8 ms·

I have a boring solution to the Fermi paradox. It is old, but really, really boring. Start looking at things that are weird about our Solar System and the Ear

by btilly 8y ago

I have a boring solution to the Fermi paradox. It is old, but really, really boring. Start looking at things that are weird about our Solar System and the Earth. Figure out which ones are probably necessary for intelligence. Add those into the Fermi calculation. And see that it is likely that we're the first intelligent life in this galaxy. What are some of those special things? It is not enough to have a planet that has the right ingredients to start life. It is necessary that it's progress not be constantly wiped out by major disasters over a very long time scale. What kinds of disasters? You don't want a supernova going off too close. We have been lucky to avoid that. Our odds were greatly improved by the fact that we spend most of our time out of the galactic plane, away from other stars that could be about to go boom. This is an unusual orbit. You don't want to be hit by too many comets. We've been hit by some, but far, far less than we would have without Jupiter acting like a sweeper to clean up dangerous stuff in our neighborhood. How rare is that? We have cataloged planets in hundreds of other solar systems. We see ones with only rocky planets. Ones with only gas giants. But we're the only one we know of with both gas giants and rocky planets. The only one where the rocky planets wind up protected from most of dinosaur killer kinds of impacts. Oh, and get this one. Without the Moon, the tilt of the Earth's spin is unstable. Without it, in simulations we would wind up with one pole aimed at the Sun and the other not once every few tens of millions of years. Probably not good for the development of intelligent life. Again we don't know how rare this is, but we suspect that it is rather uncommon. Suppose that each of these only happens to one star out of a thousand. Suppose further that there is one more, as yet unidentified, special factor about us that is also required. Again make that a 1/1000 coincidence. That would make the odds good that of the ~250 billion stars in our galaxy, we're the only ones with intelligent life. Or if you do the back of the envelope just with the three that I named, and made them 1/10,000 coincidences, you get the same result. As a sanity check, the fact that no other intelligent life has been observed is evidence that it is unlikely. And given Fermi's argument, it is probably unlikely at least on the scale of 100 billion to one against.

ars 8y ago
You also need an ocean.
- acpetrov 8y ago
  imo you also need dry land, for the tool-making flavor of intelligent life
  - scarecrowbob 8y ago
    Naive question: why is that?
    - vasama 8y ago
      It seems unlikely that an aquatic species could ever develop ceramics, metalworking, or any other technology requiring the use of fire. Any ocean covering an entire planet is likely very deep, making construction difficult or impossible. Early power sources such as coal would also be unavailable.
bg4 8y ago
See also: https://en.wikipedia.org/wiki/Drake_equation https://en.wikipedia.org/wiki/Drake_equation
- the8472 8y ago
  The problem with the drake equation is that we're not really working with means of normal distributions as estimates, we're working with wildly different, skewed distributions for each factor, due to uncertainties spanning orders of magnitude for some factors. Instead of multiplying point estimates you need to convolve the distributions, which yields quite different results. https://arxiv.org/pdf/1806.02404.pdf https://arxiv.org/pdf/1806.02404.pdf
  - bg4 8y ago
    Interesting, thanks for the link
pvg 8y ago
Doesn't this boil down to an even more specific version of an 'anthropic principle' argument with a good deal of sampling bias added and easier-to-spot problems? For instance, there's no reason to assume the only way to get a long-term, stable-enough environment for the development of intelligent life is precisely a planetary system with a gas giant (why does it have to be a gas giant?) and a rocky inner planet with a chonker of a satellite.
- reallydude 8y ago
  gas giants dont eject material as often and tend to be large gravity wells because thats the defining characteristic that maintains cohesion? (giant)
  - pvg 8y ago
    As often as what? Plus, we've seen some pretty huge rocky planets. Another way of looking this is that it's akin to erroneously calculating the probability that someone might win the lottery twice by multiplying 1/gazillion by 1/gazillion and concluding it can't realistically ever happen.
- btilly 8y ago
  This is a version of an anthropic principle argument. However it is not arbitrary, and not an assumption. When you run simulations you can test different combinations of factors and see what difference they make. See, for example, https://www.space.com/31577-earth-life-jupiter-saturn-giant-impacts.html https://www.space.com/31577-earth-life-jupiter-saturn-giant-... to see how important gas giants are for blocking large impacts on small rocky inner planets. That said, there may be another way to get long-term stability. But if so, then we haven't found it. And yes, we've looked.
  - pvg 8y ago
    and not an assumption. What do you mean? 'You have to replicate the solar system to come up with intelligent life' is a gigantic assumption, on top of the 'solar system-like planetary system are rare' assumption. Is this a conceivable narrative for the Fermi paradox? Sure. But it's hardly supported enough to make a reasonable probabilistic argument out of it.
r721 8y ago
https://en.wikipedia.org/wiki/Rare_Earth_hypothesis https://en.wikipedia.org/wiki/Rare_Earth_hypothesis
lmilcin 8y ago
I think there are very many things about Earth that are underappreciated as possible limiting factors. I think that plate tectonics is absolute prerequisite for life to evolve. Not only that, you need to have plate tectonics for a very long time for life to evolve. You need sharp temperature gradients stable for very long time on geologic scales and you only get that with plate tectonics. Without plate tectonics and with presence of atmosphere and voluminous bodies of water (other requirements) everything just gets obliterated quickly and the entire planet becomes flat without much features or temperature gradients. At later stages of evolution I think geographic features are important as they create niches which promote specialization and differentiation. I am currently reading on origins of political order (https://www.audible.co.uk/pd/The-Origins-of-Political-Order-From-Prehuman-Times-to-the-French-Revolution-Audiobook/B006P47PT4 https://www.audible.co.uk/pd/The-Origins-of-Political-Order-...). I think it might be possible large brain and high intelligence are not inevitable evolutionary results. The author speculates, and very convincingly, that the intelligence is result of human and chimpanzee males and females having different goals that cause them to deceive each other. The one who could better deceive would have evolutionary advantage and this caused humans to grow in intelligence as a result. But this level of intelligence is not inevitable as we see other species dealing with the problem in different ways. Large brain is a huge liability to an animal as it consumes a lot of energy and causes lots of other issues. It is true that animals use large brains to avoid predators or, being predators, to be more effective at the task. But it also seems that most animals don't seem to be growing their brains more with relation to their body size as it seems there are diminishing returns at some point and bigger brain costs exponentially more than it is worth.
- Mbioguy 8y ago
  Nothing in evolution is inevitable. Granted some things are more likely (oxygen-binding hemoglobin has independently evolved several times from its related non-binding globin family). Brains, nervous systems, even multicellularity are not inevitable. The specific combination of astronomical, geological, and biological features that lead to our development might not lead to similar outcomes if ran a million times. As other responders have pointed out, brains are just one possible substrate for intelligence. We can't account for other systems (biological or otherwise) that could lead to the development of intelligence, so of necessity any probability estimate based on us has to be a lower bound of possibility. One bit of our earth history that is worth noting is that the conditions when life presumably arose are hostile to multicellular life as we know it. Earth's early oceans were hot, anoxic and reducing, and under heavy pressure from far thicker atmospheres. The great oxidation event essentially turned earth's atmosphere into a bacterial waste dump, the waste being oxygen produced by early cyanobacteria. Life had to evolve ways to cope with oxygen or learn to hide. This is still true of our own cells. While we need oxygen to survive, it is still and will always be toxic. Free radical damage such as from reactive oxygen species is a constant threat, and is the ultimate form of irrecoverable information death when we die. Might it be that the conditions under which life can arise, and under which intelligent life can arise, are different? We got lucky that earth traversed from the first to the second. Add this to the list of a million things that had to go right for us to exist at all. The same might well be true of any other intelligences out there. And the odds of two arising close enough in time and space to contact each other would be far less common than lonely civilizations looking out into the dark.
mbell 8y ago
> We have cataloged planets in hundreds of other solar systems. We see ones with only rocky planets. Ones with only gas giants. But we're the only one we know of with both gas giants and rocky planets. The only one where the rocky planets wind up protected from most of dinosaur killer kinds of impacts. Not true: https://en.wikipedia.org/wiki/Kepler-90 https://en.wikipedia.org/wiki/Kepler-90
- btilly 8y ago
  Thank you for that correction. I am having trouble finding the reference that I found that claim in. But note that Kepler-90 does not have rocky planets that look like the Earth. It has super-earths, and gas giants. A gas giant will do a worse job of protecting a super-earth than it will of protecting small rocky planets. So Jupiter still seems rare. Incidentally while looking for the article that I saw before, I stumbled across https://www.reddit.com/r/askscience/comments/4ohkkn/how_unique_is_our_solar_system/ https://www.reddit.com/r/askscience/comments/4ohkkn/how_uniq... which pointed out something I had not thought of. Our Sun is an unusual combination of old and metallic. It is likely that a neutron star collision happened near the stellar nursery where the Sun is born. This is important for a couple of reasons. The first is that metallic stars give rise to more planets. The second is that metallic stars can give rise to planets with richer chemistry. This is another way in which we are weird, which could be potentially important for the development of intelligent life.
  - cgriswald 8y ago
    Jupiter is hard to find. It’s orbit is ~11 years making it harder to measure and more time consuming. It’s pull on the sun is a lot harder to measure than a hot Jupiter, making the radial velocity method more difficult. We aren’t finding average systems. We are finding systems that are easy (and quick) to find using the methods we have available.
    - btilly 8y ago
      Harder but not beyond us. Per https://physics.stackexchange.com/questions/230973/how-can-we-see-planets-thousands-of-light-years-away-but-dont-know-if-there-are https://physics.stackexchange.com/questions/230973/how-can-w... at this point we would be able to pick up Jupiter and Saturn around another star.
millstone 8y ago
I think there is no way we can know what is necessary for intelligence. Life is not necessary for intelligence. As a counter-example, intelligent robots are certainly possible. What other substrates might support intelligence? Life does not require proper axial tilt or distance from supernovas. There is life on the bottom of the ocean that survive on the heat and chemicals from hydrothermal vents, a metabolic pathway that does not depend on the sun. What other possibilities are there that don't happen to be present on earth? We are biased towards human size, time scales, and biochemistry. And time and again, we have been surprised by forms of life that work differently.
- deleted 8y ago
  [deleted]
- TomMarius 8y ago
  Optical computing fascinates me. Imagine an intelligence based on that.
  - ethbro 8y ago
    There was an argument somewhere that biological computational substrate density (with respect to round trip signal speed) was critical. If you've only had time for 3 thoughts (to simplify) since evolving intelligence... a civilization of your beings probably isn't doing too well.
Joakal 8y ago
Civilizations probably ended because it's hard to control their own populations. Imagine a society where population is set to 5 billion, the limit only increased when capacity is increased. This is compounded by: 1) a lot of planets are not hospitable for a variety of factors. A society might resent the limit for many years if it was possible to implement such a limit. 2) the technology era is short-lived and not ongoing. A new civilization starts 10,000 years later. How will they even know homo-sapiens existed if a plague wipes out homo-sapiens tomorrow? A few tiny satellites in the vast emptiness of space?
- ethbro 8y ago
  It'd be ironic if the great filter was that "population required for development and construction of interstellar travel" is very close to "population at which civilizations exhaust their resources and collapse."
temporallobe 8y ago
The fact that we have never observed other intelligent life does not it doesn’t exist. The unimaginable size of the universe leads me to believe that our special set of conditions are possible elsewhere, though it might be exceedingly rare. And because of this, we will never know about it anyway. You might say that’s the same as it not existing at all, but that’s a question for philosophers braver than I. One of the scariest thoughts I have ever had is that we truly are alone, but the sheer size of the universe makes me feel slightly better about that prospect.
- hardatwork 8y ago
  > One of the scariest thoughts I have ever had is that we truly are alone As someone quite new to this discussion, can I ask why? My only immediate reaction is a mild one going the other way: that being alone is reassuring as it means there is not this extra potential threat out there.
- Reese63 8y ago
  My idea is we are not alone, never have been and never will be. We are the extraterrestrial big brains that have developed intelligence over millions of years. We long for the others that continued to travel while our ancestors chose to stay and inhabit this planet and in doing so in time forgot about the others and our chosen mission.
root_axis 8y ago
There are so many impossibly complex factors and unknowns regarding how life and the universe works that this type of speculation seems odd to me. The reality is, we don't know how life would or could adapt to any of these differences, or how likely other differences or anomalies we are simply unaware of might have countered or exacerbated various knock-on effects. It's simply guessing.
- ethbro 8y ago
  It is. But it's a very important guess. In the same way game theory makes guesses about nuclear standoff strategy.
  - Pharmakon 8y ago
    The critical nature of the guess doesn’t in any way improve our ability to make it accurate or useful. Bad assumptions are bad assumptions, regardless of the stakes. We have a sample size or just one, and precious little good information. Now, in a couple of decades that will probably have changed and we’ll have better data, but until then there’s a real masturbatory quality to discussions involving extraterrestrial life.
thaumaturgy 8y ago
Right. This has been my preferred solution to the paradox as well, for the last several years. More and more evidence seems to point towards the Drake Equation simply not sufficiently accounting for uncertainty [1]. There are a few planets and moons in our system that have or had the potential for life, but upon which there's been no evidence for intelligent life, if any life is to be found on them at all: Mars, Europa, Ganymede, among others. While this would seem to increase the probability of life in other solar systems, seeing observable life on only one of the worlds in our system really has a negative impact on the overall odds of life in the universe. Whether a moon is necessary or not for life on Earth [2], it remains that a stable tilt is currently thought to be critical for the development of complex life. We also had the benefit of an asteroid that obliterated the dominant species of the planet and changed the environment sufficiently to allow for new species to take their place. Hundreds of millions of years of flourishing life also provided us with the abundant, cheap energy sources in the forms of coal and oil that we needed to build civilizations. There's also an open question as to whether evolution necessarily leads to intelligent species. Earth had large, complex lifeforms for 165 million years, and none of them appear to have developed civilizations. Human societies have existed for just 50,000 years if you take a very liberal definition of "society". Research has found an evolutionary fluke that fed lots of oxygen-rich blood to hominid brains [3]; other research has suggested that intelligence is not only not an evolutionary advantage, it's a disadvantage, due to the much higher calorie diet required to sustain it. And finally, our universe may not have been hospitable to advanced civilizations until only (geologically) recently. It took a billion years for the universe to form galaxies and stars and planets [4]; it was a more chaotic, hot, radiation-rich universe before our solar system was born. Any civilizations which developed much before our own solar system may have met a premature end by radiation or cosmic debris. Given the empirical lack of observable life in the universe so far, and that continuing research keeps growing rather than reducing the number of special cases that led to human civilization on Earth, it seems likely to me that even if there are other intelligent civilizations in the cosmos, they are approximately as young as we are, too far away and technologically primitive to make contact. [1]: A good paper on this from last year: https://arxiv.org/pdf/1806.02404.pdf https://arxiv.org/pdf/1806.02404.pdf [pdf] [2]: https://www.astrobio.net/news-exclusive/the-odds-for-life-on-a-moonless-earth/ https://www.astrobio.net/news-exclusive/the-odds-for-life-on... [3]: https://theconversation.com/how-our-species-got-smarter-through-a-rush-of-blood-to-the-head-73856 https://theconversation.com/how-our-species-got-smarter-thro... [4]: https://en.wikipedia.org/wiki/Chronology_of_the_universe https://en.wikipedia.org/wiki/Chronology_of_the_universe
Pharmakon 8y ago
We have cataloged planets in hundreds of other solar systems. We see ones with only rocky planets. Ones with only gas giants. But we're the only one we know of with both gas giants and rocky planets. The only one where the rocky planets wind up protected from most of dinosaur killer kinds of impacts. Right, because that’s what or current techniques mostly allow us to find. Big planets close to their primaries are most favorable for techniques based on transiting such as light curve analysis. Drawing conclusions based on limited data with primitive tools is a poor notion though, and it tells us nothing about the typical makeup of extrasolar systems.
- novaleaf 8y ago
  I think you are both forgetting about Venus. And kinda Mars.
jarvuschris 8y ago
On top of all this there's the theory that gas giants typically migrate towards their star, it may be rare for a gas giant like Jupiter to find a stable orbit where it can shield the habitable zone Another thing making earth rare is its high proportion of iron ore. That and our abnormally large moon are thought to be the result of Earth colliding with another large rocky planet. The tidal force of an extra large moon + our extra ironey core give us an extra strong magnetic field to keep the nasties out and hold our atmosphere
jcranmer 8y ago
The most likely solution to the Fermi Paradox is probably the most depressing for the people who are interested in it: space colonization is basically impossible. The fastest object we've sent outside of the gravitational field of the Sun would take about 75,000 years to reach the nearest star (if we pointed it at it). For perspective, the last glacial advance started in earnest about 75,000 years ago. We don't have any technology that can maintain an automated craft for that long, let alone life support for sentient creatures. Hell, our current technology is insufficient to permit a self-sustaining colony on any other planet or satellite. Ultimately, the Fermi Paradox is based on the assumption that, given enough chances, an unlikely event is basically certain. While this is true, to do a proper analysis, you do need to look at orders of magnitude to see if there really have been enough chances. And we have so little information to base the computations on that the dominating term is your priors: if you think we ought to have seen alien life by now, you'll pick priors that suggest life is quite likely and find that we ought to have seen it; if you think we oughtn't, your prior will reflect that.
- Faark 8y ago
  It obviously dependents on priors, and figuring out realistic ones is kind of the point. We haven't observed other life in the universe, so any result of adding up all those chances necessarily has to be low. The question is what makes it so low. And most importantly: Is it a check we humans already cleared or something still coming? That should be a huge warning to us.
- lumost 8y ago
  It's worth looking at Project Orion: "Later studies indicate that the top cruise velocity that can theoretically be achieved are a few percent of the speed of light (0.08–0.1c).[17] An atomic (fission) Orion can achieve perhaps 9%–11% of the speed of light. A nuclear pulse drive starship powered by fusion-antimatter catalyzed nuclear pulse propulsion units would be similarly in the 10% range and pure Matter-antimatter annihilation rockets would be theoretically capable of obtaining a velocity between 50% to 80% of the speed of light. In each case saving fuel for slowing down halves the maximum speed. The concept of using a magnetic sail to decelerate the spacecraft as it approaches its destination has been discussed as an alternative to using propellant; this would allow the ship to travel near the maximum theoretical velocity.[18] At 0.1c, Orion thermonuclear starships would require a flight time of at least 44 years to reach Alpha Centauri, not counting time needed to reach that speed (about 36 days at constant acceleration of 1g or 9.8 m/s2). At 0.1c, an Orion starship would require 100 years to travel 10 light years. The astronomer Carl Sagan suggested that this would be an excellent use for current stockpiles of nuclear weapons" https://en.wikipedia.org/wiki/Project_Orion_(nuclear_propulsion) https://en.wikipedia.org/wiki/Project_Orion_(nuclear_propuls...
oh_sigh 8y ago
> As a sanity check, the fact that no other intelligent life has been observed is evidence that it is unlikely. I'm not sure this is particularly useful. It could be like a medieval European saying land to the west of the Atlantic doesn't exist, because they've never once seen it through their looking glasses. How far could we detect intelligent life, say on a similar level of current humans? If it is based off of radio ways, we would only be able to detect life within a 100 light year radius of earth, which is merely 2% of the way across our galaxy.
sliken 8y ago
Seems like you got it backwards. Being outside the plane of the galaxy INCREASES the threat from supernova, not decreases it. The further from the plane the less gas/dust/stars etc between you and ever other star in the galaxy.
- btilly 8y ago
  Um, no. Intervening material does very little to cut out light. If it did, we couldn't see distant stars. However the intensity of radiation falls off as the square of the distance from the source of the radiation. Therefore the primary determinant of risk is the number of stars that could be about to go boom within the critical distance of the Sun. If we're in a less densely populated neighborhood, then our odds of seeing a dangerous supernova go down. Full stop.
  - sliken 8y ago
    Er, there's a giant cloud of dust called the dark rift that blocks a fair bit of the center of the galaxy. We only recently started looking though it at xray wavelengths to see the center of the milky way (and the black hole there). On a clear night you can see the edges of the milky way and the giant cloud of dust.
    - btilly 8y ago
      That cloud is about 2000 light years away from us. The fact that there are patches of dust doesn't change the fact that we are seldom in the middle of such patches. And even when we are, it is a lot like the difference between being in light mist versus seeing it from a long ways away. We are, in fact, in the middle of a patch of "mist" called the "local fluff". See https://en.wikipedia.org/wiki/Local_Interstellar_Cloud https://en.wikipedia.org/wiki/Local_Interstellar_Cloud for more. This does not noticably cut out light between us and stars that are under 100 lightyears away.
Keysh 8y ago
You don't want a supernova going off too close. We have been lucky to avoid that. Our odds were greatly improved by the fact that we spend most of our time out of the galactic plane, away from other stars that could be about to go boom. This is an unusual orbit. Not really. The amplitude of the Sun's vertical motion is about 100 parsecs (~ 300 light years), but since the main ("thin") stellar disk has a vertical exponential scale height of about 300 parsecs, the local density of stars at the top/bottom of the Sun's orbit is only about 30% less than when the Sun is crossing through the midplane. (And this isn't at all an unusual orbit.) What makes a real difference is being relatively far out in the disk from the galactic center: if we were ten times closer to the center, the local density would be almost 100 times higher, and you might indeed have to start worrying about nearby supernovae.

by btilly 8y ago

ars 8y ago

You also need an ocean.

acpetrov 8y ago
imo you also need dry land, for the tool-making flavor of intelligent life
- scarecrowbob 8y ago
  Naive question: why is that?
  - vasama 8y ago
    It seems unlikely that an aquatic species could ever develop ceramics, metalworking, or any other technology requiring the use of fire. Any ocean covering an entire planet is likely very deep, making construction difficult or impossible. Early power sources such as coal would also be unavailable.

bg4 8y ago

See also: https://en.wikipedia.org/wiki/Drake_equation https://en.wikipedia.org/wiki/Drake_equation

the8472 8y ago
The problem with the drake equation is that we're not really working with means of normal distributions as estimates, we're working with wildly different, skewed distributions for each factor, due to uncertainties spanning orders of magnitude for some factors. Instead of multiplying point estimates you need to convolve the distributions, which yields quite different results. https://arxiv.org/pdf/1806.02404.pdf https://arxiv.org/pdf/1806.02404.pdf
- bg4 8y ago
  Interesting, thanks for the link

pvg 8y ago

Doesn't this boil down to an even more specific version of an 'anthropic principle' argument with a good deal of sampling bias added and easier-to-spot problems? For instance, there's no reason to assume the only way to get a long-term, stable-enough environment for the development of intelligent life is precisely a planetary system with a gas giant (why does it have to be a gas giant?) and a rocky inner planet with a chonker of a satellite.

reallydude 8y ago
gas giants dont eject material as often and tend to be large gravity wells because thats the defining characteristic that maintains cohesion? (giant)
- pvg 8y ago
  As often as what? Plus, we've seen some pretty huge rocky planets. Another way of looking this is that it's akin to erroneously calculating the probability that someone might win the lottery twice by multiplying 1/gazillion by 1/gazillion and concluding it can't realistically ever happen.
btilly 8y ago
This is a version of an anthropic principle argument. However it is not arbitrary, and not an assumption. When you run simulations you can test different combinations of factors and see what difference they make. See, for example, https://www.space.com/31577-earth-life-jupiter-saturn-giant-impacts.html https://www.space.com/31577-earth-life-jupiter-saturn-giant-... to see how important gas giants are for blocking large impacts on small rocky inner planets. That said, there may be another way to get long-term stability. But if so, then we haven't found it. And yes, we've looked.
- pvg 8y ago
  and not an assumption. What do you mean? 'You have to replicate the solar system to come up with intelligent life' is a gigantic assumption, on top of the 'solar system-like planetary system are rare' assumption. Is this a conceivable narrative for the Fermi paradox? Sure. But it's hardly supported enough to make a reasonable probabilistic argument out of it.

r721 8y ago

https://en.wikipedia.org/wiki/Rare_Earth_hypothesis https://en.wikipedia.org/wiki/Rare_Earth_hypothesis

lmilcin 8y ago

I think there are very many things about Earth that are underappreciated as possible limiting factors. I think that plate tectonics is absolute prerequisite for life to evolve. Not only that, you need to have plate tectonics for a very long time for life to evolve. You need sharp temperature gradients stable for very long time on geologic scales and you only get that with plate tectonics. Without plate tectonics and with presence of atmosphere and voluminous bodies of water (other requirements) everything just gets obliterated quickly and the entire planet becomes flat without much features or temperature gradients. At later stages of evolution I think geographic features are important as they create niches which promote specialization and differentiation. I am currently reading on origins of political order (https://www.audible.co.uk/pd/The-Origins-of-Political-Order-From-Prehuman-Times-to-the-French-Revolution-Audiobook/B006P47PT4 https://www.audible.co.uk/pd/The-Origins-of-Political-Order-...). I think it might be possible large brain and high intelligence are not inevitable evolutionary results. The author speculates, and very convincingly, that the intelligence is result of human and chimpanzee males and females having different goals that cause them to deceive each other. The one who could better deceive would have evolutionary advantage and this caused humans to grow in intelligence as a result. But this level of intelligence is not inevitable as we see other species dealing with the problem in different ways. Large brain is a huge liability to an animal as it consumes a lot of energy and causes lots of other issues. It is true that animals use large brains to avoid predators or, being predators, to be more effective at the task. But it also seems that most animals don't seem to be growing their brains more with relation to their body size as it seems there are diminishing returns at some point and bigger brain costs exponentially more than it is worth.

Mbioguy 8y ago
Nothing in evolution is inevitable. Granted some things are more likely (oxygen-binding hemoglobin has independently evolved several times from its related non-binding globin family). Brains, nervous systems, even multicellularity are not inevitable. The specific combination of astronomical, geological, and biological features that lead to our development might not lead to similar outcomes if ran a million times. As other responders have pointed out, brains are just one possible substrate for intelligence. We can't account for other systems (biological or otherwise) that could lead to the development of intelligence, so of necessity any probability estimate based on us has to be a lower bound of possibility. One bit of our earth history that is worth noting is that the conditions when life presumably arose are hostile to multicellular life as we know it. Earth's early oceans were hot, anoxic and reducing, and under heavy pressure from far thicker atmospheres. The great oxidation event essentially turned earth's atmosphere into a bacterial waste dump, the waste being oxygen produced by early cyanobacteria. Life had to evolve ways to cope with oxygen or learn to hide. This is still true of our own cells. While we need oxygen to survive, it is still and will always be toxic. Free radical damage such as from reactive oxygen species is a constant threat, and is the ultimate form of irrecoverable information death when we die. Might it be that the conditions under which life can arise, and under which intelligent life can arise, are different? We got lucky that earth traversed from the first to the second. Add this to the list of a million things that had to go right for us to exist at all. The same might well be true of any other intelligences out there. And the odds of two arising close enough in time and space to contact each other would be far less common than lonely civilizations looking out into the dark.

mbell 8y ago

> We have cataloged planets in hundreds of other solar systems. We see ones with only rocky planets. Ones with only gas giants. But we're the only one we know of with both gas giants and rocky planets. The only one where the rocky planets wind up protected from most of dinosaur killer kinds of impacts. Not true: https://en.wikipedia.org/wiki/Kepler-90 https://en.wikipedia.org/wiki/Kepler-90

btilly 8y ago
Thank you for that correction. I am having trouble finding the reference that I found that claim in. But note that Kepler-90 does not have rocky planets that look like the Earth. It has super-earths, and gas giants. A gas giant will do a worse job of protecting a super-earth than it will of protecting small rocky planets. So Jupiter still seems rare. Incidentally while looking for the article that I saw before, I stumbled across https://www.reddit.com/r/askscience/comments/4ohkkn/how_unique_is_our_solar_system/ https://www.reddit.com/r/askscience/comments/4ohkkn/how_uniq... which pointed out something I had not thought of. Our Sun is an unusual combination of old and metallic. It is likely that a neutron star collision happened near the stellar nursery where the Sun is born. This is important for a couple of reasons. The first is that metallic stars give rise to more planets. The second is that metallic stars can give rise to planets with richer chemistry. This is another way in which we are weird, which could be potentially important for the development of intelligent life.
- cgriswald 8y ago
  Jupiter is hard to find. It’s orbit is ~11 years making it harder to measure and more time consuming. It’s pull on the sun is a lot harder to measure than a hot Jupiter, making the radial velocity method more difficult. We aren’t finding average systems. We are finding systems that are easy (and quick) to find using the methods we have available.
  - btilly 8y ago
    Harder but not beyond us. Per https://physics.stackexchange.com/questions/230973/how-can-we-see-planets-thousands-of-light-years-away-but-dont-know-if-there-are https://physics.stackexchange.com/questions/230973/how-can-w... at this point we would be able to pick up Jupiter and Saturn around another star.

millstone 8y ago

I think there is no way we can know what is necessary for intelligence. Life is not necessary for intelligence. As a counter-example, intelligent robots are certainly possible. What other substrates might support intelligence? Life does not require proper axial tilt or distance from supernovas. There is life on the bottom of the ocean that survive on the heat and chemicals from hydrothermal vents, a metabolic pathway that does not depend on the sun. What other possibilities are there that don't happen to be present on earth? We are biased towards human size, time scales, and biochemistry. And time and again, we have been surprised by forms of life that work differently.

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TomMarius 8y ago
Optical computing fascinates me. Imagine an intelligence based on that.
- ethbro 8y ago
  There was an argument somewhere that biological computational substrate density (with respect to round trip signal speed) was critical. If you've only had time for 3 thoughts (to simplify) since evolving intelligence... a civilization of your beings probably isn't doing too well.

Joakal 8y ago

Civilizations probably ended because it's hard to control their own populations. Imagine a society where population is set to 5 billion, the limit only increased when capacity is increased. This is compounded by: 1) a lot of planets are not hospitable for a variety of factors. A society might resent the limit for many years if it was possible to implement such a limit. 2) the technology era is short-lived and not ongoing. A new civilization starts 10,000 years later. How will they even know homo-sapiens existed if a plague wipes out homo-sapiens tomorrow? A few tiny satellites in the vast emptiness of space?

ethbro 8y ago
It'd be ironic if the great filter was that "population required for development and construction of interstellar travel" is very close to "population at which civilizations exhaust their resources and collapse."

temporallobe 8y ago

The fact that we have never observed other intelligent life does not it doesn’t exist. The unimaginable size of the universe leads me to believe that our special set of conditions are possible elsewhere, though it might be exceedingly rare. And because of this, we will never know about it anyway. You might say that’s the same as it not existing at all, but that’s a question for philosophers braver than I. One of the scariest thoughts I have ever had is that we truly are alone, but the sheer size of the universe makes me feel slightly better about that prospect.

hardatwork 8y ago
> One of the scariest thoughts I have ever had is that we truly are alone As someone quite new to this discussion, can I ask why? My only immediate reaction is a mild one going the other way: that being alone is reassuring as it means there is not this extra potential threat out there.
Reese63 8y ago
My idea is we are not alone, never have been and never will be. We are the extraterrestrial big brains that have developed intelligence over millions of years. We long for the others that continued to travel while our ancestors chose to stay and inhabit this planet and in doing so in time forgot about the others and our chosen mission.

root_axis 8y ago

There are so many impossibly complex factors and unknowns regarding how life and the universe works that this type of speculation seems odd to me. The reality is, we don't know how life would or could adapt to any of these differences, or how likely other differences or anomalies we are simply unaware of might have countered or exacerbated various knock-on effects. It's simply guessing.

ethbro 8y ago
It is. But it's a very important guess. In the same way game theory makes guesses about nuclear standoff strategy.
- Pharmakon 8y ago
  The critical nature of the guess doesn’t in any way improve our ability to make it accurate or useful. Bad assumptions are bad assumptions, regardless of the stakes. We have a sample size or just one, and precious little good information. Now, in a couple of decades that will probably have changed and we’ll have better data, but until then there’s a real masturbatory quality to discussions involving extraterrestrial life.

thaumaturgy 8y ago

Right. This has been my preferred solution to the paradox as well, for the last several years. More and more evidence seems to point towards the Drake Equation simply not sufficiently accounting for uncertainty [1]. There are a few planets and moons in our system that have or had the potential for life, but upon which there's been no evidence for intelligent life, if any life is to be found on them at all: Mars, Europa, Ganymede, among others. While this would seem to increase the probability of life in other solar systems, seeing observable life on only one of the worlds in our system really has a negative impact on the overall odds of life in the universe. Whether a moon is necessary or not for life on Earth [2], it remains that a stable tilt is currently thought to be critical for the development of complex life. We also had the benefit of an asteroid that obliterated the dominant species of the planet and changed the environment sufficiently to allow for new species to take their place. Hundreds of millions of years of flourishing life also provided us with the abundant, cheap energy sources in the forms of coal and oil that we needed to build civilizations. There's also an open question as to whether evolution necessarily leads to intelligent species. Earth had large, complex lifeforms for 165 million years, and none of them appear to have developed civilizations. Human societies have existed for just 50,000 years if you take a very liberal definition of "society". Research has found an evolutionary fluke that fed lots of oxygen-rich blood to hominid brains [3]; other research has suggested that intelligence is not only not an evolutionary advantage, it's a disadvantage, due to the much higher calorie diet required to sustain it. And finally, our universe may not have been hospitable to advanced civilizations until only (geologically) recently. It took a billion years for the universe to form galaxies and stars and planets [4]; it was a more chaotic, hot, radiation-rich universe before our solar system was born. Any civilizations which developed much before our own solar system may have met a premature end by radiation or cosmic debris. Given the empirical lack of observable life in the universe so far, and that continuing research keeps growing rather than reducing the number of special cases that led to human civilization on Earth, it seems likely to me that even if there are other intelligent civilizations in the cosmos, they are approximately as young as we are, too far away and technologically primitive to make contact. [1]: A good paper on this from last year: https://arxiv.org/pdf/1806.02404.pdf https://arxiv.org/pdf/1806.02404.pdf [pdf] [2]: https://www.astrobio.net/news-exclusive/the-odds-for-life-on-a-moonless-earth/ https://www.astrobio.net/news-exclusive/the-odds-for-life-on... [3]: https://theconversation.com/how-our-species-got-smarter-through-a-rush-of-blood-to-the-head-73856 https://theconversation.com/how-our-species-got-smarter-thro... [4]: https://en.wikipedia.org/wiki/Chronology_of_the_universe https://en.wikipedia.org/wiki/Chronology_of_the_universe

Pharmakon 8y ago

We have cataloged planets in hundreds of other solar systems. We see ones with only rocky planets. Ones with only gas giants. But we're the only one we know of with both gas giants and rocky planets. The only one where the rocky planets wind up protected from most of dinosaur killer kinds of impacts. Right, because that’s what or current techniques mostly allow us to find. Big planets close to their primaries are most favorable for techniques based on transiting such as light curve analysis. Drawing conclusions based on limited data with primitive tools is a poor notion though, and it tells us nothing about the typical makeup of extrasolar systems.

novaleaf 8y ago
I think you are both forgetting about Venus. And kinda Mars.

jarvuschris 8y ago

On top of all this there's the theory that gas giants typically migrate towards their star, it may be rare for a gas giant like Jupiter to find a stable orbit where it can shield the habitable zone Another thing making earth rare is its high proportion of iron ore. That and our abnormally large moon are thought to be the result of Earth colliding with another large rocky planet. The tidal force of an extra large moon + our extra ironey core give us an extra strong magnetic field to keep the nasties out and hold our atmosphere

jcranmer 8y ago

The most likely solution to the Fermi Paradox is probably the most depressing for the people who are interested in it: space colonization is basically impossible. The fastest object we've sent outside of the gravitational field of the Sun would take about 75,000 years to reach the nearest star (if we pointed it at it). For perspective, the last glacial advance started in earnest about 75,000 years ago. We don't have any technology that can maintain an automated craft for that long, let alone life support for sentient creatures. Hell, our current technology is insufficient to permit a self-sustaining colony on any other planet or satellite. Ultimately, the Fermi Paradox is based on the assumption that, given enough chances, an unlikely event is basically certain. While this is true, to do a proper analysis, you do need to look at orders of magnitude to see if there really have been enough chances. And we have so little information to base the computations on that the dominating term is your priors: if you think we ought to have seen alien life by now, you'll pick priors that suggest life is quite likely and find that we ought to have seen it; if you think we oughtn't, your prior will reflect that.

Faark 8y ago
It obviously dependents on priors, and figuring out realistic ones is kind of the point. We haven't observed other life in the universe, so any result of adding up all those chances necessarily has to be low. The question is what makes it so low. And most importantly: Is it a check we humans already cleared or something still coming? That should be a huge warning to us.
lumost 8y ago
It's worth looking at Project Orion: "Later studies indicate that the top cruise velocity that can theoretically be achieved are a few percent of the speed of light (0.08–0.1c).[17] An atomic (fission) Orion can achieve perhaps 9%–11% of the speed of light. A nuclear pulse drive starship powered by fusion-antimatter catalyzed nuclear pulse propulsion units would be similarly in the 10% range and pure Matter-antimatter annihilation rockets would be theoretically capable of obtaining a velocity between 50% to 80% of the speed of light. In each case saving fuel for slowing down halves the maximum speed. The concept of using a magnetic sail to decelerate the spacecraft as it approaches its destination has been discussed as an alternative to using propellant; this would allow the ship to travel near the maximum theoretical velocity.[18] At 0.1c, Orion thermonuclear starships would require a flight time of at least 44 years to reach Alpha Centauri, not counting time needed to reach that speed (about 36 days at constant acceleration of 1g or 9.8 m/s2). At 0.1c, an Orion starship would require 100 years to travel 10 light years. The astronomer Carl Sagan suggested that this would be an excellent use for current stockpiles of nuclear weapons" https://en.wikipedia.org/wiki/Project_Orion_(nuclear_propulsion) https://en.wikipedia.org/wiki/Project_Orion_(nuclear_propuls...

oh_sigh 8y ago

> As a sanity check, the fact that no other intelligent life has been observed is evidence that it is unlikely. I'm not sure this is particularly useful. It could be like a medieval European saying land to the west of the Atlantic doesn't exist, because they've never once seen it through their looking glasses. How far could we detect intelligent life, say on a similar level of current humans? If it is based off of radio ways, we would only be able to detect life within a 100 light year radius of earth, which is merely 2% of the way across our galaxy.

sliken 8y ago

Seems like you got it backwards. Being outside the plane of the galaxy INCREASES the threat from supernova, not decreases it. The further from the plane the less gas/dust/stars etc between you and ever other star in the galaxy.

btilly 8y ago
Um, no. Intervening material does very little to cut out light. If it did, we couldn't see distant stars. However the intensity of radiation falls off as the square of the distance from the source of the radiation. Therefore the primary determinant of risk is the number of stars that could be about to go boom within the critical distance of the Sun. If we're in a less densely populated neighborhood, then our odds of seeing a dangerous supernova go down. Full stop.
- sliken 8y ago
  Er, there's a giant cloud of dust called the dark rift that blocks a fair bit of the center of the galaxy. We only recently started looking though it at xray wavelengths to see the center of the milky way (and the black hole there). On a clear night you can see the edges of the milky way and the giant cloud of dust.
  - btilly 8y ago
    That cloud is about 2000 light years away from us. The fact that there are patches of dust doesn't change the fact that we are seldom in the middle of such patches. And even when we are, it is a lot like the difference between being in light mist versus seeing it from a long ways away. We are, in fact, in the middle of a patch of "mist" called the "local fluff". See https://en.wikipedia.org/wiki/Local_Interstellar_Cloud https://en.wikipedia.org/wiki/Local_Interstellar_Cloud for more. This does not noticably cut out light between us and stars that are under 100 lightyears away.

Keysh 8y ago

You don't want a supernova going off too close. We have been lucky to avoid that. Our odds were greatly improved by the fact that we spend most of our time out of the galactic plane, away from other stars that could be about to go boom. This is an unusual orbit. Not really. The amplitude of the Sun's vertical motion is about 100 parsecs (~ 300 light years), but since the main ("thin") stellar disk has a vertical exponential scale height of about 300 parsecs, the local density of stars at the top/bottom of the Sun's orbit is only about 30% less than when the Sun is crossing through the midplane. (And this isn't at all an unusual orbit.) What makes a real difference is being relatively far out in the disk from the galactic center: if we were ten times closer to the center, the local density would be almost 100 times higher, and you might indeed have to start worrying about nearby supernovae.