Eh , I ' d rather be able to interact with everyone I see rather than having to guess who has dialogue and who doesn ' t . <| sep |> Thank you for your reply . I have a different interpretation of this statement . From what I understood , heat transfer occurs when there is a temperature difference , and the heat is transferred from high temp medium to low temp medium until the systemsuppose a two body system is at thermal equilibrium . When temp difference dT is infinitesimally small , saying 0 . 000000000 . 001 , it is impossible for two bodies to reach the same temperature , so the tiny amount of heat is transferred back and forth between the two bodies . Thus , we call this process reversible . I don ' t know if I understood correctly . I couldn ' t find any further explanation of this statement in the textbook or the internet . However , I don ' t think it meant that there is no temp difference at all . edit Missing a word smalledit 2 Forgot to say thank you