Here is my understanding of how the anisotropies of the CMB are used to determine the geometry of the universe:(adsbygoogle = window.adsbygoogle || []).push({});

The fluctuations represent fluctuations in temperature just at the moment of last scattering, and therefore are a 'fingerprint' for the fluctuations in density of particles.

We can measure how big these fluctuationsshouldbe and therefore compare the angular size of what we observe to what we expect, and the geometry of the universe determines how the photon path will distort the image, ie angular size of fluctuations should be unchanged form our prediction for a flat universe, or appear larger/smaller for a closed/open universe.

Firstly, am I right in thinking the above is true, and accurate to a simple degree?

Also, my main question ishowcan we calculate the expected size of a fluctuation on the sky? Is it something to do with the intrinsic properties of the material at that time, eg can we determine the temperature etc? if so,how?

Another issue I have is with the cmb power spectrum.

Im not really sure what this graph represents. The x-axis is of increasing spherical harmonic number or something, is it not? Ther more of them there are, the more fluctuations, and the fluctuations get smaller with increasing value of x-axis.

I dont really get what the y-axis is, and therefore have no idea what the physical interpretation of the "first peak" is.

Can someone explain this graph to me, in somewhat simple terms, and how it is used to determine the geometry of the universe??

Thanks

Dan

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# CMB Power spectrum/CMB anisotropies -> Geometry of Universe

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