| By considering the path of a photon, show that the comoving proper distance between an object and the origin is given by | |
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| where te is the time of emission and to is the time of observation. | [2] |
| Hence show that, in an expanding universe, the observed light will be redshifted such that | |
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| where λe is the emitted wavelength and λo is the observed wavelength. | [4] |
(2008 Q5(a).)