Quantum Field Theory for Legspinners

The notion of a particle in quantum field theory is dependent on the observer. This fundamental ambiguity in the definition of what seems a basic “objectively” observable concept is unsettling. In this short note I will survey the basics of field quantization and then discuss the Unruh effect which illustrates this phenomenon. I will describe an abstract version of quantum field theory in which a single mathematical object, a complex structure, captures all the ambiguity in the definition of a particle. There is nothing original in this paper, however, this particular presentation is not easy to extract from the extant literature and seems not be be known as widely as it deservers.