The Big Bang was the appearance of space everywhere in the universe, researchers have said. According to the Big Bang theory, the universe was born as a very hot, very condensed, single point in space.
When the universe was young — about a hundredth of a billionth of a trillionth of a trillionth of a second — it experienced a huge growth spurt. During this burst of expansion, the universe doubled in size at least 90 times.
After expanding, the universe continued to grow, but at a much slower rate. As space expanded, the universe cooled down and matter came about.
Light chemical elements were created in the first three minutes of the universe’s formation. As the universe expanded, temperatures cooled and protons and neutrons crashed to make deuterium, which is an isotope of hydrogen. Much of this deuterium combined together to make helium.
For the first 380,000 years after the Big Bang, the intense heat from the universe’s creation made it essentially too hot for light to shine. Atoms crashed together with enough force to break up into a dense, opaque plasma of protons, neutrons and electrons that spread light like fog.
About 380,000 years after the Big Bang, matter cooled down enough for electrons to mix with nuclei to form neutral atoms. This phase is known as “recombination,” and the captivation of free electrons caused the universe to become transparent. The light that was released at this time is detectable today in the form of radiation from the cosmic microwave background.
The era of recombination was trailed by a period of darkness before stars and other bright objects were formed.
Roughly 400 million years after the Big Bang, the universe started to come out of its dark ages. This period in the universe’s development is called the age of re-ionization.
This dynamic phase was thought to have continued more than a half-billion years, but based on new observations, scientists think re-ionization may have occurred more rapidly than previously thought.
Throughout this time, clumps of gas collapsed enough to form the very first stars and galaxies. The released ultraviolet light from these energetic events cleared out and destroyed most of the surrounding neutral hydrogen gas. The progression of re-ionization, plus the clearing of foggy hydrogen gas, caused the universe to become transparent to ultraviolet light for the first time.
Our solar system is estimated to have been born a little while after 9 billion years after the Big Bang, making it around 4.6 billion years old. According to present estimates, the sun is one of more than 100 billion stars in our Milky Way galaxy alone, and orbits roughly 25,000 light-years from the galactic core.