Testing non-commutative QED, constructing non-commutative MHD

The effect of non-commutativity on electromagnetic waves violates Lorentz invariance: in the presence of a background magnetic induction field b, the velocity for propagation transverse to b differs from c, while propagation along b is unchanged. In principle, this allows a test by the Michelson-Morley interference method. We also study non-commutativity in another context, by constructing the theory describing a charged fluid in a strong magnetic field, which forces the fluid particles into their lowest Landau level, and renders the fluid dynamics non-commutative, with a Moyal product determined by the background magnetic field. (C) 2001 Elsevier Science B.V. All rights reserved.