Comprehensive Study Guide on the Universe and Solar System Origins

Composition and General Characteristics of the Universe

The universe is defined as the totality of everything that exists. It is composed of three primary components: Baryonic Matter, which makes up $5\%$ of the universe and includes "us" (all ordinary matter); Dark Matter, which constitutes $27\%$; and Dark Energy, which accounts for the remaining $68\%$.

The universe is approximately $13.8$ billion years old. One of the oldest known objects within it is the HD 140 283 star, also known as the "Methuselah" star.

Non-Scientific Origins of the Universe

There are two primary categories for the non-scientific origin of the universe. The first is Biblical, which relies on religious creation accounts. The second is Mythological, which encompasses various cultural myths and legends regarding the beginning of existence.

Scientific Theories: The Big Bang and The Big Crunch

The Big Bang Theory is a physical theory that describes how the universe "expanded" from an initial state of high density and temperature. This theory was developed by Georges Lemaitre in $1920$ (who was also a priest) and Edwin Hubble. The progression of the Big Bang follows the sequence: singularity, inflation, and recombination. A critical piece of evidence for this theory is the Cosmic Microwave Background (CMB), which is identified as the oldest light in the universe.

The Big Crunch Theory was proposed by the Russian scientist Alexander Friedmann in $1922$. It suggests that the universe will one day stop expanding and begin to contract. This process will continue until the universe has collapsed back into a super dense singularity.

Scientific Theories: Oscillating and Steady State

The Oscillating Theory, proposed by Richard Tolman in the $1930\text{s}$, views the universe as a cyclical event. It effectively combines elements of the Big Bang and the Big Crunch, suggesting a repeating cycle of expansion and collapse.

The Steady State Theory was proposed in $1948$ by Fred Hayle, Herman Bondi, and Thomas Gold. This theory posits that the universe is infinite in the past and in the future. According to this model, the universe is always expanding but maintains a constant average density. It remains the same in extent and the same in all directions at all times.

The Solar System and its Characteristics

The Solar System is defined as the gravitationally bound system consisting of the sun and everything that orbits it. In terms of composition, components such as asteroids are composed of Rock, while Gas giants are associated with elements like He (Helium). Significant regions of the system include the Asterical Belt and the Kuiper Belt. Space exploration of these regions has been conducted by missions such as Voyager I, which has been active from $19$ to the present.

Origins of the Solar System: Planetesimal and Tidal Theories

The Planetesimal Theory was introduced in $1905$ by Forrest Moulton and Thomas Chamberlin. It suggests that planets formed from small bits of matter called planetesimals that were revolving around the sun. These pieces originated from gases pulled out of the sun by a near collision with a passing star.

The Tidal Theory was proposed in $1918$ by Sit James Heans and Sir Harold Jeffreys. This theory involves another star approaching our Sun, which created tidal forces. The resulting instability of the Sun led to part of its mass being torn off to eventually form the planets.

The Nebular Theory (Solar Nebular Disk Model)

The Nebular Theory, also known as the Solar Nebular Disk Model, was developed through the contributions of Emanuel Swedenborg ($1734$), Immanuel kant ($1755$), and Pierce Laplace ($1796$). This theory states that a spinning cloud of dust, made mostly of light elements and called a nebula, flattened into a proto planetary disk. This disk eventually became a solar system consisting of a star with orbiting planets.

The formation process according to the Nebular Theory occurs in four specific stages: Stage 1: Gravitational Collapse. Stage 2: Spinning and Flattening. Stage 3: Accretion and Planetesimal Formation. Stage 4: System Stabilization and Clearing.