How Our Universe Will Die.

Our universe is big. It is unfathomable and infinite. We cannot predict it's size and shape. We think that the universe is eternal but its not true, everything have its own destination and demise. None of us are going to live forever. Even the biggest stars and galaxies in the universe will die after billions of years. This is a very serious concequence about the universe that how it will end and what will happen to us. We are living on a small blue planet that becomes invisible on the map of our universe. Our universe is approximately 14 billion years old. So what would happen to us when universe started to taking its last breathe. Everything comes to an end. Everything tends towards the state of minimal energy state. And because of this, three possible and dramatic apocalypse are waiting for us.

So let's explore...................................................

To understand this event we must first understand that what decide the future of our universe. You must have been fimilar with- "Dark Energy". The story of dark energy had began in 1998, when the scientists observed a new supernova - a type '1A supernova'.
"The brightness of the explosion of such stars is almost always same so measuring the brightness of the explosion as seen from the Earth one can determine the distance to the place where it occurred."

"There is another way to determine distances in the space, it is called 'redshift method'. In this method scientists use to measure the redness of light coming from the celestial bodies. When the light from a distant objects flies towards the Earth it gradually shifts to the red part of the spectrum. So measuring the redness of light from distance objects one can determine how far that object is from us".

According to the first method the new supernova was seven billion light years away from us and according to the second method it was twelve billion light years away from us. So where that additional 5 billion light years of distance came from?. The only way to explain those extra five billion light years is to assume that our universe is expanding and that expansion is constantly accelerating. So scientists theorised a new type of topic "Dark Energy", that is responsible for the expansion of our universe. In nutshell, it is like "anti-gravity". If somehow we developed an spacecraft, which travels at the speed of light, then also we can't explore most of our universe, we will be limited to the local group of our galaxies which includes the MilkyWay, the Andromeda galaxy and magellanic clouds.

Even if you sat down now on a ship, which travels at the speed of light, then also you could never leave the local group, because all other galaxies and clusters including our local group will fly away from you faster than you can approach them. Scientists believe that the dark energy is evenly distributed throughout all of the universe and most likely always had and always will have a constant density value.

According to astrophysicists the dark energy can always have three possible values that is:-

               Less than -1, Greater than -1 and
              Equal to -1

So now let's starts our journey to the death of the universe.
1.The Big Rip:

If the density of the dark energy is less than -1, then the death of the universe is occur as "The Big Rip". According to the scientific research and observations, the lowest possible value of the density of the dark energy is, "-1.08". So in this case everything in our universe will end almost after the 80 billion years. All the observeable universe expect for our own galaxy, the local group will fly away from us forever. All the things present in the universe will accelerate until the speed of this expansion itself reaches the speed of light and after this we won't be able to see anything, expect darkness.

Beyond our cluster the first most distant groups of galaxies will started to disappear in about ten billion years. The nearest group will started to disappear after about sixty billon years.  About two hundred years before the Big Rip our local group will begin to distorted.Due to the collision, at that time there will be a new largest combination of galaxies including our own Milkyway and Andromeda. About a dozen of other small galaxies that somehow not merged into this largest group will orbit around it.

60 million years before the Big Rip, this new Galaxy, which scientists loved to calling "Milkomeda", will begin to lose stars from its periphery and will completely disintegrate in another 40 million years. Solar system will started to disintegrate after a few months before the end of "Milkomeda". The remnants of the solar system will stop spinning around the corpse of our own dead sun, which now will shines as a white dwarf and it will then fly into the rapidly expanding universe about three months before the end. The planets will started to broken about an hour before the end and the building blocks of our world, "the atoms", will started to disintegrate in a nanosecond just before the final teardown of our universe. Only non-composite particles such as electrons, quarks and gluons will remain from this wildest dance of death. They will never collide again or form any new thing. Each elementary particle will then move away from one another faster than the speed of light and nothing new will happen again.

Now let's move to our second theory................

2 .The Big Crunch:

If the density of the dark energy is greater than -1, then after 100 billion years from now the force of attraction so called "gravity", will win the war and the death of our universe will occur as something intresting and dramatic, and that is called "The Big Crunch". But still scientist can't understand clearly, how Dark Energy works. That's why the Big Crunch still remain possible because of the fact that the properties and features of the Dark Energy are not fully identified. So in this case it is impossible to tell that how much time we have left for this apocalypse. You can only describe the events that will come before the end without being exactly telling the time.

In this senario, all the galaxies, clusters and superclusters will started to converge including the size of our universe itself will started to shrink. When the size of our universe decreases five times from its current size to a diameter of 20 billion light years, all the stuffs like stars, planets, comets galaxies, clusters, etc, will merge into one supercluster. Since that time the galaxies will be the constituent elements of supercluster. These galaxies will still spin around each other and collide, but they will not be separated to any overwhelming distances. Unlike the previous version of the universe, where it takes light years to reach the distances between stars and planets, here in this one you can reach any place, anywhere you want to go unless moving at the near speed of light.

When the universe shrinks to about one billion light years the superclusters will merge into one giant galaxy and the cosmic microwave background radiation tempreature will reach about 32° Fahrenheit (0°C) and all the rocky planets will become suitable for life if they have water on them. So this will provide a new opportunity for growing a new life, but only for a while. The cosmic background temperature(CMB) will increase furthur for millions and even billions of years. The tempreature will  increase higher and higher
and the space will become smaller and smaller.

Finally, the atoms will split and disintegrate and everything will return to the state like that before the big bang. And at the end the universe will finally consists of one single dot of infinite density, tempreature and mass. What will happen next is unpredictable, because modern physical laws don't apply in such place, but there is a possibility that the big bang will happen again and a new universe will born again.

Now let's move to the third theory....................

3.The Heat Death:

If the density of the dark energy is equals to -1, then the universe will die a death called, "The Heat Death". In this case, the universe will slowly but infinitely expand at the constant rate. The clusters of galaxies will forever fly apart, but the object within the clusters will remain tightly bound by the gravity.

After a few 100 billion years, the galaxies will run out of their supplies of dust and gas, which are necessary for forming stars. So no new stars will form and the main scource of light will be red dwarfs and small dull stars. After about 10 trillion years the last remain red dwarfs will stop glowing and will turn into black dwarfs. The universe will turn into a deep  and dark place. Only there will be some neutron stars and white dwarfs which will cajole our universe with their dim light. Gradually, all the matters will be eaten up by our lords of nothingness called "The black holes", which will then grow to unimaginable sizes for trillions of years.

After the 1000 trillion years all the black holes will evaporate due to the hawking radiation. This happens because the photons with a very very low probability can escape beyond the event horizon of a black hole. So over a long period of time the black holes will evaporate leaving only th he photons, electrons, quarks and gluons in the universe. Occasionally, the electrons and positions will collide forming positronium atoms and immediately they annihilate. And then the universe will turned into a deep frozen and dark place because there will be no other sources of light will remain in the universe at that time. The Thermal death has come.

If it sounds like a nightmare to you then don't worry. Because at present we have a beautiful universe with full of shining stars and galaxies. No matter what happens after billions and trillions of years from now, we should enjoy that we are lucky to live in the world that is full of colours and diversity. At this time we can learn many thing about our universe and rejoice it's beauty, because it is wonderful.