The unusual properties of plasmas

Sixty years ago Enrico Persico gave two seminars, one in Messina and one in Palermo, with the title “Le strane proprietà del plasma” which we freely translated as the title of the present article. Is what was unusual 60 years ago, in a sense, still unusual now? Possibly the “non reductionist approach” that the study of plasmas requires. Again, freely translating from the seminar notes [1] “ This field of physics is characterised by the fact that, even if the laws that describe the elementary microscopic forces are known, the different phenomena that take place in plasmas are so intertwined that predicting, or even just interpreting, the plasma macroscopic behaviour is often extremely difficult”. Where does this intertwining come from? And, is it universal? Often in multibody systems the presence of thermodynamic equilibrium puts to rest most of the details in the system behaviour that arise from the peculiarities of the interaction forces. But in plasmas even local thermodynamic equilibrium is generally not present: this is a fundamental property of electromagnetic interactions in dilute systems. And plasmas constitute most of the visible matter in the Universe.