Observational cosmology is the study of the large-scale structure, evolution, and properties of the universe through observations using telescopes and other instruments. It seeks to understand the origin, composition, and behavior of the universe on a cosmic scale.
The LCDM (Lambda Cold Dark Matter) model is the current standard model of cosmology that explains the evolution and structure of the universe. It is based on the Big Bang theory and includes dark energy (represented by the Greek letter lambda) and dark matter (represented by CDM). It is the most widely accepted model that is supported by various observations and experiments.
There are several lines of evidence that support the LCDM model. These include the cosmic microwave background radiation, the large-scale distribution of galaxies, the observed acceleration of the expansion of the universe, and the formation and evolution of structures in the universe.
Dark energy is a hypothetical form of energy that is thought to permeate the entire universe and contribute to its expansion. It is believed to make up about 70% of the total energy in the universe. Its repulsive force counteracts the gravitational pull of matter, causing the expansion of the universe to accelerate.
The LCDM model is the most successful model in explaining the observations of the universe, but it is not without its limitations. Some of the limitations include the inability to fully explain the nature of dark energy and dark matter, the lack of a satisfactory explanation for the observed distribution of matter in the universe, and the inability to reconcile the theory of gravity with observations on a cosmological scale.