  We perform detailed comparison of the experimental data of the experiment on
the determination of the Casimir pressure between two parallel Au plates with
the theoretical values computed using the Lifshitz formula at zero temperature.
Computations are done using the optical data for the complex index of
refraction of Au extrapolated to low frequencies by means of the Drude model
with both most often used and other suggested Drude parameters. It is shown
that the experimental data exclude the Lifshitz formula at zero temperature at
a 70% confidence level if the Drude model with most often used values of the
parameters is employed. If other values of the Drude parameters are used, the
Lifshitz formula at zero frequency is experimentally excluded at a 95%
confidence level. The Lifshitz formula at zero temperature combined with the
generalized plasma-like model with most often used value of the plasma
frequency is shown to be experimentally consistent. We propose a decisive
experiment which will shed additional light on the role of relaxation
properties of conduction electrons in the Casimir effect.
