Why aren't we hip-deep in Martians?
Aug. 1st, 2005 02:17 pm![[personal profile]](https://www.dreamwidth.org/img/silk/identity/user.png){kind=small}
fishsupremeThe Universe is amazingly hospitable to life. That may seem an odd statement at first, considering as most of it is made up of hard vacuum. However, consider that the laws of physics are such that planets with atmosphere can form at all (what if gravity didn't exist?), or taking it even further back, that matter can form at all, and that the amount of matter and antimatter after the Big Bang wasn't precisely balanced so that a decent amount of matter was left.
Some would say that this is evidence of a divine creator, or at least suspicious -- how did we end up with a Universe so hospitable to us? But this is circular -- what other kind of Universe could there be? If the Universe were not well-suited for evolving us, we wouldn't be here to complain about it -- instead there would either be no life at all, or perhaps more likely, a completely different form of life that would itself be wondering how it ended up with a Universe so perfectly suited to it. And it's kind of an odd thing to ponder, the probability of the Universe being any certain way, as we don't have any other universes to compare it to. Without a baseline, how do we know if our particular set of cosmological constants and matter/energy balances is peculiar? Maybe all universes are like that.
Given the laws of physics, it does not seem to be incredible that complex life evolved -- quite the opposite, it seems inevitable. But that leads to another question that I don't have a good answer for. Why aren't we hip-deep in Martians? Of course, I don't mean literal Martians, but given a universe where intelligent life can evolve, and the age of the universe, it seems unlikely that we would find ourselves in the present condition -- namely, an advanced, intelligent race capable of looking to the skies for others... and not finding anybody at all.
Consider this: there are approximately 400 billion stars in the galaxy. If only 1 in a million is capable of supporting life, that still leaves 400,000 biospheres to work with. If one of these proceeds to evolve to the level of sapient spacefaring race (as we have), it could begin colonizing the galaxy.
It's taken us about 50,000 years to go from spear-chucking primitive to working on molecular nanotechnology. If we started a space colony, how long would it take to advance to the level of sending out colony ships of its own? 5,000 years should be plenty of time to fill a planet with long-lived disease-free people when they're starting off in the modern era instead of Bronze Age technology -- look how far we've come in 5,000 years. And the original planet could continue sending out additional colony ships all the while.
Disregarding travel time (a huge caveat to which I will return), assuming each colony sends out another colony ship every 5,000 years, it takes only 95,000 years to fill all 400,000 biospheres with colonists. In geological or astronomical time, this is an eyeblink. And raising the number of habitable worlds makes it take longer to fill them all (but not much longer; this is after all an exponential doubling), but also means you should have more civilizations to begin with.
Travel time is a huge problem, though. The galaxy is 54,000 light years across. Even with the fastest propulsion systems we can currently conceive (a nuclear saltwater rocket boosted with hydrogen fusion... basically a ship being propelled by a continuous H-bomb explosion coming out the back) you're not going to get above 0.05c with any reasonable amount of reaction mass (and even 0.05c is being very generous; acceleration in vacuum by throwing stuff out the back of a rocket is horribly inefficient), and even then I'm not sure how you'd stop once you reached the destination. At that rate, it takes a million years to go from one end of the galaxy to the other, but you don't have to worry too much about time dilation.
But our hypothetical colonists don't have to go from one end of the galaxy to the other, at least not at first. Each colony would presumably send out its ships to nearby stars, not ones all the way across the galaxy. This does dampen the rate of colonization, though, as the original planet can't keep spitting out a colony every 5,000 years, since the travel time is longer on each one, with the last ones taking a million years to reach their destination (and they'd probably get there to find that a much-closer colony world had already beaten them there by half a million years.)
And that might all be moot if there turns out to be some currently-unknown method for travelling faster than light. You can't accelerate to those speeds, but there could be some currently-unimagined shortcut.
Even with travel time taken into account, though, it still doesn't take much more than 10 million years to colonize all the habitable worlds in the galaxy, and certainly not over 100 million years.
So, how much earlier than us would the aliens need to evolve in order to have already filled the galaxy with teeming colonies before we look up at the sky? They'd need to reach the spear-chucking primitive phase during Earth's Cretaceous period, when we were still fish, insects, and dinosaurs. Basically, they'd need to achieve sapience about when Earth's evolution achieved birds.
With 400,000 biospheres to choose from, that's not a very big head start. Are we supposed to believe that, if we're not alone in the universe, we're at least first? That nothing achieved civilization only 3% earlier than we did (100 million years is about 3% the age of the Earth, very conservatively)?
On one hand, it seems very implausible. There's kind of a general axiom of statistics that says "Chances are, you are not special." On the other hand, somebody had to be first. But given the relative youth of our sun, it does seem awfully unlikely to be us.
So... where are all the little green men? I can see a variety of weird possibilites, but I really have no idea... this is the question that puzzles me in the same way that questions like "why are we here?" or "how did life manage to evolve?" puzzle other people. Some possibilities include:
1.) The galaxy is full of life, and they're screaming at us, but we're just not listening the right way. That is, there's some undiscovered faster-than-light communication method that, when we discover it, will ask us, "Where the hell have you been all these years? Oh, you mean you were still listening for radio waves? How quaint!"
2.) The galaxy is full of life, but it's so transcendent that it doesn't consider us sapient lifeforms. If we discovered a planet inhabited only by insects, we would, after all, not attempt to make contact with it -- there's no life there capable of meaningfully communicating.
3.) There is a faster-than-light travel mechanism, so the galaxy was colonized in 95,000 years rather than 100 million. However, due to galactic distances, we just haven't noticed. After all, we're looking at snapshots of the galaxy between 5 years and 1 million years old, depending on where we look... we see galactic history, not the galaxy as it is. If the colonization did occur quickly, we might not see it yet. Likewise, any messages sent to us wouldn't have arrived yet.
4.) We just got "lucky" -- we're first. If we explore the galaxy, we'll find many planets with lower life-forms, but will have to wait for them to evolve sapience.
5.) There is some reason that no race capable of colonizing the galaxy wants to. Perhaps they all eventually replace themselves with sentient computer programs, who (not needing space and needing very little in the way of natural resources) construct universes in virtual reality rather than bothering with actual space travel. Still, it seems odd that all races would hit some sort of no-colonization dead end. It only takes one of them with a 95,000-year head start and the galaxy's full of 'em. Even if the reason is "it's just not worth the time", I'd figure some of them would do it anyway -- I mean, does "it's not worth it" ever stop humans?
6.) Everybody wipes themselves out before they get that far. This is the pessimistic answer, but this seems even more ridiculous than all the others to me... not to mention that it kind of counters #5 -- preventing this sort of thing is, itself, a reason to colonize.
It's quite the mystery, at least to me.
Some would say that this is evidence of a divine creator, or at least suspicious -- how did we end up with a Universe so hospitable to us? But this is circular -- what other kind of Universe could there be? If the Universe were not well-suited for evolving us, we wouldn't be here to complain about it -- instead there would either be no life at all, or perhaps more likely, a completely different form of life that would itself be wondering how it ended up with a Universe so perfectly suited to it. And it's kind of an odd thing to ponder, the probability of the Universe being any certain way, as we don't have any other universes to compare it to. Without a baseline, how do we know if our particular set of cosmological constants and matter/energy balances is peculiar? Maybe all universes are like that.
Given the laws of physics, it does not seem to be incredible that complex life evolved -- quite the opposite, it seems inevitable. But that leads to another question that I don't have a good answer for. Why aren't we hip-deep in Martians? Of course, I don't mean literal Martians, but given a universe where intelligent life can evolve, and the age of the universe, it seems unlikely that we would find ourselves in the present condition -- namely, an advanced, intelligent race capable of looking to the skies for others... and not finding anybody at all.
Consider this: there are approximately 400 billion stars in the galaxy. If only 1 in a million is capable of supporting life, that still leaves 400,000 biospheres to work with. If one of these proceeds to evolve to the level of sapient spacefaring race (as we have), it could begin colonizing the galaxy.
It's taken us about 50,000 years to go from spear-chucking primitive to working on molecular nanotechnology. If we started a space colony, how long would it take to advance to the level of sending out colony ships of its own? 5,000 years should be plenty of time to fill a planet with long-lived disease-free people when they're starting off in the modern era instead of Bronze Age technology -- look how far we've come in 5,000 years. And the original planet could continue sending out additional colony ships all the while.
Disregarding travel time (a huge caveat to which I will return), assuming each colony sends out another colony ship every 5,000 years, it takes only 95,000 years to fill all 400,000 biospheres with colonists. In geological or astronomical time, this is an eyeblink. And raising the number of habitable worlds makes it take longer to fill them all (but not much longer; this is after all an exponential doubling), but also means you should have more civilizations to begin with.
Travel time is a huge problem, though. The galaxy is 54,000 light years across. Even with the fastest propulsion systems we can currently conceive (a nuclear saltwater rocket boosted with hydrogen fusion... basically a ship being propelled by a continuous H-bomb explosion coming out the back) you're not going to get above 0.05c with any reasonable amount of reaction mass (and even 0.05c is being very generous; acceleration in vacuum by throwing stuff out the back of a rocket is horribly inefficient), and even then I'm not sure how you'd stop once you reached the destination. At that rate, it takes a million years to go from one end of the galaxy to the other, but you don't have to worry too much about time dilation.
But our hypothetical colonists don't have to go from one end of the galaxy to the other, at least not at first. Each colony would presumably send out its ships to nearby stars, not ones all the way across the galaxy. This does dampen the rate of colonization, though, as the original planet can't keep spitting out a colony every 5,000 years, since the travel time is longer on each one, with the last ones taking a million years to reach their destination (and they'd probably get there to find that a much-closer colony world had already beaten them there by half a million years.)
And that might all be moot if there turns out to be some currently-unknown method for travelling faster than light. You can't accelerate to those speeds, but there could be some currently-unimagined shortcut.
Even with travel time taken into account, though, it still doesn't take much more than 10 million years to colonize all the habitable worlds in the galaxy, and certainly not over 100 million years.
So, how much earlier than us would the aliens need to evolve in order to have already filled the galaxy with teeming colonies before we look up at the sky? They'd need to reach the spear-chucking primitive phase during Earth's Cretaceous period, when we were still fish, insects, and dinosaurs. Basically, they'd need to achieve sapience about when Earth's evolution achieved birds.
With 400,000 biospheres to choose from, that's not a very big head start. Are we supposed to believe that, if we're not alone in the universe, we're at least first? That nothing achieved civilization only 3% earlier than we did (100 million years is about 3% the age of the Earth, very conservatively)?
On one hand, it seems very implausible. There's kind of a general axiom of statistics that says "Chances are, you are not special." On the other hand, somebody had to be first. But given the relative youth of our sun, it does seem awfully unlikely to be us.
So... where are all the little green men? I can see a variety of weird possibilites, but I really have no idea... this is the question that puzzles me in the same way that questions like "why are we here?" or "how did life manage to evolve?" puzzle other people. Some possibilities include:
1.) The galaxy is full of life, and they're screaming at us, but we're just not listening the right way. That is, there's some undiscovered faster-than-light communication method that, when we discover it, will ask us, "Where the hell have you been all these years? Oh, you mean you were still listening for radio waves? How quaint!"
2.) The galaxy is full of life, but it's so transcendent that it doesn't consider us sapient lifeforms. If we discovered a planet inhabited only by insects, we would, after all, not attempt to make contact with it -- there's no life there capable of meaningfully communicating.
3.) There is a faster-than-light travel mechanism, so the galaxy was colonized in 95,000 years rather than 100 million. However, due to galactic distances, we just haven't noticed. After all, we're looking at snapshots of the galaxy between 5 years and 1 million years old, depending on where we look... we see galactic history, not the galaxy as it is. If the colonization did occur quickly, we might not see it yet. Likewise, any messages sent to us wouldn't have arrived yet.
4.) We just got "lucky" -- we're first. If we explore the galaxy, we'll find many planets with lower life-forms, but will have to wait for them to evolve sapience.
5.) There is some reason that no race capable of colonizing the galaxy wants to. Perhaps they all eventually replace themselves with sentient computer programs, who (not needing space and needing very little in the way of natural resources) construct universes in virtual reality rather than bothering with actual space travel. Still, it seems odd that all races would hit some sort of no-colonization dead end. It only takes one of them with a 95,000-year head start and the galaxy's full of 'em. Even if the reason is "it's just not worth the time", I'd figure some of them would do it anyway -- I mean, does "it's not worth it" ever stop humans?
6.) Everybody wipes themselves out before they get that far. This is the pessimistic answer, but this seems even more ridiculous than all the others to me... not to mention that it kind of counters #5 -- preventing this sort of thing is, itself, a reason to colonize.
It's quite the mystery, at least to me.
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no subject
Date: 2005-08-02 02:50 am (UTC)Maybe it isn't "nuclear war" style wiping out, but if we just keep building the government up more and more, and turning ever inwards, using more resources to create bureaucracy, we might just not ever get off the rock.
We've had nuclear weapons for 50 years. But that doesn't seem to have provided much impetus to spread the race out off the rock, to make sure someone survives if everything goes boom.
-Ogre