A number defined by its own exponent
A googol is 10¹⁰⁰: a 1 followed by 100 zeros. A googolplex is 10 raised to the power of a googol, or 10^(10¹⁰⁰). In ordinary decimal notation, that means a 1 followed by 10¹⁰⁰ zeros.
The notation makes the number easy to specify, but it does not make its full decimal expansion manageable. The exponent tells you exactly how many zeros belong there; it is a compact instruction, not a shortcut for producing each digit.
Why the written version runs out of room
The observable universe contains roughly 10⁸⁰ ordinary matter particles—an immense quantity, but still tiny beside the 10¹⁰⁰ digits needed to write a googolplex. Even the wildly unrealistic plan of assigning one particle to every digit would fall short. Turning those digits into paper and ink would require far more material still.
That contrast is what makes the googolplex useful: it separates describing a number from physically writing it out. A short expression can define something whose complete decimal form cannot fit into the universe that contains the expression.
