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In this specific instance: The idea that astronomers had stumbled on such a structure triggered headlines round the globe – though not for long. Subsequent res

In this specific instance: The idea that astronomers had stumbled on such a structure triggered headlines round the globe – though not for long. Subsequent research has now undermined the idea. “We have found that light of different wavelengths is blocked in different amounts: exactly what you would expect from starlight passing through a dust cloud,” said Lintott.

imglorp 2y ago
It's not just some dust There's no way it's just some dust It was just some dust
- pfdietz 2y ago
  I mean, if alien species could build star-spanning structures, they could easily do interstellar travel and colonization. So the Fermi argument says this couldn't actually have been aliens -- someone would have turned the Milky Way into a completely colonized urban area billions of years ago. All the other galaxies would have been colonized too (IR observations say < 1 in 100,000 have been urbanized.) I think people are misled by all the SF stories with galactic empires that somehow left Earth alone for billions of years, not realizing stories are there to entertain, not reflect what could be real.
  - jvanderbot 2y ago
    That's not clear actually. We could, given a religious like motivation, build massive space stations right now with today's rockets, materials, and lifetimes. It's incremental building. We could not get to the nearest star with today's rockets (or eq.), materials, or lifetimes. There's no incremental engineering there.
    - pfdietz 2y ago
      The star is just 1470 light years from our solar system. So, either a huge coincidence occurred, or there are many stars like this in the Milky Way. In the latter case, you are proposing that every one of the alien civilizations that built each of these things had the same motivational inhibition to colonization. Even more, you are proposing that all such civilizations in the past, and all such civilizations in other galaxies, were similarly inhibited. A star-spanning civilization would have far more than enough energy to propel interstellar vehicles, for example by laser beaming.
      - jvanderbot 2y ago
        I'm proposing no such thing. GP said that if they had built large structures then it was obvious they could do interstellar travel. I said that implication was false, it's clear how we might build large orbital structures but not clear how we might to interstellar travel. As a counter example.
        pfdietz 2y ago
        The implication is as clearly true as such things could be. The barrier to interstellar travel is largely economic(*). The resources needed to construct star-spanning structures are many orders of magnitude greater than needed to construct and launch a starship (or a laser with an aperture capable of projecting a beam to interstellar distances). (*) https://galileo.phys.virginia.edu/classes/109.jvn.spring00/nuc_rocket/Dyson.pdf https://galileo.phys.virginia.edu/classes/109.jvn.spring00/n...
        jcranmer 2y ago
        One of the problems with this stuff is most of the problems are analyzed by physicists, who tend to reduce the problem to "can we make the physics work" rather than looking at more practical problems like "do we know if any materials will stand up to getting front-row seats to nuclear explosions?" and the other kinds of engineering problems that have bedeviled rocket science in its entire existence. And that's before getting into more fundamental issues like "what is the effect of space life on human biology?" (to which the answer appears to be somewhere between "maybe unmitigatably harmful" to "catastrophic"). There's a lot of questions that need to be answered before we can truly answer the question "what does it take to make interstellar travel", and the fact that many boosters for space exploration are glibly ignoring those questions is perhaps the biggest barrier of all.
        Nevermark 2y ago
        We are getting close to fusion with magnetic containment. So at some point, regular materials won’t be a limit But materials are improving at a rapid pace. So many orders of scale to co-optimize meta materials. Materials in the future will be magic compared to the limits we have now. Materials won’t be a barrier to interstellar travel We are only decades away from being able to do it, for very low mass ships/probes with AI. Long before we will be able to create mega structures
    - dotnet00 2y ago
      The technologies within our reach which would be very helpful with building massive space stations are such that they would very much allow for getting to the nearest star within a human lifetime. The only reason we don't actually reach out for those technologies right now is that many of us have a religious fear of anything nuclear.
      - pfdietz 2y ago
        Nuclear energy isn't needed for interstellar travel. Beamed propulsion would likely be faster.
        dotnet00 2y ago
        Beamed propulsion is a farther out technology, requiring development of more powerful lasers capable of pushing a crewed vehicle in reasonable amounts of time and has the issue that it is difficult to slow down at the destination. Nuclear rocket engines were already being developed during the cold war. Both suffer from the irrationality that the more useful they are capable of being, the more they can be misconstrued as orbital weapons.
        pfdietz 2y ago
        I am amused you are objecting to a technology for interstellar travel on the grounds it is "farther out", especially in the context of what hypothetical aliens that are around for millions or billions of years would be using. We could build a 1% c starship using hydrogen bombs. But it wouldn't make much sense to build it, since in the time it would take to get to even the nearest star we'd likely have something much faster.
        dotnet00 2y ago
        I'm not objecting to it, my initial post was trying to emphasize the closeness of technologies capable of reaching the nearest stars, lasers are an option, but imo nuclear propulsion is "closer" in terms of time taken to achieve the energy densities needed to take humans there. Sure it's only a difference of a couple of decades at worst between the two but in the context of a human lifetime, that's significant.
    - 0-_-0 2y ago
      Oh we absolutely could, we could have done it with 1960s technology in fact: https://en.m.wikipedia.org/wiki/Project_Orion_(nuclear_propulsion) https://en.m.wikipedia.org/wiki/Project_Orion_(nuclear_propu...
      - jvanderbot 2y ago
        The propulsion may have been theorized to get us up to speed, but there are many other factors, not least of which is shielding from objects while you're going a decent fraction of the speed of light. There's no obstacle avoidance routines with that much momentum.
        pfdietz 2y ago
        At 1% of the speed of light, the energy of a proton is 47 keV. This is trivially easy to shield against. The energy of an electron is just 26 eV. One would need to shield against galactic cosmic radiation, but this really isn't much more of a problem than shielding a vehicle in the solar system.
        ThalesX 2y ago
        What about a micrometeoroid?
        pfdietz 2y ago
        The risk with these if they are sufficiently large would be an explosion on impact. This is dealt with by placing a thin barrier in front of the vehicle. The particle explodes on impact with the barrier, cutting a small hole. The debris shoots forward, spreading, and is absorbed on a shield. At 0.01 c, a 1 microgram particle deposits 450 joules of energy. This is called a "Whipple Shield". If necessary, parts of this system could be replaced during the journey.
        jvanderbot 2y ago
        I just want to be clear that this is all heavily theorized. The density of interstellar space has an assumed ablative rate based on speed of travel, but it wouldn't take much to exceed that. We are at least a few trial runs away from knowing, and that alone makes the prospect of interstellar travel far into the future. (again, repeating my main point)
  - fnordpiglet 2y ago
    This line of logic doesn’t hold. Star spanning structures requires the ability to move mass at scale which requires enormous but diffused in time and space amounts of controlled energy. Moving between stars requires immense energy focused on a single thing. The amount of acceleration required to any meaningful mass to speed necessary to travel between stars and maintain a coherent civilization is extraordinary and implies many things about the mass being accelerated as well. Most things would simply be crushed instantly, including any organism. The speed of light is also a major impediment as is time dilation, as is the need to decelerate, which require equal and opposite energy away from the destination. Ok - accelerate with large lasers based at home - how do you then stop? You first need to build large lasers both at home and destination. The problems expand, and this only helps for very local travel between close stars. It’s difficult but plausible with today’s technology scales up to build star spanning structures because they’re built incrementally and the need for near light speed travel doesn’t exist. Further the existence of a star spanning structure might enable interstellar travel, but not intergalactic. I’d also note that SF is meant to entertain with a story that is possible given some assumptions of progress or hidden nature of reality or small modifications to what is. It’s not meant to be built on magic and other absurdities (not meant as a pejorative!). Many science fiction stories become true and many more will. Often science fiction inspires us to achieve what doesn’t exist today but could. To couch it in something that’s dismissible as say Gandalf the Wizard fighting a Balrog is to greatly underestimate what science fiction is. It’s a roadmap to the future that helps us understand what to avoid on the road.
    - pfdietz 2y ago
      Building a starship reaching 1% of the speed of light seems quite reasonable without substantial technological advance (Dyson's 1968 H-bomb propelled Orion). What it would need would be lots of deuterium, but that's just a matter of large scale industry, which this putative civilization would have. If you are saying this civilization does its work over very extended periods of time, you're saying they're comfortable with efforts that take centuries or millenia or even longer. That alone makes interstellar travel and colonization much easier; the energy needed scales as the inverse square of the travel time (assuming Isp optimized for the travel time chosen and assuming non-relativistic travel). We (or they) do not need close to light speed travel for interstellar colonization.
bilsbie 2y ago
It’s not advanced alien technology because it doesn’t work like advanced alien technology.
- bayouborne 2y ago
  It’s not advanced alien technology because it doesn’t work like our concept of advanced alien technology.
  - roywiggins 2y ago
    The Moon isn't a space station because it doesn't look like our concept of a space station. More likely it's just the Moon than an advance alien space station though.

imglorp 2y ago

It's not just some dust There's no way it's just some dust It was just some dust

pfdietz 2y ago
I mean, if alien species could build star-spanning structures, they could easily do interstellar travel and colonization. So the Fermi argument says this couldn't actually have been aliens -- someone would have turned the Milky Way into a completely colonized urban area billions of years ago. All the other galaxies would have been colonized too (IR observations say < 1 in 100,000 have been urbanized.) I think people are misled by all the SF stories with galactic empires that somehow left Earth alone for billions of years, not realizing stories are there to entertain, not reflect what could be real.
- jvanderbot 2y ago
  That's not clear actually. We could, given a religious like motivation, build massive space stations right now with today's rockets, materials, and lifetimes. It's incremental building. We could not get to the nearest star with today's rockets (or eq.), materials, or lifetimes. There's no incremental engineering there.
  - pfdietz 2y ago
    The star is just 1470 light years from our solar system. So, either a huge coincidence occurred, or there are many stars like this in the Milky Way. In the latter case, you are proposing that every one of the alien civilizations that built each of these things had the same motivational inhibition to colonization. Even more, you are proposing that all such civilizations in the past, and all such civilizations in other galaxies, were similarly inhibited. A star-spanning civilization would have far more than enough energy to propel interstellar vehicles, for example by laser beaming.
    - jvanderbot 2y ago
      I'm proposing no such thing. GP said that if they had built large structures then it was obvious they could do interstellar travel. I said that implication was false, it's clear how we might build large orbital structures but not clear how we might to interstellar travel. As a counter example.
      - pfdietz 2y ago
        The implication is as clearly true as such things could be. The barrier to interstellar travel is largely economic(*). The resources needed to construct star-spanning structures are many orders of magnitude greater than needed to construct and launch a starship (or a laser with an aperture capable of projecting a beam to interstellar distances). (*) https://galileo.phys.virginia.edu/classes/109.jvn.spring00/nuc_rocket/Dyson.pdf https://galileo.phys.virginia.edu/classes/109.jvn.spring00/n...
        jcranmer 2y ago
        One of the problems with this stuff is most of the problems are analyzed by physicists, who tend to reduce the problem to "can we make the physics work" rather than looking at more practical problems like "do we know if any materials will stand up to getting front-row seats to nuclear explosions?" and the other kinds of engineering problems that have bedeviled rocket science in its entire existence. And that's before getting into more fundamental issues like "what is the effect of space life on human biology?" (to which the answer appears to be somewhere between "maybe unmitigatably harmful" to "catastrophic"). There's a lot of questions that need to be answered before we can truly answer the question "what does it take to make interstellar travel", and the fact that many boosters for space exploration are glibly ignoring those questions is perhaps the biggest barrier of all.
        Nevermark 2y ago
        We are getting close to fusion with magnetic containment. So at some point, regular materials won’t be a limit But materials are improving at a rapid pace. So many orders of scale to co-optimize meta materials. Materials in the future will be magic compared to the limits we have now. Materials won’t be a barrier to interstellar travel We are only decades away from being able to do it, for very low mass ships/probes with AI. Long before we will be able to create mega structures
  - dotnet00 2y ago
    The technologies within our reach which would be very helpful with building massive space stations are such that they would very much allow for getting to the nearest star within a human lifetime. The only reason we don't actually reach out for those technologies right now is that many of us have a religious fear of anything nuclear.
    - pfdietz 2y ago
      Nuclear energy isn't needed for interstellar travel. Beamed propulsion would likely be faster.
      - dotnet00 2y ago
        Beamed propulsion is a farther out technology, requiring development of more powerful lasers capable of pushing a crewed vehicle in reasonable amounts of time and has the issue that it is difficult to slow down at the destination. Nuclear rocket engines were already being developed during the cold war. Both suffer from the irrationality that the more useful they are capable of being, the more they can be misconstrued as orbital weapons.
        pfdietz 2y ago
        I am amused you are objecting to a technology for interstellar travel on the grounds it is "farther out", especially in the context of what hypothetical aliens that are around for millions or billions of years would be using. We could build a 1% c starship using hydrogen bombs. But it wouldn't make much sense to build it, since in the time it would take to get to even the nearest star we'd likely have something much faster.
        dotnet00 2y ago
        I'm not objecting to it, my initial post was trying to emphasize the closeness of technologies capable of reaching the nearest stars, lasers are an option, but imo nuclear propulsion is "closer" in terms of time taken to achieve the energy densities needed to take humans there. Sure it's only a difference of a couple of decades at worst between the two but in the context of a human lifetime, that's significant.
  - 0-_-0 2y ago
    Oh we absolutely could, we could have done it with 1960s technology in fact: https://en.m.wikipedia.org/wiki/Project_Orion_(nuclear_propulsion) https://en.m.wikipedia.org/wiki/Project_Orion_(nuclear_propu...
    - jvanderbot 2y ago
      The propulsion may have been theorized to get us up to speed, but there are many other factors, not least of which is shielding from objects while you're going a decent fraction of the speed of light. There's no obstacle avoidance routines with that much momentum.
      - pfdietz 2y ago
        At 1% of the speed of light, the energy of a proton is 47 keV. This is trivially easy to shield against. The energy of an electron is just 26 eV. One would need to shield against galactic cosmic radiation, but this really isn't much more of a problem than shielding a vehicle in the solar system.
        ThalesX 2y ago
        What about a micrometeoroid?
        pfdietz 2y ago
        The risk with these if they are sufficiently large would be an explosion on impact. This is dealt with by placing a thin barrier in front of the vehicle. The particle explodes on impact with the barrier, cutting a small hole. The debris shoots forward, spreading, and is absorbed on a shield. At 0.01 c, a 1 microgram particle deposits 450 joules of energy. This is called a "Whipple Shield". If necessary, parts of this system could be replaced during the journey.
        jvanderbot 2y ago
        I just want to be clear that this is all heavily theorized. The density of interstellar space has an assumed ablative rate based on speed of travel, but it wouldn't take much to exceed that. We are at least a few trial runs away from knowing, and that alone makes the prospect of interstellar travel far into the future. (again, repeating my main point)
- fnordpiglet 2y ago
  This line of logic doesn’t hold. Star spanning structures requires the ability to move mass at scale which requires enormous but diffused in time and space amounts of controlled energy. Moving between stars requires immense energy focused on a single thing. The amount of acceleration required to any meaningful mass to speed necessary to travel between stars and maintain a coherent civilization is extraordinary and implies many things about the mass being accelerated as well. Most things would simply be crushed instantly, including any organism. The speed of light is also a major impediment as is time dilation, as is the need to decelerate, which require equal and opposite energy away from the destination. Ok - accelerate with large lasers based at home - how do you then stop? You first need to build large lasers both at home and destination. The problems expand, and this only helps for very local travel between close stars. It’s difficult but plausible with today’s technology scales up to build star spanning structures because they’re built incrementally and the need for near light speed travel doesn’t exist. Further the existence of a star spanning structure might enable interstellar travel, but not intergalactic. I’d also note that SF is meant to entertain with a story that is possible given some assumptions of progress or hidden nature of reality or small modifications to what is. It’s not meant to be built on magic and other absurdities (not meant as a pejorative!). Many science fiction stories become true and many more will. Often science fiction inspires us to achieve what doesn’t exist today but could. To couch it in something that’s dismissible as say Gandalf the Wizard fighting a Balrog is to greatly underestimate what science fiction is. It’s a roadmap to the future that helps us understand what to avoid on the road.
  - pfdietz 2y ago
    Building a starship reaching 1% of the speed of light seems quite reasonable without substantial technological advance (Dyson's 1968 H-bomb propelled Orion). What it would need would be lots of deuterium, but that's just a matter of large scale industry, which this putative civilization would have. If you are saying this civilization does its work over very extended periods of time, you're saying they're comfortable with efforts that take centuries or millenia or even longer. That alone makes interstellar travel and colonization much easier; the energy needed scales as the inverse square of the travel time (assuming Isp optimized for the travel time chosen and assuming non-relativistic travel). We (or they) do not need close to light speed travel for interstellar colonization.

bilsbie 2y ago

It’s not advanced alien technology because it doesn’t work like advanced alien technology.

bayouborne 2y ago
It’s not advanced alien technology because it doesn’t work like our concept of advanced alien technology.
- roywiggins 2y ago
  The Moon isn't a space station because it doesn't look like our concept of a space station. More likely it's just the Moon than an advance alien space station though.