According to the principles of quantum mechanics, atoms are in constant motion, even at temperatures close to absolute zero. This motion arises from the inherent properties of atoms and the nature of their constituent particles, such as electrons and nuclei.
At absolute zero temperature (-273.15 degrees Celsius or 0 Kelvin), the atoms comprising a substance will reach their lowest possible energy state, known as the ground state. In this state, the atoms will exhibit minimal thermal motion. However, even at absolute zero, atoms will still possess some residual motion due to quantum mechanical effects.
The Heisenberg uncertainty principle, a fundamental principle of quantum mechanics, states that there is a fundamental limit to the precision with which certain pairs of physical properties, such as position and momentum, can be simultaneously known. This implies that even in the ground state, atoms will exhibit inherent quantum fluctuations, causing them to undergo spontaneous fluctuations in their position and momentum.
Additionally, atoms are subject to zero-point energy, which is the lowest possible energy that a quantum mechanical physical system can possess. This energy arises from the fact that particles, such as electrons, cannot be at rest due to their wave-like nature. As a result, even at absolute zero, atoms will still possess a residual amount of energy and motion.
Therefore, due to quantum mechanical effects and zero-point energy, atoms never truly come to a complete stop, even at temperatures approaching absolute zero.