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Space is really big, and radio emissions are really weak. The strongest isotropic radio emissions from Earth (e.g. high power TV broadcasts) would be indistingu

Space is really big, and radio emissions are really weak. The strongest isotropic radio emissions from Earth (e.g. high power TV broadcasts) would be indistinguishable from background radiation at only a light year or two away. One study [0] suggests that directed radio emissions an order of magnitude more powerful than the most powerful radio emitters on Earth could be detectable at ~100 light years (1/1000 the diameter of the Milky Way), but our detector would have to be perfectly aligned with the transmission at the exact time it reaches Earth. [0] https://arxiv.org/pdf/astro-ph/0610377.pdf https://arxiv.org/pdf/astro-ph/0610377.pdf

kypro 4y ago
This still doesn't explain why we don't see evidence of life though, just why finding evidence of alien life via eavesdropping on extra-terrestrial radio emissions would be unlikely. If the galaxy really was full of intelligent life it's likely we would see evidence of it in some form. For one, it seems probable that any expansionist intelligent life in our galaxy would eventually notice our Earth is likely to be an interesting place. Even if they didn't visit us personally it seems strange they wouldn't send a simple probe or try to make their presence known to us in one way or another. But to your point, perhaps intelligent life is quite common, it's just rare for it to be expansionist - at least beyond it's own solar system. In which case yeah, there could be a lot of Earth-like civilisations out there, but we'd be unlikely to see evidence for them.
- FredPret 4y ago
  Sending a probe takes very, very long, and is just as expensive, so it seems even less likely to arrive than a radio signal. And we might not even notice either one if it gets here.
- pmoriarty 4y ago
  "it seems strange they wouldn't send a simple probe or try to make their presence known to us in one way or another" Alien behavior is likely to seem strange to humans. It would be much more surprising if they did what we expected them to do.
  - slfnflctd 4y ago
    This is brought up a lot, and while there is likely some truth to it - with plenty of fun examples in science fiction - it seems to me there is a strong counterpoint in that the mechanics of physics, biology and even civilization have many mathematically predictable properties. The environments capable of supporting life will nearly all likely have certain similar features which shape how that life behaves. Finite resources are one of the better examples. It has always been interesting to me how there are several prominent instances of architectural feats or scientific/technological breakthroughs which arose independently from people groups who had no contact with each other. I don't think extrapolating this to potential life in other star systems is too much of a stretch-- and there are certain behavioral traits you can reasonably expect in such scenarios, like large scale cooperation. Some of the most capable & best equipped minds we know of, when faced with how to communicate with intelligent extraterrestrial life, decided that math and basic physics were the best initial overtures. From those basics (along with the assumption that someone eventually perceives them) I believe a great deal more about such life can be probabilistically inferred.
- Loquebantur 4y ago
  Interstellar meetings are bound to happen first with a large developmental gap. Applicable here is obviously us being the Cavedwellers, Sumerians, Azteks, Egyptians, whathaveyou. What happens? Astronauts appear as effectively gods, being literally superior beyond comprehension in every aspect. Religions sprout, sacrifices are made, wars fought...all because you thoughtlessly wanted to be nice and sey 'hello'. Self-knowledge is a prerequisite to fruitful, non-destructive communication between civilizations. The ability to comprehend the scientific technicalities is likewise necessary and we are just on the brink of that. There are (many) other requirements. Importantly, you have to be able to imagine a superior entity other than as playing the role of your "master".
- mannykannot 4y ago
  > This still doesn't explain why we don't see evidence of life though... It is an adequately plausible explanation of why we haven't yet seen evidence of life elsewhere. To argue against it seems to require one or more question-begging premises.
  - singularity2001 4y ago
    Or we are seeing life everywhere, we just don't “see” (i.e. grasp) it.
    - swagasaurus-rex 4y ago
      Obligatory – They're made out of meat https://www.mit.edu/people/dpolicar/writing/prose/text/thinkingMeat.html https://www.mit.edu/people/dpolicar/writing/prose/text/think...
  - goatlover 4y ago
    Such as intelligent life having billions of years to send probes, build powerful radio beacons, and form galactic civilizations? It is called the Fermi Paradox because the physicists did some basic calculations at how long it would take to colonize the galaxy.
    - mannykannot 4y ago
      So we have two sets of calculations: the ones you are referring to here, and those that MontyCarloHall brought up. Of this pair, only the latter predicts the observation that kypro brought up.
- schwartzworld 4y ago
  > personally it seems strange they wouldn't send a simple probe If we detected something we thought was intelligent life, could we send a probe like you describe? Our nearest star is 4 light years away.
  - shakezula 4y ago
    Could we feasibly send one? Yes. Could we feasibly get data back from it? Less certain. It would necessarily be a multi-generational project in either case.
  - spacedcowboy 4y ago
    I mean we physically could send a probe... We effectively have, with "VGER". At some point, the voyager probes will hit another star system, it's just going to be a very very long time. If we actually wanted to aim a probe at another star system, I think that's probably within our technical grasp, but again we don't have any real way to get there in a reasonable timescale, or send data back once we're there. Not much use sending a probe 4 light years if the transmitter isn't powerful enough to send a signal back, and a transmitter that powerful would probably be too large to fit on a probe we could currently launch. Perhaps lasers could be used, but you'd still need a fairly powerful one, and then you have to worry about interstellar absorption of the signal if you go through a dust "cloud". I guess with a laser you're also really pinpointing where you're sending information to, if you care about that. [edit: huh, shakezula and I think alike :)]
    - jointpdf 4y ago
      So what if we sent a bunch of them, and chain them together? (i.e. like a relay network: https://en.wikipedia.org/wiki/Relay_network https://en.wikipedia.org/wiki/Relay_network)
    - schwartzworld 4y ago
      > Not much use sending a probe 4 light years if the transmitter isn't powerful enough to send a signal back And that's only if we're lucky enough to find life next door.
- breakpointalpha 4y ago
  There's a growing body of evidence that Earth has already been visited numerous times by something other than humans. Certain classes of UAPs demonstrate flight characteristics that are not possible given our current understanding of gravity and aerodynamics. Dozens of credible eye witnesses from multiple countries; fighter pilots, commercial pilots, nuclear physicists, and high ranking government officials. Source "In Plain Sight", US Navy fighter pilots David Fravor and Ryan Graves, etc. People are quick to dismiss these stories as hoaxes or bad memory, but scientific discovery almost always starts with an unusual or unexplained observation. Uranium was discovered in 1785 and ionizing radiation wasn't discovered for another 110 years in 1895. True scientific understanding of new observations takes quite a while.
  - rvba 4y ago
    Those aliens would bring own bacteria that could kill a lot of things if not everyrhing on Earth. Somehow people have this "star trek" thinking, that hypothetical unknown microbes from other planet wont eat you alive, because you are somehow immune to them.
    - Ancalagon 4y ago
      A species which has mastered inter-stellar travel and tractor beams (/s) probably has some higher control over their own biology and sanitation practices.
      - Narishma 4y ago
        Just because they're advanced in one domain doesn't mean they are also in an unrelated one.
    - captainclam 4y ago
      I've never understood why alien bacteria are a perceived threat. Viruses and bacteria share the same genetic material as we do, and literally evolved to infect organisms of that ilk. I have always supposed that alien viruses would just be inert, and alien bacteria would rapidly die off in the inhospitable environment of an earth-organism's body.
im3w1l 4y ago
We noticed GRB221009A despite it being 2.4billion light years away. Makes you wonder if someone took the opportunity to encode data in it. Edit: Another reason to analyze it is that existential threats are a universal language. Any sufficiently advanced civilization must pay attention to possible threats, so that it can avert them. It then follows that if you want to get the attention of another civilization about which you know almost nothing, threatening them is a viable method. Of course you don't want to overdo it, lest they actually hunt you down. A blast of high energy (but non-lethal) radiation will draw attention without making anyone panic. Intelligent civilization within a huge radius will certainly be tuning in.
deleted 4y ago
[deleted]

kypro 4y ago

This still doesn't explain why we don't see evidence of life though, just why finding evidence of alien life via eavesdropping on extra-terrestrial radio emissions would be unlikely. If the galaxy really was full of intelligent life it's likely we would see evidence of it in some form. For one, it seems probable that any expansionist intelligent life in our galaxy would eventually notice our Earth is likely to be an interesting place. Even if they didn't visit us personally it seems strange they wouldn't send a simple probe or try to make their presence known to us in one way or another. But to your point, perhaps intelligent life is quite common, it's just rare for it to be expansionist - at least beyond it's own solar system. In which case yeah, there could be a lot of Earth-like civilisations out there, but we'd be unlikely to see evidence for them.

FredPret 4y ago
Sending a probe takes very, very long, and is just as expensive, so it seems even less likely to arrive than a radio signal. And we might not even notice either one if it gets here.
pmoriarty 4y ago
"it seems strange they wouldn't send a simple probe or try to make their presence known to us in one way or another" Alien behavior is likely to seem strange to humans. It would be much more surprising if they did what we expected them to do.
- slfnflctd 4y ago
  This is brought up a lot, and while there is likely some truth to it - with plenty of fun examples in science fiction - it seems to me there is a strong counterpoint in that the mechanics of physics, biology and even civilization have many mathematically predictable properties. The environments capable of supporting life will nearly all likely have certain similar features which shape how that life behaves. Finite resources are one of the better examples. It has always been interesting to me how there are several prominent instances of architectural feats or scientific/technological breakthroughs which arose independently from people groups who had no contact with each other. I don't think extrapolating this to potential life in other star systems is too much of a stretch-- and there are certain behavioral traits you can reasonably expect in such scenarios, like large scale cooperation. Some of the most capable & best equipped minds we know of, when faced with how to communicate with intelligent extraterrestrial life, decided that math and basic physics were the best initial overtures. From those basics (along with the assumption that someone eventually perceives them) I believe a great deal more about such life can be probabilistically inferred.
Loquebantur 4y ago
Interstellar meetings are bound to happen first with a large developmental gap. Applicable here is obviously us being the Cavedwellers, Sumerians, Azteks, Egyptians, whathaveyou. What happens? Astronauts appear as effectively gods, being literally superior beyond comprehension in every aspect. Religions sprout, sacrifices are made, wars fought...all because you thoughtlessly wanted to be nice and sey 'hello'. Self-knowledge is a prerequisite to fruitful, non-destructive communication between civilizations. The ability to comprehend the scientific technicalities is likewise necessary and we are just on the brink of that. There are (many) other requirements. Importantly, you have to be able to imagine a superior entity other than as playing the role of your "master".
mannykannot 4y ago
> This still doesn't explain why we don't see evidence of life though... It is an adequately plausible explanation of why we haven't yet seen evidence of life elsewhere. To argue against it seems to require one or more question-begging premises.
- singularity2001 4y ago
  Or we are seeing life everywhere, we just don't “see” (i.e. grasp) it.
  - swagasaurus-rex 4y ago
    Obligatory – They're made out of meat https://www.mit.edu/people/dpolicar/writing/prose/text/thinkingMeat.html https://www.mit.edu/people/dpolicar/writing/prose/text/think...
- goatlover 4y ago
  Such as intelligent life having billions of years to send probes, build powerful radio beacons, and form galactic civilizations? It is called the Fermi Paradox because the physicists did some basic calculations at how long it would take to colonize the galaxy.
  - mannykannot 4y ago
    So we have two sets of calculations: the ones you are referring to here, and those that MontyCarloHall brought up. Of this pair, only the latter predicts the observation that kypro brought up.
schwartzworld 4y ago
> personally it seems strange they wouldn't send a simple probe If we detected something we thought was intelligent life, could we send a probe like you describe? Our nearest star is 4 light years away.
- shakezula 4y ago
  Could we feasibly send one? Yes. Could we feasibly get data back from it? Less certain. It would necessarily be a multi-generational project in either case.
- spacedcowboy 4y ago
  I mean we physically could send a probe... We effectively have, with "VGER". At some point, the voyager probes will hit another star system, it's just going to be a very very long time. If we actually wanted to aim a probe at another star system, I think that's probably within our technical grasp, but again we don't have any real way to get there in a reasonable timescale, or send data back once we're there. Not much use sending a probe 4 light years if the transmitter isn't powerful enough to send a signal back, and a transmitter that powerful would probably be too large to fit on a probe we could currently launch. Perhaps lasers could be used, but you'd still need a fairly powerful one, and then you have to worry about interstellar absorption of the signal if you go through a dust "cloud". I guess with a laser you're also really pinpointing where you're sending information to, if you care about that. [edit: huh, shakezula and I think alike :)]
  - jointpdf 4y ago
    So what if we sent a bunch of them, and chain them together? (i.e. like a relay network: https://en.wikipedia.org/wiki/Relay_network https://en.wikipedia.org/wiki/Relay_network)
  - schwartzworld 4y ago
    > Not much use sending a probe 4 light years if the transmitter isn't powerful enough to send a signal back And that's only if we're lucky enough to find life next door.
breakpointalpha 4y ago
There's a growing body of evidence that Earth has already been visited numerous times by something other than humans. Certain classes of UAPs demonstrate flight characteristics that are not possible given our current understanding of gravity and aerodynamics. Dozens of credible eye witnesses from multiple countries; fighter pilots, commercial pilots, nuclear physicists, and high ranking government officials. Source "In Plain Sight", US Navy fighter pilots David Fravor and Ryan Graves, etc. People are quick to dismiss these stories as hoaxes or bad memory, but scientific discovery almost always starts with an unusual or unexplained observation. Uranium was discovered in 1785 and ionizing radiation wasn't discovered for another 110 years in 1895. True scientific understanding of new observations takes quite a while.
- rvba 4y ago
  Those aliens would bring own bacteria that could kill a lot of things if not everyrhing on Earth. Somehow people have this "star trek" thinking, that hypothetical unknown microbes from other planet wont eat you alive, because you are somehow immune to them.
  - Ancalagon 4y ago
    A species which has mastered inter-stellar travel and tractor beams (/s) probably has some higher control over their own biology and sanitation practices.
    - Narishma 4y ago
      Just because they're advanced in one domain doesn't mean they are also in an unrelated one.
  - captainclam 4y ago
    I've never understood why alien bacteria are a perceived threat. Viruses and bacteria share the same genetic material as we do, and literally evolved to infect organisms of that ilk. I have always supposed that alien viruses would just be inert, and alien bacteria would rapidly die off in the inhospitable environment of an earth-organism's body.

im3w1l 4y ago

We noticed GRB221009A despite it being 2.4billion light years away. Makes you wonder if someone took the opportunity to encode data in it. Edit: Another reason to analyze it is that existential threats are a universal language. Any sufficiently advanced civilization must pay attention to possible threats, so that it can avert them. It then follows that if you want to get the attention of another civilization about which you know almost nothing, threatening them is a viable method. Of course you don't want to overdo it, lest they actually hunt you down. A blast of high energy (but non-lethal) radiation will draw attention without making anyone panic. Intelligent civilization within a huge radius will certainly be tuning in.

deleted 4y ago

[deleted]