- #1

ChrisVer

Gold Member

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## Main Question or Discussion Point

http://pdg.lbl.gov/2013/reviews/rpp2013-rev-cosmic-microwave-background.pdf

Here one reads in sec. 26.2.4 that:

I am not getting these statements. Also I find it difficult to understand, since most of the times, the power spectrum (eg. Fig. 26.1 in the above reference ) shows a figure of the amplitude versus on the lower axis the multipoles [itex]l [/itex] and on the upper axis the angles [itex] \theta [/itex]. If there is no one-to-one correspondence between [itex]\theta \text{-} l [/itex] how does these figures make sense?

Here one reads in sec. 26.2.4 that:

However it states that a single [itex]Y_{lm}[/itex] corresponds to angular variations of [itex] \theta \sim \pi /l[/itex].There is no one-to-one conversion between multipole [itex]l[/itex] and the angle subtended by a particular spatial scale projected onto the sky

I am not getting these statements. Also I find it difficult to understand, since most of the times, the power spectrum (eg. Fig. 26.1 in the above reference ) shows a figure of the amplitude versus on the lower axis the multipoles [itex]l [/itex] and on the upper axis the angles [itex] \theta [/itex]. If there is no one-to-one correspondence between [itex]\theta \text{-} l [/itex] how does these figures make sense?