Question

why universe expanding continusely???

Answer 1

★ EXPANDING UNIVERSE ★

the research to answer this question spans about 100 years. But, in simple words, the universe is expanding. The more stunning fact is that this expansion is accelerating.
To understand in simple terms, the Universe is made of 4% known matter that the cosmologists call the baryons, 26% dark matter and 70% dark energy. Out of this, all the known detected matter is just 4%. The remaining 96% is still unknown. We know nothing about them. The only thing we know is the dark matter follows gravitational laws just like normal matter, but the dark energy imparts repulsion to the matter. In other words, the objects in the universe attract each other because of gravity and they repel each other because of dark energy. These two opposing forces are always in play. When the objects are sufficiently close to each other, the attractive forces are more prominent. But, as the distance between the objects increase, the repulsive forces become more important.

If we look at nearby galaxies, like the Andromeda(M 31), we see that they are coming towards us. This is because the Andromeda and MW are getting pulled towards each other by gravity. In fact, MW and M31 will collide to form a larger galaxy in about 4.5 billion years. But, if we look at galaxies that are far away from us, we see that they are receding away from us. As a matter of fact, Hubble found that the farther the galaxy is from us, the faster it is moving away from us. This leads to the conclusion that the Universe is expanding. In addition, based on study of supernovae, Brian Schmidt and his team concluded that the Universe is just not simply expanding, but its expansion is accelerating. This won him Nobel Prize in 2011.Scientists believe that the universe formed 13.7 billion years ago in the Big Bang, and encompasses everything in existence, from the smallest atom to the largest galaxy. The part of the universe of which we have knowledge is known as the observable universe, the region around Earth from which light has had time to reach us.

Early astronomers thought that the universe was finite. But when Isaac Newton discovered the law of gravity, he realized that gravity is always attractive. Every object in the universe attracts every other object. If the universe truly were finite, the attractive forces of all the objects in the universe should have caused the entire universe to collapse on itself. This clearly had not happened, and so astronomers were presented with a paradox.

In the early twentieth century, large telescopes were built that were able to accurately measure the spectra of faint objects. Using these new data, between 1912 and 1922, astronomers discovered that these nebulous objects were distant galaxies and the spectra of light from many of these objects was systematically shifted to longer wavelengths, or red-shifted. The light coming from distant objects would be red-shifted as it traveled through the expanding universe. The redshift would increase with increasing distance to the object.

It was the American astronomer Edwin Hubble (1889-1953) who made the observations in 1925 and was the first to prove that the universe is expanding. Once scientists understood that the universe was expanding, they immediately realized that it must have have been smaller in the past. At some point in the past, the entire universe must have have been a single point. This point, later came to be known as THE BIG BANG was the beginning of the universe as we understand it today. The question still was, why was the universe expanding?

Until about 15 years ago, astronomers thought that the universe was expanding because of momentum. The idea was that the Universe received all the energy it needed for its expansion in the first few moments after the Big Bang. All the time, astronomers thought that the mutual gravity of all the objects in the Universe will eventually cause it to slow to a halt at some point in the distant future, or maybe even collapse in on itself, leading to what they called a Big Crunch. Or just clump up in piles and stay static.

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