AST5220/9420 –
Course presentation
Hans Kristian Eriksen
17. 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:
”The background cosmology” (February 24th)
1.
•
Solve the Friedmann equations, to know how the average, large-scale
and uniform space itself behaves
”Recombination” (March 22th)
2.
•
•
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
”Evolution of matter in the universe” (April 14th)
3.
•
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
”The CMB power spectrum” (May 31st)
4.
•
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?