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Does anyone have a detailed analysis of why we believe we have the technology to detect distant alien civilizations? Given interstellar distances, travel betwee

Does anyone have a detailed analysis of why we believe we have the technology to detect distant alien civilizations? Given interstellar distances, travel between stars seems unlikely without some new science we don't know yet. Also, do we know we would be able to detect our own radio transmissions with our own telescopes from lighyears away? I think the great filter hypothesis always relied on the assumption that intelligent life would eventually develop Star Trek level technology and be extremely detectable, but what if we're near the end of what's physically possible with respect to energy production, speed, radio astronomy, and communications? What if the aliens are out there, but statistically so far away that we will never detect each other?

eindiran 6y ago
In the case you are talking about, the Great Filter is that technology advancing to Star Trek levels that allow colonizing star systems is unlikely or impossible (ie step 9 here: https://en.wikipedia.org/wiki/Great_Filter https://en.wikipedia.org/wiki/Great_Filter).
Emma_Goldman 6y ago
One issue with the way Bostrom and others frame the Fermi paradox is that they assume the teleological end of any intelligent civilization will be the maximisation of its exploitation of natural resources through the creation of self-replicating probes that will slowly populate the universe. That's why they think the Fermi paradox is a paradox - if there is life, it should be everywhere. That may well be a reflection of ourselves, however, rather than a universal motivation of intelligent life.
- jandrese 6y ago
  I think the Fermi paradox simply underestimates the enormous difficulty and expense of traveling between solar systems.
  - 3pt14159 6y ago
    It won't be difficult once it has been figured out once. It won't be expensive once we've truly started to unleash energy from matter. On a geological timespan, the milky way is very explorable. I think the most likely reason there isn't any observable alien life is that we're being intentionally undisturbed. Or at least, seemingly undisturbed.
    - jandrese 6y ago
      Isn't this like saying it won't be difficult once we develop a FTL engine? Or a reactionless drive? The very lack of contact with aliens might be interpreted as strong evidence that FTL travel is either outright impossible or so impractical that it is effectively impossible. The answer to the Fermi paradox might be the tyranny of the rocket equation.
      - 3pt14159 6y ago
        No. FTL travel is impossible without breaking causality. While unleashing energy from matter is something we can already (crudely) do. Even at only 1% of the speed of light, we should be able to explore the entire Milky Way in a dozen million years or so and there are plenty of proposals to transfer energy to an already high speed spacecraft. Even forgetting high speed travel. If it takes a billion years (less than 10% of the age of the universe) we would still be able to colonize the Milky Way if we're able to either exist on spacecraft for prolonged periods of time or if replicating probes with AI could do so in our stead. I'm much more of the opinion that exponential tech is self-terminating or that we're being observed by aliens but not largely interfered with or that we're in some sort of simulation or even that we're the first life forms with advanced intelligence and long life spans. The idea that mere physics is what would stop us from reaching the stars when we've already explored our local neighbourhood is just so unbelievable to me. At the very, very least we should be able to communicate over long distances and we've (as yet) been unable to pick up extraterrestrial signals that show signs of intelligence like enumerating the prime numbers, say.
- philwelch 6y ago
  At the numbers we’re looking at, even if only 1% of civilizations (maybe even 1 in 1000) would be exponentially expansionary, they would still make themselves fairly obvious and outcompete all the others. The Fermi paradox doesn’t assume that all extraterrestrial intelligence behaves this way, but this rebuttal has to assume that no ETI would behave this way. And that seems improbable, if only because aggressive, exponential expansion is a fairly valid Darwinian strategy.
  - acqq 6y ago
    > aggressive, exponential expansion is a fairly valid Darwinian strategy. Earth exists for around 4.5 billion years, life on Earth for 3.5 billion years, the whole known Universe just less than 14 billion years (and we can send some small probes to the limits of our own Solar system only during the last decades). So the Universe is not "old" and the distances between the areas suitable for the life to "expand" are immense and real barriers. Knowing the distances involved, I believe that had we discovered that we are in much later age of the Universe, not seeing "others" would mean more than it means now. For now, knowing the distances, whatever could be somewhere far could simply be too far from us, nothing more. Edit: Re: "The galaxy is only 100,000 light years across" note that that are the light years -- the distance that the light has to travel that much. We know that the whole islands on Earth were unreachable for many otherwise common species for millions of years. But these distances are nothing compared with problems of maintaining complex life over the cosmic distances and in the cosmically hostile environment. Also "10-50 million years ahead of us" doesn't have to mean what we think it could mean. For a context, the dinosaurs were, historically, 60 million years "ahead of us". Nobody can "just assume" the we will cross the limits that are ours limits now. Biologically, we did multiply "exponentially" as soon as we were able to use the natural resources to do so (1). But apart from that (the certainty of life using available resources for biological growth), the growth in technical capability for interstellar travel is not guaranteed. Not to mention that the resources are by definition limited. So nobody should ask "why aren't others here" when we can't even claim that we reached somewhere else. What we surely can ask is "why don't we get some signals" because, for example, we are able to send a radio message, but I personally wouldn't assume that the other civilizations make such kind of intentional signalling that we must necessarily be able to detect, being where we are now. It's not "just connect the headset to the wire and a crystal and listen." It's something that has to concentrate immense amounts of energy to reach exactly us. At the moment it's not "is there anybody anywhere" but "is there anybody in the conveniently close neighborhood who's capable to send exactly what we expect to receive, and, most probably, to target exactly in this direction." It's immensely hard to even "see" the planets by the closest stars, that how far everything is. I think that probability for that "targeted messaging" is too low, not to mention that I don't think that the "intelligence" in our sense is inevitably happening on every planet -- we know that from the 3.5 billion years of life on Earth, not even plants existed for 3 billion years. Life can indeed be relatively common but the development that the Earth up to now had could still simply be uncommon enough. 1) https://ourworldindata.org/grapher/world-population-since-10000-bce-ourworldindata-series https://ourworldindata.org/grapher/world-population-since-10...
jandrese 6y ago
This is one thing that I think is underestimated: just how big of a hurdle it is to travel between solar systems. It took the Voyager probes almost 40 years to leave our solar system, which is like taking 40 years to get out your front door on your planned walk across all of Europe and Asia. By the time we have the technology to do so, we will necessarily have the technology that makes it unnecessary. The primary thing you need is something that can survive effectively indefinitely in deep space where there are no resources available. But if you have that you can build stellar colonies that have unlimited access to solar power and can survive indefinitely just as easily. It's not like we are short on mass in the solar system either. It will be a long long time until we've used up Jupiter, Saturn, Uranus, the belt, etc...
- adrianN 6y ago
  We basically have the technology to reach Alpha Centauri in less than 200 years for reasonable amounts of money [1]. I don't find it unlikely that alien civilizations could either do better, or have significantly longer lifespans than us. [1] https://en.wikipedia.org/wiki/Project_Orion_(nuclear_propulsion) https://en.wikipedia.org/wiki/Project_Orion_(nuclear_propuls...
  - ChrisSD 6y ago
    Say we invent life extending technology or generational ships. What happens when someone gets to Alpha Centauri? What can they do?
    - adrianN 6y ago
      Alpha Centauri might not be the best destination, but for suitable systems the travelers could go forth and multiply, eventually sending out ships of their own.
      - ChrisSD 6y ago
        But that makes it a much more costly operation (both in money and risk). Even a nearby star system with a habitable planet would be hard to get going because the settlers that go there would be cut off from their home planet. They would need to take with them everything necessary not only to establish a colony but to thrive (and stave off potential extinction level events which, when your population is small, is far more likely). And there would be little help from homeworld. Even information would take at least the speed of light to get there. And this is just the tip of the ice berg. I agree with jandrese that people underestimate just how much of a hurdle this is.
philwelch 6y ago
If nothing else, we would see stars fade away as civilizations built Dyson swarms around them to collect more and more of their energy. That wouldn’t even require interstellar travel. Interstellar travel would in turn enable exponential growth across star systems, which would show up.
- elorant 6y ago
  Dyson spheres are a stupid idea to harness power. You need ridiculous amount of resources to cover even a fraction of the surface of a star. An advanced civilization could simply harness fusion.
  - philwelch 6y ago
    At which point they need to get hydrogen, and guess where all the hydrogen is.
    - credit_guy 6y ago
      Our Sun burns 1 GT of hydrogen every 2 seconds [1]. This is the mass of the hydrogen in 9 GT of water. The dwarf planet Ceres was discussed just yesterday on HN. It contains about 200 million GT of water. If that's not enough, we can go and use Jupiter, which contains about 1 quadrillion GT of hydrogen. Enough to last for a few billion years. [1] https://en.wikipedia.org/wiki/Nuclear_fusion#/media/File:The_Sun_by_the_Atmospheric_Imaging_Assembly_of_NASA's_Solar_Dynamics_Observatory_-_20100819.jpg https://en.wikipedia.org/wiki/Nuclear_fusion#/media/File:The...
      - TeMPOraL 6y ago
        A star IS a fusion reactor. Already built, already working, already fusing hydrogen. If you want to power an interplanetary civilization, there's zero point in building your own, when you already have a working one, and all you need is to keep adding energy collectors as the demand grows.
        6y ago
DrBazza 6y ago
Direct detection of a radio signal or some other EM emission is possible (hence SETI), but given the inverse square law (double the distance, a quarter of the signal strength), it's more likely we'd detect a planet with excess oxygen which is believed to be only a by product of life. Also there some fascinating alternatives of biochemistry for life that might work: https://en.wikipedia.org/wiki/Hypothetical_types_of_biochemistry https://en.wikipedia.org/wiki/Hypothetical_types_of_biochemi... How we detect those is another question.

eindiran 6y ago

In the case you are talking about, the Great Filter is that technology advancing to Star Trek levels that allow colonizing star systems is unlikely or impossible (ie step 9 here: https://en.wikipedia.org/wiki/Great_Filter https://en.wikipedia.org/wiki/Great_Filter).

Emma_Goldman 6y ago

One issue with the way Bostrom and others frame the Fermi paradox is that they assume the teleological end of any intelligent civilization will be the maximisation of its exploitation of natural resources through the creation of self-replicating probes that will slowly populate the universe. That's why they think the Fermi paradox is a paradox - if there is life, it should be everywhere. That may well be a reflection of ourselves, however, rather than a universal motivation of intelligent life.

jandrese 6y ago
I think the Fermi paradox simply underestimates the enormous difficulty and expense of traveling between solar systems.
- 3pt14159 6y ago
  It won't be difficult once it has been figured out once. It won't be expensive once we've truly started to unleash energy from matter. On a geological timespan, the milky way is very explorable. I think the most likely reason there isn't any observable alien life is that we're being intentionally undisturbed. Or at least, seemingly undisturbed.
  - jandrese 6y ago
    Isn't this like saying it won't be difficult once we develop a FTL engine? Or a reactionless drive? The very lack of contact with aliens might be interpreted as strong evidence that FTL travel is either outright impossible or so impractical that it is effectively impossible. The answer to the Fermi paradox might be the tyranny of the rocket equation.
    - 3pt14159 6y ago
      No. FTL travel is impossible without breaking causality. While unleashing energy from matter is something we can already (crudely) do. Even at only 1% of the speed of light, we should be able to explore the entire Milky Way in a dozen million years or so and there are plenty of proposals to transfer energy to an already high speed spacecraft. Even forgetting high speed travel. If it takes a billion years (less than 10% of the age of the universe) we would still be able to colonize the Milky Way if we're able to either exist on spacecraft for prolonged periods of time or if replicating probes with AI could do so in our stead. I'm much more of the opinion that exponential tech is self-terminating or that we're being observed by aliens but not largely interfered with or that we're in some sort of simulation or even that we're the first life forms with advanced intelligence and long life spans. The idea that mere physics is what would stop us from reaching the stars when we've already explored our local neighbourhood is just so unbelievable to me. At the very, very least we should be able to communicate over long distances and we've (as yet) been unable to pick up extraterrestrial signals that show signs of intelligence like enumerating the prime numbers, say.
philwelch 6y ago
At the numbers we’re looking at, even if only 1% of civilizations (maybe even 1 in 1000) would be exponentially expansionary, they would still make themselves fairly obvious and outcompete all the others. The Fermi paradox doesn’t assume that all extraterrestrial intelligence behaves this way, but this rebuttal has to assume that no ETI would behave this way. And that seems improbable, if only because aggressive, exponential expansion is a fairly valid Darwinian strategy.
- acqq 6y ago
  > aggressive, exponential expansion is a fairly valid Darwinian strategy. Earth exists for around 4.5 billion years, life on Earth for 3.5 billion years, the whole known Universe just less than 14 billion years (and we can send some small probes to the limits of our own Solar system only during the last decades). So the Universe is not "old" and the distances between the areas suitable for the life to "expand" are immense and real barriers. Knowing the distances involved, I believe that had we discovered that we are in much later age of the Universe, not seeing "others" would mean more than it means now. For now, knowing the distances, whatever could be somewhere far could simply be too far from us, nothing more. Edit: Re: "The galaxy is only 100,000 light years across" note that that are the light years -- the distance that the light has to travel that much. We know that the whole islands on Earth were unreachable for many otherwise common species for millions of years. But these distances are nothing compared with problems of maintaining complex life over the cosmic distances and in the cosmically hostile environment. Also "10-50 million years ahead of us" doesn't have to mean what we think it could mean. For a context, the dinosaurs were, historically, 60 million years "ahead of us". Nobody can "just assume" the we will cross the limits that are ours limits now. Biologically, we did multiply "exponentially" as soon as we were able to use the natural resources to do so (1). But apart from that (the certainty of life using available resources for biological growth), the growth in technical capability for interstellar travel is not guaranteed. Not to mention that the resources are by definition limited. So nobody should ask "why aren't others here" when we can't even claim that we reached somewhere else. What we surely can ask is "why don't we get some signals" because, for example, we are able to send a radio message, but I personally wouldn't assume that the other civilizations make such kind of intentional signalling that we must necessarily be able to detect, being where we are now. It's not "just connect the headset to the wire and a crystal and listen." It's something that has to concentrate immense amounts of energy to reach exactly us. At the moment it's not "is there anybody anywhere" but "is there anybody in the conveniently close neighborhood who's capable to send exactly what we expect to receive, and, most probably, to target exactly in this direction." It's immensely hard to even "see" the planets by the closest stars, that how far everything is. I think that probability for that "targeted messaging" is too low, not to mention that I don't think that the "intelligence" in our sense is inevitably happening on every planet -- we know that from the 3.5 billion years of life on Earth, not even plants existed for 3 billion years. Life can indeed be relatively common but the development that the Earth up to now had could still simply be uncommon enough. 1) https://ourworldindata.org/grapher/world-population-since-10000-bce-ourworldindata-series https://ourworldindata.org/grapher/world-population-since-10...

jandrese 6y ago

This is one thing that I think is underestimated: just how big of a hurdle it is to travel between solar systems. It took the Voyager probes almost 40 years to leave our solar system, which is like taking 40 years to get out your front door on your planned walk across all of Europe and Asia. By the time we have the technology to do so, we will necessarily have the technology that makes it unnecessary. The primary thing you need is something that can survive effectively indefinitely in deep space where there are no resources available. But if you have that you can build stellar colonies that have unlimited access to solar power and can survive indefinitely just as easily. It's not like we are short on mass in the solar system either. It will be a long long time until we've used up Jupiter, Saturn, Uranus, the belt, etc...

adrianN 6y ago
We basically have the technology to reach Alpha Centauri in less than 200 years for reasonable amounts of money [1]. I don't find it unlikely that alien civilizations could either do better, or have significantly longer lifespans than us. [1] https://en.wikipedia.org/wiki/Project_Orion_(nuclear_propulsion) https://en.wikipedia.org/wiki/Project_Orion_(nuclear_propuls...
- ChrisSD 6y ago
  Say we invent life extending technology or generational ships. What happens when someone gets to Alpha Centauri? What can they do?
  - adrianN 6y ago
    Alpha Centauri might not be the best destination, but for suitable systems the travelers could go forth and multiply, eventually sending out ships of their own.
    - ChrisSD 6y ago
      But that makes it a much more costly operation (both in money and risk). Even a nearby star system with a habitable planet would be hard to get going because the settlers that go there would be cut off from their home planet. They would need to take with them everything necessary not only to establish a colony but to thrive (and stave off potential extinction level events which, when your population is small, is far more likely). And there would be little help from homeworld. Even information would take at least the speed of light to get there. And this is just the tip of the ice berg. I agree with jandrese that people underestimate just how much of a hurdle this is.

philwelch 6y ago

If nothing else, we would see stars fade away as civilizations built Dyson swarms around them to collect more and more of their energy. That wouldn’t even require interstellar travel. Interstellar travel would in turn enable exponential growth across star systems, which would show up.

elorant 6y ago
Dyson spheres are a stupid idea to harness power. You need ridiculous amount of resources to cover even a fraction of the surface of a star. An advanced civilization could simply harness fusion.
- philwelch 6y ago
  At which point they need to get hydrogen, and guess where all the hydrogen is.
  - credit_guy 6y ago
    Our Sun burns 1 GT of hydrogen every 2 seconds [1]. This is the mass of the hydrogen in 9 GT of water. The dwarf planet Ceres was discussed just yesterday on HN. It contains about 200 million GT of water. If that's not enough, we can go and use Jupiter, which contains about 1 quadrillion GT of hydrogen. Enough to last for a few billion years. [1] https://en.wikipedia.org/wiki/Nuclear_fusion#/media/File:The_Sun_by_the_Atmospheric_Imaging_Assembly_of_NASA's_Solar_Dynamics_Observatory_-_20100819.jpg https://en.wikipedia.org/wiki/Nuclear_fusion#/media/File:The...
    - TeMPOraL 6y ago
      A star IS a fusion reactor. Already built, already working, already fusing hydrogen. If you want to power an interplanetary civilization, there's zero point in building your own, when you already have a working one, and all you need is to keep adding energy collectors as the demand grows.
      - 6y ago

DrBazza 6y ago

Direct detection of a radio signal or some other EM emission is possible (hence SETI), but given the inverse square law (double the distance, a quarter of the signal strength), it's more likely we'd detect a planet with excess oxygen which is believed to be only a by product of life. Also there some fascinating alternatives of biochemistry for life that might work: https://en.wikipedia.org/wiki/Hypothetical_types_of_biochemistry https://en.wikipedia.org/wiki/Hypothetical_types_of_biochemi... How we detect those is another question.