From the Beginning

According to the big bang theory, the universe began by expanding from an infinitesimal volume with extremely high density and temperature. Space itself began expanding from that moment on. The big bang is not like an explosion of matter in otherwise empty space; rather, space itself began with the big bang and carried matter with it as it expanded [3].  [1] When the word first got out that the expansion of the universe was accelerating, many astronomers questioned the results. They felt that the observations had to have been wrong, or there was some sort of mistake in interpreting the results. The whole concept was so difficult to believe because it requires significant changes in our understanding of the way the universe works. Before scientists had discovered dark energy, there were two theories on how expansion would work. [2] One theory was in a “Big Crunch” where there would be enough matter in the universe to slow down expansion until it reached the point where it would come to a stop and start to retract. [3] The other theory and what was thought to be the most likely, the “Big Chill”, said there would be too little matter to stop the expansion and everything would just drift on forever, slowing down yet never stopping. It would continue to expand until everything was faded and died out, ending in a vast, dark, and cold state. According to this theory, the universe should be expanding more slowly now than it did in the past due to gravity. Astronomers were stunned to read the results stating there is some force appearing to be pushing the universe apart which they called dark energy. [3] With the discovery of dark energy came a new and more violent theory for the future of the universe called the “Big Rip”. This theory stated that as the universe expands ever faster, all of gravity's work will be undone. Clusters of galaxies will disband and separate. Then galaxies themselves will be torn apart. The solar system, stars, planets, and even molecules and atoms could be shredded by the ever-faster expansion. The universe that was born in a violent expansion could end with an even more violent expansion.

                                      

                                      Image of the possible outcomes of the universe

                   http://sumire.ipmu.jp/wp-content/uploads/2010/10/Future-View-of-the-Universe.jpg

References:

1.       1. "What is Dark Energy?", Nola Taylor Redd, http://www.space.com/20929-dark-energy.html

2.       2.“Dark Energy Explore More: Fate of the Universe”, Hubble Discoveries, http://hubblesite.org/hubble_discoveries/dark_energy/de-fate_of_the_universe.php

3.       3.“Big Bang: How Did the Universe Begin?”, Yuki D. Takahashi, Spring 2000, http://www.ugcs.caltech.edu/~yukimoon/BigBang/BigBang.htm