The size of the universe is unknown.

The diameter of the observable (where "observable" refers to the universe that can theoretically be observed since the light coming from that area has had time to reach us since the Big Bang) universe is estimated to be about 93 billion lightyears (about 29 billion parsecs or about \(8.8 \times 10^{23}\) kilometers).[1] As nothing can exceed the speed of light, some nonastronomers and laymen assume that the observable universe is actually 13.8 billion light-years in size, as this is the scientifically hypothesized age of the universe in years. The curvature of the universe makes it much larger than this.[2]

The diameter of the actual universe is unknown. One source estimates that the whole universe is at least 250 times larger than the observable universe,[3] whereas other sources give lower bounds of \(3 \times 10^{23}\) times[4] and \(10^{10^{10^{122}}}\) times.[5]

Cosmologist Andrei Linde estimates possible number of universes in the multiverse as \(10^{10^{10^7}}\).[6]

If the universe's geometry is flat (i.e. it has zero curvature), it will be infinite in size. A NASA study showed that the universe is flat with only a 0.4% margin of error.[7]

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Large numbers in science