Surreal numbers are created by adding values between two given preexisting numbers. If you look at 0 and 1, for example, 1 / 2 is in the middle, 1 / 4 is between 0 and 1 / 2 , and so on.

Infinity Plus One, and Other Surreal Numbers With innovative arithmetic, manipulating infinitely large and infinitesimally tiny quantities is as simple as one, two, three. By Polly Shulman. Dec 1, ...

So far, the surreal numbers have not been used in physical theories. But this is typical; new mathematical developments often find applications only years or decades after their discovery.