The smallest number in the world?

Answer 1

There is no such number. There are two possible interpretations of the question: the smallest number being the most negative or the one with the smallest absolute value.

In the first case, negative numbers, like positive numbers go on forever. One less than the previous smallest will always be smaller.

In the second case, numbers are infinitely dense. So for positive fractions, half of the previous smallest will be smaller still.