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The exam and project have now been graded and will appear in a few days on StudentWeb.
The project results were very good this year with an average score of 90% and a low spread (most of you got 80-100%).
The exam results were not as good as this with an average of 70% and a big spread from 40% up to 90%.
The project counted 50% and the exam 50% for the final grade and it was computed from A = 92-100 %, B = 77-91 %, C = 58-76 %, D = 46-57 % and E = 40-45 % (but if you were within 1-2% of a higher grade we pushed it up).
If you have any questions about your grade just ask for a justification of the grade via Inspera and we will get back to you.
Congratulation with completing the course. We have put up a (rough) example solution to the exam at [ https://cmb.wintherscoming.no/pdfs/exams/ast5220_v24_eng_with_answers.pdf ].
We aim to have the exam and the project graded before the end of the month (~26 June).
If there are any final questions before the exam then we can do that in the usual lecture slot 1215-1300 on Tuesday (tomorrow).
We have received your reports and should have replied with "Received" on all of them so you can be sure all is ok. In case you have delivered and not received a confirmation then let us know as soon as possible (just in case there are issues with devilry).
We will have a final project session if you have any last minute questions on (Tuesday 4th 1315-1400) combined with us going through some old exam questions (Tuesday 4th 1400-1500).
We will focus on the exam from 2010 (found here) as this does not have solutions posted on the website. Take a look at the following problems before coming:
Problem 1 - “Background questions”
Problem 2 - “Physical interpretation of Phi”
Problem 4 - “The Boltzmann equation for free photons“
The goal with this session is to train for the exam by having you guys doing the problems together and then presenting the solutions (instead of me solving problems for you).
If you want a session to go through exam problems and train for the exam fill out this poll [ https://doodle.com/meeting/participate/id/bqM90MGb ]
There will be a project session tomorrow, Thursday, at 1400-1530.
From the Doodle poll we will do:
Wednesday 1300-1400 and Thursday 1400-1500
If you want a session this week fill in the poll https://doodle.com/meeting/organize/id/av952Ere
We will meet tomorrow at 1400-1530 at ITA.
Fill out the doodle poll if you are interested.
I will try to have all the feedback ready for next week.
Milestone IV is availiable at https://cmb.wintherscoming.no/milestone4.php
The tentative final deadline for handing in the whole project is Friday 7th of June.
As agreed upon in the lecture today, there will be a session this week on Friday at 1315 in room 303.
I got some questions regarding Phi and Psi and which one is really the gravitational potential? Both of these are informally referred to as “Gravitational Potentials” in the literature and we cosmologist often mix up what we call them.
In most derivations of the Newtonian limit of GR we find that its the g00 component (i.e. “Psi”) that gives us the Newtonian equations (see e.g. this):
x’’=-DPsi
D^2 Psi = 4piG rho
This is why “Psi” is perhaps most often called the Newtonian potential in the literature (see e.g. the discussion in Bertschinger and Ma).
If we look at the perturbations we are implementing in the Newtonian gauge (in the sub-horizon limit k >> Hp where we can ignore small terms like Psi and Phi’ for big terms like k^2 Phi and “delta”’s) then they can be written:...
The poll says Thursday 25th April at 1315-1500 (I will be away 1400-1430) and we will also do Friday 1400-1500. Room 303 ITA.
For Thursday: room 303 was taken so we will be in the ITA basement.
Fill in this poll: https://doodle.com/meeting/participate/id/b6zWrNnb
We will have a session Wednesday 17 April 1315-1400 and Thursday 18 April 1415-1500 in room 304.
In the lecture on Monday we will focus on Milestone 3. We will go through the project (both in terms of what you are to do, but also discuss the physics taking place so you know a bit more what to expect from your calculations).
It was generally better on all aspects than last time which is good. Here is just a few points to keep in mind:
- Some of you write that recombination happens as soon as k_b T = 13.6 eV, but actually it happens when k_b T ~ 0.3 eV or so. Remember that the photons have a Planck distribution so there will be photons with high energy even though the mean temperature is less than 13.6 eV. And since there is almost a billion photons per baryon (n_photon / n_baryon ~10^9) in our Universe there will be enough photons with high energy to delay it significantly.
- When it comes to the approximation sqrt(1+x) = 1 + x/2. Remember that the error is O(x^2) so if you apply this when |x| < eps then the error is ~eps^2. Some used eps = 0.1 which is way too high.
- Remember to always give some physical insight into the quantities you are introducing, if possible, like tau, g, r_s. Most of you do a good job here.
- Regarding last scat...
The description of the second milestone of the project can be found here: https://cmb.wintherscoming.no/milestone3.php
If you want feedback (highly recommended) then the deadline for handing in the report is Tuesday May 5th. If you have any questions send me (Hans) an email.
I'm free on Wednesday or Thursday if you want an intro to the project (tell David in lecture Tuesday if you want this).
I got a request for a last minute session for milestone 2. I will be in 303 at 14-1515 today in case anybody is interested.
We will have a project session on Thursday 21 Mar 1415-1530 and Friday 22 Mar 1415-1530 in Room 303 at ITA.
Update: some people could not make it at 14 Thursday. If you are one of those then you can come at 1315 (I'll be in the kitchen or peisestua if 303 is busy).
Figures:
You have generally done a good job here. The figures are nice.
Theory and implementation:
Again generally good. Make sure all relevant things are included. E.g. if you want to talk about 1sigma constraints you should add some details about how these are computed.
Demonstrating your code is correct:
Some of you have done a good job on this, while some of you have very little. If it is possible to do a simple analytical estimate for what quantity X (e.g. in the radiation dominated regime you can show that Hp ~ 1/a and eta ~ a so we should have Hp’/Hp = 1 and eta Hp/c = 1 in this regime) should be then this is a nice and simple thing to include in the plots or simply mention it when you discuss the results. This will not always be possible, but the few places you can easily do this then this is a good idea.
MCMC fitting:...
The description of the second milestone of the project can be found here: https://cmb.wintherscoming.no/milestone2.php
If you want feedback (highly recommended) then the deadline for handing in the report is Tuesday April 2nd. If you have any questions send me (Hans) an email.
I'm free on Thursday or Friday if you want an intro to the project (tell David in lecture Tuesday if you want this). I'm away next week, but we can also do a project session in 2 weeks time.
The results generally look very good. Most of you have managed to get the correct results. The thing that separates the reports most is the writing. Some have managed to write almost too much and some have not written much at all yet.
It is not easy to explain all the things in all the plots: we are working in Fourier space and with multipoles and what have you, but let me give a few pointers on this.
In general when it comes to explaining the results one way to start is to forget about the specific plots and think of it as writing a story of how structures in CDM, photons and baryons form from early times till today. In telling this story you need to bring in the important events and the physics that goes on. We don’t expect you guys to explain every little detail about the plots, this is not the goal, we wa...