DARK MATTER AND DARK ENERGY

Manjit Ray

B.Sc 1^st Semester(Phy Major)

The visible universe- including the Earth, the Sun, other stars and galaxies are made up of protons, neutrons and electrons bundled together in to atoms. Perhaps one of the most surprising discoveries of the 20^th century was that these ordinary or baryonic matter make up less than 5% of the universe. The rest of the universe appears to be made up of a mysterious, invisible substance called dark matter (25%) and a force that repels gravity known as dark energy (70%).

What is dark energy?

It is more unknown than it is known. We know how much dark energy there is because we know how much it affects the universe’s expansion. Space has amazing properties. The first property, discovered by Einstein is that it is possible for more space to come into existence. Then one version that contains a cosmological constant makes a second prediction that ‘empty space’ can possess its own energy because this energy is a property of space itself. Another explanation of dark energy is that it is a new kind of dynamical energy fluid or field something that fills all expansion of the universe is and is the opposite of matter and normal energy. Some theorists have named this ‘quintenssence’ after the fifth element of the Greek philosopher’s. But if quintenssence is the answer, we still don’t know what it is like , what it interacts with or why it exists. So the mystery continues.

What is dark energy?

We are much more certain what dark matter is not than we are what it is. First it is dark means that it is not in the form of stars and planets that we see. Observations shows that there is far too little visible matter in the universe to make up the 25% required by the observations. Dark matter is not antimatter annihilates with matter. Finally we can rule out large galaxy-sized black holes on the basis of how many gravitational lenses we see. High concentration of matter bend light passing near them from object further away but we don’t see enough lensing event to suggest that such objects make up the required 25% dark matter contribution.