Wikipedia:Reference desk/Archives/Science/2024 February 22

= February 22 =

Aliens have killed themselves
There are reasons to think that extraterrestrial life should be common, but so far we have never find any. The Fermi paradox provides several possible explanations for it, such as that aliens may self-destruct after discovering atomic power or other advanced technologies. But today I was thinking, should that be an obstacle? Let's say that the Klingons started an atomic war and killed themselves before we could get anywhere near a Star Trek situation. Shouldn't we still be able to detect anyway an exoplanet with an atmosphere polluted with high levels of radiation, that could not be explained by natural processes? Wouldn't other ways of an alien civilization to self-destruct (chemical war, mere pollution, etc) leave detectable clues as well?

I don't think I need to explain that such a discovery (a world where life existed, and more, intelligent life!) would still be a revolutionary one, even if there was nobody left by now. Cambalachero (talk) 18:15, 22 February 2024 (UTC)


 * Well, for one, the Fermi paradox presumes that civilisations spread through the galaxy. If they self-destroy before reaching that phase (as we very well might still do, assuming we even are civilised to begin with), then they are much less frequent, and hence much harder to detect. Also, we can sometimes get some spectroscopic data for some exoplanet atmospheres, but I doubt we can distinguish between radioactive and other isotopes that way. --Stephan Schulz (talk) 18:54, 22 February 2024 (UTC)
 * That depends on the method of spectroscopy, element, and compound. Infrared techniques and microwave techniques, or redshifted forms of them, are molecular spectroscopy, see infrared spectroscopy and microwave spectroscopy. These are tools for measuring molecular vibrations and molecular rotations, respectively, and the masses of the atoms within the compounds play a major factor in the spectral signature. The frequencies of their absorptions are inversely proportional to the square root of the reduced mass of the system. In a diatomic molecule, for example, a significant change in the mass of of the atoms by isotopic substitution is easily detectable, and is often used as a tool in studying molecular systems by intentionally substituting for isotopes. Take the case of HCl; it's infrared spectrum is made up of doublets due to the presence of both chloride-35 and chloride-37 isotopes, which exist in known ratios (under natural conditions) reflected in the relative intensities of the doublet peaks. If that ratio were to be different, that would at least indicate something unusual had happened. The difference in frequency there is fairly small, but the difference in frequency between HCl and DCl is quite large and incredibly easy to detect. While it would be harder to detect than chlorine-37, HCl composed of chlorine-36 could, if detected, be an indicator of the use of nuclear weapons, since our underwater testing of nuclear weapons produced a great deal of chlorine-36. That's just one example, though. I'll bet a careful examination of the isotopic products of a nuclear exchange was done, others examples could be found, and a potential model for IR/MW examination for extra-terrestrial nuclear weapons use could be designed. --OuroborosCobra (talk) 19:29, 22 February 2024 (UTC)
 * Good point - I had only thought about atomic spectra. --Stephan Schulz (talk) 19:39, 22 February 2024 (UTC)


 * Also, going by our own example, it wouldn't take much to cause the collapse of a single-system technological civilization at our own level or beyond (which needn't cause total extinction), and any effects detectable at long range would be short lived in astronomical terms. Such civilizations might arise not uncommonly Galaxy-wide, but too far separated in time for their technological eras to overlap. {The poster formerly known as 87.81.230.195} 176.24.45.226 (talk) 19:27, 22 February 2024 (UTC)
 * There is no way of establishing ferm lower bounds on most of the variables featuring in the Drake equation. If a technologically advanced civilization arises about once every million years in our galaxy and then inevitably blows itself up, the signature of the calamity will have disappeared by the time we examine the planet. --Lambiam 22:49, 22 February 2024 (UTC)
 * The Fermi Paradox has always struck me as being misnamed. The idea that the galaxy should be full of aliens rests on so many assumptions that it us not having found evidence of any (let alone evidence that they have visited us) hardly seems to constitute a "paradox". Iapetus (talk) 10:55, 23 February 2024 (UTC)
 * It has that in common with many puzzling facts named "paradoxes": Antarctic paradox, Denny's paradox, Elevator paradox, Potato paradox, Willpower paradox. Informally, the term paradox is often used to describe a counterintuitive result. Case in point: our page Counterintuitive redirects to the article Paradox. --Lambiam 13:52, 23 February 2024 (UTC)
 * Our article Date of Easter talks about the "Easter paradox", meaning that it is not observed on the Sunday after the full moon, or it is observed on the Sunday after the "wrong" full moon.  Kepler gave the answer to that:  "Easter is a feast, not a planet."   Incidentally, following the introduction of a new table acceptable to everyone Special:Permalink/1188536894 it is anticipated that this year's divided celebration (split between 31 March and 5 May) will be the last.   It was the 31 March celebration ordered by the Romanian Orthodox Church which led to the peasants' revolt and the disappearance of the Gregorian Easter from Orthodox eastern Europe (barring Finland, where the government offers the Orthodox church there money to keep the Gregorian Easter, to which their response is "Why not?") 81.154.229.214 (talk) 17:19, 23 February 2024 (UTC)
 * It may be that the Earth was one of the first planets where life could develop well. We'd really need to know the distibution of kilonovas through time to estimate when that happpened first, without enough of them a rocky planet would have very little of the heavy elements and having life evolve and a technological civilization develop could be quite difficult. Not quite so heavy elements come from the death of stars like our sun but that would also be billions of years after the big bang. NadVolum (talk) 22:24, 23 February 2024 (UTC)
 * Alpha Centauri A and B are kind of like the Sun a bit bigger and smaller but hundreds of millions of years older and about 2 decibels higher iron:hydrogen ratio which is a proxy for non-first 2 elements content. Sagittarian Milky Way (talk) 00:13, 24 February 2024 (UTC)
 * Yes: the number of a specific star's preceding 'stellar generations' is not well correlated with its absolute age (or rather youth), because stars' 'life cycles' are so heavily dependent on their masses, and the interstellar medium is variable in its composition. {The poster formerly known as 87.81.230.195} 176.24.45.226 (talk) 13:31, 24 February 2024 (UTC)