About 70% of the Earth is covered with water. Imagine not knowing what water is!
That is the problem the scientists are now facing with the discovery of dark energy.
Cosmologists believe that about 70 percent of the universe consists of dark energy, 25 percent of dark matter, and only 5% of 'normal matter' (known elements such as stars, planets, etc.).
The essential is invisible to our eyes.
Astronomy, astrophysics and modern cosmology inform us that almost the entire universe is invisible to our eyes even though optical observations are now more sophisticated.
With Albert Einsteinís relativity theory, the universe has become, in the twentieth century, a physical object like the planets. True scientific cosmology has been developed.
What is dark matter and what is dark energy?
These are two huge questions, in their complexity, depth, and their scientific implications and beyond (the articulation of many questions of modern astronomy around these themes also strongly resonates among artists and philosophers). This underpins the purpose of "Invisible Universe" - UNESCO Paris, 29 June to 10 July 2009.
Scientists admit that, although they have some theories to explain them, they are years away from understanding what these forces could be.
What excites scientists most about dark energy is that it reveals flaws in our current understanding of the Universe. Just about everyone was surprised by its discovery.
Understanding dark energy, scientists say, will lead to a new and deeper understanding of nature itself.
Scientists rely on two main theories to explain the workings of the Universe. One is Einstein's theory of general relativity, also known as the theory of gravity. This is used to describe the large-scale Universe. A separate theory called quantum mechanics---developed partially by Einstein but primarily by his contemporaries---describes the small-scale, or subatomic, forces: electro-magnetism (light), weak forces (seen in radioactivity) and strong forces.
:: UNESCO International Year of Astronomy (website)