# Modern relevance of canonical quantisation [closed]

In some modern field theory texts such as Siegel's Fields it is claimed that canonical quantisation of fields is obsolete as it is not used it modern research papers. Thus, it should be removed from curricula and replaced with more modern methods.

Siegel says that the path integral should be the primary technique taught. However, canonical quantization makes it obvious that the quanta of the fields are particles. I have never seen this done using path integrals. Indeed I have only seen path integrals used for calculating things such as S-matrix elements, which it is certainly much more efficient at.

Essentially my question boils down to this; Can one show the particle content of fields using the path integral? If not, can canonical quantization really be considered obselete when first learning field theory?

## closed as primarily opinion-based by ACuriousMind♦, user36790, Kyle Kanos, Gert, Daniel GriscomDec 31 '15 at 2:08

Many good questions generate some degree of opinion based on expert experience, but answers to this question will tend to be almost entirely based on opinions, rather than facts, references, or specific expertise. If this question can be reworded to fit the rules in the help center, please edit the question.

• $\uparrow$ Which page? – Qmechanic Dec 18 '15 at 18:34
• It's mentioned on the webpage for the book insti.physics.sunysb.edu/~siegel/errata.html as well as pages 6, 31, 77 of ver.4 of the book. – Okazaki Dec 18 '15 at 19:57
• As both formulations of QFT are equivalent, this question is kind of opinion based. Anyway, IMHO, canonical is not obsolete at all, and a deep understanding of it is essential even though one uses path integrals in one's research (not to speak of the pedagogical value of operator quantisation, which IMHO should always be taught in full detail before path integrals) – AccidentalFourierTransform Dec 18 '15 at 20:19