Strelnikov wrote:That was the fear of the dearly departed Stephen Hawking. My point is, we have already been broadcasting into the Universe for a long time both through radar and AM/VHF/UHF radio and television. The "damage" is done; thanks to things like Project Diana (where radar was bounced off the moon in 1946) and a decade-plus of high-power military moonbounce communication, signals from fifty-sixty years ago are still spiraling out into the void.
Um, I'm not an expert on radio astronomy, but you have to realize how far apart stars and their solar systems are from each other. When a radio signal is transmitted, it is usually more-or-less omnidirectional (or at least cardioid) once it gets out of the planet's atmosphere. Radar and microwave signals from a parabolic dish antenna are highly directional when they start, but begin to spread out quickly. The problem is that its intensity declines as the square of the distance. Even if you had a gigawatt transmitter (which has never existed) running 24/7 into a highly directional antenna, by the time the signal reached the nearest star (Proxima Centauri, 4.3 light years or 25.8 trillion miles away), it would be measured in the yoctowatt range, probably less than a jansky (look it up). It would be DAMN weak. Even if you used a relatively quiet frequency band in the "microwave window", like the usual 1420 MHz hydrogen line, there's still so much background noise it's difficult to assure detection. And this is only if you're TRYING to be detected.
http://www.setileague.org/general/waterhol.htmI could show the math if you want. Proxima Centauri is 25.8 trillion miles, or 4.15 x 10^13 kilometers. If the transmitter was emitting a signal of 1 gigawatt/sq meter (and I'm not sure that's even physically possible) with a rather narrow spectrum bandwidth of 100 Hz, the signal arriving there would be something like 5.8 x 10^-27 watts/m squared. That is in the millijansky range. ANY kind of natural or nearby artificial signal source in a nearby frequency range will probably drown it out. Even the best microwave front ends aren't perfect "brickwall" filters. Stars and other astronomical radio sources transmit radio signals that are observed on earth in the hundreds or thousands of janskys, depending on their distance, brightness and other things.
The "WOW" signal from 1977 is still a total mystery. No information, just a single powerful carrier that disappeared quickly and was never seen again. Astronomers are going to argue about it for decades to come. It's useless until it is observed again and again on other telescopes. And it doesn't help that radio telescope time is fought over by scientists from all over the world; most of them don't give a shit about detecting alien civilizations. They tend to be like artists; egomaniacs with "ideas" they want to test. Personally I'm in favor of punching scientists in the mouth when they get too shrieky. No one does it often enough. (Remember Mathsci?)
This paper goes into great detail on the "probability" of detecting a signal. It depends on a lot of unknown factors, but it isn't really very encouraging.
https://arxiv.org/ftp/arxiv/papers/0707/0707.0011.pdfHere's another paper, about intentional interstellar two-way communications. Also not encouraging. It seriously proposes communicating via neutrinos. How the hell do you generate large amounts of neutrinos on a spacecraft? The receiver they proposed is a "single crystal of absolutely pure cobalt-60, weighing about 9 tons (a cubic meter in volume) and maintained at a constant cryogenic temperature of 0.01 K." Good luck with that!
https://www.academia.edu/2086485/Inters ... Spacecraft