The Big Bang Theory is a widely accepted scientific explanation for the origin and evolution of the universe. It proposes that the universe began as a single point of high-density and high-temperature and has been expanding ever since. This theory is supported by various lines of evidence, including the observed expansion of galaxies, the abundance of light elements in the universe, and the cosmic microwave background radiation.

The Big Bang Theory can be explained in detail as follows:

1. Initial Singularity:
According to the Big Bang Theory, the universe originated from an extremely hot and dense state known as the initial singularity. At this point, all matter, energy, space, and time were concentrated in a single infinitesimal point.

2. Expansion and Cooling:
Shortly after the initial singularity, the universe began to rapidly expand and cool down. This expansion is often referred to as the "Big Bang." As the universe expanded, the temperature and density decreased, allowing the formation of subatomic particles like protons, neutrons, and electrons.

3. Formation of Matter:
As the universe continued to expand and cool, the subatomic particles started to combine and form atoms, primarily hydrogen and helium. This process is known as nucleosynthesis. These atoms then clumped together under the influence of gravity, eventually forming stars, galaxies, and other celestial structures.

4. Cosmic Microwave Background Radiation:
Around 380,000 years after the Big Bang, the universe had cooled down enough for atoms to capture electrons and become neutral. This event, known as recombination, allowed photons to travel freely through space, resulting in the release of the cosmic microwave background radiation (CMB). The CMB is a faint radiation that permeates the entire universe and is considered as one of the strongest pieces of evidence supporting the Big Bang Theory.

5. Expansion of the Universe:
Observations of galaxies and their redshifts have provided strong evidence for the ongoing expansion of the universe. The farther away a galaxy is, the faster it appears to be moving away from us. This observation supports the idea that the universe is expanding from a single point, as predicted by the Big Bang Theory.

In conclusion, the Big Bang Theory states that the universe began as a single point of high-density and high-temperature and has been expanding ever since. The theory is supported by various scientific observations and provides a comprehensive explanation for the origin and evolution of the universe.