So a probe travelling between galaxies at 99%c can't hit anything bigger than 1.46×10−12 kg? It is ~2.5 million light-years between us and Andromeda. I don't know how much matter there is between the galaxies (does anyone?). But travelling that sort of distance without hitting anything above that tiny mass seems very unlikely. Also how is your tiny robot probe supposed to power any guidance or maintenance systems for that sort of duration of trip?
The concept of "Dyson spheres" was a joke by Freeman Dyson. It was never meant to be taken seriously. There's a clip about this floating around somewhere in which he finds it funny that the thing he's most well-known for was not even a serious paper. Dr. Angela Collier did a video about it.
The only person who seems to claim that Dyson Spheres were a "joke" is Angela Collier and people quoting her. I've seen no other source for this claim.
But even if it's true, which I don't think it is, it doesn't matter. Why? Because the idea is actually sound and a lot of thought has gone into it by people who have backgrounds in physics and engineering.
It's worth adding that "Dyson Swarm" is the more common nomenclature now because of a mistaken belief that a Dyson sphere was a rigid spherical shell you build around a star. That was never the case and there's no even theorized material that could support this kind of rigid structure. It was always a cloud of small orbitals so the "Dyson Swarm" should alleviate any confusion (hopefully).
Our civilization is ultimately energy-limited. I've seen estimates that we use ~10^11 Watts of energy. The Sun's entire output is ~10^25 Watts. That's a truly staggering amount of energy. We can barely comprehend what might be possible with that much energy. But one of those things is interstellar travel.
Many discussions on interstellar travel gloss over just how large the energy budgets are. But propelling objects with solar sails, particularly if you concentrate energy, seems feasible. At least the physics holds up.
Spreading throughout the galaxy becomes an almost inevitable consequence once you have the capability to do so.
I recently saw an interesting criticism of this paper: That by the end stages of the disassembly of Mercury, the amount of heat generated would be so much as to melt the surface, calling into question whether the mass driver system could work at such a high rate.
Is there already a name for that effect where grandiose plans somehow appear to be more feasible than the simple mundane step-by-step issues resolution that even though they clearly stand in the way of said grand plans, are not worth investing thought and effort in?
When it comes to software projects my pet-name for it is the "big-bang theory", but in the article's domain that's kind of already taken.
It appeals to me because if you've ever taken a flight you can see how the details get progressively erased as you lift. Details that matter for a lot of reasons even if you can't see them.
Has someone answered why a civilization would send "von Neumann probes" or similar into space? It would take so long for any answers from those probes to arrive that there really doesn't seem much value in them.
Right. We have no idea how another species perceives time. This could be nothing to them.
And even if they do perceive it like us, that hasn't stopped humans from great projects. How many generations did it take to complete Stonehenge or the Great Wall of China? We're still on top of Voyager too after 50 years.
of course by the time we had the ability to do von Neumann Probes our anthropomorphic assumption of time scales may have changed.
How much would human life span need to increase for a von Neumann Probe to seem reasonable. I would think a life span of 600 and you're thinking, sure I won't get to see it through, but my allotted genetic offspring that I am allowed at age 500 if either of my other two have failed might.
If you expect to live past a few hundred years it isn't clear why your lifespan wouldn't be indefinite. The prerequisites for achieving the former appear to be more or less the same as those of the latter.
If we're talking about civilizations that have access to energy that's on the order of many stars, the civilization itself can be considered a meta-organism that spans many millennia. Launching probes that take hundreds or thousands of years to report back becomes a small fraction of overall lifespan.
Well, if you personally were building von Neumann machines do any purpose in the solar system, would YOU be interested in sending some to neighboring systems knowing that you could conceivably get a response in your lifetime.
Would you be at all interested in expanding that project to outlast you?
And even if you personally wouldn’t be so inclined, surely you know or have met people who might?
Once you have the self replication, expanding scope may just be additional code…
Sure, but you then can't access the computronium, because communication is so bad.
Also, I wonder if good old-fashioned computing is interesting at all to a civilization that's had access to advanced AI and quantum computing for a while.
Like we haven't really figured out how to get an ML model to run on a quantum computer, or how to build a quantum-native computer (i.e. surface of a black hole, or some other way that doesn't rely on our current sense of quantum error correction), but I don't know of any physical laws that preclude it.
I'd bet if aliens invaded our galaxy, they'd go for the super black holes in the center, or some other resource beyond our use and understanding, not this random water planet on the edge.
Are there any serious papers or theories that postulate that DNA is the self replicating matter sent to colonize the galaxy? It appears to be quite adaptable to its environment and able to hold a surprising amount of encoded information.
Sending an acorn-sized probe to another galaxy to make more acorn-sized probes: what even is the point of that? To make very slow grey goo a reality?
If actual humans find a way to go to Andromeda (other than waiting for it to arrive, heh) and want to, good for them. Otherwise we should actively discourage anything like the project proposed
This is a study of the feasibility of launching an intergalactic colonization wave (and its implications re: the Fermi paradox), not a proposal that humans should do that (it would be just slightly ahead of its time for that!), or a discussion of the ethics or higher-level utility of doing so. It would be refreshing to see someone discuss the things paper actually discusses. To use early-2000s terminology, the paper's future shock level is higher than that of most HN readers, leading to rather banal discourse.
In any case, I'm fairly sure the authors agree that sending mindless automata to colonize the universe doesn't seem like a great idea. Nevertheless some alien intelligence (including an Earth-based AGI) might find it a completely reasonable, even imperative, goal.
But sentient machines or uploads (assuming for the sake of this this thought experiment that they are possible)? That's a different thing.
This isn't my field, but I see a huge gap between what in the abstract they say it would be feasible for us and what we're currently capable of. I mean, we're able to send space probes around, but self-replicating space probes and Dyson spheres feel on another level. Am I the only one?
Life itself could arguably be a Von Neumann probe. It's so good at spreading that it's a problem, when we send probes to other bodies in our own solar system we often sanitize them because we worry life will hitch a ride and start colonizing.
Life on a planet is a lot like a continuous fire, fires often send out embers that start new fires elsewhere.
You send out little packets of life to new places, wait single-digit billions of years (a blink of an eye for the universe, really), boom: new intelligent species with potential to shoot more seeds out into the universe.
Do we have anything that self-replicates physically?
Software, sure. I know 3D printer folks will sometimes 3D print parts for new machines. But nothing that fully replicates itself, right? Especially autonomously.
Additionally, you also have to consider that a self-replicating space probe should be able to find, retrieve, and process the raw materials needed to build new probes on its own. A 3D printer can print some of its own parts, but with externally-provided material that it isn't able to produce on its own.
I guess the OP meant something that is more flatous for human vanity to feel like a demiurge when at most it would be a tool of cosmos in its experiment.
What we're capable of != what we're doing / not doing because of political will. We are technically capable of reaching significant fractions of c with tech from the 1960s. We'll never do that because there's no will to do it, but the tech is there.
Same for self replicating stuff. We could build self-contained factories that build stuff from raw minerals, but we'll likely not do it until there's a will for it. Or need for it.
Political will is part of the Fermi paradox. So are technical reliability and cultural stability.
The idea that you can just build a thing and send out a swarm and (slow) boom - you've colonised the galaxy, and all the adjacent galaxies - is hopelessly naive. To the point I'd call it stupid and silly.
Let's say you have a replicator thing that works. You send them out in swarms.
And then what? Some die, some miss, some are destroyed by accidents.
Some work.
But "a replicator landed and made some more" is not colonisation. Colonisation implies there's some kind of to-and-fro traffic, maybe trade, some kind of information exchange at a minimum.
And that implies the source civilisation has political, technological, and cultural stability, which can survive an incredibly slow diaspora.
Colonisation worked on Earth because it didn't take long to cross the Atlantic by sailing ship. Successful colonisers landed where humans already existed and trade was easy.
It doesn't work on interstellar, never mind intergalactic time scales, because nothing stays stable for that long. Not hardware, software, politics, or culture.
Nor, on slightly longer periods, biology. On much longer periods, geology, and eventually astrophysics, because stars change, and planetary systems aren't unconditionally stable.
So a colonising wave from a unified culture is an incredibly unlikely thing, not at all an obvious necessity.
This would mean bootstrapping current advanced manufacturing technologies to a new planet. You would need so many different tools to do that that I seriously doubt we are currently capable of making it compact enough to be sent into deep space with current technologies. We're currently sending at most small capsules into deep space, my gut tells me that for self-contained factories we would need to send something in the size order of a skyscraper.
When you zoom this far out, anything can look possible… or impossible.
This is the same fallacy, but taken toward rather than away from infinite possibility, that underlies things like the Club of Rome’s world models and their limits to growth thesis.
Zoom way out and the details disappear. Look only at aggregate statistics and extrapolate. Do this and you tend to get graphs that go to infinity (this paper) or to zero (limits to growth).
But the details are where things actually happen.
Also look up computational irreducibility, which is kind of another way of approaching what I’m getting at here. You can only treat details in aggregate for systems whose causality is strictly hierarchical. If one detail can change the whole system, every detail must be considered or a simulation is invalid.
In his 1999 book "Entering Space: Creating a Spacefaring Civilization", Robert Zubrin mentioned checking the math for Bussard ramjets with Dana Andrews in their 1988 join paper "Magnetic Sails and Interstellar Travel" and found that they aren't capable of reaching more than a few percent of the speed of light before drag overcomes propulsion:
That's not to say that they don't work. But they'll probably be used primarily for braking to enter orbit around destination stars.
Probably the only way to reach a high fraction of the speed of light is to construct a giant laser to beam energy to a spaceship (which uses a reflector to receive light pressure momentum) and leave it behind orbiting the origin star. That's the premise of the Breakthrough Starshot project, which is ambitious with today's technology. But with self-replicating makerbots, building one may not be a big deal.
Unfortunately the force of light pressure (by F=2P/c for full reflection) is only about 2/3 of a kg or 1.5 lbs per GW, so a TW or greater would be needed for practical thrust. However, light pressure becomes the most efficient form of propulsion above about 25% to 50% c, if fusion or antimatter is used to create a gamma ray rocket.
Personally, I find it unlikely that aliens use these methods. I think that they probably worked out how to build neutrino lasers, since they don't burn up objects in their wake, perhaps by scaling superradiant Bose Einstein condensates:
In embarrassingly oversimplified layman's terms, I think that works by recruiting the macro-scale quantum state of the condensate (increased cross-section or barn) to overcome the short interaction distance of the weak force. Or by cooling the atoms to such an extent that they don't have the energy to hold themselves apart anymore, which accelerates their decay. I'm sure my explanations are wrong somehow.
Soon we may be able to investigate stuff like gravity waves and how the fabric of spacetime may be able to rebound above flat to create tiny ripples that allow mass energy to escape black holes, for example. I know that current theories don't state it quite that way, but if we consider stuff like the no-hair theorem and black box thought experiments, it's hard to see how Hawking radiation could exist without the wavelike nature of spacetime. We can even experiment with it on a relatively large scale by measuring the Casimir force. If we can rebound space, then we can play with stuff like negative energy and Alcubierre drives.
I looked up a Dyson sphere made from Mercury and it would be 1.5 mm thick, so aliens almost certainly aren't building them. But Dyson rings and swarms are probably a thing.
Some people in the tinfoil hat crowd think that UFOs can move 4th dimensionally and just travel orthogonally to our space and appear somewhere else. Theoretically, that might only require the energy difference (delta v) between planets. That hinges on if gravity spans higher dimensions and also touches on the multiverse. I'm way outside my wheelhouse so I'll stop blabbering about that.
In all honesty though, I question whether aliens travel. I think civilizations ascend about 10 years after they implement AI, or annihilate themselves in a Great Filter, their equivalent of WWIII. We're already staring the secrets of the universe in the face with automated theorem provers. And FUD around that and other accelerating tech drives people to become Luddites and elect amoral people who would gladly see the world burn for profit. So things could go either way really.
In my heart, I feel like we have a childlike understanding of consciousness. It probably transcends 4D spacetime. It's not hard to imagine aliens scaling what was learned from the CIA Gateway Program and doing stuff like FTL message passing via remote viewing. At that point FTL teleportation comes into the realm of possibility, sort of like in Dune.
If so, then aliens are probably everywhere, know about us, and maybe had a hand in our evolution. The probably live in what we think of as a Matrix, where years could go by for every second of our time. Another interpretation might be that they're able to return to source consciousness and exist as one, rather than in separation like we do. Maybe they periodically choose to reincarnate in us to study what transitioning to a spacefaring civilization looks like.
I probably shouldn't have bothered writing all of this, but it's Sunday, and I also really don't want to do my taxes.
In one case "we" is an imaginary humanity as a whole acting to fulfill a grand species defining mission, in the other case "we" is the real, decadent, ignorant and divided population of some countries.
So a probe travelling between galaxies at 99%c can't hit anything bigger than 1.46×10−12 kg? It is ~2.5 million light-years between us and Andromeda. I don't know how much matter there is between the galaxies (does anyone?). But travelling that sort of distance without hitting anything above that tiny mass seems very unlikely. Also how is your tiny robot probe supposed to power any guidance or maintenance systems for that sort of duration of trip?
The concept of "Dyson spheres" was a joke by Freeman Dyson. It was never meant to be taken seriously. There's a clip about this floating around somewhere in which he finds it funny that the thing he's most well-known for was not even a serious paper. Dr. Angela Collier did a video about it.
https://www.youtube.com/watch?v=fLzEX1TPBFM
is there anything Collier doesn't sneer at? her purpose seems to be discouraging free and creative thinking.
The only person who seems to claim that Dyson Spheres were a "joke" is Angela Collier and people quoting her. I've seen no other source for this claim.
But even if it's true, which I don't think it is, it doesn't matter. Why? Because the idea is actually sound and a lot of thought has gone into it by people who have backgrounds in physics and engineering.
It's worth adding that "Dyson Swarm" is the more common nomenclature now because of a mistaken belief that a Dyson sphere was a rigid spherical shell you build around a star. That was never the case and there's no even theorized material that could support this kind of rigid structure. It was always a cloud of small orbitals so the "Dyson Swarm" should alleviate any confusion (hopefully).
Our civilization is ultimately energy-limited. I've seen estimates that we use ~10^11 Watts of energy. The Sun's entire output is ~10^25 Watts. That's a truly staggering amount of energy. We can barely comprehend what might be possible with that much energy. But one of those things is interstellar travel.
Many discussions on interstellar travel gloss over just how large the energy budgets are. But propelling objects with solar sails, particularly if you concentrate energy, seems feasible. At least the physics holds up.
Spreading throughout the galaxy becomes an almost inevitable consequence once you have the capability to do so.
>intergalactic colonisation is not far beyond our current capabilities today.
That is a ridiculous thing to say. We can barely get to the moon today.
I recently saw an interesting criticism of this paper: That by the end stages of the disassembly of Mercury, the amount of heat generated would be so much as to melt the surface, calling into question whether the mass driver system could work at such a high rate.
Refreshing to see a technical criticism of this paper for a change.
Is there already a name for that effect where grandiose plans somehow appear to be more feasible than the simple mundane step-by-step issues resolution that even though they clearly stand in the way of said grand plans, are not worth investing thought and effort in?
When it comes to software projects my pet-name for it is the "big-bang theory", but in the article's domain that's kind of already taken.
I use the term "30,000 foot view" a lot: https://nanoglobals.com/glossary/30000-foot-view/
It appeals to me because if you've ever taken a flight you can see how the details get progressively erased as you lift. Details that matter for a lot of reasons even if you can't see them.
"Far-mode thinking".
https://www.lesswrong.com/w/near-far-thinking
Has someone answered why a civilization would send "von Neumann probes" or similar into space? It would take so long for any answers from those probes to arrive that there really doesn't seem much value in them.
We don't know however "It would take so long" is an anthropomorphic assumption of time scale.
Right. We have no idea how another species perceives time. This could be nothing to them.
And even if they do perceive it like us, that hasn't stopped humans from great projects. How many generations did it take to complete Stonehenge or the Great Wall of China? We're still on top of Voyager too after 50 years.
of course by the time we had the ability to do von Neumann Probes our anthropomorphic assumption of time scales may have changed.
How much would human life span need to increase for a von Neumann Probe to seem reasonable. I would think a life span of 600 and you're thinking, sure I won't get to see it through, but my allotted genetic offspring that I am allowed at age 500 if either of my other two have failed might.
If you expect to live past a few hundred years it isn't clear why your lifespan wouldn't be indefinite. The prerequisites for achieving the former appear to be more or less the same as those of the latter.
requirements change with purpose.
a "kilroy was here" sign has different purpose than "eat at joes".
is it enough to say "hi, your not alone" ? would we actually want to encourage discourse, or visitation.
If we're talking about civilizations that have access to energy that's on the order of many stars, the civilization itself can be considered a meta-organism that spans many millennia. Launching probes that take hundreds or thousands of years to report back becomes a small fraction of overall lifespan.
Well, if you personally were building von Neumann machines do any purpose in the solar system, would YOU be interested in sending some to neighboring systems knowing that you could conceivably get a response in your lifetime.
Would you be at all interested in expanding that project to outlast you?
And even if you personally wouldn’t be so inclined, surely you know or have met people who might?
Once you have the self replication, expanding scope may just be additional code…
To build more computronium than you can in your own system, assuming the demand for that will always rise.
Sure, but you then can't access the computronium, because communication is so bad.
Also, I wonder if good old-fashioned computing is interesting at all to a civilization that's had access to advanced AI and quantum computing for a while.
Like we haven't really figured out how to get an ML model to run on a quantum computer, or how to build a quantum-native computer (i.e. surface of a black hole, or some other way that doesn't rely on our current sense of quantum error correction), but I don't know of any physical laws that preclude it.
I'd bet if aliens invaded our galaxy, they'd go for the super black holes in the center, or some other resource beyond our use and understanding, not this random water planet on the edge.
Some will do it, some won’t. The ones that do will be overrepresented in the universe.
You can ask same question about any decision that outlasts you. E.g. why write a will for your children?
There are no answers expected. This is a colonization wave.
Are there any serious papers or theories that postulate that DNA is the self replicating matter sent to colonize the galaxy? It appears to be quite adaptable to its environment and able to hold a surprising amount of encoded information.
Over the past 163 years, our capacity for eternity has decreased by a factor of six [0].
[0] https://www.poetryfoundation.org/poems/43650/auguries-of-inn...
No humans go, no information returns.
Sending an acorn-sized probe to another galaxy to make more acorn-sized probes: what even is the point of that? To make very slow grey goo a reality?
If actual humans find a way to go to Andromeda (other than waiting for it to arrive, heh) and want to, good for them. Otherwise we should actively discourage anything like the project proposed
This is a study of the feasibility of launching an intergalactic colonization wave (and its implications re: the Fermi paradox), not a proposal that humans should do that (it would be just slightly ahead of its time for that!), or a discussion of the ethics or higher-level utility of doing so. It would be refreshing to see someone discuss the things paper actually discusses. To use early-2000s terminology, the paper's future shock level is higher than that of most HN readers, leading to rather banal discourse.
In any case, I'm fairly sure the authors agree that sending mindless automata to colonize the universe doesn't seem like a great idea. Nevertheless some alien intelligence (including an Earth-based AGI) might find it a completely reasonable, even imperative, goal.
But sentient machines or uploads (assuming for the sake of this this thought experiment that they are possible)? That's a different thing.
"And with this papyrus, we conclude that in five thousand years, mankind will finally build a staircase to the Moon"
This isn't my field, but I see a huge gap between what in the abstract they say it would be feasible for us and what we're currently capable of. I mean, we're able to send space probes around, but self-replicating space probes and Dyson spheres feel on another level. Am I the only one?
Life itself could arguably be a Von Neumann probe. It's so good at spreading that it's a problem, when we send probes to other bodies in our own solar system we often sanitize them because we worry life will hitch a ride and start colonizing.
Life on a planet is a lot like a continuous fire, fires often send out embers that start new fires elsewhere.
You send out little packets of life to new places, wait single-digit billions of years (a blink of an eye for the universe, really), boom: new intelligent species with potential to shoot more seeds out into the universe.
Do we have anything that self-replicates physically?
Software, sure. I know 3D printer folks will sometimes 3D print parts for new machines. But nothing that fully replicates itself, right? Especially autonomously.
Maybe we'll see what a moon base can bring us.
Additionally, you also have to consider that a self-replicating space probe should be able to find, retrieve, and process the raw materials needed to build new probes on its own. A 3D printer can print some of its own parts, but with externally-provided material that it isn't able to produce on its own.
Basically all of life is self replicating, physically.
I guess the OP meant something that is more flatous for human vanity to feel like a demiurge when at most it would be a tool of cosmos in its experiment.
Yes, but this isn't what the paper is talking about.
> what we're currently capable of.
What we're capable of != what we're doing / not doing because of political will. We are technically capable of reaching significant fractions of c with tech from the 1960s. We'll never do that because there's no will to do it, but the tech is there.
Same for self replicating stuff. We could build self-contained factories that build stuff from raw minerals, but we'll likely not do it until there's a will for it. Or need for it.
Political will is part of the Fermi paradox. So are technical reliability and cultural stability.
The idea that you can just build a thing and send out a swarm and (slow) boom - you've colonised the galaxy, and all the adjacent galaxies - is hopelessly naive. To the point I'd call it stupid and silly.
Let's say you have a replicator thing that works. You send them out in swarms.
And then what? Some die, some miss, some are destroyed by accidents.
Some work.
But "a replicator landed and made some more" is not colonisation. Colonisation implies there's some kind of to-and-fro traffic, maybe trade, some kind of information exchange at a minimum.
And that implies the source civilisation has political, technological, and cultural stability, which can survive an incredibly slow diaspora.
Colonisation worked on Earth because it didn't take long to cross the Atlantic by sailing ship. Successful colonisers landed where humans already existed and trade was easy.
It doesn't work on interstellar, never mind intergalactic time scales, because nothing stays stable for that long. Not hardware, software, politics, or culture.
Nor, on slightly longer periods, biology. On much longer periods, geology, and eventually astrophysics, because stars change, and planetary systems aren't unconditionally stable.
So a colonising wave from a unified culture is an incredibly unlikely thing, not at all an obvious necessity.
This would mean bootstrapping current advanced manufacturing technologies to a new planet. You would need so many different tools to do that that I seriously doubt we are currently capable of making it compact enough to be sent into deep space with current technologies. We're currently sending at most small capsules into deep space, my gut tells me that for self-contained factories we would need to send something in the size order of a skyscraper.
When you zoom this far out, anything can look possible… or impossible.
This is the same fallacy, but taken toward rather than away from infinite possibility, that underlies things like the Club of Rome’s world models and their limits to growth thesis.
Zoom way out and the details disappear. Look only at aggregate statistics and extrapolate. Do this and you tend to get graphs that go to infinity (this paper) or to zero (limits to growth).
But the details are where things actually happen.
Also look up computational irreducibility, which is kind of another way of approaching what I’m getting at here. You can only treat details in aggregate for systems whose causality is strictly hierarchical. If one detail can change the whole system, every detail must be considered or a simulation is invalid.
Turns out that living systems are like this.
In his 1999 book "Entering Space: Creating a Spacefaring Civilization", Robert Zubrin mentioned checking the math for Bussard ramjets with Dana Andrews in their 1988 join paper "Magnetic Sails and Interstellar Travel" and found that they aren't capable of reaching more than a few percent of the speed of light before drag overcomes propulsion:
https://www.goodreads.com/book/show/54728.Entering_Space
https://www.researchgate.net/publication/236447908_Magnetic_...
That's not to say that they don't work. But they'll probably be used primarily for braking to enter orbit around destination stars.
Probably the only way to reach a high fraction of the speed of light is to construct a giant laser to beam energy to a spaceship (which uses a reflector to receive light pressure momentum) and leave it behind orbiting the origin star. That's the premise of the Breakthrough Starshot project, which is ambitious with today's technology. But with self-replicating makerbots, building one may not be a big deal.
https://en.wikipedia.org/wiki/Breakthrough_Starshot
Unfortunately the force of light pressure (by F=2P/c for full reflection) is only about 2/3 of a kg or 1.5 lbs per GW, so a TW or greater would be needed for practical thrust. However, light pressure becomes the most efficient form of propulsion above about 25% to 50% c, if fusion or antimatter is used to create a gamma ray rocket.
Personally, I find it unlikely that aliens use these methods. I think that they probably worked out how to build neutrino lasers, since they don't burn up objects in their wake, perhaps by scaling superradiant Bose Einstein condensates:
https://arxiv.org/abs/2412.11765
In embarrassingly oversimplified layman's terms, I think that works by recruiting the macro-scale quantum state of the condensate (increased cross-section or barn) to overcome the short interaction distance of the weak force. Or by cooling the atoms to such an extent that they don't have the energy to hold themselves apart anymore, which accelerates their decay. I'm sure my explanations are wrong somehow.
Soon we may be able to investigate stuff like gravity waves and how the fabric of spacetime may be able to rebound above flat to create tiny ripples that allow mass energy to escape black holes, for example. I know that current theories don't state it quite that way, but if we consider stuff like the no-hair theorem and black box thought experiments, it's hard to see how Hawking radiation could exist without the wavelike nature of spacetime. We can even experiment with it on a relatively large scale by measuring the Casimir force. If we can rebound space, then we can play with stuff like negative energy and Alcubierre drives.
I looked up a Dyson sphere made from Mercury and it would be 1.5 mm thick, so aliens almost certainly aren't building them. But Dyson rings and swarms are probably a thing.
Some people in the tinfoil hat crowd think that UFOs can move 4th dimensionally and just travel orthogonally to our space and appear somewhere else. Theoretically, that might only require the energy difference (delta v) between planets. That hinges on if gravity spans higher dimensions and also touches on the multiverse. I'm way outside my wheelhouse so I'll stop blabbering about that.
In all honesty though, I question whether aliens travel. I think civilizations ascend about 10 years after they implement AI, or annihilate themselves in a Great Filter, their equivalent of WWIII. We're already staring the secrets of the universe in the face with automated theorem provers. And FUD around that and other accelerating tech drives people to become Luddites and elect amoral people who would gladly see the world burn for profit. So things could go either way really.
In my heart, I feel like we have a childlike understanding of consciousness. It probably transcends 4D spacetime. It's not hard to imagine aliens scaling what was learned from the CIA Gateway Program and doing stuff like FTL message passing via remote viewing. At that point FTL teleportation comes into the realm of possibility, sort of like in Dune.
If so, then aliens are probably everywhere, know about us, and maybe had a hand in our evolution. The probably live in what we think of as a Matrix, where years could go by for every second of our time. Another interpretation might be that they're able to return to source consciousness and exist as one, rather than in separation like we do. Maybe they periodically choose to reincarnate in us to study what transitioning to a spacefaring civilization looks like.
I probably shouldn't have bothered writing all of this, but it's Sunday, and I also really don't want to do my taxes.
Can we have a science paper that explains why we can colonize Andromeda but we can’t build high speed rail?
In one case "we" is an imaginary humanity as a whole acting to fulfill a grand species defining mission, in the other case "we" is the real, decadent, ignorant and divided population of some countries.
Because we don't refer to the same entities in each case?
There's no NIMBYs in Andromeda