It could explain why we haven't encountered aliens despite the advanced age of the Earth. The Earth has been around for roughly 1/3rd the age of the universe,

It could explain why we haven't encountered aliens despite the advanced age of the Earth. The Earth has been around for roughly 1/3rd the age of the universe, but because space time is expanding exponentially, only a fraction of the universe (roughly 20%) is theoretically reachable, even when travelling at the speed of light. A planet like Earth that formed around the same time, or earlier, even relatively close to the Earth, may now be in the unreachable zone. By the same token, the longer it takes for an intelligent species to evolve, the less likely it is that they will ever be able to contact us.