Our universe may contain a hundred billion galaxies, each with billions of stars, great clouds of gas and dust, and perhaps scads of planets and moons and other little bits of cosmic flotsam. The stars produce an abundance of energy, from radio waves to X-rays, which streak across the cosmos at the speed of light. Yet everything that we can see is like the tip of the cosmic iceberg. More is unknown than is known. This is because everything and anything ever observed or detected with all our instruments including people and stars, you and me, constitute only 5% of the bulk created at the time of big bang. One may think, if it should even be called “normal” matter at all, since it is such a small (insignificant) fraction of the universe. The remaining 95% is mysteriously dark comprising (68 % dark energy and 27 % dark matter). Most of our universe is hidden to plain sight. This leads us to understand that what we do not realize by sight is much more in quantity and may be in significance than what we realize by sight. One is reminded of the adjuration in the verses 38-40 in Chapter 69 of the glorious Quran where Almighty bears witness to the truth of HIS prophet by choosing the following heavy weight words “But nay! I swear by all that ye see and all that ye see not that it is indeed the speech of an illustrious messenger”. The visible universe is made of protons, neutrons, and electrons bundled together into atoms of different tangible substances, living and nonliving. On the other hand, dark matter is invisible to light or other forms of electromagnetic radiation, making it undetectable to current instruments. But scientists are confident of its existence because of the gravitational effects it appears to have on galaxies and galaxy clusters. In fact, the existence of dark matter is so widely accepted that it’s part of the so-called standard model of cosmology, which forms the foundation of how scientists understand the universe’s birth and evolution. Without it, we can’t explain how we got here. But at the same time, that lofty status puts pressure on cosmologists to find definitive proof that dark matter exists and that their model of the universe is correct. For decades, physicists all over the world have employed increasingly high-tech instruments to try and detect dark matter. So far, they haven’t succeeded. From this one can get a sense of the boastful claim of our proud LORD when HE says, “I know what you don’t know.” This darkness is also in context of our knowledge as would Africa be called a dark continent till it got discovered later. Galaxies in our universe seem to be achieving an impossible feat. They are rotating with such speed that the gravity generated by their observable matter could not possibly hold them together and logically they should have torn themselves apart long ago. The same is true of galaxies in clusters, which leads scientists to believe that something we cannot see is at work which is giving these galaxies extra mass, generating the extra gravity they need to stay intact. This strange and unknown matter was called “dark matter” since it is not visible. Astronomers are more certain about what dark matter cannot be than what it can be. As for instance it can be said with great confidence that dark matter is not smoke or clouds or antimatter or black holes but something else that we are yet to understand and aim at hitting. It is a well known fact that the expansion of Universe is halted by the force of gravity. Previously, physicists had assumed that the attractive force of gravity would slow down the expansion of the universe over time. But when two independent researcher teams tried to measure the rate of deceleration, they found that the expansion was actually speeding up. Scientists now think that the accelerated expansion of the universe is driven by a kind of repulsive force generated by quantum fluctuations in otherwise “empty” space. What’s more, the force seems to be growing stronger as the universe expands. For lack of a better name, scientists call this mysterious force as dark energy. In short, dark matter slows down the expansion of the universe, while dark energy speeds it up. Dark energy is the latest addition to the contents of the Universe. Originally, Albert Einstein had introduced the idea of an all-pervading ‘cosmic energy’ before he knew that the Universe was expanding. However, in the 1990s observations of exploding stars in the distant Universe suggested that the Universe was not just expanding but accelerating as well. The only way to explain this was to reintroduce Einstein’s cosmic energy in a slightly altered form, called ‘dark energy’. No one knows what the dark energy exactly might be. I don’t know what Shakespeare meant by saying, “The prince of darkness is a gentleman”. But if brought to my context, it fits the hero who cracks the mystery of darkness. However according to Christopher Pike, “Darkness approaches from outside. I feel no light inside me strong enough to resist it.”
Dr. Qudsia Gani, Assistant Professor, Department of Physics, Cluster University Srinagar