In this context, "information" means "any sort of physical interaction". In accepted relativistic physical theories, no information can travel faster than the speed of light. In a more general sense, there are portions of the universe that are visible to us, but invisible to each other, outside each other's respective particle horizons. This means that the light from the first has not yet reached the second because the universe is only about 13.8 billion years old. If one were to look at a galaxy ten billion light-years away in one direction and another in the opposite direction, the total distance between them is twenty billion light-years. A galaxy measured at ten billion light-years appears to us as it was ten billion years ago, because the light has taken that long to travel to the observer. We use the light-year (the distance light can travel in the time of one Earth year) to describe these cosmological distances. The distances of observable objects in the night sky correspond to times in the past. Different solutions propose a cyclic universe or a variable speed of light.īackground Astronomical distances and particle horizons The most commonly accepted solution is cosmic inflation. It was first pointed out by Wolfgang Rindler in 1956. It arises due to the difficulty in explaining the observed homogeneity of causally disconnected regions of space in the absence of a mechanism that sets the same initial conditions everywhere. The horizon problem (also known as the homogeneity problem) is a cosmological fine-tuning problem within the Big Bang model of the universe. The two points indicated on the diagram would not have been able to contact each other because their spheres of causality do not overlap. In that time light would have only reached as far as the smaller circles. However, when the light was emitted the universe was much younger (300,000 years old). When we look at the CMB it comes from 46 billion comoving light-years away. For the problem relating to artificial intelligence, see Horizon effect. This article is about the astronomical "horizon problem".
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