The Night Sky Should Be Brighter Than the Sun

Summary by Krater

This video explains Olbers' paradox—why the night sky is black despite an infinite number of stars—and explores how the expansion of the universe stretches starlight into the cosmic microwave background and why human eyes perceive eigengrau instead of true black.

From the video

Answers: Why is the night sky dark if there are an infinite number of stars?

• Olbers' paradox
• Cosmic Microwave Background
• Starlight brightness and distance
• Expanding universe
• Eigengrau
• Human vision and retinal thermal noise

What it concludes

• The apparent brightness of a tiny patch of a star's surface stays the same regardless of distance because size and light decrease by the exact same factor.
• The night sky is not infinitely old and the universe is expanding, which stretches visible starlight into the microwave range known as the cosmic microwave background.
• Human eyes cannot see true black because random thermal motion in the retina activates cells in the absence of photons, producing a dark grey known as eigengrau.