A falling apple from a tree inspired Sir Isaac Newton to formulate a theory that tell us that a moving body keeps on moving on a straight line unless any disturbing force may change its path. Newton's laws impact is experienced in our daily lives.
However, in the quantum world, our instinct towards the motion of objects, completely fails or gets strongly challenged. A marble falling through water in an oscillating manner instead of moving straight downwards is unimaginable.
Yet, experimental physicists have discovered such a strange behavior from a quantum particle. This surprising behavior is referred to as 'quantum interference' where particles in quantum mechanics behave like waves.
For observing the quantum particle, they cooled a gas of Cesium atoms above absolute zero temperature and enclosed it to a setting of very thin tubes via using high-power laser beams. They made the atoms to strongly interact with each other. Then they accelerated an impurity atom through the gas. It was observed that as the particle moved, it scattered off the gas particles and reflected backwards. This caused an oscillatory motion, instead of falling downwards, demonstrating that Newton’s law is inapplicable in the quantum realm.