Theory of Everything by Stephen Hawking
1. Early Cosmological Models Aristotle (340 BC): Argued that the Earth was a round sphere rather than a flat plate, based on observations like the shape of Earth's shadow during eclipses. Ptolemy (2nd Century AD): Developed a complete model with Earth at the center, surrounded by eight spheres carrying the heavenly bodies. It was adopted by the Christian church as it left room beyond the stars for heaven and hell. Nicholas Copernicus (1514): Proposed a much simpler model where the Sun was stationary at the center and the Earth and planets moved in circular orbits around it. 2. The Newtonian Era & Gravity Universal Gravitation (1687): Newton postulated that every body in the universe is attracted to every other body. This force is stronger the more massive the bodies are and the closer they are together. The Static Universe Problem: Newton realized that in a finite universe, stars should eventually fall together due to gravity. To avoid this, it was argued that the univers...