The authors write that Earth could detect an Earthlike planet from 12000 light-years away via Earth's strong radio emissions -- specifically, the intermittent, celestially targeted radar beams (for example, those originally from Arecibo’s planetary radar).
But we'd need to be laser-focused on the planet, and we'd need to catch them when they're emitting.
Earth has only been emitting powerful radio waves for ~50 years, so our detection radius is ~50 LY.
Besides radio, most other means have a very low range.
Sure, that says nothing of technological advancement, but biosphere signatures are roughly a prerequisite for technological advancement.
On Earth, that process is the biosphere.
I'm wondering if we could detect radio transmissions from a planet which we otherwise couldn't detect?
With the natural question, could we have already observed something like what we're producing? I understand without a reproducible signal, no-one knows, but do any of those once-off signals work as a potential similar match?
This is something I’m curious about - I’m led to understand that modern digital signaling is almost impossible to tell from noise, unless you know what you’re looking for (encryption and compression both conspire against obvious structure), is that not the case? Would it be obvious from a signal construction level that we were looking at, well, signal, and not noise?
> This is something I’m curious about - I’m led to understand that modern digital signaling is almost impossible to tell from noise, unless you know what you’re looking for (encryption and compression both conspire against obvious structure), is that not the case? Would it be obvious from a signal construction level that we were looking at, well, signal, and not noise?
Wouldn't that just be a barrier to decoding the message but not detecting that it was a signal? I'm not an electrical engineer, but wouldn't any digital signal rise up from the noise floor with some detectable artificial structure (like regularly timed but varied pulses; e.g. 1001 1011 1110 0001, each pair of 1s is separated by an integer multiple of the pulse time).
We won't see accidental emissions, because they will be lower power: To a first approximation, we talk to each other we use the lowest power to guarantee a certain signal to noise ratio, partly to save money and partly to not interfere with other transmissions on the same frequency.
We expect to recognise high power emissions sent deliberately by the equivalent of Aracibo, because they won't be compressed or encrypted, precisely because doing either would make it nigh impossible for the aliens at the other end to decode.
I think it may be a relatively short distance, which could have implications for resolving the Fermi paradox, but I haven't seen any definitive estimates & I'm curious to learn more.
>If an extraterrestrial civilization existed with technology similar to ours, would they be able to detect Earth and evidence of humanity? If so, what signals would they detect, and from how far away?
We know how to do that, but we also know how to build an O'Neill cylinder, a phased array optical telescope covering the surface of the moon, or an orbital ring — but practical considerations mean we actually can't.