The breakthroughs in materials science that enabled the construction of skyscrapers were formulations for concrete, and mass production of steel. Steel used to be incredibly labor intensive (and hence expensive) to create. Then industrial processes were created to churn out steel in unimaginable quantities, and now you could build a goddam building out of steel beams, which would have been ridiculous in 1818. So the first megastructure of this typehad to wait until 1885.
Exactly. Today, we can make say carbyne, graphene and carbon nanotubes, but it’s a labor intensive process that hasn’t been mass produced on industrial scales. We could see some of the ways you COULD use the stuff if only we could make it cheaply and in huge quantities. Same goes for fusion power…we could see how you could, possibly, do it (with you know the whole mass of a star part), but thus far actually doing it so that it returns more energy than it requires to create the reaction eludes us.
It’s amazing to look back a few hundred year to what people thought were the limits then look at today to see how we have surpassed them and in ways they didn’t imagine…and to think what will they be doing in another hundred years?
The answers are “no”, and “yes, but not for the same reason”. The galactic core explosion of Known Space is a chain reaction of stars going supernova in the core.
Back when Niven came up with the idea not nearly as much was known about the behavior of black holes or he’d have probably used a black hole powered cataclysm instead. But there certainly are active core black holes that produce radiation capable of devastating a galaxy. The “Death Star galaxy” even has one that’s projecting a beam that’s hitting another galaxy with fatal-to-life levels of radiation.
Much less time for the crew actually, if you take into account relativistic time dilation.
Time dilation only matters close to the speed of light, and we ain’t getting there.
Yeah, it’s pretty small though definitely measurable. I get (using 10% of the speed of light and 4 light years distance) 39.97994974842648 on a 40 year trip (it would actually be double that at least as you have to slow down as well…and obviously you wouldn’t be going at a constant 10% of the speed of light the whole way, so this is just for fun) from here.
The assumption is that the civilization does or is anticipating having that size of a population. This begs the question of how this would benefit an advanced civilization; in a primitive sustenance agricultural or industrial society having more population is a benefit as it provides more physical labor, and incidentally, more artisans, engineers, and natural philosophers to advance the state of the art. For a modern industrial or advanced technological society, the only real advantage to having more people than necessary for the largely automated labor and agricultural tasks is as consumers to sustain a largely service-based economy, which is a self-fulfilling prophecy. An advanced society, and particularly a post-industrial civilization where virtually all labor is automated would likely place a premium on intellectual effort and apply a cost to having excess people who are not capable of contributing to advancing some field of art or science. It is certainly cheaper, and practically easier, to control population growth to an optimax size to produce the desired rate of technical and intellectual achievement rather than to build fantastical megastructures with magical technology.
So, it would seem unlikely that a future human civilization will dismantle Jupiter to construct a large spinning habitat at Earth orbit for the purpose of providing living and cropping surface. However, there are other reasons that one might construct a massive, interplanetary-sized structure; specifically, to collect energy from the central star (if they haven’t found some other source of essentially inexhaustible energy such as cheap controlled nuclear fusion or some way to tap into ‘zero point’ energy of the quantum ground state), or to store massive amounts of data at the limit of thermodynamics. These wouldn’t be large spinning rings full of retro-primitive natives to explore and exploit, so they don’t make great stories, but there you go.
Once a civilization becomes truly capable of inhabiting space, rather than just building outposts that have to be regularly resupplied by resources from deep within a gravity well, there really isn’t much need for planets or planetary habitats other than for exploration. There is a vast wealth of resources in even near Earth space, much less the asteroid belt or Trojan asteroids, which is far easier to access than mining on Earth, provided you have the necessary propulsion and energy conversion technology to get in the same orbit. The notion of terraforming Mars or traveling to other stars to inhabit worlds is really thinking about space exploration along Age of Sail lines of finding South Pacific islands or the ‘New World’ with easily converted natives and bountiful edible resources. Realistically, even the most ‘Earth-like’ of extrasolar worlds are not likely to be more habitable than Mars or Titan (unless they have indigenous life producing free oxygen and nitrogen), and the likelihood of finding a world which would be constituted with the right atmosphere, gravity, solar insolence, axial tilt, hydrology, et cetera to be suitable for growing crops is about as great as finding a comet made of ice cream.
There are even bigger problems with the notion of ‘generation ships’ and other attempts as sending people across interstellar distances with any kind of conventional propulsion. Setting aside the problems of keeping a complex vessel operating for hundreds or thousands of years necessary to reach the nearest stars and keeping the occupants (they couldn’t be ‘crewing’ the vessel to any degree of utility) in a stable society, there are fundamental problems with the thermodynamics of operating a massive closed energy and resource cycle, having to obtain nearly perfect recycling while expelling all of the waste heat, notwithstanding the heat produced by whatever propulsion system is being used. The vessel will generate waste heat, and the higher power (energy per unit time) that your power operates at the greater the waste heat problem will be. Heat dissipation in space (where there is no atmosphere to convect away heat, so radiation is the only heat transfer mechanism) is a major problem even with low power systems used in present spacecraft.
With a very high power propulsion system, heat energy will build up rapidly and will require some kind of thermoregulatory system and a massive radiating surface to reject the heat to the background of space. Even with the large absolute difference between the spacecraft thermal environment and the 2.7 Kelvin microwave background, it just isn’t plausible that a high power source could be used to propel a spacecraft for decades or centuries without exceeding its capacity to store excess generated heat, even if the thermal efficiency of the propulsion process were only a fraction of a percent.
There are no technologies extant or plausibly proposed which could achieve that speed. Even assuming very high temperatures (~10[SUP]8[/SUP] K) for fusion for a thermal rocket using hydrogen as the propellant, the I[SUB]sp[/SUB] comes out to be around 10,000 to 20,000 seconds; to achieve a speed of 0.01c (which would take over four centuries to visit the nearest star system) would require a propellant:payload mass ratio in the millions, so even nuclear fusion doesn’t provide temperatures sufficient to attain sufficient exhaust velocity and specific impulse for interstellar transit in a human lifetime. An I[SUB]sp[/SUB] exceeding 80,000 s would be necessary to make even achieving that speed remotely viable, which itself would be a heroic undertaking.
Realistically, when we decide to start exploring beyond our own solar system, we’ll do so via proxy, with autonomous, self-maintaining probes that can operate for millennia and replicate themselves or any tools they need upon reaching another star or other interesting destination and then relay information back to us. That also required near-magical technology but at least it doesn’t violate any fundamental laws of thermodynamics or require the power output of a medium sized star to achieve.
Stranger
Proposed? I can think of several proposed ones. Plausible? To who? You? Me? Doesn’t matter though…here is one that has been proposed and is at least marginally plausible, though I know you disagree.
They’re great for demonstrating idealized physical situations for physics teachers.
No, Project ORION nuclear pulse propulsion is not remotely feasible for interstellar propulsion, a fact that Dyson acknowledged privately even when he was using the claim to try to keep the program alive for interplanetary use. A simple calculation of specific impulse and exhaust velocities of the material ejected off the pusher plate (not the initial speed of the material from the explosion of the bomblet which is often mistakenly used) will demonstate this. Any propulsion system that invokes antimatter is not feasible, either, as we have no natural reserve of antimatter available and the cost and effort to produce it in any quantity (notwithstanding the inability to store it for an extended duration) is literally astronomical.
We may one day discover some loophole in physics that permits violating conservation of momentum, or draw energy freely from the quantum ground state, or construct wormholes and stablize the termini using some kind of repulsive ‘exotic matter’, but today this is all in the realm of fantastical science fiction. No conventional means of rocket propulsion is going to permit transit between stars in anything like a human lifetime, not are we going to send massive arks of frozen passengers to other star systems at enormous expense in some vague hope that they’ll somehow find a habitable world to colonize and spread the seed of humanity like interstellar conquistadors.
Stranger
The safest configuration I know of is a kind of torus proposed by Bob Jenkins. First you arrange the individual elements into a ring, with each element about a million kilometres apart. Then you add another ring, with a different inclination and a different argument of periapsis; repeat this until you have a ring of rings making a full circle. The result is a kind of torus where every element is about a million kilometres from every other element.
Here’s an image I’ve made to illustrate the concept; in this image, the elements in the rings are a bit closer together than a million klicks, but more than a hundred thousand – you should be able to keep these apart just using the power emitted by the local star.
But even this kind of swarm would need constant station-keeping - leave it alone and it will be dust in less than a million years.
Making images of dyson spheres is a bit of a hobby of mine; in any search for Dyson Sphere or Dyson Swarm my images tend to come up a lot of the time (sometimes re-use without permission, but often with).
This is mine; so is this, and this, and this, and this, and this. I’ve usually got a fairly detailed sketch for how these things are constructed, although some of them require a certain amount of unobtanium.
One image that has been used quite often by others is this one, which is probably one of the least practical designs.
The underlying idea of a Dyson structure is the efficient use of matter and energy. A planet like the Earth can intercept only about one-billionth of the luminosity of the Sun. Using the same matter in various configurations could increase the amount of collected energy by at least a million-fold, probably more. And the population such a swarm could support could also be a million times greater. Note that many designs (such as the Matrioshka Brain) aren’t primarily intended to support a population of humans - a Matrioshka Brain would be a vast computer, or network of interlinked computers, thinking inscrutable thoughts about the Meaning of Life, the Universe, and Everything.
You’re right. I ran the numbers and at 20% c you only shave off about 3% of the time.
No, I get that. I’m just wondering how much matter and energy is required to build it in the first place.
No one ever says how that energy gets transmitted somewhere in a format that is useful? It’s not like they are running power cables to the stars. And I think reflecting all the energy of the sun directly back at Earth would have the unintended consequence of evaporating it.
Maybe instead of mirrors, you can use prisms or power big lasers to push a solar sail to nearby stars using the sun’s energy?
XT - I did watch the videos you posted and they are pretty interesting.
He makes a couple of interesting points. In particular, that sci fi often underestimates the scale and populations of a lot of these structures. Specifically, an ecumenopolis or “city world” like Coruscant supposedly has a population of a trillion people (according to some sources…others say 40 billion). Assuming it is roughly the size of Earth, that’s only a population density of 17,000 people per sq mile. Or approximately the same density of Cambridge, MA or half that of Hoboken, NJ. Urban to be sure, but not the density one might expect from cities with miles-high buildings.
A ringworld might comfortably support a population of a million trillion people. He also makes a good point about the unlikelihood of such a society regressing into some sort of agrarian culture. At any time, it might have a trillion scientists working out how to re-invent technology they already have working examples of.
This can be calculated by dividing the gravitational binding energy of all the planets in the solar system by the amount of energy put out by the Sun in a year. Assuming you want to use all the mass in the Solar System to make your swarm, it would take about a thousand years to disassemble all the planets. There is, of course, a logical problem here- you can’t collect the energy to disassemble the planets without first building a Dyson Sphere. There is a work-round, however - you could make a very lightweight dyson swarm first, by disassembling a few asteroids, or the planet Mercury, and work up from there. The absolute minimum weight for a Dyson Sphere which covers the entire star would be similar to the mass of the asteroid Pallas- this would be so lightweight that it could be supported by light pressure alone. But you’d have to re-radiate the heat very quickly, or the bubble would evaporate in a matter of minutes.
The equilibrium temperature of a dyson sphere 2AU in radius would be the same as the Earth, assuming heat can be radiated away freely; so it is unlikely to evaporate. Earth would be disassembled in most such schemes- although you could locate the Earth outside the Sphere and re-direct a fraction of the Sun’s luminosity towards our planet.
Google Nicoll-Dyson Laser.
And, interestingly enough, they actually did that calculation on the site I linked to. I’ve also used a specific impulse calculator to see what it is I’m missing…and I’m not seeing it. I checked on IA’s channel, and, sure enough, he’s got an episode that discusses Orion variants (it’s here, and he starts discussing it at the 21-minute mark) and he is saying that the specific impulse ranges from 6000 seconds to an estimated 100k seconds). I’ve done some searches and I see a lot of sites talking about a range in speed from 3% of light speed to 13% of light speed (and a few outliers saying over 20% but I’m discounting those). That’s pretty different than what you seem to be saying.
The formula for specific impulse is pretty easy, as you note (it’s in the wiki I linked to if anyone is interested) and all of the data is in there (their listed data is on the low end…but not as low as what you were saying), so, what numbers are you using and where did you get them? Are you using the old NASA figures from the 60’s based on regular fision bomblets (from here they seem to be saying 10-100 second specific impulse per bomb and had a payload of around 800 bombs half of which would be required to slow the vehicle down)?
Consider this a great opportunity to impart some of your knowledge. There is a ton on the internet about Orion, with a wide range of information that is all over the place. Most of the sites I visit or patronize list it as the only technology that we currently have that could get us to the next star over, with the range in time to get there between 100-400 years…not millennium plus you stated earlier. So, what are they getting wrong?
Glad you found it interesting. 
I don’t know if we will ever need those levels of population, but if we do it’s good there are ways to do it. His channel is definitely worth a look.
If you want to look at what the earliest stages of what building something like the stuff asked about in the OP might look like, IA has a new video on spaceports that’s pretty interesting.