Horizon problem

This article is about the astronomical "horizon problem". For the problem relating to computers, see Horizon problem in computer programs. The horizon problem is a problem with the standard cosmological model of the Big Bang which was identified in the 1970s. It points out that different regions of the universe have not "contacted" each other due to the great distances between them, but nevertheless they have the same temperature and other physical properties. This should not be possible, given that the exchange of information (or energy, heat, etc.) can only take place at the speed of light. The horizon problem may have been answered by inflationary theory, and is one of the reasons for that theory's formation.
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The problem of explaining how the cosmic background radiation became isotropic when separate regions of the sky cannot be linked to one another. The cosmic background radiation, from every part of the sky is a black body radiation curve produced by an emitter at about three degrees Kelvin. The problem is that the observable universe is not yet old enough for light to have travelled from one side of it to the other. Thus, thermal reactions to equalise the temperature cannot yet have taken place. Astronomers are therefore puzzled as to how the uniform temperature came into being. The horizon problem and the flatness problem are solved, for now, by the cosmological theory of inflation.