Saved on this device

Follow your curiosity

What discovery has been shared with you?

FACTREE gives you something interesting to discover every day — and something worth talking about together.

Start with one fact. Explore it, go deeper, then follow whichever branch catches your imagination.

Choose subjects for a surprise

Exploring any topic

Begin your discovery

Your next discovery is one click away.

Choose one or more subjects above, or leave Any Topic selected and let curiosity decide.

Astronomy

Cosmological Constant

Quick fact

The cosmological constant was originally inserted by Albert Einstein in 1917 to force the universe to be static, but after Hubble discovered expansion, Einstein called it his 'biggest blunder.' Today it's back as the simplest model for dark energy.

Why this is interesting

What if the empty space between galaxies wasn't truly empty, but contained a hidden repulsive force? That's exactly what the cosmological constant proposes—and it's accelerating the universe's expansion.