Dark Matter and Dark Energy: The Invisible Constituents of the Universe

  Physicists say that only 5% of this universe is created of matter or atoms (electrons, protons, and neutrons). Then what is the rest 95% made of if not atoms? Well, we call that dark matter and dark energy! 

Illustration of Dark Matter

Dark Matter:

Earlier we thought that this universe of ours was made up of only baryons and leptons, i.e. electrons, protons, and neutrons. But subsequently, we found out that this theory was not fully accurate and only 5% of this universe is made up of visible matter. The rest 25% consists of "Dark Matter". Dark here is used because we cannot see this, yet we can only sense its presence because of its gravitational pull. We deduced that it has mass because it creates a gravitational field. 

An Image of a Cluster.
Pink here is normal matter and blue indicates Dark matter which is overpowering the pink one.
Image Credit: NASA

Dark Energy: 

It is more peculiar than Dark Matter because it takes up the rest of 70% of the universe. It repels gravity, and not only this, it is accountable for the expansion of the universe.

It is discovered in the 1990s. 

Image Credit: Symmetry Magazine

Discovery of Dark Energy and Expansion of the Universe:

Gravity, which seems to attract everything, must attract the universe to converge, rather than diverge and scatter as it is. But this seems not to be happening. The universe is accelerating and speeding up at an alarming rate, expanding away farther and farther and certainly not decelerating. Physicists concluded that an invisible force is responsible for this which is the exact opposite of gravity. They called it "Dark Energy". It must take up a massive amount of space, more than normal matter, even more than dark matter. 

The discovery of dark energy was a wonder for all the scientists and it still is, because nobody knows the true nature of dark energy and it hasn't been seen yet. The proper knowledge of dark energy could revolutionize Physics.

Expansion of the Universe.
Image Credit: BBC Sky at Night Magazine

Is Dark Matter a New Particle?

Many scientists and physicists think that dark matter could be a particular particle of its own that doesn't interact with normal matter particles. It must be too heavy to behave as dark matter and could imitate "neutrinos" but neutrinos themselves are too light and regarded as massless or "ghost particles". Understanding dark matter is as crucial as dark energy but still dark energy wins the race in mystery. Particle accelerators and Large Hadron Collider in CERN are being worked at to understand the nature of dark matter but none has been successful in fully understanding it.