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Space Science

Extraterrestrials Probably Haven't Found Us - Yet 588

Posted by Zonk
from the hello-up-there dept.
kasparn writes "The Guardian today has a story about the Danish astrophysicist Rasmus Bjoerk, who recently conducted simulations on how long it will take to colonize the Milky Way. The basic idea is to send out probes in different directions (including various heights above the galactic plane). He estimates that it will take some 10 billion years to explore 4 % of the Milky Way. Since the age of the Universe is of the same order, his conclusion is that aliens can't have had time required to find us yet."
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Extraterrestrials Probably Haven't Found Us - Yet

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  • Well obviously you would use a TARDIS, which makes it more like 100%.
  • by creimer (824291) on Thursday January 18, 2007 @02:46PM (#17668688) Homepage
    We will be in a lot of trouble if the Cylons find us first.
    • Re: (Score:3, Informative)

      by Homr Zodyssey (905161)
      Silly! They aren't aliens. They are man-made robots.
    • Well, it seems the Cylons are already running the U.S. Government, and it would explain the NSA spying.

    • by AHumbleOpinion (546848) on Thursday January 18, 2007 @03:14PM (#17669326) Homepage
      We will be in a lot of trouble if the Cylons find us first.

      Actually the "cylons" will find us first, it is far cheaper to send robotic explorers out. Then if anything interesting is found send the "manned" missions.
    • by Dareth (47614) on Thursday January 18, 2007 @03:33PM (#17669736)
      We are currently broadcasting the galactic equivalent of "Eat at Earth" sign. Remember we consume "lesser" lifeforms for food. I do love a good steak! Who knows if the aliens who find Earth will consider us as equals or as appetizers.

      I am sure their galactic physicians will recommend they don't eat too many humans from the Northwestern Continent due to cholesterol or something, but that they can eat all the yellow humans from the east they want, even if they will be hungry again in a few parsecs.

  • I haven't RTFA (at work) but I'm guessing this is assuming that they haven't developed signals/travel faster than the speed of light.
    • by IgLou (732042)
      I read some of it and the biggest assumption was that probes would travel at most 1/10 the speed of light.

      I think if you're going to go through the trouble of writing a paper like this it would be interesting to consider an FTL scenario as well. Say compare the numbers for 1/10c, c, and 10c. But then again, what would the realistic assumption be on speed?
    • by Marxist Hacker 42 (638312) * <seebert42@gmail.com> on Thursday January 18, 2007 @03:16PM (#17669370) Homepage Journal
      Worse than that- the researcher assumes:

      1. That they can't develop PROBES that travel faster than 1/10th the speed of light.
      2. That probes of this form that would keep running long enough would be so massively expensive that even the most ambitious race would only be able to build 8 of them (He does address this complaint, and also considers 200 probes instead of 8, and von Neuman machines instead of static probes, neither of which drop the figures below 4x10^6 years to explore a mere 4% of the Galaxy).
      3. He doesn't even consider non-material, photon-based probing methods, which would increase the rate of exploration by a factor of 10.
      • by hjo3 (890059) on Thursday January 18, 2007 @03:41PM (#17669892) Homepage
        "photon-based probing methods"

        You mean looking at stuff through a telescope?
      • by Dr. Spork (142693) on Thursday January 18, 2007 @04:03PM (#17670392)
        More puzzlingly, he assumes these probes can repair themselves for and keep running for billions of years, but they can't self-replicate. Really? If the probe can repair every potential internal probem on its own, the capacity to self-replicate should come almost for free.
      • by raehl (609729)
        He doesn't even consider non-material, photon-based probing methods, which would increase the rate of exploration by a factor of 10.

        Doesn't matter. Light only travels so fast, and we've only been here, what, 10,000 years? Nobody further than 10,000 light years away could have possibly found us yet. And a 10,000 light year sphere is well less than 4% of the galaxy.

        This whole study is kind of dumb, because it doesn't matter that you can explore 4% of the galaxy in 4 billion years when we've only been here f
  • by BadERA (107121) on Thursday January 18, 2007 @02:47PM (#17668728) Homepage
    Why 1/10th c? Why not 99% of c? Why not faster than c? Granted faster than light travel is nothing more than theory and dreams at this point, but this article makes the assumption that other civilizations have not progressed in the field of physics any faster nor further than we ourselves have, to date.
    • by QuantumG (50515) * <qg@biodome.org> on Thursday January 18, 2007 @02:55PM (#17668916) Homepage Journal
      Yeah, imagine a civilization that, having discovered enlightenment, actually embraced it and dedicated their industrial base to further it, instead of shuffling it off to the minor specialists who they then make beg for funding, typically by militarizing their research.
    • Re: (Score:3, Insightful)

      Nasa's current Cassini mission to Saturn is plodding along at 32km a second

      c/10 is 30,000km/s. The article makes the assumption that alien civilizations have advanced enough that their spaceships are 1,000 times faster than ours - not unreasonable.
      • by Alsee (515537) on Friday January 19, 2007 @04:16AM (#17678232) Homepage
        The article makes the assumption that alien civilizations have advanced enough that their spaceships are 1,000 times faster than ours - not unreasonable.

        No, it is quite unreasonable. The Cassini probe is going 32km a second (71,000mph / 115,000kph). That is more than a thousand times faster than the record less than a hundred years earlier.

        We pretty much already have the technological capability to get a small probe up to c/10. We have the knowlege and basic designs to do it... it is already "mere" enginering and $$$$ problem for us today. If we simply chose to allocate several gigabucks to do it, we could with absolute certainty get something up to c/10 within 10 to 20 years.

        Assuming our civilization doesn't implode in one way or another in the next few hundred years, getting well over c/10 is a certainty. The only uncertainty is whether the speed of light really is an inviolate limit, or whether some unimagined phyisics will have us exploring the universe way beyond the speed of light.

        But looking at his paper I see that the real problem with his figure isn't his c/10 speed limit, but his laughable assumptions and exploration strategy of tiny fixed number of probes zig-zaging between stars almost one at a time. Even with conservative assumptions.... assuming just 0.5c and an interstellar civilization manufacturing just one probe per year... and assuming a reasonable strategy... the entire Milky Way could be explored in just a few million years.

        With more reasonable assumptions, the entire exploration rapidly becomes light-speed limited. After the initial local exploration, an advanced technology civilization could mass produce replication-capable miniprobes or microprobes and use a maximized galactic search strategy. Send those probes out on a straight line courses directly to the various sectors of the galaxy... with the worst case probe taking between 150,000 years and 225,000 years to reach the opposite side of the galaxy. Within a handful of years the probe locates an uninhabited rock and sets up an automated factory to send out a few million miniprobes or microprobes, which scout all of the stars in that sector within about 20,000 years. Elapsed time: less than a quarter million years to get a probe to every star.

        And really you only need the tech and pay the $$$$ to make and launch *one* such replicator miniprobe. After that, the entire exploration proceeds automaticaly and "for free". We will probably have this technology within a hundred years. Some time within the next 10,000 years... hell lets call it some time in the next 100,000 years of civilization... someone can and will do somthing like this (if we are still around). Once anthing remotely like this gets started, it doesn't much matter how you tweak the assumptions. The most it does is add in a small multiplier factor to the timeline. It is almost inconceivable that we (assuming we are still around) will not have probed every star in the Milky Way within a million years from today.

        10,000 years or 50,000 years of technology and manufacturing is an insignifigant blip in the analysis. That technology level and time span means that a civilization can and will trivially produce the resourses needed to explore at a stbstantial fraction of the speed of light. Actual strategy and behavior only accounts for a small constant multiplier. the defining factor is the speed of light, and it locks down the final answer somewhere between 160,000 years and just a few million years. His result of needing 10 BILLION years to explore just 4% of the Milky Way is comical.

        The only real question is whether the speed of light really is inviolable. If that falls, then I say we only need between 100 and 1,000 years of technology and then we explore at close to the limit of whatever that new physics makes possible. If we can explore and *get answers* at far faster than the speed of light, then there is vastly more incentive to actually do so.

        -
    • by dyslexicbunny (940925) on Thursday January 18, 2007 @03:09PM (#17669252)
      I agree. He's only basing his assumptions on our current capabilities and applying them to an unknown alien civilization. Great that he's making these assumptions but his final conclusion, We have not yet been contacted by any extraterrestrial civilizations simple because they have not yet had the time to find us. Searching the Galaxy for life is a painstakingly slow process., is just jumping to conclusions, perhaps invalid for the work he did.

      No one knows what aliens are going to look for in a planet. Our planet could be written off as an inhabitable nitrous sphere. They might be non-carbon based life forms. They could have progressed technologically much faster than we did as you suggested. By assuming aliens match our capabilities, he made an unstated assumption that was key to actually understanding the conclusion.

      A more fitting conclusion from his work would be that it would take US 10 billion years to search a small portion of the Milky Way for life at our current technology levels.
    • by teslar (706653) on Thursday January 18, 2007 @03:23PM (#17669526)
      Why 1/10th c? Why not 99% of c? Why not faster than c?
      You're still thinking Star Trek when you should be thinking Stargate.
      1. Obtain a good enough understanding of space-time to create wormholes to any destination you want.
      2. Make a list of all destinations you are aware of.
      3. Send a probe to all of them, evaluate each destination and scan for more destinations from there.
      4. Go to step 2.
      Space ships are just such a small-planet-with-water way of thinking.
      • SURVEY (Score:5, Funny)

        by russ1337 (938915) on Thursday January 18, 2007 @05:03PM (#17671678)
        I reckon theres a Slashdot survey on the best way to explore:

        How would you prefer to travel?

        a. A blue Police Box that can traverse space and time, with a hot British former 'teen star' that is obviously in love with your weirdness.
        b. A big ancient ring that can take you anywhere where there is a corresponding ancient ring, but you keep bumping into Egyption dog people who try to kill you.
        c. A large dinner shaped spaceship that does warp factors, but you get to shoot at klingons and make sexy time with green chicks (remember its all about the Journey!) Just dont get assimilated by Bjork!
        d. Travelling with the Robinson family and a stupid robot that shouts "Danger" long after it stopped being funny. Oh and a pedophile.
        e. In a ship that can make the Kessel Run in less than twelve parsecs - With a great big hairy Wooky and a gay robot.
        e. Spending time on the only ship to have survived an attack by robots with KITT in their face, where it is a daily battle to stay alive.
        f. On a moon that was flung out of orbit by a massive thermonuclear explosion initiated by the build up of magnetic radiation, which there is much debate as to it being caused by global warming.
        g. Traveling across universes with a guy that looks like Mike Moore, where each new universe you 'slide' into is exactly like being on LSD.
        h. On a ship with a dorky hologram an evolved cat, a computer with an IQ of 6000 and a very stupid robot, but every day is hilarious!
        I. The space shuttle. (yawn)

    • by Nyeerrmm (940927) on Thursday January 18, 2007 @03:25PM (#17669580)
      Also, assuming they use some kind of rocket technology (that is, technology that shoots stuff out one side to propel the vehicle in the other), 1/10 c is much more realistic than something approaching c. Assuming a technology that has 100 times the specific impulse as our current vehicles (the best ion thrusters get ~4500 s,) I get using the rocket equation that the initial mass to move 1 ton of cargo is:

      1/10 c: 3.263e29 tons .99 c: 1.534e292 tons

      Even then this seems absolutely ridiculous. If you used a matter/antimatter reaction so that your propellant was pure electromagnetic radiation (thus your exit velocity is c), you'd get these results

      1/10 c: 1.105 tons .99 c: 2.69 tons

      Of course, these are not adjusted for relativity, since I don't know any simple equations to do that. I would imagine (as a wild-ass guess) that the 1/10 c estimates are close, but the .99 c results are off by thousands of orders of magnitude.

      Basically all I'm saying is that 1/10 c seems fairly reasonable. It's not feasible given our current technology, but its within reason. If you start looking at things like space-time warpage, then we have no idea on any usage or capabilities, so any kind of theory based on it gets even further and further from reality.

      By the way, I am a rocket scientist, but only a student, and not a physicist at all, only an interested amateur.
      • by inviolet (797804) <slashdot.ideasmatter@org> on Thursday January 18, 2007 @04:00PM (#17670314) Journal
        Also, assuming they use some kind of rocket technology (that is, technology that shoots stuff out one side to propel the vehicle in the other), 1/10 c is much more realistic than something approaching c. Assuming a technology that has 100 times the specific impulse as our current vehicles (the best ion thrusters get ~4500 s,) I get using the rocket equation that the initial mass to move 1 ton of cargo is [...]

        Why do you assume that any sane civilization would send out macro-sized probes?

        Nanoscale or even microscale probes would completely change the economics of space exploration. And they would avoid the very serious problem of atomic abrasion that occurs at and above 0.1c.

        That's why I laugh when people spot human-sized UFO craft. If there are UFOs here, they're microscopic.

        • by Steeltoe (98226) on Thursday January 18, 2007 @04:57PM (#17671544) Homepage
          That's why I laugh when people spot human-sized UFO craft. If there are UFOs here, they're microscopic.

          Assumptions are just that, assumptions. You can laugh all you want, but to me, it just shows one more scientific dogma. The attitude of "knowing it all" is sadly very prevalent here on Slashdot, and probably why so many spend time writing here, instead of discovering new stuff.

          The problem is lack of creativity. In 0.5 seconds, I thought of nano-UFOs. Send one, or trillions of those, and let them dig into a moon or planet to rebuilt itself into a fully fledged macro-sized "UFO". Or, maybe if you want to "recreate yourself in your own image", why not send out organic "bombs"? Etc. etc. There are so many possibilities when you dont restrict your mind.

          Just because you cant think of it, doesnt mean it isnt possible or thinkable. Please free your mind! There is so much more to know than we already know! And instead of giving focus to more effective ways to kill people, why not science of life?
        • by StikyPad (445176) on Thursday January 18, 2007 @07:50PM (#17674350) Homepage
          Nanoscale or even microscale probes would completely change the economics of space exploration. And they would avoid the very serious problem of atomic abrasion that occurs at and above 0.1c. That's why I laugh when people spot human-sized UFO craft.

          That's why *I* laugh when people think we haven't solved the issue of atomic abrasion. Teflon was named after our home planet, after all. Ha ha ha...

          Puny human!
  • Duh (Score:5, Insightful)

    by Reality Master 101 (179095) <RealityMaster101@noSpAM.gmail.com> on Thursday January 18, 2007 @02:47PM (#17668738) Homepage Journal

    Sheesh, talk about "proof by lack of imagination." This is supposed to answer the Fermi Paradox?

    You can't explore a galaxy with a handful of probes. 72 probes??? First of all, if you're going to do it that way, you'd create hundreds of thousands of probes, if not millions of probes (mass production would reduce the cost). Second, you still probably wouldn't do it that way. You'd wait until you had the technology to make self-replicating probes, and the galaxy could potentially be explored in thousands of years.

    Not impressed by this guy's argument.

    • Funny I thought the galaxy was 100k ish light years across. So it would take half of that if we started at the center and the probes moved at light speed. It would take the same half of that to get the final results back so the minimum time is 100k years, without going faster than light.
      • Funny I thought the galaxy was 100k ish light years across. So it would take half of that if we started at the center and the probes moved at light speed. It would take the same half of that to get the final results back so the minimum time is 100k years, without going faster than light.

        The galaxy is 30,000 light years across. I actually thought of that after I posted, but I figured "thousands" covers everything up to a million. :)

    • Re: (Score:3, Funny)

      by Gropo (445879)
      u'd wait until you had the technology to make self-replicating probes, and the galaxy could potentially be explored in thousands of years.
      Yes, and let's hope beyond all hope that once the probes arrive they don't require vast amounts of O and/or H2O to replicate themselves. And that they'll recognize Sol 3 as a planet fostering 'advanced' life.
    • Re: (Score:3, Insightful)

      You're right, this guy hasn't thought things through. He rejects self-replicating probes because they'd compete with the original explorers. I think that's a lame argument, but let's accept it. Even human colonies spreading out from Earth, and moving onto new stars every generation or two (and sending out some non-self-repicating probes while they're at it), would explore the galaxy far faster than these probes. If humans survive the next century or two I'm sure they'll explore the galaxy in person far fast
      • Re:Duh (Score:5, Funny)

        by flyingsquid (813711) on Thursday January 18, 2007 @03:16PM (#17669372)
        You're right, this guy hasn't thought things through.


        Negative. I find your argument untenable. I am in agreement with the Danish monkey-being. Probabilities of non-human life spreading through the Galaxy and discovering primitive monkey-beings in Sol System are minimal. Probability is on the same order of probability of a F'narthag slime-weasel evolving wings and taking flight. It is also highly improbable that extraterrestrial beings would colonize the pathetic planet Earth and blend into the primitive monkey-being society. They would be forced to hide in internet discussion groups and the tech sector so that they are mistaken for geeks when they display lack of monkey-being social skills.

    • Re:Duh (Score:5, Informative)

      by isomeme (177414) <cdberry@gmail.com> on Thursday January 18, 2007 @02:58PM (#17668984) Homepage Journal
      You'd wait until you had the technology to make self-replicating probes, and the galaxy could potentially be explored in thousands of years.

      Bingo. As usual, Wikipedia has a good article [wikipedia.org] on the topic.
    • Re:Duh (Score:5, Funny)

      by myowntrueself (607117) on Thursday January 18, 2007 @03:04PM (#17669114)
      You can't explore a galaxy with a handful of probes. 72 probes???
      Not impressed by this guy's argument.

      He is probably just assuming that the aliens have a pretty much exact parallel to NASA.

      • Re:Duh (Score:4, Insightful)

        by terjeber (856226) on Thursday January 18, 2007 @03:58PM (#17670256)
        If the aliens have an organization like NASA, and some Alien-Aliens drop by and donate Faster than Light technology and two space elevators to our Aliens, they still wouldn't be able to colonize their own solar system in 10 billion years.
    • Re: (Score:3, Insightful)

      by Mr. Slippery (47854)
      you'd create hundreds of thousands of probes, if not millions of probes..You'd wait until you had the technology to make self-replicating probes, and the galaxy could potentially be explored in thousands of years.

      Uh-huh. And how many self-replicating probes traveling at .1 c have you developed?

      The fact that we can imagine self-replicating interstellar probes doesn't mean they are practical or possible.

    • Re:Duh (Score:4, Insightful)

      by muellerr1 (868578) on Thursday January 18, 2007 @03:06PM (#17669166) Homepage
      I tend to agree. Think about it this way: how much of *our* resources are we currently using to explore the entire galaxy? And how much are we likely to in the future? The answer is, not much. It's a vanishingly small return on a huge investment to explore the galaxy, especially when we've got bigger problems at home and so much raw material in our own solar system. The costs of sending crap into deep space will probably outweigh the benefits of mineral riches for far into the future, despite Ridley Scott's imagination. Unless there are aliens within a few hundred light years of us (which at this point is a vanishing probability given that we've found under 200 exoplanets within 200 parsecs [exoplanets.org]) we won't find any aliens -- and they won't find us, either.
    • RTFP (Score:3, Informative)

      by HBI (604924)
      He covers these issues. The article summary is misleading.

      Self replicating is ruled out due to risk. That sounds fairly silly since computers are computers. They do what we tell them to and not a thing more. But I suppose a few worrywarts are a good thing.

      The number of probes is more like 2.08 million probes, if i'm reading him right, as his simulation was done at 1/260000 scale.
    • Re:Duh (Score:5, Funny)

      by lucifig (255388) on Thursday January 18, 2007 @03:33PM (#17669732)
      Well Darth Vader found Hoth with fewer probes than that and it only took him like 4 minutes.

      So I guess you are both wrong.
    • by AHumbleOpinion (546848) on Thursday January 18, 2007 @03:36PM (#17669790) Homepage
      I'd hold off on criticizing others for a lack of imagination. Don't you realize that self replicating probes will doom us? We will be galactic spammers, the aliens will wipe us out as a nuisance. Or our probes will harvest the planet they pray towards, the aliens will wipe us out as heretics and blasphemers. At a very minimum the probes will be crossing the border without proper documentation, the fines and impound fees could leave us in "debtors prison" for millennia.
  • by neo (4625) on Thursday January 18, 2007 @02:48PM (#17668750)
    Come on. 4% is a hell of a lot better than your odds of winning the lottery and that happens *everyday*.

    Plus he's not taking into account multiple alien races. So that's like double 4% which is almost 8%. Do that a few hundred times and you get 108%. This guy clearly doesn't understand math.
  • Humans will have killed themselves off with war before they have the chance to find us!
  • Wrong, wrong, wrong (Score:5, Interesting)

    by Ignorant Aardvark (632408) <cydeweys.gmail@com> on Thursday January 18, 2007 @02:49PM (#17668784) Homepage Journal
    This figure of taking billions of years to explore the galaxy is utterly wrong. Actually, it only takes a few dozen million years to colonize the entire damn galaxy, which is a lot more effort than merely exploring it.

    This figure is based on some very reasonable assumptions. Colony ships travel at much below the speed of light. Each colony gets a thousand years of development time from first colonization before it starts sending out its own colony ships. As you can see, even though it seems quite "slow", thanks to the magic of exponential growth, the entire galaxy is colonized in short order.

    We won't merely be discovered if aliens exist - we'll be colonized. That's the most likely scenario for running into aliens. If they never spread beyond their home planet, they'll just be one star out of trillions - but if they do start colonizing, we'd find them everywhere.
    • Wouldn't the speed of the ships increase during the thousand years? HEll what is to say we won't find a way around tha pesky speed of light.
  • aliens can't have had time required to find us yet.

    So it would take 10 billion years to visit 4% of the Milky Way. In theory, if there are any aliens within the nearest 4% to us, they may have had time to visit us. Realistically, let's say the nearest 2%, to allow time for intelligent life to evolve and develop space travel. 2% of the galaxy is still a pretty big space, though you'd think we'd have seen some evidence of an alien civilization that (relatively) nearby.

  • Well, DUH! (Score:4, Insightful)

    by QuantumG (50515) * <qg@biodome.org> on Thursday January 18, 2007 @02:50PM (#17668796) Homepage Journal
    To paraphrase: But Sir! If we only send 8 probes it'll take billions of years to search a mere 4% of the Milky Way galaxy!

    That's why you have to make the probes self replicating.. utilizing in-situ resources to make more probes at each star they visit, the growth becomes exponential and it only takes a few thousand years to search the entire galaxy. And seeing as we're visiting all these stars anyway, how about looking for planets that don't have life on them, but have nice suitable conditions for starting life on them. Cover a virgin planet with a wide variety of Earth lifeforms and fly on.

    • Re:Well, DUH! (Score:5, Insightful)

      by Ignorant Aardvark (632408) <cydeweys.gmail@com> on Thursday January 18, 2007 @03:00PM (#17669032) Homepage Journal
      To be pedantic ... the absolute minimum time to explore the whole galaxy from Earth is about 80,000 light-years, because the farthest part of the galaxy is about 80,000 light-years away from us. Although to be even more pedantic, double that, because you can't really say you've explored until the information about what you've found has made it back to you.

      So, yeah, you can't explore the galaxy in only a few thousand years.
    • Re: (Score:3, Insightful)

      by myowntrueself (607117)
      That's why you have to make the probes self replicating

      Hopefuly they don't need to see any Earth-based SciFi to know that self replicating probes are a phenomenally *bad* idea.
  • Wrong (Score:3, Funny)

    by TheWoozle (984500) on Thursday January 18, 2007 @02:51PM (#17668836)
    I need to introduce this guy to my next-door neighbor...
  • ...his conclusion is that aliens can't have had time required to find us yet."

    Under what time frame? If an alien race has had advanced technology for 100,000,000 Trillion years, then they'd have plenty of time (and would probably have technology more advanced then sending out physical "probes"). It doesn't see likely from what we know, but I don't think we actually know that much.

    Why is it that scientists think that only what we can achieve is possible? It's like us looking for aliens using our tech
  • by Anonymous Coward on Thursday January 18, 2007 @02:53PM (#17668878)
    Traveling at the speed of light, it would take a quarter million years to reach Andromeda. What's more is that if I went into statis now, the compound interest on my savings would pay for the journey.

  • We can always give their computer systems a virus.
  • They models used to reach the conclusion mentioned in the summary were calculated using a maximum speed of 10% the speed of light. Suppose that FTL travel had been developed by these advanced extraterrestrials - what then? I know it seems now like science fiction or fantasy, but you know the old adage about sufficiently advanced technology...
  • What about probes that land and replicate on foreign terrestrial bodies? 1 probe lands and makes 10 or a hundred of itself. Send out 10 of these type of probes, and exponential growth will do your work for you.
  • More than one... (Score:4, Insightful)

    by neurocutie (677249) on Thursday January 18, 2007 @02:56PM (#17668930)
    Whatever his assumptions are that leads him to 4%... it seems that he is considering only the probability that any ONE alien civilization is looking. But in all likelihood there are many, if not millions of alien civilizations out there than may be search, so the probability that any ONE of those million will find us seems quite a bit higher than 4%.
  • in case one comes back wanting to be one with the creator - vger I anybody?
  • by Red Flayer (890720) on Thursday January 18, 2007 @02:58PM (#17668974) Journal
    1. Probes sent by extraterrestials cannot travel faster than our probes.
    2. The ET search is not targeted.
    3. The ETs are not much closer to Earth and found us by luck, early in their search.

    At any rate, while the math is interesting, it just shows that we're not likely, as in snowball's-chance-in-hell likely, to have been found already. From a logical point of view, though, one cannot say that we haven't been found yet.

    As far as we know for certain, the Vogon construction fleet could be circling our system as we type these responses... though the chance of that being the truth is small enough that we could very well see an Improbability-driven ship come in for a landing at JFK or LAX.
    • Re: (Score:3, Insightful)

      by LWATCDR (28044)
      "1. Probes sent by extraterrestrials cannot travel faster than our probes."
      Actually he is claiming that extraterrestrial probes can travel 1000 times faster than our probes.
      So far propulsion systems are not following Moore's law and there is no evidence that they ever will.
      This is a simulation made using guesses I would say that it is very interesting.

      • Re: (Score:3, Informative)

        by soft_guy (534437)
        Actually I think propulsion systems have gotten faster in the last 200 years.
  • Did he do any research showing that it's impossible for 8 people to find a needle in a haystack by evaluating one needle at a time?

    Maybe he could then go on to propose that these people "self-replicate" and create more people to look for the needle? That would make it go faster. However this obviously would cause problems because inevitably they would end up competing for resources or start forming unions to demand that they only need to look at 3 needles at a time.

  • Am I mistaken, or are this guy's statistics based on there being one other colony of "aliens" in the galaxy? What if there are a hundred colonies or a million? (A recent popular guess for number of starts in the milky way is 100 billion).
  • "I think there will be never a quantum theory to prove that the universe is non-deterministic, a perfect case against my God proofs, so hereby I announce that my belief in God is staunch."

    What's common in both viewpoints? Obviously one is real and the other is fictional, but what they have in common is that they both make predictions that we can't possibly do something in the future, so basically assuming no new technologies or scientific understanding.
  • I call BS (Score:3, Informative)

    by Spazmania (174582) on Thursday January 18, 2007 @03:14PM (#17669340) Homepage
    If you've ever played "Spaceward Ho" you'll recognize that the author has proposed an asinine strategy for exploring the galaxy. Indeed, if you try to play Spaceward Ho by that sort of probing you'll rapidly get your tail kicked.

    A more rational approach is exponential: You colonize a solar system. Then from that system you launch probes at anything reachable. Then you colonize everything reachable that qualifies. Rinse and repeat.

    The main disc of the galaxy is about 100,000 light years across. Assume 10% light speed for probe travel time, light speed for information return and 50 years for each new colony to build infrastructure to a point where they can launch probes. You'd have 90% of the galaxy explored in three or four million years -- almost 4 orders of magnitude less than this fellow's estimate.
  • by grumpyman (849537) on Thursday January 18, 2007 @03:21PM (#17669470)
    Come on, they haven't visited us yet? There were yet another case of alien abduction as reported by the World's Weekly last week.
  • by 140Mandak262Jamuna (970587) on Thursday January 18, 2007 @03:25PM (#17669576) Journal
    The aliens knew they could not send out probes that carry enough energy to beam back the information. So they built generalized adaptive Turing machines, (a machine that can build itself) of incredibly small dimension. They created billions and billions of these machines and scattered them. These machines are so tiny, they get carried by the solar wind and other cosmic radiation.

    One of these Turing machines reached Earth about 4 billion years ago. It first had to start by building very simple amino acids, then it graduated to proteins, then to RNA and then to DNA, and then these DNA machines built bodies around them and started using natural selection to evolve into more and more capable organisms. The final aim of these DNA structures is to build powerful radio beacons and send the information back to the original aliens who created these molecules and scattered them to the (solar) wind.

    • Re: (Score:3, Interesting)

      by btempleton (149110)
      You have confused a Turing machine (which is an idealized model of a computation device) with a Von Neumann self-replicating machine.
  • by gelfling (6534) on Thursday January 18, 2007 @03:27PM (#17669608) Homepage Journal
    IT's not the ACCELERATION, it's the DECELERATION. Even if you could apply some force to slowly accelerate a massive space ship, once you got it up to that speed wouldn't it take K^2 (squared) units of fuel to slow it down it again? So let's say it takes a million tons of some super fuel to get your space ark up to speed. Wouldn't it take a million million tons to park it again?
    • Re: (Score:3, Informative)

      by theGreater (596196)
      Actually, it would take substantially less as you've already shed a lot of mass, AKA superfuel. So you wouldn't accelerate halfway and decelerate halfway, you'd accelerate 2/3 and decelerate 1/3. Or something like that -- someone better at the various calculus-based disciplines than me might be able to give a better ballpark.
  • by Dr. Spork (142693) on Thursday January 18, 2007 @03:56PM (#17670222)
    This work is irrelevant to the Fermi paradox since Fermi assumed the probes would replicate themselves. Here is what Bjork says about self-replication:

    In fact if self-replicating probes, or von Neumann probes as they are also termed, were used to explore the Galaxy it has been shown that a search of the entire Galaxy will take 4 106 3 108 years dependent on the speed of the probes (Tipler 1980). This is much faster than using the non-replicative probes proposed in this paper. However, one should note that there could be complications with using self-replicating probes. Tipler (1980) himself points out that the program controlling the self-replicating probes would have to have so high an intelligence that it might "go into business for itself" and become out of control of the humans who designed it, resulting in unforeseeable consequences. Since the machines uses the same resources as humans, a self-replicating machine might regards humans as competitors and try to exterminate them. Chyba (2005) also points out that self-replicating probes-might evolve to prey on each other, creating a sort of machine food-chain. This would of cause drastically reduce their exploration rate. Therefore the conclusion is that if perfect selfreplicating probes could be built, these could explore the Galaxy much faster than the probes suggested here. However, building less-then-perfect self-replicating probes could, in the worst case scenario, have fatal consequences for the human race.

    I think the real debate should be about self-replicating probes. Is the author assuming that every civilization capable of building these is automatically freaked out by potential doomsday scenarios, to the extent that none will be built? Even if it is foolish, I found that it pays to expect more foolishness in the universe rather than less.

  • by CohibaVancouver (864662) on Thursday January 18, 2007 @04:10PM (#17670572)
    I can just imagine the conversation in the ET's 'mission control' -

    I think we've got something, sir. The report is only a fragment from a probe droid in the sol system, but it's the best lead we've had.

    We have thousands of probe droids searching the galaxy. I want proof, not leads!

    The visuals indicate life readings.

    It could mean anything. If we followed every lead...

    But, sir, the sol system is supposed to be devoid of humaoid forms.

    That's it. The humans are there.

    There are so many uncharted worlds...

    That is the system! Set your course for the sol system. General, prepare your men!

  • Let's assume you have a civilization capable of building, fuelling, and launching an autonomous probe like the one described. What is this civilization going to look like?

    1. It's incredibly stable. It's launching an exploration program using probes that are going to take billions of years to get a result back to the original civilization. It expects to be around to pick them up.

    By the same logic:

    2. Individual members are incredibly long-lived, or the society is static and conservative enough that individual goals are submerged. They expect that the people around in a few billion years still care about the stuff they're doing, AND they care about the people who'll be around then.

    The technology he's postulating is also very advanced.

    3. Large scale space-based industry is routine enough for them to build probes capable of refuelling themselves using the raw materials in an as-yet-unexplored solar system, with surplus fuel to launch and recover the sub-probes. If they can do that, they can do the same thing in their own solar system.

    If the probes are cheap by their standards, there's no reason not to keep building them indefinitely. So let's say they're expensive. Let's say it takes this civilization a hundred years to build a probe. Why do they stop after 800 years? They're long-lived, stable, conservative, so assuming they have the will to do it in the first place why would they stop building probes? As the author notes, probes break down.

    So what happens when you add another probe into the search every century, indefinitely? Well, after a million years you've got 10,000 probes out there. Now you're looking at a search time measured in millions rather than billions of years, and it only takes millions of years to do it.

    But why are they doing this? Looking for planets to colonize, perhaps? If they're just looking for civilizations they'd do much better depending on "signal intelligence".

    But if they've got the ability to send out colonies, even the most conservative long-lived space-based civilization is going to figure out eventually that they don't actually need habitable planets to support a permanent colony. It's riskier without habitable planets, but even if the planetless colony is 10 times less stable than the home system you're still better off with your civilization in two baskets. And before long (in the terms of this civilization) you've got a roughly spherical shell of colonized star systems, expanding as fast as they can reach new systems. At 0.1C colonizing (not just exploring) the galaxy is going to take mere millions of years.

    However, one should note that there could be complications with using self-replicating probes. Tipler (1980) himself points out that the program controlling the selfreplicating probes would have to have so high an intelligence that it might "go into business for itself" and become out of control of the humans who designed it, resulting in unforeseeable consequences.


    On the other hand, what if the self-replicating probes are members of the designing species themselves?

    So either this level of technology is impossible to achieve, or we're back to the question of why no species has done it yet. There's lots of plausible answers, of course, but this paper sheds no light on them.

This process can check if this value is zero, and if it is, it does something child-like. -- Forbes Burkowski, CS 454, University of Washington

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