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In brightness, a nuclear detonation is comparable to the Sun.

Source: "The light of the Atomic Bomb," Clay P. Butler, Science Vol. 138 No. 3539 pg. 483-489, 26 October, 1962

How likely are the atomic bomb tests that we did (and still doing to some extent) to be detected by an alien civilization in the future at say 50-500 light-years away from the Sun?

Assume that such a civilization, at the time of the signals reaching them, would be at an equivalent level of technology as us today.

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    $\begingroup$ Half of this question is a rant. The final two sentences are two questions, the first being unanswerable, the second with an answerable core: whether it would be possible to detect our atomic bomb tests from a distance of 250 light-years. $\endgroup$
    – DarkDust
    Jan 10 at 15:57
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    $\begingroup$ "how likely are the atomic bomb tests that we did (and still doing to some extent) to be detected by an alien civilization, say within 250 ligth-years from the Sun?" -- I think that this is a good question, but the rest of the text does not add anything to it. $\endgroup$ Jan 10 at 15:58
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    $\begingroup$ I have edited the question. Hope this corresponds to the direction of the comments $\endgroup$
    – Ng Ph
    Jan 10 at 18:04
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    $\begingroup$ @NgPh if it were me I'd adjust the question to ask first something much more answerable, then perhaps follow up with a second more speculative question once answered. For example "What signatures would be detectable with current technology from a nearby exoplanet with a civilization performing nuclear testing similarly to what was done on Earth?" That question can be answered with a combination of facts and some simple $1/r^2$ algebra, and would be at least somewhat illuminating for your long-term question goals. $\endgroup$
    – uhoh
    Jan 10 at 21:24
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    $\begingroup$ @NgPh no, SETI is current technology to explore space. Terraforming is currently actively discussed and early efforts could actually happen within the lifetime of a young person today. If you disagree or see an inconsistency in this site, then raise it as a new question in meta. comments should not be used for discussions! I'm just recommending how to ask on-topic questions. $\endgroup$
    – uhoh
    Jan 10 at 21:48
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The correct question might not be: "Are the tests detectable?" (since we don't know the capabilities of possible alien civilizations) but rather "How detectable were the tests compared to other human techno-signatures?" The second question is more answerable, and the answer is "Not very." The reasons are that the tests were brief and not modulated or spectroscopically distinctive-- a nuclear fireball is basically a hot but rapidly cooling black-body.

By contrast, the powerful Distant Early Warning radars used in the Cold War to detect possible nuclear attacks ran continuously at a sharply defined frequency with a predictable modulation pattern; it would probably be much easier to pick out these signals from the background radiation emitted by our solar system, particularly if you were only looking occasionally.

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  • $\begingroup$ The fact that we don't know does not forbid us to make working hypotheses, of which the most logical one is that such alien civilizations have reached (or surpass) ours now (in ~50-250 years time), which means they would have the awareness of the existence of other worlds, which means that they would have a systematic plan to review habitable planets and have zeroed in to a few. Which means they could have the tools like JWST. True, the transient nature of the explosions makes it harder to detect, but how long was the Wow! signal? Consider that over 40 years we made over 2000 tests, too. $\endgroup$
    – Ng Ph
    Jan 10 at 21:17
  • $\begingroup$ I am very interested to know which "techno-signatures" of our civilization are detectable, over 250 ly, and much easier than our nukes at such distances? $\endgroup$
    – Ng Ph
    Jan 10 at 21:24
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    $\begingroup$ @NgPh then perhaps that's the question you should have asked! $\endgroup$
    – uhoh
    Jan 10 at 21:33
  • $\begingroup$ @uhoh, for me, which way you put it (how best can we look for them, or how best can they find us), the answers would be the same. Those who do not understand the symmetry of the SETI problem, until we establish "first contact", would not have any chance getting any funding. $\endgroup$
    – Ng Ph
    Jan 10 at 22:00
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    $\begingroup$ @NgPh disagree; there is only symmetry for (potential) civilizations of folks similar to humans that have technology very similar to our current technology. Comments and answer(s) are also pointing this out, consider reexamining your position that there is symmetry. $\endgroup$
    – uhoh
    Jan 10 at 22:36
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If as the quote in the question states, the brightness of a nuclear detonation is comparable to the brightness of the Sun, then an atmospheric or a high altitude nuclear detonation might be detectable, but ET better quick.

If ET can see our Sun then the light from our atmospheric & high altitude nuclear detonations will get to ET. Such light would be akin to fast radio bursts we receive: intense & very short in duration. If ET blinked, it might be missed.

Assuming ET was aware of nuclear detonations, one of the signs that such a brief light source was artificial would be a double flash produced by an atmospheric nuclear detonation. The Vela Incident of 1979 was a cause of concern amongst some countries.

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  • $\begingroup$ Why quick? Any advanced civilization which has reached to the point of searching for other civilizations in the Universe would have used some automatic recording mechanism, as we have been doing, since we have SETI. But until a civilization has developped better means to detect fainter signatures that correspondingly last longer, it might have concluded that this one is a good one to start with (perhaps not the only one though). It is a signature of life and a certain state in the evolution. $\endgroup$
    – Ng Ph
    Jan 11 at 9:19
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    $\begingroup$ The "double-flash" is an excellent remark on how ET can differentiate various flash signs. Some may be quick to object that "but this assumes that ET has detonated a nuclear device in his own atmosphere, and such atmosphere produced the same effect". To this I would respond that we have now the simulation tools to predict the effect of a nuclear blast. $\endgroup$
    – Ng Ph
    Jan 11 at 9:24
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    $\begingroup$ @NgPh "Quick" is probably not the right word. The observer would have to a) be looking at Earth at that moment, and not somewhere else (there's a lot of sky to cover and only so many telescopes!) and b) pick up not only both flashes but also the gap between them. If they do a but not b, the flashes blur together and it just looks like a single event, a bolide maybe. $\endgroup$
    – Cadence
    Jan 11 at 18:21
  • $\begingroup$ @Cadence, in a report of the SETI.org they lamented that they have been "scooping the ocean one cup at a time, to determine if there are fish in the ocean". But I think they have changed paradigm. A smart observation is that, we have to assume that ET has made the same assumption: getting in other's mind. As we are cataloging livable planets, they have assumed that ET would do the same. They came up with the concept of "Earth Transit Zone" (ETZ) as the best place to find ET signals (or signatures). ETZ is sky's part where it is most likely to detect Earth. $\endgroup$
    – Ng Ph
    Jan 12 at 16:01
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If the Aliens can have visuals on our planet that can identify the light or radiation of a nuclear explosion and distinguish it from other background radiation , they probably are advanced enough to have very detailed view of our atmosphere and planet and would have a pretty clear understanding that we are here(nuclear explosion not making that much of a difference as it would fade in comparison to our sun's light).

basically if "they" have devices to detect such light in our atmosphere the resolution of their telescopes or sensors is already good enough that they could probably do it without nuclear explosions as well.

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  • $\begingroup$ You probably know that we do not have such high precision telescopes and sensors to analyze the atmosphere of the planets at 39 ly from us (TRAPPIST-1). What do you suggest that we develop to be on par with the Alien civilizations that have gone past the use of nuclear detection? $\endgroup$
    – Ng Ph
    Jan 11 at 9:52
  • $\begingroup$ I mean If I knew the answer I would be a multi billionaire, but there are a few ideas are out there that could help with that. One particular one that I like is making an array of large telescopes strategically placed in a plane in specific orbits in our solar system aimed at one spot to capture as much light as we possibly can, and then use machine learning to predict the missing information to get a super-resolution telescope that is basically equivalent to a gigantic telescope, we could have detailed views of at least nearby star systems, perhaps even detailed enough. $\endgroup$ Jan 11 at 16:14
  • $\begingroup$ @ZmelgarK1R3D2 I don't buy it. Machine learning can fill in the gaps in an image by assuming that's broadly similar to a huge library of existing images, e.g., one human face probably looks like millions of other human faces. It can't "predict" imagery that is the first of its kind because it has no baseline for comparison. $\endgroup$
    – Cadence
    Jan 11 at 18:29
  • $\begingroup$ I am a machine learning engineer and have been working in the field for many years, trust me it can be done. It would need a lot of effort and training data, but it is doable. The only difficulty would be having enough data to do precise training, which is a physical restraint untill we can actually go to these places and gather at least some samples other than our own solar system, but the fact that the technology can work (and similar data enhancing project in different fields have been done.) is not debated. $\endgroup$ Jan 11 at 19:20
  • $\begingroup$ If you are thinking of becoming a billionnaire, I will not continue pushing. Yet ... your approach of combining interferometry (to increase resolution) with AI (to extract features and reduce noise) is attractive (lots of military use BTW). I would still be less frustrated if you could, in a back-of-the-envelope way, give some numbers to demonstrate that it is much efficient than searching for a MAD nuclear war in our galaxy. $\endgroup$
    – Ng Ph
    Jan 12 at 16:06

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