Some musings on possible long term futures etc.

I wrote this to a polymath friend of mine who's mostly interested in history, law and politics (and to a lesser extent, religion), but is also a gamer, a Tolkien fan, and a reader of science fiction. (Which, mostly, I no longer read because I find it too arbitrarily fantastical, for the same reason I rarely enjoy fantasy). It was part of a far ranging dialog that is still ongoing. Anyway, some of my farflung correspondents will find this familiar (overly familiar perhaps) territory from me, others just won't be interested, and to those readers, I recommend the delete button. Not everyone is interested in everything. 

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Talking of science fiction, vs. potential real futures, may I make one or two possibly obvious points that sci fi almost always ignores? If you have reason to disagree with any of this, I'd be interested in why. 

I.    The speed of light is pretty slow from the point of view of creatures wanting to create interstellar civilizations, or even just seed life to other stars' systems. And this will never change. We must adapt to the necessity of very long travel times between stars, which will limit our capability to grow, but not prevent interstellar colonization and development. It will prevent the development of a "galactic village," because there is no way around the fact that it takes 100,000 years to send so much as a telegram from one edge of the galaxy to the other. (Communication takes almost as long as transportation, with c the limit). We will never be a cohesive galactic empire. But we may, nonetheless, fill up our whole galaxy and even beyond with advanced life from Earth, assuming (as I tend to) that we don't find competitors nearby. 

Forget about the Alcubierre warp drive or any other means of FTL. They all take either infinite energy or necessitate the conversion of matter and information into the deeply scrambled quantum goo that is what happens to ordinary matter and energy near singularities. FTL is impossible because it violates causation and the speed of light is an essential characteristic of all matter and energy. There is no way around it and never will be. If you think "science delves into the unknown and perhaps they'll solve this someday," I have two reasons why this is not the case. Science does delve into the unknown. It isn't really concerned with accumulating "truth," and anywhere near its frontiers it doesn't do that too well, which is why new theories are almost always wrong, at least in some details, and people get the impression that science is just another religion. It's not. It's a method. And it does build up a body of "knowns." Newton wasn't wrong. F does equal ma in the realm of physics we actually live in. Einstein expanded on that, but in context, Newton is still true. Thing about the speed of light is that it's everywhere. It's in all the relativity equations, all the quantum equations. The universe as we see it stretching out to the visible horizon (and it continues far beyond) could not exist if it were possible for ordinary matter with mass to translate at speeds faster than c.

The second reason is Fermi.* This is purely observational. We look out and we're looking back in time. So 5 billion light years out we're looking at a universe only a bit more than half as old as the one we're living in. Beyond that are more and more galaxies, but we don't see much detail. What we don't see anywhere is evidence of super advanced technological civilizations. Do they exist? Who knows. Maybe. But, even 5 billion years ago, if a civilization figured out how to make starships that could travel FTL, they would've had all that time to colonize all the galaxies between here and there, but the light from their galaxy would only now be reaching us. So we only know about the rough present relatively nearby. EXCEPT, we can be pretty damn sure that no one, anywhere near here, has figured out how to travel FTL, because if they had, I'm pretty sure they would be here now. And they aren't. Spiral galaxies are all much the same, and there's a whole hell of a lot of them. If even one in a million spawns a tech civilization, and such civilizations behave as you'd expect, exploring exponentially (OK, that's not a given but seems pretty likely given how all life seems to behave), there would be an enormous number of inhabited galaxies, from a small number of discrete origins of life. There may well be tech civilizations, but they don't expand or travel FTL. And since conditions in galaxies have been much as they are now for at least half the time the universe has existed, many of them would likely be immensely old. I would not be surprised if we eventually find evidence of very ancient galactic civilizations out there, even without FTL, because, as noted, interstellar colonization and even galactic colonization is still possible; it's just a lot slower. So we will not be visited by them or they by us, ever. (Eventually the accelerating expansion of the universe will cause even relatively nearby galaxies to be invisible to each other anyway, but that's a long time in the future). 

 The same rationale means that it's highly unlikely that a spacefaring civilization already exists in the Milky Way. Because we (humans and our successors) will likely visit every single star system (at least with robot probes) within just a few million years at most, if we succeed. And I'm pretty sure if that had ever happened before, we would know about it and our reality would be completely different. If this isn't clear, think about this. Let's say we develop a tech solar system civilization and begin building starships, with the grand plan to replicate the process, star by star, until we've visited and/or colonized all 200+ billion systems in the Milky Way. How long would that take? I won't even try to do the math (others have), but even if it's just one begets two, or even 1.1, and each one takes 1,000 years, the entire galaxy could be Earthized in less than 20 million years. Probably a lot less. That's how long hominids have already existed on Earth. If we did it in two million years (possible, but would require a bit more energetic development), that's only as long as the genus Homo has already existed. And it's a teeny fraction of the length of time that the galaxy has been more or less like it is now, with stars and planets, some of them potential abodes of life and all of them potential sites for technological life. We will likely do this if we don't die first. So the conclusion that in all that time no one has come along with this same capability (at least in this galaxy) seems pretty inescapable. If another civilization were out there in this galaxy now at roughly our same level, it would be a coincidence akin to winning the Irish Sweepstakes three times in a row. 

II. Energy will cease to be the issue, in terms of habitability. You've probably heard about Dyson swarms and ringworlds and all that, which is interesting and probably quite real as a potential. We can construct huge structures and live in them. (BTW, you didn't take large scale rotation as a substitute for gravity into account; it will almost certainly be used to make large structures habitable). If you want a big technological community, better to keep everyone close. The problem won't be getting enough energy, because we will figure out fusion and the star already leaks out huge amounts we can harness. Possibly dark matter or other unknown physics will yield new sources of energy, but even if they don't, this is all possible. A harder problem is waste heat. It will literally be hugely difficult to keep habitats with trillions of beings (even cyber beings) from getting too hot to function. But that's soluble, too. We will build systems to keep the inner system cool by transporting and radiating waste heat, although this actually is a hard limit to growth. (We should look harder for infrared "stars"... they could be civilizations). But space migration is its own imperative. I can't give you a reason why an advanced civilization would want to spread its version of life and explore the galaxy and even beyond, except that it's what we do. It's who we are. It is possible, and if we don't die, we'll do it. (We, including our successors who may not resemble us that closely). 

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*Reference is to the Fermi Paradox. In 1950 the eminent Italian American physicist Enrico Fermi interjected in a conversation with colleagues about the possibility of extraterrestrial intelligence, something like If they exist, where are they? Which is a much more intractable question than it may seem. Because peace to all saucerheads, but they very, very definitely are NOT here.