I asked my teacher what protons were made of and when he said "quarks" I thought he said "cork" and for a long time after that I thought that cork was the fundemental substance of the universe and that the cork on wine bottles were made of "pure" matter.
A childhood belief about physics

others believed things like this
- I believed that linguini was made of tape worms and was scared to eat pasta for a long time!— Mojo!
- i thought salt made food cold, since pepper made it *hot* — cattiva
- I long believed that Ronald Reagan was Ronald McDonald's brother. And I thought it made him more impressive!— JB
- The first time I saw a black person (I was about 3), I thought he was made of chocolate.— Ronne
- I always thought there was a drinking age for coffee, because it was an adult drink like beer and wine.Anon
- I thought common as muck was a substance called commoners muck— oddsox