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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.

To add more speculation, the idea from the movie "Tenet" could be a way to effectively surpase C in long distance communications: reversed entropy matter.

You could just send a ship or some kind of vesel with reversed entropy to a star and it will arrive years later, but years sooner that it was launched.

Matter is more or less energy, what if this trick could be done with reversed entropy energy: radio, x-rays, gamma rays, etc.

Sorry, I didn't wanted to write it like that was psychosis somehow.

I meant, causality as I understand, it could be not a fully understood concept. We could still find evidence - in the future - that there are phenomena capable of "evade" the cause-effect principle.

https://en.wikipedia.org/wiki/Faster-than-light_neutrino_ano...

This would be correct if causality is an absolut certainty in all the universe, the whole time,

but what if causality it actually isn't a certainty in some contexts? Tadah..you would get ala "FTL" comms enabled.

Just reading the comments.. if there are aliens reading over our shoulders, we'd be looking like neanderthals speculating about electricity or nuclear reactors...

if the technology described in the paper actually exists, it would be far away from our current understanding of the reality.

* Matching the wrong photon will produce only random noise.

Not really related to what you have commented, but I wanted to mention it:

Back in Earth, our communication protocols usually have lots of redundancy. Whatever redundancy you can get into the channel, it usually gets inserted at whatever cost it takes - slowing down things a bit here and there - but ensuring a proper message gets to arrive to the other side (at the receiver).

I'm far (FAR) away from trying to sketch here an interstellar quantum comms protocol, but I find certain that if there aliens out there deploying quantum networks, they almost certainly will have redundancy at the level required (to overcome entropy), to get proper messaging in the used channel.