Most people think that SETI is worth doing, whether or not they actually believe there are other technological civilizations in the galaxy. Ben Zuckerman, a professor of astronomy at UCLA, is certainly in the skeptics’ camp, thinking there are no technological ETs in the Milky Way, but he’s quoted in this story from QUEST (KQED San Francisco) as calling for more SETI. “Given that the costs are not very high,” says Zuckerman, “why not continue the search?” Zuckerman, who once worked with Carl Sagan in graduate school, no longer thinks we live in a crowded galaxy, but a potential discovery of this magnitude justifies the relatively modest expenditure.
It’s not surprising to find Jill Tarter echoing Zuckerman. The recent funding problems of the Allen Telescope Array have not daunted the woman who more than anyone else has come to represent the search for other intelligent life. And although she believes we may one day come to the ‘extraordinary conclusion’ that we really are alone, the time for drawing that conclusion is hardly near. We have hundreds of billions of stars to choose from in the Milky Way and hundreds of billions of galaxies beyond our own, and in those terms, we’ve barely begun to search.
Image: SETI searcher Jill Tarter. Credit: Sven Klinge.
The KQED story takes note of the new element in SETI research, which has to do with the Kepler mission. With the discovery of more than a thousand planets orbiting stars in its field of view, Kepler may well have found the first true Earth analogues — we’ll know as its data continue to be analyzed. The Kepler findings give us a targeted list of stars that should be high priority for the SETI hunt. “This,” says Kepler team member Dimitar Sasselov, “is where we should be looking for the signals coming from other civilizations.”
Just a month after the hibernation of the Allen Telescope Array due to money problems, the Green Bank radio telescope facility in West Virginia announced its own effort to study 86 of the stars chosen from the Kepler list, scanning an 800 mHz range of frequencies simultaneously (that’s 300 times the range available at Arecibo). Among the 86 stars Green Bank will be studying are 54 candidate systems identified by Kepler as potentially having a planet in the habitable zone. Thus the largest steerable radio telescope in the world picks up on the Kepler work, another case of SETI soldiering on when resources are scarce.
And fortunately, the Allen Telescope Array itself is back in business, thanks to more than $200,000 in donations from some 2400 donors and an infusion of money from the U.S. Air Force, which should keep the project running for the next several months. In the longer term, the ATA needs $2.5 million per year to keep operational, so fund-raising will doubtless become a permanent fixture of the facility’s operations. The SETI Institute’s page supporting a search of the Kepler candidates using the ATA continues to gather donations, a reminder that while SETI may be for now a relatively low-key project, it’s one that generates wide public interest.
Image: A single antenna of the Allen Telescope Array, night. Credit: Allen Telescope Array.
My own views on SETI parallel those of Ben Zuckerman. I doubt intelligent life is widespread in the galaxy, but the whole point of science is to extend our knowledge. By all means, let’s keep SETI in business, and maybe we skeptics will be proven wrong. And just letting the imagination run, it’s fascinating to ponder the world we might live in if one of the Kepler planets turns out to be leaking some kind of artificial radiation. Remember that Kepler is looking out along the Milky Way’s Orion arm, in an area where fewer than one percent of the stars the mission examines are closer than 600 light years. If we were to detect a transmission, it would take 1200 years to receive any return to our potential response. I suspect a detected signal, after revolutionizing our view of ourselves in the cosmos, would probably remain unrepeated and untranslatable, a mystery for our time, an enigma speaking of all we have yet to learn.
To Paul, would you please expound a little bit on the reasons you think intelligent life in our galaxy is rare. Reasons to do with the Fermi Paradox, and/or biology perhaps? This kind of speculation is so interesting
Searching for E.T is a waste of time, but what I want to know is: Why would we want to find other inteligent species? Without any inteligent species, we can take all planets and the Milky Way for ourselves. We will have no competition. We will never have a war like in a SF movie’s. It is far better that we are alone than that there are other E.T’s out there. We will only have a problem with our own species. Maybe it is better to accept that we are alone in this galaxy.
Mike, I’d never want to sound doctrinaire on the point, but I do tend to go more with the Fermi paradox than anything else. From my perspective, life should spring up abundantly — we see evidence of how widely spread the resources are. Although there are many possible answers to the Fermi paradox, my hunch is that the simplest one is correct: No other intelligent species — or very few — in the galaxy. My deep hope, of course, is to be proven wrong.
Thanks Paul, my own hunch is that intelligent, even technological (bronze age and up) ETs are in fact common. But interstellar travel is extremely difficult and expensive, perhaps nearly impossible. For them as well as us. Cheerfully hoping to be proved wrong.
To Henk, you think doing scientific research is a waste of time?
For myself, I find that any conclusion about ET abundance is so dependent on overloading the available data with assumptions as to be no better than rank speculation. Instead of reaching for conclusions, I instead accept that the reality that the data is scarce and that we simply do not know.
Whether or not we choose to look for ET tends to require subjective assessment of those assumptions; that is, we make assumptions of what we may or may not find, and what we do or do not look for. At least the search itself delivers more data, which is what we most need. If someone wants to pay for that, I will applaud the effort.
It is also possible that faster than light travel is impossible. That could also be a explanation of the the Fermi paradox, but still I believe that other intelligent life forms are extremely rare. I even think we are the only intelligent life form in the local group. What is rare if there are 1 billion E.T’s scattered in 125 billion galaxies. That means that every 125 galaxies has 1 E.T. Then intelligent life is still rare. We will never make contact with them.
Re Mike’s thought on interstellar travel, I think that while it will indeed be difficult and extremely expensive, it’s likely that a sufficiently advanced civilization will try it. But you’re right that it could account for the Fermi paradox if those who did try it didn’t find ways to reduce that cost. A few exploratory probes don’t necessarily translate into an outward wave of colonization. So many questions, as Ron S points out, and so little by way of data! Henk, it’s possible we are the only intelligent life in the Local Group, but with so little information, that’s nothing more than a guess. Just as my own speculation about intelligent life is basically a personal hunch.
Yes Ron S, hunch means rank speculation for sure. We need more data.
That surely means we need more funding for the projects that can produce more data. I don’t want to guess, I want to know.
Gentlemen. I do tend to agree with your lines of reasoning. The nearest advanced societies are probably hundreds or thousands of light years away. But we are not only dealing with vast distances we must also consider the unimaginable elements of time involved, 100 of millions or years or perhaps a few billion years. Civilizations may have developed long before ours and have come and gone. We have seen the rise and fall of civilizations here on earth…Greeks, Romans, etc. Just because a society is high tech does not mean it will last for long periods of time. How long can a civilization last before a natural disaster or a self inflicted one brings it to an end….?????
There is a scifi novel by Poul Anderson called “Starfarers” that deals with this subject. It is kind of a heavy read, but IMHO is worth the effort. For those interested in this topic I suggest this novel as a must read…….
Regards
Tom
The problem with SETI is that its methodology is flawed; so no matter if the amount of money put in is relatively modest it is unlikely to be worth it.
According to the Wiki article on the Fermi paradox we would be able to detect TV & radio from an earth civilization from about 0.3 light years. As civilization becomes more efficient (i.e. leaking less radiation into space) and compress signals (as we have started to) this distance is likely to decrease. Of course there is still the possibility of intercivilization communication, but such communication is likely to be target (in order not to waste energy and decrease the risk of eavesdropping).
I think the Fermi paradox is relevant from the perspective “why are we here, where are the UFOs and green men?” rather than “why haven’t they called us yet?”.
The conclusion that SETI is strongly indicated as “a waste of time” by the Fermi paradox, is not just due to am implied lack of ETI’s. We need two minimal conditions for SETI to work
1) that our galaxy in heaving with ETI’s
2) that a very large subgroup of these have such an incredible outward-looking worldview that they undergo continually bouts of spending many times the current total human energy budget on (unsolicited) signal sending.
The Fermi paradox merely points out, that if even one of those signalling civilisations, transferred the energy of its transmitting budget into interstellar travel, it would colonise every unoccupied portions of our galaxy within a few million years. Even if slow-boat worldship travel was the only possibility, this process should only take a few ten’s of millions of years.
Conclusion: they’re either here in Sol, or we are alone in the Milky Way. We should be looking for the front door of their local office, yet some persist in thinking it productive for intensive searches for their telegrams – that is the paradox.
I fully concur with the thoughts in this article. We don’t know if the galaxy is rich in technologically intelligent life or not, but there is no harm in looking, especially with the very low cost involved. The ATA though not cheap, is not a dedicated SETI instrument, but rather piggybacks SETI onto other observations.
I fully expect that we will find evidence of life elsewhere long before we either find evidence of technological civilization or exhaust the search.
@ Tom Baty: “Just because a society is high tech does not mean it will last for long periods of time.” Actually I disagree. Look at the logic of it. A high-tech society (by my definition) is one which colonises its local planetary system. The size of the system and of the opportunities for growth are so large that the result is a reversal of the current trend towards global unification, and a variety of human and post-human civilisations result — on Mars, in the asteroid belt, in the Jupiter trojan swarms, the centaurs, the major giant planet moons, and so on. Because of the large distances involved, these civilisations are only weakly mutually interdependent in physical terms. In the current global society, according to the saying, if New York sneezes, the rest of the world catches a cold. But in the Solar System it must be different: civilisation on Earth, or Mars, on in a swarm of space colonies can fall without dragging down the rest of the multi-global economy with it. No doubt civilisation will collapse from time to time in one location or another, but so long as the spread of civilisation is large enough, other locations will survive, and may later move in to recolonise the fallen locations. On an interstellar scale, clearly, the security of the heritage of civilisation is vastly enhanced. So once a species colonises space, then that is the big bang of life in the Galaxy, and only a short time later (even without fast interstellar transport) the whole Galaxy is permeated by that species and its descendants.
Light speed communication limitations for giga-Milena advanced interstellar civilizations communicating across the mega-parsecs? I doubt it…. IF they are there. We’ve just got to learn how to listen…
Perhaps there are many civilizations in the galaxy, but not at the same time. I suspect were we to travel extensively through the Milky Way, we’d find plenty of Earthlike planets littered with the ruins of civilizations past. And we’d find an equal number of planets inhabited by something akin to our dinosaurs, the time for their advanced civilization hundreds of millions of years in the future. Not only is space vast, but time also. It is folly to think that the other advanced civilizations must exist during our time. They each have their own time. What few do overlap in time are likely so far away as to escape detection.
Even if there is no other life in the Universe or at least the Milky Way galaxy – which even Rare Earthers like Brown find doubtful, at least when it comes to simple organisms – the idea that humanity can own and dominate the galaxy is laughable in terms of comparing our size to the rest of the Cosmos. We may dwell on various rocks out there, but rule something so vast is hubris and arrogance at its finest.
Some of the comments here also show how much humans still think they are the literal and social center of everything, despite several centuries of astronomical research showing just the opposite. And if we have not seen any aliens trying to contact us, then they must not exist according to this logic. Humanity has a LONG way to go.
An extraterrestrial civilisation wouldn’t pick up signals from Earth even if it’d be located on a planet around Alpha Centauri, unless we’re talking about tight, directed beams sent out by huge radio telescopes. Even the strongest of our artificial signals incidentially sent out into space are barely detectable a light year out.
So even if there’s a large number of extraterrestrial civilisations out there in the galaxy, or even our stellar neighbourhood, we couldn’t detect them unless they have their own SETI and send messages directly to us using powerful telescopes.
The Sun itself is a star which is pretty hot compared to the majority of stars we find in the galaxy. Perhaps most civilisations evolved on life-bearing planets orbiting Red Dwarfs, so the Sun is only a low-tier target in their own search for alien life, if they do such a thing at all!
What we could do with a dedicated effort is to search for energy intensive alien activitiy, such as starflight. Antimatter engines powering large (1,000,000t) starships could be detected over tens of light years, if they are pointed directly at us, fusion too, with larger telescopes.
I think the odds favour life and intelligence. There could be Billions of earthlike worlds in our galaxy alone and given our current understanding of life and evolution, life will probably have evolved on quite a few of them and where there is complex life, intelligence may evolve as well. Here on Earth, the mammal-hominid path is not the only conceivable route to intelligence. Imagine if the dinosaurs hadn’t been wiped out. Some dinosaurs, pack hunters such as Velociraptor, had large brains and probably were pretty intelligent already. Imagine where that could have led if it had been allowed to go on for another 65 Million years?
My explanation for the Fermi Paradox is not that we’re alone – considering what we know about the abundance of planets in the universe that’s pretty unlikely – but that detecting incidental artificial signals over the vast distances of interstellar space is incredibily difficult.
I think that the ‘life is rare” hypothesis will crumble as we discover more about the cosmos, just like the belief that other solar systems are rare or do not exist at all did in the past.
Here’s Michael Shermer’s 2002 essay on why Et hasn’t called:
In science there is arguably no more suppositional formula than that proposed in 1961 by radio astronomer Frank Drake for estimating the number of technological civilizations that reside in our galaxy: N = R fp ne fl fi fc L
In this equation, N is the number of communicative civilizations, R is the rate of formation of suitable stars, fp is the fraction of those stars with planets, ne is the number of Earth-like planets per solar system, fl is the fraction of planets with life, fi is the fraction of planets with intelligent life, fc is the fraction of planets with communicating technology, and L is the lifetime of communicating civilizations.
Although we have a fairly good idea of the rate of stellar formation, a dearth of data for the other components means that calculations are often reduced to the creative speculations of quixotic astronomers. Most SETI (search for extraterrestrial intelligence) scientists are realistic about the limitations of their field; still, I was puzzled to encounter numerous caveats about L, such as this one from SETI Institute astronomer Seth Shostak: “The lack of precision in determining these parameters pales in comparison with our ignorance of L.” Similarly, Mars Society president Robert Zubrin says that “the biggest uncertainty revolves around the value of L; we have very little data to estimate this number, and the value we pick for it strongly influences the results of the calculation.” Estimates of L reflect this uncertainty, ranging from 10 years to 10 million years, with a mean of about 50,000 years.
Using a conservative Drake equation calculation, where L = 50,000 years (and R = 10, fp = 0.5, ne = 0.2, fl = 0.2, fi = 0.2, fc = 0.2), then N = 400 civilizations, or one per 4,300 light-years. Using Zubrin’s optimistic (and modified) Drake equation, where L = 50,000 years, then N = five million galactic civilizations, or one per 185 light-years. (Zubrin’s calculation assumes that 10 percent of all 400 billion stars are suitable G- and K-type stars that are not part of multiples, with almost all having planets, that 10 percent of these contain an active biosphere and that 50 percent of those are as old as Earth.) Estimates of N-range wildly between these figures, from Planetary Society scientist Thomas R. McDonough’s 4,000 to Carl Sagan’s one million.
I find this inconsistency in the estimation of L perplexing because it is the one component in the Drake equation for which we have copious empirical data from the history of civilization on Earth. To compute my own value of L, I compiled the durations of 60 civilizations (years from inception to demise or the present), including Sumeria, Mesopotamia, Babylonia, the eight dynasties of Egypt, the six civilizations of Greece, the Roman Republic and Empire, and others in the ancient world, plus various civilizations since the fall of Rome, such as the nine dynasties (and two republics) of China, four in Africa, three in India, two in Japan, six in Central and South America, and six modern states of Europe and America.
The 60 civilizations in my database endured a total of 25,234 years, so L = 420.6 years. For more modern and technological societies, L became shorter, with the 28 civilizations since the fall of Rome averaging only 304.5 years. Plugging these figures into the Drake equation goes a long way toward explaining why ET has yet to drop by or phone in. Where L = 420.6 years, N = 3.36 civilizations in our galaxy; where L = 304.5 years, N= 2.44 civilizations in our galaxy. No wonder the galactic airways have been so quiet!
I am an unalloyed enthusiast for the SETI program, but history tells us that civilizations may rise and fall in cycles too brief to allow enough to flourish at any one time to traverse (or communicate across) the vast and empty expanses between the stars. We evolved in small hunter-gatherer communities of 100 to 200 individuals; it may be that our species, and perhaps extraterrestrial species as well (assuming evolution operates in a like manner elsewhere), is simply not well equipped to survive for long periods in large populations.
Whatever the quantity of L, and whether N is less than 10 or more than 10 million, we must ensure L does not fall to zero on our planet, the only source of civilization we have known.
So there is it—most likely 2.44 civilizations in the Milky Way galaxy. Lucky for us they’re on the far side of the galaxy; I say this recalling the theme from the 1960’s Territorial Imperative book. But keep looking SETI! Arthur C. Clarke held the view that another great alien race just might share with us their keys to the stars.
James D. Stilwell
There are other solutions to the Fermi Paradox apart from the all or nothing “already here or not there at all”. The one I have some non-binding interest in, if only as a counterexample to that perhaps false dichotomy, is best known from Charles Stross’ book Accelerando, although he’s not the first to propose it. Basically, notions of interstellar travel may just be the product of our little monkey brains extrapolating the Age of Exploration into seemingly analogous environments that are in fact profoundly different. If – and this is of course as speculative an “if” as any other notion about ETs – if posthuman augmentation is possible then perhaps our descendants or AI replacements will be living in a world so interconnected and informationally rich that the prospect of moving interstellar distances with the huge transmission delays and severely limited bandwidth that would entail may not be analogous to exchanging mail across the Atlantic by boat so much as lobotomising yourself. Malcontent superbeings may not be able to elect to pull up stumps because they can’t bring enough of their infosphere with them to make it worth the attempt. So they stay put and self-limit themselves to a Kardashev level 2 society that as it becomes more energy efficient will disappear from galactic view. The future of our species may not lie in sailing the ebon seas so much as lotus eating, navel gazing or immersion in a cybercosm far richer than the meagre offerings of the conventional universe.
Utterly speculative and full of handwaving, of course, but the point is that there may be solutions to the paradox that just haven’t occurred to us yet at our current stage of technological development. SETI is IMHO still worth it even if the chances are as infinitesimally close to zero as you care to call it, as the cost is very small indeed and lets us set at least some concrete limits to the issue.
@James: I don’t think the rise and fall of political or economic systems among subgroups of humanity has any bearing on the L of the Drake equation. L should describe all of humanity, and so far the evidence has been consistent with L = infinfity: Humanity has evolved from a small tribe in Africa and never stopped expanding until filling the entire Earth.
We have been “intelligent” for a few million years, “technological” for a few millenia, “observing” for a few centuries and “communicating” for a few decades. If we become starfaring (a parameter lacking from Drake’s equation), the boundaries of the Earth will disappear and we will be set to expand across the galaxy in the same way we did across the Earth, in not that much more time.
@Mark: This makes it very unlikely that during our own expansion we will come across ruins of civilizations past: Any ruins of extinct non-starfaring species should have been thoroughly picked over by starfaring archeologists, over and over again. And we would should be finding these archeologists and their artifacts all over our own backyard.
The real wild-card in Drake’s equation is not L. It is fl, the probability that life arises spontaneously on a planet. We have a lower limit of 1 divided by however many planets we think are in the universe. That is an astronomically small number. The fact we have not discovered other life despite searching for it provides an upper limit. Not much of one, admittedly, making it well worth to keep searching. However, the Fermi argument (as above per the “archeologists”) provides strong evidence that fl is indeed astronomically small. Also, I know of no convincing argument that it should not be very small, given the huge gap between random chemistry and the self-sufficient, self-replicating systems we sometimes call the “miracle of life”. To peg it to a value of 0.2 is completely unwarranted and relegates any conclusions depending on this assumption to pure fantasy.
I’d love to be proven wrong, but I think all the real evidence there is points to the conclusion that we are alone, for better or worse.
@Mark
“we’d find plenty of Earthlike planets littered with the ruins of civilizations past. ”
Depends on what you mean by ruins. If you are thinking pyramids, stone temples etc, I doubt it. Over millions of years the remains of a civilization may be no more than a smear of carbon and iron in the rock strata. Once civilized worlds will have reverted to a natural state. We would have to be very lucky to find standing ruins from a [recently] dead civilization. Our best hope may be artifacts and ruins on or in quiet, stable dead worlds, like our moon.
@Paul: I agree that there is a good chance that as we evolve we may turn inwards and contract our communities to decrease communication latency, rather than expand them. Even so, I believe, we will have the urge to send out “spores” of ourselves throughout the galaxy in order to have descendants that can do the same in more and more locations. We would also appreciate the information coming back in from those other worlds, even if meaningful two-way communication is impractical. The effect, then, would be the same, except for the nature of expected alien artifacts. Perhaps we should be looking for small balls of superconducting nanocircuits floating among the Oort cloud.
Mark and James. I thank you both for the contribution on the concept of limited lifespans of civilizations, you both perhaps explained it better then I did. The value of “L” , the lifespan of civilizations and their colonies is in fact the determing factor of “N” in the Drake equation. The text “Interstellar Migration and the Human Experiences” which is a collection essays on this subject had one essay which I found interesting (sorry I forgot the author).
He put forward the concept that cultures go through a growth pattern just like an individual..ie…childhood, to adolences, to young adult, to maturity and then to old age and finally death. While the idea that the galaxy is filled with the ruins of interstellar civilization from ages past is rather morbid it may explain many things and give an answer to some of our questions.
This has been a very enlightning discussion, while we are not all going to come to agreement on every point I believe that we are in a common mind that SETI needs to continue. If for no reason that we never know if don’t try. Absence of proof is not proof of absence.
Tom
Paul Talbot, your concept that an intensive information sphere drives a third alternative to the Fermi paradox only works if every technological society, without fail, goes through such a phase before startravel becomes possible. Since we haven’t hit the technological singularity yet (if, indeed, we ever will), and yet are close to being able to design starships, your hypothesis looks unlikely, though it is a very interesting idea
I agree with Gunnar Larsson: the methodology of SETI is flawed. They won’t send us a detectable message unless they already know we are here, and they won’t know we are here unless they already have a ship in our Solar System. Therefore SETI is targeting every star except the right one — our own!
Much more likely, as Max says, that we’d pick up some signs of alien engineering such as starship exhaust or Dyson spheres. NB at the Worldships symposium Alan Bond pointed out that his Daedalus engine seen from afar would look very much like a pulsar, opening the possibility that we have already observed starships accelerating. (I don’t believe a word of it, but that’s what he said.)
Stephen
Oxford, UK
James D. Stilwell, I agree that we have no reason to believe that technological human civilisations should last any longer than previous civilisations of similar spread – the problem is that there are none. If we further spread to other parts of Sol, we would become very hard to eradicate completely, and eradication is important here. For your argument to be meaningful the end of technological society must indicate that no further reconstitutions would follow.
Also you should only put fl at 0.2 and call it conservative if you were joking. The limits of the phenomenon that is life would have to be incredibly finely tuned to this universe for it not to be either be 1 or very, very close to zero.
The simplest known organisms are amazingly complex, and, of even greater importance, they all have a single common ancestor that we know to also be amazingly complex. This implies that that the chances of abiogenesis may be thousands of orders of magnitude to one against. On the other hand take the assembly of life as being inevitable, once a certain simple core for it is achieved. Given the complex chemistry and higher energy state of the prebiotic world, it would be hard to conceive that such a core (if life could really be generated this way) did not assemble once every few millennia somewhere on our planet. That would put the chances that life did not develop here in the thousands of orders of magnitude to one against. So fl =1 or 0.
I kind of hestitate to bring this up as it is an overworked theme in science fiction. The zoo concept is still with us, but I must say I have some strong doubts about it. For us or other non-star traveling civilizations to be off limits to advanced civilations would require coordination between them. A prime directive and a zoo hypothesis is to me very unlikely for this reason. I view that star travel will be so resource intensive and difficult that a United Federation of Planets to be nearly impossible. Commincation let alone traveling interstellar distances will be so time consumming that I find such an idea to extremely out in left field. Intersteller travel to my thinking is not impossible but is going to be so energy intensive that except for exploration and colonization in the local area it will just not be practical and realistic.
Still would like to hear your thoughts on the zoo hypothesis???
Tom
I have to side with ENIAC for the high value of L but take issue with calling it infinity. If all technological civilizations are effectively immortal then, for the purpose of the drake equation, their lifespan collapses to a calculation of their average time of emergence to the present. We really should acknowledge that the minds and mindset of each independent emergence would likely be very different from each other. Some nascent advanced civilizations may be very self-destructive, others less so and some not at all. If we take humanity and place it on a million planet systems, how confident can we be that not a single one of these will find a permanent solution to its own destruction? If we do the same exercise with a million very different intelligent species, it seems very hard to believe that less than a tenth of these will also find a solution. Indeed, is seems probable that at least 10% of them would be totally immune from the problem in the first place. This would place the very lowest limits of L at 100 million years, and the maximum at just a billion or two. Of cause its MEDIAN value might well be range from 1,000 year to a billion, but that is not relevant to calculating L
@Rob: I think you are onto something here with the “finely tuned”.
In order for life to be possible, there would have to be heavier elements, which can only be made through certain incredibly fine-tuned nuclear resonances. Even with heavy elements, as you say, the spontaneous formation of life seems incredibly unlikely, and it would require the universe to be incredibly big to allow it to happen even just once.
Well, as it turns out, those incredibly fine-tuned resonances do exist, the universe is incredibly big, and we are here.
A couple of controversial thoughts. The method used for the value of L, as a an average lifespan, implies all civilisations die out. If FTL is possible then any civilisation attaining it becomes effectively immune from extinction apart from cosmological scale processes. Metallicity was sufficient by 6bya for terrestrial type planets and life. Unless we are incredibly improbable on a 4 or 5bya time period some (perhaps relatively few) advanced civilisations should have appeared over the past billion years or so. If one or more achieved FTL ability they will probably still be around, very widespread and not using EM radiation to communicate.
I agree with others that the best place to look is right here. If you are prepared to be challenged (and I was shocked to the core), then take a look at Leslie Kean’s latest book on the taboo subject of UFOs… curious reading indeed and unusually rigorous
Tom:
This makes sense, and there will not be interstellar empires, federations, or zoos for that reason. However, it needs to be emphasized that “colonization in the local area” still means unlimited expansion. Even though each step in the expansion is local, it will not stop until the galaxy is filled.
It would take coordination to hold up the expansion, and lack of practical travel and communication would make that more difficult. Total lack of coordination leads to expansion at constant speed. This speed would be determined by the amount of time it takes a colony to take hold and mount their own “local” colonization effort, plus travel time. As operational experience and technological progress accumulate, this process will most likely accelerate rather than slow down.
A constant speed expansion front will lead to cubic growth with time until the flat boundaries of the galactic disk are reached, then square growth for a while until it levels off as further and further limits are reached. It will all be over in much less than a billion years.
The only alternative is no colonization at all.
Rob:
If there was such a thing as coherent civilizations over interstellar distances (with FTL, perhaps) you’d have a point. However, without FTL we are talking many, many independent colonies. For all of the ones that happen to originate from the same home world to self-destruct together would take an incredible amount of determination and coordination over interstellar distances. Not likely.
If just a few self-destruct, that means nothing: The void is quickly filled by recolonization, the expansion not even slowed a bit.
Regarding the zoo hypothesis, see this paper, looks like it is very unlikely that it would be possible to maintain such a state given the finite upper speed limit imposed by the laws of physics.
Eniac. Thanks for your response and I do tend to agree. I remember reading somewhere an essay comparing intersteller colonization to the polynesians island expansion in the Pacific. An interesting comparision,but in my view not totally valid for many reasons.
Andy. I appreciate your sending me that link, very interesting indeed!!!
Tom
With little data science tends to follow trends, much like those seen in fashion or entertainment. The trend now seems to be shifting towards “intelligent life is rare in the galaxy” . (the one important new data point is that earth analogs appear to be rare, especially around the K stars which were very recently thought to be the best places to look for ETI. Kepler has plumbed that well pretty effectively and it appears to be largely empty, unfortunately). Thus, obviously, we need more data and the ATA can provide some of that. The question remains, though, is it cost-effective? Drs. Tarter and Shostak keep throwing around a figure of $2.5 million a year. That’s just about exactly half the operating budget for the Kitt Peak National Observatory! I challenge anyone to make a reasonable case that the scientific output per year of the ATA is within two orders of magnitude of that of KPNO (you pick the metric, papers in peer-reviewed journals, scientists trained, etc). So, once again Ben Zuckerman is wrong, the costs, at $2.5M/year ARE VERY HIGH (I say once again because Dr. Zuckerman is known within the community for being the first person to discover a brown dwarf, on roughly 10 different occasions. One might want to google him and “sierra club” to find another famous instance.) Yes, you can make the “win the lottery” argument but it’s a very weak one, especially now. My position is that the $250K or so raised is just about right, and perhaps a bit generous.
With respect to the Fermi paradox, I still do not think that people have really taken on board the DEEP TIME aspect.
The AVERAGE intelligent race in the MW should be many millions of years older than us. The AVERAGE Earth like planet is c. 1 billion years older than Earth. Earth-like planets should have arisen in the inner galaxy SEVERAL billion years ago.
I’m sorry but I find it just inconceivable that every single race either destroys itself almost immediately or that interstellar travel (even by unmanned probes) is impossible over these timescales.
Eniac: “The real wild-card in Drake’s equation is not L. It is fl, the probability that life arises spontaneously on a planet. We have a lower limit of 1 divided by however many planets we think are in the universe. That is an astronomically small number. The fact we have not discovered other life despite searching for it provides an upper limit.”
I disagree and am actually puzzled by such an unfounded assertion, especially by a well-informed person like Eniac. It is both scientifically and statistically meaningless.
The fact that we have not yet discovered (any biological) life on extrasolar planets, has, of course, nothing to do with its existence, but with our present utter inability to discover and spectroanalyze any signs of it. Our galaxy and the universe may be teeming with life, but we still wouldn’t know about it. All that we know right now is that sunlike stars and planets, including small rocky planets, as well as water, are very common. All the rest is still speculation.
Personally I think that the weakest links in the chain are not fl nor L, but rsther fi and fc, resp. the arising of intelligence and technological civilization. Life on earth and its history have shown that intelligence is not an inevitable outcome of life, bacteria have been extremely succussful for billions of years without it. Even organization is possible without high intelligence (termites, ants, etc.).
And even the rare higher intelligences that we know of, such as primates, cetaceans, elephants, parrots, crows, …, have rarely given rise to any technology worth mentioning.
Humans themselves have lived on earth for hundreds of millennia without developing much technology.
There have been some informed estimates, mentioned in several posts here that the number of truly habitable terrestrial planets orbiting sunlike stars in our MW galaxy probably ranges in the order of 50 to 200 million. This meaning a terrestrial planet in the Continuously Habitable Zone (CHZ) with atmosphere and liquid water for at least 3 gy.
Let’s take 100 million as a reasonable guesstimate. That is a wonderful number with regard to potential future real estate for colonization, but a lousy number with regard to the chances of intelligent life and civilization.
Let’s assume the following, not too unreasonable:
1) All of those 100 million give rise to some kind of primitive (prokaryote equivalent) celled life;
2) 10 % of those give rise to higher (eukaryote equivalent) cells; that’s 10 million;
3) 10% of those give rise to higher life, meaning multi-celled, specialized organs; that’s 1 million;
4) 10% of those give rise to some form of intelligence; that’s 100 thousand;
5) 10% of those give rise to higher intelligence capable of some form of civilization and technology; that’s 10 thousand;
6) 10% of those actually make it to high-tech; that’s 1000.
Let’s reasonably conclude here that the total number of technological civilizations in the entire MW galaxy’s lifespan is not more than a few thousand. And that is (very) optimistic. The lifespan of a terrestrial planet near a sunlike star suitable for higher life is about one to a few gy. Before that the planet (crust, atmosphere, oceans) aren’t ‘ripe’ yet, after that it gets too hot for higher life. That is the ‘window of opportunity’. If the mean lifespan L of a techno civ is indeed ten to a few tens of thousands of years, and all of those techno civs are randomly spread across the the windows of opportunity of all those habitable planets, then the chance of two techno civs significantly overlapping is probably on the order of a percent orso.
I see only two ways of having a higher chance of more than one techno civ overlapping long enough for contact.
One way is if for some reason planets, life and intelligence are maturing across a galaxy at about the same time to get a chronological ‘concentration of civilizations’. I see no compelling reason for that.
The other way of is if one techno civ has made it to a stage where is has overcome its childhood self-destructive tendencies and has become virtually immune to extinction, probably a multi-planet species already.
We may become the first one of that kind in our MW galaxy.
A bit further to my previous comment: as I always say, first things first. Although I do not object against spending such a small sum on SETI (less than half an hour military presence in Iraq), I strongly suggest that we should first get a good overview of planetary systems in our galactic neighborhood, plus thorough spectroanalysis of their atmospheres for any biosignatures.
We are talking about sending messages to neighbors, but we don’t even have a good idea what our neighborhood looks like.
Missions like TPF, Darwin, E-ELT, etc. should be top scientific priority.
Ronald
“1) All of those 100 million give rise to some kind of primitive (prokaryote equivalent) celled life;”
Ronald, what is your argument for this ludicrously large probability of life appearing – 100% on clement worlds!?
That our instruments cannot yet detect lower life? Well, our instruments could detect those thousands of high tech civilizations you asssume exist – civilizations which become effectively immortal once they start colonising the galaxy.
Why should life’s apparition be rare?:
Biologiststs have been trying to create life in a laboratory starting from inanimate substances for some time now, by creating environments highly amenable to the apparition of life – and, so far, have utterly failed.
That’s a rate of success significantly lower than 100% – 0%, to be exact.
And, of course, these scientists planned their experiments, they sought to recreate the early-earth processes that have the greatest likelyhood to create life, unlike the random chemical reactions that occured on early earth.
Further, in any given environment (inncluding primordial earth or other planets), there’s a large, but limited number of chemical reactions that can take place – throughout billions of years, evolution didn’t stumble upon a magic chemical reaction that gives birth to life.
Life appeared through a process involving thousands of chemical steps (at the very least) that had to take place in a specific order.
Why thousands of steps? Why specific order?
Because, if that were not the case, we would already have laboratory created life – the recipe for life would be so simple as to be already figured out.
Because, if that were not the case, there would be more than one tree of life on earth, more than a single primordial cell who managed to come into existence in billions of years of random chemical processes.
Because life is just that complex.
What’s the mathematical probability of one chemical step of this kind occuring?
It differs from step to step, but, considering that each such chemical reaction translates into the need for a specific environment to exist (from a multitude of possible environments) – not very large. On the other hand, it may not be very small, either.
What is far more interesting is – what’s the mathematical probability of thousands of steps occuring in just the right order?
Well, the probability decreases FACTORIALLY with each added step:
If there are N STEPS, the probability of a specific arrangement of steps is n(n-1)(n-2)…1 aka n factorial
For example – 2 steps – the probability of a specific arrangement is 1 in 2.
3 steps – 1 in 6; 4 steps – 1 in 24; ……………….
100 steps – 1 in 9.3326215444×10^157 (as in TO THE POWER 157); ……………..
1000 steps – 1 in 4.0238726008×10^2567 (yes, TO THE POWER 2567):…………….
10000 factorial – 1 chance in 2.8462596809×10^35659 (TO THE POWER 35659!!)
Do you have any ideea how small these numbers are?
If you take 200 million candidate worlds (let’s say, existing in the Milky Way), each supporting 4 billion years worth of random chemical reactions, and you insert such incredibly small numbers, the result will tell you, with near-certainty, that Earth is the only planet where life appeared in the Milky Way since the Big Bang!
The result will tell you that, probably, Earth is the only planet where life appeared in the Local Group!
And this, of course, explains the Fermi Paradox nicely – as Eniac and others said upthread:
The reason no civilization colonised the galaxy in the last few billlion years is because no such civilization existed.
@Ronald,
Your calculation assumes all civilizations are confined to their home stars. If they can travel, then the potential for meeting a current extant civilization is going to be a lot higher.
Civilizations on earth, while short in span, are constantly replaced by newer ones. I would argue that once a civilization arises, civilizations will continue until at least the extinction of that species, which in terrestrial terms is about 1 million years.
Apologies if this has been posted here before, but here is a recent paper covering much the same area as Lineweaver, i.e about the spacial and temporal extent of the GHZ :
A Model of Habitability Within the Milky Way Galaxy
Gowanlock et al July 2011
http://arxiv.org/PS_cache/arxiv/pdf/1107/1107.1286v1.pdf
I find it inconceivable that intelligence, once developed, can be wiped out on such short timescales as some on here believe. Once a civ has populated more than one system they are almost extinction-proof. Interstellar travel in the inner galaxy (where most habitable planets exist according to the paper) is that bit less daunting because the stars are nearer together.
Avatar2.0 I take it that you consider fusion in stars highly unlikely as well, as we have failed so far to create self-sustained fusion reactions?
Your maths example is fortunately not that relevant since not all configurations are equally likely. Configurations that can multiply themselves successfully are much more likely than configurations that can’t. For example humans tend to have all the limbs in the right places as that makes them competitive, as opposed for example having the head and one leg switch places or any other configuration (though such an organism would consist of the same number of atoms and hence be considered just as likely if only the number of atoms were considered).
One reason that life is consider likely is that it developed almost as soon as it was possible on our planet. Complex life on the other hand took billions of years to evolve.
@Ronald. I very much agree with your last comment. I think people are a bit too impatient when it comes to “solving” the Drake equation. Right now we only have some idea about the first two (and just tw0 decades ago we had no clue about the second one). We can make some more or less educated guesses about the other ones, but in the absence of data to test against it is more belief than science. Trying to close in on the right magnitude for the following variables by getting an estimate of how common non-equilibrium atmospheres are as well as if any other life (micro organisms) exists in the solar system is something that is achievable within the next few decades and where we have good chances of progress. While SETI might be cheaper the the likelihood of success/progress is probably reduced even more than the cost.
@kzb
Wasn’t there a recent paper that suggested that the inner systems of the galaxy were unsuitable for life due to high radiation? Otherwise I agree, once a civilization starts, even when it falls, it will be replaced by another, ensuting a long lifetime for civilization as a whole.
@Ronald I can’t disagree with your calculation (I, and probably others, have done very similar ones here over the past year). I suspect you’re correct to within an order of magnitude or two, which is all one can expect at this time. If the second of your ways of getting more than just a few techno civilizations at the same time is true, then it’s possible, if one of them develops interstellar travel, that number of “effective” civilizations at any one time could still be a much larger number. The idea being that speciation time scales (on earth) are such that the separate colonies will likely become effectively different civilizations, if they survive for that long. Which naturally leads us back to the Fermi paradox again. My guess is that the number of effective civilizations is also quite low, so that even they are far apart. It also appears, from the increasingly good survey data at all wavelengths, that really advanced civilizations capable of significant astro-engineering are extremely rare, if they exist at all. Kepler is capable of putting some constraints on this eventually.
We could have quite a good New Worlds Explorer type mission capable of doing spectroscopy of many planets, some in the habitable zone of their stars, for about the cost (within a factor of two) of the next Mars rover or for about an additional $1B on top of JWST if/when it’s ever finished.
Its seems so strange to deny that life on Earth can provide information important to Drake’s fl. Since under the precepts of modern synthesis, natural selection drives, not just for ever more efficient forms, but also for ever simpler forms, it would be hard to explain how the last common ancestor of all extant life could exceed the complexity of the first life form by more than an order of magnitude. It is even more instructive if we just look at creatures that occupy special niches for complex creatures today, and compare them with those in simple niches. For example humans have about 50% more genes than some morphologically simple worms, and almost ten times as many as is typical for bacteria. For our planet the last universal ancestor had at least 500 genes. To specify even one enzyme so that it is residually functional should require in the order of a hundred bits of information. Thus for those that feel supremely confident that the correct figure for fl is greater than the reciprocal of the number of planets in the observable universe, we should explain our confidence that the implied original life-form was so many times simpler than the last ancestor of all life today.
Gunnar Larsson, in my opinion, the details of your criticism of Avatar2.0 only serve to further obscure the problem. The only fundamental problem that I can see with Avatar2.0’s scheme is that it takes the same assumed path for abiogenesis as Urey-Miller and followers as the only possibility.
Although he is right that we have screeds of data on the lack of potential for progression from amino acids to peptides to useful enzymes to coordinated metabolic pathways, this problem of experimental failure is harder to apply to other potential pathways to the original life form, and seems stretched if we allow potential for such extreme suggestions as that of Cairns-Smith’s non-organic origin.
You analogy with self-sustaining fusion would only be correct if Avatar2.0 meant to imply that the failure of the experiments was in producing life then and there. I think that if you reread his post you will find that he was more likely pointing out experimental failure of proof of concept at virtually every step in most orthodox schemes for abiogenisis.
Gunnar Larsson
“Avatar2.0 I take it that you consider fusion in stars highly unlikely as well, as we have failed so far to create self-sustained fusion reactions?”
This is a straw-man comparison, Gunnar Larsson.
We do know how stars create fusion – it’s a simple enough recipe. We can’t copy it due to the gigantic masses involved.
This is NOT the case with life chemistry.
“Your maths example is fortunately not that relevant since not all configurations are equally likely. Configurations that can multiply themselves successfully are much more likely than configurations that can’t.”
Actually, it’s highly relevant.
You see, I’m talking about the apparition of life, NOT the evolution of life aka how did configurations that can multiply themselves successfully appear in the first place, not how they evolved.
“One reason that life is consider likely is that it developed almost as soon as it was possible on our planet.”
And afterwards, no other tree of life developed despite billions of years worth of paradisiac conditions.
@Gunnar Larsson: I have seldom read a comment that summarizes the essence of matters so pointedly and clearly. Bravo!
Avatar2.0: please (re)read my comment more thoroughly and you will find that you and I are largely on the same side of the discussion with regard to other civilizations:
– I do NOT assume that there would be many (thousands) of techno civs in our MW galaxy right now, on the contrary: I state that I consider the chance of two techno civs existing at the same time in our MW quite small, roughly on the order of one percent, and even that being optimistic!
– The only reason why I put the probability of ‘prokaryote’ life on suitable planets at an optimistic 100% was (besides the fact that we don’t know the real chance) to show that even with such a high head start, the outcome for techno civs is still very low.
The rest of your argumentation and in particular your calculation efforts with regard to the probability of life arising I strongly disagree and I think that they are very faulty, in way that I have also seen among creationists, also referring to Gunnar’s excellent comment:
The nucleus of your wrong argument is the statement “the probability decreases FACTORIALLY with each added step”. Plain wrong, not so. Each step takes place from a previous one as a more or less stable starting situation, and because it has some added selective advantage.
Your calculations are useless, because complex molecules originating is not (NOT!) a pure chance event. It is biochemistry; the required characteristics are already available in the material, in this case particularly C atoms, organic chemistry. Even in lifeless nature complex molecule chains of several hundreds of C atoms length exist and spontaneously originate all the time, that ‘could not exist’ from a pure chance perspective. And yet they do.
In fact nowadays chemical and pharmaceutical industry uses this principle in what is known as ‘molecular evolution’, put bluntly: throw a mix of certain chemicals in a large vessel, see what comes up, select what you want from that and continue in the same fashion. In a few steps you can have very long and complex macromolecules of several hundred C plus side-chains.
Your argumentation is about the same as stating that the beautiful and complex ‘flower’ shapes of some crystals cannot arise spontaneously, because the end result has a too small calculated chance of happening.
In fact, your argument is doubly wrong: it seems that with each step the likelihood of even more complexity becomes increasingly, even exponentially, greater, as is shown by the great diversification of life from the Cambrium onward. People often tend to draw a fundamental line between life and lifeless, but let’s not forget that the fundamental laws and chemical principles are just the same, it is still biochemistry, not magic. It rather looks as if, beyond a certain threshold that we call ‘life’, biochemical complexity can really take off.
Summarizing, the key concept here is not ‘chance event’, but ‘natural selection’ and ‘incremental steps’, even at the molecular level.
So, yes, I fully agree on your point of view with regard to intelligence and techno civs, but at the same time I think that ‘life’, even in its simplest and most primordial forms, will appear to be rather common.
In fact, Gunnar sums up my own point of view well: ‘One reason that life is consider likely is that it developed almost as soon as it was possible on our planet’.
Likewise, I do not believe that life was a pure and rare chance event on earth but rather that the earth, and any planet, had to be ‘ripe’ for it.
@Alex Tolley
The paper I link to above explicitly takes supernova radiation into account in its model. The probability of a planet being “sterilized” is taken as 100% within 8pc of a SN. By “sterilized” they mean all complex life is erased, but microbial life persists. A very large proportion of life-bearing planets do indeed experience such “sterilizations” according to their model, and the likelyhood is increased towards the inner galaxy.
Personally I think this is far too pessimistic. It’s all based on this paper by Gehrels:
OZONE DEPLETION FROM NEARBY SUPERNOVAE
http://acdb-ext.gsfc.nasa.gov/People/Jackman/Gehrels_2003.pdf
The mechanism of sterilization is explicitly NOT radiation from the SN affecting life directly, but the ozone-depletion effect of that radiation, letting in more UV from the sun.
If you look at the figures in that paper the ozone depletion is only high near the poles -it’s only 15% at the equator. So why this is held to equate to sterilization of all higher lifeforms is anyone’s guess !
Avatar2.0: the fact that life did not arise more than once, is most likely because of biochemical and ecological niches already been taken. In fact, we do not know whether it did not arise multiple times, all we know is that it did not persist.
In other words, precursors to life (e.g. prions and the like) may be originating all the time, but not getting any foothold.