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Are we sending data for extraterrestrial SETI/METI?

Space Exploration Asked on January 22, 2021

The SETI project is trying to detect radio transmissions of aliens.

Assuming the ET have their own SETI using very similar technology to ours, are we sending data for them to receive?

If we are not sending data then it is very likely they are not sending either.

It is unrealistic to not send signals but to expect them to do the opposite.

Amateur radio can not exist when everyone is listening but nobody bother to transmit.

The question is about present and past attempts

2 Answers

Arguably, we don't have to make an explicit effort to broadcast an intersteller "hello"; we have been leaking radio signals into space for decades. Anyone with a sufficiently sensitive receiver could detect our leaked signals and know we are a civilization at least technologically advanced enough to do that much. However, these signals aren't aimed anywhere in particular in space (they are intended for terrestrial reception) and would be extremely weak at the distance of even our nearest neighbor star. It would take a much more advanced civilization and/or a rather substantial effort to detect our emissions at the likely much greater distances of a possible listener.

There have been efforts to send a deliberate signal (see Active SETI), but doing so raises a number of questions:

  • Where do you aim it? Broadcasting in every direction would require impractical amounts of power in order to ensure a detectable signal at interstellar distances. To make a signal easier to detect using practical power levels, you need to transmit a narrowly focused beam, which means you need to choose a target. How do you decide on an appropriate target?
  • What do you say? Attempts to-date have constructed messages based on certain assumptions about how a message might be decoded and what might be a worthwhile thing to say.
  • What if someone actually receives it? What might that recipient do? Have we endangered ourselves by advertising our presence?
  • Assuming a benign alien at the other end, how do you converse when decades, if not centuries, elapse while each message is in transit?

Without good answers to these questions, it's difficult to justify a concerted METI effort. On the other hand SETI listening is just radio astronomy analyzing for signatures of artificial rather than natural causes.

Correct answer by Anthony X on January 22, 2021

Consider the millions of short wave radio listeners sitting safely and quietly at home by the table late into the night trying to pull in broadcasts from around the world.

The question imagines approximate parity in levels of development between civilizations, but I think the premise of SETI activities are usually that there are significant disparities in development. We listen for signals we couldn't possibly produce.



This is what we'll be like if/once we can start receiving anything at all:

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dated 1928. Source: Library of Congress https://www.loc.gov/item/2017680266/ Rights Advisory: No known restrictions on publication. For information, see "American National Red Cross photograph collection," https://www.loc.gov/rr/print/res/717_anrc.html

Answered by uhoh on January 22, 2021

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