Infinite Universe
The hypothesis that the universe extends without bound in space and/or time. This concept is central to several cosmological models and paradoxes regarding the nature of light, matter, and the observable horizon.
Key Implications & Paradoxes
Olbers’ Paradox
A fundamental contradiction arising from the assumption of an infinite, static, and eternal universe.
- The Paradox: In an infinite universe uniformly filled with stars, every line of sight should eventually intersect a star, making the night sky as bright as the surface of the sun.
- Resolution: The night sky is dark because the universe has a finite age (~13.8 billion years) and is expanding. Light from distant stars has not had time to reach us, and cosmological redshift reduces the energy of photons from distant sources.
- Related Note: Olbers’ Paradox: Why the Night Sky is Dark
Observable Universe
- Due to the finite speed of light and the age of the universe, we can only observe a spherical region centered on Earth.
- The boundary is defined by the particle horizon.
- An infinite universe may contain regions forever causally disconnected from us.
Cosmological Principle
- Assumes the universe is homogeneous (same everywhere) and isotropic (same in all directions) on large scales.
- Supports the idea that local observations can be extrapolated to the global structure.
Related Concepts
- Big Bang Theory
- Observable Universe
- Cosmological Horizon
- Dark Energy
- Expansion of the Universe