Expansion of the Universe
The expansion of the universe is the increase in distance between gravitationally unbound parts of the observable universe over time. This fundamental concept resolves several cosmological paradoxes, including the darkness of the night sky.
Key Concepts
- Olbers’ Paradox: The question of why the night sky is dark if the universe is infinite and static. The expansion of the universe (and its finite age) provides the primary resolution by redshifting light and limiting the observable horizon.
- For detailed analysis, see Olbers’ Paradox: Why the Night Sky is Dark.
- Cosmological Redshift: As space expands, the wavelength of light traveling through it stretches, shifting towards the red end of the spectrum. This reduces the energy of photons from distant galaxies.
- Finite Age: The universe has a finite age (~13.8 billion years). Light from stars beyond a certain distance has not had time to reach us, preventing the sky from being uniformly bright.
- Observable Universe: The spherical region of the universe comprising all matter that can be observed from Earth at the present time, limited by the speed of light and the age of the universe.