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The Fermi paradox is good for a nice chat at a party. But it's not a paradox at all. Imagine there's an alien civilization in our galactic neighbor Proxima Ce

The Fermi paradox is good for a nice chat at a party. But it's not a paradox at all. Imagine there's an alien civilization in our galactic neighbor Proxima Centauri. How would we know they are there? To make it more plausible. Let's say we figure out a way to send a space probe to Proxima Centauri. How do we communicate with that probe? Easy, you say, just like we communicate with the Voyagers: they point a reasonably large parabolic antenna at us, we point a point a much larger one at them, and we chat all day long. Except that Proxima Centauri is 2000 times farther that Voyager. And signals decrease with the square of the distance. By the time Voyager gets to be 4.25 light years away from Earth, their puny 22W antenna will send us a signal that's 4 million times weaker than what they send us now (when we get less than 200 bits/second). It's actually worse than that, of course. If Voyager were to send a signal from some arbitrary place 4.25 light years away, we'd get it as something 4 million times weaker. But if that place is in the solar system of Proxima Centauri, it's like us looking straight at the headlights of an incoming car. That very weak signal will need to be extracted from the extraordinarily bright noise coming from the star that's roughly speaking about 1 second of arc away from it. Now imagine that instead of Voyager, it's just some aliens that are not pointing an antenna straight at us, but just minding their own business. They could be launching rockets, watching satellite TV, waging wars, and from time to time lobbing Himars at each others, and even nukes. How would we know they are there? And now finally imagine that there are no aliens in the Proxima Centauri system, by the luck of the draw, but there are in 5% of all the star systems in the galaxy. Only the closest ones to us are 40 light years away, instead of 4. That's another reduction in signal by a factor of 100. The only question is not why we didn't "see" any aliens so far. It's why we wasted so much money on SETI. Was Carl Sagan not able to do the back of the envelope calculation I just did here?

twawaaay 4y ago
We've been able to fly or emit radio signals only for a bit more than 100 years. If there exist any other civilisations and we assume they start independently, there should be ones that started billions of years ago. Which is enough to visit entire galaxy even at very slow speeds. The paradox is that we are not seeing any signs of any other intelligent life.
- credit_guy 4y ago
  Only if they are in our own Solar system. But you can easily imagine a supercivilization visiting lots of solar systems, but not establishing permanent colonies everywhere. As I said, what if 5% of the solar systems are teaming with life? That would still be tens of millions of solar systems in our galaxy. The diversity of life could be something to make Star Wars look unimaginative. And we'd have no idea they are out there.
  - twawaaay 4y ago
    What kind of argument is this "only if they are in our own solar system"? Even at the speed of Voyager 2, (15km/s), in a billion years it would cover about 4 * 10^17 km or about 40 thousand light years. I am pretty sure people who have been developing for hundreds of millions of years can do better than that, by orders of magnitude. Also you put a totally strange assumption that all civilisations will only restrict themselves to visiting planets. If there is a lot of civilisation it is more likely they will have different motivations.
    - Valgrim 4y ago
      If the dark forest hypothesis is true, you can bet any civilization advanced enough to detect us will go out of their way to avoid being detected by us. For all we know, there could be a gigantic tungsten rod slowly and purposefully accelerating toward us that would destroy all life on earth in ten thousand years, and we'd have no way of knowing.
      - oAlbe 4y ago
        Why a tungsten rod in particular?
        legutierr 4y ago
        https://en.wikipedia.org/wiki/Kinetic_bombardment https://en.wikipedia.org/wiki/Kinetic_bombardment
m4rtink 4y ago
We might be able to see their drive plumes if they use some of the theoretical high performance reactive drives we know of on big crafy. Eq. various fusion plasma drives, Orion, Nuclear Salt Water Rocket release so ludicrous ammounts of energy that they might be visible over interstellar distances, especially if pointed in our general direction when running. Massive solar sails as well would be very very big and very reflective.
- simonh 4y ago
  > release so ludicrous ammounts of energy that they might be visible over interstellar distances Ludicrous at human scales, but utterly insignificant compared to the output of even the smallest stars. Bear in mind that small stars are hard to detect more than a few dozens of light years away. Well you can detect them, but they are hard to range. It’s difficult to pick out nearby stars in the dense stellar background as being nearby. Take a look at the deep field images to get an idea of the clutter. A drive plume would just be utterly lost in all that background noise. People imagine the sky as being inky black with a few bright objects to look for, and that even a drive plume light years away would stand out against the blackness, but that’s not how it is at all. The sky is full of distant clutter that makes picking out particular objects extremely difficult. And if your plume is in a system anywhere near a star, forget it. You’d have to know exactly what you’re looking for and make extremely precise long term observations to have any chance whatsoever.
- credit_guy 4y ago
  Space is large. If you don't look in some direction, you don't see what's there. Big, or not. Let's take the Orion engine. It keeps blasting away thermonuclear bombs. Are we looking straight at it? Why? Ah, maybe because they are in the neighborhood of a star. But then we are also looking at the star, which is trillions or quadrillions times brighter. Same for fusion plasma drives or anything else. If the Orion engine is traveling between stars, we'd have a chance, but then how would we know where to look ?
  - dredmorbius 4y ago
    If they're approaching us, they might be using the Orion engine to decelerate on long final.
Ancalagon 4y ago
There are other methods of detection and signatures that, assuming similar civilizations to our own also follow similar energy use growth patterns, should be detectable at very far distances in other ranges of wavelength.
AlbertCory 4y ago
Well said. The "Drake Equation" is complete and utter garbage. There is no such thing as a "probability" of any of those terms, in the way we normally understand probability, i.e. dice or card games. That said, there probably are intelligent civilizations somewhere in the universe, but we have that pesky problem of distance and the speed of light, as you said. People like to imagine that eventually civilizations find a way around it, but in all likelihood they don't.
- gcanyon 4y ago
  > There is no such thing as a "probability" of any of those terms... > That said, there probably are intelligent civilizations somewhere in the universe ...pick one :-)
  - AlbertCory 4y ago
    I gather you're getting all triumphant there: "Hah! A contradiction! So there." Not really, sorry. "Probability" as in "something you can assign an exact number between 0 and 1 to." "Probably" as in "I dunno, maybe."
    - pfdietz 4y ago
      No, he was rightly pointing out that your "there probably is" statement was bullshit, not supportable from the evidence.
      - AlbertCory 4y ago
        > bullshit, not supportable from the evidence Two different things. You can't prove there aren't, and I can't prove there are.
        pfdietz 4y ago
        "Bullshit", as I use the term, is misrepresentation of the state of your knowledge by confident assertions you can't back up with evidence. The statement is precisely that, bullshit.
postalrat 4y ago
The paradox is that the our solar system should have been visited. But so we haven't been able to detect anything. It's much closer than the centauri system.
- nobody9999 4y ago
  >The paradox is that the our solar system should have been visited. But so we haven't been able to detect anything. >It's much closer than the centauri system. That assumes there have been other(s) technological civilizations in our galaxy. Which isn't necessarily the case. We may well (or not) be one of the first space faring (for some values of that term) civilizations in our (part of) the galaxy. A recent discussion about this can be found here[0] (PBS Space Time episode from 9 November 2022). [0] https://www.youtube.com/watch?v=uTrFAY3LUNw https://www.youtube.com/watch?v=uTrFAY3LUNw
  - postalrat 4y ago
    That is a possible solution for the paradox. The comment I replied to was talking about a different star system.
floxy 4y ago
>How would we know they are there? How about pointing an optical telescope at them to take a look? Direct Multipixel Imaging and Spectroscopy of an Exoplanet with a Solar Gravity Lens Mission https://www.youtube.com/watch?v=NQFqDKRAROI https://www.youtube.com/watch?v=NQFqDKRAROI https://arxiv.org/abs/1802.08421 https://arxiv.org/abs/1802.08421
- omnicognate 4y ago
  Which is absolutely amazing and I desperately hope it happens in my lifetime. But we haven't done it yet, so it's hardly relevant to the "why haven't we seen any?" part of the "Fermi" "Paradox".
alfiedotwtf 4y ago
Flip the point of view for a moment - what's the absolute best way we could try to say "hey, we're here" to the universe in the hope of detection from far away civilizations? I like the idea of Contact's Prime Number signal but how would you do this on a large scale? I was thinking Dyson Sphere a star as a huge Flag Semaphore to send the message, but then what rate do you flip bits to make it optimal for the receiving end far far away? Now flip it back... would the current SETI pick up this signal if this were happening somewhere close in the Milky Way? If not, then yeah maybe SETI should be wound down :(
- withinboredom 4y ago
  And what if we broadcast and whomever hears us wants us dead? Maybe it’s so quiet because to be loud results in death of the entire civilization.
  - yreg 4y ago
    If you are an advanced civ that fears new competition, you don't wait for hearing random radio transmissions. You build replicating factories to build relativistic kill missiles and preemptively destroy all the planets in the galaxy.
    - krapp 4y ago
      Given that planets currently exist in our galaxy, either no advanced civilizations exist that fear competition or... apparently not?
      - yreg 4y ago
        Yep, I think it makes little sense for them to fear competition (if they exist). I suspect that intergalactic warfare is impractical and there is nothing to gain. Reasons being: There is no stealth in space, there is no FTL, resources are abundant everywhere, destroying planets/megastructures is rather easy.
    - withinboredom 4y ago
steve76 4y ago
robocat 4y ago
> it's just some aliens that are not pointing an antenna straight at us Even worse, don’t modern digital signals look similar to noise, are usually encrypted, use much higher frequencies, and have less gap between bands? Good luck trying to spot a cellphone signal from Proxima Centauri (my phone has trouble getting signal at home!) Many analogue broadcast signals have been replaced by digital, and broadcast as a technology is in its twilight years (although my parents do still get TV and listen to the radio!) So signals might only be detectable in nascient technology civilisations - they then move on to undetectable signals?
- anvuong 4y ago
  Yup, information theory says that Gaussian signalling is optimal in term of bandwidth utilization in many cases. And we've spent decades trying to achieve this by various techniques in coding and modulation. And yes encryption/secrecy adds another layer of randomization. I believe a radio signal eavesdropped from a US military base is not much different than some random noise. That being said, the question is to tell if a signal is man-made or not, which is much easier than to discover what information it conveys. Based on modulation carrier frequency and the transmit (on/off) pattern you can still very much tell if that signal is man-made or not.
aortega 4y ago
Your calculation is likely wrong. See, you can build a laser in a spectrum not generally emitted by stars, and point directly to another star system. You dont need much power, yes, perhaps some terawatts, but it can be pulsed, total energy would be low. And getting a low power signal doesnt means its impossible to detect, but that the bandwidth is short. Instead of 200 bits per second, you would get 1 bit per hour. But that´s enough.
- Enginerrrd 4y ago
  That's really not much of a rebuttal. The simple truth is, if a clone of the human race existed on proxima centauri, long enough for signals to propagate, we'd have no idea and that's an extremely optimistic scenario. Why would a race be casually pointing terawatts of laser at every star around them. Tremendous waste of resources for essentially no gain within human scale lifetimes.
- Balgair 4y ago
  All beams will broaden and distort though. No matter the wavelength or pulsing, anything made by not-a-pulsar is likely to get garbled and shifted beyond comprehension. You can fix this with some really really big fancy lenses, maaaaaybe. But you'd have to know the distance of the point you're trying to image the laser onto first. Collimated light over those distances just isn't ever going to stay that way.
- simonh 4y ago
  OP is saying how would we detect a civilisation unknown to us, and for who we are also unknown. A system such as you describe would only be practical for a civilisation trying to communicate with a known counter-party. Otherwise which stars do you target your laser on, and for how long? Let’s say the Centaurans developed advanced technology 100 million years ago, would they beam this signal at our star for all 50 million years until we happened to evolve? Why our star system, why not any of millions of others? As this system is so directional each detector could only monitor one star at a time. How many do we build, and which stars do we point them at, and for how long? For direct communication with an established target this would be fine, but as a broadcast system it’s way too target specific to work at galactic scale.
yyyk 4y ago
>The only question is not why we didn't "see" any aliens so far. It's why we wasted so much money on SETI. Was Carl Sagan not able to do the back of the envelope calculation I just did here? Sagan was perfectly capable of doing these calculations. However, SETI was a nice way to divert funds to radioastronomy. Not the first time Sagan was 'creative' - per his Nuclear Winter model, if sometimes lights a match in the poles the entire planet will burn.
29athrowaway 4y ago
How does the interstellar medium interact with communication signals like radio waves?
Balgair 4y ago
Just want to point out the currently known composition of the universe: ~5% matter. The stuff you and I are made of. Most of this is H and He though, bit of Li in there too. And it's all mostly burning in a star. Like, 99.99999% of it. ~25% dark matter. We know little about it. We do know that it falls down though and doesn't like to touch other stuff. But that's kinda it. ~70% dark energy. We know pretty much nothing about it. It falls ... up (?!). Considering that the stuff we're all made of is the 5%, and even then most of that is down in a deep gravity well and on fire, I think we may need to look at the other 95% of the stuff out there too if we want to find friends.
- simonh 4y ago
  Dark matter appears to be a very weakly interacting fluid, completely unsuitable for developing any kind of structure at the local level. Dark energy is, well, energy. Also incapable of local structure. I’m afraid conventional matter it is.

twawaaay 4y ago

We've been able to fly or emit radio signals only for a bit more than 100 years. If there exist any other civilisations and we assume they start independently, there should be ones that started billions of years ago. Which is enough to visit entire galaxy even at very slow speeds. The paradox is that we are not seeing any signs of any other intelligent life.

credit_guy 4y ago
Only if they are in our own Solar system. But you can easily imagine a supercivilization visiting lots of solar systems, but not establishing permanent colonies everywhere. As I said, what if 5% of the solar systems are teaming with life? That would still be tens of millions of solar systems in our galaxy. The diversity of life could be something to make Star Wars look unimaginative. And we'd have no idea they are out there.
- twawaaay 4y ago
  What kind of argument is this "only if they are in our own solar system"? Even at the speed of Voyager 2, (15km/s), in a billion years it would cover about 4 * 10^17 km or about 40 thousand light years. I am pretty sure people who have been developing for hundreds of millions of years can do better than that, by orders of magnitude. Also you put a totally strange assumption that all civilisations will only restrict themselves to visiting planets. If there is a lot of civilisation it is more likely they will have different motivations.
  - Valgrim 4y ago
    If the dark forest hypothesis is true, you can bet any civilization advanced enough to detect us will go out of their way to avoid being detected by us. For all we know, there could be a gigantic tungsten rod slowly and purposefully accelerating toward us that would destroy all life on earth in ten thousand years, and we'd have no way of knowing.
    - oAlbe 4y ago
      Why a tungsten rod in particular?
      - legutierr 4y ago
        https://en.wikipedia.org/wiki/Kinetic_bombardment https://en.wikipedia.org/wiki/Kinetic_bombardment

m4rtink 4y ago

We might be able to see their drive plumes if they use some of the theoretical high performance reactive drives we know of on big crafy. Eq. various fusion plasma drives, Orion, Nuclear Salt Water Rocket release so ludicrous ammounts of energy that they might be visible over interstellar distances, especially if pointed in our general direction when running. Massive solar sails as well would be very very big and very reflective.

simonh 4y ago
> release so ludicrous ammounts of energy that they might be visible over interstellar distances Ludicrous at human scales, but utterly insignificant compared to the output of even the smallest stars. Bear in mind that small stars are hard to detect more than a few dozens of light years away. Well you can detect them, but they are hard to range. It’s difficult to pick out nearby stars in the dense stellar background as being nearby. Take a look at the deep field images to get an idea of the clutter. A drive plume would just be utterly lost in all that background noise. People imagine the sky as being inky black with a few bright objects to look for, and that even a drive plume light years away would stand out against the blackness, but that’s not how it is at all. The sky is full of distant clutter that makes picking out particular objects extremely difficult. And if your plume is in a system anywhere near a star, forget it. You’d have to know exactly what you’re looking for and make extremely precise long term observations to have any chance whatsoever.
credit_guy 4y ago
Space is large. If you don't look in some direction, you don't see what's there. Big, or not. Let's take the Orion engine. It keeps blasting away thermonuclear bombs. Are we looking straight at it? Why? Ah, maybe because they are in the neighborhood of a star. But then we are also looking at the star, which is trillions or quadrillions times brighter. Same for fusion plasma drives or anything else. If the Orion engine is traveling between stars, we'd have a chance, but then how would we know where to look ?
- dredmorbius 4y ago
  If they're approaching us, they might be using the Orion engine to decelerate on long final.

Ancalagon 4y ago

There are other methods of detection and signatures that, assuming similar civilizations to our own also follow similar energy use growth patterns, should be detectable at very far distances in other ranges of wavelength.

AlbertCory 4y ago

Well said. The "Drake Equation" is complete and utter garbage. There is no such thing as a "probability" of any of those terms, in the way we normally understand probability, i.e. dice or card games. That said, there probably are intelligent civilizations somewhere in the universe, but we have that pesky problem of distance and the speed of light, as you said. People like to imagine that eventually civilizations find a way around it, but in all likelihood they don't.

gcanyon 4y ago
> There is no such thing as a "probability" of any of those terms... > That said, there probably are intelligent civilizations somewhere in the universe ...pick one :-)
- AlbertCory 4y ago
  I gather you're getting all triumphant there: "Hah! A contradiction! So there." Not really, sorry. "Probability" as in "something you can assign an exact number between 0 and 1 to." "Probably" as in "I dunno, maybe."
  - pfdietz 4y ago
    No, he was rightly pointing out that your "there probably is" statement was bullshit, not supportable from the evidence.
    - AlbertCory 4y ago
      > bullshit, not supportable from the evidence Two different things. You can't prove there aren't, and I can't prove there are.
      - pfdietz 4y ago
        "Bullshit", as I use the term, is misrepresentation of the state of your knowledge by confident assertions you can't back up with evidence. The statement is precisely that, bullshit.

postalrat 4y ago

The paradox is that the our solar system should have been visited. But so we haven't been able to detect anything. It's much closer than the centauri system.

nobody9999 4y ago
>The paradox is that the our solar system should have been visited. But so we haven't been able to detect anything. >It's much closer than the centauri system. That assumes there have been other(s) technological civilizations in our galaxy. Which isn't necessarily the case. We may well (or not) be one of the first space faring (for some values of that term) civilizations in our (part of) the galaxy. A recent discussion about this can be found here[0] (PBS Space Time episode from 9 November 2022). [0] https://www.youtube.com/watch?v=uTrFAY3LUNw https://www.youtube.com/watch?v=uTrFAY3LUNw
- postalrat 4y ago
  That is a possible solution for the paradox. The comment I replied to was talking about a different star system.

floxy 4y ago

>How would we know they are there? How about pointing an optical telescope at them to take a look? Direct Multipixel Imaging and Spectroscopy of an Exoplanet with a Solar Gravity Lens Mission https://www.youtube.com/watch?v=NQFqDKRAROI https://www.youtube.com/watch?v=NQFqDKRAROI https://arxiv.org/abs/1802.08421 https://arxiv.org/abs/1802.08421

omnicognate 4y ago
Which is absolutely amazing and I desperately hope it happens in my lifetime. But we haven't done it yet, so it's hardly relevant to the "why haven't we seen any?" part of the "Fermi" "Paradox".

alfiedotwtf 4y ago

Flip the point of view for a moment - what's the absolute best way we could try to say "hey, we're here" to the universe in the hope of detection from far away civilizations? I like the idea of Contact's Prime Number signal but how would you do this on a large scale? I was thinking Dyson Sphere a star as a huge Flag Semaphore to send the message, but then what rate do you flip bits to make it optimal for the receiving end far far away? Now flip it back... would the current SETI pick up this signal if this were happening somewhere close in the Milky Way? If not, then yeah maybe SETI should be wound down :(

withinboredom 4y ago
And what if we broadcast and whomever hears us wants us dead? Maybe it’s so quiet because to be loud results in death of the entire civilization.
- yreg 4y ago
  If you are an advanced civ that fears new competition, you don't wait for hearing random radio transmissions. You build replicating factories to build relativistic kill missiles and preemptively destroy all the planets in the galaxy.
  - krapp 4y ago
    Given that planets currently exist in our galaxy, either no advanced civilizations exist that fear competition or... apparently not?
    - yreg 4y ago
      Yep, I think it makes little sense for them to fear competition (if they exist). I suspect that intergalactic warfare is impractical and there is nothing to gain. Reasons being: There is no stealth in space, there is no FTL, resources are abundant everywhere, destroying planets/megastructures is rather easy.
  - withinboredom 4y ago

steve76 4y ago

robocat 4y ago

> it's just some aliens that are not pointing an antenna straight at us Even worse, don’t modern digital signals look similar to noise, are usually encrypted, use much higher frequencies, and have less gap between bands? Good luck trying to spot a cellphone signal from Proxima Centauri (my phone has trouble getting signal at home!) Many analogue broadcast signals have been replaced by digital, and broadcast as a technology is in its twilight years (although my parents do still get TV and listen to the radio!) So signals might only be detectable in nascient technology civilisations - they then move on to undetectable signals?

anvuong 4y ago
Yup, information theory says that Gaussian signalling is optimal in term of bandwidth utilization in many cases. And we've spent decades trying to achieve this by various techniques in coding and modulation. And yes encryption/secrecy adds another layer of randomization. I believe a radio signal eavesdropped from a US military base is not much different than some random noise. That being said, the question is to tell if a signal is man-made or not, which is much easier than to discover what information it conveys. Based on modulation carrier frequency and the transmit (on/off) pattern you can still very much tell if that signal is man-made or not.

aortega 4y ago

Your calculation is likely wrong. See, you can build a laser in a spectrum not generally emitted by stars, and point directly to another star system. You dont need much power, yes, perhaps some terawatts, but it can be pulsed, total energy would be low. And getting a low power signal doesnt means its impossible to detect, but that the bandwidth is short. Instead of 200 bits per second, you would get 1 bit per hour. But that´s enough.

Enginerrrd 4y ago
That's really not much of a rebuttal. The simple truth is, if a clone of the human race existed on proxima centauri, long enough for signals to propagate, we'd have no idea and that's an extremely optimistic scenario. Why would a race be casually pointing terawatts of laser at every star around them. Tremendous waste of resources for essentially no gain within human scale lifetimes.
Balgair 4y ago
All beams will broaden and distort though. No matter the wavelength or pulsing, anything made by not-a-pulsar is likely to get garbled and shifted beyond comprehension. You can fix this with some really really big fancy lenses, maaaaaybe. But you'd have to know the distance of the point you're trying to image the laser onto first. Collimated light over those distances just isn't ever going to stay that way.
simonh 4y ago
OP is saying how would we detect a civilisation unknown to us, and for who we are also unknown. A system such as you describe would only be practical for a civilisation trying to communicate with a known counter-party. Otherwise which stars do you target your laser on, and for how long? Let’s say the Centaurans developed advanced technology 100 million years ago, would they beam this signal at our star for all 50 million years until we happened to evolve? Why our star system, why not any of millions of others? As this system is so directional each detector could only monitor one star at a time. How many do we build, and which stars do we point them at, and for how long? For direct communication with an established target this would be fine, but as a broadcast system it’s way too target specific to work at galactic scale.

yyyk 4y ago

>The only question is not why we didn't "see" any aliens so far. It's why we wasted so much money on SETI. Was Carl Sagan not able to do the back of the envelope calculation I just did here? Sagan was perfectly capable of doing these calculations. However, SETI was a nice way to divert funds to radioastronomy. Not the first time Sagan was 'creative' - per his Nuclear Winter model, if sometimes lights a match in the poles the entire planet will burn.

29athrowaway 4y ago

How does the interstellar medium interact with communication signals like radio waves?

Balgair 4y ago

Just want to point out the currently known composition of the universe: ~5% matter. The stuff you and I are made of. Most of this is H and He though, bit of Li in there too. And it's all mostly burning in a star. Like, 99.99999% of it. ~25% dark matter. We know little about it. We do know that it falls down though and doesn't like to touch other stuff. But that's kinda it. ~70% dark energy. We know pretty much nothing about it. It falls ... up (?!). Considering that the stuff we're all made of is the 5%, and even then most of that is down in a deep gravity well and on fire, I think we may need to look at the other 95% of the stuff out there too if we want to find friends.

simonh 4y ago
Dark matter appears to be a very weakly interacting fluid, completely unsuitable for developing any kind of structure at the local level. Dark energy is, well, energy. Also incapable of local structure. I’m afraid conventional matter it is.