Konwersatorium im. Leopolda Infelda

The essence of the above title is the question mark. As stated in the Stanford Encyclopedia of Philosophy, "In contrast to many other physical theories there is no canonical definition of what Quantum Field Theory (QFT) is. Instead one can formulate a number of totally different explications, all of which have their merits and limits".
One important limitation of the current understanding of QFT is an unsatisfactory description of strongly coupled systems. In this talk I will discuss some attempts to formulate such a description, which – in certain simplified settings – revealed deep dualities between QFTs, intimate links between QFT and string theory, led to classification of certain classes of QFTs, etc. While these lessons so far have not led to an ultimate answer to the question of what QFT is, they indicate what features such an answer should involve.