Hubble space telescope images of three of the most distant supernovae known. By tracking these exploding stars, astronomers can trace the expansion rate of the universe, and determine how it is affected by dark energy (NASA -- STScI).

[PureInsight.org] In February 2004, the National Aeronautics and Space Administration (NASA) issued an announcement that dark energy indeed exists. According to observation, nearly all galaxies in the universe are receding from our galaxy at an ever-increasing pace. Astronomers think, based on the present understanding, our galaxy will become lonelier, like a lonely soul and roaming ghost in the universe.

The invisible strong force -- dark energy

In 1998, scientists discovered that nearly all galaxies in the universe were receding from each other at an ever-faster pace. They thus proposed an explanation to interpret the ever-expanding universe. For a long time, scientists thought that all cosmic structure -- from planets to clusters of planets were maintained in place by gravitation. Then, what force overcomes this gravitational force to cause the rapid separation of stars? Scientists claim that this is due to an invisible strong energy called dark energy.

The future of galaxies and the universe

Scientists think that galaxies are leaving us at an ever-increasing speed. As time passes, all galaxies will be receding at a speed faster than the speed of light. Since the speed of the light being emitted from the galaxies will be slower than the speed of galaxies leaving us, we will not be able to see them any more. By then, when we look at the sky, except for our own Milky Way, we will not see stars in the sky. Even observing with a telescope, we will only see pitch-black sky.

Scientists conjecture that as this situation continues, eventually all stars will be unable to sustain this constant expansion at the speed of light and thus will disintegrate. All stars, down to their atoms, will disintegrate. Time would then stand still.

Scientists do not have any clue what dark energy is. There are two main ideas for the source of dark energy: One opinion is that dark energy might percolate from empty space and is unchanging and have fixed strength. The other holds that dark energy is associated with a changing energy field. In that scenario, it means some day the strong mysterious, repulsive force will change its behavior. Whichever explanation holds, dark energy, which is invisible and yet constitutes a major portion of the energy in the universe, will decide the future of the universe.

In recent years, understanding of the universe has changed a lot based on astronomical observations. Many new theories have emerged to fit the new discoveries. Thus, conjectures on the future of the universe are different. The crux of the matter is the lack of understanding of the true nature of dark energy and how it works. It's thus impossible to predict the future status of the universe with confidence and the time it will take. It is possible all the theories are wrong and people will see amazing changes in the near future.

Reference: http://www.msnbc.msn.com/id/4327735/