> Non-directional radio transmissions (e.g. TV, radio) would not be distinguishable from cosmic background radiation at more than a light year or two away
this is going to come across as sarcastic in text, I genuinely mean this.
Because I suspect that under focused analysis the signal won’t quite look like cosmic radiation background.
Now I also haven’t done the analysis, but information, and entropy are funny things. Will they get to watch a human TV show ? Hell no. Would it look “random” versus showing that it once contained some structured information ? I think that’s a very open question.
There are probably more serious papers that deal with the matter and how long and far “techno-signatures” survive in the noise.
An old NTSC video signal has a clear periodic structure. Simply counting lines is going to reveal a lot about the structure and if anyone gets the idea of plotting lines they will figure out how to decode it.
An efficient digital signal is going to maximize the use of bandwidth if it looks like white noise. That said, a signal like that needs a carefully calibrated receiver, so part of the signal in time-frequency space is going to be allocated for something that is easy to acquire and will tell to how to decode the main signal. You might see a periodic structure: if you want to run a "signal frequency network" with multiple transmitters with the same signal, have to deal with a lot of reflected signals, or listen from a mobile terminal that suffers from the Doppler Effect you will probably turn off the signal for part of the cycle so that reflections can die down and you can reset your echo cancellation algorithms.
Thus digital signals aren't going to be invisible but they are going to spend maybe 5% of the energy in a way that is easy to interpret as opposed to all of it.
Makes me wonder if alien life will actually not find our messages simply because we're using such "ancient" techniques. Perhaps they invented a TV like object and used a NTSC like signal, but like 100k years ago and no one in their race knows to look for our old signals. Maybe our comms look like hieroglyphics to them ?
Periodicity is a clear signal that is useful for natural objects like pulsars. I think it would be very clear that analog videos are periodic at the line level and periodic at the frame level. If somebody gets the idea of plotting signals on a grid they will get a sequence of frames. Even creature that don’t see the way we do might develop some kind of raster basted signal processing.
On top of that TV signals would have additional periodicity because the transmitters will be hidden behind the Earth once every 24 hours.
this is going to come across as sarcastic in text, I genuinely mean this.
Why don't the authors know this? Why doesn't someone tell them?