Mathematical question: procedural generation of a galaxy

Question

I\'m going to make a space/trading/combat game that is completely procedurally generated. But, I know that storing all of the details of the whole galaxy in memory is unfeas

Answer 1

I use the Mersenne Twister. It is PRNG that accepts as its seed array of any length.
For example, I want to generate galaxy on coordinates x=25,y=72. I re-init twister with seeds [25,72].
If I want to generate 1138th planet in this galaxy, I use [25,72,1138].
Country? [25,72,1138,10]
City? [25,72,1138,10,32]
and so on.
With this method you can generate billions of trillions of zillions of objects using just one number (the one before x coordinate, in our case before 25).
There are some projects now that use it.
Noctis: anynowhere.com/
Infiniverse: http://www.infiniverse-game.com/