"The problem is that replacement of Quantum Mechanics by Quantum Field Theory is still very demanding"

This quote by Martin Fleischmann is referring to the problem of replacing Quantum Mechanics with Quantum Field Theory. Quantum Mechanics is a branch of physics that handles the behavior of matter and energy on the atomic and subatomic level. Quantum Field Theory is a more advanced version of Quantum Mechanics that considers the interactions between particles and fields. The issue is that changing Quantum Mechanics with Quantum Field Theory is a really tough and demanding job. It needs a deep understanding of the underlying concepts of both theories and a great deal of mathematical understanding. Moreover, the shift from one theory to the other is not always straightforward and can be quite tough. Therefore, the replacement of Quantum Mechanics by Quantum Field Theory is still an extremely demanding job.