The deceleration parameter in `tilted' Friedmann universes

Understand

Large-scale peculiar motions are believed to reflect the local inhomogeneity and anisotropy of the universe, triggered by the ongoing process of structure formation.

• As a result, realistic observers do not follow the smooth Hubble flow but have a peculiar, `tilt', velocity relative to it.
• Our Local Group of galaxies, in particular, moves with respect to the universal expansion at a speed of roughly 600~km/sec.
• Relative motion effects are known to interfere with the observations and their interpretation.