Taking into account signal attenuation.

If there was anyone there to hear them.

Only considering those signals already produced by us on Earth.

Assuming the technology we have right now is available to any aliens when they receive the signal.

And taking into account our best guess with our current knowledge for the number of rocky Earth like planets orbiting within habitable zones of Sun like stars (Stella density for the given region etc).

Question: How many habitable planets are there within Earths detectable radio bubble?

I'm not expecting (or hoping for) it, but if it can be justified then zero is an acceptable answer.

  • $\begingroup$ Comments are not for extended discussion; this conversation has been moved to chat. $\endgroup$
    – L.Dutch
    Sep 6 at 3:14

None. SETIs latest estimate puts total scrambling of non-targeted radio and television signals at slight less than 1 light year. It's not that the energy of the signals doesn't keep travelling but beyond 1, maybe 2, light years the amount of interference makes the signals undetectable as anything but a tiny bit of extra noise.


They do estimate that the old high power radar systems used during the Cold War were detectable up to 100 Light Years away with something like the Square Kilometre Array. That would put an estimated 14600 stars "in the neighbourhood" and, eventually, able to detect Earth.

  • $\begingroup$ "total scrambling" just so I'm clear, total scrambling would be the point at which what I called signal attenuation causes the signal to be pretty much indecipherable to our best receivers? $\endgroup$
    – Pelinore
    Sep 6 at 1:07
  • 1
    $\begingroup$ @Pelinore Yes sorry David Brin uses the term "scrambled" but yes that would be signal attenuation in proper engineering parlance. $\endgroup$
    – Ash
    Sep 6 at 1:21
  • $\begingroup$ Cheers [+] it's disappointing, but not at this point an entirely unexpected answer // I was looking more for the broadcasts of a TV & radio nature than the pings & bursts of a cold war radar system // so I guess that pretty much means nada in range o7 $\endgroup$
    – Pelinore
    Sep 6 at 2:15

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.