AST5220/9420 – Course presentation

Hans Kristian Eriksen17. januar 2011

Fact: The universe has structure

Our main question: How did these form?

AST5220/9420 in three bullet points

• Goal: – Understand the structure formation processes in the early

universe

• Main method:– Compute numerically and (where possible) analytically the

evolution of structure

• Main deliverable in the form of a project:– CMB power spectrum code; takes in cosmological parameters,

outputs spectrum

Main topics to be covered• Short introduction to General Relativity

– One of two lectures given by David Mota

• Boltzmann equations– How do particles behave in non-equlibrium conditions?

• Baryons, photons, dark matter

– Recombination; how did the universe become transparent?

• Einstein equations– How do space behave when matter is present, and moves around?

• Inflation– How were the very first structures generated?

• Observables– How can we predict what we will observe, given a theoretical

model?

Lectures, times etc.• Two lectures per week

– Tuesday at 14.15-16.00 in Peisestua

– Thursday at 14.15-16.15 in Peisestua

• Style will vary: – PowerPoint for review material– Blackboard for derivations– Sometimes I will sit at the computer, ”coding” live– Sometimes the ”lecture” will be a workshop where you either

code or do analytic calculations

• I will give most of the lectures– David Mota will give one of the GR lectures

• If people are interested, we’ll organize a weekend trip to the mountains (Valdres), where we’ll go through the first milestone– We do have internet access there..

Evaluation

• The evaluation will consists of two parts– Written exam – 70% of the grade– Project – 30% of the grade

• The project will consist of four milestones, each counting 25% of the project score– Deadlines are February 18th, March 18th, April 29th

and June 8th

• Date for exam is not settled yet– Open for suggestions from you

The project• The project forms the skeleton of the

course

• What are you supposed to do?– Compute the CMB temperature power

spectrum given cosmological parameters!

• How will you do it?– Write a computer code that solves the

linearized Boltzmann and Einstein equations for photons, baryons and dark matter

– Follow step-by-step procedure; the code will be built up piece by piece

• Why will you do it? – Completing this project will form an

excellent foundation for both theoretical and observations Master and Ph.d. projects

More on the project• Four milestones:

1. ”The background cosmology” (February 24th)• Solve the Friedmann equations, to know how the average, large-scale

and uniform space itself behaves

2. ”Recombination” (March 22th)• Compute the electron density of the universe as a function of time, to

know how often photons scatter at any time• Done by solving the Saha and Peebles’ equations

3. ”Evolution of matter in the universe” (April 14th)• Track the evolution of a single Fourier mode from just after inflation until

today, by solving the Boltzmann and Einstein equations in space and time

4. ”The CMB power spectrum” (May 31st)• Compute the CMB temperature spectrum, by averaging the photon

fluctuations over all scales and random realizations, and projecting them onto a sphere

Rules for the project• Deliverables:

– For each milestone, a short report (~1-2 pages of text, not counting figures) is to be written

– Computer code is to be submitted using Mercurial

• Collaboration:– No collaboration on ”future” milestones– No restrictions at all on passed milestones; copy codes if you

want!– Note that I should be considered a legal aid; do ask me if

something doesn’t work or is unclear – I’ll do my best to help!

• Grading:– Each milestone can give 25 points– Errors, bad coding practice will lead to lost points

• Note: Coding style gives points; write clear and well documented code!

Programming language?

• You are completely free to choose whatever language you want

• However, I only know F90 very well, and if you want help from me, you better choose F90 too.

• Recommendations:– If you trust yourself to be an experienced

programmer, choose whatever you are most comfortable with

– If you are less experienced, choose F90, so that I can help you out if and when you get stuck

Exam

• Written exam will be held ~10th to 15th of July– Suggestions?

• Problems will be a mix of – analytic calculations

• e.g., linearize some equations

– interpretation of plots derived during project work• e.g., what does this plot of the visibility function tell us?

– questions on physical intuition• e.g., what is the reason that the third peak is higher than the second

peak in the CMB spectrum, if the baryon density is high?

• Last year’s exam (and test exams) are available online

AST5220 vs. AST9420

• Main differences are:

– Ph. D. students will have to implement support for neutrinos and polarization in their computer codes

– One problem will be different on the final exam

• Note that only the AST5220 web pages will be continuously updated, but not the AST9420 pages

Textbook, curriculum etc.

• The curriculum is defined by– Chapter 1 to 8 in ”Modern cosmology” by Scott Dodelson

– The material covered in the project work

• In addition, there are several other useful sources of information:– ”How to calculate the CMB spectrum” by P. Callin

– ”Numerical recipes”; pdfs are available online at www.nr.com

– For those who chooses F90 as their programming language, Bo Einarsson’s online reference is highly recommended

• http://www.nsc.liu.se/~boein/f90/

– And you will learn how to use Mercurial for version control

Comparison with earlier years

• Main differences from earlier years (before 2010):

– 30% less material covered in twice as many lectures

– Fewer heavy-duty analytic calculations

– More numerical calculations

– Hopefully tighter interaction between students and teachers• Whenever something is unclear, come and ask me, and we’ll try to

figure it out!

Tips and hints!• Set up your coding environment (editor, directories,

Makefiles, Mercurial etc.) as soon as possible!– You don’t want to struggle with infrastructure problems just

before a deadline

• Take a quick look at the project summary pages, and keep the various sections there in mind as we go along

• If possible, spend a weekend reading through chapter 1 to 8 in ”Modern cosmology” from start to finish, early in the course– You won’t understand everything, but you will get a rough idea of

what we are going to do, and even more importantly, why.

• As you start programming, you will probably find Callin (2005) even more useful than Dodelson!

Practicalities

• Email addresses

• User accounts at ITA

• Exam date?

• Laptops?

• Mountain trip?