Einstein's equation

E = mc²

links mass and energy by the square of the speed of light.

That means that mass can be converted into energy and vice versa

.... something 'material' becomes pure energy - no matter remaining - just energy

... or we get something material 'out of thin air'.... equally mindblowing!

We come across this relationship in several areas of study:

Nuclear binding energy

Pair Production

Annihilation

Cosmic Rays

Radioactivity