  It is well known since a long time that all lossy conductors at finite
temperature display an electronic noise, the Johnson-Nyquist noise, arising
from the thermal agitation of electric charges inside the conductor. The
existence of this noise implies that two nearby discharged conductors at finite
temperature should repel each other, as a result of the electrodynamic
interaction between the Johnson-Nyquist currents in either conductor and the
eddy currents they induce in the other. It is suggested that this force is at
the origin of the recently discovered large repulsive correction to the thermal
Casimir force between two lossy metallic plates. Further support for this
physical picture is obtained by studying a simple system of two linear noisy
antennas. Using elementary concepts from circuit theory, we show that the
repulsive force engendered by the Johnson-Nyquist noise results in the same
kind of thermodynamic inconsistencies found in the Casimir problem. We show
that all inconsistencies are however resolved if account is taken of capacitive
effects associated with the end points of the antennas. Our findings therefore
suggest that capacitive effects resulting from the finite size of the plates,
may be essential for a resolution of the analogous problems met in the thermal
Casimir effect.
