Nov 02 2012

How Common Is Life in the Universe

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17 Responses to “How Common Is Life in the Universe”

  1. Mark Ericksonon 02 Nov 2012 at 11:19 am

    I’ve heard the Jupiter comet sweeper argument before, but I don’t understand how that could be such a big deal. Considering that the planets are all on one plane, anything that comes at Earth from the “bottom” or the “top” wouldn’t get swept away by Jupiter. Even if you say one-fourth of the year Earth is close enough to Jupiter that it could influence oblique approaches to the Earth, that leaves plenty of time for the Earth to be less protected. Does this objection make sense?

  2. Bronze Dogon 02 Nov 2012 at 11:29 am

    Given what I know, it seems pretty unlikely to me that there are any nearby technological species, and by “nearby,” I think I mean within our galaxy. Most of our planet’s life was spent in single cell form, and the time we’re going to spend as a technological species could likely be very short with all the doomsday weapons we stockpile. Presumably, advanced aliens might face similar crises. Of course, it could very well be that advanced civilizations that last long enough become stable on larger timescales, raising the chances, but I wouldn’t bet on it.

    Add on all the hypothetical necessities like a stabilizing moon around the life bearing planet, an outer jovian planet, and so on, and I’m even more skeptical.

  3. Steven Novellaon 02 Nov 2012 at 11:36 am

    Mark – but most objects that would threaten the Earth are also in the plane of the solar system, not coming from above or below. At some point at their journey to the inner solar system they are likely to encounter Jupiter’s gravity and either be swallowed up or shot out of the system.

  4. Mark Ericksonon 02 Nov 2012 at 11:55 am

    Thanks, I went to Wikipedia “Comet” to get this: “Most short-period comets (those with orbital periods shorter than 20 years and inclinations of 20–30 degrees or less) are called Jupiter-family comets. Those like Halley, with orbital periods of between 20 and 200 years and inclinations extending from zero to more than 90 degrees, are called Halley-type comets. As of 2012, only 64 Halley-type comets have been observed, compared with nearly 450 identified Jupiter-family comets.”

    Should have done this first, but maybe others had the same question.

  5. SARAon 02 Nov 2012 at 12:20 pm

    I agree about your weakest link thought. It strikes me that if the hydrogen and o2 exist on the planet, then it just needs conditions, not asteroids to get water.

    In fact all of the theory rides the assumption, as you noted, that the only way to evolve life is the way earth did.

    Considering chaos, it just feels to me, very unscientifically, that there would be more than one way to crack this egg. I mean just because we are the delicate creatures that need a soft and warm world, doesn’t mean that life couldn’t develop in a world that we could not survive in.

  6. eiskrystalon 02 Nov 2012 at 12:41 pm

    it seems very likely that billions of years of stability is necessary

    If by stability you mean a constantly evolving atmosphere, random ice ages and some mass extinctions. ;)

  7. Bronze Dogon 02 Nov 2012 at 12:52 pm

    I’m certainly open to weirdness like silicon-based life and such, which would have different needs (Though regular meteor/comet bombardment would probably still be bad for them). I don’t remember where, but I vaguely remember some weird concept of life that would form around neutron stars, powered by the electromagnetic forces. Can’t say if the show was serious or if they were just trying to woo the audience.

    Given what I’ve heard of abiogenesis experiments succeeding at producing complex organic molecules under many conditions and one clip of Tyson talking about how the elements in our body are pretty close to the proportions they make up in the universe as a whole, I suspect simple organic life is probably pretty abundant in the universe.

  8. Karl Withakayon 02 Nov 2012 at 2:45 pm

    How common is life? I suspect that it’s probably extraordinarily rare (that is, you’d have to look at an exceptionally large number of star systems and planets before you found another one with life*), but in a universe with on the order of 10,000 billion billion stars, the number of planets in the universe with life on them is probably quite large.

    Consider that if there is only one planet with life for every one hundred billion stars (which would make life extremely rare), that would still mean there would be on the order of 100 billion planets with life in the universe, though probably only around one per galaxy.

    Life is likely both abundant and rare at the same time, depending on how you look at it.

    * At least life that does not have a common origin with life on Earth. Discovering life on Mars that shared a common origin with Earth’s organisms wouldn’t change my opinion on this matter at all. Finding life on Mars with an origin distinct from that of earth’s life would cause me to reverse my opinion.

  9. hoebywanon 02 Nov 2012 at 6:32 pm

    If I was to bet money on it In would say there have to be many civilisations more advanced technologically than us. Why? Just sheer enormously, stupendous numbers and for me we seem to have an over inflated opinion about how well we have done with what we have. We could have done better and probably should have and with better conditions it is likely we would have too.

  10. locutusbrgon 03 Nov 2012 at 12:10 am

    Our relatively large satellite does more than sweep life killing asteroids from the sky. It stabilizes the earths axis which in turn helps keep climate stable. There is also the relative tidal effect due to its large size. This probably contributed to the evolution of life outside of the sea. That is just one small part of the complexities of finding a similar world as a livable planet.
    Life and evolution of “advanced life on earth” is also subject to time. Given our N-1 example, we are just a “Planck Length” second of the history of the universe. Given a finite life to our star, and current lack of faster than light travel we”humans” in some form will have a short finite existence on a galactic scale. It took us one third of our stars life to appear and if we don’t figure out how to leave or prolong the life of our solar system we will only be around a tiny fraction of the remaining life of the universe. That is also assuming we don’t kill ourselves some other way. Even if we make maximum solar life of our system it will be unlivable well before the collapse of our star into a dwarf star. My point is that I am sure that there is life somewhere in the universe but finding even simple life is a lottery ticket win within our short lives. Little chance we will ever see evidence of “Advanced” life resembling ours. If we say there are 1.6 trillion Goldilocks’s earths in our “local” part of the universe, it is entirely possible that 2/3 are either in early formation or late life resulting in unlivable conditions. Given factors of time, distance and our short lifespan odds weigh heavily against us. For all we know we are the fruit flies of the universe with ridiculously short lifespans.

  11. norrisLon 03 Nov 2012 at 5:43 pm

    The Drake Equation is an estimate of the probability of there being a technological civilisation that releases detectable signals into space.

    The Drake equation states that:

    where:
    N = the number of civilizations in our galaxy with which communication might be possible;
    and
    R* = the average rate of star formation per year in our galaxy
    fp = the fraction of those stars that have planets
    ne = the average number of planets that can potentially support life per star that has planets
    fℓ = the fraction of the above that actually go on to develop life at some point
    fi = the fraction of the above that actually go on to develop intelligent life
    fc = the fraction of civilizations that develop a technology that releases detectable signs of their existence into space
    L = the length of time for which such civilizations release detectable signals into space

    This is all very well, but the thing is we have no real idea of what any of the actual numbers pertaining to the above equation may be.

    As Steven has said, we have an N of 1. While this may change tomorrow, it may also never ever change. That would be quite sad.

  12. norrisLon 03 Nov 2012 at 5:50 pm

    Historical estimates of the parameters

    Considerable disagreement on the values of most of these parameters exists, but the values used by Drake and his colleagues in 1961 were:[8][9]
    R* = 1/year (1 stars formed per year, on the average over the life of the galaxy; this was regarded as conservative)
    fp = 0.2-0.5 (one fifth to one half of all stars formed will have planets)
    ne = 1-5 (stars with planets will have between 1 and 5 planets capable of developing life)
    fl = 1 (100% of these planets will develop life)
    fi = 1 (100% of which will develop intelligent life)
    fc = 0.1-0.2 (10-20% of which will be able to communicate)
    L = 1000-100,000,000 years (which will last somewhere between 1000 and 100,000,000 years)
    Drake states that given the uncertainties, the original meeting concluded that N ≈ L, and there were probably between 1000 and 100,000,000 civilizations in the galaxy.

    The above info comes from that “wonderful source of scientific information”, Wikipedia. :)

    Given that, as of this morning we still have an N of 1, I still believe the above estimates can be nothing much more than pure speculation.

  13. Jared Olsenon 04 Nov 2012 at 5:48 am

    Even though I SO want to believe there are other civilizations out there, I think it’s unlikely. I’m pretty sure that the universe is teeming with micro-life, but intelligent life? not so sure. Intelligence is just one of the myriad ways an organism evolves to deal with it’s environment, not the teleological end goal that it’s sometimes made out to be. Amongst our 50 million or so organisms only one (us) developed high end smarts.

  14. Alex Clarkon 04 Nov 2012 at 11:49 am

    “There almost certainly is life elsewhere in the universe”. This is just a guess — we don’t have an N of 1, we have an N of 0. The solar system we know about is not a random one, but one that has life in, so its existence doesn’t tell us anything about the probability of life other than that it is nonzero. If the probability of life is 10^{-100} on a given planet, then there will still be intelligent life on the planet that we live on.

    As a result there is no argument that says there is likely to be other life in the universe, since we have absolutely no way of estimating the quantities in the Drake equation, which lends a spurious air of precision to what is basically just an exercise in handwaving.

  15. Aardwarkon 05 Nov 2012 at 3:28 am

    The most important thing, when life in the Universe is concerned, is not to jump to any conclusions based on fragmentary data.

    However, to say that we ‘just don’t know’ would be equally unfair and ultimately untrue. There is a lot of data that could help drive the investigation of various hypotheses. And plenty of room for the unexpected, of course.

    The ongoing astrobiological revolution is based on integrating the knowledge gained by various disciplines investigating various fields by various methods and applying some creative (but highly critical) thinking to it all. In this sense, it becomes the most exciting and gratifying scientific endeavour of all times.

    But if we are to jump to our feet and shout every time there is a new piece of the puzzle brought to the table (such as ‘methane on Mars’, or ‘no methane on Mars’) and be drowned under a vast mountain of senseless media sensationalism, than crucial points will likely begin to fade from the picture. So will the interest of serious people for the, otherwise fascinating, subject.

    Specifically, since this article mainly discusses Rare Earth Hypotheses (REH), which include, but are not limited to ‘Rare Jupiter’, ‘Rare Moon’, and ‘Rare Asteroid Belt’, I would like to bring to the attention of this community a recently published book. It is titled “The Astrobiological Landscape” and one chapter is specifically devoted to discussing REH. It is the most clear, concise, comprehensive and well-written treatment of the subject that I personally have had the chance to encounter so far (although I admit there may be some ‘observation selection effect’ at play).

    In the same book you will also find highly enlightened review of other astrobiological ‘big questions’ and the underlying philosophical foundations – in brief, I highly recommend the book. I also apologize to all who are already aware of it, or have read it.

    http://www.amazon.com/Astrobiological-Landscape-Cambridge-Astrobiology-ebook/dp/B008CDSB30

  16. Christopher Newellon 12 Nov 2012 at 12:17 am

    An often over looked factor in discussions of this kind is distribution of life in the universe and how it might be effected by interstellar migration. It could be that even in a universe where life seldom emerges and where that life seldom develops advanced enough technology to travel to nearby stars, that the total population of the universe would be quite high due to this sort of technological panspermia. Once a civilization passes through the bottleneck it would become tenacious enough to persist almost indefinitely due to the low probability of interstellar disasters and by sheer numbers. In a universe of this kind, we might expect to see a kind of large scale clumpiness where whole galaxies or even galactic clusters are populated by life which originated from a single point, while other areas would be devoid of life. There would be the equivalent of urban areas, rural areas and wilderness. Given enough time, this sort of universe might mature into a more homogeneous one, but with most life stemming from a handful of planets. This alludes to the Fermi paradox, which isn’t really a paradox because due to our limited knowledge, we could be right in the middle of a cosmic “downtown” and not even realize it. Alternatively, if we’re in the desert, it might be very difficult for SETI searches to turn up anything, even with improved methods; because of the great distances of these “cities” and even if the populated areas are quite large.

  17. Doctorrickon 12 Nov 2012 at 6:08 pm

    I echo what a few have already said. Based on extremophiles found here on Earth, I think life is probably relatively common in the universe. Perhaps even “complex” (i.e. multicellular) life. What I am far less certain about, is how common intelligent life is. It doesn’t seem to me that intelligence is that huge an evolutionary advantage, especially in terms of its biological cost. A number of different events have brought human to near extinction, and intelligence really didn’t help much (asteroids, ice age, pandemic). At this point in our intelligence development, we like to think our intelligence would help with survival, and that is probably true. However not sure how true that is for most of our history on the planet.

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