### Van der Waals and Casimir Forces: Effects of
Finite Temperature and Dissipation

**Bo E. Sernelius**

*Department of Physics and Measurement
Technology*

*Linköping University*

*SE-581 83 Linköping, Sweden*

I will discuss the zero-temperature dispersion-forces in terms
of changes in the zero-point energy of the electromagnetic normal-modes
of the system. The van der Waals and Casimir forces are due to
different types of mode. In the simplest cases the result can
be found from summing the changes of each mode. In the more complex
situations one may use a generalization of the *Argument Principle*,
a well-known theorem from complex analysis, and end up with integrations
or summations along the complex-frequency axis.

I will address the dispersion forces between metal plates and
discuss effects from finite temperature and dissipation. Results
for "perfect" metals, from simple Drude approximation,
from full Drude approximation and from using the experimental
dielectric function will be presented.

I will also briefly discuss the analytical properties of the
dissipation correction in the dielectric function, the dynamic
relaxation time.

At the end I will raise some questions or discussion topics:

The first is about thermal equilibrium. Our system consist
of two parts: the interior of the metal plates and the surrounding
vacuum. The interior is kept at 300 K. The vacuum in the outer
space is kept at 3 K. Can we assume that the vacuum between and
near the plates is at equilibrium at 300 K?

Why do the **TM**-modes but not the **TE**-modes contribute
to the dominating term at high temperatures and/or large separations?

Are the boundary conditions used by us and by others O.K.?