Timeline for Need a way for Earth not to detect an extrasolar civilization that has radio
Current License: CC BY-SA 3.0
13 events
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| Jun 16, 2020 at 11:03 | history | edited | CommunityBot |
Commonmark migration
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| Dec 6, 2016 at 13:17 | comment | added | jwenting | @Damon what the signal looks like is irrelevant for our ability to detect it as a signal. All we need to know (or suspect) is that it's not of natural origin. Which btw is exactly the criteria SETI uses to classify signals as being of potential interest (whether or not it falls into a list of known natural signals). And of course it needs to be strong enough to be detected at all, which a signal from 200LY away is very unlikely to be unless an extremely powerful narrow sideband transmitter were aimed directly at the point the earth would be 200 years after transmission, unlikely... | |
| Dec 6, 2016 at 13:09 | comment | added | Damon | @MikeP: That's my point. We do not know what alien signals may look like. They might use AM or FM (highly unlikely, but possible), or something QAM-alike, they might use some more or less obvious or not-obvious, or not even intuitive different encoding. Without knowing, it is practically impossible to distinguish anything they might send from noise. In particular, if there is compression involved, which you can take for granted. Compressed data looks like noise. Even in the simplest "easily identifiable" case it's harsh to tell apart signal from noise if you don't know the signal's amplitude. | |
| Dec 6, 2016 at 11:53 | comment | added | specializt | @MikeP i think you might want to re-read ... pretty much everything you have read about the topic, you seem to have mixed up most of it. There is no "trigital" in current technology, literally everything is digital. QAM is a modulation for digital information onto analog signals - this basically means that the amplitude (Y) of a sinus wave is segmented into parts, all of which are declared to be a combination of binary bits. There is no "at one time", the X-positions on a sinus wave literally are infinite but the clock cycle divides that wave into a specific amount of steps | |
| Dec 6, 2016 at 11:17 | comment | added | specializt | this answer is so full of misguided, made up stuff ... i would'nt even know where to begin - let me just throw this one thing here : quantum communication is impossible, neither is it "in development" / "not ready for mainstream yet" nor will it be, thats entirely made up. What has been proven experimentally is quantum encryption, which has got nothing to do with quantum communication since the communcation itself is done like it always has been done before : via optical fibers and lasers, even quamtum nonlocality can be explained via the pilot wave theory | |
| Dec 5, 2016 at 19:15 | comment | added | MikeP | Current earth technology has long surpassed digital and "trigital" - we use PSK or QAM for transmitting 256, 512 or more "signals" in the time of one digital bit. This means 8 or 9 bits gets transmitted at one time. Work is in progress for up to 4096 or 12 bits. So, if they use 12-bit/4096QAM, even directed at us, we wouldn't see it. | |
| Dec 5, 2016 at 17:39 | comment | added | kingledion | @Damon You should edit your answer and put that in. | |
| Dec 5, 2016 at 17:31 | comment | added | Damon | @kingledion: Neglegting the small constants which multiply up to approx another 1-2 orders of magnitude (like 4*pi, or like the first digit of the 200 light years in meters), you get 10^-36 W/m^2. The best radiotelescope arrays that we have today are more like 10^-29, which is a tiny 7 orders of magnitude amiss, and it is not clear what they are able to receive at all (in order to receive something meaningful, you need information about the kind of signal, which we do not have -- think modulation or such). | |
| Dec 5, 2016 at 16:45 | comment | added | HDE 226868♦ | Additionally, dark matter doesn't interact with electromagnetic waves. Therefore, it would have no impact on radio signals. | |
| Dec 5, 2016 at 16:34 | comment | added | kingledion | Your first five bullet points are not hard-science related and basically irrelevant to the question. In the last bullet, would you like to finish the math? If you plug in 100kW as EIRP to the radiant flux density equation, what do you get? Is that signal strong enough to detect on Earth? | |
| Dec 5, 2016 at 15:42 | history | notice added | HDE 226868♦ | Hard Science | |
| Dec 5, 2016 at 15:42 | comment | added | HDE 226868♦ | By "black matter", are you referring to dark matter? | |
| Dec 5, 2016 at 15:28 | history | answered | Damon | CC BY-SA 3.0 |