Why is the night sky dark?#
Look up on a clear night.
Most of the sky is black.
Imagine a universe that is#
- infinite
- eternal
- static
- stars, spread evenly, everywhere
Look in any direction#
· · ★ · · · ★ ·
★ · · ★ · · · ·
· ↑ · ★
youFollow that line far enough. It ends on a star.
So every direction should end on something bright.#
The whole sky should glow.
It does not.
So the darkness is evidence.
What has to give#
Not eternal. Not static.
It has a history — and it is expanding.
Finite age isn’t the whole story#
- stars don’t shine forever
- expansion stretches and reddens light
- matter isn’t spread perfectly evenly
The dark between the stars is doing work.