What does the 64 mean in the name Universe64?

Sounds retro, like Commodore 64 or Nintendo 64 doesn't it?

Actually the real reason has to do with the 64-bit size of the universe that is generated for this game. You have 18,446,744,073,709,600,000 places to visit on the X axis, and 18,446,744,073,709,600,000 places to visit on the Y axis.

Think you can make it to the edge of the universe?