Irreversible phenomena embrace all bodies of the physical world and the entire Universe on the whole, they introduce development to the Universe setting the motion and the pace to time. The latter is flowing just in one direction, from the past to the future, and no physical action can turn it back. Why is such an asymmetry? In this work the relation between entropy and granular spatial structure is established and the cause of the irreversibility of physical processes is thereby settled. The concept of time filled with a new physical meaning.