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I read that only a narrow band of radio waves are reserved for astronomical observation, and humans emit all sorts of electromagnetic waves, which leads to my question:

Could there be signals of advanced life lost in the chaos of all the other EM bands *the technology we use emits? We haven't been listening for aliens as long as we've been blasting out waves, and any far off source would be very quiet, so are we potentially drowning important signals out?

Wikipedia seems to at least partly back up my question, I would like more details though!

Many radio frequencies penetrate Earth's atmosphere quite well, and this led to radio telescopes that investigate the cosmos using large radio antennas. Furthermore, human endeavors emit considerable electromagnetic radiation as a byproduct of communications such as television and radio. These signals would be easy to recognize as artificial due to their repetitive nature and narrow bandwidths. If this is typical, one way of discovering an extraterrestrial civilization might be to detect artificial radio emissions from a location outside the Solar System.

https://en.wikipedia.org/wiki/Search_for_extraterrestrial_intelligence#Ongoing_radio_searches

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The majority of the EM emissions of human beings are in the infrared part of the spectrum. Those emissions are many, many orders of magnitude smaller than those of the Earth in the same IR band, and many, many, many orders of magnitude less than those of the Sun.

So any (remote) civilization would not "see" humans at all, because the Sun would totally swamp out and overload their IR detectors.

It has been postulated that remote civilizations would instead zero in on emissions which are 1) the product of intelligence and 2) not strongly emitted by stars and 3) at wavelengths at which the Universe is almost completely transparent. Coded transmissions at the frequency of the 21 centimeter hydrogen line would fill the bill.

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  • $\begingroup$ I didn't mean energy the human body emits, I meant radio waves, cellphone signals etc etc etc. $\endgroup$
    – joeyfb
    Commented May 8, 2022 at 4:13
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    $\begingroup$ @joeyfb in my opinion the term phrase "the EM emissions of human beings are in the infrared part of the spectrum" includes the radio transmissions too, humans make them by electronics". $\endgroup$
    – anna v
    Commented May 8, 2022 at 4:37
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Your question is based on the false assumption that we couldn't detect extraterrestrial radio waves just because we happen to emit radio waves at the same frequencies. Antennas are directional, and we can use that directionality along with shielding and other techniques (such as putting antennas in space) to reject human-based signals.

We can and do look for radio signals at the same frequencies that are emitted by humanity every day.

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  • $\begingroup$ This comment on wikipedia seems to support my hunch and is more in line with what I was asking. Details re too spares though! en.wikipedia.org/wiki/… $\endgroup$
    – joeyfb
    Commented May 8, 2022 at 15:24

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