Cosmology: Origin of the Universe

Study Notes

Cosmology investigates the universe's origin, development, structure, history, and future.
Different theories have emerged over time to explain how everything came into being.

Religious Cosmology:
- Genesis: Describes God's creation of light, darkness, earth, and living creatures in six days.
- Rigveda: Presents the universe as brahmanda or "cosmic egg," originating from Bindu and undergoing cyclical expansion and contraction.
Philosophical Views:
- Anaxagoras: Proposed a primordial universe created by "nous" or mind.
- Leucippus and Democritus: Introduced the atomic universe, consisting of atoms and void.
- Pythagorean Model: Suggested that celestial bodies orbited an "invisible fire," not the sun.
- Aristotle's Theory: Advocated for the four elements and a geocentric model with Earth at the center, supported by Eudoxus.

Geocentric Model: Proposed by Aristotle and Ptolemy; Earth is motionless at the universe's center with celestial objects revolving around it.
Heliocentric Model:
- Copernicus (1543): Rejected geocentrism, placing the Sun at the center.
- Giordano Bruno (1584): Extended the idea to consider many star systems.

Sir Isaac Newton: Formulated laws of motion; described a static, infinite universe that was gravitationally balanced yet unstable.
René Descartes: Proposed a static universe filled with swirling matter, influencing concepts of gravitational effects.
Albert Einstein: Developed the Theory of General Relativity, initially considering a static universe.
Edwin Hubble: Demonstrated in 1929 that the universe is expanding via observations of galactic redshift.

Big Bang Theory:
- Proposed by Georges Lemaître in 1927; explains that the universe expanded from a singularity approximately 14 billion years ago.
- Supported by Edwin Hubble’s findings of an expanding universe.
Steady State Universe:
- Introduced by Fred Hoyle, Thomas Gold, and Hermann Bondi; suggests that new matter is continuously added to maintain consistent density as the universe expands.
Oscillating Universe:
- Concept of expansion followed by contraction, leading to repeated cycles of Big Bang and Big Crunch.
Inflationary Universe:
- Alan Guth's model incorporates an early phase of exponential cosmic inflation to address gaps in the Big Bang theory.
Multiverse Theory:
- Developed by Andrei Linde; proposes the existence of multiple, potentially infinite, universes beyond our known cosmos.