7 ms·

If ETs are expected to be found, where are the Bracewell-von Neumann probes? If any tech civilization ever launches a self-replicating interstellar probe, it w

If ETs are expected to be found, where are the Bracewell-von Neumann probes? If any tech civilization ever launches a self-replicating interstellar probe, it would only take a few million years for the probes to reach every system in the galaxy. The observed lack of B-vN probes implies that no tech civilization has ever done so. And the probability of any civilization capable of launching B-vN probles actually doing so seems very high -- we'll be able to do it ourselves pretty soon. You have to explain the lack of B-vN probes if you want to argue that ETs are/have been common. (Scarier thought: if B-vN probes are inevitable, so are berserkers.)

api 10y ago
Oh no I started a Fermi paradox thread! I don't have time for this but I'd suggest looking into other discussions on this. The Fermi paradox opens an entire monstrous tree of possibilities, but it's not quite as simple as "there are no VN probes therefore there are no aliens." My two favorites are: (1) Interstellar travel might just be too damn hard. Going fast enough to get there in a reasonable time seems to require insane physicists' nightmare propulsion systems like antimatter or fusion rockets or artificial black hole drives, while taking too long means cosmic radiation has too much time to cook both organic matter and electronics... or you can't build a power source that will last that long, etc. (2) The "uniform cooling hypothesis" -- maybe life is common but intelligences able to build (or become) VN probes are so far incredibly rare. Since the entire universe is (according to the leading theory) the same age, such things simply haven't happened yet. (1) and (2) could work together-- maybe there are pretty advanced aliens everywhere but so far very few are advanced enough to attempt interstellar flight. If the probability of interstellar flight is less than, say, once per galaxy per billion years, then we would not see VN probes. Neither (1) nor (2) rules out signals at all.
- pklausler 10y ago
  I don't buy (1). B-vN probes don't care about transit time or cost. (2) is arguing for some kind of middle ground between "it's just us" and "lots of tech civs"; i.e., that life can get to the point of sending signals way easier than it can get to the point of launching a probe. But in our case the delta's just going to be a couple centuries, so no, that doesn't work for me either.
  - TallGuyShort 10y ago
    Both your points assume a lot of knowledge about the future.
    - pklausler 10y ago
      They're reasonable extrapolations from current capabilities. Build a self-replicating 3-D printer, make it capable of finding and refining raw materials on asteroids, slap it on a Voyager-like slow interstellar platform, and off you go. (Yes, I'm being glib, but it's not that much of a stretch.)
      - TallGuyShort 10y ago
        Yeah but the energy efficiency required to pull that off? That's not just futuristic, that's astronomically close to violating physical laws...
      - inimino 10y ago
        "reasonable extrapolations" is a far cry from "airtight logical argument". But these discussions rarely seem to go anywhere...
  - brenschluss 10y ago
    If you use the earth as an analogy: why isn't every island on the earth populated with people, since humans are probes, self-replicating beings that communicate with others? There's a lot of reasons there. Certain areas are unhabitable, or at least annoying to create a habitat (the arctic tundra, for example). Beings may want to cluster together (cities). There may be no interest in going to one territory over another - why bother spreading to all places, where there's so much out there? Finally, you could have situations in which a probe or a highly advanced civilization could deliberately not contact a lesser-advanced civilizations. How do we know that we're not the less-advanced civilization? See: https://en.wikipedia.org/wiki/Uncontacted_peoples https://en.wikipedia.org/wiki/Uncontacted_peoples
    - 10y ago
- pault 10y ago
  My favorite theory is an extension of #1: interstellar travel is so expensive and difficult that advances in AI and virtual reality make it undesirable. There's no point in spending a non-trivial fraction of your civilization's resources colonizing another solar system when you can do anything you want at arbitrary time scales in a simulation.
- credit_guy 10y ago
  One other possible solution to the Fermi paradox is that the aliens exist, but they leave us alone, just like the Indian government leaves the Sentinel people alone.
GregBuchholz 10y ago
>where are the Bracewell-von Neumann probes? How sure are you that you are not (part of) one?
- pklausler 10y ago
  If we were, then the galaxy would be positively stuffed with all of the other copies.
  - api 10y ago
    Maybe it is. I think the parent was suggesting directed panspermia-- that the Earth's biosphere is itself a B-vN probe in the process of self-replication. That's one way to do it.
    - pklausler 10y ago
      That's how I read that comment, too. If there are ETs, I really want to know whether they're using DNA with triplet codons that map to the same 20 amino acids.
bbctol 10y ago
If ETs are expected to be found, where are the [extremely specific hypothetical construct that depends on certain technologies that may or may not be possible and a unique cultural context that isn't even universal to humanity, let alone all known life]? I don't know. Maybe the vast, sentient ooze of distant moons doesn't understand why anyone would want to explore the universe. Maybe the dissipant entities of gas giants don't use materials commonly found in the rest of space for construction. Maybe the chittering hivemind of habitable worlds reached incredible advancement without developing a concept of individual intelligence, and thus has no understanding of how to make a single self-sufficient AI on a probe. Maybe there are more things in heaven and Earth than are dreamt of in etc.
- corecoder 10y ago
  Yes, thank you!
mrfusion 10y ago
My theory is that the smallest possible self replicating space probe is a planet with billions of inhabitants. Sure cells can reproduce but they can't build spaceships.
- JoeAltmaier 10y ago
  But maybe they can travel between planets
  - Neeek 10y ago
    they have traveled between planets
Udo 10y ago
> If ETs are expected to be found, where are the Bracewell-von Neumann probes? Posing a question like "if [X] was expected, then how come we haven't found [very specific indicator of X]" does not make a lot of sense right now, neither from a logical point of view nor scientifically. First of all, the absence of detectable vN probes does not somehow retroactively change the expectation we had for the presence of alien life, because that expectation arose from a statistical perspective on environmental and biological factors. Until invalidated, this is still the default expectation. It may well turn out that expectation was based on faulty assumptions at some point, but the deciding factor will not be the absence of your favorite arbitrary indicator. It also makes no sense to stop looking based on the argument that we haven't found anything yet. Resolving the Fermi paradox is a higher stakes game than many people realize: Either we're just isolated from discovery for whatever reason (which would be fine as a class of explanations), or there is something fundamentally wrong about the universe. Based on the information we have right now, ET must be out there. If it turns out he definitely isn't, we'd better find out why, because it's one of the biggest areas in modern science where prediction dramatically mismatches observed reality. We can't afford to just call off the search because we haven't found probes.
- pklausler 10y ago
  Relax, I wasn't suggesting that we stop looking.
  - Udo 10y ago
    Not trying to be polemic here, but what then was the point of asking the question that way? I apologize if I read too much into it. I think almost everybody agrees that looking for drones is a worthy endeavor, but it can't be the pivot point of the entire ET discussion for the simple reason that it's one more probability stacked on top of an already unknown probability (= the probability that any civilization will colonize the galaxy with a runaway drone program that can be easily detected). That's a very specific thing. Depending on where you're coming from, you may assign a big probability to it, but there is by far no consensus. So for now the best we can do is to look at as many possible indicators as we can.
pmarreck 10y ago
> where are the Bracewell-von Neumann probes? Seriously? We probably shot them down: https://www.youtube.com/watch?v=cZWs8116Q-E https://www.youtube.com/watch?v=cZWs8116Q-E
- AIMunchkin 10y ago
  And yet no gun camera footage or even pictures... Funny that...
  - pmarreck 10y ago
    sort of a "moving the goalposts" fallacy, but you also can't assume that that tech was available on an F-4 in 1980, for every mission. Anyway there's a bunch of these "pilot encounters UFO with description not matching any known aircraft" stories. http://ufos.about.com/od/bestufocasefiles/p/mantell.htm http://ufos.about.com/od/bestufocasefiles/p/mantell.htm
aaroninsf 10y ago
IMO at least as plausible an answer is that species with the capabilities to produce such probes also have good reason not to do so. We ourselves arguably have good reason not to broadcast our presence, reasons which we have come to belatedly but which are now widely known; e.g. the widely-cited belief that 'whenever' two cultures of significantly different technological prowess have interacted, the less-advanced one invariably went extinct / degraded / whatever. I haven't read it yet but IIRC the Three-Body Problem trilogy proposes a universe in which advanced species stay silent for fear for just such interaction. I can myself propose a variant idea, which is this: if we conclude from perceived silence/solitude that other species are likely out there but keeping their heads down, ...maybe we should do the same, not knowing what we might invite by broadcasting our presence. If the first species to encounter this question incorrectly guessed its own probability of being first, and came to the same conclusion, we might actually be surrounded by a saturated sea of advanced species... all playing it unnecessarily safe... <shrug>

api 10y ago

Oh no I started a Fermi paradox thread! I don't have time for this but I'd suggest looking into other discussions on this. The Fermi paradox opens an entire monstrous tree of possibilities, but it's not quite as simple as "there are no VN probes therefore there are no aliens." My two favorites are: (1) Interstellar travel might just be too damn hard. Going fast enough to get there in a reasonable time seems to require insane physicists' nightmare propulsion systems like antimatter or fusion rockets or artificial black hole drives, while taking too long means cosmic radiation has too much time to cook both organic matter and electronics... or you can't build a power source that will last that long, etc. (2) The "uniform cooling hypothesis" -- maybe life is common but intelligences able to build (or become) VN probes are so far incredibly rare. Since the entire universe is (according to the leading theory) the same age, such things simply haven't happened yet. (1) and (2) could work together-- maybe there are pretty advanced aliens everywhere but so far very few are advanced enough to attempt interstellar flight. If the probability of interstellar flight is less than, say, once per galaxy per billion years, then we would not see VN probes. Neither (1) nor (2) rules out signals at all.

pklausler 10y ago
I don't buy (1). B-vN probes don't care about transit time or cost. (2) is arguing for some kind of middle ground between "it's just us" and "lots of tech civs"; i.e., that life can get to the point of sending signals way easier than it can get to the point of launching a probe. But in our case the delta's just going to be a couple centuries, so no, that doesn't work for me either.
- TallGuyShort 10y ago
  Both your points assume a lot of knowledge about the future.
  - pklausler 10y ago
    They're reasonable extrapolations from current capabilities. Build a self-replicating 3-D printer, make it capable of finding and refining raw materials on asteroids, slap it on a Voyager-like slow interstellar platform, and off you go. (Yes, I'm being glib, but it's not that much of a stretch.)
    - TallGuyShort 10y ago
      Yeah but the energy efficiency required to pull that off? That's not just futuristic, that's astronomically close to violating physical laws...
    - inimino 10y ago
      "reasonable extrapolations" is a far cry from "airtight logical argument". But these discussions rarely seem to go anywhere...
- brenschluss 10y ago
  If you use the earth as an analogy: why isn't every island on the earth populated with people, since humans are probes, self-replicating beings that communicate with others? There's a lot of reasons there. Certain areas are unhabitable, or at least annoying to create a habitat (the arctic tundra, for example). Beings may want to cluster together (cities). There may be no interest in going to one territory over another - why bother spreading to all places, where there's so much out there? Finally, you could have situations in which a probe or a highly advanced civilization could deliberately not contact a lesser-advanced civilizations. How do we know that we're not the less-advanced civilization? See: https://en.wikipedia.org/wiki/Uncontacted_peoples https://en.wikipedia.org/wiki/Uncontacted_peoples
  - 10y ago
pault 10y ago
My favorite theory is an extension of #1: interstellar travel is so expensive and difficult that advances in AI and virtual reality make it undesirable. There's no point in spending a non-trivial fraction of your civilization's resources colonizing another solar system when you can do anything you want at arbitrary time scales in a simulation.
credit_guy 10y ago
One other possible solution to the Fermi paradox is that the aliens exist, but they leave us alone, just like the Indian government leaves the Sentinel people alone.

GregBuchholz 10y ago

>where are the Bracewell-von Neumann probes? How sure are you that you are not (part of) one?

pklausler 10y ago
If we were, then the galaxy would be positively stuffed with all of the other copies.
- api 10y ago
  Maybe it is. I think the parent was suggesting directed panspermia-- that the Earth's biosphere is itself a B-vN probe in the process of self-replication. That's one way to do it.
  - pklausler 10y ago
    That's how I read that comment, too. If there are ETs, I really want to know whether they're using DNA with triplet codons that map to the same 20 amino acids.

bbctol 10y ago

If ETs are expected to be found, where are the [extremely specific hypothetical construct that depends on certain technologies that may or may not be possible and a unique cultural context that isn't even universal to humanity, let alone all known life]? I don't know. Maybe the vast, sentient ooze of distant moons doesn't understand why anyone would want to explore the universe. Maybe the dissipant entities of gas giants don't use materials commonly found in the rest of space for construction. Maybe the chittering hivemind of habitable worlds reached incredible advancement without developing a concept of individual intelligence, and thus has no understanding of how to make a single self-sufficient AI on a probe. Maybe there are more things in heaven and Earth than are dreamt of in etc.

corecoder 10y ago
Yes, thank you!

mrfusion 10y ago

My theory is that the smallest possible self replicating space probe is a planet with billions of inhabitants. Sure cells can reproduce but they can't build spaceships.

JoeAltmaier 10y ago
But maybe they can travel between planets
- Neeek 10y ago
  they have traveled between planets

Udo 10y ago

> If ETs are expected to be found, where are the Bracewell-von Neumann probes? Posing a question like "if [X] was expected, then how come we haven't found [very specific indicator of X]" does not make a lot of sense right now, neither from a logical point of view nor scientifically. First of all, the absence of detectable vN probes does not somehow retroactively change the expectation we had for the presence of alien life, because that expectation arose from a statistical perspective on environmental and biological factors. Until invalidated, this is still the default expectation. It may well turn out that expectation was based on faulty assumptions at some point, but the deciding factor will not be the absence of your favorite arbitrary indicator. It also makes no sense to stop looking based on the argument that we haven't found anything yet. Resolving the Fermi paradox is a higher stakes game than many people realize: Either we're just isolated from discovery for whatever reason (which would be fine as a class of explanations), or there is something fundamentally wrong about the universe. Based on the information we have right now, ET must be out there. If it turns out he definitely isn't, we'd better find out why, because it's one of the biggest areas in modern science where prediction dramatically mismatches observed reality. We can't afford to just call off the search because we haven't found probes.

pklausler 10y ago
Relax, I wasn't suggesting that we stop looking.
- Udo 10y ago
  Not trying to be polemic here, but what then was the point of asking the question that way? I apologize if I read too much into it. I think almost everybody agrees that looking for drones is a worthy endeavor, but it can't be the pivot point of the entire ET discussion for the simple reason that it's one more probability stacked on top of an already unknown probability (= the probability that any civilization will colonize the galaxy with a runaway drone program that can be easily detected). That's a very specific thing. Depending on where you're coming from, you may assign a big probability to it, but there is by far no consensus. So for now the best we can do is to look at as many possible indicators as we can.

pmarreck 10y ago

> where are the Bracewell-von Neumann probes? Seriously? We probably shot them down: https://www.youtube.com/watch?v=cZWs8116Q-E https://www.youtube.com/watch?v=cZWs8116Q-E

AIMunchkin 10y ago
And yet no gun camera footage or even pictures... Funny that...
- pmarreck 10y ago
  sort of a "moving the goalposts" fallacy, but you also can't assume that that tech was available on an F-4 in 1980, for every mission. Anyway there's a bunch of these "pilot encounters UFO with description not matching any known aircraft" stories. http://ufos.about.com/od/bestufocasefiles/p/mantell.htm http://ufos.about.com/od/bestufocasefiles/p/mantell.htm

aaroninsf 10y ago

IMO at least as plausible an answer is that species with the capabilities to produce such probes also have good reason not to do so. We ourselves arguably have good reason not to broadcast our presence, reasons which we have come to belatedly but which are now widely known; e.g. the widely-cited belief that 'whenever' two cultures of significantly different technological prowess have interacted, the less-advanced one invariably went extinct / degraded / whatever. I haven't read it yet but IIRC the Three-Body Problem trilogy proposes a universe in which advanced species stay silent for fear for just such interaction. I can myself propose a variant idea, which is this: if we conclude from perceived silence/solitude that other species are likely out there but keeping their heads down, ...maybe we should do the same, not knowing what we might invite by broadcasting our presence. If the first species to encounter this question incorrectly guessed its own probability of being first, and came to the same conclusion, we might actually be surrounded by a saturated sea of advanced species... all playing it unnecessarily safe... <shrug>