5 ms·

Quasi-related fact: Radio frequencies with a wavelength of 21cm are one of SETI's favorite places to look for artificial signals. Since it originates from atom

Quasi-related fact: Radio frequencies with a wavelength of 21cm are one of SETI's favorite places to look for artificial signals. Since it originates from atomic hydrogen (of which there is a lot), it's one of the notes that the universe likes to hum to itself---and radio-using species everywhere would probably figure that out.

duncan_bayne 9y ago
So, do we deliberately transmit at that wavelength, with the intention of attracting the attention of ETIs?
- radicaldreamer 9y ago
  Breakthrough Message project would probably consider this.
- pharrington 9y ago
  It's certainly one of the better ideas for that purpose. I like to imagine, though, that the sufficiently advanced aliens, upon receiving the signal, would say "huh, there's this weird low energy 1420Mhz emission coming from Sol. Guess we'll file it next to the other million aberrant emissions in the Local Group we can't explain."
pohl 9y ago
I remember in Contact the signal came through on hydrogen times pi.
- raverbashing 9y ago
  Yeah I think that's more for dramatic purposes rather than anything practical
  - pohl 9y ago
    Of those many possibilities, Carl Sagan chose the product of pi times the hydrogen spin-flip transition frequency, for use in his novel Contact. In fact, several SETI scientists in Australia had independently arrived at that same target frequency when Carl was writing his novel in 1985, and were already monitoring there. So, great minds think alike (let us hope on other planets, as well as our own!) http://www.setileague.org/askdr/HtimesPi.htm http://www.setileague.org/askdr/HtimesPi.htm
    - raverbashing 9y ago
      As an arbitrary number it is fine, but to me it sounds like "Mysterium Cosmographicum" In essence, while it could be, I think it's a plausible explanation given our understanding at the time but it might 'get old' soon. For all we know maybe they might be trying to communicate in an ultra-wide BW that sounds like noise to us. Or using some other method we know nothing about or have just heard about it, like Higgs field perturbations, or ultra-high frequencies.
      - pohl 9y ago
        Which number is it that you’re taking to be arbitrary? I would expect that the product of two non-arbitrary numbers to be non-arbitrary. (Although I think tau might be a small improvement upon pi.)

duncan_bayne 9y ago

So, do we deliberately transmit at that wavelength, with the intention of attracting the attention of ETIs?

radicaldreamer 9y ago
Breakthrough Message project would probably consider this.
pharrington 9y ago
It's certainly one of the better ideas for that purpose. I like to imagine, though, that the sufficiently advanced aliens, upon receiving the signal, would say "huh, there's this weird low energy 1420Mhz emission coming from Sol. Guess we'll file it next to the other million aberrant emissions in the Local Group we can't explain."

pohl 9y ago

I remember in Contact the signal came through on hydrogen times pi.

raverbashing 9y ago
Yeah I think that's more for dramatic purposes rather than anything practical
- pohl 9y ago
  Of those many possibilities, Carl Sagan chose the product of pi times the hydrogen spin-flip transition frequency, for use in his novel Contact. In fact, several SETI scientists in Australia had independently arrived at that same target frequency when Carl was writing his novel in 1985, and were already monitoring there. So, great minds think alike (let us hope on other planets, as well as our own!) http://www.setileague.org/askdr/HtimesPi.htm http://www.setileague.org/askdr/HtimesPi.htm
  - raverbashing 9y ago
    As an arbitrary number it is fine, but to me it sounds like "Mysterium Cosmographicum" In essence, while it could be, I think it's a plausible explanation given our understanding at the time but it might 'get old' soon. For all we know maybe they might be trying to communicate in an ultra-wide BW that sounds like noise to us. Or using some other method we know nothing about or have just heard about it, like Higgs field perturbations, or ultra-high frequencies.
    - pohl 9y ago
      Which number is it that you’re taking to be arbitrary? I would expect that the product of two non-arbitrary numbers to be non-arbitrary. (Although I think tau might be a small improvement upon pi.)