Page "Quantum mechanics" Paragraph 13

Quantum mechanics is essential to understanding the behavior of systems at atomic length scales and smaller.

For example, if classical mechanics truly governed the workings of an atom, electrons would rapidly travel toward, and collide with, the nucleus, making stable atoms impossible.

However, in the natural world electrons normally remain in an uncertain, non-deterministic, " smeared ", probabilistic wave – particle wavefunction orbital path around ( or through ) the nucleus, defying classical electromagnetism.