Whee are the aliens?

Discussion in 'Science and Technology' started by Warped9, Aug 25, 2013.

  1. FPAlpha

    FPAlpha Vice Admiral Admiral

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    You are talking about empty regions.. what constitutes a region in interstellar terms? A region in earth terms may be something you could traverse by car within an hour or two so how do you apply that to interstellar distances?

    If FTL is possible by any means it might be that Earth-Alpha Centauri is just a short hop around the block, who knows? Maybe we live in a greater region that has a few civlizations and we just didn't encounter them or catch their radio signals because there's a ton of it flying through space on all frequencies.

    All i'm saying is that maybe we are not interesting enough to make official contact or we are in such a fragile state that official contact would do more harm than good so we are left alone for now. Maybe we are being studied in secret out of scientific curiosity and maybe some alien students are doing their xenobiology doctorates about us but so far no one seemed to think to contact us directly.
     
  2. JarodRussell

    JarodRussell Vice Admiral Admiral

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    The nearest planet that MIGHT be able to sustain life is Gliese 581 d and is 20 lightyears away. And not every planet in the habitable zone of a star will automatically develop life.

    Life is rare. The idea of a vastly overpopulated galaxy as in science fiction is, well, fiction.

    Alpha Centauri highly likely doesn't contain any traces of life. And that's the point. Even if FTL travel is possible, it's not just "a hop" from one system to the next.

    Planets with intelligent civilizations might be thousands, ten thousands of light years apart.
     
  3. CorporalCaptain

    CorporalCaptain Admiral Admiral

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    The Milky Way is about 100,000 light years in diameter and about 1,000 light years thick. Its volume is therefore roughly 7.9 trillion cubic light years. (This assumes a cylindrical shape, and neglects the central bulge; see the note at the end of the paragraph.) A sphere with a radius of 1,000 light years has a volume of approximately 4.2 billion cubic light years. That's less than one tenth of one percent of the overall volume of the galaxy. The actual figure is about .05 of one percent. (If the whole central bulge were counted, then that fraction would be even smaller.)

    Of course, stars are not evenly distributed. By http://imagine.gsfc.nasa.gov/docs/ask_astro/answers/980123d.html, there are approximately 14,600 stars within 100 light years of Earth. If we assume that stars are distributed with the same density out to 1,000 light years, then, extrapolating outward, there are about 10^3 as many stars, or roughly 14,600,000 stars within 1,000 light years of Earth. (The sun is probably less than 100 light years from the galactic plane.) The presently accepted figure of the number of stars in the Milky Way galaxy is conservatively 100 billion. Therefore, within 1,000 light years of Earth are only about one percent of one percent of all the stars in the galaxy.

    However you slice it, it is highly premature to say that life is rare, just because there's no sign of it in our immediate stellar neighborhood.
     
  4. YellowSubmarine

    YellowSubmarine Rear Admiral Rear Admiral

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    Unless you know how life started, you have no way of telling how easy it is.

    Well, you do, but it involves finding alien lifeforms.
     
  5. MacLeod

    MacLeod Admiral Admiral

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    Can you prove your statement that alien life is rare? For all we know there is life under the ice on Europa, Life could have existed on Mars at one point. We only really have life on Earth to act as a basis of what we call life, so there might be life existing somewhere were we didn't think it could exist. At one point didn't we believe that life couldn't exist in the deep oceans on Earth?

    I suspect when alien life is discovered it might not be exactly what we were expecting it to look like.

    Life might be rare it might be fairly common or anywhere inbetween we have no way of knowing. All we can perhaps say we is to a reasonable degree the number of celestial objects which have life on them is infinitesimal when comapred to the number of celestial objects
     
  6. Edit_XYZ

    Edit_XYZ Fleet Captain Fleet Captain

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    There are compelling arguments to believe that life is rare - at least in the Milky Way galaxy:

    1. Abiogenesis.
    What is the road from a bunch of chemicals to the "simplest" molecules that can replicate themselves halfway reliably?
    Let's - VERY optimistically - assume that a specific chain of 100 chemical reactions are enough to create this "simplest" molecule.

    Now - Darwinian selection has no part in creating this molecule; for Darwinian selection, you need self-replication, which you do not yet have.
    Which leaves probability in charge. For a very rough approximation, calculate factorial 100. It gives a number so close to 0 as the chance of this "simplest" molecule emerging, that the chances are life on Earth is alone in the observable universe (and a huge chunk of the unobservable one).

    Conclusion - abiogenesis is rare. VERY rare. Even if my factorial 100 approximation is exceedingly rough and even if there are hundreds of billions of Earth-like worlds in our galaxy, the chances are only ours ever gave birth to life.


    2. The Fermi paradox.
    This is based on a crucial and highly relevant fact:
    An intelligent species, bound by the speed of light and various other engineering constraints (let's say, it can only reach 20% c) can colonise the entire Milky Way galaxy in 500.000+change years. And, once an intelligent species colonised other solar systems, this species (including its descendant species) is effectively immortal; no catastrophe can destroy it any longer.

    The galaxy had enough heavy elements to evolve life since ~6-7 billion years ago. So, where are these ancient species? The entire galaxy should have been colonised may times over; they should be here, in our solar system - and everywhere else in the galaxy.
    And then there are the robotic emissaries - von Neumann probes - of these species; also absent.

    The immensity of time is FAR greater than the immensity of space (within our galaxy).

    The pro 'life is common' argument relating to this fact tries to implausibly lump ALL these hypothetical species into a single planet-of-hats, adverse over billions of years to interstellar exploration/colonisation - choosing to ignore that even a single species will create many civilisations with different values and priorities during its history; that each species will be different from the others.


    The Fermi paradox is NOT about whether intelligent species can send strong radio signals or about how their home planets look like.
    It's about the fact that such intelligent species, if they exist, should already be in our solar system - and everywhere else in the galaxy.

    They are not here; that's a very strong argument for their non-existence within the Milky Way galaxy.
     
    Last edited: Aug 27, 2013
  7. FPAlpha

    FPAlpha Vice Admiral Admiral

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    The Fermi Paradox expects alien life to contact us or that we discover it.. as i already said what if the Aliens just don't want to contact us for whatever reason (we know also nothing about alien psychology so it's useless to apply our psychology and in extension our feeling of curiosity to aliens) and given the vast space and our limited technology we just may missed it or didn't discover it yet.

    We discover planets by mathematical methods and we draw conclusions based on the data we receive. If aliens do the same and looked at our system all they would be able to deduct (given the same methods) is the number of planets and that one or two of them are in the habitable zone.. one might actually carry water.

    That's all so the Fermi Paradox, as interesting as it is, is really a flawed assumption.
     
  8. Edit_XYZ

    Edit_XYZ Fleet Captain Fleet Captain

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    FPAlpha, as I said, diverse alien species each creating many civilisations are not a planet-of-hats. And your other objections are already answered to in my previous post, as well.
     
  9. Warped9

    Warped9 Admiral Admiral

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    Every generation is so sure of its grasp of science only for later generations to learn how to shine a light into previously dark rooms.

    The universe is so vast and stranger than we can imagine that's it's folly to assume we already have definitive answers. I suspect we don't even know we're overlooking something, perhaps something crucial, in trying to answer this question.
     
  10. Lindley

    Lindley Moderator with a Soul Moderator

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    Two objections to this argument. First, chemical reactions are highly sensitive to conditions. If the right conditions exist, they can easily drive a particular product from 1% to 99%. We aren't entirely sure what the right conditions are for ambiogenesis, of course.

    Second, even an exceptionally unlikely event becomes probable when there are enough chances. Winning the lottery is exceptionally unlikely, yet someone seems to win every few weeks because there are so many players. Similarly, there could be trillions of ambiogenesis precursor molecules out there. Granted, 100! is much larger than one trillion, but the odds are at least improved somewhat.
     
  11. Relayer1

    Relayer1 Rear Admiral Rear Admiral

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    Possible, but you also have to take into account 'deep time'. Even if there have been many intelligent civilisations within detectable range, over the (pretty unimaginable) length of time they could have developed in, the chances of them evolving at the same time as us (or at least at the right time for us to have picked up their traces) are very very small.
     
  12. Edit_XYZ

    Edit_XYZ Fleet Captain Fleet Captain

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    Indeed - the conditions needed for the first of 100 chemical reactions must exist; followed by the conditions needed for the second of 100 chemical reactions; etc; etc. Throughout the process, conditions that destroy the fledgling molecule-to-become-self-replicating must not come to pass.

    The chances of 100 such conditions existing in the right succession are - very roughly - approximated as factorial 100.

    One more thing - abiogenesis is not a case of 'all roads lead to Rome'; we have tried to create life in the laboratory mimicking primordial Earth conditions or not, etc, etc - and failed.
    We can be quite sure that there are only a limited number of '100 chemical reactions'* chains that lead to life. Only one such chain is confirmed to exist - the one that lead to life on Earth, to us.

    *Realistically, a LOT more than 100 chemical reactions are necessary in order to create a self-replicating molecule. Such a molecule is so complex, we have trouble even theoretically designing it.
    I was just being highly optimistic in my 100 steps estimate.

    100! is 9.3326215444×10ˆ157.
    That means there is a chance in 9.3326215444×10ˆ157 for life to come into being.
    Lindley, the number of atoms in the observable universe is generously estimated at 10ˆ80. And only a small fraction of these are amenable to giving birth to life.

    This means that, in order to win the 'lottery' of life, you need more than the atoms in the observable universe. A LOT more.

    As I already said, 100! gives a number so close to 0 as the chance for the "simplest" self-replicating molecule to emerge, that the chances are life on Earth is alone in the observable universe (and a huge chunk of the unobservable one).
    Even considering the abyss of time (6-7 billions of years), of space, considering Earth-like planets as a dime a dozen and taking my 100! only as a very rough/high estimate.
     
    Last edited: Aug 27, 2013
  13. Edit_XYZ

    Edit_XYZ Fleet Captain Fleet Captain

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    I recommend reading:
    http://chem.tufts.edu/answersinscience/relativityofwrong.htm

    Also, we're talking about biochemistry in conditions we can recreate, not about massive black holes or other such extreme phenomena.
    Our theoretical/empirical knowledge in biochemistry is pretty good.
     
  14. Lindley

    Lindley Moderator with a Soul Moderator

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    At any one time, yes. When you have millions of years to work with that acts as a multiplier on "lottery tickets" as well---a fairly large one.

    Our ability to design a self-replicating molecule is irrelevant; there are lots of things nature does better than our designs.

    I'm also going to question your conclusion that evolutionary forces are irrelevant. Certainly, it wouldn't work in the traditional sense. However, it's possible that certain molecules had advantages (or disadvantages!) of some sort given a particular environment, and this could prune the decision tree considerably.

    I'm not saying it's not unlikely, mind.
     
  15. CorporalCaptain

    CorporalCaptain Admiral Admiral

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    Care to explain just what 100! is a "very rough approximation" of in this context and how you know it even is an approximation?
     
  16. Edit_XYZ

    Edit_XYZ Fleet Captain Fleet Captain

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    Lindley, if a molecule can't self-reproduce, it cannot 'spread' its 'advantages'. Other molecules disappearing from the environment also doesn't help it, if it can't self-reproduce. AKA NO Darwinian evolution.
    Feel free to post a scenario for Darwinian selection where the actors are not self-replicating - if you have one.


    Our inability to design a self-replicating molecule is highly relevant, showing us we're talking about a highly complex construct - that is not easily achievable by putting some environments one after the other. You need some very, very specific environments - so subtle, we didn't figure out which despite a lot of searching (not blindly, but guided by science).


    And we're talking about, VERY generously, 100 orders of magnitude between the chances of life existing and the number of atoms in the observable universe that can give birth to life (between ~10ˆ157 and a small fraction of 10ˆ80).
    Good luck winning this lottery.

    As said, Lindley, you can have all the 6-7 billion years of abyss of time. It barely makes a dent in the improbability.
    And you can have the universal abyss of space, considering Earth-like planets as a dime a dozen and taking my 100! only as a very rough/high estimate. The probability of life appearing twice in the observable universe remains practically 0.

    I take it as a very rough approximation because it leaves out many factors:
    -In the primordial earth, there were many environments, not just 100;
    -As such, the problem of abiogenesis is more correctly stated as: 'these 100 steps should follow one after another without one or more destructive environments appearing between them, destroying the future self-replicating molecule';
    -The number of steps necessary to create a molecule that can replicate half-way reliably is probably larger than 100;

    In essence, 100! is a simplification, only there to give a rough idea about the improbability of self-replicating molecules emerging.
     
    Last edited: Aug 27, 2013
  17. CorporalCaptain

    CorporalCaptain Admiral Admiral

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    So, in other words, it's just something you pulled out of your ass.

    The issue isn't so much the 100 part, but the factorial. You seem to have settled on that, because you like the fact that 100! is astronomically huge.

    Here are just two problems with your assumption that factorial is the correct function.

    First, the steps that need to be performed in order are not all independent of each other. Certain later steps can occur only if their reactants are available. Therefore, not all of the combinations counted by your function are equally likely to occur, since some of them are in fact impossible, namely the ones describing sequences in which steps occur before their reactants are available. For example, if C depends on both A and B, then CAB, CBA, ACB, and BCA are four of the 6=3! sequences counted by your function, but they couldn't possibly occur, since C simply can't happen without the products of both A and B. This is one reason why your function grossly underestimates the odds of the final product occurring randomly. The impossible combinations, being ruled out, can't muck things up.

    The overwhelming majority of the combinations you've counted are in fact impossible for this first reason alone. The number of impossible combinations is at least 99!. Just consider the combinations where the final step occurs first, and then count all ways of reordering the remaining 99 steps. Those are all impossible combinations, unless the molecule in question only needs one step to be produced. Similarly, the ones where the final step occurs second are also invalid. Assuming 100 steps are required to produce the molecule in question, then since the final step has to occur last, only at most 99! of the counted combinations are valid, which is at most 99!/100!=1% of the total counted. Further dependencies place further restrictions on the ordering.

    A second problem is that steps that are independent of each other can be interchanged. For example, if A and B are independent of each other, but C depends on both A and B, then ABC and BAC are both valid sequences. Your function only admits one of them.

    The factorial function counts the number of ways of reordering sequences. That's the wrong function to use in this case. There is no valid argument that it is even a rough approximation of the correct value.
     
    Last edited: Aug 27, 2013
  18. Lindley

    Lindley Moderator with a Soul Moderator

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    I'm not referring to Darwinian selection per se (that requires reproduction). More that if certain environments favor a particular molecular intermediate heavily, then that form may dominate in that environment; and the probability of any other outcome *prior* to that point in the chain becomes of little importance. Hence, the decision tree could be heavily pruned in places.

    This works on the theory that many reactions are reversible, so even if a molecule undergoes the "wrong" reaction at some point it may eventually end up in the "right" state due to conditions. Also, there can be more than one way to synthesize a given molecule, so that needs to be considered as well.

    You're the one arguing the number of possibilities is immense. I'm not convinced "science" gives us enough of an advantage to claim we could find in a few years when nature took billions of years to figure out. Heuristics only improve state space search if you pick the right one.

    I'm not sure how it affects the math, but I'd also point out that even though the number of possible molecules increases incredibly fast, the number of possible *reactions* at each step does not. There are a (comparatively) restricted number of ways functional groups can interact. This *might* indicate your assumption of 100! possible outcomes is overly pessimistic.
     
  19. Edit_XYZ

    Edit_XYZ Fleet Captain Fleet Captain

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    Annoyed much, CorporalCaptain?
    BTW, a simplification is far from 'pulling out of one's ass'.

    Really?
    You don't say?

    You are confusing the environments and the chemical steps to which they give birth.
    I posited 100 environments that must occur in order, in order to create in the 'warm pond' or wherever the chemical steps for the appearance of life.
    These environments are independent of each other, one can occur out of order* - in which case, of course, the fledgling molecule not being available, bye bye future self-replicating molecule.

    *Unless you want to post a magical environment that creates the successive ones/a large number of the successive ones.

    Cute. See above.

    The chemical steps necessary you achieve a self-replicating molecule cannot be interchanged (especially when talking about as few as 100*) - even if the 100 environments can appear independently of each other (although, if they have no fledgling molecule, they go nowhere).

    If you interchange these chemical steps you will end up with a boring chemical soup - nothing self-replicating.

    *When you want to talk about a more realistic ~1000 chemical steps - sure, you can probably interchange a few.
     
  20. CorporalCaptain

    CorporalCaptain Admiral Admiral

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    Not at all. You're just posting nonsense.