Comment by api
2 days ago
It’s a logical extrapolation if you think life is a natural phenomenon. It would be exceedingly weird to see no evidence for it, but of course we have not been looking long or far.
And yes, space flight is brutally hard. Look up the history of sailing. Look up the Polynesian indigenous peoples and how long that took, through multiple waves of exploration, or the people who walked across a land bridge to North America during the ice age. Space flight is easier and safer than some of those feats, given the tech they did it with at the time.
If there is a fantasy it’s the idea that we’d have bases on the Moon and Mars by now. What we are doing today is the equivalent of early Polynesians hollowing out some logs and going fishing.
Natural doesn't mean likely. Say life rarely gets started, because it requires some kind of accidental evolutionary engine involving rivers and clay crystals, some unusual conditions of weather and geology. Then say life rarely gets complex and big, because mats of bacteria can be the dominant species indefinitely. So the universe is mostly dead, and the living parts are mostly slime. Then say actual human-like intelligence, the kind that tries really hard to imagine new things to meddle with and new spaces to explore, such as exploring the space space, is a freakish mutation and is unlikely to be adaptive at first. So it rarely happens and then usually dies out straight away. The rare instances of complex life, then, are mostly just floating around in oceans wiggling their complex limbs fecklessly. So those are two terms in the Drake equation, with an extra one about complexity added in the middle, and they multiply together to make things very unlikely by an unknown amount. We don't know what the numbers are. It might be natural that there isn't any sign of life out there, if the small probability of spacefaring life is smaller than space is big.
Ultimately we don’t know. We have not been looking far or long.
SETI BTW is kind of a joke. The only way we would hear anything is if someone was very close or was intentionally blasting a signal at us at incredible transmit power (like terawatts or more). Radio signals fade pretty quickly.
> It’s a logical extrapolation if you think life is a natural phenomenon.
No, it really isn't. Taking life on Earth as an example, almost all of our technological signatures are effectively undetectable as little as 5 light years away. See e.g. the paper "Earth Detecting Earth" (https://arxiv.org/pdf/2502.02614). The maximum detectable distance for unintentional signal leakage is 4 light years - about the distance to Proxima Centauri, the nearest star. So if we're looking for that kind of signal, we have a population of exactly one star system that we might be able to detect something from, at the maximum end of the detectable range.
The paper also lists a couple of exceptions, which are the highly directional Deep Space Network and planetary radar, theoretically detectable at 65 ly and 12,000 ly respectively. But these only cover small parts of the sky for short periods, making interception of such signals extremely unlikely. Also, signals like that have only been transmitted for decades at most, so there are at most a few thousand star systems that could conceivably have intercepted one of these signals.
All in all, while the probabilities involved can't be calculated with certainty, they do certainly lean towards it being very unlikely for us to have detected another technological civilization. Which is consistent with what we actually observe.
Detecting non-technological signs, like atmospheric gases, is more feasible but also not necessarily definitive. E.g., the recent evidence for dimethyl sulfide in the atmosphere of K2-18b is considered a tentative candidate for a biosignature, but is in no way definitive.
In short, the Fermi "Paradox" mainly confirms what we now know about the difficulty of detecting life beyond our solar system.
As for spaceflight vs. sailing, at some point extrapolation from analogies just breaks down, and interstellar travel is certainly one of those cases. The energy demands, distances, timescales, technological limitations, radiation issues, economic and political issues, etc. all combine to make it an effectively impossible project.