What Is Dark Matter?

Dark Matter

Ever since the phenomenal success of Isaac Newton in explaining the motion of the planets in 1687 unseen matter has been invoked to explain puzzling observations of cosmic bodies. At the Kitt Peak National Observatory in Arizona Vera Rubin and her co-worker Kent Ford measured rotational rates of number of distant galaxies by measuring Doppler shifts of bright clusters. Their results were surprising. The orbital speed of stars at the outer visible edge of galaxy is about the same as that of stars close to the galactic centre. The only explanation for the findings of Rubin and Ford that is consistent with Newtonian mechanics is that typical galaxy contains much more matter than what we actually see. In fact, the visible portion of galaxy represents only 5-10% of total mass of the galaxy. In addition to these studies of galactic rotations, many other observations lead to the conclusion that the universe abounds in matter that we cannot see. This unseen matter is called dark matter. Dark matter is thought to be mostly composed of exotic particles formed when the universe was a fraction of second old. Evidence suggest that the mass of dark matter in galaxies, clusters of galaxies and the universe as whole is about 5 or 6 times greater than mass of ordinary baryonic matter such as protons and neutrons. However, according to various calculations this dark matter is very small part of total dark matter.

Dark energy

Now we all know the famous, Big Bang Theory. We know the basics that the universe is still growing bigger. Now the question arises that how fast is it growing?

Earlier people thought that if it is solely growing due to the energy at the initial bang, it should get slower with time as the gravity might eventually get the better of it. But on further research, people found that, shockingly, the rate at which the universe is growing is NOT slowing with time but rather increasing. This puzzled a substantial number of scientists and researchers and so was born the theory of dark energy. This energy was held responsible for the speeding process of expansion that was inexplicable. Still, there is hardly any other theory that can further explain it with as much precision.

Thus, by definition, dark energy is an ‘unknown’ form of energy which is ‘hypothesized’ to permeate all of space, tending to accelerate the expansion of the universe.

The dark energy is more hypothetical than the dark matter. It is elusive and we barely know anything about it. It is thought to be very homogenous and not very dense. Also, it does not react with any form of fundamental forces except of course, gravity.

“Since it has a very rarefied un-massive form, it is unlikely to be detectable in a laboratory experiment.”