# Quantum Weinberg's 3 Volumes too difficult?

1. Nov 1, 2017

### Tio Barnabe

I'd like to hear opinions from those who have already some experience on Quantum Field theory, what do they think of Weinberg's 3 volumes, whether they are so hard compared to other books or not.

It happens that I have been reading some books on QFT, the last being Ryder's book from 1996.

I had an excellent experience with Weinberg in Special/General Relativity, and found no major problems while reading his book. However, after many readings, I was able to understand only the first ~ 50 pages of his 1 volume on QFT.

So, is it more likely that I have not the minimum knowledge required to understand the book content, or is it that those three books are really hard to go through?

2. Nov 1, 2017

3. Nov 2, 2017

### Demystifier

Yes, Weinberg's QFT is hard. (Much harder than his Gravitation and Cosmology.) It is not recommended for beginners.

4. Nov 2, 2017

### MathematicalPhysicist

When can you say that you have knowledge of an intermediate or advanced level in QFT?

I mean after reading such and such books, when can you say that you are ready for Weinberg?

5. Nov 2, 2017

### Demystifier

Well, it's not that you are ready to master a book with hardness $n$ just because you have mastered a related book with hardness $n-1$. It that was so, then, by induction, anybody could master any book on physics, math, computer science, or any other hard science. In reality, everyone sooner or later arrives at a book which is too difficult for him. Perhaps you will be ready for Weinberg after Ryder, perhaps after Schwartz, or perhaps never. But then again, even if you will never fully understand Weinberg, perhaps you will understand some other difficult book which will never be understood by someone who understands Weinberg. Hardness is not 1-dimensional.

6. Nov 2, 2017

### vanhees71

Well, Weinberg's books on QFT are "hard" in the sense that they provide very general insight into the structure of the theory. E.g., he treats the complete representation theory of the Poincare group for particles of arbitrary spin (for both the massive and the massless case) instead of restricting himself to the most simple cases of $s \in \{0,1/2,1 \}$ relevant for the Standard Model.

Nevertheless these three volumes are the best books on the subject, I've ever seen, and it's particularly for this reason: He provides indeed the insight, "why QFT looks the way it does", from very general principles, as promised in the preface. So it may be hard to study the books, but it's well worth the effort.

I'd say, if you have some knowledge on the level of Schwartz or Ryder, you should be able to work through Weinberg's books, which are very clearly written, if you have some insight (including some intuition on the physics).

In general, to really get something out of any QFT book, you have to do calculations yourself. After struggling through some one-loop integrals (say, in dimensional regularization) and renormalizing them by appropriate counter terms the enigma of renormalization looses a lot of its scare :-)).

7. Nov 2, 2017

### Demystifier

Does it mean that you have studied the 3rd volume on supersymmetry? I thought that you are more like down-to-earth type of physicist.

8. Nov 2, 2017

### vanhees71

I've not studied vol. 3 in as much detail as the other volumes, but I think it's as good as the 1st two. Well, whether or not SUSY is worth a study depends on your taste. It's very interesting from a mathematical point of view. Whether or not it is useful to describe Nature is a different question. At the moment the prospects look rather grim for physics beyond the Standard Model, although it's pretty sure that there should be some!

9. Nov 3, 2017

### Tio Barnabe

I'd like to ask you guys, how much time do you usually take for reading a whole book such as Weinberg's book? It usually takes me a week for reading (and understanding 80% of) about 100 pages. Of course, this question depends on what knowledge one has on the subject one is reading about. But just let me know your mean time?

10. Nov 3, 2017

### vanhees71

Wow, that's quick. I've not worked through the entire Weinberg at all. To get some understanding of relativistic QFT takes rather years than months or days, and I'd not dare to say I understand the subject completely at all, although having some experience in research using the theory for some years.

11. Nov 3, 2017

### MathematicalPhysicist

Technical books shouldn't be read as a novel, I am not sure you really grasping by only reading a book, you should also solve problems to assimilate the knowledge and writing the material in your notebook; unless you don't mind forgetting all this knowledge.

Why do you think we still have pen and notebooks? it's all about not forgetting the material, after reading so many textbooks as myself, you bound to forget it.

Also, I once took a graduate course in Ergodic Theory, the lecturer always sent us via email the notes he were to use in class, I still wrote my notes, cause you cannot keep track with the reasoning without some writing.

12. Nov 3, 2017

### vanhees71

Yes, indeed. Writing up the material yourself, in your own words, do the calculations to derive the results in the textbook (or in the lecture by the professor) and last but not least solving problems realted to the material is mandatory to start understanding a subject. What I also find very important is to discuss about the material with others. Also explaining something to others is of great value. The final step is to teach it yourself to students (hopefully asking demanding questions). Often then you realize that you haven't understood something yourself!

13. Nov 3, 2017

### Tio Barnabe

I agree with both of you. I usually don't have the equations memorized. That one week for 100 pages I mentioned above is just to get a basic understand of the theory. I hope to be some day as good as a certain Van Hees is

14. Nov 3, 2017

### Dragon27

I like it slow and painful.

15. Nov 3, 2017

### Demystifier

My style of learning is similar to yours. If one is satisfied with 80% understanding, that's not too fast at all. I usually want first to get a big picture, to see the forest rather than the trees. Later I may study some particularly interesting part in more depth, but I rarely do that with the whole book.

16. Nov 3, 2017

### George Jones

Staff Emeritus
Even though I love Weinberg's advanced books, I say the following.

I am glad that: 1) they are on my shelf; 2) I am not taking a course that uses any of them as the text; 3) I am not teaching a course that uses any of them as the text.

17. Nov 3, 2017

### Tio Barnabe

18. Nov 3, 2017

### George Jones

Staff Emeritus

Don't ask me for specific examples of the following.

Weinberg explains (at a technical level) some things better than anyone. Sometimes I read a passage in Weinberg, and I think to myself "Wow, I finally understand what is really going on."

There are, however, passages in Weinberg's that I find difficult to understand. Also, sometimes it is difficult to see past the clutter of Weinberg's notation. A typical course might cover approximately 250 pages of a text. Consequently, ...

If I were a student registered in course that used Weinberg, I would not feel comfortable with 80% mastery of the 250 pages. Attaining higher-level with which I would feel comfortable while possibly taking another course and/or doing grad student research would constitute a severe strain.

If I were required to teach a course that used Weinberg, I would only feel comfortable with at least 95% mastery of the 250 pages. Attaining the level with which I would feel comfortable while possibly other courses and/or doing research and while meeting my familial obligations would constitute a severe strain. Also, because of the previous reason, I would not want to impose this on the students.

Last edited: Nov 3, 2017
19. Nov 3, 2017

### MathematicalPhysicist

Aren't we being masochist here?! :-D