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Matter with an equation of state p0ex0ex=0ex0ex-ρ/3 may arise in certain scalar field theories, and the energy density of this matter decreases as a^-2 with the scale factor a of the Universe. In this case, the Universe could be closed but still have a nonrelativistic-matter density Ω₀<1. Furthermore, the cosmic microwave background could come from a causally connected region at the other side of the Universe. This model is currently viable and might be tested by a host of forthcoming observations.
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Kamionkowski et al. (1996) studied this question.
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