The Nature of Universe

 Cosmology is the study of the Universe as a whole which is a field of Astronomy that seeks to answer to fundamental questions concerning the size, age, and structure of the Universe.

Philosophers and Astronomers have been grappling with such questions for thousands of years, with mixed success. The answers to one of the biggest - whether the Universe is finite or infinite in extent - is still not known for certain (though an infinite Universe seems more likely). Other fundamental questions about the nature of the Universe for which answers are now known include how and when the Universe began, whether it has any center or edges, and whether it encompasses more than just our galaxy. Now, we can start from ancient era until present.....

1. Cosmic Egg (c.1500-1200BCE)

Hindu text Rigveda contains a hymn that describes the Universe as originating from a Cosmic Golden Egg or Womb known as Hiranyagarbha. This floated in darkness, before breaking apart to give rise to Earth, the heavens (space), and underworlds.

2. Aristotle's Earth - Centered Universe (4th century BCE)

The Greek philosopher Aristotle proposes a Universe that is finite in extent, but infinite in time and has a stationary Earth at it's center. Aristotle outlined a complex system containing 55 spheres, the last of which marked out the "edge" of the Universe.

3. Sun-Centered Universe (3rd Century BCE)

The Greek Astronomer Aristarchus of Samos puts forward his idea that it is the Sun that sits at the center of the Universe, with the Earth orbiting it. Aristarchus also suspects that stars are bodies similar to the Sun, but much farther away.

4. A Convincing Mathematical Model (1543)

Polish Astronomer Nicolaus Copernicus's book "De revolutionibus orbium celestium" is published. It contains a detailed and convincing Mathematical Model of the Universe in which the Sun is at the center with Earth and other planets orbiting it.

5. An infinite multitude of Stars (1584)

Italian philosopher and mathematician Giordano Bruno proposes that the Sun is a relatively insignificant star among an infinite multitude of others. He also argues that because the Universe is infinite, it has no center or specific object at its center.

6. Argument against infinite Universe (1610)

German Astronomer Johannes Kepler argues that any theory of static, infinite, and external Universe is flawed, since in such a Universe, a star would exists in every direction and the night sky would look bright. This argument later comes to be known as Olber's paradox.   

7.Objects exist outside our Galaxy (1755)

German philosopher Immanuel Kant suggests that some fuzzy - looking objects in the night sky galaxies outside the Milky Way Galaxy - implying that the Universe consists of more than just the Milky Way, being considerably bigger.

8. Space time Continuum (1905)

German physicist Albert Einstein's Special Theory of Relativity proposes that space and time form a combined continuum, space time. An inbuilt assumption of hid theory is that no location is special - so the Universe has no center and no edge.

9. General Theory of Relativity (1915)

Einstein publishes his General Theory of Relativity, viewed today as the best account of how gravity works on cosmic scales. It proposes that concentrations of mass warp space time. He also devises equations that define various possible Universes.

10. Expanding Universe (1920s)

American Astronomer Edwin Hubble proves that galaxies exist outside our own and observes that distant galaxies are moving away from us at a rate proportional to their distance. Other astronomers calculate that the whole universe must be expanding.

11. Primeval Atom (1931)

Belgian Astronomer and priest Georges Lemaitre proposes his "Hypothesis of the Primeval Atom". This suggests that the Universe has expanded from an initial extremely hot, dense state. His model also provides a solution to Olbers' Paradox.   

12. The first elements (1948)

 Russian - American physicist George Gamow and others work out how - starting with just subatomic particles (in this case protons and neutrons) - the nuclei of different light elements could have formed soon after the start of a very hot, dense, but rapidly expanding Universe.

13. Hoyle Coins the term "Big Bang"(1949)

British Astronomer Fred Hoyle coins the term "Big Bang" for theories that propose the Universe expanded from an exceedingly hot, dense state at a specific moment in the past. The term becomes popular, though Hoyle himself believes in a different theory.

14. Cosmic Microwave Background Radiation(1965)

Arno Penzance and Robert Wilson, astronomers at Bell Labs in New Jersey, discover the Cosmic Microwave Background Radiation (CMBR) - a faint glow of radiation coming from everywhere in the sky. It comes to be realised that this is a relic of the Big Bang.

15. Inflationary Big Bang Theory (1980)

The American physicist Alan Guthrie and colleagues suggest that the Univwrse expanded at a fantastically fast rate during an extremely early phase of its existence after the Big Bang. The theory helps explain the large- scale structure of the cosmos.

16. Variations in the CMBR (1992)

Measurements by the COBE (Cosmic Background Explorer) satellite revial tiny variations in the CMBR, providing a picture of the seeds of large - scale structure when the Universe was a tiny fraction of its present size and just 380,000 years old.

17. The existence of dark energy (1999-2001)

High - precision measurements of the CMBR and the recessional velocities of galaxies at different distances provide evidence for dark energy - a mysterious phenomenon that seems to be accelerating the universe's expansion.

18. Gravitational Waves detected (2016)

Physicists in the United States announce that they have detected gravitational waves. The existence of these waves supports the inflationary Big Bang Theory and provides further confirmation of Einstein's General Theory of Relativity.