# Spin - any book recommendations?

1. Dec 1, 2009

### dreamspy

Hi

I am currently taking my first course in Quantum Mechanics, and I'm having difficulty getting a grip on the spin concept. The book I am reading is "Introduction to Quantum Mechanics" by Griffiths. This is a great book, but the coverage on spin isn't as clear as the rest of the book. Can anyone recommend me another source of information, some introductory text on the concept of spin.

Regards
Frímann Kjerúlf

2. Dec 1, 2009

### mccoy1

Electron has spin up and spin down; it works, so go and use it.

Okay ....well....In my opinion, there's no book that can do a very good job in helping you understand what actually spin is. You just have to accept it like a religion as an intrinsic property of an electron(just like its mass).

Good luck in applying the concept of spin up/down.

3. Dec 1, 2009

### dreamspy

I'm mostly looking for a book that goes well into the notation of spin, and maybe gives some basic examples/problems so I can "learn by doing".

4. Dec 2, 2009

### dextercioby

My advice would be to read the 3rd volume of the Feynman lectures on Physics. And if you want rigorous notation, then Sakurai's book should be the choice.

5. Dec 2, 2009

### ansgar

Sakurai chapter 3 is the best reference I have tried/read regarding spin and angular momentum in QM. It is simply a representation of an underlying symmetry.

6. Dec 2, 2009

### ansgar

why should one "just accept it"? It is very simple to derive and to experimentrally observe. In my previous answer, I told OP that spin is a representation/manifestation of an underlying symmetry.

When you come to relativistic QM, you will find that spin (spionors) are just the irreducible representation of the Lorentz Group, i.e. related to symmetry.

7. Dec 2, 2009

### Ben Niehoff

I'll second (third?) Sakurai. The very first chapter has some thought experiments that help clarify what spin really is.

8. Dec 2, 2009

### Spinnor

As a second opinion try:

Quantum Mechanics (Student Physics Series) by Paul Davies (Paperback - Sep 1988) ISBN-10: 0710099622
11 Used & new from \$1.31 (Amazon used books)

Make sure you can answer any test questions, some math involved. Get a grip latter %^)

9. Dec 2, 2009

### mccoy1

You don't derive spin man..One can only derive the mathematical representation of spin.
What the poster wants is not to "derive spin" because griffiths has that calculation. However, he wants explanation of it is.Okay, now that you have experimentally observed it, can you explain what you have observed to others who want to learn it? And as I read your post, you haven't done a good job in explaining it to him. It's easy for some people to pretend that they intuitively understand "spin" as in QM, but the reality is that they don't.

I think those who recommended some books have done a good job. Let him read by himself to have a feel of what spin is actually is.

10. Dec 2, 2009

### ansgar

Just because you don't know what spin is does not mean that everyone else doesn't know.

Here lies the heart in all physics understanding, if one understands the mathematical representation of a physical phenomena one understands the physics. We can not have any other understanding of physics (except for things like newtonian gravity and basic electricity, fluid dynamics etc hehe) but the mathematical "mapping".

As pointed out, first chapter in sakurai does a good job in explaining spin from an experimental point of view.

In a very similar way, electromagnetism is due to a symmetry principle, gauge symmetry - which relates E and B. Now would you claim that this is just a mathematical representation, that we have no understanding of what EM is?

11. Dec 3, 2009

### sokrates

I vehemently disagree.

Just because you get good at some math tricks, some taylor expansions, infinitesmall rotations, or translations does not at all mean you understand what spin is. Why don't you "derive" spin in some spare time so everyone benefits?

While Math is the only way we know of representing reality (i.e predicting/explaining experiments), it hardly means it is the only way.

There are at least 10 ways of "defining", "adjusting", "tuning" the math to get to the SAME experimental fact in many cases, (Sakurai himself talks about his "way" of defining angular momentum as the generator of rotations) so this by itself is an indication of
the fact that a single theory or representation is probably not uniquely related to what we call the "underlying reality".

To the OP: Sakurai - Feynman is probably a very good combination. Read Sakurai as much as you can and resort to Feynman when it becomes very hard.

Last edited: Dec 3, 2009
12. Dec 3, 2009

### ansgar

As I said, spin is a consequense of Lorentz symmetry.

Of course on can argue forever what criterion for "understanding" one should employ.

13. Dec 3, 2009

### sokrates

I don't think Lorentz symmetry is the only way one can use to decide on the consequences.

One can argue forever about even that.

14. Dec 3, 2009

### ansgar

The issue is that in non-relativistic QM, spin can be a somewhat ad-hoc / fuzzy thing - on that I agree - but in relativistic QM/QFT it is transparent.

And even if Lorentz Symmetry is just ONE way to deduce spin - a priori there might be in principle several way to obtain spin-1/2 representations of particles. But that does not per se mean that we don't know what spin is. Every question concerning understanding should be asked within a paradigm. If not, then discussions are pointless. Now the current paradigm of physics at scales larger than String Theory regimes - is that the Poincare Symmetry should hold. I.e. particles and dynamics should be related to representations of the Poincare group.

One can of course ask if a human beeing can understand anything - i.e. are there any objective criteria one should fulfil in order to gain understanding which is applicable to all regimes of human activity?

I would say that one understands a physical phenomena if one can derive and manipulate the mathematical representation of it and appreciate the experimental predictions and outcome of measurements if that phenomena.

And there are of course different levels regarding understanding, the teacher (very often) has a deeper and wider understanding of what he teach than the students who gains the highest grade in his class.

15. Dec 3, 2009

### dreamspy

Gentlemen, I want to thank you for your answers.

16. Dec 3, 2009

### ansgar

I hope you find a good book, I am embarrassed due to the first reply of mccoy1 - certainly he is probable just a troublemaker who has not gone far in QM business. So he have to impose this on everyone else, he can't just accept that he is the one having an issue.

Now besides Sakurai, you can try the book by Shankar, or Ballentine.

17. Dec 3, 2009

### dreamspy

Well there are always black sheeps. But must admit that I was surprized to this kind of discussion on this forum.

I'we located all the books recommended in her, except Ballentine, so now it's only a matter of "time" :)

18. Dec 3, 2009

### ansgar

There is also a science book discussion forum here:

Academic Guidance (44 Viewing)
Which college and degree? Grad school and PhD help
Educators & Teaching - Science Book Discussion

Please have a look there also, recommendations of QM books is a frequently asked question.

19. Dec 3, 2009

### mccoy1

Doing the maths and understanding are two completely different things. You can do/calculate QM but you still don’t understand it. Mostly those who assume they understand QM because they can follow calculations tend to be the very people who just don’t understand QM. In fact, it’s safe to say no one understand QM, not even the fine physicist, Einstein.
Okay spin was deduced from the stern – Gerlach experiment...so, can you explain it to us or ‘derive’ its explanation as you just said?
bye

20. Dec 3, 2009

### ansgar

The question was related to a book recommendation, if you can't answer then don't write anything in the first place.

It depends on, as I said earlier, what definition and criteria one has for "understanding". OF course we can not understand QM on the same level as we understand that hitting someone with a bat in the head is gonna hurt really really bad. But one can not see things as black and white as you do, that if something can not be related to intuitive feelings, then it is not something that can be understandable.

Understanding in physics is, as from my viewpoint, if one can relate theory and experiments.