The problem with communicating across even a few hundred light years is that everybody's bored and gone to do something else before the response arrives.
You'd need a spectacularly static civilisation to engage in any meaningful communication over the timespans involved.
Maybe not bidirectional communication per se, but it’d still be pretty valuable to receive a live feed of what the other civilization was up to hundreds of years ago. Especially for things like scientific advances and important works of literature – but I suspect people would also be interested in the day-to-day trivia. I mean, as an individual I’m already largely powerless to influence any of the events I read about in the newspaper, but I still read the newspaper.
Besides, if you’re an AI or an uploaded brain, you can send yourself over a communications link. That’s pretty valuable, regardless of whether you ever intend to return!
How much do you pay attention to the live feed of news from Mauritius? (If you live anywhere close to that country, or have ties there pick a different country on a different continent). Somewhere in my family history is the towns where my family immigrated to the US from, but I don't care at all about news from those towns.
The news in my town is of interest to me, nobody else would care about the latest live music at the local stage.
Science might be of interest, but the problem is both cultures will work in parallel, so we can assume that majority of advances one planet discovers are discovered by the other planet in the mean time.
The nearest star (which might not even have a habitable planet) to earth is too far away for science collaboration other than the "here is new type of signal we are sending your way, see if you get it", and even then you take the risk that the other planet chooses to not listen for whatever reason (it wouldn't surprise me if some theory require this level of cooperation). It is close enough that some "we are studying this lead, so you probably want to look at something different to avoid duplicate work".
As we get farther and farther from the other planet collaboration is less and less useful. You quickly reach a point where the planets can advance faster by duplicating effort than talking to each other (other than as a much latter verification of current theories)
Of course if we colonize a planet 100 light years away you can assume a few hundred years of the colonists working hard to establish the colony and so getting science and technology feeds from Earth will be useful since then they can make a copy of widgets without having to design it from scratch. Eventually they will get established and start producing their own science locally, and soon the feed will be useless and not of interest.
That's a very young-civilization perspective. 100 years seems like a long time to us because it's approximately 1% of the age of our civilization. But it's possible that civilizations that are hundreds of millions of years old exist. To such civilizations 100 years would be a flash in the pan.
Also keep in mind than until recently on earth we used transmission mechanisms for long-on-earth distances that were closer to the order of magnitude of 100-year transmission time (a few months) than to present transmission time (a few milliseconds).
>But it's possible that civilizations that are hundreds of millions of years old exist. To such civilizations 100 years would be a flash in the pan.
I don't know if it is possible for a civilization to connect the past to the present over such long periods of time. The individuals in each generation would have to pick up, use and pass on all the information that came before.
Our capacity to take past information into account, individually and collectively, is very limited, even if it gets stored somewhere. We can see that in many debates on here where arguments of the past are repeated many times over without younger participants having any awareness of what's been said before.
We can compensate for that to some degree by continuously retelling old stories. But relearning old stuff necessarily competes with new information for our limited mental capacity and so old information inevitable degrades over time.
Even religions, where there is a strong emotional incentive to retell old stories, are struggling mightily with even understanding what the original authors meant by the words they used and how to apply any of it to the current situation.
I think for a civilization to retain its collective memory over much longer periods of time requires completely different individuals. It requires individuals that are able to grow their mental capacity at the same pace as the amount of accumulated information grows.
If you consider the combinatoric explosion, this is unimaginable in a biological organism based on evolution and ultimately even in an AI.
I also want to add that age-wise we might be pretty old. Our galaxy (13B) solar system (5B), our planet(4.5B)are pretty old considering the Big Bang happened 14B year ago.
Definitely in civilization time that leaves a lot of room for a few milion years here and there, but still, we could be the oldest and most advanced (at the same time I do hope there is a civilization out there less eccentric and egocentric as ours...)
100 years doesn't seem like a long time to me because of the age of our civilisation or species, it seems like a long time to me because of the lifespan of our species. I certainly can't communicate at all on a 200 year RTT, as I'll be dead and forgotten before I get an answer.
If it's communication, that implies a two-way exchange of ideas. The galactic equivalent of blogging would be like all such communications: typically of more interest to the sender than the receiver.
If we assume a long-lived species that can receive a response within its lifetime, we must also assume that during the intervening time little enough of the context has changed that the answer is still relevant. That means a species and a civilisation that has extremely little change over hundreds of years.
This is what I mean by an extraordinarily static civilisation.
(But if it's so static, what could possibly be said that has material bearing on anything? :-)
That is the first time I've ever thought about that particular obstacle to EM technologies as a means of hyper-distant, bidirectional, purposiveful communication between advanced civilizations. I've always thought of EM (Radio/Communication Technologies) as potential tools to confirm specific sources/locations of other intelligent life as well as possibly their purported agenda/intention/lifestyle/threat-level? (or level of intelligence and even to develop [flawed but useful, a.i. based] predictive algorithms of their future likelihood of physical contact/threat and/or their rate of scientific advancement, based on analysis of numerous factors including their encoding used, past broadcasts compared to current, means of broadcast, etc. Etc. Etcetera.) [STRICTLY LIMITED TO/AT the time of the broadcasts, not at the time we receive them... BIG DIFFERENCE IN ASSUMING THAT THE TWO ARE THE STILL THE SAME!]. Never in my wildest dreams, would I consider us as humans advanced enough to ACTUALLY RESPOND (IN WAY THAT WAS COMPLETELY SAFE, FORETHOUGHT, LOGICAL, CALCULATED, MORAL, AND MUTUALLY-BENEFICIAL!). We shouldn't knowingly, directly communicate or reply to forces beyond our wildest comprehension, for what we wish to be a dream for the future of mankind could quickly turn to its worst nightmare, if we are not careful, moral, loving, prudent, and conscientious. We should not have the audacity to treat our supposed Galactic neighbor(s) based on behavioral assumations, if we ever resort to treating them any way whatsoever, which until we reach a far greater point of advancement (both materially, defensively, socially, scientifically, technologically, and, in all honestly, Spirtually) I advise against, 100% completely. Just my take. Learn what we can without exposing ourselves.
You'd need a spectacularly static civilisation to engage in any meaningful communication over the timespans involved.