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18

Neutrinos are difficult to detect. Much of neutrino physics starts with a gazillion neutrinos and hopes to detect a few interactions. These guys published a rough map of terrestrial emissions from all sources with their 2015 paper. This guy proposes a gigaton detector for identifying reactors here on earth. Deriving location information would take on the ...


17

If you can detect unusually large quantities (superabundance) of Xe-129 or higher isotopes of Xenon that would naturally only be present in trace amounts without explosions of thermonuclear weapons, then yes. Potentially even millions of years after the event (Xe-129 has a half-life of 16 million years). It is hard to estimate what weapon yield would be ...


15

Assuming best case? According to this page, about half the energy from a normal nuclear explosion is radiation. That means we can simplify it to all energy radiated for an order of magnitude estimate. For reference I will use the Tzar bomba, the largest nuclear weapon ever tested. It was about 50 megatons worth of TNT. According to unit conversion , a ...


13

I can't give a precise answer to your primary question besides "Extremely unlikely", but here are some facts on cosmic rays that might help coming to a conclusive answer: Current models are able to describe the distribution of energies and ion masses rather well. What we do not know precisely is the source of this radiation. There are plenty possible ...


11

Assuming that by signal you mean radio signals, there were many attempts. All this has already been described in detail on Wikipedia, so I'm not inclined to repeat it. What you are looking for is available in these two pages: Active Search for Extra-Terrestrial Intelligence (Active SETI) Communication with Extraterrestrial Intelligence (CETI). Probably ...


10

The first message in the history of humanity was: "Мир, Ленин, СССР". The English translation being, "World, Lenin, USSR". A lot of people will try to bring up that "мир" actually has two meanings, the second one being "peace". My opinion is, that in this case, it only means "world", or in stricto sensu "Universe". It was long ago, in 1962, when this radio ...


10

A couple of issues with the Fermi paradox: The Fermi paradox is closely tied to the Drake equation. This equation is the best method we currently have for thinking about the probability of intelligent life in our galaxy. The problem is that there are so many assumptions you have to make in that equation, that the results vary drastically. If you plug some ...


10

Neutrino emissions are very hard to detect. There are a few neutrino detectors, but they can only detect massive events (supernova explosions etc). We haven't made any that are sensitive enough to detect emissions from individual stars (yes, except our sun), let alone nuclear reactors on exoplanets.


8

Using current technology (and by that I mean experiments and telescopes that are available now) we would probably be unable to detect life on Earth even if observed from a distance of a few light years. A "blind" search could look for radio signatures and of course this is what SETI has been doing. If we are talking about detecting "Earth-like" signals, ...


8

I don't see how it could possibly be the cause--it would make interstellar travel harder, it wouldn't make it impossible and it wouldn't destroy the species--once they found out about it they could beef up the defenses of their starships.


8

They were called "secret" because the media doesn't really understand what "encoded" means, and in any case "secret" attracts more attention in a headline, which is what sells. There is nothing secret about the message. The encoding is really a set of logical structures to hopefully make it understandable to another intelligence that may not have anything ...


6

It is actually the Drake Equation that applies best to this. The Fermi Paradox framed the issue, the Drake Equation tries to wrestle it into an analyzable framework. This io9 article gives an idea of what we are facing when we try to narrow down the possibilities here. It is an extremely compelling matter for which we have no data points. We don't even ...


6

SETI@home uses data collected from other projects and searches it for patterns. Pattern searching can go infinity deep as you look for increasing combinations of modulation bandwidth so for a reasonable volume of data you could search it effectively forever for increasingly more improbable patterns at less probable frequencies. At least when the initial ...


5

I think the answer to your question is "yes". The combination of "space is big" and "humans haven't been around long" is a valid (as opposed to good) explanation for the Fermi paradox. I replaced "good" with "valid" because "good" is subjective and can be colored by one's own opinions, and desires, about the possibility of alien life. But as logical ...


5

It would certainly be possible to construct a message that doesn't start with pictorial elements, but certain concepts are much easier to get across if you can "point to a picture". It's also easier to synthesize information and recognize patterns if you can view a lot of it at once in a structured way; organizing the data in multiple dimensions helps with ...


5

SETI has published "a" protocol for efforts under their banner, but isn't something that can be enforced on other organizations. Even that protocol is vague in many many areas (doesn't seem to suggest timeframes for example), but it does give a framework for how the followup could proceed.


5

Yes, SETI has listened to Alpha Centauri. Here's a 2003 list of targets for SETI, which includes all of the 100 closest stars.


5

This is a question of philosophy, clearly. Basically people are looking for every type of signal which supposedly can not occur naturally/inartificially. The general assumption is, that e.g. prime numbers can not be found in any significant role in nature thus every occurrence of them must come from some kind of thinking process-intelligent life. On the ...


5

Some rarely discussed option also include naturally occuring self-organising and self-replicating helical plasma structures, at least in theory: DOI:10.1088/1367-2630/9/8/263 This article studies the theoretical possibility that some plasma structures with properties usually used to describe living organism. Given the right environment, these structure ...


4

If anyone anywhere anytime did space travel, they should have been here by now. The Milky Way is small compared to its age and travel times. The Sun has made about twenty orbits around it. The dinosaurs actually lived on Earth when it was on the other side of the galaxy. Either we are alone as a space faring society, or we have company very close by. The ...


4

Wikipeida has a decent article about hypothetical forms of life. Silicon shares many chemical properties with Carbon, making it a good candidate. However, carbon is much more versatile than other similar elements in terms of what they can bond to. Silicon has limitations and interacts with much fewer elements than Carbon. One characteristic of "life as we ...


4

With lasers we could alter Earth's light curve to an artificial shape (maybe an Ulam spiral portion?), so that we would be visible to whatever star system we pointed our lasers at. The star system would have to be able to view our transit of the Sun. This is from a recent paper "A Cloaking Device for Transiting Planets" by David M. Kipping and Alex Teachey ...


4

I think this problem is often approached too explicitly, with the assumption that we have to explain all the basic concepts before someone can decode a complex message. However, research into unsupervised deep learning of embedded features in images and text shows that an explicit set of concept definitions is not required to capture the meaning of the ...


4

Light speed does make it more difficult to have a conversation. It doesn't make it impossible though. But SETI is about one question: are we alone in the universe? We don't need to be able to communicate to answer that. A comment asked for 'other options than EM' for communications, assuming there are ways to communicate faster than light speed (FTL). ...


4

Stars emit neutrinos. Even if we could detect them easily (hard because as you point out they're very weakly interacting, see other answer), neutrino emissions are hardly a "clear channel" where nuclear technology is likely to be the main source of signals. (Possibly viable if you can filter by neutrino energy, though, but maybe still not.) Even on earth ...


3

SETI analyses signals in the 1000MHz to 9000MHz range. So you would expect communications modulated on these frequencies to utilise the high frequency to include more data rather than less. That said, the data on, say, the hydrogen line at 1420 MHz and the methanol line at 6667 MHz are stored, and analyses are run on these over short, medium and long ...


3

Searching for radio signals is probably the most mainstream method. Transit Photometry is another method that has been in the news lately. Theoretically, it should be able to detect alien megastructures around stars. One candidate has already been identified. Optical searches for laser communications has also been attempted. Spectroscopy is a method for ...


3

They basically look for unnatural signals, for example a carrier signals (one narrow band which is very energetic against the noise background is a good example). The problem with this approach is that you can't differentiate between noise and highly compressed data (so the propability to catch usual communication data is very very impropable). Another ...


3

A brief search led me to the conference proceedings for the "Life in the Universe" conference held at Ames Research Centre in 1979 (yes, this is old, but serves as a good baseline from which to begin). The paper "Eavesdropping Mode and Radio Leakage from Earth" notes that early warning systems for ballistic missiles beam intense radio signals that could be ...


3

Interstellar travel isn't the issue — stars are close together and even at 10%c the Milky Way could be traversed safely in 10M years. 10M years isn't a factor. Even if it's 100x slower at 0.1%c, 1bn years to colonize an 11 or 12bn year old galaxy with 6-10bn year old metallic stars (thought to be required for life) isn't a strong filter. If a filter ...


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