Dark energy what is it? Dark energy is a unknown energy said to take up 70 percent of the universe. The energy is a repulsive gravitational effect that is causing the universe to accelerate out-ward. No one knows exactly what dark energy is or where it comes from. Dark Energy is a new idea.

Little is known about dark energy, yet it takes up a huge amount if the universe. Scientist were able to show the universe was expanding at an accelerated rate by measuring the red-shift of an object by comparing the spectral lines of the elements and the spectral lines of the same elements measured in a lab. The more distant the objects that emit light the brighter the spectral lines. In 1998 scientist observed that the supernovas are becoming dimmer, which means they are getting closer instead of farther away.

They were able to show that dark energy has an influence on light particles and photons. When a photon passes a galaxy it falls into the gravitational pull, and the dark energy because it repulses gravity makes the photon pass right through the galaxy with even more energy than when it entered. These findings make dark energy completely independent of the supernova observations. Astronomers have found the first direct evidence of dark energy in the afterglow of the Big Bang, the radiation caused by the Big Bang called cosmic microwave background (CMB). The cosmic microwave background is hotter in spots where there are more galaxies in a cluster. Dark energy is also, what keeps space flat.

Not until to long ago, there was an inconsistency between the matter in space, the energy in the universe, and the flatness of space. Scientist studied the cosmic microwave background and a large-scale structure, and they were able to conclude that the energy that keeps space flat is dark energy. Scientists are still trying to learn more about this mysterious energy. They conduct red-shift surveys of the galaxy clusters; a galaxy cluster is consisted of thousands of galaxies, dark matter, and hot gases, bound together by gravity. When scientist conduct a red-shift survey, the electrons from the hot gases scatter off the protons and produce X-rays, which weaken with a higher red-shift. Once and a while the electrons give some energy to a photon of the cosmic microwave background, which makes the black body spectrum to shift causing distortion, called the Sunyaev-Zeldovich effect.

Comparing the X-rays to the Sunyaev-Zeldfovich effect help scientist observe the faintest red-shift in clusters. Various types of dark energy have been thought to be found, one is a cosmic field associated with inflation, a low-energy field called quintessence, and the cosmological constant in its present living form does not balance gravity in order to keep a static universe, it has a negative pressure that cause the universe to accelerate. There are three views of the universe, the first is the universe has a positive curvature; the second is it has a negative curvature, and the third and most reasonable is that the universe is flat. If the universe had a positive curvature then all the hot spots from the big bang would appear much larger the actual size. At a negative curvature, all the hot spots would be much smaller then normal.

In a flat universe, the hot spots are normal in size. So, what is dark energy actually doing to our universe? Well dark energy is causing all the galaxy clusters to break up and move away from each other. Since they are getting farther apart, we say the universe is expanding. In about 20 billion years scientist see the universe ripping apart because of dark energy. If dark energy accelerates the universe fast, enough it will force galaxies, stars, solar systems, and even atoms to fly into pieces.

""Dark Energy" Dominates the Universe" Science Daily, 2003. web "Galaxy Clusters Surveys May Help Explain "Dark Energy" in the Universe" Science Daily, 2002. web "Dark Energy Fills the Cosmos" Paul Press, Science beat. web "Direct Evidence Found for Dark Energy" Philip Ball, July 23, 2003. web Coming, Neil F, and William J. Faufmann III.

Discovering the Universe, 6 th ed. New York: W. H. Freeman and Company, 2002.