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A googolplex is the number 10^{googol}, i.e. 10^{(10100)}, or equivalently, 10^{10100}.
In 1938, Edward Kasner's nineyearold nephew, Milton Sirotta, coined the term googol, which is 10^{100}, then proposed the further term googolplex to be "one, followed by writing zeroes until you get tired". Kasner decided to adopt a more formal definition "because different people get tired at different times and it would never do to have Carnera be a better mathematician than Dr. Einstein, simply because he had more endurance and could write for longer".^{[1]} It thus became standardized to 10^{10100}.
In the PBS science program Cosmos: A Personal Voyage, Episode 9: "The Lives of the Stars", astronomer and television personality Carl Sagan estimated that writing a googolplex in standard form (i.e., "10,000,000,000...") would be physically impossible, since doing so would require more space than is available in the known universe.
A typical book can be printed with 10^{6} zeros (around 400 pages with 50 lines per page and 50 zeros per line). Therefore it requires 10^{94} such books to print all zeros of googolplex.^{[2]}
Writing the number takes too long: if a person can write two digits per second, then writing a googolplex would take around about 1.51×10^{92} years, which is about 1.1×10^{82} times the age of the universe.^{[3]}
In pure mathematics, there are several notational methods for representing large numbers by which the magnitude of a googolplex could be represented, such as tetration, Hyperoperation, Knuth's uparrow notation, SteinhausMoser notation, or Conway chained arrow notation.
One googol is presumed to be greater than the number of hydrogen atoms in the observable universe, which has been variously estimated to be between 10^{79} and 10^{81}.^{[4]} Thus in the physical world it is difficult to give examples of numbers that compare to the vastly greater googolplex. However, in analyzing quantum states and black holes, physicist Don Page writes that "determining experimentally whether or not information is lost down black holes of solar mass ... would require more than 10^{1076.96} measurements to give a rough determination of the final density matrix after a black hole evaporates".^{[5]} And the end of the Universe via Big Freeze without proton decay is expected to be around 10^{1075} years into the future.
In a separate article, Page shows that the number of states in a black hole with a mass roughly equivalent to the Andromeda Galaxy is in the range of a googolplex.^{[3]}
