DARK ENERGY & DARK MATTER.

 What are Dark Energy and Dark Matter and how did they come about?

We know that Dark Energy (68%) and Dark Matter (27%) account for 95% of the mass density of the Universe with matter comprising of 5% of the remaining.  

When Einstein propounded his General Theory of Relativity in 1915 he later introduced a constant known as the Cosmological Constant in the year 1917 (signified by the Greek letter Lambda) into his theory in order to provide an explanation for the static universe idea which was prevalent at that time. 

This Cosmological constant was considered to be the energy density of space or of the vacuum. When in 1931 Hubble confirmed the expansion of the Universe Einstein abandoned this concept. So from the 1930’s to late 1990’s physicists assumed this constant to be zero.

It was discovered in 1998 through the Hubble Space Telescope that the expansion of the Universe is in fact accelerating, and this baffled the physicists and gave them the idea that the Cosmological constant would have a positive non zero value. The Cosmological constant is the possible explanation for Dark Energy.

The Universe that is visible to us is fully made up of Baryonic matter (that is matter made up of Protons, Neutrons and Electrons).  

Some scientific deductions of observed data on gravitation clearly indicate that there is much more amount of matter in the Universe that is not visible to us. This has been named as Dark Matter.

The Dark matter Dark energy cannot be observed by us directly because they do not interact with Baryonic matter and energy and are invisible to light. So we cannot know anything about it. But it does exert gravity and can be detected on account of the gravity it exercises.  

That means we know about only 5% of the matter in the Universe that is observable by us. The rest 95% is merely implied by the gravitation being exerted but we know nothing about it as none of our instruments are capable of discovering or measuring it.