Origin and Future of the universe

Introduction

We don't know what happened at the exact instant of the big bang. However, over the last few decades physicists have pushed our understanding back further and further to very beginning of time and applied the known laws of physics to arrive at the rough timeline of what happened during the very early evolution of the universe.

The vast majority of scientists believe in the big bang theory , which would have started the universe we know. According to the theory, about 13. 7 billion years ago all the matter that constitutes the universe was concentrated in the single point, which exploded, giving rise to everything we know.

Before our universe existed, there would be another one before it, which also emerged from a supermassive point, expanded and began to shrink, reaching the singularity of the big bang. 

The universe is 13.7 billion years old, with a margin of error of 0.2 billion more or less. To reach this figure, scientists have struggled for almost 80 years. 

The expansion of the universe 

In the early part of the twentieth century, there was a great deal of uncertainty about how big the universe was. Some astronomers believed the universe did not extend beyond the milky way galaxy, whereas others believed the universe was much, much larger. 

In 1990s,two independent teams of astrophysicists turned their eyes to distant supernovae, that emerged after the explosions of stars with more that 10 solar masses, to calculate the slowdown. To their surprise, they found that the expansion of the universe was not slowing but accelerating. 

In 1998 discovery, a opinion was presented that the expansion of the universe is not slowing down, as any sensible universe should be doing, but speeding up. The universe is made up of 73% of dark matter and 23%dark energy, while the rest is made up of galaxies, stars, planets etc which corresponds to 4% of the entire universe. This "dark energy" acts as a kind of cosmic antigravity - empty space appears to produce a repulsive force, which is the opposite of the attractive force exerted by all the forms of matter. These 2 competing forces have affected the expansion of the universe, since aftermath of the big bang.

Dark matter attracts and dark energy repeals, that is dark matter is used to explain a greater than expected gravitational attraction, which dark energy is used to explain a negative gravitational attraction. 

The expansion of the universe mean that objects which are not tightly bound by gravity get further away from each other. So although individual galaxies don't get any bigger the distance between them increases. 

Einstein's theory of gravity relativity gave the results that the effect of the gravity due to the matter in the universe would be to slow the expansion down. The more matter in the universe, the more the expansion would be slow down. 

There are 2 possibilities :-

1) If the average density of matter in the universe was high enough, then the expansion would slow down, stop and the universe would start contracting. The universe would then contract at a faster rate and would eventually collapse entirely in a "big crunch". Astronomers call this scenario a close universe. 

2)If the average density was not high enough then the rate of expansion would slow down but not stop. The universe would just expand forever at a slower rate. Astronomers call this scenario an open universe. 

But as the universe has expanded, the density of matter has decreased while the amount of matter has remained constant and as the braking effect of gravity has diminished, the expansion has accelerated. 

When we look at very distant galaxies then because of the time it takes for light to reach us, we are seeing them as they were billions of light years ago. For these galaxies, the Hubble constant, which is the gradient of the graph gives the rate of the expansion of the universe is lower than it is for closer galaxies. Therefore, billions of years ago the universe was expanding more slowly than it is now. 

So because the expansion of the universe was lower in the past than it is now it must be speeding up and it will go on expanding forever. 

Spherical universe

For a long time, scientists considered the universe flat, but now a study published in the scientific journal Nature Astronomy has shown that, in fact, we live within a gigantic closed sphere. On the fact that supports, the sphere Shape of the universe is the existence of a phenomenon in which gravity bends the path of light, an affect predicted by the theory proposed by Albert Einstein. 

In the research, the conclusion that the universe is spherical came when scientists saw that gravity was bending the path of light far more. They noticed using data from the European Space Agency 's(ESA), from Plank Space Observatory, which show differences in concentration between dark matter and dark energy. 

Future of the universe 

To predict what will be the future of the universe is a very difficult task as right now we have a very limited knowledge about the universe. 

Astronomers predict that a comet or asteroid large enough to cause global devastation will smash into the earth about every 100 million years or so. Other cosmic smash - ups, however, cannot be averted, no matter how much advance warning we have. The inexorable tug of gravity that enabled the formation of the milky way has also put us on a collision course with our neighbouring galaxy, Andromeda. As Andromeda and the milky way merge, both will then lose their disk-like structure, forming a single elliptical galaxy that some astronomers have dubbed, "milkomeda". 

Until we understand the true nature of dark energy, the tale of the cosmos will remain a mystery. The universe might yet have a surprise ending.