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Because space-time is expanding at an extraordinary rate, such that vast portions of the universe are forever inaccessible? "For example there are stars which
by codex 13y ago
Because space-time is expanding at an extraordinary rate, such that vast portions of the universe are forever inaccessible?
"For example there are stars which may be expanding away from us (or each other) faster than the speed of light, and this is true for any object that is more than approximately 4.5 gigaparsecs away from us." [1]
That said, 4.5 gigaparsecs is 10^10 light years, which is still pretty damn big.
[1] https://en.wikipedia.org/wiki/Metric_expansion_of_space https://en.wikipedia.org/wiki/Metric_expansion_of_space
- baddox 13y agoIsn't the expansion of the universe way out of scope of this article and discussion? Obviously, if there are aliens that far away, they by definition cannot reach us.
- codex 13y agoIt 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.