Space, time, and everything inside them are made up of planets, stars, galaxies, and all other forms of matter and energy. The Big Bang theory offers the most widely accepted account for how the cosmos came into being. According to this theory, the universe began to expand after the Big Bang, which happened 13.787 0.020 billion years ago. The current observable universe may be measured to have a diameter of approximately 93 billion light-years, even if the overall scale of the universe's space is unknown. 
Some of the earliest geocentric, or Earth-centered, cosmological conceptions of the universe were developed by Greek and Indian philosophers. Centuries of improved astronomical observations led Nicolaus Copernicus to develop the heliocentric theory, which positions the Sun at the centre of the Solar System. Isaac Newton developed the law of universal gravitation based on the work of Copernicus, Tycho Brahe's discoveries, and Johannes Kepler's principles of planetary motion. 
Improved observational capabilities led to the discovery that the Sun is one of a few hundred billion stars in the Milky Way, one of a few hundred billion galaxies in the observable universe. There are numerous stars in a galaxy that have planets. At the largest scale, the universe is devoid of a core or an edge, with galaxies dispersed uniformly and similarly in every direction. Galaxies develop enormous filaments and holes in space when grouped into clusters and superclusters at smaller sizes, giving the appearance of a foamy mass. The idea that space had a beginning and has been expanding rapidly ever since was brought up by discoveries made in the early 20th century. 
According to the Big Bang theory, the initial density of matter and energy has decreased as the universe has expanded. After an initial, accelerated expansion known as the inflationary period at roughly 1032 seconds, which caused the separation of the four known basic forces, the universe slowly cooled and continued to expand. As a result, basic atoms and subatomic particles were able to form. Over time, dark matter collected under the force of gravity, creating a structure resembling foam composed of voids and filaments. Massive clouds of hydrogen and helium were progressively drawn to the areas of the universe where dark matter was most dense, giving rise to the first galaxies, stars, and everything else we see today. 
Galaxies' motion has shown that the universe contains significantly more matter than can be explained by the observable objects we can see, like as stars, galaxies, nebulas, and interstellar gas. This substance is invisible and is referred to as "dark matter" despite a strong body of circumstantial evidence to the contrary. The most generally recognised model of the universe is the CDM. It indicates that about 69.2%1.2% of the mass and energy in the universe is made up of dark energy, which speeds up the expansion of space, while about 25.8%1.1% is made up of dark matter. Thus, the universe contains just 4.84%0.1% of ordinary (or "baryonic") matter. Six percent of ordinary matter forms stars, planets, and nearly all observed gas clouds. 
The ultimate fate of the universe and what, if anything, existed before the Big Bang are the subject of numerous competing theories. Nevertheless, some physicists and philosophers decide against making any predictions because they don't think information about previous states will ever be accessible. Some physicists have proposed a number of multiverse theories that suggest there might be a large number of other universes outside our own.