Olbers' Paradox
The apparent paradox that if the universe were static, infinite, and uniformly populated with stars, the night sky should be uniformly bright as the Sun.
Governing formula
Night sky brightness J = ∫ 4 π I r² dr / (4 π r²) → ∞ (in static infinite universe)
SI unit
Cosmological Paradox
In depth
Resolved by modern cosmology: the universe has a finite age (~13.8 billion years), so light from distant stars has not had time to reach us (finite observable universe horizon), and space is expanding, redshifting distant light.
Examples in the real world
Understanding why the night sky is dark despite trillions of stars existing in the universe.