Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Will we contact aliens soon?

  1. Aug 18, 2010 #1
    I recently made my first blog post on the subject of whether http://reptoavian.blogspot.com/2010/08/alien-contact-forthcoming.html" [Broken]. Do you agree or disagree with my estimates of the variables in the Drake equation? What do you think of my conclusions for the number and spacing between civilizations? Will we receive a communication in the near future?
    Last edited by a moderator: May 4, 2017
  2. jcsd
  3. Aug 18, 2010 #2
    I agree, for the simple reason that the probability of ribonuclease, the simplest protein of life being formed, with all the correct amino acids, is 1x10^167, (can't remember the exact number). Statistic improbability is 1X10^60, and the probability of the 2nd Law of Thermodynamics being reversed (i.e. your car engine freezes upon ignition) is 1x10^80. So, the only way for life to have been formed is through a miracle. I won't go into exactly how life is formed, having previously found that religious discussions tend to generate flame wars, but suffice it to say that from this (and many other reasons, some mentioned in your post) that contacting life is very unlikely. I would go so far as to say impossible.
  4. Aug 18, 2010 #3
    Nobody has ever claimed that all of the correct amino acids spontaneously fell together at one time, which is where you get your absurd number.

    You also make the baseless assumption that life can only be based on one specific protein.

    I refuse to make any predictions about the possibility of life outside of our planet, but think it's incredibly shortsighted to wave off the idea as impossible.

    Then you go a step further and make the incoherent argument that since life cannot exist without some religious explanation, there can be no life elsewhere. Yet, there is life here. YOU are life. If there is some sort of supernatural creator as you suggest, then that creator could have created life elsewhere. Therefore, contact with alien life is not impossible. Your argument is self-contradictory.
  5. Aug 18, 2010 #4
    Re: Will we contact aliens soon? (@Jack21222)

    Nobody has ever claimed that all of the correct amino acids spontaneously fell together at one time, which is where you get your absurd number.

    I went and found the source. It is a paper in Biology Today (which was peer reviewed!) published by Eugene. V. Koonin. In it he states:

    The requirements for the emergence of a primitive, coupled replication-translation
    system, which is considered a candidate for the breakthrough stage in this paper,
    are much greater. At a minimum, spontaneous formation of: - two rRNAs with a
    total size of at least 1000 nucleotides - ~10 primitive adaptors of ~30 nucleotides
    each, in total, ~300 nucleotides - at least one RNA encoding a replicase, ~500
    nucleotides (low bound) is required. In the above notation, n = 1800, resulting in E
    <10-1018. <http://www.biology-direct.com/content/2/1/15>​

    Evolutionist and theoretical physicist Paul Davies, for example, considers random self-
    assembly of proteins to be “a nonstarter”. (Paul Davies, The Fifth Miracle, The Search for the Origin of Life (New York: Simon & Schuster, 1999),
    p. 91).)

    Together with Chandra Wickramasinghe, Sir Frederick Hoyle, a prominent atheist astronomer stated:

    Precious little in the way of biochemical evolution could have happened on the
    Earth. It is easy to show that the two thousand or so enzymes that span the whole
    of life could not have evolved on the Earth. If one counts the number of trial
    assemblies of amino acids that are needed to give rise to the enzymes, the
    probability of their discovery by random shufflings turns out to be less than 1 in 10
    to the power of 40,000.[8] (Sir Fred Hoyle and Chandra Wickramasinghe, Where Microbes Boldly Went, New Scientist, vol. 91 (August 13, 1991), p. 415.)​

    You also make the baseless assumption that life can only be based on one specific protein.

    Ribonuclease is the simplest protein of life and as far as I know, necessary for life. It is hard to reproduce without RNA, and that is one of the qualifications of life.

    Then you go a step further and make the incoherent argument that since life cannot exist without some religious explanation, there can be no life elsewhere. Yet, there is life here. YOU are life. If there is some sort of supernatural creator as you suggest, then that creator could have created life elsewhere. Therefore, contact with alien life is not impossible. Your argument is self-contradictory.

    I was wrong in making the blanket statement "Life is unlikely". What I should have said, was "My view of that supernatural creator makes life unlikely; I don't think the creator created life elsewhere than earth." Exactly why I don't want to go into, but you made a good point. Note that I am not saying truth is relative , but I am accepting that my conclusion is based on belief (a well-founded belief IMO, but that is out of the scope of my argument).

    I hope that made sense.

    Edit: I really (really) hope that I am abiding by the board rules here; I tried to make my explanation as religiously neutral as possible. If the moderators would like to edit or delete the last part of my post, that would be fine.
    Last edited: Aug 18, 2010
  6. Aug 18, 2010 #5
    You proved my point, those people are saying that RNA didn't spontaneously fall together randomly. That does NOT mean their explanation was "god did it." If that was their conclusion, you would have quoted that. Quoting scientists out of context to make them appear to defend creationism is a very old tactic.

    Your belief that a creator would only create life on earth and nowhere else seems odd to me. I can't wrap my head around it at all. If you'd like to explain it to me, feel free to use the PM function, I won't argue that point here. I have a feeling this thread is heading for a lock anyway.
  7. Aug 18, 2010 #6
    I'm trying to keep this discussion as friendly and non-religious as possible. My apologies for anything else! I am also sorry if this thread got hijacked into an 'origin of life thread'.

    I don't think I'm misquoting the scientists. All I was trying to find is peer-reviewed evidence which says that abiogenesis is improbable/impossible and then stating my conclusions from that evidence. And they aren't only my conclusions. Sir Fred Hoyle, one of the scientists quoted above, stated:

    If one proceeds directly and straightforwardly in this matter, without being deflected by a fear of incurring the wrath of scientific opinion, one arrives at the conclusion that biomaterials with their amazing measure or order must be the outcome of intelligent design. No other possibility I have been able to think of...​

    Edit: I did a little research and I think what you are getting at is Hoyle's Fallacy (the term is coined by Dawkins). I have heard of people (e.g. Richard Dawkins) who think that Hoyle did commit a fallacy, but I also know of (and personally know) many research scientists who IIRC did not believe Hoyle committed a fallacy. Also, please don't go to Wikipedia's page on the subject, as it is almost a direct quote from Ian Musgrave's website (he is one of the leading anti-Hoyle scientists, and his site is not peer-reviewed). In fact, Wikipedia treats all of ID as pseudoscience, so it is not a good source. I think that the board is out on this one. However; I enjoyed the discussion!
    Last edited: Aug 18, 2010
  8. Aug 18, 2010 #7
    I was mainly referring to the abuse of Gould's argument for evolutionary stasis. Dawkins runs into a similar thing with his writings.

    Any author that starts off by outlining a scenario showing something to be improbable (such as the evolution of the eye) but then goes on to demonstrate exactly how it happened runs the risk of somebody else only quoting the first part and throwing away the second. Based on what you chose to post and what to omit, your post at least looks like the same sort of thing.
  9. Aug 18, 2010 #8
    Do you mean Koonin? Or Davies? I went through all of my posts and I didn't quote from Gould. I thought he mainly was a proponent of Punctuated Equilibrium, which I didn't mention at all.
  10. Aug 18, 2010 #9


    User Avatar
    Staff Emeritus
    Gold Member

    There is a thread right now in the Biology subforum here that goes into great length regarding hypotheses and experiments into abiogenesis and a small discussion of what non-RNA based life might look like. Well, not really on the second count, but the point is just that life doesn't need to be made of any particular thing; it just needs to be self-replicating and capable of locally reversing entropy. How many ways that is possible is not possible to know a priori through any form of human reasoning, because frankly, our imaginations just aren't good enough.

    Besides that, we actually know that many of the organic chemical precursors of RNA and protein are found elsewhere because they've arrived on meteorites.

    I would also expect that evidence of intelligent intervention to cause life to come into existence against its otherwise improbability would actually constitute good evidence that life is more likely to exist elsewhere rather than less likely. Why would a creator create such a huge universe only to shove life into a tiny little random corner?
  11. Aug 18, 2010 #10
    Oh. My high school biology text (I'm not in college yet--only 9th grade) said that DNA and therefore RNA was one of the criterion for life. Now I have another thing to research...
  12. Aug 18, 2010 #11


    User Avatar
    Science Advisor
    Homework Helper

    Going to the original question:


    Sounds good.

    ne isn't the fraction of planets/moons that can support life. It's the number of planets per star that can support life. So ne would be 1 or 2 for the sun, not 1/50. I think a number for ne on the order of 0.5-1 would be reasonable.

    Strongly disagree with your reasoning here. You are using an incredibly biased sample as your 1 data point. I think a number on the order of 0.01 - 0.1 would be much more reasonable.

    Again, I strongly disagree with your reasoning, because you are using an incredibly biased 1 data point. I think something like 0.01 would be much more reasonable.

    1/6 seems ok, but maybe a bit too optimistic.

    10,000 years seems reasonable.
  13. Aug 18, 2010 #12
    I was stating that the way you presented your quotes is very similar to how Gould and Dawkins have their quotes twisted.

    I won't comment on the quotes you posted until I get a chance to read them in-context. I don't have that opportunity at the moment.
  14. Aug 18, 2010 #13
    it's always amusing to see science turned to religion, politics and other completely irrelevant issues.

    but back to the topic:

    my intuition is that alien contact is extremely improbable. i did my own version of the drake calculation roughly as follows:

    number of galaxies: 1 (ours, including the magellanic, globular clusters and other remnant satellites). i know, there are hundreds of billions of galaxies. this assumption only factors in a multiple that you have to take out later; nobody can justify a physical mechanism for travel over red shift multiples.

    number of stars: 120 billion (more or less).

    now, we have good empirical evidence that planets form primarily around smaller, cooler, G or F stars. these also burn longer, which would be necessary for life to evolve. the current census suggests these stars comprise about 25% of all stars in the galaxy. so:

    number of stars with planetary systems: 30 billion.

    unfortunately, planets seem to come in a wide range of sizes, and seem to form at various distances from their parent star. neither planets as small as mars, nor as large as jupiter, seem likely to form carbon based life of any durability, based on what we see. size matters a lot. in addition, a right sized planet has to be at the right distance from the star.

    now, many of the recent candidate planetary systems discovered show enormous planets very near and very far from their stars; in other words, size and location seem distributed somewhat randomly. the probabilistic approach, then, would be to take our solar system as a representative result of the typical planetary lottery: a range of sizes in a variety of orbital locations. for simplicity, assume the planetary size distribution is representative and only the orbital locations are randomly swapped around. then the total permutations are 8!, or roughly 40,000 permutations. if we consider the earth and venus as interchangeable physical sizes, then the probability of a planetary system having the right sized planet in the right sized orbit is 1/20,000.

    number of stars with earthlike planets: 150,000.

    from here we have to look at life processes on this planet. everyone says it's possible for other kinds of life forms to exist, but water, oxygen, carbon molecules, simple carbohydrates and amino acids are plentiful in the universe, and chemistry makes a steep argument for a silicon or aluminum based life form. in addition, life evolved relatively quickly on earth, within the first 500 million years or so, so carbon seems very eager to get complex things rolling. therefore i estimate the probability of life as that emergence period over the current total age of the earth: 4.5 billion years. that's a probability of about 90%.

    number of earthlike planets with carbon based life form: 135,000.

    one of the strongest arguments for evolution is just how much time it has required for really complex life to evolve. but one of the strongest arguments against intelligent life is just how much time it takes to evolve. now, i prefer to date "intelligent life" on earth from the time of isaac newton, because it was not until then that a terrestrial life form had any clear conception of what the universe was like. but newton lived only 300 years ago. we therefore have a much smaller probability of *intelligent* life in our galaxy, 300 years over 4.5 billion years, or 1 in 15 million.

    number of planets with intelligent life: 0.009 (lower limit)

    clearly that estimate is too conservative, because after intelligent life evolves, it may continue for a considerable period. however, mammalian species on our own planet do not seem to endure for very long, between 1 million and 10 million years (with some outliers). and while we can conjecture that one intelligent species might evolve into some other, even more intelligent but different species, it's also possible that the intelligent life form will simply go extinct. so split the difference and assume an intelligent life form goes extinct after 5 million years, and assume also that the hypothetical earthlike planet exists for the entire normal life of its smallish star, about 10 billion years. this gives us a probability that an earthlike planet has intelligent life of about 1 in 200.

    number of planets with intelligent life: 675 (upper limit)

    that's a huge range, in logs from about 3 to -2, but taking the middle order of magnitude implies that the number of contemporaneous (relativistically) intelligent civilizations in our own galaxy is in the low single digits.

    most reasonable estimate of the number of intelligent civilizations in our galaxy: log ~0.4 (3).

    admittedly this kind of analysis is fitted with a lot of conjecture, but i've suggested that, cosmological principle applied right down to our own species, there isn't a lot of reason to be optimistic about alien visits anytime soon. and i haven't even considered the probability that the civilization must not only evolve beyond newton and then beyond einstein, but beyond any manner of physical transportation we can conceive of now, and in addition manages the exploratory problem of surveying the billions of G or F type planetary systems necessary to find those two other intelligent civilizations.

    we are almost certainly not alone in a universe of uncountable galaxies and stars, all churning out carbon at a copious rate; but we are certainly isolated from the few other intelligent civilizations that exist, in our own galaxy and elsewhere.
  15. Aug 18, 2010 #14


    User Avatar
    Staff Emeritus
    Gold Member

    It's necessary for life that we've observed to exist, but that's like saying oxygen inhalation is necessary for mammalian life. Sure, but there are other kinds of life. We don't know if there are forms of life that are not based on nucleotide encoding but there is no logical or physical reason to rule out the possibility.
  16. Aug 18, 2010 #15
    ok, but don't stop there. what's the probability of your possibility? what specific type of alternative life form do you have in mind? what evidence do you have that an alternative metabolic chemistry can produce the required energy to sustain an organism that will require the components of "intelligent" life -- perceptual organs, complex nervous system, appendages necessary to physically manipulate the environment, and so on? what kind of planetary environment is presupposed for that kind of metabolism to evolve?

    there seems to me a kind of unjustified fear of anthropocentrism in the idea that we are somehow bizarre, or that many other types of life form are possible (though we can't say what they might be), or that life on earth is somehow a "biased sample" (whatever that means). explain; show your work.

    true, the appearance of life forms anywhere near our level of social complexity may be stupefyingly rare. but those rarities, gathered together, probably show remarkable similarities across many different attributes -- language, for example. indeed, the cosmological principle almost requires it.

    at the same time, if there are grounds for constructive conjecture, then reveal them. waving away one assumption with the argument that it might not possibly everywhere always be true seems to forget newton's advice not to make hypotheses -- at least, not hypotheses you can't back up.
  17. Aug 18, 2010 #16
    Quite all right, the probability of the origin of life is one of the variables in the equation, so it seems like a topic related tangent.

    I'll have to check out those threads in the biology section. True that life is probably more diverse and tough than we suspect, but since I only have Earth's example I chose to play it safe and stick with our kind of life. I remain hopeful that an alien message is on its way. Nature always seems to have some tricks up her sleeve.

    Thanks for keeping the thread focused. I'm glad you agree with most of my estimates. True that Earth is my only data point and I'm biased with things like the probability life and complex life evolving, but I stand by my estimates. I basically stuck with the old Copernican principle that we're average. Why do you exclude moons from the number of worlds per star capable of supporting life?

    Its likely life is rare, but there is cause for optimism in your analysis. I notice you haev a large number of earthlike worlds in the galaxy with some sort of life form on them. If only a few intelligent life forms evolve and their civilizations last for a really really long time, then we would be quite likely to be able to communicate since they could colonize all those habitable worlds.
  18. Aug 18, 2010 #17


    User Avatar
    Staff Emeritus
    Gold Member

    My point is more that there is no way to back up such a hypothesis. I'm just laying out the limits of physical and logical possibility. I'd guess life probably requires carbon and water. I highly doubt it is impossible for life to arise without RNA, however. Scientists and science-fiction writers and laypeople alike have been warning for decades not to assume that life "out there" is going to necessarily look or act anything like we do. I never thought there would be controversy in expressing such a maxim.

    If you want exacting detail of what non-RNA based life might look like, there are scientists who explore alternative biochemistries. I'm not one of them.
  19. Aug 19, 2010 #18


    User Avatar
    Science Advisor
    Gold Member

    Well, life may not require oxygen - although any other catalyst appears improbable. Perhaps some weird combination of chlorine and strong electrical fields would work. Perhaps also not all life 'lives' at our speed. Some species may blaze in and out of existence in the twinkling of an eye, or at the speed of detectable neutrino or dark matter annihilation. The possibilities are endless. The point remains it only makes sense to search for oxygen fueled carbon life forms. There are surely many in a galaxy this size, even assigning pessimistic values to the drake equation. How many are 'intelligent' - who knows? How many of those would consider us any more fascinating than a fungus - who knows?

    Say an intelligent, civilized, life form [not unlike our own] had a mere million years head start in a star system not terribly far away. Would they need, care or even be able to colonize distant star systems? If relativity is absolute, it would be economically impractical, if not impossible, to colonize any planet more more than a few light years distant. Expecting to communicate with them over the RF spectrum - priceless. You probably have a better chance at alerting the US president of your presence by tapping your finger on a hollow gourd from a root cellar.
  20. Aug 19, 2010 #19
    Correction: Life DOESN'T require oxygen; at least not free oxygen. There are plenty of species on this planet who do not use O2, both microscopic and macroscopic.
  21. Aug 19, 2010 #20

    Life is thought to have arisen on earth in an oxygen free (anerobic) environment. Oxygen even posed a threat to early life. Natural selection just resulted in a preference for oxygen breathing life forms. Also, if a civilization lasted for a million years, it could send out machines. I'm a big fan of the idea that extraterrestrial machine intelligence will likely be the first contact we make. Machines could colonize any world that would offer resources to build futher machines and could spread throughout the galaxy. A civilization that lasted a million years could also send out probes to engineer life on previously barren worlds.

    In response to the earlier more religion oriented discussion, I wrote a second blog post on intelligent design: http://reptoavian.blogspot.com/2010/08/intelligent-design.html
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Similar Discussions: Will we contact aliens soon?
  1. If there were aliens (Replies: 26)

  2. Humanoid Aliens (Replies: 11)

  3. Living with aliens (Replies: 2)

  4. Alien life (Replies: 78)