Fermi’s paradox solved?


We have little to guide us on the question of the existence intelligent life elsewhere in the universe. But the physicist Enrico Fermi came up with the most obvious question: if the universe is teeming with advanced civilizations, where are they?

The so-called Fermi Paradox has haunted SETI researchers ever since. Not least because the famous Drake equation, which attempts put a figure on the number intelligent civilisations out there now, implies that if the number of intelligent civilisations capable of communication in our galaxy is greater than 1, then we should eventually hear from them.

That overlooks one small factor, says Reginald Smith from the Bouchet-Franklin Institute in Rochester, New York state. He says that there is a limit to how far a signal from ET can travel before it becomes too faint to hear. And when you factor that in, everything changes.

Smith uses this idea to derive a minimum density of civilizations below which contact is improbable within a given volume of space. The calculation depends on factors such as the lifetime of a civilization and the distance that it might be possible to communicate over and it produces some interesting scenarios:

Assuming the average communicating civilization has a lifetime of 1,000 years, ten times longer than Earth has been broadcasting, and has a signal horizon of 1,000 light-years, you need a minimum of over 300 communicating civilization in the galactic neighborhood to reach a minimum density.

So if there are only 200 advanced civilizations in our galaxy, the chances are that they’ll never notice each other.

Of course, we’ve no way of knowing how many advanced civilizations are out there. But this kind of thinking could, for the first time, put a limit on the number that could be out there: less than 200 perhaps?

It also has significant implications for Fermi’s line of thinking.

Would it be too early to say the paradox has been solved?

Ref: arxiv.org/abs/0901.3863: Broadcasting But Not Receiving: Density Dependence Considerations for SETI Signals

59 Responses to “Fermi’s paradox solved?”

  1. I believe that gravity waves are restricted to the same speed limit of photons in free space, whereas gravity waves, according to A. Einstein, are the actual distortions and wave(s) of space/time, which I understood travels at c.

    Perhaps the Drake equation needs to be refined somewhat. Recently, we found that our galaxy is really about as big as Andromeda or bigger, just that anomaly could change our estimation of sapient civilizations nearby.

  2. Rolf says:

    I myself find the technological ingularity hypothesis very plausible. If it comes, it means that there is only an about 100 years of radio broadcasting available and right after the singularity something else will take over for communication.

    It is of course completly possible that already another or even many have passed this singularity and are kind of hiding themselves from us. In SETI we are not restricting us to communication with us but to any form or artificial radio broadcasting.

    I very much understand Nick Bostroms logic which comes to the conclusion that we are alone. He comes to the conclusion that any civilization passing the technological singularity will e.g. via self replicating probes populate its own galaxy in a “short” time and after that the rest of the universe. The ideas are plausible and we only need to be able to think big to understand them.

    The singularity is near, lets enjoy the ride.

  3. steven walden says:

    The reason ET has not been found is because it is too easy. Sounds strange, let me explain. The question is not where is ET but where is the evidence of ET that we can see e.g., self-replicting machines. What would prevent the need is if ‘over time’ it is in fact relatively easy to find ET. Ultimately all sentient life will find an ET message – there is no need to waste resources on expanding communications through the universe. The key point here is ‘over time’. We tend to anthropomorphicise time, yet ET is likely to work on an entirely longer scale. Remember if this is correct any alien sentient species is likely to be in a position to link up relatively easily to the ET with the highest level of development as all will find each other – extreme life times will thus be common in this group, this is after all what most species seek. So the fact that it may take 200 years to find a message – well so what. Another key point to this is that messages are likely to be found at key beacon sites in the universe – mathematical points that any species can find. As an example, if it existed you could say the centre of the universe or the centre of galaxies or as these are not an option something else like an exact pi radial distance from the centre point of galaxies etc… Have we searched at points identifiable by any species at any point in the universe – no – but this is where they will be found.

  4. […] Fermi’s paradox solved? – physics space astronomy fermi […]

  5. sent2null says:

    I think the Drake equation is missing many important factors, case in point Gamma Ray Bursts and the metalicity of galaxies serving as a cosmic restart button for potential life forms. I haven’t seen much discussion on the importance of both metalicity to enable sufficient chemical soup for complex molecules (of which we are made) to form.

    I discussed some implications of these galactic realities in a post.


  6. unclesharkey says:

    Where is ET? Forget the prime directive. Where the hell is he? You know if we could go out into the universe we would be looking for life and other species. It is human nature. So then why wouldn’t ET. The only thing I can think of is that maybe they are machines and not other humanoids.

    To all you Startrek people out there.

    “Space… the Final Frontier.” “to explore strange new worlds, to seek out new life and new civilizations, to boldly go where no man has gone before.” So you are trying to tell me that we would go out into space and have some stupid prime directive? Hell no we would be looking for another alien life that we could have sex with. Get real people. Think of all the booty that Captain Kirk got. If we were not going to seek out other life forms and share what we know with them then why bother.
    Columbus should have just stayed home…….

    Sharing information is the way of the universe. For us the printing press, now computers and the internet, next……? machine and mind merge…..you down load information directly into your brain. Who knows. So I say it again, where is ET? Probably not out there……yet….

  7. Erik says:

    Matthew, it may well be likely that any intelligent extra terrestrial species will be the alpha predator of its planet, just like we are the alpha predator of ours.