Preston Guynn Thanks very much for your detailed explanation. What I am trying to comprehend is why the temperature of matter must be greater than the absolute (> 0 K). And why is it so hard, practically, to approach the zero Kelvin? What would happen to the matter or atoms when they approach the zero?

The absolute zero, according to the third law of thermodynamics, is the point at which entropy turns 0 (for an ideal crystal). That means all motion modes (translation, rotation, vibration, electronic excitation) of all atoms have been frozen out and thermal defects have returned to their ideal position.

Regarding "why can't we go below", the answer is easy from that point: you can't do more than freezing out the motion. If there is no motion left, that's it, you can't stop something that has already ceased to move.

Regarding "why can't we reach it", I could just refer to the Nernst heat theorem which states that cp->0 for T->0 and if you try integrating that with respect to the entropy, the integral diverges which equals "it wouldn't make sense physically". But since it feels kind of lazy to just feed you a formalistic answer, here is an image: as mentioned above, all thermal motion must be frozen at T=0 and all defects must be cured. However, in order to freeze out those defects, you need to provide the atoms with the energy necessary to move back to their perfect position and that involves going up again, so essentially "the cat is biting its own tail".