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Something that's occurred to me is that radio is a bit more than a century old, and at the present time, we are still using EM radiation, but a huge portion of our data bandwidth is being transported along enclosed waveguides, i.e., fiber optics, and transmission lines that have no long range dipole, such as coaxial and twisted pair cable. The net bandwidth of our open-air comms has increased by orders of magnitude, but all the while being designed to operate at ever lower power levels using modulation strategies that increasingly resemble noise, using antennas that avoid radiating into space for the sake of power savings. It could be that our civilization had a 1-2 century time window for being detectable from afar, before we effectively go dark.

A superior method of communication might be a robot that, while it can't travel as fast, can engage in much more elaborate communication when it reaches its destination, e.g., carrying out trade, negotiations, cultural exchange, whatever. Also, the energy delivered by a robot, if it can steer itself to its destination, is not subject to the inverse square law of intensity. We have sent robots to visit the planets, because there's a limit to what we can learn by interrogating them with telescopes and antennas from Earth.

Speaking of smoke signals, we may be inadvertently communicating our presence by the rapid change of the chemical composition of our atmosphere. Aliens equipped with a sufficiently sensitive spectrometer could scan the heavens for unusual chemical activity on known planets.

We (as in human race), metaphorically could be - right now - in the middle of a city like NY, looking for someone sending signals with smoke, and being surrounded by multiple modern communication systems, everywhere around us.

Maybe we have always been surrounded by aliens communications and we didn't notice it, like what happened with electricity, it was all around humanity, all the time humans existed, and it was discovery just recently.

> Alien civilizations have found such a vastly superior method of communications that they have given up on electromagnetism as a method.

There are a lot of problems with this idea and it comes up predictably in every SETI discussion ever.

For starters the inverse square law makes it extremely unlikely any two civilizations would ever detect each other's spurious emissions. Omnidirectional sources of EM radiation readily detectable at interstellar distances are called stars. If you tried to build an omnidirectional gigawatt TV transmitter it would melt itself rather than transmit anything. So the only way any civilization will have a signal detected by another is if they send an intentional and high gain (highly directional) signal towards other stars.

To that end the universe is filled with natural EM sources. Everything from the Big Bang to stars to giant clouds of gas emit some EM radiation. Even a planet like Earth with a strong magnetic field and a dense relatively moist atmosphere can see a large number of EM bands from the surface.

Even if some alien civilization uses sub-etha quantum blockchain to send e-mail it doesn't matter in terms of interstellar signals. Even on Earth a majority of our communication happens over cables (copper or fiber) or transmitters optimized for terrestrial reception. Our terrestrial communication systems might as well be sub-etha quantum blockchain since they're not useful at all for interstellar communication or detection.

Unless there's lots of natural sources of sub-etha quantum blockchain radiation there's not going to be many sub-etha quantum blockchain astronomers. There will be radio and visible (IR and UV included) EM astronomers because the universe is full of that radiation. If a civilization wants to send a detectable signal it's more likely to do so in the EM spectrum than some spectrum where alien astronomers are unlikely.

Of the EM spectrum it's also most likely intelligent civilizations would pick bands near natural sources. That way another civilization mapping has clouds or surveying pulsars might stumble across the signal.

It's entirely possible a civilization only broadcasts on sub-etha quantum blockchain because they're only interested in other civilizations with that same technology. It's pointless to wonder about them. They might as well not exist as far as we're concerned. You might as well try to deduce the mating habits of unicorn dragons. They have the same level of influence on humanity as the sub-etha quantum blockchain aliens.

I like where your head's at, but consider that email is vastly superior to snail mail.

We haven't abandoned it entirely, we've just started ignoring it and let the parasites fill it up with spam.

If humanity is typical of civilizations, I'd expect the EM spectrum near more advanced civilizations to be buzzing with ads, scams, and malware--most of which is ignored by that civilization.

They haven't said hi because our broadcasts are caught in their spam filer, and we don't know about their spam because it's down out by their star.

It works the other way too: Back when we were single celled organisms, we used to communicate with chemical markers. Now that we're bigger, we mostly ignore that space because our immune systems (read: spam filter) let us get away with that ignorance (mostly).

This is highly unlikely in my opinion. At least a few of such civilizations would absolutely retain the ability to and actively track EM and more primitive methods of communication for no other reason than intellectual curiosity. Just consider how much time humans spend on such endeavors.

> for no other reason than intellectual curiosity

Well, that and [shared sensory experiences] just [feel/digest/reflect] better when they’re transmitted via EM. [untranslatable concept] gives a more accurate, high-fidelity reproduction, sure, but I have always found the EM distortion pleasing to the [untranslatable sensory apparatus].