In fact, in some forms of the Big Bang theory, the universe's expansion causes an overall decrease in average temperature. In contrast, an expanding universe continually increases its volume, which accommodates the increasing quantity of energy produced by stars, therefore the temperature of the universe does not increase.This kind of universe heats up over time ( example). A static universe, one that is not expanding, cannot dispose of stellar energy.But the Big Bang theory and the expanding universe turn out to be the best answer to Olbers' question. It is important to realize that these advances in cosmology did not take place to answer Olbers' Paradox - in fact, many of the workers in this field may have forgotten that the question had even been posed. Another scientist, Fred Hoyle, coined the name "Big Bang" to disparage this idea, but the term became popular and has prevailed to the present day. In 1948, Russian-born physicist George Gamow took the next step by realizing that if all the galaxies are flying apart at high speed (an idea originally proposed by Georges Lemaître), the entire universe must have been concentrated in a single point at some time in the past. It turns out that a different version of this everyday effect applies to light as well - if an astronomical object is moving away from Earth, its light will be shifted to longer (red) wavelengths 1. This conclusion is based on a cosmological effect roughly similar to the everyday "Doppler shift." Doppler shift is what makes a car's horn sound lower-pitched as it moves away from you. Click here for an example of doppler shift.
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