Dark Matter and Energy

Long ago people thought the world was flat, then they realized that the Earth revolved around the Sun and discovered that the Earth is part of the Milky Way galaxy. Later people discovered the universe and that it was made up of many galaxies. All of these discoveries  were all due to scientific observations and theories. Science is constantly updating our thinking about things. To this day we are still making observations about the universe, for example the discovery of dark matter and energy. Dark matter is a type of matter that is invisible. It can be detected by the strong gravitational force. Dark matter has a large mass and the Hubble study showed areas where dark matter has become so dense that it totals 100 trillion times the sun's mass. Dark energy is a repulsive force. It is like the counter force of gravity and the equivalent of the Einstein's cosmological constant. It is the force that keeps the universe expanding and keeps it from collapsing.http://hubblesite.org/newscenter/archive/releases/2008/03/full/http://hubblesite.org/newscenter/archive/releases/2009/08/full/