Okay, so you know how sometimes when you play with toys or blocks, you can change their positions around? Maybe you move a block from one pile to another or you flip a toy car upside down. Unitary operators are basically like special toys that you can use to move things around in a very specific way.
But instead of using blocks or toys, we are using special things called matrices. Matrices are like a grid of numbers.
A unitary operator is like a special set of instructions we can use to move around our matrices in a very specific way. And the cool thing about these instructions is that they make sure our matrices keep all their important properties, even after we've moved them around. It's kind of like playing a game of Jenga where you have to move blocks around without making the whole stack fall down.
These operators are very helpful in things like quantum mechanics, where we're trying to understand how tiny particles behave. Using unitary operators, we can do things like change the state of a particle (which means changing its different properties like its position or energy) without actually changing any of the important information we know about that particle.
So unitary operators are like special toys that help us move our matrices around in a way that keeps all the important information intact. And scientists use them to learn more about the universe, just like how you might use toys to learn about how things fit together or move around.