Thesis abstract:

«p»The Cosmological Principle (CP) posits that co-moving observers see the Universe as spatially isotropic and homogeneous at sufficiently large scales. The CP underpins our modern cosmological view, with isotropy and homogeneity inherently within the Friedmann–Lemaître–Robertson–Walker metric of spacetime in the standard concordance cosmological model, ΛCDM. The anisotropy of the Cosmic Microwave Background (CMB) from the ‘cosmic rest frame’ has been interpreted as evidence for the Solar System’s departure from the local Hubble Flow. The CMB temperature anisotropy (the dipole) places us with a peculiar velocity of 369.825 ± 0.070 km s¯¹ towards (l, b) = (264.021 ± 0.009°, 48.253 ± 0.004°). If the interpretation of the CMB dipole as a kinematic imprint from our peculiar motion is correct, we should find a kinematically induced dipole in our observations of other cosmological sources. Analyses of the number count dipole of cosmological sources find a velocity that generally agrees with the CMB direction but disagrees with amplitude, being significantly greater. This unreconciled tension has grown to question the fundamental CP. We further test the CP by investigating the effects of local structure and source evolution on the number count dipole by using synthetic catalogues of radio sources.«/p»