If we could somehow rewind time to the earliest days of the Solar System and start over again, would life — and intelligence — reappear? It’s an experiment science fiction authors are able to try, but it defies real world science. Nonetheless, we can make approaches to the problem through the analysis of probabilities. In particular, we can use statistics, and the technique known as Bayesian inference, which weighs probabilities updated by new evidence.
This is a helpful exercise given that so often I hear people referring to the idea that intelligent life must be everywhere because the universe is so vast and there are so many opportunities for it to arise. But does life inevitably emerge on what we might consider habitable worlds?
What if this process of abiogenesis is rare? The question points to the fact that we have absolutely no idea what the likelihood is, and therefore assumptions about intelligent life based solely on numerical opportunity are nothing but speculations.
Enter Columbia University’s David Kipping, whose work has been featured often in these pages. Kipping tackles the question of the likelihood of life and the development of intelligence in a new paper in Proceedings of the National Academy of Sciences. He has a chronology to work with, one involving life’s earliest appearance as found in fossils, the emergence of humans, and the habitability constraints of our planet’s surface conditions, using it to draw inferences on how quickly life can arise, and how unusual intelligence may be.
The scenarios — derived as what in Bayesian terms are called ‘objective priors’ — are relatively straightforward, each of them worth examining in light of the fact that we have no observational evidence for life beyond the Earth. Our planet is our data point, and with all the disadvantages that produces, we can still draw inferences about life elsewhere from the constraints we can establish here. We know that abiogenesis is possible because we are here to write about it. But Kipping applies statistical methods based on Bayesian mathematics to consider the odds.
The first scenario (and the one I favor): Life is common, but rarely develops intelligence. I suspect we’re going to find evidence for simple life all over the Orion Arm as we extend our technologies outward, but little evidence for technologies. But other scenarios exist: Life is common and so is intelligence. And perhaps abiogenesis is rare. In that case, we may find life unusual but intelligence a common consequence when it does happen. Finally, life may be as rare as intelligence.
Image: Are we alone in the universe? A new study uses Bayesian statistics to weigh the likelihood of life and intelligence beyond our solar system. Credit: Shutterstock/Amanda Carden.
Which scenario to choose? Bayesian techniques involve testing a position against new evidence that can be applied to the question, which allows estimates to get better as they are refined. Bayesian mathematical formulae tackle how to model one scenario against another. And I found the result Kipping arrived at encouraging. Let me quote him on the matter:
“In Bayesian inference, prior probability distributions always need to be selected. But a key result here is that when one compares the rare-life versus common-life scenarios, the common-life scenario is always at least nine times more likely than the rare one.”
Drawing on our single data point — Earth — Kipping points out that we know life emerged quickly. We have to factor in the impact with the Mars-sized “Theia” some 4.51 billion years ago (leading to the formation of the Moon), but mineralogical evidence from zircons points to an atmosphere and liquid water present on Earth’s surface by roughly 4.4 billion years ago. The earliest evidence for life is found in 4.1 billion year old zircon deposits in the form of depleted carbon inclusions, a controversial datapoint, but undisputed evidence for life turns up in microfossils found in 3.465 billion year old rocks in western Australia.
We can come up, then, with the length of time for which Earth is expected to persist as habitable for intelligent beings, factoring in the growing luminosity of the Sun and the increased rate of weathering of silicate rocks on Earth and eventual depletion of carbon dioxide in the atmosphere. Kipping arrives at a habitable ‘window’ of 5.304 billion years. That’s from the beginning of life to its likely end, and it shows how significant is the question of how fast abiogenesis happens. If it takes too long, life would never emerge under the conditions most planets would face as their star continued to evolve. 900 million years from now, Earth will be a hostile place indeed.
But back to the key result — and I have to send the reader to the paper for the complex Bayesian mathematics involved — Kipping draws on a 2012 paper from Spiegel and Turner to refine the Bayesian formalism produced there for interpreting life’s early emergence on Earth. He considers it against the broader context of the habitable ‘window.’ From the Kipping paper:
The early emergence of life on Earth is naively interpreted as meaning that if we reran the tape, life would generally reappear quickly. But if the timescale for intelligence is long, then a quick start to life is simply a necessary byproduct of our existence—not evidence for a general rapid abiogenesis rate. Using our objective Bayesian framework, we show that the Bayes factor between a fast versus a slow abiogenesis scenario is at least a factor of 3—irrespective of the prior or the timescale for intelligence evolution. This factor is boosted to 9 when we replace the earliest microfossil evidence… with the more disputed 13C-depleted zircon deposits…
Thus the common life scenario gains odds, and markedly so. As for intelligence, Kipping’s analysis precludes the possibility that it emerges quickly (in less than billions of years), while the idea that intelligence is rare remains viable. Even so, he finds betting odds of only 3:2 that intelligence rarely emerges — this slight preference for rare intelligence is consistent with our lack of SETI results but leaves the question of searching for intelligence elsewhere wide open. Life is likely to emerge on other worlds, in other words, but our one data point — Earth — tells us that intelligence emerges only with time and difficulty. We have no outstanding way to choose here one way or another. Let me quote from the paper on this:
…our work supports an optimistic outlook for future searches for biosignatures…The slight preference for a rare intelligence scenario is consistent with a straightforward resolution to the Fermi paradox. However, our work says nothing about the lifetime of civilizations, and indeed the weight of evidence in favor of this scenario is sufficiently weak that searches for technosignatures should certainly be a component in observational campaigns seeking to resolve this grand mystery.
Life commonly found, the prevalence of intelligence still a mystery. Keep looking, but you now have some insight into where to place your chips in your next trip to the astrobiological casino.
If you’re interested in learning about Bayesian inference and the surprising successes of Bayesian analysis, I recommend Sharon McGrayne’s book The Theory That Would Not Die: How Bayes’ Rule Cracked the Enigma Code, Hunted Down Russian Submarines, and Emerged Triumphant from Two Centuries of Controversy (Yale University Press, 2011) as an excellent backgrounder.
The paper is Kipping, “An objective Bayesian analysis of life’s early start and our late arrival,” Proceedings of the National Academy of Sciences 18 May 2020 (full text). You can see Kipping’s lively video presentation on this work at https://www.youtube.com/watch?v=iLbbpRYRW5Y.
The problem is the metaphysical framework we’re using is likely wrong. For example Nick Bostrom throws in the possibility that we are living in a computer simulation. This is also probably wrong, but illustrates that the space of possibilities is really big.
https://www.nickbostrom.com/aievolution.pdf
The concept that we might be living in a computer simulation does not illustrate that the space of possibilities is really big, it illustrates that our science has become bankrupt.
How so? The thought experiment is simply that it is conceivable given some assumptions without making any claims regarding the possibility. That’s hardly a sign that “science has become bankrupt”.
LOL. A moment of clarity.
You wrote, “We know that abiogenesis is possible because we are here to write about it.” I think we do not know it. We _believe_ it because we believe the big bang precludes any other possibility. I look forward to reading the article. Thanks.
I agree–we just don’t know how life came to be here. Other possibilities include special creation and “seeding”–either intentionally or accidentally–by at least one (or perhaps more, with only one of them apparently “taking,” if it happened that way) alien interstellar expedition to our Solar System in those very distant days, and:
Chemists consider life to be, for all practical purposes, a miracle; it need not (and should not, due to its almost unimaginable complexity) exist at all. It is a far, FAR more complex–than is necessary–solution to the problem that mixtures of non-inert elements and/or molecules, in the presence of a source or sources of energy (visible, UV, or IR sunlight, ionizing radiation, and/or electrical discharges), have. That problem is:
The chemicals “want” to reach the lowest valence levels, by forming stable compounds. As we have found on all other worlds–comets, asteroids, moons, and planets–that we have examined thus far (via spectroscope from afar, from flybys or orbit, and from their surfaces [and a bit below them]), mixtures of the same chemicals as those found on the Earth–including in living organisms–have achieved stability by forming much, much simpler compounds. Also:
I would love to be wrong. I *want* there to be common life–including intelligent life, even though that could possibly involve some danger to us–in the Galaxy, and in the universe. But expecting to find common life (even of the lowest order) is–to use a chemical analogy–like igniting a mixture of hydrogen and oxygen in a closed container, and expecting to find that it reacted to form hydrogen peroxide (H2O2), instead of the simpler–and far more stable–water (H2O).
If you adopt the idea of ‘seeding’ then you have to explain how life started in that place instead. But no need for that, but no need for that we have a quite good idea on the kind of environments where life might have started on Earth. (There’s two hypotheses both of which have their good points, perhaps both were needed.)
Even so it’s indeed a miracle how RNA/DNA could be made before there were any actual ‘life’ and it is required to maintain the replication and evolution of more primitive cells.
We have no idea how that could have occurred, what path or sequence of events that led that to happen.
Even so I do think such very basic life processes will get started now and then when conditions permit.
The next step which is equally difficult to overcome, and here we do actually have some data. Is to get enzymes to work properly and the incorporation of mitochondria as a symbiont – I subscribe to the idea that those are devolved examples of RNA life.
Even so for the first billion years not much did happen, and Earth seem to have been one big petri dish where this very basic life did try all kind of combinations to overcome these first hurdles.
The LUCA have been found in hydrothermal vents and date back to about 3,5 billion years. So the idea that life got started there might not be correct, but the life that eventually did colonize the planet do indeed come from there.
Even so life here spent another 2,5 billion year barely getting past the multi cell stage, and if this time frame is to be used as a measuring stick for how slow life might develop, many planets will loose out as the age of habitability and be past the prime.
The more we learn of planets elsewhere, Earth seem to be one very unusual world in so many ways.
This should not exclude us from listening for signals of any kind, both radio, optical and perhaps even other ones. We might be lucky, but my educated guess is that our first finding will be a planet with an odd chemical imbalance, that suggest biological activity but nothing as fancy as on our own planet.
We have only found organisms that are descendants of LUCA, but not LUCA itself. Unless there is some refuge inaccessible to the forms we do know about, LUCA organisms would have been outcompetes and become extinct. We can make guesses as to what it might have been like, but that is a far as we can get.
I stand corrected, my choice of words should have been more exact there. The original LUCA quite likely have been outcompeted by today, but yes who know what refugia that might exist inside Earths crust.
I agree it’s difficult to see how RNA/DNA survived without cells to shelter in, while protocells wouldn’t do much without RNA/DNA inside them. Sort of chicken and egg.
Mitochondria have circular DNA, not RNA as their chromosomes, so they can’t be in themselves “devolved” RNA life. Or did you mean the cells that originally ingested them? But current thinking seems to be that THEY were members of the Archaea which are also DNA-based. In any case not LUCA per se.
Unlike chemistry, life is a dissipative system with constant energy inputs that allow for “unlikely” outputs. The other difference from chemistry is that “Darwinian selection” can take place, increasing the number of the unlikely output.
On theoretical grounds, Kauffman has shown emergent complexity from sufficient varied starting components for a range of biological systems, including metabolisms. Experimentalists like Cronin’s group have devised/are devising experiments to show this can happen in real systems.
It isn’t unnecessary complexity, just sufficient complexity to allow the emergence of complex systems that eventually lead to life.
If they, and others, are correct, we should see life as common. If there are some special conditions that cannot be replicated elsewhere, then life might be unique to Earth. Either way, we will know within the foreseeable future, and this speculative game, fun as it can be, can end.
In the far future, either eventuality offers an interesting path. If life is very common, then we can explore the galaxy and do eons of “stamp collecting”. If life is unique (or extremely rare) then we can implant life and start the evolutionary clock ticking on a vast number of worlds. There will be enough worlds to test any number of ideas.
[I just hope we are not some experiment of the “Old Ones” who are about to end the experiment and sterilize the culture platform to run another experiment.]
The problem is that we should be able to copy life–to reproduce even the simplest algae in laboratories, from the same raw materials–but we can’t. (When I was younger, that capability was perennially, confidently expected “in the next few years,” like controlled nuclear fusion.)
Every other chemical phenomenon (for want of a better word) found in nature–and a good many that don’t occur in nature–we have been able to reproduce or produce “from scratch,” and the same should be the case with life, and even RNA and DNA. But even the simplest single-celled organisms are so almost unimaginably complex that even if we do one day manage to reproduce one–which will require a level of technology well beyond anything we now have–it will make the odds of such a thing having happened more than once, by blind chance–truly infinitesimal.
I think you are making the “watch and watchmaker” argument, more recently updated as “a whirlwind cannot turn a junkyard into a Boeing 747”.
While it is true that we cannot make life yet, it is also true that we can recreate components, as well as produce plausible options for precursors. We also know that some of life’s components can self assemble, and we have replaced whole genomes in cells successfully. One can take teh contrary view and say that biologists are just using “unknown conditions & time” as magic pixie dust to explain away the origin of life, but we are making progress. We also know that we do not have to replicate even the simplest functioning cell because that is not how evolution works. I chemistry terms, evolution has, by trial and error and differential success, to select the necessary ingredients and conditions to construct a fully self-replicating cell. The space of such ingredients and conditions is so vast that chemists have never explored even the smallest space of the possibilities. Progress has been slow and incremental, but progress is being made.
Infinitesimal is a big figure. Irrelevant too as life did not occur by chance. Or divine intervention. Or seeding . Or ID.
Just humdrum chemistry, lots of phase space and a shed load of time. Presumably down some favourable energy gradient. Or other. Or other.
Why on Earth ( quite literally ) would we want to create life after the fashion already finely tuned by nearly four billion years of evolution ? It would prove nothing. Nothing.
Better devoting time to coming up with an FTL drive , teleportation system or anti-grav device. Or summit. Perhaps something ‘more humble’ like a 3000 unit telescope Space Optical interferometer/ Labeyrie telescope .
More useful by far for rooting out extraterrestrial life rather than a poor mens’ verisimilitude of what we have already.
“Why on Earth ( quite literally ) would we want to create life after the fashion already finely tuned by nearly four billion years of evolution ? ”
Obviously because the fine tuning is only fine for 80 years. Evolution messed up by including death in the package, so an artificial reconstruction might offer a workaround for this small problem.
I don’t care how rare life formation is ; it would be imbecilic to think it only occurred on this planet. It is strictly a numbers game. We can’t begin to comprehend the actual # s of galaxies, let alone suns or planets. I will guarantee. Life all over the universe. And some percentage intelligent. Not sure if we can consider life here in the intelligent range.
I need to read teh paper, but a priori, I think it is an abuse of statistics to apply Bayes to an outcome that appears highly contingent. IOW, you cannot apply Bayes to determine the monkeys correctly typing out Hamlet when you have one data point. I don’t doubt that there are a number of ways intelligence can arise, but human intelligence has been subject to an evolutionary history that is highly contingent on chance events, not least is the preceding extinctions, the arrival of the hominid line, and whatever initiated teh “cultural explosion” some 40-80,000 years ago.
It is more belief and bias that I think that life if\s probably common. but intelligence is very rare, or even unique, as Lovelock believes. The Fermi Question still seems like the best argument for very rare intelligence, especially as cosmically, we may be on teh brink of colonizing the galaxy one way or another.
Thanks Paul for introducing us to David’s thoughtful and well written Bayesian analysis of abiogenesis and the emergence of intelligence. Having written a few articles on the topic I must say David’s math is straight-forward and comprehensible. The hard part for most people when it comes to all things Bayesian (even scientific ones) is not the math itself, but the way you have to suspend your “normal” way of reasoning to make sense of it. I do think, however, that the true kernel of this problem/question lies in abiogenesis. We simply have no concrete pathway to it, only some good/contradictory theories.
The same could be said for the use of “priors”‘and “posteriors”. Less “ab intio” as much as reductio ad absurdam . Bayes theorem is majestic and I see it used daily in my own field of medicine . More still ( regrettably ) in the world of gambling . The big difference of course is that both of these fields have vast data sets with which to inform priors – and posteriors. It doesn’t mean they are any good here though and to describe them as limited would be an understatement.
The Drake “equation” was developed by Frank Drake at Carl Sagan’s prompting essentially as a quasi quantitive philosophical question to help provoke debate and launch SETI. As far as I can see here Bayes theorem is being used as no more than a cloak for a glorified 21st Century take on Drake’s long abused narrative device . A Rare Earth one at that. I can’t see what utility there is in this exercise.
Who needs Bayes theorem to confirm that the chances of human intelligence evolving on Earth are effectively 0 ? And zero anywhere else.
In terms of priors , the text correctly describes their (total) geocentric biases early on . But then goes on to ignore these to reach bold and misleading conclusions. To say that the priors here are naive at best and ill informed at worst would be an understatement. The very definition of intelligence is vague and linking it to “civilisation”, which is a mere social construct – stretches credulity.
Worse still is the lack of appreciation of evolution. As far as I can tell it is seen here as a directed process rather than a haphazard accumulation of random events and outcomes . This is the classic “irresistible fallacy” whereby evolution is seen as a focused sequence that progresses life from simple to complex. Essentially prokaryote all the way to a pinnacle – with humans at the top. Due to their intelligence. Imagining this as a long trail creates a misleading but very human story of a hard and long slog to the top . Like climbing Everest. How could the rise of intelligence not take so long after all that effort ? There are countless other species on Earth today and their ongoing existence is only due to the fact that they are ALL as evolved as humans. There is no pinnacle and especially not one that equates to intelligence.
The article also refers to the Silurian hypothesis which essentially posits “human like” ( again !) intelligence arising from reptilian life tens to hundreds of millions of years ago. ( basically smart dinosaurs ) Whilst I don’t believe this, it does not rule out that with a different evolutionary pathway intelligence might indeed just have occurred on Earth much earlier.
Complex life arose on Earth on two occasions, Eukaryotic endosymbiotic first, 1.3 billion Gyrsa and then in the Ediacaran/ Cambrian multi cellular “explosion” of 0.8 Gyrs ago . Both were very closely associated with the rise of O2 to contemporary levels. One undeniable factor of all intelligent animals alive today ( including but not limited to humans ) is that their brains have a massive metabolic demand – one for which oxidative respiration is ideally suited. Intelligence may indeed have arisen late in Earth’s history – rather arbitrarily dismissed in the text with variations of a few million years or so as unimportant as a consequence and by way of historical context. Though in terms of the civilisation concept used, anything but arbitrary when one considers the achievements of such a construct over the last hundred years alone.
However this ignores the fact that whatever we call intelligence in hominids sure appeared quickly when the time arrived. Late isnt necessarily correlated with slow. Just three million years or so from the first bipedal hominid to present day Homo Statisticans .
So why not intelligence arising at any point during the last “Aerobic Earth” 800 million years or so ? Not human intelligence ( thorough still anthropocentric if a little “softer” ) for sure but some other form of intelligence if evolution was rerun. Aerobic Earth constitutes an anything but non significant period of Earth’s existence. More than a sixth. Presumably the origins of intelligence are multi factorial and including amongst many others a complex interaction of biological , geophysical and even astronomical happenstance . Happenstance that not necessary limited to recent history. All of which could very easily varied . Will have elsewhere . Randomly aligning to inadvertently create the correct evolutionary pressures required for the rise of intelligence .
Any extrapolation to exoplanets is thus meaningless and anthropocentric beyond the possibility that O2 in the right quantities is a useful high energy source for complex life .
If we are establishing a scientific view of life in the universe, we must consider abiogenises as an invariant principle. Consequently, in order to determine if abiogenesis is rare, we must know what are the physical constraints. Therefore we must differentiate between the physical conditions necessary intelligent life and the most common or hardy type of primitive life, the mircoorganism, archaea, prokaryotic microbes.
Intelligent life might have more contingencies and requirements in order to become a reality. The star might have to a G class star, the exoplanet might have to have a Moon to keep the wobble on it’s axis small, stable and the climate moderate. Also the Moon would give the exoplanet a fast rotation, and a magnetic field which would stop the solar wind stripping and loss of atmosphere over deep time.
Kipping’s habitable ‘window’ of 5.304 billion years is too large since it would have to include K stars and smaller stars with a longer life than G class stars. The maximum habitable window of Earth is 4.7 billion years so we have roughly only another 200 million years before our Earth will be too hot to be considered habitable. The Sun has to slowly become brighter or 7 percent brighter every billion years due to the loss of hydrogen in the core which has been fused into helium, the Sun has to burn hotter in order to keep the same pressure to balance the contraction of gravity with less hydrogen fuel in the core.
The only wiggle room is possible large meteor impacts which cause the dinosaurs to become extinct. If there was no large impact, then the dinosaurs would eventually become extinct because of the carbon cycle, and natural loss of carbon dioxide through the Urey reaction, i.e. rain and the oceans and the photosynthesis of plants. If there was a large impact collision with our Earth at an earlier time, would save us time and make us one million years more advanced than today if the impact occurred one, five or ten million years earlier or would that set us back with a loss of time in evolution or even make intelligent life impossible through extinction, I don’t know. The collision time is an interesting thing to consider.
If we consider the contingencies I wrote to include the above mentioned physical requirements, we still might have from 100 to one thousand exact Earth twins. This is only an educated guess considering 100 billion stars in our galaxy, maybe half of them are double star systems and half of the double systems might not have planets so 50 billion stars might have planets. Only seven or eight percent of the stars in our galaxy are G class stars which will lessen the amount of habitable homes for intelligent life. A wider range or less conservative model could include K class stars, but I think I have to rule out M dwarf stars due to tidal locking which makes a Moon and a strong magnetic field impossible. There are other reasons I rule out M dwarfs for indigenous ET exoplanet life.
I have to reject the idea of the rare Earth hypothesis which does not use scientific principles. For me, the idea that SETI has not got a signal yet, does not support the rare Earth hypothesis since they have not been looking for a signal for very long. Also I don’t think ET communication is restricted to radio signals and we may listening at the wrong frequencies. Consequently, I don’t limit my for judgment for the the potential and probability of intelligent life in our universe to SETI and radio signals. It also might take a long time and searching a large number of exoplanets before we find an Earth twin with the spectra of biosignature gases in it’s atmosphere. I know the hopeful view is we won’t have to look for long, but I think astronomers and astrophysicists should not assume early that Earth is the only place to have intelligent life if we don’t find any atmospheric biosignatures with the exoplanets that are already known because at least half of the stars in our galaxy must have planets, and exoplanet finding takes time and there are a lot of stars.
”For me, the idea that SETI has not got a signal yet, does not support the rare Earth hypothesis since they have not been looking for a signal for very long. Also I don’t think ET communication is restricted to radio signals and we may listening at the wrong frequencies.”
The mainstream model of SETI-that is to search for directed radio signals, always seemed flawed to me, that is a terrible waste of time and resources.An advanced civilization just 10,000 years more advanced than us, would already be able to identify all life bearing planets in the Galaxy.And it is more likely that if it would exist , than it would be millions of years ahead of us. So in all likelyhood they would knew where to look if they wanted to. It means that either they aren’t there, are indifferent or don’t want contact. I think newer Dysonian type of SETI makes more sense, and I wouldn’t disregard all of SETI findings, of which some are a bit ambiguous.
But you raise a good point about expectations being too high-the search will only start with new telescopes and we shouldn’t expect immediate results, nor should lack of them discourage us from further exploration.
Skimming teh paper, I cannot help but feel this is a modern version of a theological argument with math used instead of theological “logic”.
I appreciate that Kipping caveats his work that the argument may only apply to Earth, but then the possibly rare contingent factors might well mean this is irrelevant to generalizing to exoplanets.
We don’t really have to make these arguments for the emergence of life. We will likely know how prevalent life is from biosignatures obtained within this century.
But regarding the intelligence argument. Our system was born in the last 1/2 of the age of the universe. Even allowing for our type of star being necessary for life to emerge on a rocky world, the universe must have many worlds that are remarkably Earth-like but are far older, perhaps by many billions of years. Therefore if life emerges fairly easily, it will be ubiquitous, even without panspermia. But this also means that intelligence may have emerged in the past around these stars. If so, then at least one will have explored our galaxy, perhaps even beyond. There should be colonies of biologicals and machine civilizations everywhere. Their signs might be difficult to recognize, but they should be present if we know what to look for. If the Fermi Question is to be answered despite the prevalence of these civilizations, then it is only our inability to recognize them that is at issue. Either that, or intelligence is so rare, or even unique to us, that the universe is truly purely a wild place unmarried by technological ETI emergence.
Searching for technological signatures with no results will never tell us whether such civilizations exist of not, just that they might exist if only we had the right tools. There will be no way to rule out their existence.
Perhaps life arises only in conditions like on Earth in its first few hundred million years–at a time when the environment was far more energetic than since. In any case, it will take the discovery of one more example of life to convince me it’s common. Especially very different life, to prove it wasn’t due to leakage.
We really only need to detect unambiguous biosignatures. I am quite certain that the answer to whether life is common or not will come in due course. I just hope I am still alive, and reading about the results on this blog when it happens. We will either get reports, just like other phenomena, or, like SETI, an absence. From this, we will start to get some idea of the situation.
“We will either get reports, just like other phenomena, or, like SETI, an absence.”
Absence of evidence is not evidence of absence. I encountered it most frequently in connection with the rejoicing at negative findings in tests for the spread of cancer, in spite of quite adverse known probabilities.
But it is universally true. It takes only one unequivocal instance to be evidence of presence. But no number of negatives short of the entirety will serve as evidence to the contrary.
Granted that it is not possible to prove a negative. But while a black swan invalidates the “all swans are white” statement, at some point, we should move on, otherwise, we are forced to allow any statement might be true however outrageous.
Those who insist METI is dangerous can use the argument that we should continue to stay silent until we can be “certain” it is safe. But we cannot be certain as this cannot be proved.
Hi Alex,
I always like reading your thoughts in this forum and agree with you, not that consensus furthers science so much. The temporal dispersion of the emergence of intelligence, as you correctly point out, means that if they exist, then they have had quite some time to traverse this galaxy alone many many times and yet have left no trace and left us alone. If there are many old intelligences, then they have been purposefully leaving us alone. This seems highly unlikely since even these old intelligences have vast temporal dispersion among themselves. Imagine a billion year old intelligence travelling at just one percent of the speed of light. They could have explored and observed from a distance every star system within just the Milky Way alone. We are either alone or they purposefully leave us alone. I doubt that if these temporally displaced ancients exist that they are in communication over thousand plus light year time delays and it would take just one of them to abrogate some Zoo Hypothesis scenario for them to have made their presence known. The most straight forward solution, which is usually correct, is that we are utterly alone within our galaxy. PS I published an article (an easy read) in Astrobiology in 2011 on this subject. You can find it on my university website.
Thomas,
Can you post the link to the essay?
Here it is…
https://www.fgcu.edu/cas/departments/math/files/Temporal-Dispersion.pdf
If I understand your results correctly, should we be the first, we will have a very long to ourselves before a competing civilization emerges from another biology on another world.
Given that time, I think that our civilization will fragment and become the upcoming civilizations, just as happened on Earth. It will be an Asimovian type of galaxy, rather than a Star Trek one. The dangers will come from within, or mutant Mules, rather than the Borg.
No, we would 75% from the first based upon the rate of star formation since we are that far down the right skew bell curve. Without a doubt, the emergence of intelligence is directly correlated with the rate of star formation. Without stars and their planets then life cannot emerge.
I’m sorry, but linking star formation with the intelligence of one species ( and human “intelligence” at that- still far from clearly defined even now ) on one planet , does not a correlation make.
“If ETs exist then they must visit us” is not a physical law. One could argue that every advanced civilization should become AI civilizations in finite period of time or all of them will eventually degenerate and die out in their future lightcones; in this case most if not all AI don’t have much interest in biological life forms hence on one gives a damn about our existence. Second, visiting backward civilizations costs energy and time, but the benefit is almost none like one could spend years observing ant colonies and gain almost nothing.
Tell that to E O Wilson.
hiro, You make quite a few huge assumptions, but the key word you used in your post that I have been trying to explainfor years is that “one could argue that every advanced blah blah blah”. You lose the discussion with the word every. There is not a one size fits all, even for billion year old intelligences, if they exist at all. PS Using the term intelligence versus civilization is probably a better way to go when dealing with something this ancient…and just because they are different/advanced doesn’t mean they won’t be interested in us. We are not ants compared to them. I can comprehend the possibility of them, an ant can’t comprehend anything.
Ah about that, one size doesn’t fit all only apply to biological life forms, in the scenario of AI, the best optimization is unique, the efficient of using energy & time is the most important goal in stead of chasing something that brings more chaos into the equation. I completely disagree about the second PS part; if you know where to look you could spend several lifetimes pushing the boundary of physics ( & mathematics too ), I do admit that I’m too stupid to reach that domain, but it’s there allright. Therefore when ET civilizations transform from ordinary biology to “synthetic biology” ( including nanomachines inside artificial cells…), their goal will shift to something more important not studying chimps…
PS, an example is similar to Mr. Bezos or Mr. Gates never bother to visit poor black communities in Mississippi, they are able to do it but they choose not to do it because they have their important own goals.
Just in case, the above example is a scenario of the same species with different social classes, the other scenario of different species is even worse.
It is untrue that intelligence implies exploring the galaxy. It could be that intelligent civilizations always destroy themselves before that. Great Filter. Kipping even pretty much says so in the conclusion.
So I don’t really know what impact this paper has in terms of the Fermi Paradox.
Whatever “filter[s]” exists, it must apply to every civilization for the Fermi Question to remain in force if civilizations have arisen elsewhere. Even if there is a deadly predator out there (as anti-METI advocates caution), it should be detectable. As Clarke describes in 3001: The Final Odyssey, the destruction of a star by advanced technology was believed to be the Monolith ETIs weeding out a civilization.
If there is one more intelligence out there, then there are many more. Alex hits it spot on once again. The “maybe they all self-destruct” trope, like so many other Fermi Paradox cliches, breaks down under the non-uniformity of motive concept. If they exist, then some subset will have transitioned into a long lasting form of existence and then can “explore” using vast telescopic tech from their home star system if they are so inclined not to venture. Better yet from ten thousand light years above the galactic plane they could directly imaged nearly every star system in the galaxy with a sufficiently large device…remember, a billion year head start is a very good lead.
The Great Filter of Bostrom is most likely abiogenesis and we are, by extension, likely alone.
BTW here are some Fermi Paradox papers I was perusing:
https://arxiv.org/abs/2002.08776
https://arxiv.org/abs/1905.03146
I always found the idea that we would see giant waves of colonisation quite far fetched. It is equally likely that civilisations past certain stage would limit their natural desire for expansion and growth, once they master biology. Furthermore there is also a bit of ignorance similar to what SF authors often show in terms of understanding scale of space in regards to resources it offers. A civilisation can spend its millions of years of existence in one solar system and not exhaust its resources, which is one of many arguments against wide scale colonisation.
Of course we can debate all these wonderful ideas, there are as many as there are minds debating the subject-but ultimately we require empirical evidence, and that is where the new generation telescopes come in. It is good to remain guarded against too much enthusiasm as we can’t be certain what we will find, and biosignatures can unfortunately be deceiving from what I understand. Still, it will exciting to learn about new discoveries.
Personally my view is that while very simple life is perhaps not very rare, high self-awareness and technological ability is(for many species are intelligent even on our planet, but more advanced tool use is lacking). If there are any civilisations I would suspect millions of years of difference of development make direct communication and contact unlikely, colonisation isn’t widespread and their attitude is probably indifference. I also wouldn’t really say we haven’t seen anything yet-it is somewhat possible that certain detections and events we observe as natural could perhaps be artificial(contrary to popular belief Tabby’s Star for example is one of tens of dozens of possible Dyson Sphere candidates, and there are even scientists who boldly propose that objects like Hoag’s Object could be signs of mega-engineering ; ) ). Time will tell, but we are at least seeing the beginning of these questions being answered on the horizon.
I’m glad you raised teh growth issue. We often assume Earth’s GDP will grow at some rate so that at some point a much larger GDP will support building starships.
Unfortunately, it doesn’t take more than a few thousand years of constant growth to require the total energy of our sun as a KII civilization. Another few thousand years and we would be a KIII level civilization harvesting the total energy of the galaxy.
At some point we must experience a logistic growth curve in our energy use and with it, an implied stagnation of our economic growth. Any very long-lived ETI civilization must have gone through that phase. Where they would decide to halt is an interesting question. If it takes a minimum of say 100,000 years to colonize every star, this is slower than the growth rate increase needed to maintain economic growth. This might mean that civilizations can reach KII, but KIII requires such a slow rate of growth that it might not be deemed worthwhile to invest in starships as the ROI or NPV may be negative.
Good points all, Alex.
But for now I would settle for a measly few billon bucks to build a telescope capable of increasing the life sample size to 2. Exploding anthropocentrism once and for all.
One answer to Fermi’s question is :
“Common as muck Earth” .
Whereby the Cosmos is teeming with Earth facsimile KI (Kipping ) civilisations. That never communicate with each other.
Why bother ?
Much better to devote precious time boring themselves into extinction whilst developing increasingly complex statistical simulations that predict how unique and lucky they all are.
Where is the total perspective vortex when you need it ?
– requiring a piece of fairy cake to initiate the sequence.
From a completely deterministic machine to the “infinite improbability drive” that required a highly random source to be invented, – a nice hot cup of tea.
So starting with high tea on an English lawn on a warm summer day, one could predict the whole universe and then visit places and times with just the repast on the table.
Nick Lane has lots to say about abiogenesis, or at least the endosymbiosis of the Eukaryote. I agree with him. If correct, prokaryote bacterial life may be common. But Eukaryotic (complex life) is exceedingly rare, even in a galaxy full of “Earth”like planets.
While I wouldn’t like this to be true, nature is what it is. And if such life is very rare, while it would make it a lonely universe, it also would mandate at least to some people and groups that we spread life in all its forms in the Universe-a big argument for perhaps not even terraforming, but making sure that complex life develops based on planets improved conditions.
Bayesian statistics 10/10.
Evolutionary biology 0/10.
This is essentially a conflation of all the worst elements of Gaia, Rare Earth, SETI and anthropomorphism . Garnished with the same misassumptions about the Fermi paradox .
Common but simple life, intelligence very rare. As defined by hominids and human civilisation . On Earth.
If the history of the Earth was run again It would obviously be totally different. Totally. The Rare Earth authors never realised how ironic their title was. How could it not be given the chaos driven vagaries of natural selection and evolution ? And that’s just on Earth. There are so many variables over so long.
We might be able to reasonably surmise that life arises easily given how quickly it appeared on Earth . But that’s it. Any such life , even if based around carbon et al , would be totally different. No RNA, no DNA, no nucleic acids , no amino acids, no peptides or proteins . No cell membranes and mitochondria . Definitely no nuclei or neurones . No nachos. Maybe analogue molecules made up of similar elements , maybe, but with entirely different chemical and structural make ups . Maybe, I grant, even some universal biological adaptations such as photosynthesis . ( given its early and successful appearance in various iterations )
That’s just for basic life.
Biologists snd neuroscientists such as myself struggle to even define intelligence. The literature on it is immense . Not just a couple of lines by an astrophysics team. Humans are intelligent for sure, but in a way so are dogs and dolphins. Crows and octopus too. Hence the need here to delve deeper still into the world of anthropomorphism by adding in The extra layer of ‘civilisation’ as a determining factor . A VERY human factor. But also a convenient segue into how we haven’t been in touch with any aliens to create an extraterrestrial case for lack of intelligence.
So if even the most basic life would be totally different on a rerun , where does using human intelligence and rise of civilisation fit in to predict the likelihood of intelligence arising elsewhere ?
No where .
No amount of clever Bayesian statistics, Markov chains et al – which are indeed the gold standard for prediction – can make up for the flawed starting premises and weak bordering on minimal ‘prior‘ data.
No one can say if ‘intelligence‘ is a common commodity in the universe for sure but nor does this work prove that it is rare.
What it DOES prove is that human , erm, hominid intelligence – and civilisation, is not just rare in the universe BUT unique. Rarer than ever Earth and everything that sails ( or has sailed) on her.
As any evolutionary biologist could tell you.
As to Fermi’s paradox and one of the many possible solutions that doesn’t involve us being all alone in the Anthropocene?
The more complex a data transmission the more it needs to be both compressed and likely encrypted . So much so that it would very quickly be perceived as noise by all but those who sent it.
By way of example, if a modern day digital telecommunications satellite signal went back in time and was picked up by a 60s radio dish it would simply sound like static. So even the Cosmic background radiation might contain a myriad of ancient alien transmissions.
“No amount of clever Bayesian statistics, Markov chains et al – which are indeed the gold standard for prediction – can make up for the flawed starting premises and weak bordering on minimal ‘prior‘ data.”
I strongly agree. I admit I quickly lost interest in this work and didn’t look further into it for this very reason. Mathematics and logic are tools. Using the best rules based systems you can prove anything with carefully selected premises. Tools do not create data or truth.
About the only thing I agree with is that simple life is going to be more common than complex life (for a workable definition of complexity!). After all, complex life can only arise from less complex life, so if you take a global (universal) snapshot less complex life must be more common. But this says nothing about the likelihood of increasing complexity or how far it will go, nor the rapidity of that evolutionary development.
Exact matches probably, but perhaps close matches? We really don’t know the distribution space of possibilities. There may be attractors.
The late paleontologist Niles Eldredge seemed to think that there was a limited space of preferred forms organisms could take. Again, this is the concept of an attractor.
Indeed. It was quite recent that FRBs were being excitedly discussed as possible ETI transmissions. But even without decoding, signal strength in a narrow band is unusual in nature, hinting at artificial generation.
Having all alien transmissions squeezed into one short beep is teh idea behind James Blish’s novel The Quincunx of Time.
Despite these caveats, I agree with your general points.
We simply don’t know enough right now.
Best to assume we’re alone in every sense and expand into our neighborhood while building off-world biospheres. Save and expand ourselves….
Reasoning from a single data point is very very very very bad statistics.
I blame Frank Drake. The Drake Equation has one term for “life” and one term for “intelligence” and so ever since he published it, the SETI community tends to focus on those two and ignore all the steps in between. Given Earth’s history it seems obvious that _multicellular_ life, or maybe “complex” life is as big a jump as the formation of life itself. More than half the history of life on Earth passed before multicellular organisms appeared.
To me this is a strong suggestion that there may be a great many worlds inhabited by the alien equivalents of algae and bacteria, while multicellular forms turn out to be very uncommon. Given that, the rarity of intelligence becomes less of a puzzle.
It also means that astrobiologists should be paying more attention to the evolution of eukaryotes and multicellularity. How many times did it happen on Earth independently? What necessary preconditions are there?
Yes… I agree with that. At the same time, there is now in our planet multiple organisms with relative big brains, but mammal brains are a sequence of previous but durable steps, so probably is a very probably sequence of events that has a high chance of occur if multicellular and advanced diversity mechanisms for complex life forms (like sex) appears.
I remember a very, very old game named “SimEarth” where the time scaled changed from simple-life to multicellular-life and from multicellular to civilization.
The game ended if the planet end of life was reached… and really the only event where that could happen was in the simple to multicellular step, because the time scale was so fast that if the event didn’t occur, the end of time was reached.
I think that it’s not so far from reality here. The other steps are a lot faster to happen, so the slowest step is the hardest.
Big brains are a consecuence of small steps, none of that too difficult. The whole scale takes time, but its more probable to retain the gained evolution trait and diverse from here than the opposite, so if the first most difficult step happen enough soon, there is a high chance to big brains to occur.
Big brains to technology? I don’t know. We have no data about that. But mammals are only a small window time from human in the geological Earth scale so I think there is a high chance to repeat the event if humanity become extinct soon. Probably a new technological species could appear again in some millions of years. (Assuming no destruction of biosphere, of course)
There is time to happen again.
Bear in mind that when Drake defined his equation in 1961, it was just 8 years after the structure of DNA was elucidated and very little was known about the details of biology. There was no knowledge of the early stages of evolution before hard body parts could fossilize. The aim of teh equation was just to try to guesstimate if there might be a sufficient number of technological, radio transmitting civilizations to justify spending time and resources to try to listen for signals. While SETI has broadened its scope since then, that is still its primary goal.
The equation is still a useful tool, especially as the earlier terms are well characterized now, and we should get a good sense of the probability of life term this century. There have been attempts to modify the equation, but not with much success. The probability of technological ETI is just a guessing game and tells us more about the beliefs of those placing values on that probability than any reality. If Bracewell’s “Galactic Club” is out there communicating, we are not using the right tools to join. Clarke once characterized this as stone age islanders not hearing distant drums and supposing there are no humans elsewhere, whilst oblivious to the signals filling the radio spectrum.
Plenty of options.
Life is rare or life is common but complex life is rare, or intelligence is rare, or technology is rare even in intelligent species, or technology appears frequently but is too short living (so scarce in shared time), or technology is abundant but difficult to detect because its diversity and size (we are searching for wrong tech signatures) or we are under info suppression, etc. etc.
There is also an amusing morbid option-life is common, intelligence is common, but they don’t care. Perhaps intelligent life happens often, but gets self-destructive and ends itself sooner or later. The few really long lived civilisations have seen hundreds of upstart civilisations come and go and they aren’t really interested in the same old story repeating itself and just leave them alone to their own fate ;)
And yet we watch the infinite variations of the same few plots dressed up with new characters and scenery. If we got that bored, a lot of media would simply die. Or civilizations that still got bored might make bets on outcomes “5:1 Earth civilization makes it past the next 100 orbits around its star”.Maybe there is some cosmic “glass bead game” using upstart civilizations as the ideas to be connected.
“These crude civilisations are such fun – We could watch them for Aeons” :-)
We are finding more and more exoplanets (I just finished working on another round of TESS data along with thousands of others). Among the candidates we will find many rocky worlds around other suns. Eventually we will be able to detect biosignatures as Alex says. This will finally give us some data to chew on about the prevalence of life in this part of the galaxy. The next step will possibly be long observing campaigns of these targets. It will have to be one step at a time as with most things. We are moving quite quickly now but it may take centuries or longer to find a “friend” out there. I’m deliberately being optimistic with the friend part :).
Granting that Bacterial analougues are common, and arise commonly (also because they are probably hard to eradicate through massive disruptions).
But more advanced life has two events that are counter intiutive as far as evolution is concerned is the Eurkaryotes Advancement, and Multi-cellular Advancement. These are a hard sell statistically. Both involve radical reorganization and the giving up of indepence(by Mitorcondria and ATP energy in one case and Cell individuality in the case of Multi-cellular life. Dr Kipping has a YouTube Video explaining how these all work to keep the nearby universe free of evidence of advanced civs because nothing is out there yet. I agree that what he writes about is still speculation, but at least he presents the case that intelligent life is not something Invevitable in the time of the life cycle of SUN like stars, this type of voice is seldom heard from SETI or other Science educators.
Caveat.
More advanced life on Earth. Life anywhere else would follow a totally different evolutionary pathway. As it would on a Earth if re-run. Law of the adjacent possible and all.
That said, the appearance of complex multiorganelle eukaryotes and then of multicellular life occurred in very close proximity to the only two times O2 levels reached contemporary levels.
The Great Oxygenation Event, GOE of 2.3 Gyrs ago and the Neoproterozoic Oxygenation Event, NOE of 800 million yrs ago. The latter persisted to present day – following a period of extended global glaciation – whilst with the former O2 levels collapsed – following a period of extended global glaciation. How ?
With a ‘Boring Billion” mysterious years of ‘Mothball Earth‘ in between .
‘Post hoc ergo propter hoc’ or is there something with this high energy source O2 stuff ?
Macroscopic animal life appeared on Earth nearly 600 million years ago. But human civilization is less than 12,000 years old. So what does that tell you about the chances of finding intelligent life on Earth during the history of life on Earth!
Maybe I’m just stating the obvious, but it seems that the wrangling over definitions of “life” and “intelligence” are missing the point. Why do we want to speculate about the prevalence of either? Well, it seems to come down to basic goals:
– We want to explore, and life and intelligence are interesting things to find more of. But this doesn’t provide much constraint
– We want to learn from others, and “intelligence” implies the possibility of having learned something we don’t know, even if that is just “what is the weather like in your part of the galaxy?” But that also implies we can communicate. We might consider more effort in learning to communicate with earth-bound intelligences first. Maybe the whales or apes can teach us something before we wipe them out?
– We want to know whether we could live elsewhere. Colonizing an alien biosphere may be ethically dubious, but at least we learn whether we could outlive our planet and even our star. “Life” could show us that possibility, and “intelligent life” may provide an actual example of how it was done
So, now the definitions boil down to “life” = something that shows us we could live elsewhere, and “intelligence” = something which we could communicate with and learn from directly (rather than empirically). Armed with those definitions, “cells” and “humans” are reasonable local examples that the paper uses.
Also, it makes one wonder whether we need to consider “multi-stellar life” and “multi-stellar intelligence” as explicit goals for SETI and SETL. Unfortunately, now we have *zero* certain data points from which to speculate :)
It’s important to know that right now we really don’t even have the technology in place to easily see the spectral biosignature gases in exoplanet atmospheres. There was a time when we did not even know that bacteria and viruses existed, but at one point we suspected there was some kind of small organisms, but we didn’t have the technology to see them.
Also how long might it take to find a an exoplanet with biosignature gases? I like Alley Tolley would like to see it in the next ten years, but it could take a much longer time than that because astronomers might have to look at millions of exoplanets even millions of star systems before we detect biosignature spectra. A good idea might be to restrict the search to G class stars if no biosigntures are found in close stars or M dwarf star exoplanets or K stars.
It seems to me quite presumptuous to assume that the universe has no intelligent life if we have not been contacted with our primitive, radio technology by ET’s especially if we can’t yet have a radio transmitter even strong enough send a radio to reach another star system without it becoming to weak to be detected due to the inverse square law. If anything, we have just became intelligent and technological and are closed out from communicating with a galactic society if there is one since we don’t have the technology, the new kids on the block.
If every other ET civilization in the galaxy is exactly at our level of advancement, some of those humanoid ET’s would be thinking the same thing as us. We haven’t received a radio signal yet, so we are the only intelligence in the entire galaxy or all the other ones have destroyed themselves or intelligence life and life itself is too random, rare and it we are the only intelligent life is only found on our planet in the galaxy or even universe. I don’t think this is correct because there are many G class stars which are older than the Sun in our galaxy. It would only apply to the stars at our Sun’s age.
The reason why I reject the rare Earth hypothesis is that it is based on superficial observations, but is not scientific. The idea that life is rare may be true, but the potentials of the DNA are always based on the physics of the environment and restricted to it. The ruling principle of nature is survival, necessity and Darwinism. What is not adapted to the environment will not survive. Conversely, an environment which is too hostile for the DNA will not allow for it’s development. The DNA equals the physics of the environment, so that the same environmental conditions must exist for life to flourish anywhere in the universe which is why I suspect that we will only find intelligent life on an exact Earth twin which includes a similar sized Moon. This theory seams limiting, but it is anthropomorphic and even anthropometric. I am postulating that all intelligent life is humanoid, or anthropometric and premordial, so that it is a principle based on the physics of the environment and therefore existed long long before our world was born from the protoplanetary cloud of dust and gas collapsed to make our solar system. Our so called uniqueness is not so unique, but universal. It only superficially appears to be unique since we have yet to see any ET’s. In other words, the idea that all ET’s in our universe from any time period always look physically exactly as we do is not a only subjective, human viewpoint, but fits into the impersonal, objective principles of science so that the DNA is the same everywhere in the universe. The so called first principles also apply to biology so it’s processes and chemistry are predictable and not totally random. Why assume it to be more complex if not needed, the Occams razor. It is already complex enough, yet simple.
Complex, self-replicating molecular systems in a multitude of similar systems, will be selected for if they intrinsically are better suited to survival, growth and replication than their peers. These imperatives come up against limits, but when ensconced in intelligence and culture, many of those limits can be defeated. Resource depletion can be mitigated by expansion to fresh areas.
Growth for growth’s sake is the ideology of the cancer cell: whether the imperatives will be modified intentionally or otherwise will determine the fate of civilizations. Possible outcomes could include extinction, assumption of a near steady state with further change devoted to advancement of knowlege and more efficient use of matter and energy, transition to a machine civilization and artificial intelligence.
Would abandonment of the “cancer cell ideology” by advanced civilizations account for the Fermi paradox?
I think this is part of the answer.
The resources of single solar system will likely last for aeons to reserved civilisation, and the distances involved make it unlikely for any meaningful interstellar body to exist. Besides exploration and occasional offshots there would be no real need to colonize whole galaxy
Paul, your intro brought to mind Italo Calvino’s “How Much Shall We Bet?” from Cosmicomics.
Hadn’t thought of that, George, but I see your point!
I’ve always been more concerned that we’re not detecting any technosignatures myself. If interstellar civilization is self-perpetuating and highly productive as we hope it will be (for this is the future many envisage for humanity), we should be seeing more technosignatures, up to and including traditional Dyson Swarms and attempts at stellar engineering.
Not as few as you might think
https://home.fnal.gov/~carrigan/infrared_astronomy/Other_searches.htm
The problem with such observations is that we are unable to confirm them, and in the end without direct observation they are difficult to distinguish from natural objects.
There have been some attempts to interpret certain objects in terms of Dysonian Seti as stellar engineering, but it is more of an exercise than real claim.See for example:Joseph Voros ”Galactic-scale macro-engineering: Looking for signs of other intelligent species, as an exercise in hope for our own”-where he deals with Hoag’s Object
I was watching the live webinar by the SETI Institute this evening about Europa and life there. One of the presenters made a very interesting point. Unlike Mars, there cannot be an exchange of material between Europa and Earth due to Jupiter’s gravitational field. Therefore if life should be discovered there it will have to be a 2nd genesis. In turn, this would mean that life is almost certainly common in the universe.
…and that is something we can pursue now, with a reasonable effort…… a grab and return mission sampling Europa’s plumes…… and Enceladus.
Add Mars (deep soil sample) and Venus (50km cloud layer sample) to that list too.
We need to know if life on several candidate worlds in our system exist and arose due to a separate creation, abiogentic starts… or was it panspermia. Is it prokaryotic or more advanced? Is there any evidence for complex (multi cellular) organisms.
The SETI talk video on Life on Europa
Alex, there have been studies showing possibility of material exchange between Europa and Earth. This issue isn’t settled.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3870607/
”We found that, in addition to frequent transfer of material among the terrestrial planets, transfer of material from Earth and Mars to the moons of Jupiter and Saturn is also possible, but rare. We expect that such transfers were most likely to occur during the Late Heavy Bombardment or during the ensuing 1–2 billion years. At this time, the icy moons were warmer and likely had little or no ice shell to prevent meteorites from reaching their liquid interiors. We also note significant rates of re-impact in the first million years after ejection”
Perhaps even more exotic and very faint but feasible is that some of Earth’s extremophiles were deposited by ejecta to lunar subsurface, something that Sagan theorised could potentially be possible
https://www.nap.edu/read/18476/chapter/8#35
Interesting. So the presenter was either mistaken or she felt the probability was so low it was effectively zero. (Or she was “talking up her own book” to increase the chances of funding for a Europa landing mission.)
I would like to ask a question on the selection biases inherent to transit timing:
Skimming the literature as an interested layman seems to give me estimates of 1-2 Kepler-detectable planets per star in the Milky Way. Kepler has detected (apparently) an abundance of low-multiplicity systems with high orbital eccentricities and short orbital periods. Some have even used this data to conclude that high-multiplicity systems have lower eccentricities, and therefore that the majority of star systems in the galaxy have relatively few planets (<4, that sort of thing).
To a layman, these seem horribly, horribly observation-biased. In our own Solar System, we've got undetectable dwarf planets coming out of the wazoo, Kepler can barely pick up an Earth and Jupiter clone, can't pick up a Mars clone, and would seem to tend to pick up systems with high inclination "spreads" (3 planets at 3 different inclinations = 3x probability of detection???).
How have these selection bias effects been seriously analyzed and accounted for? (I'm pretty sure the professionals will have picked up on this before me). Have the efforts to analyze the data been reasonably satisfactory?
You are forgetting that Kepler was designed to only pick up short period systems and was terrible at long period planets. The second problem is as systems get larger less chance of a transits. Earth like orbits around earth like suns were rare because they could not be picked up and anything longer then 1.3 year transit could not be confirmed. In the case of Earth transits being seen from another planet outside the solar system see:
https://i.stack.imgur.com/q4O5U.gif
https://miro.medium.com/max/1122/1*oWzdofD2ypbuUfRVpK6yDw.png
Mercury and Venus would not transit and Mars on out would not have enough transits to confirm but if they even observed for 100’s of years they would not pick up any of the planets in our solar system. The chances of the movement thru tru space may show Venus and Mercury but this would be over long time periods. So I would not worry there are many many planets out there!
A brief follow-on to my previous question: have confounding effects been studied and modelled extensively? e.g. high eccentricity systems also having high inclination variation, etc.
Thank you
The Odds, what I find very odd is the unusual coincidence that we have the only moon that completely covers the sun in total solar eclipses. This is unique in our whole solar system and as the moon moves slowly away from the earth in 650 million years the eclipses will all be annular. David Kipping hopefully in the not too distant future will have a few thousand moons discovered as the larger space and earth base giant telescopes should be able to discern them in their transits around many planets. This will give us a Bayesian Inference as to just how rare we really are. The funny part is the black hole in the sky is just like the black hole we can not discuss that created the Fermi paradox.
I agree. That very very weird coincidence of the apparent solar and lunar angular diameters has had me wondering for years.
It’s related to, but NOT the same as the idea that advanced life NEEDS tides and therefore a close, massive moon. I think that requirement could be satisfied without the angular diameters coincidence.
There are plenty of satellites that eclipse the sun as seen from their planet (e.g, the Galilean moons of Jupiter). But none of them would match the sun’s angular diameter so precisely.
As you say, the moon’s apparent diameter will decrease as it slowly spirals out, but it is weird that it happens to be such a perfect match at the time we emerged as an intelligent species.
It’s fun speculating that it’s just the kind of stimulating environment a “parental” species might engineer for its adopted “children”. “Look at the eclipse, kids!” :-) .
Or maybe eclipses really did stimulate our growing intelligence / civilisation?
Michael T, The real game is the creation and testing of relativity from the stars light being bent by mass of the Sun. This was proven by the observations of total solar eclipses in the early 1900s. Even now our understanding of sunspots, prominences and flares are leading us to a better understanding of plasma physics and the holy grail controlled nuclear fusion. The beauty of the total solar eclipse is seeing the magnetic fields of the corona and prominences and understanding of its significance.
Interesting paper on advanced ETs and nature:
Qualitative classification of extraterrestrial civilizations.
https://arxiv.org/abs/2005.13221
Biology, astrophysics, life cycles of stars and planetary environments are all in there, right. Microbial life is difficult enough to reconstruct in origin, but the jump to “civilization” in simulation is just so much more huge.
The rare Earth argument, pro or con, might not be an issue of
duplicating all the necessary requirements we ascribe to Earth – somewhere else and then looking at the odds. Intermediate between life and outward looking civilization is self awareness or consciousness.
Little if any of the Drake equation relates to that: Number of suns in galaxy that induce self awareness in life. …??? Or what is the threshold for having it? Or is it an illusion that can be explained away by another source of information that does not accept it has self awareness either.
This is not necessarily going “creationist” on here. This is just an examination of whether there is something about the universe we live in that induces self awareness as well as other features of life. We don’t know how it happens. We don’t know if it a basic chemistry or signal, whether it is local or pervasive, ancient or new.
Our explorations have not gone far enough even in the solar system to identify non terrestrial living organisms. And we don’t know if terrestrial life started here, terra in loco parentis, shall we say. We could have got seed material from elsewhere amid all the collisions in the solar system. The necessary constituents could have arrived here from somewhere where they had a significant head start. Why organic chemistry should crest with thought and self awareness is not understood in any large degree, but somehow accepted.
And when we look at other creatures on the earth with their own awareness and complex behaviors, their pre-occupations do not seem to include signaling with the stars or flying off into space – unless the tendency was a self erasing property. If intelligence or civilization exists on a water world, or a gas giant, maybe we might not ever hear from them. They might not need to communicate. A Jupiter like world with a presumed troposphere and biosphere would cover a hundred times the area of Earth. As to the thickness of an ecosphere, who knows?
So if life forms were to transform into interstellar travelers, should we really presume that they would be little green men?… We really don’t know.
Environments in our own world do tend to drive forms even in unrelated creatures such as fish, mammals and birds. The eye seems to have been invented many times. But many of the environments we infer from search so far are unfamiliar ones. If microbiotic life had existed there, something just might have happened which would be hard to picture.
It is suggested, of course, that our short run rampant might be a lesson about the shortcomings of intelligent life. Well, life on Earth did not always stay static. Something would eventually turn the tables even after long equililbria, intelligent or not. Whether past ages on Earth were responsible for their ends…? Well, what program of risk reduction did dinosaurs have with respect to asteroid impacts? Genetic code seemed to have an inherent wisdom. The “inherent” part is intriguing.
Since corporal form seems like an encumbrance going from one star to another, maybe they would not have any physical forms in transit. But would that necessarily mean a transition to artificial intelligence? …How could we tell? How is an ant hill different than a city? If we can’t the museum of fine arts on another world, does that mean we have not contacted another intelligence?… There might be life outside the Earth beyond microbes and yet we still might not succeed in SETI.
I find Jeremy England’s approach (https://www.youtube.com/watch?v=10cVVHKCRWw) to understanding life, its emergence and evolution, much more convincing than the standard model of “life by a thousand miracles of probability”. I would also wager complex life is common though not as common as simple life. There are too many examples of endosymbiosis occurring (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2817226/).
Space faring capable intelligence will be the rarest of all lifeforms , but I don’t think getting the combination of traits required can’t be repeated. The Great Silence isn’t impossible to explain. The exclusivity principle is fairly weak. Even Occam’s Razor is more robust. The extent population of ETI personalities will be smaller than the population of all possible ETI personalities and the population that can navigate deep time will be smaller still. This is analogous to the population of lifeforms on Earth. The variety of lifeforms that have occurred is smaller than the variety DNA could theoretically produce. The extent variety that have survived is even smaller. We also don’t need one grand reason applicable to all possible personalities. Indeed, many overlapping reasons offer a more robust explanation for the Great Silence.
Of course this is just speculation, but I don’t think human type intelligence pursues ever larger populations. I think they will universally pursue ever more potent cognitive states and lifestyles for those cognitive states. It is easy for high populations and complex lifestyles to conflict.
Fascinating. I am currently working on a book MS, ‘Evolution, Anthropology and the Drake Equation’. Will be a few years in the works. Here are the synopsis and provisional chapters. Will be my third book for Springer if it goes through.
Evolution, Anthropology and the Drake Equation
Cameron M. Smith
Department of Anthropology, Portland State University
This book approaches variables 4-7 of the Drake Equation with the tools of evolutionary biology and anthropology. While estimates of these variables have been attempted many times, these estimates
have historically been made by researchers unfamiliar with the workings of evolutionary dynamics and/or the anthropological record. The author’s expertise in these fields (with peer-reviewed publications in the evolution of modern cognition and evolutionary theory in general) affords a more nuanced approach to these variables, and therefore a more reasonable range of DE estimates. I estimate a technical (not popular-science) book of about 400 pages in length. Below is a provisional TOC.
Chapter 1 A History of Drake Equation Calculations
An historical review of the DE, indicating its philosophy, origins, history of estimates, and status today. Discussion of how variables 4-7 have in the past been estimated many times, but not often by experts in the fields of evolution, the evolution of intelligence, and the origins and durations of civilizations. 50 pages.
Chapter 2 Variables 1 – 3
A review of variables 1-3, and modern estimates thereof. Presentation of Maccone’s ‘Statistical Drake Equation’ approach, and state of the art regarding variables 1-3, which are significantly better understood today than even 20 years ago. 50 pages..
Chapter 3 Factor 4: The Evolution of Life
A review of current understanding of the evolution of Earth life and prospects for evolution of replicator-interactor lineages beyond Earth. Review the philosophy and substance of Dawkins’ ‘Universal Evolution’ concept. Includes a review of the Darwinian and Lamarckian modes of evolution, and other variations in the outplay of evolution among various lineages of Earth life. Identifies the major patterns of evolutionary outcomes in the history of Earth life, with some special focus on the evolution of primates. With this background, the chapter concludes in a range of reasonable probabilities for the evolution of life beyond Earth. 60 pages.
Chapter 4 Factor 5: The Evolution of Intelligence
Reviews current understanding of the evolution of intelligence on Earth. Reviews philosophy and substance of the concept of intelligence. Reviews last three decades of evolutionary approaches to the evolution of cognition and intelligence, and applies state of the art theory to the spectrum of intelligences known on Earth today. With this background, the chapter concludes in a range of reasonable probabilities for the evolution of intelligence beyond Earth. 60 pages.
Chapter 5 Factor 6: The Evolution of Technical Civilization
Reviews philosophy and substance of the concept of technical civilization. Examines models of human cultural evolution, with special attention to the dynamics of population organization arrangements into such well-known varieties as bands, tribes, chiefdoms, and civilizations. Examines also the philosophy and substance of technology. Reviews the archaeological record of the evolution of human social organization and technology, with special focus on the uniqueness of ‘runaway technical progress’ evident only in the last few centuries among all known instances of civilization on Earth. With this background, the chapter concludes in a range of reasonable probabilities for the evolution of technical civilization beyond Earth. 60 pages.
Chapter 6 Factor 7: The Duration of Technical Civilizations
Reviews philosophy and substance of the concept of civilization maintenance, resilience, and instability and disintegration / collapse. Examines the stark archaeological record of civilization collapse, and comments on whether or not this record is applicable to modern, global civilization with characteristics clearly absent from ancient civilizations, including global interconnection and ‘runaway technical progress’. With this background, the chapter concludes in a range of reasonable durations of technical civilization beyond Earth. 60 pages.
Chapter 7 Re-Evaluation of the Drake Equation: A Probabilistic Approach
Applies the lessons of Chapters 3-6 to the DE’s most modern form, as examined in Chapters 1 and 2. Applies Maccone’s statistical approach to DE estimations. 30 pages.
Chapter 8 Discussion and Conclusions
Reviews what has been learned in the writing of these chapters, and comments on priorities for future research to improve on DE estimations. 20 pages.
Good to see you again, Cameron. Was consulting one of your Centauri Dreams essays just the other day.
I look forward to seeing this book when it is published. However, I am not convinced that knowledge of terrestrial evolution to primates and our history of civilization[s] is going to be universally applicable to other planets. Isn’t all the terrestrial history just going to lead you to reason and model exoplanets with a Copernican approach?
Even worse, possibly more geocentric/Ptolemaic than Copernican :-)
But anyway it’s all we have, to plug into the equation.
We do have a wide range of evolutionary histories in various lifeforms, and a diverse range of human histories to draw on, so maybe that gives us some idea of possibilities.
If we find ETI, that may allow us to actually fix the equation, which…
So again we don’t really know how well the equation works until we find ET anyway.
It is wonderful to hear that there is a draft out there for such an examination. Though it does seem that the Drake equation in principle is a probabilistic tool for assessing likelihood of extra terrestrial civilizations, so far it seems better suited to keeping score on how many habitable planets are in the galaxy. For each of the probabilities identified we have varying observational and theoretical
capabilities. But in so far as the “advertised” capability of the Drake equation goes, it needs more work and observational data.
It certainly would do no harm to parse what we know about human civilization development. If nothing else we might even find some human thresholds perhaps applicable to the problem in the sky.
But I suspect that DE in its early formulation stage assumed something like an exo-biological mental organization threshold – and then hanging around the exo planet home a million years or so, bound to call everyone up. For a while it was even assumed we knew what wavelength. Detection of exo-biology might be forging ahead of SETI simply on the basis of our increasing ability to detect non equilibrium
gases in exoplanet atmospheres. But after that? Seasons and living organism migrations, say? And then some of our arguments for detecting civilizations are based on energy expenditures which we are beginning to question as civilized ourselves. In contrast to that, how are ever going to detect the exo-Globe Theatre?
An exo-Globe Theatre! What an inspiring thought. And yes, what a problem for detection!
The so called Copernican revolution is based on the movement from a more mythical, religious world view to a more physical, scientific one. The philosophy of science is that the principles of physics are considered to be mind independent and objective, so they should work everywhere in the universe or are universal. It wasn’t just Copernicus but Newton, Einstein, Crick and Watson an every other biologist, microbiologist and biochemist.
Science uses general or universal principles, so the idea that the evolution of all life on Earth has a convergence can be extended to the convergence of all live in the universe considering a similar exact environment. e.i., there are contingencies that must be met for the environment to be most favorable for life, the need for the planet to be in the life belt of a G class star, the same size as Earth, the need for a giant impact creating the Moon and a large Iron core since the iron core of Theia went into the Earth to give it a larger iron core and grassing collision for a large angular momentum, or rotation and a magnetic field. The right sized meteor to cause the extinction of the dinosaurs which can’t be too large or it will kill all animal life. The timing might even have to be right. My point is that if we remove any of these physical contingencies, everything falls apart for intelligent life since long term stable, fertile environment must be maintained for IL. Even with these contingencies, there still must be some ET life and nearly exact Earth twins. How many, I don’t know. There could be ten, one hundred or more on this side of our galaxy. There is certainly a lot more Earth sized exoplanets without Moons in the life belt due to probability. I assume Earth’s without Moons are more probable.
This is a only hypothesis, but the DNA has adapted to our environment and we have every reason to think that if there is an exactly similar environment, there is a one hundred percent chance of life evolving there and a good chance of it being intelligent life.
It’s not a stretch to think our DNA is universal because it is these environmental conditions where it evolved and so far as we know, no where else in the solar system. If life evolved on Mars, but died out or any exoplanet with solar wind stripping, it would have the same DNA. The principles of science are invariant and absolute, so it’s not anything goes which is why one has to plug into that knowledge and principles. I am ruling out all those other possibilities which are improbable or very impracticable since the would correspond to the imagination and all possibilities and nature works through necessity. It’s also not a stretch to apply those invariances to biology, since there are already there on our planet. The DNA is designed for an Earthlike environment.
Also if ten percent of the fifty billion single stars in our galaxy are G class stars, then astronomers have to look through five billion stars to find an an Earth twin. How long will that take with today’s technology and telescopes? It might be a long time. There are 512 G class stars withing 100 light years of the Earth. Some G class stars might be much older than Earth’s Sun and can be ruled out, but it is hard to tell the age of the single star. One has to know the mass and chemical composition. A lack of lithium is an older star, etc.
For this to be true, evolution would have to be highly convergent to overcome the contingent and path-dependent run of terrestrial evolution. IOW, despite evolution appearing to somewhat of a random walk, all reruns end up with a technological civilization at some point. Would Neanderthals have eventually developed a technological civilization if Homo sapiens had not pushed them into extinction? Maybe, or maybe not. While convergent evolution does offer up classic convergence in form, e.g. ichthyosaurs, sharks, and dolphins, AFAIK this has not happened cognitively. Whilst the late John McCarthy thought that convergent evolution applied to intelligence and that we could definitely communicate with ET, others have voiced the opposite opinion, e.g. Keith Devlin has argued that even our mathematics may not be universal, an assumption that underlies our attempts at communicating with ETI, such as the plaques on the Pioneer and Voyager probes.
I think the jury is definitely out on this. I do think that we do not live in a Star Trek universe where there are many civilizations, almost all humanoid at a similar-ish stage in technology. If ETI is out there it is vastly older than us with a technology that is even farther from being indistinguishable from magic, and literally god-like. If “the singularity” is a possible outcome of our technology, we might be approaching god-like status ourselves, or at least our machines would.
I think there IS some evidence of convergent evolution of intelligence on earth.
Apart from instances of high intelligence scattered across the mammals, there are also reasonably intelligent birds such various parrots, corvids etc. Of course these are all terrestrial vertebrates.
But there are also squid and octopuses* which haven’t had a common ancestor with us since the Cambrian, and which display quite intelligent behaviour. Some biologists think they may be on a par with dogs, even if “alien” in psychology or neurology. Their common ancestor with us wouldn’t have been much smarter than a snail at best.
Another thing is that intelligence ISN’T a luxury for many species. Carnivores need ‘smarts’ to outwit their prey, including hunting cooperatively, for example. Brain power has metabolic costs but it obviously CAN be an advantage or it wouldn’t have persisted in the first place in different lineages.
*Squabbles over the plural of “octopus” are off topic. that’s my excuse ;-) .
There is always going to be some overlap in the Venn diagram of particular aspects of intelligence. Probably the easiest to understand example of differences I can offer is the difference between human and artificial intelligence. Even though humans design AI, the differences in the way each work should be indicative. Today many think human and artificial intelligence are complementary because they operate in very different ways, each with their own strengths.. While we can apply human tests to other animals, and Corvids do quite well on basic reasoning tasks and memory, we have no way of understanding how a Corvid thinks. Still less a Cephalopod.
Intelligence however defined, is a survival factor that is tuned/limited to the organism and its environment. ETI is going to be both biologically different and with a different (possibly very different) environment. Artificial ETI is going to be very different again.
If one is going to argue for convergence, it is going to be more useful to state which features of intelligence one is talking about and why that convergence is expected.
Also without a Moon, an Earth sized exopolanet would have a large variation of obliquity and axial tilt up to 90 degrees, so the climate would drastically change over 50, 000 years which might make it hard to life to adapt. Also there would be more solar radiation at the poles and over the whole planet which might change the temperature and make it hotter long term and there is the potential long term water loss from solar wind stripping.
Hello, Is It possible within the realm of possibility of course, another Big Bang happening? Thanks Kenny
Kenny,
Probably everyone has bee thinking that someone else would answer your question.
But in principle, since there has been so much speculation in these discussions, it seems like someone ought to step up and entertain this one – assuming it has bearing on the odds of other life, intelligence or civilization in the universe.
For a “Big Bang” to happen “again” we probably need some idea of what
conditions would have been like before the occurrence in our cosmos.
That’s a difficult issue right there. Or, perhaps we could detect some vast disturbance occurring far away. This is problematic too, because signals will be moving at the speed of light. So try to imagine how destruction could be observed via a shortcut. Hard to do. If it were close, well, we would be wiped away if we had any time to observe it at all.
Another possibility might be that as our universe, which includes space, expands outward, we encounter another universe doing much the same.
Would they have some sort of interaction? Would they have the same laws? Would there be some sort of chaos between them? Would they have another consciousness on the other side of the boundary which would be able to observe that expanding realm?
Ill prepared as I am to consider those issues, I suspect that the proposition will not affect our assessment of the odds of extraterrestrial intelligence out there, unless it would be as an announcement of “game over”.
Quote by Alex Tolley: “Would Neanderthals have eventually developed a technological civilization if Homo sapiens had not pushed them into extinction? Maybe, or maybe not.” Some homo sapiens have Neanderthal DNA. We got an better immune system from their DNA, but the Neanderthals, from I recall reading and TV, the Homo sapiens out competed them, or they couldn’t adapt to the changing climate.
All of science is based on mathematics. Even most languages use Arabic numerals, but it’s not the numerals, but the actual order in nature itself that numbers describe like the math that describes nuclear fusion in stars and motion of bodies in space that control physics long before man discovered it. And the comparison of ETI technology with magic, I agree which is probably why we don’t yet have access to a possible galactic society with interstellar travel. C.G. Jung wrote that faster light travel could be explained as “a physicist’s miracle.” Jung, 1959, UFO’s a Modern Myth.
I am going to have to disagree with “All of science is based on mathematics”. One can do a lot of science without it. Biology was largely math free and based on descriptions until the 20th century. Even where math is used it is just a crude way of representing the description. Physics is very clearly well described with math, but as one moves away from it to other areas of science, the math increasingly becomes “mathiness”.
“He finds betting odds of only 3:2 that intelligence rarely emerges.” These odds are interesting because to my illnumerate brain this is close to the predictions in the 20 year old book “Rare Earth.” Those authors estimated around .67 technological civilizations per galaxy.
Well, like I said, I was not a math major. But let me rethink my previous comment. If the odds against intelligent life are 3:2, then this means that intelligence evolves around 40% of the time, right? So if life is common in the universe and intelligence evolves 40% of the time, there should be billions of civilizations in the Milky Way. So we’re back to the Fermi paradox: Where are they?
I never implied that one couldn’t do science without mathematics since science is defined as an organized body of knowledge which can be qualitative considered that a system of qualitative principles and ideas is also mind independent and objective, like the idea of nuclear fusion. It’s the mathematics that proves the qualitative ideas like special and general relativity. Consequently, the idea that our DNA is dependent on exact, Earth like conditions would be qualitative science. My point is that since I already know that the math of special and general relativity is correct, Einstein and other scientists have done the work for us, so I don’t have to do the math to plug into that physics which is also visual and uses images as well as mathematical and if an idea does not fit into the qualitative system, then it can be invalided as not being a physical reality, but imaginary.
We can do the same thing with the physics of exoplanets and biology. If an Earth sized exoplanet in the life belt does not have a Moon, then it did not have giant impact with a grazing angle like Theia, so that exoplanet would have a slow rotation, and there would also be more solar radiation over time with very long days and nights. The temperature might increase more over the day side. All these little divergences from an exact Earth twin or Earth Moon system add up to make it a lot more difficult for intelligent life to evolve on a Moon less exoplanet.
I was supposed to write that C. G. Jung believed in the possibility of faster than light speed travel for ET’s which he called a physicist’s miracle. Flying Saucers, a Modern Myth.
What will earth look like in 900 million years (based on our current models of solar evolution etc)?
Under the scenario that simple life is common in the Universe, what genetic system do you think it will use? Will the genetic system be RNA/DNA or some other organic polymer? In other words, is it more likely that the organic information carrying polymer is different on different habitable planets vs being the same as it is on earth?
Even supposing that ET life uses the exact same DNA, RNA, and amino acids, there is no reason to believe a priori that the genetic code (which codon sequence codes for with amino acid) would be the same. If the amino acid set is not identical the code must be different. It has been hypothesized that life started with a 2 base code, rather than the current 3, limiting the amino acids that could be used in proteins. Lab experiments have changed the code to allow for different amino acids to be introduced, and also to create 4-base codes. All these differences are built upon the same DNA storage molecule, the same RNA templating, but modifying the ribosomes (a complex of RNA and proteins).
Interesting, Alex, so even if the ET life uses DNA, RNA, and amino acids, the genetic code could be different from earth-based life if the amino acids available are different. What I am wondering about is an organic, carbon-based form of life that uses a completely different polymer than DNA/RNA for information storage and coding: are DNA/RNA unique in their ability to code biological information such that wherever carbon-based life arises in the Universe, it will use these polymers, or, are we biased into thinking DNA/RNA are somehow special in that regard because they form the basis of our own biology? How likely is this “alternative information polymer” scenario as opposed to the one you mention in which the ET life still uses DNA, RNA, and amino acids but with a different genetic code? Could there be an ‘XNA world’ on another planet just as some suspect that there was an ‘RNA world’ on our planet? It would seem that a fruitful avenue for studying abiogenesis might be to explore other possible molecular architectures for information coding and storage besides DNA/RNA. If nature has a larger library of organic blueprints for life, this might indicate that simple life is quite common in the Universe.
It is easy to design a minimal storage molecule. A linear carbon chain with alternating single and double bonds for teh backbone. The side groups code a 1/0 depending on teh group, e.g OH/H. Then use n reads to get the message. But the real issue is how can such molecules evolve?
One idea for life is an RNA-World, RNS, with 1 difference in the sugar in its backbone (and substitution of uracil for thymine) , as a single strand can form complex shapes, rather like proteins. So RNA has functions like proteins. But it also matches with DNA, so possibly DNA came later to take on teh storage role, while proteins took on the main functional role. RNA then retreated to being mainly a messenger and template to convert DNA storage to functional proteins. That is one idea.
All this has to evolve by natural selection, with each step satisfying the 3 requirements – storage of information, replication, and differential survival with variability. We only have our terrestrial example, so we just don’t know what might be possible. Small differences in structure and composition or large ones? We will have to either be able to do simulations, experiments, or get real alien life to find out.
As I don’t think we will get alien life samples from a probe to another star anytime soon, the best hopes are life elsewhere in our solar system, or possibly life carried to our system from elsewhere. If we found Earth life on an asteroid or comet, carried to that body in some way, it would be an existence proof that objects from another star entering our system could harbor life too. Getting those samples would be a wonderful discovery that would tell us a lot about the details of life elsewhere.
In 900 million years the surface temperature of Earth will be well above the boiling point of water and most of it’s oceans might even have been lost to space. There is a dead, dry, molten surface at some point due to the increasing brightness of the Sun as it slowly moves to a point which will eventually be off the main sequence hydrogen burning. The more the hydrogen is lost through it’s fusion into helium, the hotter it has to burn to keep balance the gravitational compression. Consequently, the Sun gets brighter by 7 percent every billion years so by 300 million years the life belt will have moved much further away from the Sun and the Earth will be outside it and Earth will look like Venus without any oceans and a runaway greenhouse. Eventually, the surface of the Earth will get so hot, that the physics of atmospheric escape will show that water vapor and the heavier gases will escape much easier than at normal temperature. The Earth will become a hot, dry, planet without any atmosphere and a molten surface.
Evolution of intelligence does not necessarily result in development of technology. Does this have any relevance to the issue under discussion? Obviously we can have no way of detecting extraterrestrial non-technological intelligence if it exists. There are some possible examples here on Earth of a certain degree of non-technological intelligence. But we humans, I suppose, must look for folks who possess skyscrapers, bombs, etc. and rocketships etc.
SETI depends of technology being developed by ETI.
“Life on Earth is based on carbon, likely because each carbon atom can form bonds with up to four other atoms simultaneously. This quality makes carbon well-suited to form the long chains of molecules that serve as the basis for life as we know it, such as proteins and DNA.” This seems to support the need for four base pairs.” Quote from Google under DNA and carbon based life.
That is not how it works. The number of bases to code for the 20 amino acids has nothing to do with the carbon bonds at all. 64 combinations (4^3) code for 20 amino acids and stop codons, all with variable redundancy. If there were just 2 bases the number of combinations would be 8, and with 3, 27. So theoretically, DNA could use 3 different bases, but this would come at a cost in replication errors, and probably translation errors too.
I figured that there might not be any connection between the four base pairs and four valence electrons in Carbon. My question is why is there four base pairs? I have made an assumption that since there has been four base pairs through out the most of the history of life, then it might be an advantageous adaptation for life. If we suddenly removed 2 base pairs from the human DNA, then half of our protein would be gone since amino acids or nucleotides are the building blocks of protein? Also with only three base pairs there would be more translation errors or less variation and complexity?
Also I do look for an a priori and teleological reasons. The outcome is that all life has four base pairs and that does not look like it is going to change not including human intervention, an empirical observation. If we have the outcome, we can infer the premise which I assume is not only random or chance based on only physical reasons.
I look at the evolution of life with more than a scientific or physical world view. I can start with a psychological, philosophical and metaphysical world view which is a priori and try and support that with a physics or astrophysics, i.e., the idea that intelligent life could only evolve if exact environmental, psychological and physical conditions are met which would include teleology. For example, We could argue that intelligent life could only evolve in a solar system very similar to ours. The exoplanet system would have to have a similar Earth sized exoplanet and Moon. In addition, it’s entire solar system would have to be very similar to ours with nine planets and four gas giants in the outer solar system in the same positions. The early and late bombardment periods might have been caused by these gas giants sending meteoroids and debris towards Earth which influenced the evolution of life. Their gravity and orbital reasonances might have influenced Theia to collide with Earth. The fifth planet has to be the largest planet like Jupiter to deflect the large meteoroids, etc. This is only a speculation of course, but it limits the number of potential intelligent worlds. The Fermi paradox does not include such a limitation, so it comes up with millions of civilizations which might not be the case. Even if there were between 10 and 100, one could still argue why don’t we hear from any of them with radio signals. Because we haven’t heard anything from them does not mean they are not there. A conservative view will advocate a rare Earth hypothesis, but we still have not looked at very many G class stars of the estimated five billion in our galaxy. Until have, the potential for intelligent will not be ruled out. The JWST will be launched next year. Hopefully, one of the priorities will be to look at some of the spectra of nearby exoplanets.
Biology is best viewed through the lens of evolution. It is teh differential in replications based on some set of factors that determines teh outcome. All we can say is that 4 bases, coding for 20 amino acids using the genetic code that is almost entirely standard across all life proved to have the best “fitness”. Whether the genetic code is a purely random affair as once believed or selected I don’t know, although I have seen work suggesting it is optimum for the objective function chosen. Even casual inspection shows how the code allows for redundancy.
As for changing teh code or adding bases. George Church has suggested changing the code so that humans would become immune to many diseases that require human cells to help in replication of pathogens. (At what cost though?). I fully expect additional amino acids and possibly bases to be engineered into new organisms for some purposes. As with the Jurassic Park dinosaurs, they would be theoretically fully confinable. This is the “biological century” after all.
I still believe believe in fermi. Their is no life other than earth. Granted I have no proof. I would be trying to prove a negative. We are alone! I have read their may be 36 intelligent civilization in our galaxy, their so far away, so we are alone. I’m just novice on this subject, what’s would be worse? To be alone, or knowing theirs know one else out their?