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> Can someone remind me how it comes to pass that there are people in the scientific community who believe we are the only "intelligent" life form? Because the

> Can someone remind me how it comes to pass that there are people in the scientific community who believe we are the only "intelligent" life form? Because the universe is 15+ bilions of years old. Considering the speed at which we have evolved technologically, assuming life developed on earth in a perfectly average way (i.e. we are not special), and given that our solar system didn't appear particularily early, there should be a lot of much older civilizations (and thus much more advanced) around, even within our galaxy. Thus, the fact that we are unable to detect any signal from even a single other civilization is quite puzzling, we should be inundated by those signals. P.S: I don't know if many people in the scientific community really believe that we are the only ones out there, more so that intelligent life forms could be extremely rare.

asou 6y ago
What if Radio waves simply don't work the same on other planets . Or one of the first things civilizations figure out is to not broadcast your presence. Or ... Everyone else in the universe found peace by stopping at the stone age , before all this social media made us miserable. It's just conjecture, but I imagine aliens exist, but they might not even be in a form re recognize.
- enkid 6y ago
  Well, to pick some nits, if radio waves didn't work the same way, that would be a pretty fundamental shift in physics, to the point of throwing all our assumptions out the window about our observational evidence.
  - asou 6y ago
    We're assuming they communicate the same way we would. I'll make up something scifi like. On planet x they use short term Seismic wave to move data around. How would we on earth ever pick that up
willis936 6y ago
> we are not special This is a very common trap. I see this way of thinking applied to the presence of life on Earth all the time. It’s gilded in the Drake equation. It is very possible that Earth is the only planet in the galaxy or even universe with life on it. As the most powerful species on that planet, we should make responsible decisions. There is zero evidence, or even a compelling argument using existing data, that contradicts this possibility.
- Voloskaya 6y ago
  > As the most powerful species on that planet, we should make responsible decisions. I think you mistake the meaning of the "we are not special" statement. From a statistic point of view, we have to assume that everything about us is roughly average (and so far our observations kind of confirm this), otherwise any probabilty you come up with is completly skewed by the bias you introduced by assuming from the get go that we are special. But interestingly, by assuming that we are average and knowing the abundance of other planets, we should see a lot of activity out there, but we don't. So maybe that indicates that we are, in fact, not average.
  - willis936 6y ago
    >From a statistic point of view, we have to assume that everything about us is roughly average (and so far our observations kind of confirm this). This is the part I disagree with. It’s a hasty generalization to extrapolate from a single data point (Earth). The law of small numbers is alluring, but we must stick to our proper statistics guns and not fall into intuitive traps.
    - Voloskaya 6y ago
      > It’s a hasty generalization to extrapolate from a single data point (Earth). But we have no choice, we have to extrapolate. And if you have a single data point, assuming that this datapoint is average makes more sense. If there is an urn containing 100 balls some red some green, 99 of one color and 1 of the other color, and you blindly pick one ball from it that is red, you should bet that there are 99 red balls and 1 green ball, not the other way around.
fiblye 6y ago
> Thus, the fact that we are unable to detect any signal from even a single other civilization is quite puzzling, we should be inundated by those signals. Or other societies realized widely broadcasting noise is bad for whatever reason. Maybe they're composed of something sensitive to certain wavelengths. Like humans don't use xrays to transmit data, maybe radio waves are harmful in some way. Or maybe broadcasting widely resulted is a case study for getting your civilization invaded, so they avoided it it or only send signals as strong as they need to be. Or maybe it's so consistently and universally done that we simple see it as cosmic background radiation. Or maybe something like quantum entanglement someday makes wave transmissions for communication seem as backwards as smoke signals. Humans have only observed a tiny slice of space over a very tiny time span--less than 100 years. It's like being born in a barren desert and never venturing out and realizing most of the world is ocean and full of activity. We don't know what to look for or where. An observer 200 light years away from earth could easily conclude that there's no life here, since all they'd have to go by is inconclusive signs of some gases in the air.
- enkid 6y ago
  IIRC, we wouldn't be able to pick up our own broadcasts from Alpha Centauri because of the loss of radio transmission power. I doubt we would know if an alien civilization was transmitting at us, even if it was trying to get our attention.
  - notsuoh 6y ago
    Attenuation of radio waves (long membrane) is way too high, that's true, but radio isn't the only way to transmit that we could theoretically pick up. Gravity waves for example would be a way to transmit across the whole universe.
    - enkid 6y ago
      Gravity waves would still have similar issues. The only gravity waves we can pick up right now are from extremely dense bodies colliding with each other. Not exactly a feasible means for intergalactic communication.
shagie 6y ago
Consider that our civilization has really only had about a 50 year window were we were rather noisy in the radio frequencies. Now, our radio transmissions (with the exception of some short pulse military ones) are much less powerful and would be much harder to detect at a distance. From https://space.stackexchange.com/a/13013 https://space.stackexchange.com/a/13013 > uoting from Tarter (2001): "At current levels of sensitivity, targeted microwave searches could detect the equivalent power of strong TV transmitters at a distance of 1 light year (within which there are no other stars)..." We barely have the sensitivity to detect the existing strong TV transmitters of today within a 1ly sphere. The inverse square law becomes rather cruel. For a 2ly sphere, we'd need 4x the sensitivity. 3ly, 9x. To get 100 stars in the sphere, we need 21ly sphere, and that would need 400x the sensitivity that we have... and in that list of 100 nearest stars, there's only 6 G type stars. So yes... there may be. But we're very small ( http://www.rainydaymagazine.com/RDM2011/RainyDayScience/RadioSignal/TheGalaxyBig.jpg http://www.rainydaymagazine.com/RDM2011/RainyDayScience/Radi... ). Our own radio signals have barely made any significant coverage of the galaxy. Our own signals are also becoming harder to detect as our radio technology becomes better (DTV only needs 1/5th the power of analog TV). That we're not hearing any random signals akin to what we've been broadcasting for the past century isn't surprising.
- Voloskaya 6y ago
  Radio signal is not the only way to detect presence of other civilizations. Von Neumann style probes, Dyson spheres etc. Current estimates place the number of planets in our galaxy at 100 billions. And some of the stars in our galaxy are ~6 billions years older than our sun, that's a hell lot of time for a civilization to develop massively considering the technological progress we have had in a just a few thousands of years.
- sjy 6y ago
  That Stack Exchange answer from 2015 is quoting a primary source describing “current levels of sensitivity” in 2001. The Breakthrough Listen initiative, launched in 2016, claims that it is sensitive to “Earth-leakage” levels of radio transmission within 5 parsecs (16 ly): https://breakthroughinitiatives.org/news/3 https://breakthroughinitiatives.org/news/3
saiya-jin 6y ago
The issue with your argument is that earth is not a special place - there are tons of positive factors that helped life to develop and sustain. Position nearby stable sun, magnetosphere and just enough volcanic activity, our moon, big planets trapping most comets/debris that would make huge meteorite impacts much more common, oceans, tectonics. At the end, we don't know and everybody's opinion is just a gut feeling. https://en.wikipedia.org/wiki/Rare_Earth_hypothesis https://en.wikipedia.org/wiki/Rare_Earth_hypothesis
- Voloskaya 6y ago
  > The issue with your argument is that earth is not a special place This is not my argument at all, it's actuall quite the opposite. The argument is that, if everything about us is average (including our host planet), and given the tremendous amount of planets everywhere, we should see life basically everywhere. But we don't! So there indeed maybe something special about us, maybe our planet, maybe some extremely rare step in our evolution.
goodcanadian 6y ago
Thus, the fact that we are unable to detect any signal from even a single other civilization is quite puzzling, we should be inundated by those signals. People overestimate the detectability of our own signals. I don't have a reference, but I read an article a few years back where someone calculated how far away we would be able to detect our own signals with our current technology. The answer was about 20 light years. There are only around 100 stars in that sample. About all we can say is that there is not a civilisation similar to ours in that sample. Anything further away would have to be deliberately trying to communicate with us. If they are similar to us, they wouldn't know we are here. If they are much more advanced, we might be uninteresting to them for any number of reasons. Technology advances, and this situation will change. The Square Kilometre Array, for example, will give us the resolving power to see whether excess radio "noise" is coming from a planet rather than a star (which might be an indication of an intelligent origin). This will increase our bubble of detectability much further out. Unfortunately, I don't have a number on that, but it is still an incredibly small volume compared to the size of the universe.
halfdan 6y ago
What signal are we expecting to be able to detect? AFAIK the radio signals we've been emitting are garbled beyond recognition and way too weak even a few light-years away from earth. After all, most of our communication is directed at earth and the remainder is for at most geo stationary orbit. We generally don't transmit anything high energy that would stand a chance to be recognisable from afar. Similarly signals from other civilisations will probably become scrambled by distance and because they might overlap heavily with the radiation emitted by their sun.

asou 6y ago

What if Radio waves simply don't work the same on other planets . Or one of the first things civilizations figure out is to not broadcast your presence. Or ... Everyone else in the universe found peace by stopping at the stone age , before all this social media made us miserable. It's just conjecture, but I imagine aliens exist, but they might not even be in a form re recognize.

enkid 6y ago
Well, to pick some nits, if radio waves didn't work the same way, that would be a pretty fundamental shift in physics, to the point of throwing all our assumptions out the window about our observational evidence.
- asou 6y ago
  We're assuming they communicate the same way we would. I'll make up something scifi like. On planet x they use short term Seismic wave to move data around. How would we on earth ever pick that up

willis936 6y ago

> we are not special This is a very common trap. I see this way of thinking applied to the presence of life on Earth all the time. It’s gilded in the Drake equation. It is very possible that Earth is the only planet in the galaxy or even universe with life on it. As the most powerful species on that planet, we should make responsible decisions. There is zero evidence, or even a compelling argument using existing data, that contradicts this possibility.

Voloskaya 6y ago
> As the most powerful species on that planet, we should make responsible decisions. I think you mistake the meaning of the "we are not special" statement. From a statistic point of view, we have to assume that everything about us is roughly average (and so far our observations kind of confirm this), otherwise any probabilty you come up with is completly skewed by the bias you introduced by assuming from the get go that we are special. But interestingly, by assuming that we are average and knowing the abundance of other planets, we should see a lot of activity out there, but we don't. So maybe that indicates that we are, in fact, not average.
- willis936 6y ago
  >From a statistic point of view, we have to assume that everything about us is roughly average (and so far our observations kind of confirm this). This is the part I disagree with. It’s a hasty generalization to extrapolate from a single data point (Earth). The law of small numbers is alluring, but we must stick to our proper statistics guns and not fall into intuitive traps.
  - Voloskaya 6y ago
    > It’s a hasty generalization to extrapolate from a single data point (Earth). But we have no choice, we have to extrapolate. And if you have a single data point, assuming that this datapoint is average makes more sense. If there is an urn containing 100 balls some red some green, 99 of one color and 1 of the other color, and you blindly pick one ball from it that is red, you should bet that there are 99 red balls and 1 green ball, not the other way around.

fiblye 6y ago

> Thus, the fact that we are unable to detect any signal from even a single other civilization is quite puzzling, we should be inundated by those signals. Or other societies realized widely broadcasting noise is bad for whatever reason. Maybe they're composed of something sensitive to certain wavelengths. Like humans don't use xrays to transmit data, maybe radio waves are harmful in some way. Or maybe broadcasting widely resulted is a case study for getting your civilization invaded, so they avoided it it or only send signals as strong as they need to be. Or maybe it's so consistently and universally done that we simple see it as cosmic background radiation. Or maybe something like quantum entanglement someday makes wave transmissions for communication seem as backwards as smoke signals. Humans have only observed a tiny slice of space over a very tiny time span--less than 100 years. It's like being born in a barren desert and never venturing out and realizing most of the world is ocean and full of activity. We don't know what to look for or where. An observer 200 light years away from earth could easily conclude that there's no life here, since all they'd have to go by is inconclusive signs of some gases in the air.

enkid 6y ago
IIRC, we wouldn't be able to pick up our own broadcasts from Alpha Centauri because of the loss of radio transmission power. I doubt we would know if an alien civilization was transmitting at us, even if it was trying to get our attention.
- notsuoh 6y ago
  Attenuation of radio waves (long membrane) is way too high, that's true, but radio isn't the only way to transmit that we could theoretically pick up. Gravity waves for example would be a way to transmit across the whole universe.
  - enkid 6y ago
    Gravity waves would still have similar issues. The only gravity waves we can pick up right now are from extremely dense bodies colliding with each other. Not exactly a feasible means for intergalactic communication.

shagie 6y ago

Consider that our civilization has really only had about a 50 year window were we were rather noisy in the radio frequencies. Now, our radio transmissions (with the exception of some short pulse military ones) are much less powerful and would be much harder to detect at a distance. From https://space.stackexchange.com/a/13013 https://space.stackexchange.com/a/13013 > uoting from Tarter (2001): "At current levels of sensitivity, targeted microwave searches could detect the equivalent power of strong TV transmitters at a distance of 1 light year (within which there are no other stars)..." We barely have the sensitivity to detect the existing strong TV transmitters of today within a 1ly sphere. The inverse square law becomes rather cruel. For a 2ly sphere, we'd need 4x the sensitivity. 3ly, 9x. To get 100 stars in the sphere, we need 21ly sphere, and that would need 400x the sensitivity that we have... and in that list of 100 nearest stars, there's only 6 G type stars. So yes... there may be. But we're very small ( http://www.rainydaymagazine.com/RDM2011/RainyDayScience/RadioSignal/TheGalaxyBig.jpg http://www.rainydaymagazine.com/RDM2011/RainyDayScience/Radi... ). Our own radio signals have barely made any significant coverage of the galaxy. Our own signals are also becoming harder to detect as our radio technology becomes better (DTV only needs 1/5th the power of analog TV). That we're not hearing any random signals akin to what we've been broadcasting for the past century isn't surprising.

Voloskaya 6y ago
Radio signal is not the only way to detect presence of other civilizations. Von Neumann style probes, Dyson spheres etc. Current estimates place the number of planets in our galaxy at 100 billions. And some of the stars in our galaxy are ~6 billions years older than our sun, that's a hell lot of time for a civilization to develop massively considering the technological progress we have had in a just a few thousands of years.
sjy 6y ago
That Stack Exchange answer from 2015 is quoting a primary source describing “current levels of sensitivity” in 2001. The Breakthrough Listen initiative, launched in 2016, claims that it is sensitive to “Earth-leakage” levels of radio transmission within 5 parsecs (16 ly): https://breakthroughinitiatives.org/news/3 https://breakthroughinitiatives.org/news/3

saiya-jin 6y ago

The issue with your argument is that earth is not a special place - there are tons of positive factors that helped life to develop and sustain. Position nearby stable sun, magnetosphere and just enough volcanic activity, our moon, big planets trapping most comets/debris that would make huge meteorite impacts much more common, oceans, tectonics. At the end, we don't know and everybody's opinion is just a gut feeling. https://en.wikipedia.org/wiki/Rare_Earth_hypothesis https://en.wikipedia.org/wiki/Rare_Earth_hypothesis

Voloskaya 6y ago
> The issue with your argument is that earth is not a special place This is not my argument at all, it's actuall quite the opposite. The argument is that, if everything about us is average (including our host planet), and given the tremendous amount of planets everywhere, we should see life basically everywhere. But we don't! So there indeed maybe something special about us, maybe our planet, maybe some extremely rare step in our evolution.

goodcanadian 6y ago

Thus, the fact that we are unable to detect any signal from even a single other civilization is quite puzzling, we should be inundated by those signals. People overestimate the detectability of our own signals. I don't have a reference, but I read an article a few years back where someone calculated how far away we would be able to detect our own signals with our current technology. The answer was about 20 light years. There are only around 100 stars in that sample. About all we can say is that there is not a civilisation similar to ours in that sample. Anything further away would have to be deliberately trying to communicate with us. If they are similar to us, they wouldn't know we are here. If they are much more advanced, we might be uninteresting to them for any number of reasons. Technology advances, and this situation will change. The Square Kilometre Array, for example, will give us the resolving power to see whether excess radio "noise" is coming from a planet rather than a star (which might be an indication of an intelligent origin). This will increase our bubble of detectability much further out. Unfortunately, I don't have a number on that, but it is still an incredibly small volume compared to the size of the universe.

halfdan 6y ago

What signal are we expecting to be able to detect? AFAIK the radio signals we've been emitting are garbled beyond recognition and way too weak even a few light-years away from earth. After all, most of our communication is directed at earth and the remainder is for at most geo stationary orbit. We generally don't transmit anything high energy that would stand a chance to be recognisable from afar. Similarly signals from other civilisations will probably become scrambled by distance and because they might overlap heavily with the radiation emitted by their sun.