In the last article, we have understood general relativity, special relativity and the brilliant thought process of Albert Einstein that came up with these concepts. In this article, we will learn the concepts of “Dark Matter” and “Dark Energy.” Before we dig in, as we observed all the modern and important concepts of modern physics, came to the existence when the classical laws of physics failed to explain the phenomena that were happening.

Dark Matter: Dark matter is a substance which has hypothetical elements which do not interact with light and cannot be seen. As they cannot be seen, it is called dark matter. In physics terms, It contains particles that do not absorb, reflect, or emit light, so they cannot be detected by electromagnetic radiation.

According to math, 85% of the universe is made of dark matter. If we cannot see it, how do the scientists know that 85% of the universe is made of dark matter? To understand this we need to go back in the history and understand it.

The foundations of dark matter go back to 1600s. When newton presented his theory of gravitation, some astronomers questioned there might be particles that don’t or emit very less light. As there were no proofs, these arguments were not considered serious. In 1933 a Swiss American astronomer named Fritz Zwicky observed that mass of a coma cluster ( a cluster is a group of galaxies) has 400 times more mass than the visible mass through light.

He named it Dunkle Materie (‘dark matter’). According to the basic law of physics, energy can neither be created nor be destroyed, it can be transformed from one form to another form. According to mass equivalence from special relativity, Energy and mass are equivalent or interchangeable. If these are true then what is the 400 times mass that is visible light and general principles of quantum theory? There must be particles which are not visible. Thus came the concept of dark matter.

In 1970s, there came another observation which led to the strong proof for dark matter. Stars move around the center of the galaxy in their specific orbits in their respective speed. Two scientists named  Vera Rubin and Kent Ford discovered that, the objects, stars which are at an edge in a galaxy , move at the same speed to the objects that are closer to the center of galaxy. This violates newtons laws of motion.

There must be some invisible particles which determine this phenomenon and thus came a mathematical proof for Dark matter. NASA used Hubble telescope to find the dark matter and that is the cherry on the top and empirical proof for dark matter. NASA captured many images but the clearest one was in 2017.

Image credit : NASA

 A new observation of gravitationally magnified faint galaxies far in the distance behind a massive cluster of galaxies is shedding new dark on the subject. This image from the Hubble Space Telescope indicates that a huge ring of dark matter likely exists surrounding the center of CL0024+17 that has no normal matter counterpart.

What is visible in the above image, first and foremost, are many spectacular galaxies that are part of CL0024+17 itself, typically appearing tan in colour. Next, a close inspection of the cluster centre shows several unusual and repeated galaxy shapes, typically bluer. These are multiple images of a few distant galaxies, showing that the cluster is a strong gravitational lens. The relatively weak distortions of the many distant, faint blue galaxies all over the image, however, indicate the existence of the dark matter ring. The computationally modelled dark matter ring spans about five million light-years and has been digitally superimposed to the image in diffuse blue.

So far, we have understood the concept of dark matter. Now we will try understanding the concept of Dark Energy.

Dark Energy: It is a type of energy which is responsible for the fast movement of the objects in the universe and therefore the universe. In physics terms, Dark energy is the name given to the force that’s causing the rate of expansion of our universe to accelerate over time, rather than to slow down.

Till now, we don’t know the exact properties of dark energy. This violates the principle of gravity in the universe. According to the properties of gravitational force, the expansion of the universe and the force between two galaxies, stars, planets etc must be constant. But with the help of hubbles telescope and mathematical calculations we found that the expansion of the universe is accelarating.

As we do not know the cause, we named the energy caused for this as dark energy. Till date scientists were not able to determine the form of energy or the properties of it.

If we can study the properties of dark matter and energy, we can have the answers for the questions like, “what was before the big bang?”, “How did the universe originate?” and more important secrets of this mystical universe. Let us hope that day comes very soon.

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