# Literature Reccomendations

1. May 2, 2006

### Ludovico

Hey,

Recently, I have been getting very interested in Cosmology and I am looking for some books to expand my knowledge base. I am not a scientist and I don't have an education is physics, so it's been difficult for me to find literature that I can comprehend. Can anyone reccomend a book(s) that will help me understand the prerequisite principles of Astrophysics so I will be better equipped to delve deeper into Cosmology?

Also, my understanding of general relativity is hazy at best - how would you reccomend I go about learning more about it? Any book reccomendations for this?

2. May 2, 2006

### yenchin

Hi. I am not sure whether you want to start with some nontechnical books or prefer books with more technical contents. Anyway if you want a nontechnical and friendly start maybe you want to try books such as "A Short History of the Universe" ?

3. May 2, 2006

### marcus

Here's a paper that just appeared today on the preprint archive.

http://arxiv.org/gr-qc/0605011

Ashtekar is a world-class senior scientist
for example he was an invited speaker at the Brussels 23rd Solvay conference last year (Quantum Nature of Spacetime), and also at the Paris Einstein Century conference. these are blue ribbon. the invited speaker-list for either one is a who's who

he is cautious and conservative and helps define the mainstream
there is no single voice, but Ashtekar is one of the voices

this paper that he just put online is the speech he gave at the Einstein Century conference at Paris July 2005.

You will probably only find one or two paragraphs you can understand but why not have a look.

(secondhand popularized accounts by people writing for mass audience can be misleading and a waste of time----in a subtle sense they dont tell you the real message, they tell you what you want to hear and will find easy to understand: they have to sell)

If you want to download the Ashtekar paper (which is 15 pages) I will help you find the paragraph in it that you can probably understand.

It is the second paragraph on page 14. By my reckoning it's dynamite especially if you take into account that it is from a senior scientist at a major conference.

Last edited: May 2, 2006
4. May 2, 2006

### SpaceTiger

Staff Emeritus
I don't think quantum gravity is the best place to start learning about cosmology, given that the theories are almost completely untestable and the formalism won't make any sense to someone without an education in physics. I suggest something more like this:

Foundations of Modern Cosmology

It describes the historical development of cosmology with very little mathematics. For a very brief overview of the current cosmological picture, you can check out the numbered posts here:

Review of Mainstream Cosmology

5. May 3, 2006

### Chronos

http://www.arxiv.org/abs/gr-qc/0503107
Understanding Our Universe: Current Status and Open Issues

There are, of course, any number of good introductory textbooks. I was weaned on Wheeler, but there are plenty to chose from these days.

6. May 3, 2006

7. May 3, 2006

### marcus

This is by Padmanabhan (another prominent figure like Ashtekar)

---quote---
The second question is: How (and why!) was the universe created and what happened before the big bang? The cosmologist giving the public lecture usually mumbles something about requiring a quantum gravity model to circumvent the classical singularity — but we really have no idea!. String theory offers no insight; the implications of loop quantum gravity for quantum cosmology have attracted fair mount of attention recently [45] but it is fair to say we still do not know...
---endquote---

Both Padmanabhan and Ashtekar were invited speakers at the Einstein Century conference last summer in Paris. A publishing house called World Scientific asked Ashtekar to compile a book called "100 Years of Relativity" and Ashtekar got several major mainstream figures to contribute chapters.
THIS WHAT CHRONOS RECOMMENDS IS PADMA'S CONTRIBUTION TO ASHTEKAR'S BOOK.

========
Your profile Ludovico says you are a cinematographer. What I am suggesting is that before you dive into routine academic cosmology, which is beautiful but based on 1915 Gen Rel: a venerable mathematical model with antique slightly musty singularities, that you try LISTENING TO WHAT THESE WORLD CLASS FIGURES OF MAINSTREAM COSMOLOGY ARE SAYING AMONG THEMSELVES.

there is a way to avoid the singularities of classical pre-quantum cosmology----and accordingly the bang is not the beginning of the universe but merely a changeover from contraction to expansion.
It comes under the heading of Quantum Cosmology.
Not yet everybody is willing to sign off on it. Sounds like Ashtekar will ratify it but Padma is not ready to. And some people might say that you SHOULDN'T EVEN BE EXPOSED to Quantum Cosmology until you have been through the undergraduate pre-quantum mill and learned the truths of the previous generation.

But I am proposing a somewhat irregular path, partly because your profile says cinema. The central figure of the QG story is a young German researcher named Martin Bojowald. His was the 2001 paper "Absence of Singularity in Loop Quantum Cosmology" that started a lot of current activity. Ashtekar was one of his teachers. But Ashtekar is now more in the role of following and confirming developments that Bojo and others of his students have spearheaded.

there is something dramatic going on in cosmology right now and one way it to symbolize it is to say that in January 2007 Bojowald will meet the string theorists in a Quantum Cosmology workshop at the Santa Barbara Kavli Institute of Theoretical Physics

KITP is a prestigeous physics institute hosts big name conferences---I dont necessarily like their research (a lot of it is string)---but the prestige is a fact. They have a website and a page about this workshop. The registration for this workshop is ALREADY CLOSED. It is full and it's still months away.

Someday Bojo and/or Ashtekar could well get the prize for changing how people view the beginning of expansion, the former singularity, the ex-big-bang----the brief episode that people once considered to be the beginning of the universe.

Sure the rest 13 billion years picture doesnt change by this. the only part of the picture I'm saying that it changes is right around bang-time.
this comes under the heading of current events and it is a dramatic shift in how some people at the top are thinking and talking about the "beginning". I am advising you to tap into that, because it is good for the imagination. I would say learn some straight pre-quantum cosmology too, but not exclusively

Last edited: May 3, 2006
8. May 3, 2006

### Ludovico

Thanks to everyone for their replies -

Marcus:
Yes, I am a cinematographer - how does that relate to cosmology?Creativity? I grabbed that article, going to give it a detailed reading when I have some uninterrupted time later tonight.

I've got some serious reading to do now, thanks again to everyone for your help. I half expected to get no responses at all, so I am very happy to see a bunch of helpful nice-enough people here.

SpaceTiger:
I'll definitely take you up on that. Thanks again!

Subquestion: I can't find avatar settings in my control panel - how do I set one?

Last edited: May 3, 2006
9. May 3, 2006

### neutrino

You have to subscribe to get an avatar. Click the upgrade link at the top of the page.

10. May 3, 2006

### marcus

can't be sure, there are all sorts of cinematographers including those without much imagination who just do routine docs, but my feeling is that it goes along with

dramatic sense
visual imagination
a feel for the underlying story line

cosmology is undergoing two quick revolutions in succession
1. is the 1998 revolution sparked by the supernova observations that showed accelerated expansion----thus a positive cosmological constant or some kind of dark energy.

the cosmological constant is denoted Lambda ($$\Lambda$$) and the 1998 revolution led to the general acceptance of the CDM-Lambda model.

after which it looked like things were not going to change any more for a while----we would just be left with a couple of riddles like What is Lambda? and What is the CDM (cold dark matter)? And maybe particle physicists would help explain what those things were---find particles etc.

2. But it didn't settle down after the 1998 revolution. for instance, in 2001 Bojowald published "Absence of Singularity in Loop Quantum Cosmology" and that helped to get a second revolution rolling.

Bojowald is a young researcher formerly Ashtekar's postdoc and he is more aggressive, Ashtekar is more conservative-----after some years of thinking about it he confirms. It takes both kinds.

Actually if you want, take a look at this Bojowald paper or at least the one-paragraph summary at the beginning (words not equations)
http://arxiv.org/abs/gr-qc/0601085

It is long, but the one-paragraph summary gives the gist and is not all that hard to understand. I will copy it here and highlight some key phrases:

"Quantum gravity is expected to be necessary in order to understand situations where classical general relativity breaks down. In particular in cosmology one has to deal with initial singularities, i.e. the fact that the backward evolution of a classical space-time inevitably comes to an end after a finite amount of proper time. This presents a breakdown of the classical picture and requires an extended theory for a meaningful description. Since small length scales and high curvatures are involved, quantum effects must play a role. Not only the singularity itself but also the surrounding space-time is then modified. One particular realization is loop quantum cosmology, an application of loop quantum gravity to homogeneous systems, which removes classical singularities. Its implications can be studied at different levels. Main effects are introduced into effective classical equations which allow to avoid interpretational problems of quantum theory. They give rise to new kinds of early universe phenomenology with applications to inflation and cyclic models. To resolve classical singularities and to understand the structure of geometry around them, the quantum description is necessary. Classical evolution is then replaced by a difference equation for a wave function which allows to extend space-time beyond classical singularities. One main question is how these homogeneous scenarios are related to full loop quantum gravity, which can be dealt with at the level of distributional symmetric states. Finally, the new structure of space-time arising in loop quantum gravity and its application to cosmology sheds new light on more general issues such as time."

there is a story here, about a handful of explorers, and about people gradually changing the way they picture the history of their universe

Last edited: May 3, 2006
11. May 4, 2006

### Chronos

My aim was only to provide useful references, not argue the issues.

12. May 4, 2006

### marcus

You did good! Padma is a fine online resource.
My aim was to argue like hell for what I believe is a better approach to learning cosmology.
We all learned the standard curriculum and you get to imagine that a singularity is something PHYSICAL. And then you have to UNLEARN and discover that it is just an artifact of the model you are using.

I think in the future Cosmology textbooks and even undergraduate General Astronomy textbooks will say a little bit about quantum cosmology. You dont have to say a lot, just let people know that a singularity is simply a place where a model breaks and there are some quantum models which give the right answers and do NOT have a bang singularity.

And after that, let them go on and learn the usual conventional curriculum. but we should NOT be giving students the impression that the universe began 13 billion years ago because there is no scientific evidence for that.

So I would tell him sure go and read standard sources on cosmology. Read Michael Turner, and Charles Lineweaver, and Padma, and Ned Wright, and so on. There is a lot of good standard stuff on line that you dont even have to buy. But don't ONLY read that. Read a few paragraphs of Loop Quantum Cosmology too. So you don't accidentally get brainwashed.

Last edited: May 4, 2006
13. May 4, 2006

### Chronos

Agreed. You are one of the most sensible people I have met on PF. I greatly respect your opinions, character, and insights. Apologies if I have insulted you. I disagree with you on some points, but am a kindred soul on most points.
.

Last edited: May 4, 2006
14. May 4, 2006

### marcus

Thanks Chronos, the respect is mutual. I wasn't at all feeling insulted or uncomfortable in any way. Something I said (not sure what) must have given the wrong impression.

Also I cheerfully admit that what I am proposing to Ludo constitutes approaching the usual Cosmology curriculum a little bit out of order.
This kind of thing happens now and then---it used to be that Freshman Physics was taught with no taste of modern physics (no special relativity, no quantum stuff, all classical) and then you had to unlearn things later that you had learned very thoroughly in the first couple of years. I think it was in the Sixties that the basic General Physics curriculum began to acquire a little taste of modern---so there wasnt so much to unlearn later.

A taste is all it takes, just enough so you are innoculated against believing that the classical stuff you are being told is Gospel.

15. May 4, 2006

### Ludovico

I started reading general relativity yesterday. Marcus, are you saying that learning general and special relativity will hinder my ability to understand the 'next' big revelation in physics?

I was talking with my brother yesterday (who is a chemist), and he was explaining to me that (in his opinion) deciding to delve into relativity at a young age is a critical decision. I've been told by others that trying to grasp the concepts at an older age is harder and it should be learned as early as possible. Are you saying the opposite?

16. May 4, 2006

### SpaceTiger

Staff Emeritus
I think your brother's advice is good. Start with the fundamentals of the field -- the current understanding, including relativity. It's good to be aware that there are possible extensions to these basic models, but trying to understand the extensions before you get the big picture is, in my opinion, a bad idea.