Alastair Reynolds is a hard scifi author with a PhD in astrophysics, and most of his works deal with this in some fashion. One is Pushing Ice (SPOILER IN REST OF POST), which tackles your question about civilizations not really having the ability to communicate with each other, not only because the galaxy 100,000 light years across, but also because it's billions of years old. That is, you could have lots of civilizations rise and fall, even in the same neighborhood of the galaxy.

So the big idea revealed at the end of the book (most of it is structured as "what is going on!?") is that one of the early civilizations planted lots of moons around the galaxy that would lure in and trap ships and then accelerate off somewhere. At high accelerations, for various small amounts of subjective time, millions or billions of years could pass. By calibrating all the moon traps then, lots of different civlizations from different corners of the galaxy, each originating in different eras, would be arriving at about the same time/place.

The Forever War, by Joe Haldeman, has both sides in the conflict sending spaceships at .99c to where they think the enemy will be.. with the unfortunate reality that if the enemy has populated & developed from that location first, the arriving fleet will be thousands of years of innovation behind and be wiped out without a chance.

Written by a survivor of the Vietnam War and a frighteningly poignant read.

"'The laws have changed sir, you no longer get a discharge after 1000 years. We're shipping you back out in 2 weeks' and of course the bastards only pay you for your subjective time, otherwise we'd have soldiers getting rich"

https://en.wikipedia.org/wiki/The_Forever_War

Yes, it's a staple of hard science fiction. It's generally assumed that interstellar cultures are isolated, extremely long lived, and/or have solved the problems of practical interstellar travel (maintaining high thrust, dealing with radiation, not going splat on a dust particle at .99999c).

It's interesting to note that a traveler on a spaceship that can maintain 1g of acceleration would experience 14 years subjective time while traversing 1480 light years. (According to http://convertalot.com/relativistic_star_ship_calculator.htm...)

And for those not familiar with relativity, in any case of course after traversing 1480 light years the civilization you intend to meet will be at least 1480 years in the future.

If two civilization were to meet the most efficient way of communication might be mediated through an AI. Exchange computer with some clear protocol for communication (probably based on elementary mathematical/physical principles) with an AI capable of conveying the intentions and the cumulative knowledge that you want to share.

  Exchange computer with some clear protocol for
  communication (probably based on elementary
  mathematical/physical principles)

I always see people talk about stuff like this, but it's never really clear to me how elementary math or physics will help us communicate with other species---species that will likely have sufficiently different biochemistry from us to make communication at least as difficult as talking to a dolphin or an elephant.

I shared the same confusion before, but I do have some ideas:

I think you could establish a communication protocol with an alien species with something like this:

First, establish the meaning of a set of mathematical symbols by choosing recognisable / universal mathematical entities and demonstrating the symbolic relationship between them

That means things like eg. a picture of euler's identity and then symbolic representations beside it, then varying the individual elements and showing the results.

This isn't easy (if you've ever played that boardgame about inferring another player's rules with pyramids, you'll know what I mean...) but it is probably doable.

And you might be able to symbolically demonstrate Peano Arithmetic or something.

Once you've established a vocabulary of mathematical symbols, you can maybe use that to pin down a basic physical vocabulary. You could maybe identify different elements based on eg. their atomic number. You can establish a time vocabulary by giving a formula for the orbit of their nearest star and asking them to solve for x. You can describe spatial relationships between things.

It seems very difficult to go from there to a yet higher level vocabulary - but who knows, it may be possible.

It's actually not a problem at all. It'll be extremely unlikely that two civilizatizations in this case are about same level in terms of science and technology (+/-1000 years). So when the two communicate, the advanced one can easily understand the other.

I believe it's assumed that if a species is capable of producing a mechanism to communicate with other interstellar species, then they necessarily have an understanding of math and physics.

A Deepness in the Sky deals with interstellar traders that do not have FTL.

The universe the book is set in has a gimmick to allow FTL, but that book doesn't use FTL (part of the gimmick is that it isn't possible in much of the galaxy).

Edit: The Revelation Space books also have lots of people moving between stars at below light speed.

The author is also a computer scientist so many of his books are well detailed for those versed in related fields (the way biologists write sci-fi books that scatter biology details other readers not versed in the subject would miss) like people here.

A Deepness in the Sky, for example, touches on open source, technical debt, project management, memory density, branching, DRM, encryption, stenography, and other more nuanced topics; but it's a sci-fi novel first. All in the backdrop of a universe with no FTL (at least for this book in the "series", more like books in the same universe).

He also does great alien races (the other book in the series, A Fire upon the Deep, has alien races which behave on different computational architectures to achieve sentience; and touches on obfuscated code (among other topics) in a great way).

> The Revelation Space books also have lots of people moving between stars at below light speed.

House of Suns (https://en.wikipedia.org/wiki/House_of_Suns) was one of the best examples of that. Starship chases lasting thousands of years, people making 200,000 year circuits of the galaxy...

I was very taken with the portrayal of the Queng Ho in 'A Deepness in the Sky'. I liked the idea that a trading culture would foster technological development across a large swath of space by broadcasting "here's how you bootstrap an advanced civilization" instructions to anyone who got as far as inventing radios. Then they'd wander around at relativistic speeds, trying to time their visits to each system to coincide with periods of high-tech development so they could do some trading (before each civilization inevitably choked on its own complexity. That part was a bummer)

There have been a number of such works. Olaf Stapledon's Starmaker takes a somewhat poetic approach to the idea. And restraining oneself to an Einsteinian universe where nothing exceeds C was a hallmark of "hard-sci-fi" although even Arthur C. Clarke fudged and went for hyperspace when the plot was otherwise going to drag for a few millennia.

For a more recent take on the topic check out Karl Schroeder's Permanence [1] which is a damn fine read and doesn't run the hyperspace cheat and is all the more operatic for that.

1. http://amzn.to/1LYhwwm

Karl Schroeder's most recent novel Lockstep[1] is also somewhat related, just set within a smaller scale than most of the books mentioned so far.

[1]: https://www.goodreads.com/book/show/17910135-lockstep

I don't think it's glossed over. It's a separate issue though.

Just knowing for certain that there is intelligent life - or any life - on other worlds would have huge ramifications for how humanity views itself and the universe.

It would be interesting to see how major religions responded to confirmation that there is other intelligent life that is not made in the same image as us.

Do aliens go to Heaven?

> Just knowing for certain that there is intelligent life - or any life - on other worlds would have huge ramifications for how humanity views itself and the universe.

I think our species chauvinism is pretty strong. I think the discovery of life on other worlds would have very little practical change to our daily lives.

For example, we seemed to have handled the fact that the dolphins and whales in our oceans are fairly intelligent. Why would finding intelligent whales in Enceladus oceans be any different?

I think your reasoning is somewhat an artifact of bias in science fiction in the first place. You see presumption of FTL all over the place, and so it's depressing to consider that it is very likely a hard impossibility, because it rules out a lot of those stories. But, there isn't a lot of science fiction which explores the consequences of eliminating biological aging, or anything else which might make 1500 years actually a rather short span of time for intelligent life.

Maybe the galaxy is full of life which thinks nothing of going on a journey that would take thousands of our years, or longer.

I don't think Seti look for intelligent life because they want to have a conversation. They are searching because finding evidence of intelligent life out there would be a very important discovery. Perhaps one of the most important discoveries we could ever make. Are we alone in the universe? It seems like we should not be, but we have a sample size of 1 so far. It's a big big big question.

Its a neophillia thing. Plenty of interesting cultural exchange topics exist pre-600 AD. Ship them the complete works of the Greco Roman era, the Pāli Tipitaka, the bible... About 110 years ago Oxford Press published a 50 book series of English translations called "The sacred books of the east" off the top of my head I believe all the originals predate 600 AD? We certainly wouldn't lack for discussion topics.

Its interesting that no era thinks they're particularly dumb or ignorant. They didn't know many cool programming algorithms, we (in general, as a population) don't know as much euclidian geometry or stoic philosophy. I'm sure we'd have plenty to say about some topic even if the topic would change over 1400 or so years.

There's also a general insistence on culture shock, which I disbelieve in. I'm not that old, and something like Plutarch isn't that much closer in age to me than to a newly graduated kid. "We" would do just fine.

Never is a strong word.

For one, we know nothing of the remote party's biology and medical achievements. In fact we don't even know whether the remote party would be a biological entity at all. They could be an engineered AI built by a species long gone or marginalized. Bottomline is we have no clue of their lifespan and mortality.

On the other hand, we can also change beyond recognition within a single roundtrip so if human progress is sufficient then by the time the conversation really gets going it may become possible.

Also, the nearest interesting stars are much closer than 1480 ly [1]. Generally under the most primitive assumptions about star distribution (uniform) we have a fast increase (O(n^3) within distance n ly) in the number of systems we could talk to.

[1] http://www.space.com/18964-the-nearest-stars-to-earth-infogr...

I think achieving step 1 of even finding intelligent life is good enough for most people. We can work on the comms later.

It's also important to keep in mind that this depressing perspective is a contemporary, anthropomorphic one.

It might be the case that communications using electromagnetic radiation are an unremarkable blip on the timeline of technological progress. The modern era has only been in full-swing for a paltry few hundred years!

I like to think that the size and scope of the universe suggests that there absolutely are many many ways to travel and communicate faster than light (and presumably well beyond), that we haven't even imagined yet. Zoom out enough, and any speed or distance scale appears tiny.

My favorite sci-fi work on this topic (and I dare say my favorite sci-fi work ever) is a series of posts on kuro5hin by localroger, together titled "Passages in the void." You can find them on http://localroger.com/ . The speed of light issue is solved without inventing new physics, which is extremely satisfying, but there is still enough of a leap of faith to make it satisfying sci-fi. Brilliant work.

> if you believe nothing can exceed the speed of light then even if we find intelligent life we will never communicate in any meaningful sense of the word.

Quantum entanglement could very plausibly allow for superluminal communication. Yes, I know that it isn't proven, or even considered plausible as yet, but call me an optimist.

https://en.wikipedia.org/wiki/Superluminal_communication

> Quantum entanglement could very plausibly allow for superluminal communication.

If by "plausibly", you mean "in contravention to all currently established theory". As the Wikipedia article you linked itself states.

That's exactly what I mean.

I think we have different definitions of "plausible", then.

Star Trek uses "subspace communication" for faster than light messages http://memory-alpha.wikia.com/wiki/Subspace_communication

That's not dealing with the limitation, it is pretending that it doesn't exist.

we might discover a method of "subspace" communication if we observe a more advanced civilisation using it.

I want to ask the opposite question. Are there any hypotheses that would explain how fictional subspace (communication) would work? Or even FTL comm.

Many. Clarke's "Songs of Distant Earth" is a very good one. "A Deepness in the Sky" is another.