The name 'googol' was coined in 1938 by Milton Sirotta, the nine-year-old nephew of the mathematician Edward Kasner, when the child was asked by his uncle to come up with a name for a very large number; at the same time, googolplex was suggested for a still larger number. Kasner defined these numbers as follows:

 

   1 googol = 10¹⁰⁰ (i.e. 1 followed by 100 zeros);
   1 googolplex = 10^googol = 10^{10^100} (i.e. 1 followed by a googol number of zeros).

 

A googol is very roughly the number of years thought to be needed for all the black holes in the universe to evaporate by a process known as Hawking radiation. It is much larger than the number of protons and neutrons in the known universe (about 10⁸⁰), but much smaller than the number of protons and neutrons needed to pack every cubic centimeter of the known universe (about 10¹²⁸). The googolplex is the largest number with a proper name of which many people have heard. It is dwarfed, however, by such esoterica as Graham's Number.