Dark Matter, Dark Energy

We as humans believe ourselves to be the center of the universe as we are alive and are made of something that is seemingly abundant in the universe, matter. From atoms to Galaxy clusters and nebulae, everything we see is made up of what we call normal matter but there's a somewhat less flashy and darker brother that goes unnoticed. We call it Dark matter. 

At a time in history, scientist believed that normal matter is the only type of matter that exists and proliferates our universe. This line of thought continues for decades until calculations were made to estimate the amount of visible matter in our universe. Fortunately, they were shocked by the result they got. From the approximations, the universe consists of <5% of normal matter which is now termed as Baryonic matter ( since baryons are it's basic building blocks). 

How? We see matter all around us it should make sense that the universe consists of mainly matter. But on finding that was not the case, it shows that what we call normal may not be normal at all. The remaining percent of matter is what fills the universe more abundantly but we can not see it. Hence, it is termed "Dark Matter".

Dark energy - Dark matter (just a simulated picture)

Dark Matter, Dark Energy

Some scientists could wrap their heads around the fact that a so-called "dark matter" proliferates the universe. From a standpoint, it makes absolutely no sense but it is actually unquestionably correct. In the year 1929, Edwin Hubble found that the universe is expanding but that's not all. That expansion is accelerating! After a brief rejection of the inference from the science community, the Hubble telescope(rightly named) was launched in the year 1990. It was able to peer deep into our universe and explore what we have never seen before. Its observation of the most distant galaxies and supernovae showed that a long time ago, the universe was actually expanding much more slowly than it is today. This bashed some ideas that gravity will eventually cause the expansion to slow down gradually. It was very unexpected and no one knew how to explain it, not even what's causing it. This discovery leads us to another enigmatic phenomenon called "Dark Energy". It can't be seen or measured with any of our equipment today but it affects the universe much more than any other form of matter or energy. It consists of ~68% of the universe signaling its influence on the rapid acceleration of the universe.

What is Dark Energy?

We do not know much about the mystery that is dark energy, but we know what it isn't?

• It isn't visible. All forms of energy we see, use and are accustomed to are measurable in a sort of way. From electrical energy, heat energy down to sound energy and nuclear energy, ways of measuring these forms of energy are known but that of dark energy escapes us till today.
• It couldn't just be a form of energy. An explanation for dark energy is that it is a property of space. The same way you and I possess energy is the supposed same way the universe possesses dark energy. Albert Einstein was the first to notice that empty space isn't nothing. It has many properties and dark energy is one of them. Since the energy is a property of space itself, it will not dilute as space expands. Rather more space equals more dark energy. Therefore, the dark energy density of space remains constant.
• It isn't dormant. Rather, it's flexible and dynamic. It fills up the fabric of space and has the opposite effect of normal matter and energy has on the universe. It isn't negative energy rather it defies gravity and expands space all the more due to one of its underlying and yet unequivocally mysterious properties.

Dark matter

We really have a primitive perception when it comes to things of space, don't we? How can we not be able to see something that makes up roughly ~27% of our universe? Though dark matter and dark energy are both invisible to us now, they're analogous to the Ying and Yang of the universe. You see, as dark energy creates a repulsive force that expands space and opposes gravity, dark matter does the exact opposite and creates an attractive force in line with gravity. This property was first theorized in 1933 by Swiss astronomer Fritz Zwicky, who noted that galaxies shouldn't be able to hold themselves together with only the matter we can see today. This attractive force exhibited is responsible for the magnificent and huge galactic structures we see today. Normal baryonic matter does not have the sufficient attractive force to hold together in massive structures like galactic clusters and galaxies.

Now if dark matter is that made up of what normal matter is made up of, what is it made up of?  There are two possible leading particles: Massive astrophysical compact Halo objects ( termed MACHOs) or Weakly Interacting Massive Particles (termed WIMPs).

©NASA, ESA, S. Band with (STScl) and the HUDF Team

Dark matter and dark energy combine for about ~96% of the known universe and each play important roles for the sustenance of the universe. Like earlier said, dark energy is an innate property of space. Without it, space wouldn't be what it is in its vastness and glory. Additionally, dark matter holds galactic structures together. Without it, the structures and systems we see today would be scattered all over the universe. Hence no formation of independent bodies like galaxies bit mainly chaos with little or no probability of surviving in the vastness of space. 

As a result, they are needed. Astronomer Dr. HongSheng Zhao of the University of St. Andrews School of Physics said; "Both dark energy and dark matter could be two faces of the same coin. As astronomers gain an understanding of the subtle effects of dark energy in galaxies in the future, we will solve the mystery of astronomical dark matter at the same time".

Dark matter, dark energy, the two most important properties in the universe have been around for a long time and will possibly be till the end of time. Our goal to decipher their mysteries started long ago and we are making groundbreaking discoveries about them. It's only a matter of time before we can see the unobstructed and explicit full picture of the universe with the paint and colors that are dark matter and dark energy.