A cosmological model is a mathematical and conceptual framework used to describe, explain, and predict the large-scale properties of the universe. These models are based on current understanding of physics, including general relativity, and aim to account for observations such as the expansion of the universe, the distribution of galaxies, and the cosmic microwave background radiation. One of the most fundamental aspects of cosmological models is that they attempt to answer profound questions about the universe's origin, composition, dynamics, and eventual fate. The most widely accepted model today is the Lambda Cold Dark Matter (ΛCDM) model, which includes the cosmological constant (denoted by Lambda, Λ) representing dark energy, and cold dark matter.
In constructing a cosmological model, astronomers and physicists rely heavily on observational data collected through telescopes and other sensing instruments. This data includes the redshift of galaxies, which provides information on the rate at which the universe is expanding. This expansion was first observed by Edwin Hubble and is encapsulated in Hubble's Law. Another critical set of observations comes from the cosmic microwave background (CMB), which is the afterglow radiation from the Big Bang and provides a snapshot of the universe when it was just 380,000 years old. These observations help in refining the parameters of cosmological models, ensuring they are consistent with what we see in the universe.
Theoretical underpinnings of cosmological models are deeply rooted in the general theory of relativity, proposed by Albert Einstein. This theory describes gravity not as a force, as Newtonian mechanics does, but as a curvature of spacetime caused by mass and energy. Applying general relativity to cosmology leads to the formulation of the Friedmann-Lemaître-Robertson-Walker (FLRW) metric, which assumes a homogenous and isotropic universe - one that looks the same in all directions and at all locations. Under this assumption, the FLRW metric simplifies the complex equations of general relativity, making it feasible to predict how the universe evolves over time from a given set of initial conditions.
As cosmological models evolve, they increasingly incorporate complex phenomena like dark energy and dark matter, which together account for about 95% of the total mass-energy content of the universe. Dark matter, which does not emit light or energy, is detectable through its gravitational effects on visible matter and radiation. Dark energy, a mysterious force driving the accelerated expansion of the universe, remains one of the most significant enigmas in cosmology. Advanced projects and observatories like the Euclid space telescope and the Dark Energy Spectroscopic Instrument (DESI) are focused on unraveling these dark components. These efforts not only enhance our understanding of the universe but also refine the parameters of cosmological models, leading to a more accurate and comprehensive picture of our cosmic environment.