The stars that we see in the night sky, speaks to us. Each star tries to tell a story of their lifetime. But it was our inability that we were unable hear or understand their words until the year 1998, when the first space telescope i.e,. the Hubble Space Telescope was installed. It was the HST that showed us that the Universe is much more complex than we thought. The complexity arises from a theory which physicist used to follow for decades. This theory is the Einstein's Theory of Gravitation. According to this theory the rate of expansion of the Universe must slow down with time. But the study of the various distant supernova explosions showed that the rate of expansion of the Universe at that time was much slower than today. With the advent of this surprising observation doubts on Einstein's Theory of Gravitation started to arise. But then Saul Perlmutter, Brain P. Schmidt and Adam G. Riess after studying the red shifts of different supernovas concluded that there was nothing wrong in the Theory of Gravitation. Wrong was in our Observation.
The Red shifts or the accelerated expansion of the Universe was due to the presence of an unknown, or undetectable presence of energy that is acting strongly against the gravitation due to the presence of 5% of matter in the Universe. This invisible form of Energy is termed as "Dark Energy".
