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.