My solution to the Fermi Paradox: Who the hell knows, who the hell can know, when all we have is a sample size of 1 to extrapolate from. The solutions to the FP seem to be representative of the personal beliefs of whomever is discussing it.
Of course no one can now right now, it's not one of these things that can be solved by theoretical work alone. At some point - assuming we don't go extinct before reaching it - we will know.
But it's still open to useful speculation, as there might be something we still need to consider in order to avoid said extinction.
The Fermi Paradox is one of the more thought-provoking signs that something might be amiss (at least in our part of the galaxy), and especially because our culture is predisposed to not take anything happening on the interstellar stage very seriously this provides an impetus for reflection that would otherwise not happen.
One of the most benign (but ultimately depressing) possibilities is that biogenesis is somehow extremely unlikely. There is no reason to assume this is true, given that we know even the more complex building blocks of life are actually very prevalent throughout the universe - but it may still be statistically unlikely that cells form from them. On the footsteps of that possibility follows the hypothesis that technological intelligence is rare. Again, that's not exactly in line with what we can observe on Earth, but it might still be the case.
Most of the other options should be positively troubling, though.
"The Fermi Paradox is one of the more thought-provoking signs that something might be amiss (at least in our part of the galaxy), and especially because our culture is predisposed to not take anything happening on the interstellar stage very seriously this provides an impetus for reflection that would otherwise not happen."
A hypothetical observer in North America, circa 1500, would have no idea that Asia and Europe existed. Perhaps we're not too far from some interstellar space empire, but since they use some exotic means of FTL communication, we can't detect them?
I'm not sure how your argument applies to what you cited of my post, but you are not wrong. You don't even need to consider exotic FTL communication, it could just be low-power directional radio traffic.
In fact, if a full clone of Earth with exactly the same culture and technology as ours was located just a dozen light years from here, chances are we would not be able to detect that civilization.
The media is always talking about our expanding radio sphere, but in reality this signal gets very weak and jumbled, very fast, with increasing distance. The means all the misinformed derps who believe aliens are coming to take our resources (a group which includes Stephen Hawking for some reason) can sleep pretty well at night knowing that we have not really advertised our existence yet.
2. civilizations have a high or inevitable chance to self destruct after <1M years of language
3. civilizations transcend our observable universe after <1m years [1]
4. due to the single observer problem, humans fail to grok some very important feature of larger scale space that prevents detection/increases isolation
I hope there's something along the lines of sub-space transmissions. Once we discover it, we'll start listening and discover a plethora of civilisations out there.
Would also be nice if they periodically transmitted decoding instructions :)
But who knows, maybe it's far more rare with life that are similar to what we can recognise?
Pretty much the scientific experiment I've been waiting for: we set up some exotic state of matter, and then spot modulated and structured signals coming out of it.
4 seems likeliest. Interstellar colonization is simply impossible because of the vastness of the distance that must be covered. It requires more energy than can be summoned to get a useful amount of hardware across multiple lightyears.
well to be fair, purely theoretically, you "just" need to accelerate once (and be able to hit the brakes many many many years later!) and find a way to sustain (food, water, air) yourself on a spaceship. Then a colonization flight might very well take serveral hundred to thousands years in the beginning.
A bit like the general idea of the recently aired tv show Ascension.
At a certain point, if you can make a self-replicating machine, with harvested solar energy for travel, you would expect that machine's descendants to slowly get everywhere intended.
when the question is: "where are they?" and the answer is: "there is nobody here." then all long living civilisations must have left. so we should answer the question "why did they leave?"
This article does a good job of covering a lot of different ideas on this paradox. I have a problem with the idea of "big numbers" in it though, like where it implies 500 billion billion is nearly infinite, or that one-in-a-billion is a freak occurrence. There is a saying that if enough monkeys pound on a keyboard, one will type Hamlet. This would take a lot of monkeys. If we take the odds of hitting one character to be 1 in 40 (which doesn't account for properly hitting the shift key to make a capital), factoring in the 130,000 letters in Hamlet (according to Wikipedia), we get the odds of a monkey typing it at 6x10^208267. This number comes from 40 keys and 130,000 letters. How about when we start taking molecular numbers of items (6x10^23) and start raising that to a large power? I don't think it is a given that the number of planets out there infer there should be other life.
We can't calculate the probability of life arising though because even if we did know how it arose here—which we don't exactly—we don't know all the possible different ways it can arise, which may or may not also be a number raised to a large power.
That is a good point. I agree with you. And people do have suggestions as to how life can be more probable than naively expected. But this answers the question why there is life at all as opposed to why we don't see more of it.
My bias is that life is highly improbable and that we will not find any other life in our universe. But I also think it is no miracle that we exist, as I will describe. Given that I am trying to say this in one paragraph, it may not sound well justified, but it is how I view the problem. I'll start with Schrodinger's cat. A cat is in a box with some radioactive source that can decay and kill the cat. You can ask if the cat is alive or dead - and the answer is both. I will ignore the next part (Schrodinger's whole point) about what happens when the human observes it. There are different interpretations about why the human thinks the cat is definitely in one of the two states as opposed to both. This has to do with the human's observation and is not important for now. The point is that the cat is in both states. The universe can be in multiple states, some with life on earth and some without. Every possible state that can exist, does. So no matter how improbable we are, we will exist in some version of the universe. And there would be lots of other life too, just maybe not in our version of the universe. So the probability of life existing doesn't impact whether or not we should exist, but it does impact whether or not we see other life. I don't think we will. But as correctly pointed out, we don't know the answer to this right now.
> My bias is that life is highly improbable and that we will not find any other life in our universe.
It's probable enough for you to be writing this. The only options are 0, one and many. We can rule out '0'. That leaves us to decide whether the chances of us being the only one are larger than the chances that we are one of many. Obviously the second one has more chance of being true the one where there is only one. But we like to consider ourselves to be special so most people will believe the 'one'. Just like the sun used to revolve around the earth, now we're essentially seeing the universe as revolving around us. The alternative, that we're not special is not compatible with a lot of our collective culture.
The point is that there are multiple universes, according to the quantum mechanics interpretation I subscribe to. So all of your options are true: 0, 1 and many. My position, which is admittedly no better than a guess, is that most universes by a far majority have 0. By virtue of me writing this, among other things, we live in a universe with at least 1. Again, my position would be that it is unlikely we have more than 1 in our universe.
What you are saying it true under the assumption there is a single universe.
I think you're trying to articulate is the Anthropic principle [1].
It basically states that the probability that "some" life exists is 1.
I'm not sure what the name of this next one is, but I believe it's a widely defended scientific principle that we're "typical" in some sense. This principle gets hard to justify cosmologically (it reduces to Occam's Razor locally), but it makes sense to me. It rejects very clearly some quirks like the Bolztmann Brain [2] argument.
> Obviously the second one has more chance of being true the one where there is only one.
That is not at all obvious to me. You are essentially taking the odds of the odds of something. A statistician can correct me, but I don't think it works the same way as calculating the odds of something.
Like, it's not as if we have a roulette wheel where "1/10^24" is an option, "2/10^24" is an option, "3/10^24" is an option, etc. In that case, "many" outweighs "1," certainly.
But if the odds of abiogenesis are so unlikely that we happen to be the only life in the universe, it doesn't seem like those odds must necessarily be wrong simply because it's logically possible for them to be more or less likely than they are.
But even then, it's kind of a wash. For as much as it could be logically possible for the odds to be more likely than they are (which would allow abiogenesis to occur more frequently), it would also be logically possible for the odds to be less likely than they are.
The WAP accounts for high improbability by positing a multiverse, but (at least as I understand it) it doesn't predict high improbability, even if there is a multiverse.
Also, in a multiverse scenario, the improbable thing might not be the formation of life, but the fine-tuning of the laws of physics which allows the formation of life. In which case life might be relatively common.
Also, in a multiverse scenario, the improbable thing might not be the formation of life, but the fine-tuning of the laws of physics which allows the formation of life. In which case life might be relatively common.
If we assume that this tuning is not an all or nothing event then the larger the possible universe size the more likely it is that we lie within an region where the features are tuned just enough to let one intelligent life form arise.
You can think of the tuned conditions that allow life to be common to be a bullseye that is surrounded by tunings that are close enough to allow life to occur infrequently. If you were to pick a region at random out of the regions that contain intelligent life then it is likely that you would pick one of the surrounding regions not the bullseye. This is also an explanation for Fermi's paradox.
You must factor in that such a region would contain a low percentage of the total number of civilizations intelligent enough to consider the question. A well-tuned universe would be teeming with life - it is therefore more likely that we find ourselves in such a universe (which was the point of the GP). You can think of it, not as a bullseye, but as a gaussian spot.
It strikes me that the issue at play here is how one chooses to "sample" the anthropic principle, for want of a better term. When you say "pick a region at random", you assume a uniform probability distribution over the set of all universes supporting life (which incidentally is not possible if the number is infinite). But you don't say how to resolve the probabilities with universes containing multiple intelligent life forms - you do select randomly among those too? If so, shouldn't you rather be picking "randomly" from the set of all intelligent life forms in all universes in the first place?
Yes it all concerns the shape of the distribution. I have not assumed any any sort of distribution by the way as I have no means of estimating it.
It may be possible in the future to estimate how well tuned a universe could be made for the appearance of intelligent life and also how large the surrounding non-tuned space could be. In the mean time we can only speculate :)
This is one explanation, but for me fails two tests. The first (pointed out below) is that it is heliocentric - it's about us.
The second is that it avoids freedom of will and consciousness in the sense of self perception. It assumes that I am a zombie, and I deny that. I concede that others may be zombies, although I think that they aren't. My actions either navigate me from state to state or create new states. Physics does not account for this; physics is incomplete.
I'll leave occams razor on the shaving table, as it's a heuristic and I don't like it for logic - but infinite infinities fails occams too.
To decide which state to move to. That I (and others) are agents that change the future of the universe by choice within the frameworks of possibility.
We can't calculate the probability of life arising though because even if we did know how it arose here—which we don't exactly—we don't know all the possible different ways it can arise, which may or may not also be a number raised to a large power.
We can't, but we can assume that any process that arises from a series of unlikely chained events (where the likelihood of each event are not correlated) will most likely occur near to the latest time possible. For example, if you run a trillion parallel 10-step chained experiments over a year starting at Jan 1 where each step is very unlikely to occur so that only 100 reach step 10, then the last steps are all likely to occur in December. The less likely each step is (or the more steps involved) then the more the experiments that reach the final step will cluster towards Dec 31. If you have a group of such events then you can actually calculate the likelihood of the chain series.
Intelligent life in a large universe is a similar to this imaginary experiment. While we only have one observed data point, we do know how close the appearance of intelligent life on earth is to the last possible time that it could occur. Outside of our geologically recent anthropogenic boost to the CO2 in the atmosphere, the long term trend of CO2 concentrations in the atmosphere is down (this is due to the sun becoming warmer over time requiring CO2 to be removal from the atmosphere to keep earth in the habitable temperature range). We are in geological terms close to the point where any further removal of CO2 will mean photosynthesis will no longer work (plants are already CO2 limited) - maybe a few 10 millions years. In geological time this is very close to our Dec 31.
What does this all mean? Basically it appears humans have evolved close to the latest time point possible. While we can't calculate the exact probability of intelligent life arising in the universe from our one example, we can say that the evolution of humans is consistent with the hypothesis that the evolution of any intelligent life in the universe is very unlikely.
I did explain it in my post, but maybe it was too short. Earth has been kept in the habitable temperature zone over the last 3.5 billion years through falling CO2 levels. Around 3.5 billion years ago the sun provided ~25% less energy than now and the CO2 levels were much higher. This is the green house effect. As the sun got brighter over time the level of CO2 in the atmosphere has fallen. For more on this see the slow carbon cycle [1].
The problem is that the level of CO2 in the atmosphere is getting very low (~0.2%). At this level plants are starved for CO2 - if it gets down to 0.01% then plants can't grow at all and the ecosystem needed to support the evolution of intelligent life would collapse.
Photosynthesis is required for the evolution of intelligent life. The point I was making is that intelligent life has evolved on Earth pretty close to the latest time possible.
C4 photosynthesis is an adaptation to higher temperatures and lower atmospheric CO2. And C4 is a very recent innovation (25 to 32 million years ago, says Wikipedia).
But yeah, I don't know if even the C4 plants could handle 0.01% ambient CO2.
Yes C4 photosynthesis is an adaption to falling CO2 levels in the atmosphere. It does come at a cost which is why in areas that are not water limited C4 plants have not out competed C3 plants.
I've always thought, given the right circumstances, life will always be formed. Instead we should be calculating the odds of life NOT forming e.g. the half-life of staying-dead.
Our planet has carbon, oxygen, water, the right temperature, a moon that sloshes it all around, rotation. Every grain of sand on every beach is going through a different cycle of heating/cooling + wetting/drying + different salts and ions depending on the local environment. For a billion years it was this enormous biochemistry experiment. Life pretty much HAD to happen, somewhere in all that.
This is essentially the problem that I have with the Drake equation. It encourages--whether that's the intent or not--taking a reasonably known and very, very large number (number of stars) and multiplying it by probabilities/percentages, some of which (we think) we know with at least order of magnitude accuracy. But others we have absolutely no idea. And saying some of those events (such as the evolution of intelligence as we understand the term) has a 1 in a billion probability of occurring SOUNDS like a worst case for-the-purposes-of-argument plug-in. But it's really not.
Another example I hate is the probability of reality being a simulation thought equation. If these equations had some confidence interval based on how little we know it would be clear how meaningless they are.
A very short distance. IIRC something like 20 or so light years, but I'm having trouble finding the citation. That's for radio waves (and the number is getting smaller as the technology is getting better -- EM radiation blasted into the universe is considered waste by hardware engineers).
For direct detection of life, that's still an open question. I remember a poster done by a grad student who looked at whether life would be detectable from the Moon, looking at the Earth. This was tested with data from one of the outer solar system probes which did a lunar flyby on its way out (Cassini?). The result, IIRC, was inconclusive -- you could see signs of life, but not anything that was absolutely definitive proof.
Indirect evidence might be provided by spectra of the atmosphere observed via solar transit. A biome is likely to have different spectra than would be predicted by inorganic atmospheric physics. Still, that's making some assumptions about what extraterrestrial life would be like, and only only visible along the elliptic plane.
The chemical composition of Earth's atmosphere (21% O2) is so far away from a long term chemical equilibrium, that any current astrobiologist would interpret it as a sign of planetary scale life. (And correctly so: the oxygen was produced by life.)
So life on Earth is pretty visible from the other planets in our solar system.
And spectroscopy to observe the composition of atmospheres of planets orbiting the nearest stars will probably happen in not-too-distant future.
Meh, it's a long way from saying that "we don't know how the O2 could have been produced except by life" to "the O2 was produced by life." Just look at the current debate about methane on Mars.
Am I supposed to disagree with that? High atmospheric oxygen content is suggestive of biology. So is seasonal blooms of methane on a planet like Mars. Is that suggestive that there is life on Mars? Yes! Can we definitively infer that there is presently life on Mars? Not yet.
Would be great if you could find the citation, because this seems like the best explanation so far. There are only about 54 stars which at some point had a distance of less than 17 light years (that we know of): http://en.wikipedia.org/wiki/List_of_nearest_stars_and_brown... . Assuming that some stellar source of energy is required for life we can already remove 9 stars from that list because they only consist of brown dwarfs. Doing the math with the conservative estimates in the blog post, this puts the chance of detecting signs of life at a pretty low percentage. Assuming that 22% of these stars have at least one planet with earth like conditions and a 1% chance that some form of life develops on these planets, we arrive at the low chance of 46x0.22x0.01, ie. ~10% of finding any life in our vicinity.
We can infer life based on atmospheric compositions NOW, but only if that planet fits an extremely narrow margin... meaning, Earth. Earth three and a half billion years ago had life on it, but you'd be hard-pressed to tell it from orbit.
If you want to move to unambiguous (intelligent) life then.......
The largest radio telescope we have (the 305 meter diameter Arecibo) would need to have it's sensitivity increased by around two orders of magnitude JUST to pick up our TV/FM/AM signals from outside the solar system. So, the crap we pump out the most couldn't even be detected by Voyager 2, if we had strapped a giant dish to it.
If we move into the narrowband signals then, depending on the source-strength, Arecibo could potentially pick up signals at up to a few thousand light years... if it happened to be pointed in exactly the right direction at exactly the right time.
So, our most sensitive instrument is only capable of measuring a fraction of a percent of the spectrum in a fraction of a percent of the possible-directions-it-could-be-pointed if the point source happened to be sending a strong enough signal (aimed at us) at exactly the right time (which would be anywhere between 2 and a few thousand years ago).
I haven't done the math, but I suspect that regardless of the frequency and amount of energy we dump into sending out a signal (within the realms of not being scifi, anyhow), it would be impossible for anyone to detect us a thousand or two lightyears out (using EM radiation) without knowing when/where to look. They also wouldn't be able to "see" that for quite a long time yet. I couldn't find a list of "when did we start sending out signals at X frequency" (and I suspect it doesn't exist), but if we take 50 years ago as a guess and we assume we pumped out noise at a frequency that could make the distance at a power level sufficient to be noticeable and that there wasn't anything to get in the way of the signal then we're only looking at something like 2000 star-systems.
The "we are the first" argument seemed less convincing than it could have been. A better argument from that perspective is the observation that Type III civilizations expand at an alarming rate. Whatever the motivation for expansion[1], basic simulations and back of the envelope calculations show that even with technology we could imagine building in the not so distant future, humans could expand into the cosmos at >0.9c. We must assume the same of ET.
Now information only reaches us at the speed of light; we are only capable of looking for ET in our own past light cone. That means that any Type I or Type II civilization like us should expect to see an empty sky for most of their existence, until all of a sudden the most distant stars go dim (Dyson sphere, or whatever energy capturing device). And the darkness spreads in a wavefront travelling at almost the speed of light, until it hits and ... the unpredictable happens.
We see an empty sky because if the sky wasn't empty, the planet we call Earth and our Sun would already be consumed by some extraterrestrial Type III civilization and Fermi would never have existed.
[1] An inflationary universe provides incentive for a hypothetical Type III civilization to spread throughout the cosmos as quickly as possible, as idle time means regions of the universe becoming permanently inaccessible. Or maybe just resource competition and a desire for some elements of a population to remain on the frontier.
Because if the events move at 0.9c the light still moves at 'c', so the furthest stars (of which there are more than nearby ones) will be the first to show you that something is up. The light from the older events will reach us before the events or the light from later events will reach us.
Unless of course the whole thing originates in one of the stars nearby but the chances of that are smaller than that it will happen in a system further away.
Wouldn't the most likely place for it to start be around halfway between us and the most distant observable stars in whatever direction it starts, then? And then we'd see the sphere of dimming stars increasing in size, while still seeing things behind, in front, or to the sides of the sphere?
The part that we can see is so much smaller than what is out there that you'd have to resort to very leaky analogies to try to get the point across.
The upper limit to how much larger the universe is compared to the observable (and not the currently observed) universe is somewhere around the 10^20 to 10^25 times larger. Those are hard numbers to grasp but large enough that the chances of an event 'x' taking place outside of the observed universe are larger than inside it.
Ah, right, the ones that will disappear are furthest-observed, not furthest-observable... you have to already have been observed to disappear from observance!
So, it would be an already-large and rapdily growing sphere intersecting with the sphere of observed stars.
edit: Wait, actually, I thought you were saying we CAN (theoretically) observe 10^20+ times as far as we HAVE observed. But re-reading your comment, this sounds wrong:
> The upper limit to how much larger the universe is compared to the observable
Did you mean to say "the upper limit for how much larger the observable universe is compared to the observed universe"?
Or are you actually talking about what might be outside of the observable universe? I figured starting points outside the observable universe were not a consideration for this problem, since they are causally unlinked from us and could not expand into the observable universe faster than it becomes causally unlinked from us as well.
Because of 3d geometry, there are a lot more distant stars/galaxies than there are nearby ones. That much I agree.
But the most distant galaxies we see, we see them 13 billion years in the past. So this type III civilization turning off starts at the edge of our observable universe would have developed in just 700 million years after the Big Bang. (If we take 13.7 billion years as the age of the universe.) That I find quite improbable.
There is a smaller amount of nearer objects than far away objects, but the far away objects are (or we see them as) younger, and the nearby objects are older. There must be some balance between the respective volumes in near and far, and the available time it probably takes for the type III civilization to have developed?
We have plenty of ideas for how that would work. Are you familiar with a Dyson sphere? A Type III civilization is just a Dyson sphere around every star in the galaxy.
Yes, never mind that Dyson spheres are hypothetical structures that are likely to be as relevant to energy harvesting as Icarus' wings are to flying humans around.
There is actually a pretty good explanation for it in my opinion, that it takes about this long since the big bang for life forms of our complexity to exist. (meaning our planet was seeded at some point with some primitive life forms that than continued on their evolutionary tracks towards this point in time).
So you have many planets starting to get to the point where space exploration on a wide scale is feasible. Maybe a few are a hundred thousand and some change years ahead or behind us but the likelihood is low that many are significantly well established, or established long enough and close enough for us to detect.
There is actually a pretty good explanation for it in my opinion, that it takes about this long since the big bang for life forms of our complexity to exist. (meaning our planet was seeded at some point with some primitive life forms that than continued on their evolutionary tracks towards this point in time).
Interstellar seeding is not required to believe that complex life becomes possible at approximately the same time throughout the universe. Other possible reasons:
- Concentration of heavy elements has increased with successive star generations.
- Galactic cosmic ray bursts (which can sterilize all complex life within thousands of light years) become less common as a galaxy ages.
I had this idea recently myself and to the best of my knowledge you're the only other person who's mentioned it. The closest I've found is the "galactic preemption" hypothesis published in the 80's, but that's more an explanation for why only one civilization would exist in a single galaxy, rather than for why a newborn civilization such as our own would look at the sky and see no signs of civilization in the whole universe.
I've read a novel that featured this, I am wracking my brains to remember the title/author. It featured a generation ship that switched to a .com mode as it approached the star to be colonized and a race of bat people who were the putative colonization targets.
I am not making this up, but I may have dreamt it!
Nope. Ken MacLeod's 'learning the world'. The alien space bats were a nice touch. Charles Stross' book accelerando has an interesting take on the Fermi paradox too.
That seems different to me. There's lots of scifi and speculation about contact between civilizations of vastly different technological development. But the idea here is that the expansion of a civilization happens so quickly that it consumes all the resources around it before other civilizations get a chance to exist at all. No malevolence ("superpredators") required.
The probability that a new civilization is born after the light from the expanding one has arrived, but before their colony ships have, is very small, so therefore we should expect that whenever our civilization was born and whatever the benevolence of the aliens, when we look into the sky we should see no sign of them.
Super-predator Civilizations solve the significant problem of blaming the silence on a psychological quirk rather than statistics.
When you are making assumptions about the millions of civilizations, it is absurd to think they ALL retreated to playing video games for eternity, or ALL nuked themselves to oblivion.
With a single super-predator civ, that has a huge leg up on everyone else, they can have unusual motivations, and techniques. The problem with a super-predator is you likely won't be able to learn anything to prove or disprove them until you meet them, with all that implies.
No, but I haven't read any science fiction since my teenage years. (Sadly, because I would like to... just don't have the time.)
I actually don't remember reading this anywhere, it just seemed an obvious idea. The idea that humanity would expand into a Type III civilization and near light speed is very old, probably dating to the work done by the British Interplanetary Society on interstellar travel. I don't have citations handy, but I remember reading a critique of generation ships which basically boiled down to "if you travel less than 0.9c, you can expect someone else to leave after you do but arrive sooner." Applying the same logic to other civilizations just seemed like common sense...
At scale it would not only have to be technologically possible but also economically feasible. If you can't afford it you can't do it even if you have the tech.
It is certainly profitable for a type 1 civilization to move to a type 2 civilization as long as energy consumption and population continue to naturally grow as has happened so far here. Same thing for type 2 to 3. Also, I think that decisions about space travel are not purely for economic reasons and probably in almost any advanced species there is a large amount of the population willing to pay something to explore.
I think it's a good assumption. If there are systems out there marginally different from our own, and the cost to send a "new civilization builder" doesn't completely exhaust Earth, how can it not be profitable?
Time delay. You're long dead before any profits return. How much current consumption are you willing to give for speculative distant future profit for others?
That depends on the average lifespan of the species in question, as well as the stability of their civilization.
If you only live 100 years and your society will be unrecognizable after 500 years, it's obviously foolish to embark on a project that will turn a profit 1000 years later.
If you can live 1M years and your civilization has been more or less stable for 10M years, you can probably afford to wait 10K years for a shipment of unobtanium. It would be just like a 17th century European merchant who sends a ship to India and waits several months for it to return.
Even if the average lifespan is short, some industries can be profitable across generations. Lumber is often harvested 30-50 years after planting, and I've heard of people investing in coastal redwood that would take 100+ years before they can be cut down.
Wow, that redwood 100+ years investment sounds interesting. Do you have a link? I have to show that to my economist friend... or save it to win an argument some time from now :)
Given a large payoff in 100 (or more) years time for a small investment now, it doesn't seem that hard to create a financial instrument that pays out a potion of the projected profits adjusted for risk, for each year that you hold it.
Profitability is not an explanation for many activities that take place here on Earth (today is one). There are many reasons that would allow non-profitable expansion to occur. If the cost is low compared to the wealth of the society and the society is not a hive mind, then some individuals within that society would undertake it purely for non-profit reasons. For example, if I could send a problem to Sirius for $1000 that would beam back pictures of system in 18 years time I would do it right now even though I am not going to make any money from the exercise.
If we want to stay on the profit driven model only then it could still be profitable to send out colonising entities once the solar systems resources are fully utilised. Remote colonies could stream back computational information (say Pixar's Toy Story 42) thus increasing our wealth.
Making money is one measure of profitability, another is reducing risk, something businesses aren't good at measuring. If there's two star systems instead of one colonized and the risk of one star system being wiped out by catastrophe is 1 in 1 million, then the risk of 2 being wiped out is only 1 in a quadrillion. A similar logic is behind why some people want to colonize the Moon or Mars. And when something has been successfully executed once, it's a lot easier for it to be done again, whether it's colonizing the rest of the planets in the solar system or the rest of the stars in the Orion spur.
I agree. That intelligent (much more so than us) beings would find the idea of littering replicating machines literally across the universe appealing doesn't make sense to me.
Drain on the home planet? I think your model of how this would occur needs updating. Let me give you a hint: Earth represents a minuscule, tiny, not even worth counting fraction of the resources readily available in the solar system.
But the Milky Way is only 50,000 light years in radius (~ average distance between stars?). That's not much at all on a evolutionary scale. So your argument explains why we're not currently observing an alien civilization (i.e. they would expand so close to light speed we would likely either be conquered or observing nothing -- so observing nothing is a consistent scenario). But it does not explain why no Type III civilizations (continuing with the assumption that civilizations all quickly go on to become Type III) has risen at all in the past hundreds of millions of years.
You can close that gap that via an anthropic principle by saying that if some civilization were colonizing our solar system, life on Earth would be extinguished/not possible.
>But it does not explain why no Type III civilizations (continuing with the assumption that civilizations all quickly go on to become Type III) has risen at all in the past hundreds of millions of years.
I find the assumption about Type III at best. It's like expecting Moore's law to go on forever.
I agree that a Type III Civilization is just an assumption of what direction a civilization would advance. The article does mention an alternative (they no longer care about meat space, or something similar).
If we do resolve the Fermi Paradox I suspect we'll be able to express the answer simply enough to not need to bring in Type III Civilizations, the anthropic principle, etc. Note that I find nothing wrong with them as useful tools for discussion, just that the answer likely isn't one we can construct by means of logic, it must be discovered -- as in, observational astronomy.
Which is what I intend to do: go out with a telescope and look at the stars. :)
The OP's post rests on the Anthropic Principle. Essentially, we don't see evidence of a Type III civilization because anyone who dies is very quickly thereafter consumed by that civilization as it expands across the observable universe. It's a terrifying idea.
Note those are two distinct explanations. OP's point about the speed of light explains only why we're not observing any civilization from the last 50,000 years, while the anthropic principle and the "quick, devouring species" assumption explain why no alien life exists at all in our past light cone.
I actually posted about this very topic a few days ago here.
Once you have von Neumann machines spreading they will take over each new star system pretty much as soon as they reach it. Assuming the von Neumann machines are small and are being powered by an energy source (i.e lasers) from their origin star system they will spread through the galaxy at close to the speed of light. This spread method creates an interesting effect in that we would not see the stars go out until the von Neumann machines had almost reached us if the origin star was within our galaxy - basically the von Neumann machines would be traveling only a little behind the light front from the origin star system (this would make a good science fiction story).
If the origin star system was far enough a way, then the slightly slower speed that the von Neumann machines would travel at should allow us to see them progressing though a distance galaxy. Such a galaxy would look to us like part of the galaxy had a chunk taken out of it. It would be worth looking through the galaxy classification data set [1, 2] to see if there are any galaxies like that out there that look like this. My feeling is we won't find any as I think intellegent life is near unique within the visible universe, but it is at least a testable hypothesis.
Stephen Baxter's Manifold novels deal with this problem quite extensively. I would recommend them from anyone interested in the implications of the Fermi paradox expressed in science/speculative fiction.
Another testable variation of this is the gravitational effect of voids. Voids[1]are regions of the universe devoid of visible matter (stars), as far as we can tell. These are predicted by the inflationary model as regions of low energy distribution in the early universe. But if we find a void that appears to have gravitational effects on its neighbors, what an astronomer might call "a concentration of dark matter", that could be a Type III civilization. I'd look around the edges and see if we can find any half-eaten galaxies...
Another testable variation of this is the gravitational effect of voids.
Yes, the only problem might be that we don't yet have a good explanation for dark matter so it would be hard to know if a void with mass is due to a Type III civilisation or just a local concentration of dark matter. A spiral galaxy with a perfectly spherical void would be pretty hard to explain as anything other than the result of intelligence.
There are stuff out there normaly tough of as "concentrations of dark matter"[1], altought nobody is really sure. I never heard about a "half eaten" galaxy, but I'd guess you hypostesis keep them that way for a very short time, so this is not surprizing.
The biggest problem I have with this family of explanations is that, unless the aliens discovered how to revert the Second Rule of Thermodynamics, they must irradiate some low temperature wave. And we measure nearly every candidate nowadays. Unless they are extremely far away, the only thing that could escape us is some very narrow band that happens to be out of range of all current telescopes - and those are not the features of a good heat sink.
Interesting. Just a note: it probably wouldn't seem as if a chunk of the galaxies was removed; in fact, I believe the luminosity (after some settling time) of a start with a Dyson sphere or the like would emit about the same light a regular star does -- the difference would be the temperature. The apparent temperature of the star should increase(?) (i.e. it emits(?) higher entropy radiation): by simple energy conservation, we wouldn't expect the energy to build up indefinitely inside the sphere. Presumable the energy would be used for computation -- so the end result is that the Star's energy is used to compensate Landauer's Principle[1], essentially cooling the computer. So instead maybe we should look for galaxies that are hotter than expected for their brightness/age?
Highter entropy radiation has lower temperature. But yes, the energy must go somewhere, thus the total energy irradiated is the same. It just shifts into infrared or radio.
Oh yea I wasn't sure which one was it! Intuitively it seemed to need to be at lower temperature, but the association of entropy of gases with their temperature made me write otherwise, but of course E=h*f dictates that the entropy from a larger number of lower energy photons must be higher. Thanks for the correction!
Such galaxies already exist [1]. They appear to be natural, but who knows for sure.
The temperature of the Dyson Sphere will determine the wave length the star apears to shine at. If the sphere is designed to capture the maximum energy possible then the temperature will be close to the cosmic background radiation temperature (2.73K) and so would be very hard to detect.
Speed of light is fast enough, considering how long the universe has been around. Our galaxy is 100 thousand light-years - a blink in geological time. We can see everything that ever happened in our galaxy right now, excepting the last few moments.
I'd instead be looking for evidence civilizations are expanding by ways we don't yet suspect. Soliton waves through gas clouds? Wormholes? Multidimensional folds? What would those things look like? Maybe they look like dark matter or something.
I am surprised a more common argument was not mentioned: other life exists but the laws of physics limit our interaction. Maybe there is undiscovered physics like wormholes or time travel, or maybe there isn't and the speed of light really is a fundamental limit that cannot be surpassed. In that case, no matter how advanced another civilization becomes, they still can't violate natural law and are thus unable to reach us.
The laws of any potential biology and the messiness of the world could together effectively limit a civilization's energy usage to much lower than indicated by the easily deducible laws of physic (the explicit laws of physics might limit the output of an internal combustion engine to a certain but the effective maximum winds up less than that. Human biological systems experience serious damage by being weightless for significant periods, etc).
I only recently realized that this "paradox" looking at the possibility not of "earth advanced" civilization but supposed advanced civilizations that would put out much more energy than humans put out.
The whole thing seems to rest on false-extrapolations of mid 20th century hard-science fiction authors. Our Western Civilization has experienced an exponential growth of some things, has expanded it's "frontiers" quickly in a variety of ways, conquering the rest of the globe and then labeling space "the final frontier".
But all this has been low-hanging fruit. We're reaching the end of population expansion, space is fundamentally hostile to human life in a way that would take tremendous progress to overcome and we're facing longer term consequences of the rapid expansions we have achieved (global warming is just one of the consequences). If humans survive this, we'll have to have somehow achieve a steady-state for energy consumption and related things. But once we do achieve that steady state, why would we want or need to suddenly start using the energy of an entire star (after the thousand years of scientific progress we'd need to under how to do that)?
The problem here is the assumption we need scientific progress to do this. We don't.
We have the technology today to launch satellites into solar-orbits which would be capable of beaming power back to Earth. It would be clean, efficient and non-disasterous to the biosphere.
With any amount of space-borne industry, the costs would also plummet and get cheaper with every additional satellite. Once you can harness the energy of an entire star, there's almost no reason not to achieve it.
Humans can build large sealed cities on the Earth-facing side of the Moon using solar-propelled remote-controlled "drone" technology. The response time is only about 1 or 2 seconds so the human operators on Earth wouldn't need the equipment to have much of its own AI (unlike later on when humans repeat the process on Mars). Once enough such specialized machinery is on the Moon, entire "cities" the size of an apartment building could be built, funded in the same way Ordos in China was. The hard part would be experimenting with different biochemical processes afterwards in each city so one of them could provide enough oxygen, water, and food for humans who'd arrive much later on.
I often wonder this as well. The speed of light isn't really a physical limit to expansion - generation ships are theoretically possible. It may just be that the Great Filter takes the form of relatively benign[1] economic and/or sociological obstacles.
At least, if you take a diff between typical beliefs at the time the Fermi Paradox was formulated vs. typical beliefs now, I would say the experience of the shutting down of Apollo and overall reduction of human space exploration is probably the most relevant new observation we have made since then.
[1] In the sense of: You don't need nuclear armageddon to stop humans from spreading to other solar systems; the price tag of interstellar travel is sufficient.
If you consider the declining birth rates of modern nations as the standard of living goes up, then it stands to reason that once a civilization reaches the point where it might be able to engage in large scale space exploration, the population that can do so has become relatively stable.
So you simply never (or rarely) get exponential cosmic expansion. There might be a few billions of that race roaming the stars, but their numbers do not increase.
But declining birth rates don't lead to stable populations, they lead to shrinking populations. So if we don't manage to restore birth rates, this would be an example of 'Great Filter ahead of us'.
It may not even require a high price tag. I present as a hypothesis that exploration is a form of competition, i.e. the most competitive societies explore the most.
As an example, the European Conquest of the Americas was driven by competition between European nation-states, it might not have occurred so swiftly or at all without some kind of competitive pressure.
Said another way, imagine yourself waking up in the court of King James of England or Queen Isabella of Spain. You establish rapport and they believe you come from the future. You communicate faithfully what you know about history. What conclusion do you think they are more likely to reach?
1) They have done the right thing by colonizing the Americas.
2) They have created what will eventually become new competitors, of whom at least one (the USA) will have subjugated them under the disguise of an alliance called NATO.
In the crucible of 15th-century European politics, neither England nor Spain may have had much choice in their desire to acquire more resources and open new markets.
And maybe the 21st Century will have cheap space travel and good reasons to take the trip. But we shouldn't ignore the possibility that Earth's governments may just decide to not let anyone leave and blast anyone who tries. Let's call it the "Nitrogen Curtain" in honor of Winston Churchill.
> I am surprised a more common argument was not mentioned: ... maybe the speed of light really is a fundamental limit ... they still can't violate natural law and are thus unable to reach us.
One of the assumptions of the article and of most serious scientific discussion of the topic is that the speed of light really is the fundamental limit that it appears to be. It's not mentioned because it's axiomatic. The only thing in favour of the speed of light not being an absolute limit is that people don't want it to be. And wishful thinking is a very weak argument.
This does not make interstellar travel impossible, just very difficult. It is not feasible for us at this time, but it does not "violate natural law".
Even without FTL, if civs can travel across stars, they should have already colonized the galaxy.
Imagine a civ arising 50 million years ago (a majority of the other stars in the Milky Way are billions of years older than the Sun). It takes 50,000 years to become interplanetary, and then 1000 years later it's ready to launch a mission to the nearest neighbor, 8 light years away. It travels at 0.02c and then arrives 400 years later. After 2000 years it has colonized that system enough that it has local resources to repeat the process.
The galaxy is 100,000 light years across, so that allows a spread from one edge to the other in 30 million years, which is long ago for us. Forming closer to the center and allowing for the mixing of star systems with galactic rotation would shrink that number.
Wormholes or warp drive would actually explain the Fermi paradox for me: since the other civs are used to their stars that are older and hotter, and they only pay attention to the prime real estate. But limited to the speed of light, a civ will spread by filling each nook and cranny it can live in.
Its unlikely any race would last unchanged for 50 million years. They could likely lose interest in colonizing long before that much time had passed. So the question becomes: how much colonization can one race accomplish before burning out their will to continue?
Just 2 million years ago, human ancestors were small-brained apemen. A million years is a long time.
Even if most lose their interest in colonization, there would still be some interested in colonization, and those would do so. Unless there were some enforcement mechanism to stop potential settlers from leaving.
How about this possibility: the Great Filter is now! We entered it, perhaps, when we developed sufficient collective nuclear weapons capability to wipe out most or all human life; we won't be out of it until the major threats our civilization poses to the biosphere have been resolved.
Even if we wipe ourselves out tomorrow, that still means that a civilization was able to broadcast its existence for about 80 years. If the Great Filter is now or ahead of us, that at least implies that pre-filter civilizations can be advanced enough to signal their existence.
At some point our signals will be too weak for anyone to pick up or distinguish from cosmic background noise, which probably limits the radius of the sphere of stars that can hear us, but anyone inside that sphere gets at least 80 years to be listening to potentially hear us.
So, even if civilizations only last for say 100 years on average, and you can only hear other civilizations within N light years, if N is big enough eventually someone should hear someone, and if N is really big enough, somewhere in that 100 years everyone should hear at least one other someone.
I've written about this elsewhere, but I'll chime in here too.
The largest radio telescope we have (the 305 meter diameter Arecibo) would need to have it's sensitivity increased by around two orders of magnitude JUST to pick up our TV/FM/AM signals from outside the solar system. If we move into the narrowband signals then, depending on the source-strength, it could pick up signals at up to a few thousand light years... if it happened to be pointed in exactly the right direction at exactly the right time.
You'd have to build an absolutely monstrous dish to be able to detect any of our signals at even the center of our own galaxy (much less at the other end)... I haven't run the numbers on it, but I doubt it's physically possible to build a receiver large enough. Add to that that they're highly directional devices and I think you'll find the "N" in your scenario is actually a startlingly small number.
A resource crunch, i.e. we simply use up the required resources before we figure out how to explore our planetary neighbourhood. e.g When we figure out that a helium engine is possible, very efficient and very safe, we no longer have sufficient quantities left.
A lot of people consider nuclear annihilation a big threat but I'm not too worried about tbh. I mean if you think about it, every major player has got a trigger to end all life at any given point, doesn't it seem reasonable that at some point you invest a lot of money into systems that can safeguard and prevent this type of catastrophe. I know a lot of people may consider the governments dangerous and selfish but they aren't stupid, major players have definitely got systems in place to neutralise these threats.
Nuclear weapons are hard enough to build that they require a coordination of resources and knowledge, so there is an amount of level headedness among those that build them. A pessimistic view follows that, if some technology in our future is as destructive yet it be simple to build then that is a candidate for a filter. In essence, if it exists then we are just sitting ducks.
I would like to share your optimism. But then I read about things like the US nuclear launch codes being set to 00000000 for quite a few years, or an incident when survival versus Armageddon depended on the judgment of one man [1], and I have to conclude that human governments should not be in possession of nuclear weapons.
I think they sort of cover this but here is my simple explanation. Think about how many slugs there are on Earth. How many of them have never seen a human? If we are slugs in comparison to advanced beings that have a billion years of evolution on us then it is no surprise we have not seen them.
I don't see why a "Great Filter" is needed to justify there being no other highly evolved lifeforms - all it needs is for there to need to be a reasonably large number of key evolutionary steps and environmental conditions with a sufficiently low probability. Multiply those and you end up with some pretty tiny chances of observing life as we know it.
I had the same thought and agree with what you wrote. But when you think about this set of evolutionary steps you still end up with the same scenarios: you are rare, you are first, you are fucked. So in that regard, you can subsume all of these steps into a filter.
I think the biggest fallacy in this rationalization is when it is assumed that advanced civilizations would want to expand like yeast; consuming everything, building dyson spheres... Why would they want that much energy, and why extract it from the sun? Trying to picture myself as one of these superlifeforms, I think would like to have the sun visible... For sunbathing and sh... plants to grow etc... Maybe they have built little fusion reactors wherever they need energy?
I agree. Why the assumption the Type 3 capable civilisations will necessarily wish to metastasise across the entire universe? One would hope that civilisations' ideas of what constitutes fulfilling and worthwhile activity will evolve and improve along with their technology.
The SUN is visible everywhere within a Dyson sphere; it's the STARS that you can't see any more. The idea isn't that a civilization wants to do this; the idea is that it needs that much energy to continue with whatever industrial or infrastructure processes it requires to support a very large population. Dyson reasoned, we need steadily increasing amounts of energy input to support what we are doing; if the trend continues, what's the limit? (Typical physicist question, no?) The limit is to harvest all the energy emitted from your star. The only way to do that is to build a spherical collector, so that every photon can be captured. Then where do you live? On the sphere's inner surface. Of what material could you build a stable sphere one AU in radius? Where would that bulk of material come from and how be processed and positioned? How would you provide gravity on its inner surface? We have no fucking idea -- but we are not a Type-whatever civilization.
I always thought that was a primitive notion. We can build the sphere, but not control the star? Imagine a caveman - "Limit to civilization when all energy from campfire captured - most people warm, most meat cooked" Clearly one can do better than a campfire.
Instead, imagine harvesting energy from the star asymmetrically - from flares or from the inside out. Or get your energy from a neighboring star. Or make your own star. Or whatever a Type-whatever civilization decides to do.
In that great expanse and time, there may also have been ample time for civilizations to rise, then fall. We might have just missed them on such grand scales. Nobody says we'll be hanging around for a billion years trying to communicate with others... if we even last that long.
How about the theory that we are the way super-civilization spreads?
If physical space travel is extremely expensive (as it should be, considering the distance), then may be it is better to send a signal that would trigger creation of life (in our case on Earth).
Then when Earth civilization is advanced enough, it would be able to receive complete boot sequence and then fully advanced alien civilization would be replicated on Earth.
... or, how about the hypothesis that we were intended to be a seed package (a.k.a. "biological rootkit") but due to a bug in the programming, we failed to develop properly. Just a mistake playing itself out...
Another possibility... there are plenty of civilisations within broadcasting distance from us that are all listening but not broadcasting for fear of predatory civilisations.
The estimates of stars seem reasonable; the estimates of Earth seem a bit ill-defined. (The study he links to discuses Earth-size planets, but there are many other factors that go into Earth's suitability for life.) The real issue though is in the "speculative" part:
> Let’s imagine that after billions of years in existence, 1% of Earth-like planets develop life... And imagine that on 1% of those planets, the life advances to an intelligent level like it did here on Earth. "
1% sounds like a small number, but it's a bit ridiculous to just throw it out there and assume it's reasonable. It's a little bit like when a startup does a top-down estimate of revenue - "If we only capture 1% of the e-commerce market, we'll be worth billions!"
I think if you do a "bottom-up" style analysis of the likelihood of atoms forming a replicating growing organism, or that organism evolving to think intelligently, you would get a far smaller number, say in the range of 0.00001% to 10^-20 for each one.
Out of all those advanced civilizations in the universe, what fraction use electromagnetic radiation for communication? We are like ants waiting for other civilizations to communicate with us using pheromones.
There are humans that try to talk with ants (and bees, and dolphins) using those creatures' own methods. Unless there were strongly-enforced no-contact laws, then some alien researcher would want to inspect those Terrans and see if we can talk. Even if they are way smarter, they'll use that smarts to talk with us in a way we can understand.
Possibility 5) There’s only one instance of higher-intelligent life—a “superpredator” civilization (like humans are here on Earth)—who is far more advanced than everyone else and keeps it that way by exterminating any intelligent civilization once they get past a certain level.
If we're the most advanced civilization right now, that will be us in a few million years. We're kind of dicks.
Exciting for a movie plot I guess. But, what could they win from exterminating another inferior intelligence?
By your context, they are already inferior, and thus, no threat to the apex civilization.
It's been suggested by Robin Hanson (who coined the name "Great Filter") that an ethical super-civ would see a galactic war with another super-civ as the worst thing possible, and so wipe out other civs to stop that worst thing possible,
I don't buy it, FWIW, because "ethical" doesn't overlap with "wipe out all other life" in my book. (Although you could certainly, say, have some system that stops any civ from leaving their planet by dropping rocks on them each time they launch something into orbit.)
But you can search Hanson's blog for more talk about this if you want to see more discussion.
I personally find the "we are first" solution to be the scariest scenario. We are not suited for the responsibility of being the only intelligent life in the universe.
What responsibility? I can see absolutely zero responsibility attached to that scenario.
Humans also may be the most responsible intelligent life that ever exists in the universe. What's the basis to judge such things to begin with?
There's an exceptionally low probability that human survival has any bearing on whether other intelligent life comes to exist (in the we're first scenario). Being first bears no responsibility because future life in the galaxy or universe is not inherently dependent on what we do.
Would discovering the fossils of some complex species on Mars (or any where else in the solar system) be any worse for getting past the great filter then the discovery of fossils of dinosours on earth. We allready know that mass extinction events on Earth are possible, and should expect them to occur on other planents with life too
We are not even listening hard. SETI covers an incredibly tiny range of possible spectrum and possibilities of intelligent life.
Are there any other attempts to find alien communication via data mining?
If I were a galactic artist, I would use pulsars to modulate their signals and create a statue that broadcasts the existence of life.
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[ 3.7 ms ] story [ 187 ms ] threadBut it's still open to useful speculation, as there might be something we still need to consider in order to avoid said extinction.
The Fermi Paradox is one of the more thought-provoking signs that something might be amiss (at least in our part of the galaxy), and especially because our culture is predisposed to not take anything happening on the interstellar stage very seriously this provides an impetus for reflection that would otherwise not happen.
One of the most benign (but ultimately depressing) possibilities is that biogenesis is somehow extremely unlikely. There is no reason to assume this is true, given that we know even the more complex building blocks of life are actually very prevalent throughout the universe - but it may still be statistically unlikely that cells form from them. On the footsteps of that possibility follows the hypothesis that technological intelligence is rare. Again, that's not exactly in line with what we can observe on Earth, but it might still be the case.
Most of the other options should be positively troubling, though.
A hypothetical observer in North America, circa 1500, would have no idea that Asia and Europe existed. Perhaps we're not too far from some interstellar space empire, but since they use some exotic means of FTL communication, we can't detect them?
In fact, if a full clone of Earth with exactly the same culture and technology as ours was located just a dozen light years from here, chances are we would not be able to detect that civilization.
The media is always talking about our expanding radio sphere, but in reality this signal gets very weak and jumbled, very fast, with increasing distance. The means all the misinformed derps who believe aliens are coming to take our resources (a group which includes Stephen Hawking for some reason) can sleep pretty well at night knowing that we have not really advertised our existence yet.
1. simulation argument
2. civilizations have a high or inevitable chance to self destruct after <1M years of language
3. civilizations transcend our observable universe after <1m years [1]
4. due to the single observer problem, humans fail to grok some very important feature of larger scale space that prevents detection/increases isolation
[1] http://accelerating.org/articles/transcensionhypothesis.html
Would also be nice if they periodically transmitted decoding instructions :)
But who knows, maybe it's far more rare with life that are similar to what we can recognise?
A bit like the general idea of the recently aired tv show Ascension.
My bias is that life is highly improbable and that we will not find any other life in our universe. But I also think it is no miracle that we exist, as I will describe. Given that I am trying to say this in one paragraph, it may not sound well justified, but it is how I view the problem. I'll start with Schrodinger's cat. A cat is in a box with some radioactive source that can decay and kill the cat. You can ask if the cat is alive or dead - and the answer is both. I will ignore the next part (Schrodinger's whole point) about what happens when the human observes it. There are different interpretations about why the human thinks the cat is definitely in one of the two states as opposed to both. This has to do with the human's observation and is not important for now. The point is that the cat is in both states. The universe can be in multiple states, some with life on earth and some without. Every possible state that can exist, does. So no matter how improbable we are, we will exist in some version of the universe. And there would be lots of other life too, just maybe not in our version of the universe. So the probability of life existing doesn't impact whether or not we should exist, but it does impact whether or not we see other life. I don't think we will. But as correctly pointed out, we don't know the answer to this right now.
- Piet Hein
It's probable enough for you to be writing this. The only options are 0, one and many. We can rule out '0'. That leaves us to decide whether the chances of us being the only one are larger than the chances that we are one of many. Obviously the second one has more chance of being true the one where there is only one. But we like to consider ourselves to be special so most people will believe the 'one'. Just like the sun used to revolve around the earth, now we're essentially seeing the universe as revolving around us. The alternative, that we're not special is not compatible with a lot of our collective culture.
What you are saying it true under the assumption there is a single universe.
It basically states that the probability that "some" life exists is 1.
I'm not sure what the name of this next one is, but I believe it's a widely defended scientific principle that we're "typical" in some sense. This principle gets hard to justify cosmologically (it reduces to Occam's Razor locally), but it makes sense to me. It rejects very clearly some quirks like the Bolztmann Brain [2] argument.
[1] http://en.wikipedia.org/wiki/Anthropic_principle
[2] http://en.wikipedia.org/wiki/Boltzmann_brain
That is not at all obvious to me. You are essentially taking the odds of the odds of something. A statistician can correct me, but I don't think it works the same way as calculating the odds of something.
Like, it's not as if we have a roulette wheel where "1/10^24" is an option, "2/10^24" is an option, "3/10^24" is an option, etc. In that case, "many" outweighs "1," certainly.
But if the odds of abiogenesis are so unlikely that we happen to be the only life in the universe, it doesn't seem like those odds must necessarily be wrong simply because it's logically possible for them to be more or less likely than they are.
But even then, it's kind of a wash. For as much as it could be logically possible for the odds to be more likely than they are (which would allow abiogenesis to occur more frequently), it would also be logically possible for the odds to be less likely than they are.
Also, in a multiverse scenario, the improbable thing might not be the formation of life, but the fine-tuning of the laws of physics which allows the formation of life. In which case life might be relatively common.
If we assume that this tuning is not an all or nothing event then the larger the possible universe size the more likely it is that we lie within an region where the features are tuned just enough to let one intelligent life form arise.
You can think of the tuned conditions that allow life to be common to be a bullseye that is surrounded by tunings that are close enough to allow life to occur infrequently. If you were to pick a region at random out of the regions that contain intelligent life then it is likely that you would pick one of the surrounding regions not the bullseye. This is also an explanation for Fermi's paradox.
It strikes me that the issue at play here is how one chooses to "sample" the anthropic principle, for want of a better term. When you say "pick a region at random", you assume a uniform probability distribution over the set of all universes supporting life (which incidentally is not possible if the number is infinite). But you don't say how to resolve the probabilities with universes containing multiple intelligent life forms - you do select randomly among those too? If so, shouldn't you rather be picking "randomly" from the set of all intelligent life forms in all universes in the first place?
It may be possible in the future to estimate how well tuned a universe could be made for the appearance of intelligent life and also how large the surrounding non-tuned space could be. In the mean time we can only speculate :)
The second is that it avoids freedom of will and consciousness in the sense of self perception. It assumes that I am a zombie, and I deny that. I concede that others may be zombies, although I think that they aren't. My actions either navigate me from state to state or create new states. Physics does not account for this; physics is incomplete.
I'll leave occams razor on the shaving table, as it's a heuristic and I don't like it for logic - but infinite infinities fails occams too.
We can't, but we can assume that any process that arises from a series of unlikely chained events (where the likelihood of each event are not correlated) will most likely occur near to the latest time possible. For example, if you run a trillion parallel 10-step chained experiments over a year starting at Jan 1 where each step is very unlikely to occur so that only 100 reach step 10, then the last steps are all likely to occur in December. The less likely each step is (or the more steps involved) then the more the experiments that reach the final step will cluster towards Dec 31. If you have a group of such events then you can actually calculate the likelihood of the chain series.
Intelligent life in a large universe is a similar to this imaginary experiment. While we only have one observed data point, we do know how close the appearance of intelligent life on earth is to the last possible time that it could occur. Outside of our geologically recent anthropogenic boost to the CO2 in the atmosphere, the long term trend of CO2 concentrations in the atmosphere is down (this is due to the sun becoming warmer over time requiring CO2 to be removal from the atmosphere to keep earth in the habitable temperature range). We are in geological terms close to the point where any further removal of CO2 will mean photosynthesis will no longer work (plants are already CO2 limited) - maybe a few 10 millions years. In geological time this is very close to our Dec 31.
What does this all mean? Basically it appears humans have evolved close to the latest time point possible. While we can't calculate the exact probability of intelligent life arising in the universe from our one example, we can say that the evolution of humans is consistent with the hypothesis that the evolution of any intelligent life in the universe is very unlikely.
Slight adjustment in how body works can easily adapt organism to new CO2 levels.
The problem is that the level of CO2 in the atmosphere is getting very low (~0.2%). At this level plants are starved for CO2 - if it gets down to 0.01% then plants can't grow at all and the ecosystem needed to support the evolution of intelligent life would collapse.
1. http://earthobservatory.nasa.gov/Features/CarbonCycle/page2....
It does not make certain CO2 levels a requirement for intelligent life.
Change in temperature does not necessarily kill intelligent life either.
But yeah, I don't know if even the C4 plants could handle 0.01% ambient CO2.
We are currently at about 400 ppm (parts-per-million), which would be 0.04%. http://co2now.org/
About 20 000 years ago, the lowest was maybe ca. 200 ppm.
Our planet has carbon, oxygen, water, the right temperature, a moon that sloshes it all around, rotation. Every grain of sand on every beach is going through a different cycle of heating/cooling + wetting/drying + different salts and ions depending on the local environment. For a billion years it was this enormous biochemistry experiment. Life pretty much HAD to happen, somewhere in all that.
http://www.scientificamerican.com/article/a-new-physics-theo...
This theory could be quite important or wrong. Or both. But it gives very interesting definition of what life is.
For direct detection of life, that's still an open question. I remember a poster done by a grad student who looked at whether life would be detectable from the Moon, looking at the Earth. This was tested with data from one of the outer solar system probes which did a lunar flyby on its way out (Cassini?). The result, IIRC, was inconclusive -- you could see signs of life, but not anything that was absolutely definitive proof.
Indirect evidence might be provided by spectra of the atmosphere observed via solar transit. A biome is likely to have different spectra than would be predicted by inorganic atmospheric physics. Still, that's making some assumptions about what extraterrestrial life would be like, and only only visible along the elliptic plane.
So life on Earth is pretty visible from the other planets in our solar system.
And spectroscopy to observe the composition of atmospheres of planets orbiting the nearest stars will probably happen in not-too-distant future.
http://www-pw.physics.uiowa.edu/~dag/publications/1993_ASear...
We can infer life based on atmospheric compositions NOW, but only if that planet fits an extremely narrow margin... meaning, Earth. Earth three and a half billion years ago had life on it, but you'd be hard-pressed to tell it from orbit.
If you want to move to unambiguous (intelligent) life then.......
The largest radio telescope we have (the 305 meter diameter Arecibo) would need to have it's sensitivity increased by around two orders of magnitude JUST to pick up our TV/FM/AM signals from outside the solar system. So, the crap we pump out the most couldn't even be detected by Voyager 2, if we had strapped a giant dish to it.
If we move into the narrowband signals then, depending on the source-strength, Arecibo could potentially pick up signals at up to a few thousand light years... if it happened to be pointed in exactly the right direction at exactly the right time.
So, our most sensitive instrument is only capable of measuring a fraction of a percent of the spectrum in a fraction of a percent of the possible-directions-it-could-be-pointed if the point source happened to be sending a strong enough signal (aimed at us) at exactly the right time (which would be anywhere between 2 and a few thousand years ago).
I haven't done the math, but I suspect that regardless of the frequency and amount of energy we dump into sending out a signal (within the realms of not being scifi, anyhow), it would be impossible for anyone to detect us a thousand or two lightyears out (using EM radiation) without knowing when/where to look. They also wouldn't be able to "see" that for quite a long time yet. I couldn't find a list of "when did we start sending out signals at X frequency" (and I suspect it doesn't exist), but if we take 50 years ago as a guess and we assume we pumped out noise at a frequency that could make the distance at a power level sufficient to be noticeable and that there wasn't anything to get in the way of the signal then we're only looking at something like 2000 star-systems.
Now information only reaches us at the speed of light; we are only capable of looking for ET in our own past light cone. That means that any Type I or Type II civilization like us should expect to see an empty sky for most of their existence, until all of a sudden the most distant stars go dim (Dyson sphere, or whatever energy capturing device). And the darkness spreads in a wavefront travelling at almost the speed of light, until it hits and ... the unpredictable happens.
We see an empty sky because if the sky wasn't empty, the planet we call Earth and our Sun would already be consumed by some extraterrestrial Type III civilization and Fermi would never have existed.
[1] An inflationary universe provides incentive for a hypothetical Type III civilization to spread throughout the cosmos as quickly as possible, as idle time means regions of the universe becoming permanently inaccessible. Or maybe just resource competition and a desire for some elements of a population to remain on the frontier.
Why the most distant?
Unless of course the whole thing originates in one of the stars nearby but the chances of that are smaller than that it will happen in a system further away.
The upper limit to how much larger the universe is compared to the observable (and not the currently observed) universe is somewhere around the 10^20 to 10^25 times larger. Those are hard numbers to grasp but large enough that the chances of an event 'x' taking place outside of the observed universe are larger than inside it.
So, it would be an already-large and rapdily growing sphere intersecting with the sphere of observed stars.
edit: Wait, actually, I thought you were saying we CAN (theoretically) observe 10^20+ times as far as we HAVE observed. But re-reading your comment, this sounds wrong:
> The upper limit to how much larger the universe is compared to the observable
Did you mean to say "the upper limit for how much larger the observable universe is compared to the observed universe"?
Or are you actually talking about what might be outside of the observable universe? I figured starting points outside the observable universe were not a consideration for this problem, since they are causally unlinked from us and could not expand into the observable universe faster than it becomes causally unlinked from us as well.
But the most distant galaxies we see, we see them 13 billion years in the past. So this type III civilization turning off starts at the edge of our observable universe would have developed in just 700 million years after the Big Bang. (If we take 13.7 billion years as the age of the universe.) That I find quite improbable.
There is a smaller amount of nearer objects than far away objects, but the far away objects are (or we see them as) younger, and the nearby objects are older. There must be some balance between the respective volumes in near and far, and the available time it probably takes for the type III civilization to have developed?
"Why don't we see a civilizations spanning a galaxy? How would that work? No idea but why don't we see it?"
We could ask why we don't see Lovecraftian gods or giant life forms that each stars. We don't know how that works either.
So you have many planets starting to get to the point where space exploration on a wide scale is feasible. Maybe a few are a hundred thousand and some change years ahead or behind us but the likelihood is low that many are significantly well established, or established long enough and close enough for us to detect.
Interstellar seeding is not required to believe that complex life becomes possible at approximately the same time throughout the universe. Other possible reasons:
- Concentration of heavy elements has increased with successive star generations.
- Galactic cosmic ray bursts (which can sterilize all complex life within thousands of light years) become less common as a galaxy ages.
Have you seen this idea published anywhere?
I am not making this up, but I may have dreamt it!
Full disclosure, my brother is the author of the first book.
The probability that a new civilization is born after the light from the expanding one has arrived, but before their colony ships have, is very small, so therefore we should expect that whenever our civilization was born and whatever the benevolence of the aliens, when we look into the sky we should see no sign of them.
When you are making assumptions about the millions of civilizations, it is absurd to think they ALL retreated to playing video games for eternity, or ALL nuked themselves to oblivion.
With a single super-predator civ, that has a huge leg up on everyone else, they can have unusual motivations, and techniques. The problem with a super-predator is you likely won't be able to learn anything to prove or disprove them until you meet them, with all that implies.
I actually don't remember reading this anywhere, it just seemed an obvious idea. The idea that humanity would expand into a Type III civilization and near light speed is very old, probably dating to the work done by the British Interplanetary Society on interstellar travel. I don't have citations handy, but I remember reading a critique of generation ships which basically boiled down to "if you travel less than 0.9c, you can expect someone else to leave after you do but arrive sooner." Applying the same logic to other civilizations just seemed like common sense...
If it isn't profitable, then it turns into a drain on the home planet. That isn't sustainable.
If you only live 100 years and your society will be unrecognizable after 500 years, it's obviously foolish to embark on a project that will turn a profit 1000 years later.
If you can live 1M years and your civilization has been more or less stable for 10M years, you can probably afford to wait 10K years for a shipment of unobtanium. It would be just like a 17th century European merchant who sends a ship to India and waits several months for it to return.
Even if the average lifespan is short, some industries can be profitable across generations. Lumber is often harvested 30-50 years after planting, and I've heard of people investing in coastal redwood that would take 100+ years before they can be cut down.
If we want to stay on the profit driven model only then it could still be profitable to send out colonising entities once the solar systems resources are fully utilised. Remote colonies could stream back computational information (say Pixar's Toy Story 42) thus increasing our wealth.
The only way that is going to happen is if a company with profit motive is willing to invest in r and d to bring down the costs.
NASA is incredible, but it isn't moving towards bringing down space exploration costs.
You can close that gap that via an anthropic principle by saying that if some civilization were colonizing our solar system, life on Earth would be extinguished/not possible.
I find the assumption about Type III at best. It's like expecting Moore's law to go on forever.
I agree that a Type III Civilization is just an assumption of what direction a civilization would advance. The article does mention an alternative (they no longer care about meat space, or something similar).
If we do resolve the Fermi Paradox I suspect we'll be able to express the answer simply enough to not need to bring in Type III Civilizations, the anthropic principle, etc. Note that I find nothing wrong with them as useful tools for discussion, just that the answer likely isn't one we can construct by means of logic, it must be discovered -- as in, observational astronomy.
Which is what I intend to do: go out with a telescope and look at the stars. :)
Yeah, "tenuous"! Thanks.
Once you have von Neumann machines spreading they will take over each new star system pretty much as soon as they reach it. Assuming the von Neumann machines are small and are being powered by an energy source (i.e lasers) from their origin star system they will spread through the galaxy at close to the speed of light. This spread method creates an interesting effect in that we would not see the stars go out until the von Neumann machines had almost reached us if the origin star was within our galaxy - basically the von Neumann machines would be traveling only a little behind the light front from the origin star system (this would make a good science fiction story).
If the origin star system was far enough a way, then the slightly slower speed that the von Neumann machines would travel at should allow us to see them progressing though a distance galaxy. Such a galaxy would look to us like part of the galaxy had a chunk taken out of it. It would be worth looking through the galaxy classification data set [1, 2] to see if there are any galaxies like that out there that look like this. My feeling is we won't find any as I think intellegent life is near unique within the visible universe, but it is at least a testable hypothesis.
1. http://www.galaxyzoo.org
2. http://en.wikipedia.org/wiki/Atlas_of_Peculiar_Galaxies
[1] https://en.wikipedia.org/wiki/Void_%28astronomy%29
Yes, the only problem might be that we don't yet have a good explanation for dark matter so it would be hard to know if a void with mass is due to a Type III civilisation or just a local concentration of dark matter. A spiral galaxy with a perfectly spherical void would be pretty hard to explain as anything other than the result of intelligence.
The biggest problem I have with this family of explanations is that, unless the aliens discovered how to revert the Second Rule of Thermodynamics, they must irradiate some low temperature wave. And we measure nearly every candidate nowadays. Unless they are extremely far away, the only thing that could escape us is some very narrow band that happens to be out of range of all current telescopes - and those are not the features of a good heat sink.
[1] http://en.wikipedia.org/wiki/Dark_galaxy
[1] http://en.wikipedia.org/wiki/Landauer%27s_principle
The temperature of the Dyson Sphere will determine the wave length the star apears to shine at. If the sphere is designed to capture the maximum energy possible then the temperature will be close to the cosmic background radiation temperature (2.73K) and so would be very hard to detect.
1. http://en.m.wikipedia.org/wiki/Luminous_infrared_galaxy
I'd instead be looking for evidence civilizations are expanding by ways we don't yet suspect. Soliton waves through gas clouds? Wormholes? Multidimensional folds? What would those things look like? Maybe they look like dark matter or something.
I only recently realized that this "paradox" looking at the possibility not of "earth advanced" civilization but supposed advanced civilizations that would put out much more energy than humans put out.
The whole thing seems to rest on false-extrapolations of mid 20th century hard-science fiction authors. Our Western Civilization has experienced an exponential growth of some things, has expanded it's "frontiers" quickly in a variety of ways, conquering the rest of the globe and then labeling space "the final frontier".
But all this has been low-hanging fruit. We're reaching the end of population expansion, space is fundamentally hostile to human life in a way that would take tremendous progress to overcome and we're facing longer term consequences of the rapid expansions we have achieved (global warming is just one of the consequences). If humans survive this, we'll have to have somehow achieve a steady-state for energy consumption and related things. But once we do achieve that steady state, why would we want or need to suddenly start using the energy of an entire star (after the thousand years of scientific progress we'd need to under how to do that)?
We have the technology today to launch satellites into solar-orbits which would be capable of beaming power back to Earth. It would be clean, efficient and non-disasterous to the biosphere.
With any amount of space-borne industry, the costs would also plummet and get cheaper with every additional satellite. Once you can harness the energy of an entire star, there's almost no reason not to achieve it.
At least, if you take a diff between typical beliefs at the time the Fermi Paradox was formulated vs. typical beliefs now, I would say the experience of the shutting down of Apollo and overall reduction of human space exploration is probably the most relevant new observation we have made since then.
[1] In the sense of: You don't need nuclear armageddon to stop humans from spreading to other solar systems; the price tag of interstellar travel is sufficient.
So you simply never (or rarely) get exponential cosmic expansion. There might be a few billions of that race roaming the stars, but their numbers do not increase.
--
Date 1: Every two people produce four offspring.
Date 2: Every two people produce three offspring.
Between Date 1 and Date 2 the birthrate declined by 25%, but the total rate is still positive.
As an example, the European Conquest of the Americas was driven by competition between European nation-states, it might not have occurred so swiftly or at all without some kind of competitive pressure.
Said another way, imagine yourself waking up in the court of King James of England or Queen Isabella of Spain. You establish rapport and they believe you come from the future. You communicate faithfully what you know about history. What conclusion do you think they are more likely to reach?
1) They have done the right thing by colonizing the Americas.
2) They have created what will eventually become new competitors, of whom at least one (the USA) will have subjugated them under the disguise of an alliance called NATO.
In the crucible of 15th-century European politics, neither England nor Spain may have had much choice in their desire to acquire more resources and open new markets.
And maybe the 21st Century will have cheap space travel and good reasons to take the trip. But we shouldn't ignore the possibility that Earth's governments may just decide to not let anyone leave and blast anyone who tries. Let's call it the "Nitrogen Curtain" in honor of Winston Churchill.
One of the assumptions of the article and of most serious scientific discussion of the topic is that the speed of light really is the fundamental limit that it appears to be. It's not mentioned because it's axiomatic. The only thing in favour of the speed of light not being an absolute limit is that people don't want it to be. And wishful thinking is a very weak argument.
This does not make interstellar travel impossible, just very difficult. It is not feasible for us at this time, but it does not "violate natural law".
Imagine a civ arising 50 million years ago (a majority of the other stars in the Milky Way are billions of years older than the Sun). It takes 50,000 years to become interplanetary, and then 1000 years later it's ready to launch a mission to the nearest neighbor, 8 light years away. It travels at 0.02c and then arrives 400 years later. After 2000 years it has colonized that system enough that it has local resources to repeat the process.
The galaxy is 100,000 light years across, so that allows a spread from one edge to the other in 30 million years, which is long ago for us. Forming closer to the center and allowing for the mixing of star systems with galactic rotation would shrink that number.
Wormholes or warp drive would actually explain the Fermi paradox for me: since the other civs are used to their stars that are older and hotter, and they only pay attention to the prime real estate. But limited to the speed of light, a civ will spread by filling each nook and cranny it can live in.
Just 2 million years ago, human ancestors were small-brained apemen. A million years is a long time.
At some point our signals will be too weak for anyone to pick up or distinguish from cosmic background noise, which probably limits the radius of the sphere of stars that can hear us, but anyone inside that sphere gets at least 80 years to be listening to potentially hear us.
So, even if civilizations only last for say 100 years on average, and you can only hear other civilizations within N light years, if N is big enough eventually someone should hear someone, and if N is really big enough, somewhere in that 100 years everyone should hear at least one other someone.
The largest radio telescope we have (the 305 meter diameter Arecibo) would need to have it's sensitivity increased by around two orders of magnitude JUST to pick up our TV/FM/AM signals from outside the solar system. If we move into the narrowband signals then, depending on the source-strength, it could pick up signals at up to a few thousand light years... if it happened to be pointed in exactly the right direction at exactly the right time.
You'd have to build an absolutely monstrous dish to be able to detect any of our signals at even the center of our own galaxy (much less at the other end)... I haven't run the numbers on it, but I doubt it's physically possible to build a receiver large enough. Add to that that they're highly directional devices and I think you'll find the "N" in your scenario is actually a startlingly small number.
A resource crunch, i.e. we simply use up the required resources before we figure out how to explore our planetary neighbourhood. e.g When we figure out that a helium engine is possible, very efficient and very safe, we no longer have sufficient quantities left.
At least they do in my optimistic viewpoint.
[1] http://en.wikipedia.org/wiki/Stanislav_Petrov
Instead, imagine harvesting energy from the star asymmetrically - from flares or from the inside out. Or get your energy from a neighboring star. Or make your own star. Or whatever a Type-whatever civilization decides to do.
"Let’s imagine that after billions of years in existence, 1% of Earth-like planets develop life" and "
"And imagine that on 1% of those planets, the life advances to an intelligent level like it did here on Earth"
Why 1% and not 10^-10%?
If physical space travel is extremely expensive (as it should be, considering the distance), then may be it is better to send a signal that would trigger creation of life (in our case on Earth).
Then when Earth civilization is advanced enough, it would be able to receive complete boot sequence and then fully advanced alien civilization would be replicated on Earth.
> Let’s imagine that after billions of years in existence, 1% of Earth-like planets develop life... And imagine that on 1% of those planets, the life advances to an intelligent level like it did here on Earth. "
1% sounds like a small number, but it's a bit ridiculous to just throw it out there and assume it's reasonable. It's a little bit like when a startup does a top-down estimate of revenue - "If we only capture 1% of the e-commerce market, we'll be worth billions!"
I think if you do a "bottom-up" style analysis of the likelihood of atoms forming a replicating growing organism, or that organism evolving to think intelligently, you would get a far smaller number, say in the range of 0.00001% to 10^-20 for each one.
If we're the most advanced civilization right now, that will be us in a few million years. We're kind of dicks.
I don't buy it, FWIW, because "ethical" doesn't overlap with "wipe out all other life" in my book. (Although you could certainly, say, have some system that stops any civ from leaving their planet by dropping rocks on them each time they launch something into orbit.)
But you can search Hanson's blog for more talk about this if you want to see more discussion.
[1] humanbrainproject.eu
Humans also may be the most responsible intelligent life that ever exists in the universe. What's the basis to judge such things to begin with?
There's an exceptionally low probability that human survival has any bearing on whether other intelligent life comes to exist (in the we're first scenario). Being first bears no responsibility because future life in the galaxy or universe is not inherently dependent on what we do.
As such, should we nurture, protect, and by all means spread the intelligence sickness? I'd think yes.
If I were a galactic artist, I would use pulsars to modulate their signals and create a statue that broadcasts the existence of life.
http://www.technology.org/2013/11/20/extraterrestrial-civili...