Explore why the night sky is dark despite an infinite universe.
Cosmological Parameters
Night Sky Analysis
Adjust parameters to see the visible star count
About this calculator
Quick Reference
cSpeed of Light
tAge of Universe
nAverage Stellar Density
ctRadius of Observable Universe
Overview
Olbers' Paradox, or the 'dark night sky paradox', is the argument that the darkness of the night sky conflicts with the assumption of an infinite and eternal static universe.
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Pro Tips
If the universe were infinite, static, and timeless, every line of sight would eventually hit a star, making the sky as bright as the Sun's surface.
The paradox is resolved because the universe is finite in age (13.8 billion years) and is expanding.
Light from very distant stars hasn't had time to reach us yet.
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Fun Facts
"The paradox is named after the German astronomer Heinrich Wilhelm Olbers (1758–1840)."
"The expansion of the universe causes 'redshift', moving light from distance stars into the infrared spectrum, invisible to our eyes."
"Edgar Allan Poe was one of the first to suggest that the finite age of the universe resolves the paradox."
