dark energy and dark matter : the cosmic mystries

Dark energy and dark matter... the two cosmic unknowns...

By today, it is very well known that a our universe is expanding at lightning fast speed and all the constituents of the universe is falling apart. This expansion and separation has begun from the event of the big bang and its rate have grown higher as time passed by and still counting. It is expected that a day would come when our sky would not look like what we see today. The heavenly bodies, the distant stars from the far located galaxies would move away... there would be only a dark sky with few bright dots. That would definitely not be so pleasant at all... 

Since we know that the universe is not expanding at a uniform rate, we father the idea that there must be something which is causing the expansion and there must be something which is retarding the expansion.  The composition of these accelerating and regarding factors is very vital and a minor change in it can change the fate of the universe and its contents.

The universe is full of matter and attractive and repulsive forces from between the tiniest particles to the largest galaxies. In 1998, an observation made by the HST( Hubble space telescope) on some distant supernovae revealed that the universe is not is expanding on a accelerated rate, unlike what scientists thought. Before this discovery, it was believed that the expansion is gradually slowing Dow due to gravity and someday everything would collapse into singularity, the state just before the big bang. The fact that universe in expanding at a accelerated rate was surprising and no could put put forwarnd any proper reason for it... but its was proved to be true. Following this many attempts were made to explain this fact but none proved to be proper. At last a name was given to this mystery, dark energy.

The dark matter... :

From this point, the question was what is dark energy ? What are its properties ? Why and how it came into its existense?

Although at present no perfect answer exists for these questions but some suggestions still hold good.

The truth is that the only thing is known about dark energy is that it exists because we know that it is the factor responsible for the expansion of the universe. Observations hav and calculations have revealed that the dark energy comprises of approximately 68% , normal matter that our instruments can detect is comprising about 5%. So what is rest ? The rest matter is named as dark matter wchih our instruments can't directly detect but its gravitational activities can't be detected. It is surprising that the billions of galaxies including our earth and everything in the universe that can be directly detected is approximately only 5% of the total universe.

This composition may seem surprising but the truth is that it decides the fate of our universe.

Attempts to sole the mystery of dark energy... :

Albert Einstein tried to solve theyatery of dark energy.

He said that empty space is not actually empty but some characteristic energy is filled the space. In fact this energy is a property itself of the space. This just one among the never ending properties of the space. Einstein described the first property as " there is possibility that more space may come into existence." Confused? This means that space is limitless.

He made another prediction considering the cosmological constant that as energy is property of the space itself, so its value can not decrease with amount of space. Intact as more space is added, the energy would increase. So this energy cause the universe to expand farther and faster with time. But till today, it is a matter of confusion about the relation between the value of cosmological constant and expansion of space. Infact the value of the cosmological constant is doubted.

If the above explanation is not correct then what can be better than this ? A new assumption was that the space is filled with something called "quintessence" . Now what is this quintessence ? This is nothing but a name given by the scientists to new dynamic energy fluid or energy field. This energy was explained in a dramatical way but it couldn't hold its grip for long as it did not make a lot of sense. They said that is something which causes the expansion of the universe and acts opposite in case ofatter and dark matter. Now it is probably clear that why this idea was dropped soon. It was never explained what it is made up of and how and why it intersects with what and even why does it exists... 

The next hypothesis is bases on the famous quantum theory of matter. It sataes that empty space is full of matter which continuously appear and disappear or more precisely speaking, they are temporary matter. But when physists tried to calculate that how much energy is constitute empty space, the result was a disaster. The number was of order 10¹²° , which is not acceptable till today.

So this theory also short lived.

The last but not the least answer is that the present einstiens theory of gravity maybe wrong. Einstein's gravitational theory is found to be correct for galaxies , the motion of all the bodies in the universe including the motion of planets around the sun. But if we reject the present theory then what could be a better one ? The more important question is the even if the new gravitational theory is able to explain the expansion of universe, will it be able to explain the rest cases as einstiens theory did ? There is no answer to this question at present but it is well understood that rejecting represent theory of gravitation is not easy and safe and getting a better theory is still needs far more information.

The dark matter... :

Enough talking about dark energy ! Now we have another big question. What is dark matter ? Most of us may think that dark energy isore important topic to be concerned about as it is causing separation of constituents of the universe. But I would like to remind you that this is not correct. We have already said that the composition of matter, dark matter and dark energy is very crucial in  deciding the fate of our universe. So keep in mind, dark matter us is equally important.

Though not fully but dark matter is much more understood as compared to dark energy. Though indirectly, it is possible to detect and understand dark after. It does not emit or reflect light Luke ordinary matter, but its presence can be determined by its gravitational effect on its surroundings. Using a technique called gravitational lensing, it is found that the dark matter's gravitational pull bends and distorts light coming from distant galaxies. Some scientists say that huge black holes may constitute these darkatyer and some say that massive compact halo objects (MACHO) or weakly intersecting massive particles ( WIMP) constitute these dark matters. MACHOs are brown dwarfs, white dwarfs fans weak stars whereas WIMPs are radically different form of matter left over of big bang .

Although many suggestions and hypothesis hold good uoto some extent, no single argument is able to completely reveals the mystery. Researches are going on at full speed and we expect there'll be an answer soon. An perfect answer ! 

There are many more about matter, darrk matter and dark energy. Everything is not possible to put down here... I've tried to present the entire set of important points only.

Hope you've enjoyed this.

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