[JuettnerDistrib]

> is there really any practical value in this sort of research

In many ways it is too early to do this research, so it is a kind of art (as is a lot of research, imho). As long as only a few people do it, it's cool and useful so we can be aware of our potential future.

On the other hand, since we have no credible evidence of extraterrestrials, it would be surprising to find a civilisation so advanced to build a Dyson sphere. If they can build Dyson spheres, wouldn't they already be all over the place?

Ok, I suppose I should actually go read the paper now...

[awb]

> If they can build Dyson spheres, wouldn't they already be all over the place?

The number I’ve seen quoted is 50M years to colonize the galaxy: http://www.sentientdevelopments.com/2012/01/new-mathematical...

> they calculated that any galactic empire would have spread outwards from its home planet at about 0.25% of the speed of light. The result is that after 50m years it would extend over 130,000 light years, with zealous colonisers moving in a relatively uniform cloud and more reticent ones protruding from a central blob. Since the Milky Way is estimated to be 100,000-120,000 light years across, outposts would be sprinkled throughout the galaxy, even if the home planet were, like Earth, located on the periphery.

It’s actually so fast that advanced civilizations would have had time to colonize the galaxy and go extinct many times over without us noticing.

Or maybe their spheres were built so long ago they’ve already collapsed and been consumed by the stars again.

It’s a great mystery and interesting thought experiment though.

[denton-scratch]

> 50M years to colonize the galaxy

Our ancestors from 50M years ago are all extinct. So a civilisation spreading through the galaxy would have evolved in all kinds of different ways. It's not obvious to me that these diverse evolutionary strands would all still be interested in Dyson spheres, or space travel, or even astronomy.

There's a belief that's hard to shake off, that the properties humans have that we think most important represent some kind of evolutionary pinnacle. Typically, those properties are language, and a large brain for processing language. But if language and a large brain are really such great evolutionary advantages, why are humans the only creatures on Earth that have evolved those properties? Possibly language and a large brain are an evolutionary backwater.

At 0.25% of the speed of light, it would take us 1,600 years to reach Proxima Centauri; but it might take a lot longer to reach a star with habitable planets. We'd definitely need generation ships. After (say) a million years, we'd presumably have evolved to adapt to life on generation ships. It's not obvious to me that such adaptations would leave us fit to inhabit a planet. And perhaps adaptation to life on a generation ship means adapting to eating your fellow passengers.

Given the history of humanity, I find it hard to believe that the population of a generation ship could survive as long as 100 years without war breaking out on-board. We've had large brains and language for about 50,000 years, as far as I can tell; we've been warring the whole time. Maybe large brains and language pre-dispose us to war? If that's right, then it seems unlikely that intelligent life would ever spread far from it's planet of origin.

I'm very sceptical of the idea that any "civilisation" could ever spread far from its home planet. There are two things that we refeer to as a civilisation: a culture, and a species. Culture changes very quickly - over a single lifetime. But on a scale of millions of years, speciation is also pretty quick. So I can't see how any kind of homogenous civilisation or species could spread through a galaxy. They would have diversified before the train even reached its first stop.

So I don't have any insurance against being kidnapped by aliens.

[awb]

Much of what you say is reasonable.

Only two minor nits:

> why are humans the only creatures on Earth that have evolved those properties? Possibly language and a large brain are an evolutionary backwater.

Nearly every animal has language, for cooperation, competition, raising their young or to find a mate. Bees, whales, primates, birds, etc. all communicate strategically with some type of language.

> Given the history of humanity, I find it hard to believe that the population of a generation ship could survive as long as 100 years without war breaking out on-board. We've had large brains and language for about 50,000 years, as far as I can tell; we've been warring the whole time.

There’s been war somewhere the whole time, but not everywhere. Costa Rica, Iceland, Panama and several minor countries have no military: https://en.m.wikipedia.org/wiki/List_of_countries_without_ar...

It’s possible to find many countries who have not fought wars in the past 100 years. If you look more narrowly it’s possible to find communities unaffected by local war in hundreds or maybe even thousands of years (in other words, they fought a war but did so by traveling great distances, not fighting each other).

A ship would be much more like a tiny, isolated island colony rather than the geopolitical tensions that dominate the news.

Finally, wars rarely result in the extinction of both sides. Even if there was a large scale conflict it would likely be resolved prior to social collapse. There would be little incentive to kill so many of your fellow crew to the point where you’re putting every survivor at risk.

[mannykannot]

>> why are humans the only creatures on Earth that have evolved those properties? Possibly language and a large brain are an evolutionary backwater.

> Nearly every animal has language, for cooperation, competition, raising their young or to find a mate. Bees, whales, primates, birds, etc. all communicate strategically with some type of language.

There is currently only one species on Earth capable of even imagining the things being discussed here. On the other hand, it seems there may well have been more, but the others are now extinct.

One of these issues only we are discussing is the evolutionary viability of those abilities, and the fact we can do so suggests that it is, to some extent, up to us whether or not they will be.

[denton-scratch]

It's just struck me that a civilisation propagating through space can be envisaged a bit like light-cones, as in GR, except that the velocity factor isn't c, it's b (the maximum speed at which beings can move), which kinda depends on the beings.

But I think the cones thing is still interesting; it means that for any given maximum travel speed, there must be other civilisations that can never know anything about you, nor you about them.

[denton-scratch]

> Nearly every animal has language

Yes, I elided that bit, in the aim of brevity. I think there is a difference between human language and animal languages, in that human language is "creative" - we can freely create new utterances with new meanings, and expect to be understood. We know this of human language, but I would be very interested to learn of evidence of it in other species (chimps come close).

[webmaven]

> Our ancestors from 50M years ago are all extinct. So a civilisation spreading through the galaxy would have evolved in all kinds of different ways. It's not obvious to me that these diverse evolutionary strands would all still be interested in Dyson spheres, or space travel, or even astronomy.

There is no need for all, or even most, of the civilizational variants to retain those characteristics. As long as some variants do, civilization would continue its inexorable interstellar spread, it would just end up being lumpy rather than a relatively even wavefront.

Indeed, survivorship bias would seemingly tend to conserve the required characteristics and possibly start constraining the ways in which civilizational offshoots can vary. And it isn't hard to imagine stay-at-home variants succumbing to the influence of later arriving spreader variants to become spreaders once more.

[ncmncm]

Indeed, any culture that actually lasted long enough to get to the next star would have become, in the interval, comfortable with not being near any star, and could roam freely, doing nothing that could attract our attention.

[awb]

True, unless their lifespans are high enough that a trip to a nearby star is only a fraction of their existence (or they travel cryogenically and aren’t conscious during transit).

[bryanrasmussen]

Being able to build Dyson spheres does not make them capable of going faster than the speed of light, so any civilization capable of building a Dyson sphere would probably still be clustered around a couple stars and that's it.

Would such a civilization spread to more than one star is actually also a question, or would they control their population rationally stay on their Dyson sphere and only start to move when the star had less than 100,000 years left to go.

Only some Dyson sphere variants, like Shkadov thrusters, are primarily conceived as ways to move around. Which personally seems to me less likely, is a civilization, as well as the ability to construct these objects, also going to have a species level interest in going exploring?

[perihelions]

> "Being able to build Dyson spheres does not make them capable of going faster than the speed of light, so any civilization capable of building a Dyson sphere would probably still be clustered around a couple stars and that's it."

Check your math: this galaxy is ~10^5 light-years in size and ~10^10 years in age.

[bryanrasmussen]

what does that have to do with anything I said? Yes, I guess they would be everywhere if their civilization was able to make Dyson spheres 1 year after the creation of the galaxy, also if they decided to

1. Not control their population for some reason.

2. Had some sort of interest in exploring.

3. Implicit also in the speed of light thing, would find it really interesting to send a portion of their population to the next available and suitable star which might be enough light years away to make communication impractical. I mean for our civilization there is some level of argument that says it would be a ridiculous idea to move to a new solar system and we have an intellectual exploratory streak in our species.

I mean we are currently not at the level of being able to do a Dyson sphere, it took us 4.543 billion years (age of earth) to get to the part that somebody could conceive of it. There is also some discussion as to whether or not our civilization is going to last, so given that and the other things I said it seems unlikely to me that any Dyson sphere civilization would actually build more than one, but maybe some build two because binary stars or some other weird circumstance which makes it worthwhile to do.

on edit: if we get to Dyson sphere building capabilities which seems really unlikely, will we build more than one? How many more?

[MattPalmer1086]

The point is that you don't need to go faster than the speed of light. There's more than enough time to cover the entire galaxy in a relatively short period of time at sublight speeds. A few million years is sufficient.

[bryanrasmussen]

yeah, sure, enough time to GO everywhere but not enough time to BE everywhere, which is a different thing entirely, even if all the other things I brought up as to why the aliens weren't everywhere were not things to take into consideration.

So again, still haven't heard any argument why an alien civilization achieving the ability to build Dyson spheres, even if they did so far enough in the past that they would then have adequate time to traverse the galaxy afterwards, would then have to be everywhere?

[MattPalmer1086]

I'm not sure I understand your argument. There is sufficient time, with waves of colonisation to spread across the galaxy many times over. This can include pauses of thousands of years between colonisation waves. Some of those colonies could also build Dyson spheres. You would end up with them scattered all over the galaxy. Even if the colonies dies out subsequently, the spheres would still be detectable.

[MattPalmer1086]

I'm not sure anyone is arguing that aliens who can build Dyson spheres HAVE to be everywhere. They could, as you say, just build one or two and live there. Or a species that colonises could build them as it goes.

[caf]

They may not be moving around to explore so much as to keep their solar system safe.

Galactic orbits are far more chaotic than the sedate stable orbits within the solar system - stars closely approach each other on a somewhat regular basis.

[bryanrasmussen]

that's a good point, but I guess at Dyson sphere level a star approaching is like discovering oil on your property.

[dave_sullivan]

No Dyson spheres, but there are black holes all over the place. Some people think those would make great computing devices, many of their origins are not well explained as super nova remnants, and they efficiently harness energy from companion stars. They have all the properties of Dyson spheres but they actually exist. Maybe with advanced enough physics, intelligent civilizations learn to manufacture and harness black holes, neutron stars, and other dense objects for societal benefit.

[jonathankoren]

> No Dyson spheres, but there are black holes all over the place. Some people think those would make great computing devices

They’re crappy computing devices. Even if you figured out how to program one — and that’s an “if” that would make Sagittarius A* look like a neutrino — there’s no way to read the information out except Hawking Radiation, and that would take 10^70 years.

https://youtu.be/0GLgZvTCbaA (8:36)

[alfiedotwtf]

This is the first time I've heard of this. Wow, yes! A blackhole is far more efficient at consuming energy than a Dyson Sphere... the hard part though is kickstarting the process I guess

[ohyeshedid]

> If they can build Dyson spheres, wouldn't they already be all over the place?

I figure they'd have to be.

They'd need more than a solar system's worth of raw resources to build the sphere. They may need more than a solar system's worth of resources just to build the tools and craft to be able to build the sphere. They're going to need an insane amount of production facilities for various components, and that's going to take a massive amount of resources. That's going to require exploring quite a bit of a galaxy.