Thermal equilibrium versus pressures

[intervoxel]

Is it possible for a closed system in thermal equilibrium possesses two regions with different pressures supposing such regions had the same pressure in the past?

 

[Mapes]

It's required by atomic theory and thermodynamics. "Pressure" is just the average force per unit area from the bombardment of vast numbers of atoms; thus, random fluctuations are inevitable. Two regions of equal pressure at one instant can hardly avoid having different pressures at the next instant, due to atomic motion. The larger the system, however, the smaller the deviations from the average value. On the human scale, these deviations are essentially unmeasurable.

 

[atyy]

Does the question require that the system was in thermal equilibrium when it consisted of a single region of uniform pressure?

 

[intervoxel]

No, it is supposed they had different temperatures in the past.