The model assumes that general relativity is the correct theory of gravity on cosmological scales. It emerged in the late 1990s as a concordance cosmology, after a period of time when disparate observed properties of the universe appeared mutually inconsistent, and there was no consensus on the makeup of the energy density of the universe.
Some alternative models challenge the assumptions of the ΛCDM model. Examples of these are modified Newtonian dynamics, entropic gravity, modified gravity, theories of large-scale variations in the matter density of the universe, bimetric gravity, scale invariance of empty space, and decaying dark matter (DDM).[2][3][4][5][6]
^P. Kroupa, B. Famaey, K.S. de Boer, J. Dabringhausen, M. Pawlowski, C.M. Boily, H. Jerjen, D. Forbes, G. Hensler, M. Metz, "Local-Group tests of dark-matter concordance cosmology. Towards a new paradigm for structure formation" A&A 523, 32 (2010).
^Pandey, Kanhaiya L.; Karwal, Tanvi; Das, Subinoy (2019-10-21). "Alleviating the H0 and S8 Anomalies With a Decaying Dark Matter Model". Journal of Cosmology and Astroparticle Physics. arXiv:1902.10636. doi:10.1088/1475-7516/2020/07/026. S2CID119234939.