EJTP 9, No. 26 (2012) 293–302 Electronic Journal of Theoretical Physics The Role of Electromagnetic Field in the Stiff and Anti-stiff L.R.S Bianchi Type II Universe Hassan Amirhashchi ∗ Department of Physics, Mahshahr Branch, Islamic Azad University, Mahshahr, Iran Received 4 November 2012, Accepted 10 December 2012, Published 17 January 2012 Abstract: In this letter the role of electromagnetic field in the L.R.S Bianchi type II universe has been investigated. To get solution, the expansion (θ) in the model is assumed to be proportional to the shear (σ). It is shown that when the matter phase changes from stiff to anti-stiff fluid the universe expansion converts from decelerating to accelerating. In case of anti-stiff fluid it is found that the electromagnetic field caused the universe to be accelerating under certain conditions. The physical and geometrical behavior of these models are discussed. c  Electronic Journal of Theoretical Physics. All rights reserved. Keywords: LRS Bianchi type II models; Electromagnetic Field; Stiff Fluid; Anti-Stiff Fluid PACS (2010): 98.80.Cq; 04.20.-q 1. Introduction Although the present day universe is satisfactorily described by homogeneous and isotropic models given by the FRW space-time but as we know the universe in a smaller scale is neither homogeneous nor isotropic nor do we expect the universe in its early stages to have these properties. In fact, to get physically realistic description of the universe one has to consider inho- mogeneous models. In this case, the solutions of Einstein’s field equations become more complicated or may be impossible. Therefore, many theoretical cosmologists are trying to use the spatially homogeneous and anisotropic Bianchi type models instead of inhomoge- neous models. These types of space-times present a ”middle way” between FRW models and inhomogeneous and anisotropic universes and hence play an important role in mod- ern cosmology. The choice of anisotropic cosmological models in Einstein system of field equations leads to the cosmological models more general than Robertson-Walker model. Bianchi type cosmological models are important in the sense that these are homogeneous * Email:hashchi@yahoo.com, h.amirhashchi@mahshahriau.ac.ir