That which we are accustomed to our attention or not he is strange. The night is dark because the sun is hidden and the light does not reach us, on the other hand, in light of the stars is not enough to brighten the night sky ... But, why?
This question has been following since the sixteenth century when Thomas Digges introduced the idea of \u200b\u200ba transition from finite to an infinite universe, maintaining the Copernican conception represented the sphere of fixed stars infinitely extended in altitude.
Johannes Kepler in the early seventeenth century was the following question: "If the stars are like our Sun and are distributed evenly space, why the sum of its light dazzles us and makes the sky glow by night? ".
This question is called Olbers Paradox in honor of H. Olbers, who popularized it in 1823. This is the apparent contradiction between the night sky is black and that the universe is infinite. If the universe is spatially infinite and contains an infinite number of stars, when we look at any point in the sky, sooner or later we should find a star in our line of sight.
An analogy that illustrates this situation was introduced by Otto von Guericke in 1672, saying the same thing happens in a dense forest where to look in any direction will inevitably find a tree trunk. 
What would you shine the sky?
Considering the stars as point objects of luminosities identical and uniformly distributed in an infinite expanse, the accumulation of all the light from an infinite number of stars would provide an infinite amount of radiation! Fortunately
stars are not points but have a finite area, the same way as in a forest nearby trees hide far, the disks of nearby stars conceal those of more distant. Thus, the brightness of the sky would not be infinite, would only take a certain number of stars to cover the entire surface of the celestial sphere.
But still, the brightness of the sky should be equal to the solar photosphere, which would make our environment was about 6000 º C!
eminent astronomers paradox arose and tried to resolve it.
T. Digges, in 1576, thought that the starlight was too weak to be visible to our eyes, because of the enormous distances that separate them from Earth.
In 1610, J. Kepler , rejecting the possibility of infinity of the universe, thought of the need to introduce a "cosmic frontier" that contains a finite number of stars, thus avoiding the idea of \u200b\u200ba field as bright as the Sun 
Edmond Halley studied the paradox in 1720, using an argument similar to that used by T. Digges almost 150 years earlier. 
Based on the work of Halley, Jean-Philippe Loys de Chéseaux began to study the paradox. Suggested that either the sphere of stars was not infinite or intensity light decreased rapidly with distance, perhaps due to the presence of some absorbent material in interstellar space. 
Later, in 1823, raised Olbers paradox, again turned to the possibility introduced by Chéseaux that space was not transparent to the radiation completely, so if you do not see the stars do not is because they are not there, but because their light has been absorbed by interstellar material before reaching Earth. 
The first intuited the right solution was not a scientist but a poet. Edgar Alan Poe in 1848 wrote: "The only way to understand the gaps of stars that telescopes find in innumerable directions, is to assume that the distance was visible in the background so immense that no ray of light that come from there have yet been able to reach us." 
That same year, John Herschel showed that the argument put forward by Chéseaux was not correct, because the material to absorb the radiation would heat up enough to start emitting radiation itself in an amount equal which received. Later in 1869, Herschel imagined an infinite universe but in which there were a number arbitrary directions in which no stars are observed. Taking up an idea in 1755 of Emmanuel Kant: a "hierarchical universe" which would star systems, now called galaxies, the galaxies are grouped into systems of galaxies (clusters of galaxies), which would focus on a higher level (superclusters of galaxies) and so on. Defended the idea that if the intensity of the clusters is reduced to increase their size, then in a hierarchical universe of infinite levels, solve the Olbers Paradox. Today, in math, this is called "fractal universe." But it is not a valid argument to solve the paradox because we now know that the universe is nearly isotropic, showing a similar look in all directions, a characteristic unbecoming a hierarchical universe. 
Johan von Mädler in 1861, regained the idea of \u200b\u200bPoe, but his work went completely unnoticed. 
Similarly happened to an article written by Lord Kelvin in 1901, which showed quantitatively that the travel time of light emanating from distant stars is greater than the lifetime of them. 
astronomer Harlow Shapley held, in 1917, the argument put forward by Kepler as the most important, although he did not appeal to the idea of \u200b\u200ba cosmic frontier. To Shapley the universe was formed by a single island (one star system infinity) in the middle of an ocean of empty space. 
In 1948, Hermann Bondi suggested that because the expansion of the universe causes light to be perceived in the distance red (lower energy), the further they are the stars, reach their lowest energy radiation up to us and we can not observe. There are still many scientists who believe that the universe's expansion is the cause the darkness of the night, but not quite right, the expansion of the universe only contributes to the result becoming the darkest night, but not the main cause. the final solution provided Edward Harrison in 1965, combining the fact that light travels at finite speed and that the stars have a limited life. Given these two facts, in light of many of the stars needed to cover the sky has not had time to reach Earth, the time interval since these stars began to shine so far has not been enough for his radiation travel the great distance that separates us. However
... The night is not dark! The sky is not all black.
In 1965, Arnold Penzias and Robert Wilson discovered (without looking) the cosmic background radiation that fills all space and our eyes are not designed to perceive. But this is another story ...
Although the paradox is named Olbers, approach and argument to resolve Olbers suggested that they were not original (minus credit to other great scientists).
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