For centuries, scientists have suspected that the Universe was not static but, without a model or proof.
If the Universe is static and filled with stars, any direction one looks in the sky is supposed to end eventually on a galaxy of stars. The night sky then ought to be very bright.
Many scientists have thought about this loudly, but it is credited to the German astronomer, Heinrich Olbers (1757 – 1840), who explained it well. This is known as Olbers’ paradox, or the Dark Night Sky paradox, and was put forward by him in 1823 and later re-formulated in 1826.
Heavenly bodies and interstellar dust in space are expected to absorb light from the stars and re-radiate the light in a very short time. Over time in a static Universe, these bodies are expected to get so hot that the night sky will be filled with their re-radiated light.
In fact, the night sky should have been as bright as the surface of the Sun.
But this is not so.
It was assumed that this is because the heavenly bodies are not static, and are always moving. This is why the night sky is dark.
The model that the Universe was not static was developed in 1917 by the Dutch astronomer, William de Sitter.
While the Universe is not static, it was difficult to imagine it then, as expanding.
A full explanation, with measurements, came from the American astronomer, Edwin Hubble, who in the 1920s discovered that the Universe is expanding.
An expanding Universe reduces the energy radiated by the galaxy of stars on other bodies which can accumulate over time. That then, is the reason that the night sky is dark and not bright.
Estimates of this expansion according to Hubble were then used to calculate, as if due to some physical force, there is a Big Crunch.
Scientists say that should not bother us now as it will take the same 13 billion years that the Universe has been existing to get to the initial size that it started-off.
photo credit: memim
