1. Apr 5, 2004

### alanzhu

Hello everyone, I am now learning QFT, this theory is really abstract and daunting. I can't understand the concept of vector field. What is vector field at last? why there are four polarization vectors? I feel that the whole theory is somewhat lack of reasoning, the postulates and assumptions really confuse me. Could someone explain why there are 3 kinds of space and what is the most distinct difference between them.

2. Apr 5, 2004

Staff Emeritus
Could you explain what three kinds of space, please?

A vector field is a phenomenon that is characterised by a magnitude and a direction at each point of space - for example the gravity field near the earth has an acceleration (a vector with magnitude and direction) at every point, and different values at different points. No?

3. Apr 6, 2004

### gnl

I suspect it also necessary for you to realize that there is a lot of classical field theory in QFT. Vector fields are a perfectly classical notion. Electric and magnetic fields are examples. In relativistic field theories, you get 4-vectors (this tells you how they transform under Lorentz transformations). I suggest you start by reviewing classical mechanics (Goldstein), then move to classical fields (Jackson on electrodynamics); then, only then, pass to something like Peskin and Schroeder or Bjorken and Drell (QFT).

4. Apr 6, 2004

Staff Emeritus
...and before those QFT texts, you also need to study a nonrelativistic QM book. Sakurai is the classic one.

5. Apr 7, 2004

### gnl

I could not agree more!!! Sakurai is a text all physicists should read. The best on QM.

6. Apr 7, 2004

### Imparcticle

What is QFT an acronym for? Quantum....?

7. Apr 7, 2004

### gnl

Qft

Quantum Field Theory. The quantised theory of fields.