Overview
This lecture introduces the origin of the universe, covering mythological and scientific explanations, key theories like the Big Bang, Steady State, Inflation, and String Theory, and clarifies essential terms.
The Universe and Our Place in It
- Earth is a rocky planet in the solar system, orbiting the sun (Sol).
- The solar system is part of the Milky Way galaxy, which contains about 200 million stars.
- The Milky Way is one of over 125 billion galaxies in the observable universe.
- The universe includes all matter and energy, from atomic particles to galaxies.
Creation Myths
- Creation myths are symbolic stories explaining the origin of the universe according to different cultures or religions.
- A well-known example is the biblical Genesis, where God creates the universe in six days.
- Creation myths often involve supernatural forces or beings.
- Key features: etiological (explains origins), philosophical, theological, assumes a spiritual world beyond the material.
Scientific Theories of the Universe’s Origin
Big Bang Theory
- The Big Bang Theory is the most accepted scientific explanation for the universe's origin.
- Proposed by Alexander Friedmann and Georges Lemaître.
- Posits that the universe began with a rapid expansion from a singularity—not an explosion.
- Matter (mainly hydrogen) formed under gravity, leading to stars and galaxies.
- Suggests the universe is still expanding.
Steady State Theory
- Proposed by Thomas Gold, Fred Hoyle, and Hermann Bondi.
- Argues the universe is unchanging over time and uniform in space (homogeneous and isotropic).
- New matter is continuously created as the universe expands, keeping density constant.
- Contradicts current evidence and does not predict the universe's future.
Inflation Theory
- Developed in the 1980s by Andreas Albrecht, Alan Guth, Paul Steinhardt, and Andrei Linde.
- Suggests a period of rapid, exponential expansion before the Big Bang.
- Addresses limitations of the standard Big Bang Theory, like the flatness and horizon problems.
String Theory
- Proposed in the 1960s by John Schwarz.
- Replaces elementary particles with one-dimensional "strings" as the universe’s fundamental building blocks.
- Strings vibrate in different ways to produce various particles.
- Attempts to unify general relativity (large scale) and quantum mechanics (small scale).
Key Terms & Definitions
- Universe — All matter and energy, including planets, stars, galaxies, and the space in which they exist.
- Creation myth — Symbolic narrative explaining the origin of the universe, rooted in culture or religion.
- Big Bang Theory — Theory that the universe began with a massive expansion from a singularity.
- Steady State Theory — Theory that the universe is eternal, unchanging, and constantly creating new matter.
- Inflation Theory — Model proposing rapid expansion of the universe before the Big Bang.
- String Theory — Theory that fundamental particles are replaced by vibrating strings.
Action Items / Next Steps
- Review key differences between the scientific theories discussed.
- Be prepared to define and compare Creation Myths and scientific explanations for a quiz.
- Read the next textbook section on cosmic background radiation.