| The picture above shows the power spectrum of the CMB as measured by WMAP and the ground-based experiments CBI and ACBAR. Explain, quantitatively if possible, | |
| (i) why the main peak is at an angular scale ∼1°, and what cosmological parameter is measured by the position of the peak; | [4] |
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You're asked to answer this "quantitatively if possible", so you should do a
calculation here. It isn't necessary to have the numbers exactly right –
an answer of the order of 1° is needed, but if it turns out to be 2°
that's no big deal (you want to show that it isn't 10° or 0.1°). As the second part of this question just wants a one-sentence answer, the likely mark breakdown [and, indeed, this was the actual mark breakdown] is 3+1 rather than 2+2. |
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| (ii) how the smaller peaks can be used to distinguish between baryonic and non-baryonic contributions to the density. | [3] |
| Here there is not much hope of answering quantitatively, since deriving the expressions governing the height of the peaks are beyond the scope of this course (the question did say "quantitatively if possible"!). So what you are being asked to do here is to explain the mechanism that relates the relative heights of odd and even peaks to the baryonic matter density. |
(2005, part of Q8.)