Why can't irreversible process be reversed by infinitesimal steps? Irreversible process is the one in which the system undergoes rapid change from initial state to the final state. 
Now, if I want to reverse the state of the system, why can't be it possible? I know the final state & initial state. Is it compulsory to go through each & every intermediate states during reversal?? Why is it impossible?
 A: Reversible by definition means to back to the original state through exactly reversing your path. So by definition you must go through each and every step.
It is clear why you can't retrace your steps one by one, because there are non! intermediate "states" are not states of equilibrium, because rapid change (faster than the speed of information in the medium) will result in nonlinear effects and turbulence etc..
Now you can go back to the original state given by its thermodynamic variables, through another process (not reverse process), in which by definition entropy must be lost (because it must have increased during the irreversible process). You can arrange for that to happen in your specific subsystem while increasing the entropy of the total as required.
A: If the process was reversible via the exact route taken to provide the current state then the creation of the initial state becomes indeterministic by definition.  This violates the conservation of information, reversibility occurs via a different path, with one path entering and exiting each state of the system in its phase space.
