Big bang theory that suggests the origin of the universe started with an explosion and expansion of a very hot, dense, compact fireball. 2. steady state theory about the origin of the universe that suggests the universe has and will continue to be at a steady, continuous state. 3. oscillating universe theory about the origin of the solar system that suggests our sun and planets formed from a cloud of dust and gas. 4. nebular theory about the origin of the solar system that agrees with the nebular theory but stresses the importance of interstellar dust in planet formation. 5. inflation theory about the origin of the universe that suggests the universe is a never-ending cycle of expansion and contraction. 6. condensation theory that upholds the big bang theory but suggests there was an extremely rapid expansion or inflation milliseconds after the big bang.

1. Big bang Theory suggests the origin of the universe started with an explosion and expansion of a very hot, dense, compact fireball.

It is a theory that stated that the universe originated from a single point in space or singularity. Despite the name, the universe was not born from an explosion. Rather, it was born from the continuous expansion of the single hot dense state, eventually cooling down which allowed more forms of matter to form. 
 
2. Steady state Theory about the origin of the universe that suggests the universe has and will continue to be at a steady, continuous state.

The steady state theory suggests that the universe expands continually but maintains a constant average density even when matter is being created continuously. It suggests also that as new stars and galaxies are formed, they continue to form at the same rate older stars and galaxies become unobservable. 

3. Oscillating Universe Theory about the origin of the universe that suggests the universe is a never-ending cycle of expansion and contraction.

Also known as the cyclic model, proposed by Richard Tolman. It proposes that when the expansion of the universe will end, it will go through a contraction phase where it will grow hotter and brighter as it contracts and eventually crush out of existence. 

4. Nebular Theory about the origin of the solar system that suggests our Sun and planets formed from a cloud of dust and gas. 

The nebular theory suggests that the solar system evolved from a nebula that contracted.  It spun faster and faster till it flattened out forming a disk. As it continued to spin, it became denser and hotter till the sun eventually formed. 

5. Inflation Theory  that upholds the big bang Theory but suggests there was an extremely rapid expansion or inflation milliseconds after the big bang.

This theory proposes that there was a period where the universe expanded exponentially before the Big Bang expansion. It was developed by Alan Guth, Andrei Linde, Andy Albrecht and Paul Steinhardt. It is now considered as an extension to the Big Bang Theory. 

6. Condensation Theory about the origin of the solar system that agrees with the nebular theory but stresses the importance of interstellar dust in planet formation. 

This theory is considered as an extension to the Nebular theory.It emphasizes that interstellar dust is a key ingredient to the formation of the different planets in the solar system. It proposes that the interstellar dust grains acted as condensation nuclei. 

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