritus, Jerry Keisler, created "Keisler's order" in 1967, which was used to make the connection.

Link: https://www.quantamagazine.org/mathematicians-measure-infinities-find-theyre-equal-20170912