My theory has always been that we have no idea what an advanced alien civilization would look like. We could easily be surrounded by alien signals we can't pick up because we don't know how to build the neutrino radio or something.
Dissolving the Fermi Paradox
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Mandemon
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And once again, all these require support. What happens when those support lines are borked? Space habitation sounds easy but those places have no natural resources, requiring some other source resources. They also have significant limitation to how big the place can grow.
Vyslanté
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Yeah, that's the other possible answer to RRoan's "but maybe civilization can live very long": maybe they can, but it's probable that in that case we can't detect/communicate with them, insert usual metaphors about ants.
My personal theory is that interstellar travel is so hard that for any civilization that is capable there is no point. I mean for sublight speed interstellar travel you need to be able to survive in the depths of space for decades if not hundreds of years on nothing except starlight. And if you can do that the next star system over offers nothing of value to be worth leaving for.
Presumably the newly launched colony has everything it needs to get started via asteroid mining, since those should be relatively abundant everywhere in the universe. The limitations to space habitation are a lot higher than you might think. An Oneill cylinder can reasonably house millions of people, and the aforementioned McKendree cylinder can easily have living space comparable to Eurasia. And when either of those start nearing their population capacity, you just crack some more asteroids and build more. Beyond the initial investment of mining equipment needed to get started on building infrastructure the colonies really should be able to be totally self-sufficient.
galahad
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what about post organic life?
Well, maybe evolved systems are necessarily messy and complicated, full of needlessly complex bits that used to perform a thousand different roles before and essentially work as self-destruct timers and making a proper post-whatever life-form is a tremendously complicated thing for all existing biologies around our galaxy. Hormone systems that are as non-orthogonal as possible, neural networks that have bits that make negative sense, interactions that constantly come out of left-field, what do you mean we use more amino acids than that? I thought we had mapped all the ones our genetic code analogue called? Some just happen outside of that?
Therefore they tend to not happen?
Therefore they tend to not happen?
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galahad
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By post organic i mean life that basically evolved to become a sentient A.I. Does not even have to be "uploads" ( which I think are inefficient and pointless, like running dos 6.1 on a core i7 8700K machine), but a whole new AGI that replaces its creators.
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That was also what I meant, you'll typically have one example of a type of computing capable of meaningful sentience, look at ours, a poxy form of neurochemical signaling with a trillion gotchas.
Building something to equal that is going to be tricky because your one example is equally tricky, and you're going to have to understand it before you can work with it.
I guess you could go all sorcerer's apprentice, but I'm not convinced about the long term ability to get results as opposed to trivial and entertaining curiosities.
Building something to equal that is going to be tricky because your one example is equally tricky, and you're going to have to understand it before you can work with it.
I guess you could go all sorcerer's apprentice, but I'm not convinced about the long term ability to get results as opposed to trivial and entertaining curiosities.
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galahad
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I don't think trying to copy the human brain is correct approach.
It's kind of like building a flying machine that flaps it's wings to fly like a bird. People trying to crack the heavier than air flight problem have tried to copy nature and gave up because it's too complex, and instead came up with simpler and better solution for aircrafts.
Today with much better understanding of biology and aerospace engineering ornithopters are finally possible, but no one bothers beyond vanity projects because fixed wing or rotary lift is just so much better for most practical purposes.
In the AI field the progress today that is being made is with computational and mathematical approaches instead of trying to copy biology. Evolution gave us one possible solution to the general intelligence problem. Does not mean it is the only solution. Evolution general!y comes up with complex answers where simpler solutions are possible, like wheels vs legs.
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I'm not thinking about performance, I'm thinking about the lifeform bit, the "meaningfully human" part, the meaningful self-reflection as we know it. You're either going to copy what you have or reduce and formalize consciousness, and that would be tricky, especially considering what we're working from on that front, which is again, mostly us chattering monkeys and perhaps a few other animal extras.
galahad
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Personally I don't see why you would want an AI to be human like. Performance is the sole metric that matters - can this thing survive and propagate in this universe better than humans can ? Then yes replace humans with it, let Darwin be the judge as has been for all forms of life for 4 billion years.
Once again either you have the capability to survive decades to centuries on nothing but starlight or you can't move between stars.
Hard drives corrupt, ram breaks down, signals flashed between world's need a receiver at both ends, and degrade with distance traveled. Just because it isn't "alive" the way we typically think of life doesn't mean interstellar space with all it's radiation, lack of physical resources for repairs, and micro meteor impacts trying to blow up your vessel for decades or centuries is trivial to survive.
And if you can survive it why colonize planets at all? You've gotten to a point where you simply don't need them.
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You're assuming such things, you know. Exist. It's sorta like going "But what about a species who teleports".
galahad
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The answer to why is it only takes one. Different motives would drive different intelligent entities. You just need one entity that acts like a Von Neumann swarm. Can you show that not one out of every single intelligent entities that arise in a universe can display VN swarm tendencies ?
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It doesn't matter what alien intelligences want if it is impossible or virtually impossible to survive interstellar travel.
Which is my point. If your von Neuman probe cannot arrive in a good enough condition to reproduce your tech base from the ground up then it doesn't matter how many Von Neuman like entities there are. One or ten million if they cannot reliably traverse interstellar space they can't fill up the galaxy.
There where plans for using an Orion drive to build an interstellar probe with 1970s tech, it'd make it in 50 years. If we crack fusion we could do even better with smaller ships, using lasers and simple nuclear engines we could send probes to nearby systems in less than a century timescales. Eminently doable if you can do big projects in space most of which make financial sense too if you have a lot of space explotation.
Some of it doesn't even need super tech, just building big, like say using an orbital ring for interstellar launches. And orbital rings have applications on planet too, you can get the speed of supersonic planes for the cost and bulk shipping of trains... But the infrastructure for it is expensive to build.
The basic problem is that either we don't understand physics, tool using life is exceedingly rare, or something is killing off civilisations. Imagine if there was a planet much like Earth 64 million years ago, and the raptors are having a thriving Stone age civilisation, and they are in luck and the asteroid misses them, they are not as smart as us so it takes them another million years to get to the iron age and a million more to go from iron-age to modern. Now they probably want to at some point tap their star for power, and mine various materials in orbit... Some of which will be used to build in orbit stuff like mining equipment and habitats for the miners etc etc. If their tech doesn't advance much beyond modern we'd still expect more and more stuff to be built up over time, more powerplants driven by sunlight, more mining etc. Use beamed power for habitats further and further out, settle the oort cloud... And the oort cloud pretty much touch the oort cloud of other systems.
As the population density and trade in the system increases habitats for comfortable living space and infrastructure like orbital rings make more and more sense... And with a big orbital ring you can send fast interstellar probes cheaply. At some point some group will spread to neighboring systems, and living in a good oneil cylinder probably beats living planet side 9 times out of 10 anyway so they don't even need good teraforming candidates. And once there are a few successfull interstellar colonies... Well people will want lebensraum, or just be away from those people, or religious freedom to persecute other religions.... Lots of colonies, especially if laser highways and such get built. But let's say that takes a few million years, and it's all happening in a galaxy two million light-years away.... Then we should still note how much of galaxy x is redshifted as if something is absorbing lots of light and emitting it as heat, unless thermodynamics is wrong, and they have 50 million years to colonize nearby galaxies too. Or maybe we notice widespread starlifting, or maybe the coordinated use of shkadov thrusters to move galaxies around.
The physics of how to do these things is understood, in many cases the basic engineering is also solved, the problem.is just the economics of getting for example multi-million tons of copper wire and helium cooled superconducting magnets in orbit to build something that will be generating a return of investment only in a century, for the first few decades is only returning billions in economic activity... Not nearly enough to even pay the interest on the loans. But if it wasn't for economics we could do a good start at much of those things with current tech.... So it's technically plausible just need more space industry first.
No existing material can be used to create an orbital elevator, and it's quite possible that no material that can physically exist has the necessary properties required to do it.
Orbital ring not orbital elevator very very different beasts. Orbital elevators require silly tensile strengths, an orbital ring needs a conductor and magnets, so basically copper wire will do. But to our current techlevel it;s like the I-70 in the time period of the Oregon trail. The idea of a 4 lane highway to the west with bridges and stuff would be understandable but the reason to build one would be non-existent because there is nothign and no-one there. Plus what could possibly need more than 2 lanes anyway. Oh it would be nice sure, but an extragavant waste of money.... it'd make the launch cost... well roughly on par with shipping by train. but unless you are shippign millions of tons a day the investment in the infrastructure to enable such doesn;t make sense. We can imagine a future with stuff buiuolt up and several asteroid mines and other stuff where it begins to make sense to build such a thing.
Wait, what is the point of an orbital ring if not as a foundation for a orbital elevator. Wikipedia only talks about them in terms of hanging cables down to earth as part of an orbital elevator system. Or as a launch point outside the earth gravity well, but you still need rockets to get anything up to it without orbital elevators.
Ok, let me give a basic primer on orbital rings, but the basics is that a space elevator needs a bridge equivalent of around 100000km, an orbital ring needs and equivalent of 100km, or if you are willing to spend oddles of money 10km. The many less 0's make the endevour so very much easier.
So lets first go into how to build an orbital ring, first start with a coper wire in orbit... lets pick a fairly low one and tell the construction workers to work fast. so an nice circular 80 km of the ground... technicaly not even in space, though the air is very very thin here and we have a few years before orbital decay becomes a problem. Spool the wire out along the orbit then weld the ends together. The wire is in orbit so it will just stay there and the forces acting on the wire are miniscule. Speed the wire up a bit and it is going too fast for it;s orbit and it will be under tension, spin it too fast and it flies apart. Now wrap the wire in a vaccum tube, lines with magnets so that the tube can't touch the wire, idealy superconducting ones like used in CERN. So we can build a tens of kilometer circle of these already. just in case you are wondering about technical feasibility. Now you have a wire with a magnetic tube around it in orbit. Not very useful yet. Use the tubes to accelerate the copper wire more, which in reaction will slow the tube down... you want the tube to be at 0 speed relative to the ground. the wire will be going way above orbital velocity but the magnets bend it down, and the combined momentum of the whole contraption is still at orbital speed so it remains in orbit. The forces invovled are confusing but mostly cancel each other out, the limiting factor becomes how strong the magnet is. As long as the magnet is strong enough to overcome the force tryign to bring it down and touch the copper wire the orbital ring will remain... and magnets can be silly strong, especially over short distances.
Anyway you now have thios pipe stationary with respect to the ground, drop some wires down to anchor it... and run elevators along those, 80km up so the elevator only needs to go 80km, long but not 100000km. It's also not terribly stable it can occilate side to side so run some wires at an angle to nearby cities within say 100km or so of the groundtrack of the ring. you have a wire 150km long, that is beyond what regular structural steels can handle but some better and more expensive alloys can manage. 80km up is well above the clouds and most of the atmosphere so add some solar panels they will be 140% of their ground based efficiency and no clouds, you can run powercables down the guy wires to power the cities... and use that electricity to speed up the copper cable too because you need to keep accelerating it as you add more mass... up to the limit your magnets can support. But the magnets in the tube... well they are strong enough that you can run a railroad track on top. And the train on top of that. At 80km up there is no air resistance so if you build maglev or so you can go up to truly silly speeds. In fact lets beef up those guy wires to nearby sities to full on bridges, 150km is straining modern tech... but physically plausible and you could use some tricks to cut that in half which is definitely doable. Oh and unlike an orbital elevator you can build a second tube and wire next to it to double the weight it can hold. So you can build an extensive rail network on top. and unlike the orbital elevator which needs to be on the equator you can have rings in any inclination.
So you hop on the train in Philly and an hour later you hop off at the on ring station. Gravity is still 99% of earth and while the atmosphere outside is thin, it is thick enough that space debree falls withing months or a few years. you can take a hyper velocity train from here to anywhere above earth in a short period of time, call it an hour or so if it isn't an express train and it makes some other stops before getting to your station then hop on a train to melbourne, doign the trip in about 3-5 hours as compared to havign to take a 24 hour flight. Also for train prices instead of plane prices. And if you want to go to space, you just hop onto a train that starts going... and going and going until the curvature of earth means you have 1g acceleration, then the train lets go of the spaceship part and it flies off in the target direction at some ludicrous speed, the spaceship only needs fuel to slow down,... or manuverign, if the target also has an orbital ring with a train that can catch the spaceship.
Because of the forces involved and how they grow you don't need to have it 80km up... you could build it 5km up, but then your vaccum tubes need to be way way better and it really helps if you have an orbital rign above you from which you can hang while you work... also that doesn't get you out of the atmosphere so less useful unless your tech is not up to building 150km bridges, then you can stagger multiple orbital rings till you get the distances down to something short enough that you can build it. Probably start in high orbit then work your way down... expensive although there are tricks that can be used to make building the rings much easier... once you have that first ring. And a ring will mass in the millions of tons even for a tiny thin one. An orbital elevator is much much lighter, but orbital rings should be cheaper per ton.... if you are shipping millions of tons a day to and from earth. Orbital rings basically approach the cost of shipping stuff by train as you ship sufficient volume, and for long haul they can do it faster than planes... so it would be a major boon for a planetary economy even if space never takes off... and once the orbital ring is build... shipping to space is the cost of shipping by train, not thousands of dollars per kilogram, but in dollars per ton. Only the space elevator comes close, and it lacks the throughput and flexibility and on planet use of a ring. And requires some exotic materials. The orbital ring is not simple, but it;s not that complex either, it just needs construction on a huge scale.
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PhoenixMercurous
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Wouldn't you need a current running through the copper wire though? In a toroid the magnetic field is constant, so circulating a wire through it wouldn't induce a current. Without a current, the Lorentz force on the wire would be zero, so it wouldn't stay in the vacuum tube. Getting a current into a wire moving at orbital velocities could be quite a challenge.
You'd also need 40512 km of vacuum tubes and superconducting magnets to loop around the entire planet at 80km up, which is a massive jump up from the 27 km circumference of the LHC. Cooling all those superconducting magnets could be quite a challenge, especially without the atmosphere to dump heat to. I recall hearing the LHC has an incredible electrical consumption, something like an entire nuclear reactor's worth, so powering an orbital ring would be another challenge.
Also, that whole contraption is just asking for one superconducting magnet to quench, throw the wire out of alignment, and risk having the whole thing fail catastrophically. And any failure would be catastrophic, the wire would be moving at 7.8 km/s at minimum (the orbital velocity for 80 km above Earth). I'll assume the orbital ring is above the equator and moving at the same speed as the Earth's surface there, 460 m/s. The wire's minimum speed relative to the tube would then be 7.34 km/s, giving it a kinetic energy of 26900 kJ/kg. For comparison, one kilogram of TNT releases approximately 4184 kJ on detonation. The wire, at minimum, is carrying roughly five times the energy per kilogram of TNT, and there would be 40512 km of this wire. Putting the ring lower makes the problem worse, orbital velocity goes as r^(-1/2).
Oh it would go way faster than that remember the wire has to go fast enough so that the whole system is at orbital velocity. But if it fails the wire shoots out onto deep space because it is way above orbital velocity, while all the infrastructure it was holding up falls down. There are ways to deal with this, like say having 3 rings in parallel and connected so if one fails the others can pick up the slack, or use atlas pillars or such... yes if it fails it's a disaster, but large infrastructure failing tends to do that, like say a dam failing, or deep water horizon, or a nuclear plant, or a major bridge.
And yes it would be hard to build with current tech... Much like how in the 18th century one could imagine building g a large highway along the Oregon trail, but they'd have a hard time building the I-70, even though they could build lesser roads.
But this thread is about the Fermi paradox, and while space elevators hover at the edge of what physics allows orbital rings are firmly withing the feasible. Imagine... Oh another 1000 years of tech and economic development. Having a collection of orbital rings around the planet would then be expected right? Unless they found something way better which is a struggle under physics as currently understood. But what that means for the paradox is that setteling a system is definitely doable and if you can do that then interstellar is... Not significantly harder. Using a ring to build up interstellarl speed... Yeah nearby star systems are reachable in under a century which our/near future tech can deal with. Then the L term drops from the Fermi paradox as galactic civilisation falls under the rubric of population Dynamics instead... At which point one has to wonder why raptor analogues didn't colonize all of Andromeda 40 million years ago. Or if they did they didn't build very much or they figured out how to break thermodynamics.
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How would you plan on getting millions of tons of copper wire moving at several kilometers per second in the atmosphere anyway?
Your whole thing is that they are "feasible". But that sort of lift capacity is just as pie in the sky as the idea of building a tower to the moon out of legos.
I do not believe technological capability can simply keep increasing indefinitely. There will not always be a better fuel or stronger material to discover.