Are Tachyons Physical?

In this 50-minute lecture, Prof. Jan Dereziński from the Department of Mathematical Methods in Physics at the University of Warsaw explores the controversial question of whether tachyons can be considered physical entities. Examine the concept of tachyons—hypothetical particles that travel faster than light—through a rigorous mathematical and physical analysis. While the short answer provided is that tachyons are not physical, the lecture delivers a comprehensive explanation of why various attempts to define tachyonic quantum field theory are fundamentally flawed. The presentation begins with a clear definition of what constitutes "physical" in this context before methodically dismantling different theoretical approaches to tachyons. This Warsaw colloquium for theoretical physics at the Centrum Fizyki Teoretycznej PAN was inspired by recent discussions at the University of Warsaw's Faculty of Physics, offering valuable insights for those interested in theoretical physics and the boundaries of our current understanding of particle physics.