Defining Olbers' Paradox
Olbers' Paradox asks why the night sky is predominantly dark, rather than being uniformly bright, if the universe is infinite in size and filled uniformly with an infinite number of stars. Intuitively, in such a universe, every line of sight should eventually end on the surface of a star, making the entire sky glow as brightly as the surface of the Sun.
The Simple Argument
The paradox arises from a seemingly logical assumption. If stars are distributed evenly throughout an infinite universe, then no matter which direction you look, your line of sight would eventually hit a star. Distant stars would appear dimmer, but there would be vastly more of them, theoretically compensating for their diminished brightness, leading to a uniformly bright night sky.
Resolutions to the Paradox
Modern cosmology resolves Olbers' Paradox primarily through two key concepts. First, the universe has a finite age (approximately 13.8 billion years), meaning light from very distant stars hasn't had enough time to reach us. Second, the universe is expanding, causing light from distant galaxies to redshift, shifting it out of the visible spectrum and making it appear much fainter than it otherwise would.
Implications for Modern Cosmology
The darkness of the night sky, explained by the finite age and expansion of the universe, provides strong observational evidence supporting the Big Bang theory. It refutes the static, infinitely old universe model, paving the way for our understanding of cosmic evolution and the limits of the observable universe.