The number of ways you can arrange 100 books on a shelf is also astronomical! Think of it, you can choose from 100 different books for the first place, then each of these choices has 99 different books for the second place, and 98 different books for each of the above choices for the third place... and so on. The answer would 100*99*98*97*...*2*1 = 100! different ways to arrange the books. 100! is an immense number, roughly 10^158, or 1 with 158 zeros after it. Just think of how absurdly large that number is, you'd have to count to 10^157 ten times to get that number. You'd have to count to 10^156 100 times... etc etc.... If you counted to a trillion a trillion times, and did that a trillion more times, and did that a trillion more times, a trillion more times, a trillion more times, a trillion more times, a trillion more times, a trillion more times, a trillion more times, a trillion more times, a trillion more times, a trillion more times you'd finally count to 10^158. <br /><br />That number actually is larger than the estimated number of atoms in the universe, and not just by a little. Space is incredibly empty, on the large scale averaging over stars and planets and so on, there are only about 2 atoms for every 10 million cubic centimeters of space. The observable universe is contains about 3 * 10^86 cubic centimeters of space (note that's an stupendously enormous number, but actually 10^72 times smaller than the number of ways to arrange 100 books on a shelf - rediculous huh?). So if you multiply the density by the volume, you get about 10^80 atoms in the universe (see for example
http://en.wikipedia.org/wiki/Observable_universe ). That's huge: 100 million trillion trillion trillion trillion trillion trillion atoms... but it's a million trillion trilllion trillion trillion trillion trillion times smaller than the number of ways to arrange 100 books on a shelf. <div class="Discussion_UserSignature"> </div>