>I doubt we’re detectable outside of a 100 light year sphere from earth and none of those stars look like they contain any habitable planets.
Do you have a source for that?
Do you have a source for that?
For comparison look at what we need to do to detect messages from the voyager 1 at 1/400th a light year, realize that’s sent from a directional antenna and we know exactly where to look for it. A signal that’s ~1/1,600,000,000th as strong would take some serious hardware even with more advanced technology because you can only collect 100% of the photons in a radio transmission quickly you need a physically larger device.
It strikes me as a pretty intuitive arguemnt to make and true by default, to show it wrong you have to find or somehow plausibly argue for the existence of some physical medium or process that human civilization (or even earth life in general) emit or modulate in unique, detectable-from-space ways other than electromagnetic waves and that we have been doing this since before radio.
Decidable radio signals on the other hand are far less ambiguous. I just can’t think of much that would be both detectable and a smoking gun.
In general, the signal from our most powerful commercial radio transmitters will go below the background noise floor well before 100 light years.
However, a very low bandwidth pumped through something on the scale of the Arecibo dish at the transmitting end, and a helium-cooled receiver, could bridge many more light years. But then we're no longer talking about a sphere of a signal or even a big cone, but in astronomical terms an extremely tight-focused point-to-point laser that is more apt to just intersect cosmic dust and gases than an alien civilization.
[1] https://www.quora.com/How-far-do-radio-signals-travel-into-s...
However if the aliens had a big telescope surely that radius would expand?
I think a more interesting question is how far away could we detect a civilisation equivalent to our own, using our current technology. Otherwise you can assume aliens (or our future selves) with arbitrarily sensitive detection equipment limited only by whether or not the detectors are inside the speed-of-light radius of the emitting civilisation.
IIRC our most powerful transmissions have been from NORAD radars looking for missiles coming over the north pole. In some ways we are now emitting less detectable signals, e.g. with lower power 5G cells and fibre broadband replacing good old radio.