There are 3 main pieces of evidence that support the big bang theory: a. evidence of the the universe. in the year edwin hubble observed that galaxies were generally receding from us provided the first clue that the big bang theory might be right b. the abundance of h, he, li) in the universe is almost exactly as what the big bang predicts. elements were first fused within the after the big bangradiation is the remnant heat leftover from the big bang.

There are 3 main pieces of evidence that support the big bang theory:

a.Evidence of the expansion of the universe.
In the year 1929, Edwin Hubble observed that galaxies were generally receding from us provided the first clue that the big bang theory might be right.

(Edwin Hubble announced that galaxies found outside our own galaxy (Milky Way), as observed in the year 1929, were systematically moving away from us, at a rate proportion to their distance from us.) 

b.The abundance of light elemets ( h, he, li) in the universe is almost exactly as what the big bang predicts. elements were first fused within the protons and neutrons after the big bang

(Nucleosynthesis is a term that refers to the formation of heavy elements from the fusion of lighter elements. A second after the Big Bang occurred, the temperature of the universe was extremely hot and filled with neutrons, protons, electrons, positrons, photons and neutrinos.)
 
c.Cosmic Microwave Background (CMB) radiation is the remnant heat leftover from the big bang.

(First predicted by Ralph Alpherin, the existence of CMB radiation was first observed by Arno Penzias and Robert Wilson.  The Big Bang was theorized as a hot place and expanded. The gas within that cooled down leaving radiation of the heat that was left.)

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