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Another perspective of the Drake Equation

  1. Feb 8, 2013 #1
    This might not be original, but I wanted to throw it out there.

    The Drake equation is typically used in the sense of the question, "Is there life in the universe, and what is the probability that WE can detect/find/communicate with it?"

    In other words the underlying assumption is that we know that we are here, but we don't now if anybody else is out there. And we are very far from pretty much anything. We are not likely to communicate or have a relationship with another civilization.

    What if we change the question a bit and ask "are there any two civilizations (besides us) out there who have communicated with each other?"

    In other words - the law of large numbers tells us that events, even improbable ones, are more likely to happen given more "trials." So the "improbable event" of intelligent life evolving (we have seen it happen at least once) has "probably" happened elsewhere, given that the universe is so large.

    Now what about the probability of it happening 3 times - two of them "not us."

    And the probability of them being in some vicinity where they might actually have a chance at communicating with each other (though not with us). The best scenario would of course be two planets in the same solar system. If we had "martians" this would have been us by now.

    Now is this more probable or less probable than then the event in which we ourselves contact another civilization?

    Of course all these numbers are speculation... The drake equation is probably more a philosophical equation than a real calculation, but I was wondering if the question has been put this way before.

    -Dave K
  2. jcsd
  3. Feb 8, 2013 #2
    I think it changes the equation to one with independent events to that with some conditional probability involved. Given "two intelligent civilizations exist somewhere" find the probability that "two civilizations have contact."

    -Dave K
  4. Feb 9, 2013 #3


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    dkotschessaa, The Drake equation is not meaningful science. Its parameters can only be selected by conjecture or guesses.

    From Wikipedia:
    “The problem, of course, is that none of the terms can be known, and most cannot even be estimated. The only way to work the equation is to fill in with guesses. [...] As a result, the Drake equation can have any value from "billions and billions" to zero. An expression that can mean anything means nothing. Speaking precisely, the Drake equation is literally meaningless...”

    Of course, the Drake equation may be used to stimulate dialogue, but that is the realm of fantasy and science fiction since no empirical evidence (what theories are validated with) exists. In my opinion this post belongs in a different section of these forums: “Science Fiction and Fantasy”.

  5. Feb 9, 2013 #4
    We will indeed have Martians in the future if we colonize Mars.

    If you mean the independent and spontaneous appearance of intelligent life, evolving into advanced communicating beings, on two nearby planets in the habitable zone of a single solar system, within the same time span, are you not reducing the chances considerably? Each time you add a requirement with a probability of less than 100%, you have to multiply. The probability of all this happening to neighbors has got to be a lot lower than it happening to non-neighbors.

    There is the possibility of the seeds or chemical elements of life arriving on two nearby planets simultaneously from external sources and this may have happened in our solar system. It only worked once though, because of all the local requirements and perhaps luck.

    The situation you envisage is much more likely through colonization, but I get the impression this is not what you mean.

  6. Feb 9, 2013 #5
    The drake equation is taken quite a bit more seriously than you are implying. It is a model. It is in some sense speculative, but it does give direction to a lot of the research that some scientists do. You would not know this if your source for science knowledge is Wikipedia

    -Dave K
  7. Feb 9, 2013 #6


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    dkotschessaa (Dave K),

    There is no need to denigrate another member’s ability to assimilate scientific knowledge.

    You have written “Of course all these numbers are speculation... The drake equation is probably more a philosophical equation than a real calculation...”
    You ask, “are there any two civilizations (besides us) out there who have communicated with each other?" And you acknowledge that the Drake Equation is “in some sense speculative...”

    I am simply claiming, with respect, that it is not appropriate to post this material here. The rules of this Astrophysics Forum state “Personal theories or speculations that go beyond or counter to generally-accepted science...” are not allowed.

    Your question for discussion about other civilizations communicating with one another is pure and unadulterated supposition. There are no generally-accepted scientific proofs of the existence of other civilizations.

    Notwithstanding the fact that serious scientists and astrophysicists use the Drake equation to speculate, it remains only that: prognostication. There is not one iota of empirical evidence of any life whatsoever, much less intelligent civilizations, in our Universe except here on earth.

    Accordingly, I respectfully maintain that, instead of posting this material here in the Astrophysics Forum, a “philosophy of science” forum, for example, would be a more appropriate place for these speculations.

  8. Feb 10, 2013 #7
    Very well, let's forget it then. In the meantime, I suggest you write to the Journal of Astrobiology, Bioastronomy (Harvard), Icarus, The International Journal of Astrobiology (Cambridge Univ Press), and Quarterly Journal of the Royal Astronomical Society, and have all Peer reviewed Journal articles regarding the Drake Equation summarily removed.

    -Dave K
  9. Feb 10, 2013 #8
    This is actually part of what I'm questioning. The Drake Equation is written as a series of independent events - which is why you multiply the parameters together. This tends to make the probability smaller and smaller as you multiply.

    If we adjust it in the way I'm speaking of, I think some of the terms will need to be re-written in terms of conditional probability, which raises the chances somewhat.

    And here again I wonder if parts of the drake equation are written correctly. Human beings are horrible at probability - this includes scientists and sometimes mathematicians. The probability of B given A if A and B are not mutually independent is higher than the probability of B times A. I think some of the terms should be written this way, though I could be wrong.

    Well - I wouldn't rule it out. Even on earth, our "different civilizations" supposedly "discovered" one another at some future point in history, though of course we can all trace our origins to Africa. On the cosmic time scales such things may be possible as well.

    -Dave K
  10. Feb 10, 2013 #9
    Did you notice, that when you are not logged in, the word "martians" in your original post and unfortunately as quoted by me, is underlined and hyperlinked to an Ebay website?

    The article on the Ebay site which is offered for sale is most inappropriate. Could you confirm that you are also seeing this in your browser when not logged in?

    Regards, John
  11. Feb 10, 2013 #10
    You don't have to change the question, because that is what the formula calculates.

    According to Wiki: "the number of civilizations in our galaxy with which communication might be possible"

    If it is interpreted as a two way communication involving a specified civilization (for example us) Drake's formula would need another parameter, which would reduce the end probability considerably.

    I don't see what's wrong with multiplying all the factors. If you want to break it down into sections, each section has still then to be multiplied.

  12. Feb 10, 2013 #11
    Yes, I'm seeing this as well. Hovering shows "Link added by Viglink." I assume that this is something that helps pay for PF so I don't have a problem with it, though the choice is unfortunate in this case. I think I'll just stay logged in for now.

    And what, you don't think the ebay martians are adorable? :biggrin:

    -Dave K
  13. Feb 10, 2013 #12
    Well, go ahead, only $9.72. We can't both have them.

    Vigilink says "When a reader buys something, PF gets paid"

  14. Feb 10, 2013 #13
    But is the sentence "the number of civilizations in our galaxy with which communication [with us] might be possible"?

    Because that number is predicated on how far we are from anything, which makes the number quite small, because we seem to be in the galactic Boonies.

    But if there are any pairs of earth like planets in closer proximity to each other, their probability of communicating with each other would be greater.

    True - I'm just saying that some of those sections will also entail some division as well. This changes/raises the overall number.

    On the other hand, I've just been pointed to a completely different model based on percolation theory which seems to address this question in a completely different way than the drake equation, by Geoffrey Landis at NASA:


    "Any given colony will have a probability P of developing a colonizing civilization, and a probability (1-P) that it will develop a non-colonizing civilization. These assumptions lead to the colonization of the galaxy occuring as a percolation problem. In a percolation problem, there will be a critical value of the percolation probability, Pc. For P<Pc, colonization will always terminate after a finite number of colonies. Growth will occur in "clusters," with the outside of each cluster consisting of non-colonizing civilizations. For P>Pc, small uncolonized voids will exist, bounded by non-colonizing civilizations. When P is on the order of Pc, arbitrarily large filled regions exist, and also arbitrarily large empty regions."
    - The Fermi Paradox: An Approach Based on Percolation Theory

    This is a little beyond me (no pun intended) at the moment, but it looks like an interesting model.

    -Dave K
  15. Feb 10, 2013 #14
    I read Landis’ paper. Very interesting. But the Wiki entry on the Fermi Paradox contains a lot more arguments.

    Some of the problems I have are:

    - There is not enough thought given to ET probes. Colonization on the scale discussed would surely only be done with intelligent inorganic probes. The same applies to visits. It’s not clear why a civilisation would want to colonize nearby planets, when it could be done with robots. The investment required to make another planet suitable for habitation would be huge. The counter argument is, that it ensures survival of the species, in case the home planet is hit. Ok, but there is a limit to how many planets it makes sense to colonize, because the cost of spreading risk has to be balanced by the payback. That brings me to my second point.

    - The second typically ignored question is, what is the motivation to colonize at all? I don’t see Darwinian-driven proliferation in the long term, because it’s goal-less. Why would a civilisation want to proliferate, when all its wishes are satisfied and it has its local environment under control, including more than enough resources? That brings me to the question of security.

    - The last factor in the Drake formula reads “the length of time for which such civilizations release detectable signals into space”, but this is passive. I have difficulties to see why an advanced civilisation would bother with us or with any other civilisation for that matter. Detected communications would be checked for threat potential, but not replied to. All that would be automated anyway, including identification of the source, and rerouting of the nearest probe, if worthwhile, to investigate the sender. Quite likely we have already been investigated, but we will likely never know.

    - Finally I would point out that we may be over-dramatizing the whole scenario. Current theory on the spontaneous appearance of the first life on Earth says that its main feature was survival and reliable reproduction. That’s still the case and all the rest is detail. We do get very egoistic, which is a survival trait. Why on earth would an ET capable of visiting us want to visit us, never mind stay hidden and watch us. For what? We have to institute security systems, for survival. More than that is totally unnecessary. Possibly most of the advanced intelligent activity in the galaxy and universe is robotic.

  16. Feb 10, 2013 #15
    Haven't we been doing this for most of our human existence? I don't think our own proliferation has always been due to lack of resources. There seem to be other motivations.

    Again, we are sending stuff out all the time, and we are constantly scanning as well. Are we that different?

    And the probability that we've already been investigated is I think, very low. I think we are still vastly underestimating cosmic scales, travel requirements (FTL) and as people we are bad at probabilities in general.

    Most work in the Drake equation comes from Astrobiologists who study how life evolves and proliferates, and I think the assumptions follow the same Darwinian paradigm that we've observed on earth. So while it's speculation in some sense, taking it as far as intelligent robots is a little much for me personally.

    -Dave K
  17. Feb 11, 2013 #16
    I don’t see proliferation as motivated, I see it as an essential inherited feature of life. However, when a life form realises that it is only proliferating due to inherited tendencies, it may choose to stop proliferating. Environmental factors and the availability of resources will influence this decision. If the proliferation process is stopped, the colonization process will be thereby severely restricted, unless robots are used.

    Why are we doing this? To make friends, or what? I think it is just an instinctive knee jerk, which we cannot necessarily ascribe to other more advance civilisations.

    My view that we have probably been investigated is of course only my personal judgement after reading Landis’ paper and Wiki on the Drake Equation and the Fermi Paradox. I agree that probability is the key word and I am not attempting my own calculations.

    Ultimately I can see only one source of life, namely abiogenesis. The question is, where did it take place and the cited papers imply in a lot of places at different times. We are only arguing about subsequent proliferation and colonization. My objections are twofold: what is the motivation to proliferate having reached an advanced comfortable stage, and if motivated, how credible is it that an organic being would try to explore the galaxy himself personally? Do you really think that we humans are going to shoot our bodies round the galaxy instead of sending robots?

  18. Feb 14, 2013 #17
    Maybe bio-engineering different hard-*** life-forms from our human genome and seeding snow-balls with it might be an option that is better than both sending bodies and expensive robots. Should be relatively cheap and scalable.
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