TLDR: The biggest number is 16 digits long
Ask an astronomer and we travel in aeons into the universe and beyond.
Ask a microbiologist and we slip into mystical quarks and preons, the building blocks of everything.
Ask my 5 year old and you get 643.
This is a question everyone can guess, but when you get to the nitty-gritty is surprisingly personal.
Infinity
I’m discounting it, like imaginary numbers, infinity is an alchemy, a symbol, rather than a practicable digit. It could never appear on a tape measure.
Here are the parameters:
1. Every individual digit must count:
It’s awesome that the universe is estimated at 93 billion light years from end to end, but it could be 93.4 or 93.5 and both would be fine. To get within the hair’s breadth of detail the largest number requires would need an application for it to make sense. Travelling from one side of the universe to the other would be great, but…
“You’re really not going to like it”
— Hitchhikers Guide to the Galaxy, Douglas Adams
Even if we felt the need, this a is number we know fluctuates. The size of the universe is useful, but the number of 93 billion light years is to showcase pure awe — a poster child for what big means.
At its best it’s merely a reference point for numbers that are far smaller, rather than something worth knowing to billions of digits of accuracy.
2. The number must have a practical, real-world, application:
There are groups dedicated to determining long numbers for the sake of the number itself. As of writing Pi is known to 62.8 trillion digits.