  The Tajmar anomaly is an unexplained acceleration observed by gyroscopes
close to, but isolated from, rotating rings cooled to 5K. The observed ratio
between the gyroscope and ring accelerations was 3+/-1.2*10^-8 for clockwise
rotations and about half this size for anticlockwise ones. Here, this anomaly
is predicted using a new model that assumes that the inertial mass of the
gyroscope is caused by Unruh radiation that appears as the ring and the fixed
stars accelerate relative to it, and that this radiation is subject to a
Hubble-scale Casimir effect. The model predicts that the sudden acceleration of
the ring causes a slight increase in the inertial mass of the gyroscope, and,
to conserve momentum the gyroscope must move with the ring with an acceleration
ratio of 2.67+/-0.24*10^-8 for clockwise rotations and 1.34+/-0.12*10^-8 for
anticlockwise ones, in agreement with the observations. The model predicts that
in the southern hemisphere the anomaly should be larger for anticlockwise
rotations instead, and that with a significant reduction of the mass of the
disc, the decay of the effect with vertical distance should become measurable.
