Suppose there is a beam of atoms moving with constant velocity in empty space. There are no collisions between the atoms. The temperature is essentially zero since velocities of atoms are all equal to the velocity of the center of mass.
Now let’s trap the atomic beam into a box. When atoms collide with walls, kinetic energy of the center of mass will be lost, and will turn into temperature. In addition, entropy of the system will increase.
Does this mean that entropy is growing due to collisions of atoms with the walls? So essentially collision events drive entropy growth? What is it about the collisions that makes them increase entropy, is it due to quantum randomness of outcomes?