________________
484
1
the alternatives requires high-precision measurements of the expansion of the universe to understand how the speed of the expansion changes over time. The rate of
expansion is parameterized by the cosmological equation of state <http:// 1 en.wikipedia.org/wiki/Equation_of_State_%28Cosmology%29>. Measuring the 1 equation of state of dark energy is one of the biggest efforts in observational cos
mology today.
Dark matter
Not dark (visible) matter
In order to understand the basic concepts of dark matter, dark energy and various other terms and vocabulary of modern astrophysics I strongly recommend the readers to read the fundamental books on astronomy, astrophysics and cosmology for which in addition to the references Thave provided the bibliography at the end of this article.
2. Unsolved problems in physics <http://en.wikipedia.org/wiki/ Unsolved problems in physics:
Why is the expansion of the universe accelerating, as we have observed? Is our understanding of redshift complete? If it is, then what is the nature of the invisible matter (dark matter and dark energy) driving this acceleration?
3. Dark Energy: 3. 1 Evidence for dark energy
During the late 1990s <http://en.wikipedia.org/wiki/1990s>, observations of type la supernovae <http://en.wikipedia.org/wiki/Supernova> suggested that the expansion of the universe <http://en.wikipedia.org/wiki/Universe> is accelerating. These observations have been corroborated by several independent sources since then: the cosmic microwave background <http://en.wikipedia.org/wiki/ 1 Cosmic_microwave_background>, gravitational lensing <http://en.wikipedia.org/wiki/ Gravitational_lensing>, age of the universe <http://en.wikipedia.org/wiki/ Age_of_the_universe, big bang nucleosynthesis <http://en.wikipedia.org/wiki/ Big_bang_nucleosynthesis>, large scale structure <http://en.wikipedia.org/wiki/ Large-scale_structure_of_the_cosmos> and measurements of the Hubble parameter <http://en.wikipedia.org/wiki/Hubble%27s_law>, as well as improved measurements of the supernovae.
The type la supernovae provide the most direct evidence for dark energy. Mea-1
