How big is the Universe?

We don’t really know.

We can see 13.8 billion light-years in every direction so we know the radius is at least that much. Accounting for the time it takes light to reach us from other stars and the rate at which galaxies are moving apart, we find that the observable Universe must be at least 93 billion light-years in diameter.

But that’s just the observable Universe, i.e. the part we can see. We don’t know what’s beyond that but most likely it’s more of the same. The size of the entire Universe depends a great deal on its overall shape, but we don’t know what that is either (see Shape of the Universe).

Based on what we do know it’s quite possible that the Universe is infinite in size, but that’s just an educated guess. In short, we don’t have enough information to answer this question... yet.

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