what is the smallest unit of a real number to which it is composed of? I searched for relevant questions but my point is different. For example take set of real numbers with usual order then is the immediate successor of one. Firstly, I ask that is there any such number?? If yes then how surprisingly we beleive existence of a number but we cannot see that???

There is always a real number between an two distinct real numbers $a$ and $b$. For example $\frac{a+b}{2}$.
