1. The universe is the total of all the potentiality of knowable objects
  2. The study of the universe on the grand scale is called cosmology
  3. The universe includes planets, stars, galaxies, the contents of intergalactic space, the smallest sub-atomic particles, and all matter and all energy
  4. The universe is currently expanding at a speed greater than the speed of light itself


  • All the heavenly bodies i.e. star, planets, satellites, asteroids, meteorites, celestial bodies which together form the universe
  • The science of studying these heavenly bodies is known as astronomy and scientist who practice this are called astronomers


  1. The universe has been fascinating since ancient times
  2. Various scholars have presented their views on the universe
  3. They have been put into two categories
  4. The early theories
  5. The modern theories


  • Geo centric theory– the theory is proposed by Ptolemy in AD140, which states the earth is the center of the universe
  • Heliocentric theory– the theory is proposed by Copernicus in AD 1543 according to which the sun is the center of the universe
  • In 1805 British astronomer Hershel studied the universe with the help of a telescope and state that the solar system is merely a small part of a galaxy
  • An American astronomer Edwin P Hubble in 1925 said that the universe has a diameter of 2.5 billion light-years and is composed of many galaxies


  • It is the most acclaimed theory proposed by Georges Lemaitre in1930s and later strongly evidenced by George Gamow which explained the modern big bang theory
  • The theory states that, in the beginning, all the matter forming the universe existed in one place in the form of a tiny ball with an unimaginable volume, infinite temperature, and indefinite density
  • Around 15billion years ago, a vast explosion occurred and the primeval atom disintegrated giving rise to space and time and the expansion of the universe that continues today
  • The expansion of matters further formed galaxies and these galaxies are continuously expanding and moving away from each other in an accelerated velocity sniff in the process cooling the universe
  • The big bang or the expanding universe is now proven by the discovery of the cosmic microwave background radiation (CMBR)and Wilkinson microwave anisotropy probe (WMAP)
  • Another important astronomical observation called the redshift also proved the expansion of the universe
  • The recent experiments at the large hadron collider (LHC) built by the European organization for nuclear researcher beneath the fransco-Swiss border near Geneva, Switzerland aims to recreate conditions just after the big bang to have a better understanding of the phenomenon


  • Light is formed of a band of colors called the spectrum- violet color has the shortest wavelength and lies at one end of the spectrum and red light has the longest wavelength and is at the other end
  • The movement of a star or galaxy affects its light as seen by the observer
  • When the star is approaching the observer, the light shifts to the blue end of the spectrum ad the light shifts to the red end when the star recedes(fade) away
  • This also known as the doppler effect or the doppler shift
  • The doppler shift of the galaxies how that they are receding and the universe is in a state of rapid and accelerated motion and state of expansion
  • This astronomical observation is called a redshift


  • Bondi, gold, and Fred Hoyle developed this theory
  • According to which, the number of galaxies in the observable universe is constant and the new galaxies are continuously created out of space which fills up the gaps caused by the galaxies
  • As a result of it, the overall size of the mass of the observable universe remains constant
  • Thus, a steady-state of the universe is not disturbed at all


  • According to this theory, the universe is supposed to be expanding and contracting alternately
  • i.e. the universe at present is expanding
  • according to pulsating theory, at a certain time, the expansion of the universe may be stopped by the gravitational pull it many contracts again
  • after it has been contracted to a certain size, explosion again occurs and the universe starts expanding
  • the alternate expansion and contraction of the universe give rise to the pulsating universe


  • astronomers estimated that the big bang occurred between 12 and 14billion years ago and the age of the universe is now accepted to be 13.7 billion years based on measurements made on the cosmic microwave background radiation (CMBR)
  • Our solar system is 4.5 billion yrs. old

The age of the universe was estimated by 2 ways

  1. By observation made on globular clusters which are a dense collection of roughly a million stars having many old stars
  2. By measuring the rate of expansion of the universe called Hubble constant (Ho) and extrapolating back to the big bang
  3. The fate of the universe is determined by a struggle between the momentum of expansion and the pull of gravity
  4. The rate of expansion and the pull of the Hubble’s constant (Ho) while the strength of gravity depends on the density and pressure of the matter in the universe
  5. If the pressure of the matter is low then the fate of the universe is governed by the density
  6. If the density if the universe is less than the “critical density” which is proportional; to the square of the Hubble constant then the universe will expand forever
  7. If the density of the universe is greater than the “critical density” then gravity will eventually win and the universe will collapse back on itself which is also called the big crunch
  8. This strange form is of the matter is now referred to as dark energy
  9. Its dark energy in fact plays a significant role in the evolution of the universe then in all like hood the universe will continue to expand forever


  • Our universe has a foamy structure
  • The largest structures are made up of filaments, superclusters, and galaxy groups and clusters called superclusters which are in turn form part of walls which are also parts of filaments
  • The visible part of the universe is concentrated in certain parts in a complex scaffold the surrounds a network of enormous cosmic voids
  • In addition to the normal matter that makes up the visible part of the universe, scientists have discovered that there are vast amounts of unseen matters called the dark matter
  • Dark energy- 68%
  • Dark matter-27%
  • Visible matter-5%
  • The visible matter of the universe is composed of
    • Hydrogen-72-75%
    • Helium-23-26%
    • Other elements-lesser than 2%
  • The process of nuclear fusion has very slightly increased the quantities of helium but the proportional composition is practically unchanged since the earliest years of the universe
  • Dark matters cannot be seen by any of the electromagnetic spectra such as radio waves, x-rays, etc but certain phenomenon such as the gravitational lensing, temperature distributions, orbital velocities and rotational speeds of galaxies, etc are pieces of evidence of missing mass and justify the existence of dark matter
  • Another invisible entity is the dark energy is believed to be therein why galaxies are speeding away at ana accelerated rate

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