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The answer to the question about the age of the universe is Hubble Law

Hubble's law is the fundamental law of observation cosmology, which connects the distances of galaxies r from their so-called. Escaping velocities v (which measure is red shift z). This law specifies that these two quantities are proportional to each other, and the Hubble constant

I will create in future new post about age of Earth, that's very interesing for me