THE UNIVERSE CONTAIN EVERYTHING, that exists, from the tiniest subatomic particles to galactic superclusters. Nobody know how big Universe is, but astronomers estimate that it contains at least 125 billion galaxies, each contains an average of 100 billions stars. The most widely accepted theory about the origin of the Universe is the Big Bang theory, which states that the Universe came into being in a huge explosion – the Big Bang –that took place between 10 and 20 billion year ago. The Universe initially consists of very hot and dense firewall of expanding, cooling gas. After about 1 million years, the gas began to condense into localised clumps called protogalaxies. During the next 5 billion years, the protogalaxies continued condensing, forming galaxies in which stars were being born. Today billions of years later, the Universe as whole is still expanding, although there are localised areas in which object are held together by gravity- for example, many galaxies are formed in clusters. The Big Bang Theory is supported by faint, Cosmic Background Radiation coming eventually from all sides of the Universe. The radiation is believed to be the remnant of the radiation produced by the Big Bang. Small “ripples” in the temperature of the Cosmic Background Radiation are thought to be evidence of slight fluctuations in the density of early Universe, which resulted in formation of galaxies. Astronomers do not yet know if the Universe is “closed”, which means it will eventually stop expanding and begin to contact, or if it is “open”, which means it will continue expanding forever.
Cosmic Background Radiation: