Albert Einstein

Imagine that mass and energy are two faces of the same coin. A small quantity of mass contains an immense quantity of energy, because we multiply by the speed of light squared. That is what makes the sun shine, and what makes the atom dangerous.

My greatest blunder was the cosmological constant, introduced to keep the universe still. Then Hubble showed me it expands. A scientist who refuses to revise his ideas is not a scientist. Doubt is the mother of discovery.