Here is a machine which seems to violate the second law of thermodynamics:
- $A$ and $B$ are point black bodies of the same temperature (initially).
- everything is rotationally symmetric around the axis $AB$
- $e$ and $f$ are ellipsoids with foci $A$ and $B$, made of a reflective material
- $CD$ and $EF$ are sections of a reflective annulus
- there is no air
The stable state of the machine is $A$ having higher temperature than $B$ because
- The heat radiated by $B$ is all absorbed by $A$ (via paths $B\rightarrow K\rightarrow A$ and $B\rightarrow J\rightarrow A$).
- The heat radiated by $A$ is either absorbed by $B$ (via paths $A\rightarrow K\rightarrow B$ and $A\rightarrow J\rightarrow B$) OR by $A$ (via paths $A\rightarrow G\rightarrow I\rightarrow A$)
This seems to violate the 2nd law.
So, where is the hole here?
PS. While point bodies and perfect mirrors do not exits, note that we have quite a lot of margin here: a huge left ellipsoid and a tiny right ellipsoid will lead to almost 50% of all radiation from $A$ reflecting back to $A$. So, "small" bodies and 90%-efficient mirrors should be fine.