The big bang theory and the timeline of our Universe

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The most widely accepted theory about the origin of the universe is the Big-Bang theory that states that the universe was born 13.8 billions of years ago as it expanded from a state of very high-density and very high-temperature. As the Universe expanded, matter began to coalesce into gas clouds, and then stars and planets. Our solar system formed about 4.5 billion years ago when the Universe was about 65% of its present size. Today, the Universe continues to expand.

Connection to Big Idea about energy: All the energy of the universe was once contained to a single point which exploded 13.8 billion years ago (Big Bang), forming everything in the universe. To explain the homogenous nature of the radiation leftover from the Big Bang, a period of inflation has been suggested, where the Universe expanded rapidly after the Big Bang.

Connection to Big Idea about forces: The Big Bang explosion had such tremendous energy that because of it, the universe keep expanding 13.8 billion years later. Gravity caused matter to accrete together, forming both the large scale structure (galaxies etc.) and smaller scale occurrences such as planets orbiting stars. One theory suggests that up to 10-43 seconds after the Big Bang, all 4 fundamental forces were of the same strength and were unified into one fundamental force.

Connection to Big Idea about particles: The elementary particles were created a few fractions of a second after the Big Bang. As time progressed they interacted to form other particles like the protons, neutrons atoms and molecules which in turn created the stars, planets and all the celestial objects we see today. 

Subjects related: Physics

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