The Hubble law relates the velocity () of the expansion of the universe to the distance () to the source. This simple physical law was established by E.Hubble who in 1929 interpreted the new observations into conclusion that the universe is expanding, and this interpretation of the evidence of redshifts found in starlight has been strengthen ever since. In simple words, the law states that the universe is indeed expanding in a way that further the galaxy receding from us, the greater its receding velocity. Nevertheless, several authors made a point that Hubble's observations suggested a quadratic rather than linear relation. The linear functional dependence was inspired by the De Sitter's model of the Universe, namely by his allegiance to general relativity. According to Capria, Hubble simply read his a priori expectations into his data[note 1] and to the end of his life did not endorse the view that his discovery was a decisive evidence for the expanding universe cosmology
According to J.Hartnett the Hubble constant is not truly constant but it has emerged that there is an inherent scale dependence to its value. Thus, its determination depends on method used and on the distances to the sources. The Hubble law written in an invariant way that enables one to derive a four-dimensional transformation similar to the Lorentz transformation is part of M.Carmeli's new theory of Cosmological special relativity.
- cf. "The outstanding feature, however, is the possibility that the velocity-distance relation may represent the Sitter effect, and hence that numerical data may be introduced into discussions of the general curvature of space."
- According to Capria, the value of Hubble constant depends on the cosmological model:
- Hartnett, John (2007). Starlight, Time and the New Physics. Creation Ministries International, 57-61. ISBN 978-0-949-906687.
- Moshe Carmeli (2002). Cosmological Special Relativity, The Large-Scale Structure of Space, Time and Velocity, 2nd Edition. World Scientific Publishing, 2, 117. ISBN 9-789-02-4936-5.
- Edwin Hubble (January 17, 1929). A relation between distance and radial velocity among extra-galactic nebulae 15: 168–173. Proceedings of the National Academy of Sciences. Retrieved on June 9, 2013.
- Marco M. Capria, Aubert Daigneaut et al. (2005). "6. The Rebirth of Cosmology:From the Static to Expanding Universe", Physics Before and After Einstein. IOS Press, 148. ISBN 1-58603-462-6.