# What Math Books Should I Read to Understand General Relativity?

1. Aug 20, 2014

### Sunnyocean

Hi,

I started reading General Relativity but concepts such as Lorentz transformations, rotations, tensors etc. are, at least in my opinion, poorly explained. Or perhaps the authors assume that the readers are already familiar with such maths?

At any rate, I would very much like to read some good books on the above math topics. Could anyone recommend me some books / textbooks?

I really need to understand it well, from the basics to the very difficult concepts.

The more detailed, the better (and preferably with exercises and solutions, if possible, so that I can also practice the maths (and check my solutions), not just read the book).

Just a few words on difficulty. It seems to me that there are two meanings for "difficult". One of them is "too much detail". I don't mind that kind of "difficult". So yes, please do tell me about "the epsilon and the delta" of Ricci calculus etc. On the other hand, if "difficult" means that the book takes you through the whole history of mathematics before actually introducing the concept, then I am afraid that's not what I am looking for. Although if the latter are the only kind of books you would recommend, then they are obviously better than nothing.

So the short of it is: I am not afraid of difficult, and in fact I really want to understand the topic THOROUGHLY, but I don't want to waste my time with unnecessary details either.

2. Aug 20, 2014

### micromass

What physics and math do you already know?

3. Aug 20, 2014

### Daverz

What is your mathematics and physics background?

Which GR books did you try?

4. Aug 20, 2014

### Fredrik

Staff Emeritus
The best place to get a good introduction to SR and tensors is "A first course in general relativity", by Schutz. Read the first three chapters.

The best place to learn the differential geometry is the books by John M. Lee. You will need both "Introduction to smooth manifolds" and "Riemannian manifolds: An introduction to curvature". (Because the "smooth" book doesn't cover connections, parallel transport, geodesics, curvature). If you haven't already studied topology, you need to either skip some stuff in those books, or get a book on topology too. (It is possible to proceed without fully understanding the topological stuff. For a physicist, that's a reasonable compromise between following a dumbed down approach and getting really deep into the mathematics). I don't know what the best book on topology is, but it's a safe bet that Lee's book "Introduction to topological manifolds" covers what you need. (I haven't read it myself).

As for the actual general relativity, I'm not sure what to recommend. I know that Wald is a pretty good standard book that takes the math seriously, and it probably was the best choice when I studied GR, but it's possible that some newer book is better.

5. Aug 20, 2014

### Sunnyocean

Fredrik, thank you very much.

I have not studied topology but I would prefer NOT to skip anything.

I am aware that it will take a lot of effort but I would prefer to avoid the dumbed down approach. I really don't like making compromises when it comes to understanding stuff.

So, could you please recommend me some good books on topology as well (I will check Lee's book, but you seem to know the topic pretty well - at any rate much better than me - so I would prefer books you did read, if that's ok).

I like books which take maths seriously very much :)

6. Aug 20, 2014

### WannabeNewton

I can assure you that learning all this extra math will not only fail to be of any use in better understanding GR, it will also be a ridiculous time sink especially given the lengths of Lee's books. But if you have the time to spare then all the power to you, learn it if it interests you. Just know that physics books which overemphasize math tend to be quite bad in my opinion. Wald for example is great for learning the basic mathematical structure of aspects of GR e.g. causality, but you will not learn a word of actual physics from the book.

7. Aug 20, 2014

### Sunnyocean

Oh, and in order to answer the previous questions, I know the math that the "average" physics student knows at the end of the second year - maybe a bit more. I was avoiding to say that because I wouldn't like people to say to me things like "oh, in that case don't read General Relativity, it's too much for you!" <--- Please don't give me that kind of reply :p

8. Aug 20, 2014

### Sunnyocean

WannabeNewton, maybe you are right and maybe I will arrive at the same conclusion as you after reading all the stuff, but at the very least I need to check it for myself. I know I may well be wrong, but somehow I feel that I really need to know the math in detail.

9. Aug 20, 2014

### Fredrik

Staff Emeritus
That first statement is probably only about 75% wrong, but you certainly reached 100% with that last one.

10. Aug 20, 2014

### WannabeNewton

Well geez looks like I must have just plucked the statements out of thin air without any experience whatsoever. Why don't we put a rain check on this while I survey the GR post-docs in my research group on their opinions regarding the matter after the next group meeting and get back to you on that.

11. Aug 20, 2014

### Fredrik

Staff Emeritus
I have picked up pieces of topology here and there. A little bit about metric spaces from Rudin's "Principles of mathematical analysis" a long time ago. The basics about topological spaces from Friedman's "Foundations of modern analysis", also a long time ago. A few years ago, I read the appendix on topology in Sunder's "Functional analysis: spectral theory", and supplemented it with Munkres's "Topology" when I needed more. This brought me up to the OK level, but I don't think this is the best path for you.

Micromass is much better at topology than I am, and he's much more familiar with the books on topology than I am. So you should check out what he has to say about it. If he doesn't answer here, you should be able to find recommendations he has made in other threads.

12. Aug 20, 2014

### Fredrik

Staff Emeritus
Good luck finding a person who thinks that there's no physics whatsoever in Wald. Or a person who thinks that understanding tensor fields or parallel transport is of no use in understanding GR.

13. Aug 20, 2014

### Mr-R

Dear Fredrik,

I don't think that when wannabenewton said "extra math" meant parallel transport and tensor field. These stuff are standard and is covered in every intro to GR books like Schutz and D'inverno. I think there is some truth in saying that you don't need that much of maths to understand the Basics of GR. For example I think D'inverno relied too much on explaining computational stuff rather than physical concepts like Schutz.

I am just a beginner in this so I will just leave it at that.

14. Aug 20, 2014

### micromass

We will obviously not give you this kind of reply. But I think you need to be a bit more specific with your knowledge. It's really difficult to give suitable recommendations if we don't know more or less precisely what you know and don't know. If anything, just give the names of books you worked through, we can figure it out from there too.

With respect to the debate between Fredrik and WBN, I think both have good points and it really depends on what kind of person the OP is. I certainly agree with WBN that you don't necessarily need any math books in order to start with GR, and that learning the underlying math takes a huge effort and takes a lot of time (we are talking about graduate level mathematics here!). However, knowing the math rigorously does sometimes have its benefits. Math texts make concepts much clearer and are sometimes easier to read because of vague explanations in the physics texts.

I guess it depends on the OP. Does he just want to learn physics or does he want to learn the foundations and the mathematics too. Both are valid approaches.

If you are interested in the mathematical approach, then I think you might want to start with linear algebra, a good book (despite its name) is Linear Algebra done wrong: http://www.math.brown.edu/~treil/papers/LADW/LADW.html
Then you should learn analysis of metric spaces and topology. Good books (but maybe far too much) are the analysis book by Zorich, these will also cover manifolds in part II. Lee's books are a good alternative (but they're also very large!), if you already know the basics of metric spaces and proofs.

Even if you're following the mathematical approach, don't wait to start with GR until you have covered all math. Try to read Schutz now already (maybe together with the math books).

15. Aug 20, 2014

### Sunnyocean

Mentor,

I really don't remember all the math books I've read, but I will give you some EXAMPLES of what I know:

Calculus - integration, differentiation, both one-variable and multivariate (however, I know the "epsilon and delta" only for one-variable calculus). As for multivariate calculus, I have been taught to "just accept" the theories, something which I do not like very much to be honest.

With respect to linear algebra, I know matrix multiplication, determinants, eigenvalues etc.

I also know some vector field calculus, curl theorem, divergence theorem etc.

I have studied the basics of what groups are (what is an abelian group etc.)

Geometry-wise, I know Euclidean geometry. (And of course trigonometric functions etc.)

I hope this is detailed enough. The above is of course an outline, not an exhaustive list of the maths I know.

With respect to what a "huge" effort is, in my experience different people mean very different things by "huge effort". I can tell you that in high school my maths teacher used to say "If you haven't sat at the table at least three hours per day doing maths, you are not really studying maths". This, to me, is "normal" effort (NOT big, let alone "huge"). Hopefully this will serve as a description for what "normal effort", "huge effort" etc. mean. Oh, and by "sitting at the table" I mean really doing maths - no tv, no watching out the window, no facebook, no family members / friends coming to do "small talk", cell phone switched off, no snacks (just some water), no headphones (the room should be as quiet as possible, earplugs are not a bad idea) etc. Going to toilet is allowed!

I hope the above is detailed enough. If it is not, please do ask in case I need to write in more detail :)

If you think I know too little maths, please do let me know.

Last edited: Aug 20, 2014
16. Aug 20, 2014

### Sunnyocean

Oh, and I really AM *very* grateful to ALL the people who took the time to reply. Especially to the people who wrote detailed replies. I am writing this because the system told me that I cannot give any more reputation (I am a beginner on Physics Forums so I don't know well how this works). But it seems to me that I should be able to thank everyone who takes even some seconds from their precious time to answer my posts, and there should not be a limit to "how many kilograms of gratefulness" I am allowed to express.

Anyway, since I am not able to thank everyone individually, I would at least like to thank you all by writing this reply! :)

17. Aug 20, 2014

### Fredrik

Staff Emeritus
If you have to apply that normal effort for more than a year, then it adds up to a pretty huge effort. It will take a very long time, probably more than a year of normal effort, to first learn topology well and then learn differential geometry well. It's probably better to do something like this:

Start with the first three chapters of Schutz (SR + tensors in the context of multilinear algebra). Then take a look (in some book on differential geometry) at the definitions of "smooth manifold" and "tangent space", and the proof that if x is a coordinate system (=chart) that covers a region that contains a point p, then $\big\{\frac{\partial}{\partial x^i}\big|_p\big\}_{i=1}^n$ is a basis for the tangent space at p. You will see that some topology is used. So then you know what topics from topology you will have to study to understand manifolds and tangent spaces. At this point you study those things in topology (the basics of metric and topological spaces, and a little more), and then give those definitions and theorems in differential geometry another shot. Then you make sure that you understand vector fields and tensor fields, in particular the metric tensor. Then you study GR until you find something that you can't understand without consulting Lee.

18. Aug 20, 2014

### WannabeNewton

I wouldn't have said it if I didn't already know the results It's not as if we (the people in the group) haven't discussed this before. And I can say with 100% confidence that going through all of Wald and doing all the problems in it will help to no extent in solving GR problems that are actually of interest. Hell it wouldn't even help solve the physics problems in Lightman et al. If your main goal is mathematical GR then all the power to you, Wald is probably the best book to get started on that. But mathematical physics isn't physics.

Mr-R said everything I have to say with regards to this. No one needs to go through Lee or a more advanced book in order to understand such material. It is very easy to understand as presented in GR texts.

19. Aug 20, 2014

### Sunnyocean

WannabeNewton, since I am just starting it is probable that I won't understand what you mean, but can you tell me more about what you mean by "mathematical physics isn't physics"? Could you perhaps give an example?

While I do want to study everything in detail, I certainly don't think that mathematics is everything.

20. Aug 20, 2014

### WannabeNewton

Sure no problem. I think the most demonstrative class of examples come from Penrose's grand sea of contributions to GR and Geroch's equally vast contributions to the subject. Both of them worked on aspects of GR that are termed mathematical GR but they also worked on aspects that one would align more with physics. For example Penrose (with Hawking) is famous for the proofs of the singularity theorems. The study of these theorems, their background, and proofs are entirely mathematical in that they really are an (elegant) use of relatively advanced differential geometry. There exist as a result entire projects on studying the kind of Jacobi fields that arise in the singularity theorems and how they classify certain manifolds.

Another example would be the contributions of Choquet-Bruhat to the field of mathematical GR. She is most famous for her work on the study of Einstein's equations in the context of PDE theory. Robert Geroch, as well as David Malament, have some extremely interesting work on the relationships between topology and causality of general space-time manifolds (Lorentzian manifolds that need not satisfy Einstein's equations) and pathological effects of causality in space-times with interesting topologies. Geroch also has papers on generating solutions to Einstein's equations for lineariztions over a curved background.

These are all instances of mathematical physics and chapters 7-10 of Wald cover the basics of everything I've mentioned. Chapter 11 is on the mathematically rigorous definition of asymptotic flatness for the most part and has a small section on the notion of energy-momentum of space-times. The latter (ADM energy-momentum of space-times) is actually an example of physics instead of mathematical physics and is still an active area of research for physicists working in GR but I didn't count it in Wald's book because he covers it so briefly and quickly that you can't learn anything from it unless you consult other books or literature (c.f. the very detailed review by Jaramillo and Gourgoulhon on arxiv).

Contrast this for example with Rindler's papers on rotation in GR which are definitely more on the side of physics. His most famous is probably his paper on using the gravitomagnetic potential in the corotating frame of observers in circular orbits in stationary axisymmetric space-times to calculate the Thomas, Geodetic, and Lense-Thirring precessions of gyroscopes at rest in the frame in an extremely elegant manner. This is work that is actually of interest to physicists who explore precessional and orbital effects in GR that can be verified by experiment (e.g. Gravity Probe B).

EDIT: Just for the record, Wald is my most favorite GR book. It is an extremely elegant and careful development of the mathematical structure of the theory and is what really made me fall in love with the subject. Since then I've worked through multiple other GR books and what I'm saying is by way of comparison. Wald's book simply does not go into any detail on calculations important for physical problems in GR (both research and textbook), it doesn't even teach you how to really think about approaching a GR problem and calculations therein, and it doesn't explore any of the interesting physics in physically relevant space-times that can eventually be compared with experiment. Wald is really something you want to look at after having seen/acquired all these things through e.g. MTW, Hartle, Straumann, Schutz, Hobson et al, Padmanabhan to name a few.

Best of luck!

Last edited: Aug 20, 2014
21. Aug 20, 2014

### Sunnyocean

Thank you very much, as I said, for the moment I am happy I can read the words in your reply :p

But I did make a copy of your reply for future reference, when I hope to be more able to understand what you wrote :)

22. Aug 20, 2014

### WannabeNewton

Haha well again best of luck!

BTW, I'm not trying to come off as a devil's advocate here or a downer on math. I'm just trying to save you time and effort. I did exactly what you are aiming to do now in this thread and I can tell you, while it helped me greatly in the short run in quickly grasping the basic mathematical structure of GR in more depth than that which is provided by GR books, in the long run it was not useful at all. It simply took precious time away from my learning the physics of GR more deeply, working on more involved GR calculations, and moving into more specialized arenas of GR.

I have yet to come across a GR paper in the literature relevant to the stuff I normally deal with either at school or in my own time when I'm reading as a hobby that required any deep knowledge of the material in e.g. Lee's topological or smooth manifolds books. Any unfamiliar math that did come up could easily be looked up or understood from a vastly superior math intellect than oneself (for me it was micromass ).

That being said, working through Lee's topological manifolds with micromass was some of the most fun I've ever had learning so if you want to learn it for the sake of learning it you will not be disappointed. It's extremely enjoyable.

23. Aug 20, 2014

### Sunnyocean

Since we are talking about it, could you please give me the exact titles of the books by Hartle, Straumann etc.? Not only for future reference but also I might just want to take a look through them, to (try to?) get a glimpse of what awaits me :)

Also, I really don't know what "MTW" means...:p

24. Aug 20, 2014

### WannabeNewton

Sorry that's entirely my fault. I'm just so used to giving only the author's last names. They're all included in a list I made in an older thread: https://www.physicsforums.com/showpost.php?p=4717552&postcount=7

MTW = "Gravitation" by Misner, Thorne, and Wheeler for future reference since almost everyone just calls it MTW.

25. Aug 20, 2014

### Sunnyocean

Thank you very much :)