The observable universe is approximately 13.7 billion years old. But yet it is 80 billion light years across. Isn't this a contradiction?
[Physics] Why is the observable universe so big
cosmologyfaster-than-lightspace-expansionuniverse
cosmologyfaster-than-lightspace-expansionuniverse
The observable universe is approximately 13.7 billion years old. But yet it is 80 billion light years across. Isn't this a contradiction?
Best Answer
This question implicitly refers to the visible universe, but we should state that explicitly, as otherwise the question doesn't make any sense.
It may seem like we shouldn't be able to see more than 13.7 billion light-years (13.7 giga-light-years, or glyrs) away, but that reasoning omits the expansion of spacetime according to General Relativity. A photon emitted from somewhere near the beginning of the Universe would have traveled nearly 13.7 glyrs if you had measured each light-year just as the photon crossed it, but since those light-years that you measured have expanded since the photon passed through, that distance now adds up to about 80 glyrs.