In the early days of quantum mechanics , Albert Einstein suggested that if it were right then quantum mechanics would mean that there would be `` spooky action at a distance . '' It turned out that quantum mechanics was right , and that what Einstein had used as a reason to reject quantum mechanics actually happened . According to the correspondence principle between classical and quantum mechanics , all objects obey the laws of quantum mechanics , and classical mechanics is just an approximation for large systems ( or a statistical quantum mechanics of a large collection of particles ) .