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For a story idea, I'm wondering about the effects that the discovery of another intelligent species without FTL travel would have.

If we discovered another species much like ours, 50-100 light years away, how would we interact with them? Obviously, radio waves would be a first, but what is the physics on that? Would it even be possible to establish reliable communication at this distance? Obviously, we would want to visit, and with future technology, a round-trip time of a few hundred years is certainly possible. But by the time you arrive, your space ship is ancient technology even on your home world.

Would we travel at all, given these circumstances? Or would we be content with communication?

How does this scenario change with distance? Obviously, at 5 light years, the setting would be very different.

Any pointers to short stories, movies, other sources that dabble with such scenarios?

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One science-fiction author who has written a series of short stories dealing with interstellar communication, as opposed to space travel, is Edward Lerner in his Interstellar Net sequence. The link gives publication details plus an article about the background to the series.

The stars where the communication is taking place are much closer than fifty to one hundred light years away.

The astrophysicist and science-fiction writer Fred Hoyle has argued the universe would be a more interesting place if space travel wasn't possible because the number and variety of alien civilizations and intelligent lifeforms would be vastly greater. Then millions of alien civilizations could communicate to each across the galaxy. Alas, no citation for Hoyle's remark.

Generally, science-fiction in any form has mostly avoided communications scenarios preferring the space travel option.

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  • $\begingroup$ Just curious, but why did you post an answer, delete it, and post it again with an extra sentence? $\endgroup$ – Frostfyre Feb 23 '17 at 13:31
  • $\begingroup$ @Frostfyre Sheer carelessness. I accidentally posted an answer and added a sentence then posted that, which meant the first answer had to be deleted. Really sounds dumb, doesn't it? $\endgroup$ – a4android Feb 24 '17 at 4:26
  • $\begingroup$ Accepting this answer as it comes the closest. Interstellar Net deals with exactly this question. I also found another trilogy, The Three Body Problem, which touches the same ideas. $\endgroup$ – Tom Sep 26 '17 at 12:37
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At that distance, even communication is unlikely. Electromagnetic waves are generally limited to the speed of light, which means any communication would still take 50-100 years to reach its destination. With a 200-year round-trip response time, you're waiting generations to receive a response. Sure, we could reliably communicate, but with such a delay it's not going to be very meaningful as any information will be obsolete by the time it is received.

Even at relativistic speeds, you're again taking a lifetime or more (for everyone not on the vessel) to reach your destination, so travel will likely not be worth the effort.

Even 5 light years is a potentially problematic distance if you want to do more with communication than just acknowledge the existence of the other population. For reasonable collaboration, you probably want to limit your radius to less than a light-month, which would clear you of our solar system by quite a ways, but the nearest star is over 4 light-years away.

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  • $\begingroup$ "Electromagnetic waves are generally limited to the speed of light" Barring some very speculative physics, make that "generally" into "always". You could still have information exchange (if not dialogue) by each side sending continually, rather than waiting for a reply, as was pointed out in one of the answers to a question I asked some time ago, "FTL travel is impossible. How is interstellar trade possible?" $\endgroup$ – Lostinfrance Feb 23 '17 at 17:11
  • $\begingroup$ I'm aware that the ping times are on the order of generations, that's kind of the whole point. I still wonder if communication by radio waves is possible at all at this distance, or they will simply vanish into the background noise. $\endgroup$ – Tom Feb 24 '17 at 8:19
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    $\begingroup$ The inverse square law at face value suggests no, in regards to "will the signal make it", at least with current tech. There are certain things that can be done to improve odds, like waveguiding and targeting specific "quiet" frequencies to help your signal stand out, but at 50 light years the intensity of the signal is an infintesimal amount of the original. 5 light years would be feasible but power-intensive. $\endgroup$ – Chris M. Feb 24 '17 at 19:32
  • $\begingroup$ Thanks, Chris. That is a good part of the answer I was looking for. $\endgroup$ – Tom Feb 28 '17 at 11:27
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An interesting account of how complicate is to communicate between very distant planets (neglecting attenuation over distance and other nuisances) has been also made by Italo Calvino in his Cosmicomics book. There, in the novel The light years

the unnamed narrator looking at other galaxies, and spotting one with a sign pointed right at him saying "I saw you." Given that there's a gulf of 100,000,000 light years, he checks his diary to find out what he had been doing that day, and finds out that it was something he wished to hide.

This trigger a lot of actions and misunderstandings.

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