Number of ET Civilizations In Our Galaxy Is 37,964 544
KentuckyFC writes "The famous Drake equation calculates the number of advanced civilizations in our galaxy right now. But the result is hugely sensitive to the assumptions you make about factors such as the number of habitable planets that orbit a host star, how many of these actually develop life and what fraction of these go on to become intelligent etc. Disagreements about these figures leads to estimates for the number of advanced civilizations ranging from 10^-5 to 10^6. Now an astronomer in Scotland has worked out how to make the calculations more precise so that different theories about the origin of planets, life and civilizations can be compared. His calculations say that the rare-life hypothesis predicts only 361 advanced civilizations in the Milky Way now. However, the so-called tortoise and hare hypothesis predicts 31,573 and the theory of panspermia says that there ought to be 37,964 extraterrestrial civilizations more advanced than our own in the Milky Way."
Only 37,964? (Score:5, Interesting)
Comment removed (Score:4, Interesting)
Then where are they? (Score:4, Interesting)
The "famous Drake equation" is NOT meant to calculate anything, it's meant to start a conversation on what the parameters of intelligent life probability are.
On the other hand, the famous Fermi Paradox [wikipedia.org] tells us that we're alone in the galaxy. And considering that's a direct piece of data, I tend to believe this view. People like to wave their hands and say, but, but, WE'RE here! That means that there "just have" to be more! Why are we so unique? This is the Sagan argument, and it's answered by the Anthropic Principle [wikipedia.org].
And yes, in this case, absence of evidence *IS* evidence of absence.
Suspiciously absent (Score:5, Interesting)
No mention of species less advanced than us, but there are apparently 37,964 more advanced. I wonder why that is... Other civilizations must look at this backwater hick-world and laugh.
Re:Then where are they? (Score:5, Interesting)
For example, we can only just see a planet that seems to be rocky and atmosphere-bearing, which therefore meets some of the criteria for "life as we know it". We've been able to see gas giants, which might harbour life as we don't know it, for a little while now. However we can't actually resolve giveaway cues for planet-spanning civilisations, never mind lower life, either kind of planet yet. And we have no reason to assume that they'll be "chatty" in any way we can detect over long distances. To a group of aliens flying through alpha centauri whose civilisation skipped radio and went straight to fibre optic and laser, 2000AD Earth and 200,000BC Earth would be indistinguishable.
Re:Then where are they? (Score:5, Interesting)
Well, I'd say the main issue with that argument is that we just plain don't have the tools to detect intelligent life outside our solar system.
Radio signals are not the only way to detect intelligent life. I think the biggest ramification of the Fermi Paradox is that we're here at all. When you do the math, even at sublight speed, it takes about 10 million years to fill a galaxy (give or take an order of magnitude) using geometric progression. That's *nothing* in the billions of years of the life of the galaxy. Yes, maybe a lot of civilizations wouldn't have expansionist goals, but it only takes one. Only one civilization has to have the desire to expand in a sublight sleep ship and the whole galaxy is filled before we even arrive on the scene.
Or, at the very least, someone would have sent out Von Neumann self-reproducing intelligent probes. We should see those everywhere, if life were common.
People hate facing up to the fact that we're alone. But it just seems to be the fact of the matter.
Re:The real answer (Score:5, Interesting)
The biggest problem I see with this person's claim is that panspermia doesn't really work well when applied to reality.
There was an experiment discussed on Science Friday where an experimenter said cosmic radiation does a good number on genetic material based on tests with actual genetic material. I think they showed that in about 80,000 years, genetic material is just broken up into a bunch of tiny, useless snippets, especially if it's on a rock passing between stars, there is much less protection against radiation than there is within a star's heliopause. Panspermia might be a workable idea for passing organisms and code between planets in one solar system, but not for interstellar travel.
Speculation? Most aliens think we're idiots... (Score:1, Interesting)
Re:Then where are they? (Score:5, Interesting)
Or, at the very least, someone would have sent out Von Neumann self-reproducing intelligent probes. We should see those everywhere, if life were common.
probes with bacteria or virusses, or even just amino-acids ?
Here is an interesting one. (Score:5, Interesting)
No kidding. Our current estimates of the number of stars in the galaxy only go to about one significant figure, with upper and lower estimates differing by a factor of two. That puts a pretty serious cap on the precision of his answer.
One of my peers is an astrophysicist. Nearly all of their calculations are done to ONE significant figure. It ends up that they typically just add up exponents. The numbers are usually so huge, eg. 1E27, that they can get away with this.
:)
When you are dealing with orders of magnitude like these, it is usually acceptable in the scientific community. Whether this de-facto standard *should* be so acceptable is still up in the air in my views
Re:Advanced? (Score:3, Interesting)
Actually we don't even have a satisfactory definition of "life". Just look at the heated arguments about artificial intelligence or abortion to get a flavor for the lack of consensus on the issue.
There may be organizations of matter that are highly complex but not obviously sentient. Maybe species that are so long-lived and slow-moving that we overlook them as just another rock. Or maybe their composition will be so different (crystal? glass? gas?) that we will dismiss them. Or maybe they will be fairly similar to us (made of carbon, etc.) but we won't recognize their behavior as life-like because their customs are so alien.
Consider for a moment questions like "Is the Internet alive?" (It is a highly complex, interconnected system that exhibits emergent behavior. So is it alive?) "Is the galaxy alive?" (The extremely slow interactions between stars and dust clouds could encode information, forming some kind of creature/mind...) "Is a human alive?" (Why?)
And even if we discovered a bunch of bipedal humanoids made of carbon, there would still end up being many humans making arguments that they are not really alive--because they lack a "soul" or the divine touch of god or something like that.
I'm bothered by the fact that in most of these discussions about intelligent aliens, the question of "how do you recognize life" is taken as a given. As if it's obvious that "we'll know it when we see it". I question that assertion. For these kinds of debates to have any meaning, we need to decide what our criteria for "life" (and "intelligence" and "advanced") really are.
Re:Then where are they? (Score:5, Interesting)
Re:Suspiciously absent (Score:5, Interesting)
Which is why they send us all the UFOs. I know that serious people like to dismiss UFO reports because of how over the decades we turned the whole topic into ridicule, and the masses of loonies interested in the topic didn't help, but you have to remember that lots of very well documented UFO events reported by military personel and pilots are far from explained by anything we know.
You can scoff off the whole UFO thing but you can't take a precise case (provided it's a good one of course) and explain the recorded flight paths and phenomena.
That's what strikes me regarding the SETI approach vs UFOlogy, we look as hard as we can hundreds of light years away, yet we can't be bothered to take a closer look at what happens in our own atmosphere. I'm not implying that any recorded UFO event is extraterrestrial in origin, but in many cases you have to consider this possibility by an absolute lack of alternative explanations. No matter what I think it's worth a better scientific examination of the whole thing. But unfortunately the scientific community devotes more time and energy to what it considers safe research, which is why we spend so much time in the cul-de-sac that is string theory while investing very little in seemingly more risky possibilities (the Garrett Lisi example springs to mind).
You won't find them (Score:5, Interesting)
Ephemeral civilizations have only a short time to detect each other; I doubt that happens often.
Re:Then where are they? (Score:3, Interesting)
Re:What about T I M E ??? (Score:3, Interesting)
Then you start relying on deliberate lighthouse efforts.
There is also a small matter of the inverse square-law.
Re:Aliens Cause Global Warming (Score:5, Interesting)
His criticism of SERI is basically saying "the hypothesis that the neutrino has a rest mass of zero is scientific, but the hypothesis that a neutrino has a rest mass that is not zero is unscientific." This is silly; the same experiments would be used to test either hypothesis. Likewise, it's silly to criticise SETI by saying it's scientific to listen for radio signals if you're trying to show that there aren't any, but it's not scientific to listen for radio signals if you're trying to see if there are any. It's the same experiment either way.
His criticism of the Drake equation is even less well informed, in that he's criticising the equation itself, not the parameters that go into it. But the equation is trivially true; it's nearly a tautology. If the correct statement is "we don't know", it's not because the equations wrong, it's because we don't know what values go on the right side. But the answer "we don't know how many civilizations are in the univererse because we don't know what the probability is that a planet with life develops a lifeform with intelligence still bounds the question-- it tells us more precisely what we don't know.
In short, Crichton should stick with novels, which he's good at, and not critiquing SETI, something he seems to know little about.
Re:Then where are they? (Score:1, Interesting)
Or maybe "inteligent" civilizations keep radio silence and only particularly noisy and naive life forms start flashing radio waves in every direction as soon as they discover those. In these cases they are quickly (10K to 100K years) found by the listening galaxy's predators :)
If it had (Score:3, Interesting)
Up until the last year or so ago all they could detect was gas giants orbiting distant stars. Now the technology has advanced to the point that they can now detect smaller rocky planets too.
I look at the plethora of life on Terra and it's hard not jump to the conclusion that if there's liquid water, there's life of some sort. Doesn't even have to necessarily be liquid water too. Hydrocarbons would work.
Re:Fermi paradox (Score:5, Interesting)
You're missing an entire aspect to the Fermi paradox.
The universe is old. VERY old. About 14 billion years. Earth is fairly young, about 4.5 billion years.
Assuming intelligent alien life take about as long as intelligent Earth life to evolve (give or take a billion years), these other civilizations would have billions and billions of years ahead of us.
Re:Then where are they? (Score:3, Interesting)
On the other hand, the famous Fermi Paradox [wikipedia.org] tells us that we're alone in the galaxy. And considering that's a direct piece of data, I tend to believe this view.
From a human point of view I find the Prime Directive has some basic sense behind it. Arguably we Westerners shouldn't have interfered in Africa, for example, and introduced stuff that disrupted their own culture and put a spanner in the works of them developing in their own time. Of course our planet is small and we couldn't help but interfere. Interstellar space is another matter. To take the argument further, before we could see planets in deep space, we thought this was evidence that they were rare. Before we learnt to fly, we thought it was impossible. There is always some reason why something is absent. Maybe we lack the tech. Maybe aliens are choosing not to land in Central Park. Maybe they are conservationists and they want to minimise their impact. All these are already reasons perfectly evident to humans; we practice this stuff. Why is it so hard to believe that aliens might not have similar reasons?
And now for my favorite Futurama quotation:
When you do things right, people won't be sure you've done anything at all.
Re:As always, no. (Score:3, Interesting)
Well, by 'why haven't we detected their radio transmissions,' there was no intelligent life on planet Earth until the late 1800s.
And I can very easily come up with a scenario where a civilization as advanced as us wouldn't bother using radio. It involves a planet with high background EM interference, a tradition of using visual signals, such as semaphores, which then evolves into using light-based communication, ending with everything long-distance being laser-based, or something else..
Re:What about T I M E ??? (Score:3, Interesting)
Take the Voyager data as a nice proxy measure of long-distance communications. With our best RTs looking in exactly the right spot, its 3W of power and moderately directional antenna could barely send 110 baud from the orbit of Pluto. Crunch, crunch ... that means that an ET lighthouse at 1000ly needs to be transmitting 75 GW (or have equivalent antenna improvements). How likely?
Re:My estimate (Score:3, Interesting)
Truly, I wouldn't consider the human race to be intelligent until we decide to look around us for answers based on available evidence. I know we do some of this already, but way too many of us are willing to just simply "believe" what we're told by others who don't really know either.
The sum of human knowledge is too great for us to consume in one lifetime while also sustaining ourselves.
To do this would be to sentence our species to stagnation.
Trust must be placed in experts because of this.
Re:What about T I M E ??? (Score:3, Interesting)
In any case, it would need to be 75 GW of power using the same receiver as was originally used with Voyager. Is it better today? My guess is that it is. We keep getting better responses out of the same bandwidth because our sensitivity to the signal increases. I bet you that NASA engineer looks back at the 3W/110 baud numbers with nostalgia and laughs on the same level many of us do about the 640k of RAM claim.
Re:My estimate (Score:5, Interesting)
....but way too many of us are willing to just simply "believe" ....
There is no way you can live your daily life without belief. When you get into a car or a plane, you BELIEVE that they will take you where you want to go. You don't know that for sure. When you go to bed at night you believe and hope that you will wake up in the morning but there is no guarantee that you will. I am sure that you have at one time or another read stories of whole families who went to bed in the evening and never saw the next day due to fire or carbon monoxide. Our lives are governed much more by belief, by faith, than the sure knowledge.
There really is no proof of anything, only evidence that we can choose to believe or not believe.
(...of the reasonably ridiculous notion that life began here when some mythical magical man in the sky...)
You and everyone else that agrees with your assumption (belief) doesn't really KNOW this, but simply believes it and then tries to pass that belief off as sure knowledge. The only evidence we have, is that life, that we are here. There is no way to do deduce from that alone how it began. Even if you invented a time machine and used it to travel back as far as necessary, what evidence would you collect there at the beginning, to bring back to convince your fellow humans at the present time? In the end, whatever evidence you did collect and bring back, would still have to be believed. It would not constitute incontrovertible proof.
If an intelligent life form came to visit us here on planet Earth, what evidence would be sufficient to convince us that this entity came from a galaxy far far away or even another universe or dimension?
Re:Then where are they? (Score:3, Interesting)
A terawatt signal radiating uniformly would produce 1e12 / (4*pi*(4e16)^2) w/m^2 = 5.0e-23 w/m^2. With a dish the size of Arecibo (7.3e4 m^2) that's -144 dBm (decibels referred to milliwatts). For comparison, the received GPS signal strength is ~ -133 dBm. With a slightly narrower bandwidth, or signal processing techniques that can work at lower SNR (eg looking for a carrier wave over extended periods -- exactly the sort of stuff SETI@home does) that extra order of magnitude isn't hard to come by.
Okay, so a civilization living around Proxima Centauri could plausibly hear our strongest signals. Two possibilities:
1) While intelligent and technologically advanced life isn't exactly uncommon, we aren't so lucky as to have a neighbor as close as 4.2 light years, and the closest is really more like 2,000 light years away, and just happens to be on the other side of a radio-wave inhibiting nebula.
2) There is a civilization around Proxima Centauri, but they no longer use radio waves of any significant wattage for transmission so we can't hear them, and The Untenable Contradiction of Fermitor the Merciless carries significant weight among their scientists, so they assume it's pointless to try to listen for us. :P
That's my biggest problem with Fermi's Paradox, which is that if you take it as an idea which should in some way guide your actions, then it becomes a self-fulfilling prophecy. If you don't take it that way, but rather merely as a point of philosophical interest which shouldn't guide your actions, then you ignore it and keep running SETI.
Distance != Time (Score:3, Interesting)
But, the diameter of the milky way is about 100,000 light years - so, if we assume that pre-Galileo civilization was oblivious to ET, we as a species are only aware of civilization signs within 400 light years or so.
Not true. It's quite possible to observe signals from much farther away; it's only a question of sorting through them to see if any of them look like evidence of intelligent life. There's no particular reason to think that they must have started transmitting at the exact moment that Galileo did his experiments.
Where the relationship between time and distance matters is when you want to communicate with those civilizations, or determine whether they are close enough to detect our signals.
There is another issue about distance that is completely independent of how long our civilization has been capable of detecting evidence of extraterrestrial life, and that is how much power such a signal would require in order to be detected. It is probably impractical for any civilization to produce an omnidirectional signal (unless, possibly, they were only interested in their immediate galactic neighborhood), so we'd have to assume that they take turns beaming the signal to a large number of "promising" stars. The exact number depends on their resources and level of technology, but again there's no reason to think that it has any relationship to pre-Galileo civilization.
The only area where the length of time we've been able to detect such signals is relevant is that that time tends to limit the window of time that such civilizations might have been sending signals that we can detect. We've only been able to detect very weak radio signals for around 60-75 years or so, so if nobody in our light cone has been on the phone to us in that time period, we couldn't have heard them - to say nothing of the fact that given our current level of technology we'd probably also need to have our equipment pointed right at them in order to be able to hear them.
I'm afraid that all that doesn't really tell us very much, except that signals from ET civilizations must be very rare - and given the continued failure to find anything, it tends to cast doubt on whether there are such signals to detect. Either they aren't there (within a detectable distance, anyway) or they're not interested in chatting.
Re:Fermi paradox (Score:3, Interesting)
Every time this thought comes up, my brain falls back to musing that the Universe's dark matter is made up of Dyson spheres, and that the stars we can see are a "nature preserve".
Totally frivolous, I know. And probably easy to test false.
Re:You won't find them (Score:3, Interesting)
Yes, but wont the entire universe die anyway? Why wouldn't any advanced civilization simply accept death and create a civilization of entertainment?
This decadence could end up dumbing them or even destroying them eventually, but this is a possibility.
Re:Aliens Cause Global Warming (Score:5, Interesting)
Not quite. It implicitly presupposes a steady-state universe, which was commonly believed at the time. However, we now know that the universe is not steady-state, and in fact is quite young (13.7 Gy) compared to the age of the Earth (4.55 Gy). Especially if the conditions in the Universe have been shifting, e.g. it has taken time for stars to build up enough metallicity, it is entirely plausible that conditions may be hospitable to life, and yet it is not common, simply because we just got there first. This is particularly important if you accept the conclusions of the Fermi Paradox, which basically states that since technological advancement is so rapid compared to evolution, the first technological civilization in a galaxy will almost inevitably colonize the galaxy before any other civilization has had time to evolve.
Re:My estimate (Score:3, Interesting)
You have just committed a fallacy of equivocation [wikipedia.org]. This is a very common fallacy committed by religionists who try very hard to make their sloppy thinking seem more reasonable.
Re:Then where are they? (Score:3, Interesting)
the famous Fermi Paradox [wikipedia.org] tells us that we're alone in the galaxy.
I tend to agree with you that the Fermi Paradox is strong evidence that there are no space-faring civilizations out there. That doesn't mean that there are no civilizations like our own, it simply means that nobody like us survives.
Are you familiar with the concept of The Great Filter? Read this, I think you'll enjoy it [gmu.edu]. In summary, it makes the case that something prevents civilizations from becoming truly space-faring. That all species face this something, and they are all stopped by it. It could be that only very competitive species create technological civilizations (because those that aren't competitive are content to sit in trees and eat bannanas) and that competitiveness prohibits the kind of cooperation needed to build generation ships. It could be just that simple.
Re:My estimate (Score:3, Interesting)
No doubt.
I'm still trying to figure out how some of them came up with a value < 1 (e.g. 10^-5). I guess they don't hold life on earth in very high regard, themselves included.
Re:You won't find them (Score:4, Interesting)
Considering that we are not ourselves members of an advanced civilization I don't believe we can say what they would do.
I imagine that even an advanced human civilization would be pretty incomprehensible to us.
The instinct to reproduce and grow in numbers is fundamental to all life.
Try telling that to today's first world societies. How many of them have negative net native population growth? So why couldn't an advanced species settle for zero population growth or even negative for a few hundred thousand years (e.g. if they did start out colonizing and then thought better of it).
To "hole up" is to accept death as the local star fades--contrary to the most basic life instinct.
...aproximately 5 BILLION years later...(or whatever) Assuming you haven't managed to figure out a way to stabilize it using, you know, your advanced civilization's technology. (reminds me of the new dr who series where they went to see earth being destroyed) Or that one couldn't wait until 10K years before catastrophe and just pick up then....etc.
Advanced civilizations don't "hole up," they spread.
cite needed, i think. :)
What's more likely is that an advanced tech society treats any form of uncontrolled emission as lost power. Sound, for example is an indication that you are losing energy. Broadcast EM spectrum waves may be similarly treated. They are not likely to be spewing massive amounts of powerful EM in all directions and certainly aren't likely to be shining massive laser/microwave/xray/neutrino/?? comm beams and such at random spots in the sky - that stuff'll be point to point and they'll even most likely recapture the transmission energy.
So, even if they spread out, there would be little way to notice them unless they get on a "call your friends when drunk" jag while we happen to be listening.
Re:Fermi paradox (Score:3, Interesting)
Assuming intelligent alien life take about as long as intelligent Earth life to evolve (give or take a billion years), these other civilizations would have billions and billions of years ahead of us.
Um, depends on the civ/species. Some species might take a half billion year to come up with a new thought or depend on environmental conditions to drive their species's evolution. Others could learn/advance faster than we do and only take 100 years to get 5000 years farther ahead than us.
There is also the thing that a civ that far ahead could just be classified godlike and though they have limits, their kids could seed the entire rest of galaxy with random life, probes to monitor it all, and do it cheaply for an elementary school project on budget of what we'd see as what any parent would waste on any given class room project... say less than about $20 worth of effort. Now what could we do to them? Nothing. We should just be happy to be their classroom project and hope that they don't sterilize the planet when they don't need us anymore.
Fermi's Paradox is flawed (Score:3, Interesting)
Unfortunately, Fermi's Paradox is based on postulating certain axioms which aren't that self-evident at all. So at best it's not a "paradox", but rather proof that you can reach a false conclusion if you start from a false hypothesis.
E.g., that if a sentient civilization exists, it will necessarily colonize every rock and planet in sight. I'm sorry, but while that's the bread and butter of SF, it's not self-obvious at all in the real world. Colonizing is a matter of too many factors which may, or may not, add up that way. E.g.,
1. Colonization happened on Earth only when overpopulation pressures made it happen. Prior to that, most "colonies" were merely trading posts. We were merely interested in buying cheap stuff there and selling it expensively over here, and viceversa.
But here's the fun stuff about over-population: on Earth it seems to have stopped and actually reversed in every country which has access to good medical care and sanitation. People make lots of kids when survival is a crapshot, and they have to beat the odds. If only 1 in 3 of your kids will likely survive, you make 6 to try to beat the odds and occasional flukes. But as soon as survival becomes just short of guaranteed, people first go through a population boom for about a generation, then it sinks in that they really don't need more than 1 child. They might make a second as a sort of a backup, but that's really it then. Most western countries either _are_ currently going down in numbers, or are only saved by immigration from the poorer ones.
So given an Earth where the vast majority of people can get medical care for their child, the population of the whole Earth would actually decline. It's not that far fetched, as possible futures go. Give it a billion years or so, and Earth will probably be no more than a few thousand people in a few quaint towns, surrounded by square miles of woods and nature preserves.
So there you go: that's one example of a civilization which might never have the pressure to offload its population to other planets.
2. Let's go back to those trading posts I mentioned. They happened because there was an economic incentive to. The same incentive doesn't exist yet even for importing anything from the moon.
Basically the hypothesis that we'll start colonizing all around, _depends_ on discovering some miracle engines and/or some miracle sources of energy, so hauling a thounsand tons of steel from Alpha Centauri is cheaper than making it at home. What if the physics we know now _is_ mostly correct, and that economics never works out that way? Who's going to pay for some trillions of dollars worth of a colony ship, if they don't ever expect a return on that investment?
3. (Or 2.a.) To further nail that coffin, what if FTL is really impossible? How's interstellar trade even going to happen without that? (To pay for that colony, you know.) No, please don't jump to a half-baked answer yet.
Let's say we build a mining colony only 5 light years away from Earth. Now let's say we have some damn good engines, that can accelerate to nearly the speed of light by the middle of that distance, then decelerate for the other half of that trip. (And I mean really _awesome_ SF engines there. Nuclear or even fusion don't come even close.) So it takes 10 years for a ship from there to come to Earth. It takes another 5 years for signals from Earth to get there. So from the moment you sent a "yes, I want to buy 1000 tons of steel" order, to the moment you get that steel, it'll be 15 years.
But let's say we build that colony on the idea that it will continuously send stuff, so Earth gets a continuous stream of shipments. Ok. So it takes 10 years for the colony ship to get there, let's say a year to really get the colony going, then 10 years back with the ore. That's 21 years from the moment you bought the ship, to when you get your first shipment. Are you willing to bet a trillion dollars on the idea that you'll still need that ore in 21 years?
Remember that on Earth some resources went
Re:Then where are they? (Score:2, Interesting)
2. Alien's find planet Earth, ideal for life but currently without any.
3. Alien's place building blocks of life on Earth, sit back and watch for a few million years until humans evolve enough to be worthwhile talking to.
4. PROFIT!!
Re:Aliens Cause Global Warming (Score:2, Interesting)
I'm not so sure about that, personally I content that only verifiable hypotheses are in realm of science, other than that its theory or mathematics. Take string theory for example, the mere act of *attempting* to describe nature doesn't mean you *are* describing nature. I maintain that string theory is not science, and I maintain that the drake equation is even further from science than string theory. When these mathematical propositions are tested and we have data to compare them to, then I will accept them as scientific, providing of course that the data matches up.
You see there is the problem, without data to compare your hypothesis against you have no idea if you have made an insightful proposition or produced something as useful to science as a Michael Chrichton novel. If it turns out to be the latter it will be rejected as a baseless and incorrect assumption, so why should it be considered science up until that point?
The problem with a sample size of 1 (Score:2, Interesting)
So if there are between 5x10-7 and 10,000 civilizations in our galaxy, where are they? The answer I think will be interesting - we simply do not know what happens to intelligent species after they evolve. The problem is with the fallacy known as the fermi paradox is that there are far to many plausible reasons why intellegent species may rise and fall, or simply decide not to show up despite having plenty of time to do it.
I consider it vastly more likely that the majority of sentient creatures in the universe have no hands or similar useful appendages and therefore never acquire technology. I reason that planets with oceans (like our own right up to mega planets with water oceans 100s of km deep)would be vastly more abundant platforms for evolution of life in the universe than land area on earthlike planets.
If we could go out in a billion star ships and turn over every rock in the galaxy maybe we'd find most sentient life will be something like a whale or dolphin.
We seem to forget what wanders about on land contemplating financial markets and marvelling at smart phones, is only a vunerably small portion of the bio mass on this rock, and here the oceans are ruled by Cetaceans who in our own example have been here longer than us, and have had some of the highly developed brain structures they share with us millions of years longer, they used to populate hundreds of millions.. but we've eaten most of them). They'd probably persist after cataclysms that would wipe us out. (Octopii and squid are also relatively intellegent too, there's a hint that the format of a ET might be)
So with the majority of ET life being underwater there's little opportunity for tool making by hypothetical aquatic beings, let alone harnessing technologies we have done - which all largely stem from the ability to make fire and bootstrap from there. Consider that the majority of these oceans would be lidded by ice (like Europa) and these types of environments will vastly outnumber earth-like planets in that perfect habitable zone around the right kind of stable star.
So considering planets with habitable land area, in a stable orbit around a stable star, avoiding bombardment or supernova sterilization long enough for life to make the leap to multicellular and upwards, are a rarity - it becomes worse, there are still reasons why ETs may not show up.
Life could evolve at the bottom of a big gravity well -- a much larger planet with such an escape velocity that makes space travel difficult. The planet could have permanent cloud cover, thus the beings inhabiting it never see the sky and never wonder what's out there. They could also be very large like elephants, and therefore won't be inclined to be building flying machines. They could also have a geology absent of fossil fuels, no easy fuel for an industrial revolution. They may just refine a peaceful culture that's stable over longer periods of time and not particularly adventurous.
They may also not develop the right kind of intelligence. Or they may be pathologically self destructive. Our desire to explore and exploit is derived from our ancestors nomadic lifestyle. Without this background we may never have dreamed up the idea of exploring beyond our own world. So who's to stay an intelligent species would inevitably bother beaming signals out to space let alone traveling?
On earth, every single rock we look under, every tiny
Re:Aliens Cause Global Warming (Score:3, Interesting)
Your example, please? Journal, volume number and page number would do - there's a good library just down the road.
Actually, you use the plural. ExampleS, please.
Also, considering that I'm a geologist and I have a sightly different understanding of the meaning of "long-term" to most people (hey, what's a gigayear between friends?), I'd be interested to read what you'd consider to be an adequate "long-term" demonstration of the effectiveness of a proposed closed-ecology system. If I were assessing such a system to commit both myself and my children (and their children, should they choose to have any) to living in ... I'd want to have seen the demonstration / test-bed system working with a real-live test group for at least a generation and a bit. That would mean, getting the first children who conceived in the closed system to the point of conceiving the next generation in the system. Say, at least 16 years (legal niceties aside). That test could be done in reasonable safety - high Earth orbit is as good a vacuum and a radiation test as interstellar space, but a lot more reachable. But the time is the critical requirement.
(Note : I'm not asking for the system to be perfect. Lessons will be learned on the way. But the crew inside the test system would have to fix any problems that occur during the test without importing anything other than data. And preferably not even that - communications links are tricky enough without Einstein sticking his oar in.)
The longest that a closed ecology has been run other than the whole planet is ... a couple of weeks. The various space missions have run on importing food, air and water while throwing away trash. That's not closed. The experiment that I'm expecting you to cite ... well I was watching the reports of it as it was happening. So, surprise me by citing a different experiment.
Are generation ships necessary? :
Assume a drive that can produce 0.1 g from here to around Alpha Centauri (not the most likely candidate - the binary nature makes life hard for planets)
4 light years at 0.1g = 1.0 m/s/s with mid-point turn-over.
4LY = 4* y 4
365* d 1,460
24* h 35,040
3600* s 126,144,000
300,000,000 m 37,843,200,000,000,000
divide by 2 for half-way point : 18,921,600,000,000,000 m
s=0.5*a*t^2 t = sqrt(2*s/a)
= sqrt(37843200000000000)
= 194,533,287 s
= 6.16 years to/ from turn-over
= 12.3 years for the one-way trip.
v = a*t
velocity at turnover : = 194,533,287 m/s
~= 0.64 times legal max. We're getting into decidedly relativistic territory, but not too far in. There would be significant time-dilation effects, making ship-time appear shorter than Earth time, but the effects aren't going to be drastic.
You could do the nearest neighbours without going into generation ships, IF you can sustain 0.1g from your drive for a decade. but if you try going much further, say to the galactic roundabout at Barnard's Star, or to Sirius, and you're into generation ship territory.
Until the physics of Star Trek becomes the physics of the Real World, you're looking at generation ships. (This should not come as news - generations of hard-SF authors have come to the same conclusion, or pulled the FTL driv