Thermodynamics states that a system cannot become more complex without some sort of input (which would make it an open system). In other words, a closed system cannot increase in complexity. I understand that complexity is a very ill-defined term. However, at least in principal, couldn't a closed system by chance become more complex without external energy? (ie: a tornado goes through a junkyard and actually goes leave a functioning aircraft in its wake) This being said, would it be more fair to say that on average, a closed system will not increase in complexity?