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.
In the open space, shades get very cold, like a few degrees over absolute zero cold, because even without a medium to facilitate convection and (atmospheric contact) conduction, the loss of heat through mere radiation (into the pitch black universe) is very efficient (for normal, non-reflective materials). Thus, for an astral body to remain in a melted state, continuous steams of energy should be poured in (and some thermo-insulating gaseous atmosphere may also help to reduce cooling, if the body in question would have enough gravity to retain it), but that's hardly a thing to worry for a project where the energy itself is carefully controlled and dosed.
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.
> 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.
She is far too dismissive. Organic life probably will never build one but it is perfectly plausible effectively immortal machine intelligences will fully surround a star with solar collectors because energy is the fundamental limit of technology.
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.
It's also called "vision". It's what provides and powers directions on large and long term scales. Those "simple" and "mundane step-by-step issues" are just chores by themselves, yet at the same time may become stepping stones in the context of a well thought vision that people buy into and rally behind.
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.
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.
>it isn't clear why your lifespan wouldn't be indefinite.
it also isn't clear why it would be, when achieving something not achieved before you end up uncovering undiscovered problems, opportunities, and constraints.
The point is that reliably making it to a few hundred years requires (AFAICT) full understanding and control over all the elementary biological processes. If you already understand and are capable of freely manipulating every primitive in the system it isn't clear what's left to break.
To put this in mechanical terms, once I know how to replace every last component in my car and have the ability to fabricate new parts for the body and frame under what conditions could my car ever be unrepairable?
and my point still remains, once I know how to do something that has never been done is there a chance that some new factor will be revealed by this ability which will somehow constrain my ability to achieve my true goals? As the description of the scenario was of course fictional I decided to describe it as though some constraint unfamiliar to us now still kept things from going onward.
One particular constraint you can imagine in this fictional situation is that psychologically people who live more than 3 centuries start to have a deep burnout of existence, because there no longer seems to be any challenge or newness, causing them to experience extreme depression and psychological illness of various sorts that most people do not experience nowadays with our short lifespans. Thus there are psychological profiles done, if you are around 500 and you are not shown to have hit the psychological end point of your existence you can be allowed one more child, also dependent on how many children you have had before. This however will be your last child, because no rebuilt human has ever managed to escape "age psychosis" after 600 years of age.
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.
It would take ~5 million years (in the sender's frame of reference) for a probe to make the journey to Andromeda and then send another back with any information. What would the point of that be?
I read an interesting book called Count to a Trillion.
Astronomers detected an antimatter star a mere 50 light–years from Earth, and the US launched an unmanned mission to go there and learn what it could. Luckily the probe was programmed to transmit its findings multiple times, because the first few transmissions were missed; terrorists had launched a bioweapon that nearly caused an extinction event. Eventually Europe recovered enough to be paying attention. Appended like a footnote to the end of the probe’s transmission of everything it found were pictures of the writing covering the surface of the only moon of the only planet in the system, a gas giant.
The Europeans launched a manned mission a few decades later. One token American, the inventor of the suspended animation technique the crew would be using, was invited along. They went, they learned quite a lot from the Monument, they harvested a quite a lot of antimatter, and then they returned.
What they could decode from the Monument was mostly mathematics. A large portion of it was proofs for various theorems of [cliometrics](https://en.wikipedia.org/wiki/Cliometrics), or quantitative history. With a proper understanding of the mathematics, anyone can predict and even control the evolution of any complex system. It could be a computer program, a network, an organism, an ecology, a society, or all of the above at once. The other interesting bit of math was a complete proof of a system for calculating the value of a trade, given the distance between the participants and their relative level of technology and intelligence. It proves that profitable trade is possible between distant star systems, provided both sides know enough. Proper use of the system allows both sides to know the profit of any trade in advance, meaning no prior coordination need be required. Any two parties can use it to launch trade missions that take millennia to arrive knowing that the other side will already have made the same calculations and be expecting the mission.
The rest of what they decode is astronomy and history. The Monument records that a group of aliens in the dwarf galaxy M3 claim ownership and responsibility for the whole galaxy. Through several layers of delegation they are organizing the creation of life here in the Milky Way. In particular, any and all life arising near the antimatter star was seeded by an intelligence inhabiting a globular cluster 1000 light–years away. Therefore humans owe that intelligence a huge debt and must repay it, effectively making everyone on Earth a slave. As soon as they detect anyone tampering with the antimatter star they are instructed to send a mission to deracinate the planet, carry away whatever life they find, and use it to colonize other star systems. This mission cannot not be sent quickly, as we’re expected to be quite primitive and thus not worth spending very much on, but it will arrive in ~11,000 years whether anyone likes it or not. The crew of the ship then depart for Earth.
When they got back to Earth they found that the whole world was strange. Hundreds of years have past, all the countries are different, and their homes are gone. They end up using some of the antimatter as weapons, defeating the militaries of the world and declaring themselves ruler of all. Between their military power, their knowledge of cliometrics (primitive though it is at this point), and the vast riches of the antimatter that they brought with them, they manage to live in some style.
The main character (the token American from before) and his fiance discover one additional proof of importance: any form of life can be elevated above their boss if they can prove themselves more capable of long–term thinking. All you have to do is engage in really long–term trade. They decide that they should make Humanity equal to their boss’s boss’s boss’s boss, the intelligence at the dwarf galaxy M3, by sending a mission there and back. It’ll take 77,000 years but as long as Humanity survives that long and doesn’t forget about them then Humanity will be vindicated and will no longer be enslaved to anyone. They plan to depart the day after their wedding. They spend the night after their wedding in a disused hotel thousands of miles above the Pacific ocean in the middle of a space elevator.
Alas, that night the main character’s rival calls him out for a duel. He agrees and meets the guy at the base of the elevator. But the duel is a trap; his rival cheats and the space elevator is severed. He is buried under the rubble, wounded but alive, as his wife makes her way up to the ship. She can’t turn the ship around and come back for him and so must continue the mission without him. He decides that one night with his wife is not enough and has to find a way to live on Earth for the next 77,000 years or so until she gets back. Cue sequels.
So there you go. Love seems like a pretty good answer to me, but technically any sufficiently long–term motivation would suffice. I’m sure that you could imagine some, if you put your mind to it.
I was never convinced by cliometrics (including the Asimov version in Foundation). Yes, there are patterns and structural forces, but history is too subject to chaos (in the mathematical sense) for any precise long range predictions.
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…
The dilemma of spending significant amount of effort and resources for a colonizing project when the result won't benefit the enterprising society is not new. When looking for a reason, considering only the (individuals' or collective's) benefits on a rational basis does not make much sense indeed. Most likely there must be something more, akin to a religious goal, aiming for species' or civilization's greater good.
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?
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.
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 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?
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.
74 comments
https://www.youtube.com/watch?v=fLzEX1TPBFM
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.
> 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.
https://www.youtube.com/watch?v=huAIfzUoyhU&t=121s
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.
https://www.lesswrong.com/w/near-far-thinking
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.
>it isn't clear why your lifespan wouldn't be indefinite.
it also isn't clear why it would be, when achieving something not achieved before you end up uncovering undiscovered problems, opportunities, and constraints.
To put this in mechanical terms, once I know how to replace every last component in my car and have the ability to fabricate new parts for the body and frame under what conditions could my car ever be unrepairable?
One particular constraint you can imagine in this fictional situation is that psychologically people who live more than 3 centuries start to have a deep burnout of existence, because there no longer seems to be any challenge or newness, causing them to experience extreme depression and psychological illness of various sorts that most people do not experience nowadays with our short lifespans. Thus there are psychological profiles done, if you are around 500 and you are not shown to have hit the psychological end point of your existence you can be allowed one more child, also dependent on how many children you have had before. This however will be your last child, because no rebuilt human has ever managed to escape "age psychosis" after 600 years of age.
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.
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.
> What would the point of that be?
I read an interesting book called Count to a Trillion.
Astronomers detected an antimatter star a mere 50 light–years from Earth, and the US launched an unmanned mission to go there and learn what it could. Luckily the probe was programmed to transmit its findings multiple times, because the first few transmissions were missed; terrorists had launched a bioweapon that nearly caused an extinction event. Eventually Europe recovered enough to be paying attention. Appended like a footnote to the end of the probe’s transmission of everything it found were pictures of the writing covering the surface of the only moon of the only planet in the system, a gas giant.
The Europeans launched a manned mission a few decades later. One token American, the inventor of the suspended animation technique the crew would be using, was invited along. They went, they learned quite a lot from the Monument, they harvested a quite a lot of antimatter, and then they returned.
What they could decode from the Monument was mostly mathematics. A large portion of it was proofs for various theorems of [cliometrics](https://en.wikipedia.org/wiki/Cliometrics), or quantitative history. With a proper understanding of the mathematics, anyone can predict and even control the evolution of any complex system. It could be a computer program, a network, an organism, an ecology, a society, or all of the above at once. The other interesting bit of math was a complete proof of a system for calculating the value of a trade, given the distance between the participants and their relative level of technology and intelligence. It proves that profitable trade is possible between distant star systems, provided both sides know enough. Proper use of the system allows both sides to know the profit of any trade in advance, meaning no prior coordination need be required. Any two parties can use it to launch trade missions that take millennia to arrive knowing that the other side will already have made the same calculations and be expecting the mission.
The rest of what they decode is astronomy and history. The Monument records that a group of aliens in the dwarf galaxy M3 claim ownership and responsibility for the whole galaxy. Through several layers of delegation they are organizing the creation of life here in the Milky Way. In particular, any and all life arising near the antimatter star was seeded by an intelligence inhabiting a globular cluster 1000 light–years away. Therefore humans owe that intelligence a huge debt and must repay it, effectively making everyone on Earth a slave. As soon as they detect anyone tampering with the antimatter star they are instructed to send a mission to deracinate the planet, carry away whatever life they find, and use it to colonize other star systems. This mission cannot not be sent quickly, as we’re expected to be quite primitive and thus not worth spending very much on, but it will arrive in ~11,000 years whether anyone likes it or not. The crew of the ship then depart for Earth.
When they got back to Earth they found that the whole world was strange. Hundreds of years have past, all the countries are different, and their homes are gone. They end up using some of the antimatter as weapons, defeating the militaries of the world and declaring themselves ruler of all. Between their military power, their knowledge of cliometrics (primitive though it is at this point), and the vast riches of the antimatter that they brought with them, they manage to live in some style.
The main character (the token American from before) and his fiance discover one additional proof of importance: any form of life can be elevated above their boss if they can prove themselves more capable of long–term thinking. All you have to do is engage in really long–term trade. They decide that they should make Humanity equal to their boss’s boss’s boss’s boss, the intelligence at the dwarf galaxy M3, by sending a mission there and back. It’ll take 77,000 years but as long as Humanity survives that long and doesn’t forget about them then Humanity will be vindicated and will no longer be enslaved to anyone. They plan to depart the day after their wedding. They spend the night after their wedding in a disused hotel thousands of miles above the Pacific ocean in the middle of a space elevator.
Alas, that night the main character’s rival calls him out for a duel. He agrees and meets the guy at the base of the elevator. But the duel is a trap; his rival cheats and the space elevator is severed. He is buried under the rubble, wounded but alive, as his wife makes her way up to the ship. She can’t turn the ship around and come back for him and so must continue the mission without him. He decides that one night with his wife is not enough and has to find a way to live on Earth for the next 77,000 years or so until she gets back. Cue sequels.
So there you go. Love seems like a pretty good answer to me, but technically any sufficiently long–term motivation would suffice. I’m sure that you could imagine some, if you put your mind to it.
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…
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.
[0] https://www.poetryfoundation.org/poems/43650/auguries-of-inn...
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
>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.
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.