We observe not just an empty galaxy, but one which apparently had hundreds of millions or billions of years before us for intelligence to develop. If there were no Great Filter this would be surprising.
(An old hat response that your comment still seems to warrant.)
The fact that we are still here reduces the surprise significantly. If intelligence did develop, we probably won’t be still here, and we know that we are. It’s not just an empty galaxy, it’s an empty galaxy where we live. It is not surprising in the same intuitive sense as observing the sequence 0101100100010 of coin flips is not surprising, once you take it as data you have (specification of which phenomenon you are dealing with) and not the property to be explained.
My perpective was that it is surprising that the entire universe is only 13.7 billion years old (WMAP) while the Earth is already 4.5 billion years old and it took about that amount of time for intelligence to evolve.
Science has taught us that we’re usually not special, but if our evolution already took a third of the time of the entire universe’s existence, it seems we’re exceptionally early. In comparison, a human lifetime is 60-100 years and I was born approximately 400-600 lifetimes into the cumulative period of human lifetimes which seems much more random than ‘3’.
Given the information that we are in the second or third time span required for evolution, the expected number of alien civilizations doesn’t have to be zero to expect that we’re the first. I don’t know the relevant statistics, but, for example, it the probability of intelligent life developing in a 3 billion year period is 1⁄50, we might just need to wait a couple more billion years for the next group. Solar systems are still being born … aren’t we objectively early in that respect?
Given the information that we are in the second or third time span required for evolution
There’s a twist that actually reinforces your point. The first stars (Population III, all dead now) were metal-free. The next generation, Population II, had low metal content. Our Sun belongs to Population I, with higher metal content. So it looks like our Sun belongs to the first, maybe the second, generation of stars that could possibly support intelligent life.
To further that point, it might be worth noting here that “metal” in astronomy parlance means anything heavier than helium. Complex life might conceivably evolve without, say, iron, but life without carbon is much less likely.
Science has taught us that we’re usually not special
Maybe, but due to anthropic effects, this is one of the times in which we definitely cannot use the we’re-not-special rule of thumb. Noting that we happen to have developed gives us absolutely no evidence about the rarity of observers that can notice that they’ve developed (except that it rules out theories that make it so rare that even 1 observer is unlikely).
if the probability of intelligent life developing in a 3 billion year period is 1⁄50 we might just need to wait a couple more billion years for the next group
Without more information about The Great Filter, most of the probability density does not reside in such perfectly balanced orders of magnitude (like 2% per 3Gyr-galaxy) to make us happen to be first. Though it’s an open possibility that we’re the first but not the only life that will develop, it’s extremely unlikely that two huge numbers that could conceivably be orders of magnitude apart, happen to line up so closely.
The numbers I have in mind are something like: total number of planets and probability of any given planet to allow life to flourish across the galaxy. These numbers are independent. You could start with ‘region of space’ or involve time, but the numbers will still be independent. (i guess I should have said a huge and tiny number balancing when multiplied)
If there is nothing making the development and survival of intelligent tool-using life intrinsically improbable, the odds are at least billions to one against Earth being first in our light cone. Any hypothetical Great Filter that has odds of mere millions-to-one against being true is a substantially superior hypothesis to “we just happened to be first”.
Not necessarily. As Wikipedia says, “According to the Great Filter hypothesis at least one of these steps—if the list were complete—must be improbable.” That is, if “Great Filter” means anything, it’s that one or more of the steps to achieving a technological civilization that can expand throughout the galaxy is very difficult (“improbable”).
What I’m talking about goes like this: suppose that none of the steps are very difficult. Of course, that doesn’t mean they’re instantaneous—each step takes time. You need elements other than hydrogen and helium for life, so you have to watch the supernova clock ticking until Population I stars form (maybe Pop II, but remember that this is hypothetical—let’s assume that only Pop I stars have enough “metals”). Then you need planets—but we’re seeing planets everywhere as the limits of our vision increase. Once the first replicator forms, you have to wait for evolution to grind its way up the complexity ladder (mandatory disclaimer: evolution doesn’t “prefer” higher complexity, but there is a complexity lower bound—there is literally nowhere to go but up). In this scenario, where none of the steps are improbable, but they do take time, what would the first intelligent species in a given lightcone see?
They would arrive on the scene, and they would see a young-looking universe. Their star would be among the first stars capable of supporting life. Their planetary formation would have been almost immediately followed by the first replicator (and returning to reality for a moment, we see fossilized life as far back as 1 billion years after the Earth’s formation). Their evolutionary history, while marked by giant impacts and mass extinctions, would appear relatively free of long reigns of nothing happening complexity-wise. And they would see an empty universe, and wonder where everyone else is.
Obviously, I don’t know the answer to the Fermi Paradox. But if anyone exists, someone’s got to be first. Maybe it’s us, and maybe that’s why the paradox is so baffling.
(Instead of “where are they”, I think the LW way of phrasing the paradox is “why aren’t we paperclips?”.)
That’s a very attractive scenario. But I don’t think ‘Someone had to be the first’ is sufficient to explain why we are the first. On your view, intelligent life takes some time to get going, but then is incredibly abundant for as long as stars and metals abound. On standard cosmological models, star formation will continue for some 100,000 billion years (or at minimum 1,000 billion years). Anthropically, our occurring only 14 billion years into our universe’s lifetime is then profoundly surprising. If a lot of intelligent life precedes us (and/or intelligent life is generically rare and will never be very abundant), then our location remains surprising, but a lot less so.
Your theory predicts what we see given that we evolved very early in our universe’s lifetime, but if we don’t build in our temporal location then it actually strongly predicts the opposite—that we’ll open our eyes and see a galaxy teeming with life, many tens or hundreds of billions of years after the beginning of the universe.
I don’t claim it’s sufficient, I just claim it’s possible. And while it’s true that most civilizations would see a galaxy teeming with life, somebody’s gotta be first.
Anything’s possible. If your claim is interesting, it’s because it’s probable, at least relative to its explanatory rivals.
The problem with ‘somebody’s gotta be first’ is that it’s either a fully general explanation or no explanation at all. Suppose you and a hundred billion of your friends are each assigned a distinct number between 1 and a hundred billion. You’re assigned the number 1. Should you dismiss this surprising outcome because ‘someone had to get 1’? No. Not without a lot of evidence that it’s a coincidence, anyway. The fact that someone had to get 1 only means that it was possible, on the terms on the game, for you to get 1. It doesn’t make that possibility, when it occurs, any less surprising or confusing. The goal of explaining our observations isn’t to show that they’re possible; it’s to show that they’re a lot more likely than they would have been in the absence of the explanans.
‘Someone had to win’ isn’t a full explanation on its own, no. (If it were, it would be a fully general explanation schema; ‘something had to happen’, for example, can explain any event.) Rather, ‘someone had to win’ is an explanation for an unlikely victory when you posit a large sample space. In most cases, selection bias will also play a role in the explanation—it will account for the prima facie salience or interestingness of the event.
If selection bias and the size of the sample space don’t help make you any less confused about why some X happened to you, then revisiting ‘someone had to X’ shouldn’t alleviate your confusion.
Yes, someone has to be first and this is what they would see. Or actually, this is what the first dozens or hundreds or thousands would see as without great filters you’d probably have many hundreds of species reaching an information age at around the same time but there would be a good while before they produce enough evidence to detect each other with any likelihood.
This era of galactic development though before the first civilizations become detectable to each other - on the order of a few thousands of years—is unimaginably short in terms of the time-span of the cosmos, unimaginably short even in terms of the lifetime of our own sun. It seems like tens of millions of civilizations would develop in the life-span of our Sun and its peers and yet we have to be among this very small sample at the beginning. That would be surprising.
A great filter is I suppose, equally surprising even though the mechanisms of it would maybe not be surprising.
My favorite hypothesis is that there is no great filter—someone’s got to be first in our light cone, and we’re it.
We observe not just an empty galaxy, but one which apparently had hundreds of millions or billions of years before us for intelligence to develop. If there were no Great Filter this would be surprising.
(An old hat response that your comment still seems to warrant.)
The fact that we are still here reduces the surprise significantly. If intelligence did develop, we probably won’t be still here, and we know that we are. It’s not just an empty galaxy, it’s an empty galaxy where we live. It is not surprising in the same intuitive sense as observing the sequence 0101100100010 of coin flips is not surprising, once you take it as data you have (specification of which phenomenon you are dealing with) and not the property to be explained.
I agree.
My perpective was that it is surprising that the entire universe is only 13.7 billion years old (WMAP) while the Earth is already 4.5 billion years old and it took about that amount of time for intelligence to evolve.
Science has taught us that we’re usually not special, but if our evolution already took a third of the time of the entire universe’s existence, it seems we’re exceptionally early. In comparison, a human lifetime is 60-100 years and I was born approximately 400-600 lifetimes into the cumulative period of human lifetimes which seems much more random than ‘3’.
Given the information that we are in the second or third time span required for evolution, the expected number of alien civilizations doesn’t have to be zero to expect that we’re the first. I don’t know the relevant statistics, but, for example, it the probability of intelligent life developing in a 3 billion year period is 1⁄50, we might just need to wait a couple more billion years for the next group. Solar systems are still being born … aren’t we objectively early in that respect?
There’s a twist that actually reinforces your point. The first stars (Population III, all dead now) were metal-free. The next generation, Population II, had low metal content. Our Sun belongs to Population I, with higher metal content. So it looks like our Sun belongs to the first, maybe the second, generation of stars that could possibly support intelligent life.
To further that point, it might be worth noting here that “metal” in astronomy parlance means anything heavier than helium. Complex life might conceivably evolve without, say, iron, but life without carbon is much less likely.
Yes—did you see that I linked to the metallicity article? (Astronomers are funny.)
Should have clicked through, in retrospect.
Maybe, but due to anthropic effects, this is one of the times in which we definitely cannot use the we’re-not-special rule of thumb. Noting that we happen to have developed gives us absolutely no evidence about the rarity of observers that can notice that they’ve developed (except that it rules out theories that make it so rare that even 1 observer is unlikely).
Without more information about The Great Filter, most of the probability density does not reside in such perfectly balanced orders of magnitude (like 2% per 3Gyr-galaxy) to make us happen to be first. Though it’s an open possibility that we’re the first but not the only life that will develop, it’s extremely unlikely that two huge numbers that could conceivably be orders of magnitude apart, happen to line up so closely.
I’m not sure I follow your last paragraph. What are the two huge numbers in this context?
The numbers I have in mind are something like: total number of planets and probability of any given planet to allow life to flourish across the galaxy. These numbers are independent. You could start with ‘region of space’ or involve time, but the numbers will still be independent. (i guess I should have said a huge and tiny number balancing when multiplied)
That really doesn’t work.
If there is nothing making the development and survival of intelligent tool-using life intrinsically improbable, the odds are at least billions to one against Earth being first in our light cone. Any hypothetical Great Filter that has odds of mere millions-to-one against being true is a substantially superior hypothesis to “we just happened to be first”.
Wouldn’t this mean that the Great Filter is behind us?
Not necessarily. As Wikipedia says, “According to the Great Filter hypothesis at least one of these steps—if the list were complete—must be improbable.” That is, if “Great Filter” means anything, it’s that one or more of the steps to achieving a technological civilization that can expand throughout the galaxy is very difficult (“improbable”).
What I’m talking about goes like this: suppose that none of the steps are very difficult. Of course, that doesn’t mean they’re instantaneous—each step takes time. You need elements other than hydrogen and helium for life, so you have to watch the supernova clock ticking until Population I stars form (maybe Pop II, but remember that this is hypothetical—let’s assume that only Pop I stars have enough “metals”). Then you need planets—but we’re seeing planets everywhere as the limits of our vision increase. Once the first replicator forms, you have to wait for evolution to grind its way up the complexity ladder (mandatory disclaimer: evolution doesn’t “prefer” higher complexity, but there is a complexity lower bound—there is literally nowhere to go but up). In this scenario, where none of the steps are improbable, but they do take time, what would the first intelligent species in a given lightcone see?
They would arrive on the scene, and they would see a young-looking universe. Their star would be among the first stars capable of supporting life. Their planetary formation would have been almost immediately followed by the first replicator (and returning to reality for a moment, we see fossilized life as far back as 1 billion years after the Earth’s formation). Their evolutionary history, while marked by giant impacts and mass extinctions, would appear relatively free of long reigns of nothing happening complexity-wise. And they would see an empty universe, and wonder where everyone else is.
Obviously, I don’t know the answer to the Fermi Paradox. But if anyone exists, someone’s got to be first. Maybe it’s us, and maybe that’s why the paradox is so baffling.
(Instead of “where are they”, I think the LW way of phrasing the paradox is “why aren’t we paperclips?”.)
That’s a very attractive scenario. But I don’t think ‘Someone had to be the first’ is sufficient to explain why we are the first. On your view, intelligent life takes some time to get going, but then is incredibly abundant for as long as stars and metals abound. On standard cosmological models, star formation will continue for some 100,000 billion years (or at minimum 1,000 billion years). Anthropically, our occurring only 14 billion years into our universe’s lifetime is then profoundly surprising. If a lot of intelligent life precedes us (and/or intelligent life is generically rare and will never be very abundant), then our location remains surprising, but a lot less so.
Your theory predicts what we see given that we evolved very early in our universe’s lifetime, but if we don’t build in our temporal location then it actually strongly predicts the opposite—that we’ll open our eyes and see a galaxy teeming with life, many tens or hundreds of billions of years after the beginning of the universe.
I don’t claim it’s sufficient, I just claim it’s possible. And while it’s true that most civilizations would see a galaxy teeming with life, somebody’s gotta be first.
Anything’s possible. If your claim is interesting, it’s because it’s probable, at least relative to its explanatory rivals.
The problem with ‘somebody’s gotta be first’ is that it’s either a fully general explanation or no explanation at all. Suppose you and a hundred billion of your friends are each assigned a distinct number between 1 and a hundred billion. You’re assigned the number 1. Should you dismiss this surprising outcome because ‘someone had to get 1’? No. Not without a lot of evidence that it’s a coincidence, anyway. The fact that someone had to get 1 only means that it was possible, on the terms on the game, for you to get 1. It doesn’t make that possibility, when it occurs, any less surprising or confusing. The goal of explaining our observations isn’t to show that they’re possible; it’s to show that they’re a lot more likely than they would have been in the absence of the explanans.
I would be surprised because that violates the pigeonhole principle.
(Yeah, I’m a programmer.)
Isn’t “someone had to win” the rationalist explanation for most lottery winners?
‘Someone had to win’ isn’t a full explanation on its own, no. (If it were, it would be a fully general explanation schema; ‘something had to happen’, for example, can explain any event.) Rather, ‘someone had to win’ is an explanation for an unlikely victory when you posit a large sample space. In most cases, selection bias will also play a role in the explanation—it will account for the prima facie salience or interestingness of the event.
If selection bias and the size of the sample space don’t help make you any less confused about why some X happened to you, then revisiting ‘someone had to X’ shouldn’t alleviate your confusion.
I see. Good answer.
Yes, someone has to be first and this is what they would see. Or actually, this is what the first dozens or hundreds or thousands would see as without great filters you’d probably have many hundreds of species reaching an information age at around the same time but there would be a good while before they produce enough evidence to detect each other with any likelihood.
This era of galactic development though before the first civilizations become detectable to each other - on the order of a few thousands of years—is unimaginably short in terms of the time-span of the cosmos, unimaginably short even in terms of the lifetime of our own sun. It seems like tens of millions of civilizations would develop in the life-span of our Sun and its peers and yet we have to be among this very small sample at the beginning. That would be surprising.
A great filter is I suppose, equally surprising even though the mechanisms of it would maybe not be surprising.