Here's why:

* Thermal Energy and Particle Motion: Temperature is a measure of the average kinetic energy of particles within a substance. At very low temperatures, particles have very little kinetic energy, meaning they move very slowly.

* Intermolecular Forces: The forces of attraction between particles (intermolecular forces) become dominant at low temperatures. These forces hold particles tightly together in a fixed, ordered arrangement.

* Solid State: This fixed, ordered arrangement of particles defines the solid state of matter.

Exceptions:

* Helium: Helium remains a liquid even at extremely low temperatures due to its weak interatomic forces.

* Bose-Einstein Condensate: At extremely low temperatures (near absolute zero), some substances can enter a state called a Bose-Einstein condensate, where individual atoms behave as a single entity.

Let me know if you'd like to explore any of these concepts further!