theory of time

Photo credit: via Carl Sagan Planetary Society/Wikimedia Commons and John Finkelstein/Pexels – Carl Sagan used a sliced apple to perfectly explain the fourth dimension.

Planet, Popular, Science

46 years ago, Carl Sagan beautifully explained the fourth dimension using a sliced apple

Tod Perry

2/9/2026
An Operation Smile volunteer reverses an oxygen mask so a child with a cleft condition can blow a bubble for the first time in Guadalajara, Mexico. (Operation Smile Photos)

In Partnership With Operation Smile →

Family, Science

How Bubbles Help Kids with Cleft Conditions

Sarah Watts

5/11/2026