As always, Wikipedia has the answer. It's worth sharing.
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 numerals (i.e., "10,000,000,000...") would be physically impossible, since doing so would require more space than the known universe occupies ... Therefore a googolplex can not be written out since a googol of '0' can not fit into the observable universe.
The time it would take to write such a number also renders the task implausible: if a person can write two digits per second, it would take around 1.1 × 1082 times the age of the universe (which is about 1.37 × 1010 years) to write a googolplex.
The more you know.