That picture is misleading... Especially the counting part. You could go through all the numbers 2^256 across a lifetime if you wanted to with a computer that was fast enough. I think it would have to assume some kind of minimum period between the counts.
I don't believe it has anything to do with the total number of atoms or matter in the world. I'm pretty sure there are more than 2^256 atoms just on earth. Many times more in the universe.
you could easily fill the entire universe with that many atoms the number is almost infinite in size
While 2^256 is unthinkably large, I'm not sure we could "fill" the universe with this many atoms.
Isn't 2^256 about 1.1579E +077 ?
"Universe Today" has the number of atoms in the entire observable universe estimated to be within the range of 10E +078 to 10E +082, this doesn't even include the dark matter mass....
Read more:
http://www.universetoday.com/36302/atoms-in-the-universe/#ixzz2pJVB892V