The concept of temperature is related to the average kinetic energy of particles in a system. In classical thermodynamics, temperature is defined in terms of the random motion of particles, where higher temperatures correspond to greater average kinetic energies. However, at absolute zero (0 Kelvin), the particles are in their lowest energy state and have minimal or no kinetic energy.
In quantum mechanics, the behavior of particles at extremely low temperatures is described by Bose-Einstein condensation or Fermi-Dirac statistics, depending on whether the particles are bosons or fermions, respectively. In these quantum states, particles exhibit unique behaviors that are distinct from classical particles.
Reaching temperatures close to absolute zero, such as a few billionths of a Kelvin, is possible using techniques like laser cooling and evaporative cooling. These methods can cool certain types of atoms or molecules to very low temperatures by removing energy from the system. However, reaching exactly absolute zero (0 Kelvin) is not achievable in practice due to the constraints of the third law of thermodynamics and the limitations of cooling techniques.
The third law of thermodynamics, also known as the Nernst heat theorem, states that it is impossible to reach absolute zero through a finite number of processes. As the temperature approaches absolute zero, the cooling process becomes progressively more challenging, and it requires an infinite number of steps to reach absolute zero.
Additionally, the Heisenberg uncertainty principle, a fundamental principle in quantum mechanics, places limitations on simultaneously measuring the position and momentum of particles. This principle implies that it is not possible to precisely determine the position and velocity of a particle, particularly at extremely low temperatures. Therefore, the notion of "making atoms move backward" and achieving colder temperatures does not align with the principles of quantum mechanics and our current understanding of the laws of physics.
While scientists have achieved extremely low temperatures, even within billionths of a Kelvin, absolute zero remains an unattainable theoretical limit in practical experiments.