We are currently working on an experimental search for violations of Newton's inverse square law of gravitation using our superconducting torsion balance.

Violations of the inverse square law have been proposed by theorists as a means of solving the hierarchy problem in particle physics and the cosmological constant problem in cosmology. Both these problems arise due to the monstrous difference between the Planck energy and the energy at which electromagnetism and the Weak force are unified.

Our experimental approach comprises the measurement of the torques produced by thin-films made from alternate stripes of materials of different density (Copper and Gold). The geometry is too difficult to describe in the space available, pop by and we can explain it! Each foil is covered with a layer of gold to ensure that the non-gravitational properties of the underlying density pattern are hidden. However, we have to be careful to avoid spurious forces due to imperfections in the masses due to surface corrugations and due to changes in the surface potential above the gold and copper stripes.

We propose to use an interferometer (see the other project proposed by myself and Stuart Aston) to measure the surface roughness of the test mass foils. This will entail setting up a homodyne interferometer and a scanning system using a slip-stick piezo micro-positioner so that the topography of the surface can be measured. The unique sensitivity of the interferometer should give uniquely sensitive results!

The other experiment involves determining the difference in contact potential between the mass foils. This will be done using the Kelvin vibrating electrode method where any voltage difference (due to differences in work function) between two electrodes can be made to generate a current if one of the electrodes is vibrated so the capacitance between the electrodes changes periodically.

This will be a crucial contribution to our experimental work.

Interferometer: measurement and modelling Stuart Aston and Prof. Clive Speake)

EUCLID is a device being developed as a new optical displacement sensor. The acronym stands for Easy to Use Compact Laser Interference Device and the device is a homodyne polarising interferometer.

In this project we aim to make an accurate and complete optical model of the device using a professional optical modelling software package called Zemax. We will purchase optical components and make measurements of their properties such as optical retardance and attenuation. We have been developing these methods and are now ready to apply them to EUCLID. We will then use this information in the Zemax model to make an accurate prediction of the performance of the final assembled EUCLID. Can we make the model agree with the measured performance?