Our best understanding of the universe is rooted in a cosmological model known as LCDM. The CDM stands for cold dark matter, where most of the matter in the universe isn’t stars and planets, but a strange form of matter that is dark and nearly invisible. The L, or lambda, represents dark energy. It is the symbol used in the equations of general relativity to describe the Hubble parameter, or the rate of cosmic expansion. Although the LCDM model matches our observations incredibly well, it isn’t perfect. And the more data we gather on the early universe, the less perfect it seems to be.
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Source: Phys.org