The US Department of Energy defines cosmology as the study of the origin and development of the entire universe. It is divided into observational and physical branches, with observational cosmology using telescopes and instruments for direct evidence of the universe’s structure and evolution, while physical cosmology studies the universe’s development and the physics that created it.
The origins of cosmology can be traced back to the 1500s when Copernicus observed the Earth’s revolution around the sun, and later in the 1600s when Newton discovered that objects in space follow the same physical laws as those on Earth. In the early 20th century, Einstein’s theory of relativity provided a model of space-time, leading to modern physical cosmology.
Modern cosmologists believe that dark matter and dark energy make up most of the universe, with dark energy accounting for more than two-thirds, and dark matter for a quarter of the universe. The study of cosmology encompasses various fields such as big bang, formation of large-scale structures, big bang nucleosynthesis, cosmic microwave background, dark matter, and gravitational waves.
Scientists estimate that there are 2 trillion galaxies in the universe, and the earliest light to reach Earth was 13.77 billion years ago. The total energy balance of the universe consists of about 5 percent ordinary matter, 27 percent dark matter, and 68 percent dark energy.
The US Department of Energy’s Office of Science supports cosmology research through its Nuclear Physics and High Energy Physics programs, which focus on the study of particles, dark matter, and dark energy to further understand the universe.