Which particle property is most noticeably affected by temperatures near absolute zero?

At temperatures near absolute zero, the energy state of particles is most noticeably affected because the thermal energy of the particles decreases significantly. When temperatures drop to near absolute zero, particles are in their lowest possible energy state, and most of the thermal motion ceases. This allows the study of quantum mechanical effects, where phenomena such as Bose-Einstein condensates become observable. In this state, particles can occupy the same quantum state, behaving collectively rather than as independent particles.

In contrast, while density, shape, and volume can be affected by extreme temperature changes, the most profound changes occur in the energy state of the particles themselves, illustrating the unique behaviors of matter as it approaches absolute zero.