Overview
Cosmology is the study of the Universe as a whole. Not just the things in it, but the container itself. How did it start? How big is it? How will it end?
Core Idea
The core idea is expansion. The universe is getting bigger. This implies that in the past, it was smaller, hotter, and denser (The Big Bang).
Formal Definition
The study of the large-scale structure and dynamics of the universe. The standard model is the Lambda-CDM model (Dark Energy + Cold Dark Matter).
Intuition
- The Balloon Analogy: Galaxies are dots on a balloon. As you blow it up, the dots move away from each other. There is no “center” of the expansion on the surface.
- The Big Bang: Not an explosion in space, but an explosion of space.
Examples
- Cosmic Microwave Background (CMB): The afterglow of the Big Bang. A faint radio static filling the sky, discovered in 1965.
- Dark Energy: A mysterious force pushing the universe apart faster and faster (Accelerating Expansion).
- Inflation: A theory that the universe expanded exponentially fast in the first fraction of a second.
Common Misconceptions
- Misconception: The Big Bang was the beginning of everything.
- Correction: It’s the beginning of our current understanding. We don’t know what (if anything) came before $t=0$.
- Misconception: The universe is expanding into something.
- Correction: The universe is (likely) all there is. It creates space as it grows.
Related Concepts
- General Relativity: The math of cosmology.
- Particle Physics: The early universe was a soup of particles.
- Multiverse: The idea that our universe is just one of many.
Applications
- Philosophy: Addressing the “First Cause.”
- Fundamental Physics: The universe is the ultimate high-energy lab.
Criticism and Limitations
- Dark Sector: We don’t know what 95% of the universe (Dark Matter + Dark Energy) is. We just know it’s there by its gravity.
Further Reading
- The First Three Minutes by Steven Weinberg
- A Brief History of Time by Stephen Hawking