How our universe could meet its doom? The big freeze, big rip and the big crunch.

 We know about our universe's past: the big bang theory predicts that all matter time and space began in an incredibly tiny, compact state- called singularity- about 14 billion years ago. The singularity suddenly expanded and all of the matter was carried away from that point after the big bang, matter had cooled down to about ten thousand million degrees,  cool enough to form protons, electrons, and neutrons. The building blocks of atoms. For the next 300,000 years, the universe continued to expand and cool until the first atoms of hydrogen, the most abundant element in the universe finally formed. About 1000 years after the big bang. The gravitational attraction between the particles caused the accumulation of matter in large familiar formations such as star's gas, galaxies, and later planets and solar systems.

How our universe could meet its doom? The big freeze, big rip, and the big crunch. 

But what about the future? How the universe is going to end? Well, the ultimate fate of the universe is determined by the battle between dark energy and the force of gravity. Sounds crazy! but this is what the recent scientific data predicts. These two forces work against each other just like it happens in the case of motion and friction. Gravitational force is making the matter in the universe attract each other, while the dark energy is pulling the matter apart-it is the reason why the universe expands. And this fight could finally end up in the big freeze, big rip, or the big crunch. 

The big freeze scenario is what happens if the force pulling the matter apart is just strong enough to overcome the force of gravity. As a result, the distance between the matter would increase and the universe would keep getting bigger. Clusters of galaxies would separate. The object within the galaxies.-suns, planets, and solar systems would move away from each other until galaxies dissolved into lonely objects floating separately in vast space. The light they emit would be redshifted to long wavelengths with low-faint energies and gas emanating from them would be too thin to create new stars. The universe would become darker and colder, approaching a frozen state also known as the heat death of the universe. 

The second possible state is the big rip of the universe. We know that the expansion of the universe is accelerating due to dark energy. If the expansion of the universe continues to accelerate, it will eventually overcome not only the force of gravity - tearing apart galaxies and solar systems- but also the electromagnetic, weak and strong nuclear forces which hold atoms and nuclei together. So, the matter that makes up the stars breaks into tiny pieces. Even atoms and sub-atomic particles would be destroyed. That is the big rip.

The third possibility corresponds to a possible future in which the force of gravity brings the universe's expansion to halt- and then reverses it. Galaxies would start rushing towards each other, and as they clumped together their gravitation pull will get even stronger. Stars too would hurtle together and collide. Temperatures would rise as space would get tighter and tighter. The size of the universe would plummet until everything compressed into such a small space that even atoms and sub-atomic particles have to crunch together. The result would be an immensely dense, hot, compact universe- a lot like the state that precedes the big band. 

How the universe will end? is still a big question for scientists. And it seems like the answer depends on the exact shape of the universe, the amount of dark energy it holds, and changes in its expansion rate. As of now, our observations suggest that we are heading for a big freeze. Whatever it looks like, you don't need to worry. Because the end would not be well-neigh for at least 200 billion years.