# Good Book for Loop Quantum Gravity

1. Oct 29, 2004

### Gecko

i have the elegant universe and am about half way through. after this, i would like to read about string theory's rival, loop quantum gravity. does anyone know of a good intro book to loop quantum gravity?

2. Oct 29, 2004

### marcus

Interestingly enough no. There is no "Brian Greene" popularizer of Loop, that I know of, and no book focused on introducing Loop to general reader.

There is however Lee Smolin's book Three Roads to Quantum Gravity
which is partly about Loop and partly about String. I don't know the book personally, but some people have praised it.

If you do not mind a piecemeal approach, using magazine articles and online sources, the picture is a bit better

Smolin's January 2004 Scientific American article was clear and accessible (really good i thought) but not online---required a trip to the library, or for you to have a subscription.
Smolin's SciAm piece was called Atoms of Space and Time

This one by Rovelli is not only good and written for general audience, but free for downloading. It prints out to 5 pages.

http://cgpg.gravity.psu.edu/people/Ashtekar/articles/rovelli03.pdf

The Rovelli article is called simply Loop Quantum Gravity and appeared in November 2003 Physics World.

I recommend reading both, they are short and complementary (good to hear the same thing said two different ways)

Both those articles have lists of suggested reading----again mostly general audience stuff.

then I would suggest browsing Ashtekar's collection of popular articles on Loop QG. That was where i found the Rovelli article and he has a bunch more.
http://cgpg.gravity.psu.edu/people/Ashtekar/articles.html

Ashtekar has written some nontechnical articles himself----introductory, for nonspecialist. You will find things like "Gravity and the Quantum" by him, and "Quantum Geometry in Action: Big Bang and Black Holes"

Finally two ideas for more technical introduction:
Lee Smolin "An Invitation to Loop Quantum Gravity"
and Rovelli's book "Quantum Gravity" (draft copy free online, finished version expensive).
Rovelli's book has a lot of parts that are nontechnical and nonmathematical. But it is not easy. It is a graduate level textbook that happens to have some parts of some chapters accessible to general educated reader.

If you want links to any of those (Ashtekar, Smolin, Rovelli) writings that I just mentioned, just say. I just have to hunt them up in the "Rovelli's program" thread which is serving as a storehouse for LQG links

Last edited: Oct 29, 2004
3. Oct 30, 2004

### Gecko

wow, thanks alot. i would also like to attempt to read the last two you posted. do you know the link to the Rovelli's program thread? and is smolin's article on the internet? or is it a book?

4. Nov 11, 2004

### john baez

To get going, you can't beat Lee Smolin's "Three Roads to Quantum Gravity". Marcus gave a lot of good suggestions, but this is the best overall introduction to the quantum gravity problem. For one thing, it explains a number of approaches and their pros and cons.

http://www.qgravity.org/

Apparently Brian Greene's second book is also good. (I hear it even admits that loop quantum gravity has a chance of being on the right track!)

5. Nov 11, 2004

### PRodQuanta

Regaurding Three Roads to Quantum Gravity, I would like to make the comment that it is not just a book about Loop Quantum Gravity, which is what I originally presumed. But, to my surprise, it is a book on both Loop Quantum Gravity and String Theory (both being Quantum Theories of Gravity).

I do agree that Smolin's article in SciAm is a very enjoyable, informative read. I was facinated by the idea of testing LQG using the gamma ray burst experiment on pg. 74 in SciAm in that article.

I think the first all out LQG book is Rovelli's. I can't wait to get my hands on it.

Also, if you enjoyed Greene's Elegant Universe, you will love his new book Fabric of the Cosmos. It gives some references to LQG, however, in the statement he made to me, it sounded as if he wished he wouldn't have put them in there. For after stating that he didn't aprove at the recent events taken place in LQG, he said that he found this information out after he wrote the book.

Well, either way, marcus covered the basics. (What's new?)

Last edited: Nov 11, 2004
6. Nov 11, 2004

### marcus

I am glad you registered your picks because your perspective may parallel Gecko, and what you find good might be just right for him.

It is true that Rovelli Quantum Gravity is focused on LQG and the first book of its kind. But if you buy it there is a risk that you will feel you wasted your money because 3/4 of it is too hard. It is a textbook for graduate students motivated to get into QG research.

It has (roughly 1/4) that is accessible and gives a lot of insight to the history of physics gradually improving ideas of space and time---and the philosophical questions---and the overview. But even that accessible 1/4 of the book is not in the slightest popularized or water-down

I think it is a great book, and a landmark book. but 3/4 is hard as hell, and the other 1/4 is real interesting but no way easy.

So I would go download the free copy and see how much you like----and then buy it if you then decide its worth the money. As you will find out when you get to university, college textbooks are majorly expensive. your calculus text can run you $60 unless you get it second hand. Rovelli's book costs$70 from amazon. It is not like a popularized science book designed to sell a million copies.

I did that (and then I liked it so i ordered it from Amazon too)

Hello Gecko, I should have answered earlier.

If you do that link you will get pointers to the free download of Rovelli's book, and here it is plus a link to Smolin "An Invitation"
Carlo Rovelli's book
Quantum Gravity
http://www.cpt.univ-mrs.fr/~rovelli/rovelli.html
contains introduction, historical and philosophical perspective as well as technical stuff.

Best general audience article available online is probably
Rovelli's November 2003 "Physics World" article which Astekar has
at his website. The title was Loop Quantum Gravity
http://cgpg.gravity.psu.edu/people/Ashtekar/articles/rovelli03.pdf

Another good general audience article (but not available online) is
Lee Smolin's Atoms of Space and Time in the January 2004 issue
of the "Scientific American".

Probably the best introduction for physics students and physicists who are not specialists in QG is by Lee Smolin
An Invitation to Loop Quantum Gravity
http://arxiv.org/hep-th/0408048
---endquote---

Last edited: Nov 11, 2004
7. Nov 11, 2004

### PRodQuanta

8. Nov 11, 2004

### marcus

Yes, your essay is in somewhat the same spirit----or aimed at the same niche of readers---as Rudi Vaas science journalism.

Rudi Vaas actually has academic credentials as a History of Science
or else a Philosophy of Science guy, maybe both.
Because he has talent as a journalist, and has the gumption and personality to go interview people like Ashtekar and Bojowald, he can be more than just a Science Historian.

but he is also a Science historian and has done some more dry more stuffy academic articles too. this is good. It is good to be able to do both.

Amazingly, Carlo Rovelli is also not just a theoretical physicist. he also minored in History of Science and has some kind of degree in that too, and has taught courses in that too. So when Carlo writes about Isaac Newton thought process in the context of his time, or likewise about Einstein, and delineates just what the key steps were----then, well maybe he is right and maybe wrong, but at least the guy has credentials that say he is an expert in the history of physics. I especially like the extra philosophical and historical light that Rovelli turns on the subject---and I think it makes his physics better too.

Anyway. Rudi Vaas articles. Sort of like your essay, Paden, in a way.

Ashtekar has links to the ORIGINAL GERMAN published form of Rudi Vaas and you might look at them too. Why? I dont expect you read German. So why? Because the computer graphics illustrations rock.

You could copy and use them for your science project.

9. Nov 11, 2004

### PRodQuanta

Lol.
Thanks marcus. I'm thinking that would be an awesome minor!!! History of Science. That just occured to me.