Why aren't we hip-deep in Martians?

[fishsupreme]

The 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.

Comments

[partywhipple.livejournal.com]

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.


That's a depressing thought but a distinct possibility. Once you get to a high enough tech level it's becomes much more probable that a single nut job can wipe out the race, right?

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.

That could be it too, though I think there is a threshold when sentience is achieved that most sensible people acknowledge. We build things, we've reached space, and we at least attempt to communicate with other races. I find it hard to believe an intelligent race wouldn't at least want to say hi. Of course they may have a Prime Directive keeping them from interfering with us monkeys. LOL

[fishsupreme]

The thing is, the same technologies that let a lone nut wipe out a planet also assist with defendng against such things -- engineered plagues, grey goo, etc. can only be countered by the same biotechnology and nanotechnology as can create them. That there would be a few dead worlds in the galaxy from just such disasters is plausible... but all of them?

There's a level of sentience that most sensible people acknowledge, of course. But by "transcendent" I mean what if alien life, before reaching the galaxy-exploring stage, reaches a stage where they change so much as to be unrecognizable? What if they move on so far that, by comparison to them, we're the insects? A population of artificial intelligences each of which has greater intelligence than the entire human race and processes data so fast that they experience a century in each second might not agree with our sensible definition of sentience.

And as for the Prime Directive hypothesis, I never found that plausible because I seriously doubt our first contact with an alien species will be with a government. I don't think they'll say "take me to your leader", but rather, "hey, want to buy a cheap used spaceship? Deals, deals, deals!"

[phanatic.livejournal.com]

7.) There's some force out there that destroys whatever sentient life it happens to notice. Either you stay quiet, or you get killed.

[fishsupreme]

Ah, the berserk-Eschaton hypothesis. Can't say I like that one, but I don't suppose I can rule it out, either. It's not out of the question for a society to decide the best way to preserve itself is to ensure there are no other societies.

[phanatic.livejournal.com]

I just finished a trilogy by Alistair Reynolds. He had Berzerkers in it, but there was a design there, not just blind rage. Their motivation is that something Really Bad is going to happen, and if there's one race of intelligent life, the eventual outcome will be not quite total disaster, whereas if intelligent life is left to spread across the galaxy by its own devices, the eventual outcome will be worse than that.

Sort of the ultimate in utilitarian arguments.

[lordshell.livejournal.com]

You're also overlooking something. We just don't know how likely a 'sentient' technological civilization really is.

I mean, just think about everything required for humanity to have reached the stage it has:

1.) Our solar system/star had to be a second or greater generation star to meet the requirements for heavier elements.

2.) A planet had to form in the liquid water zone.

3.) We had several large gas giants to act as cosmic 'vacuums', sucking up the bulk of the stellar debris and keeping earth from getting constantly pulverized.

4.) Earth had sufficient gravity to capture and keep an atmosphere.

5.) Earth had sufficient water.

6.) Earth had sufficient landmass to support a terrestrial, tool-using society.

These are just the cosmic hurdles we know. And all of that before we even talk about the factors within evolution itself.

7.) We had to be a terrestrial race, since an aquatic one would not be able to have an industrial society.

8.) We had to be social, since lone predators aren't prone to the cooperation necessary for a civilization.

9.) We had to have language, so as to share and pass on information.

10.) We had to have precise digits to manipulate our enviroment (i. e.- opposable thumbs.)

11.) We needed to be aggressively expansionist, to drive us on to greater goals, either geographical or intellectual.

12.) And we had to keep from being wiped out by a stray asteroid or our own more destructive technology.

And we don't yet know if intelligence is really all that good a survival trait. After all, we've been around since just yesterday, evolutionarily speaking. The jury's still out on us. There are plenty of damn stupid lifeforms that have been around far longer than we have. It might be that our traits are a fluke. An evolutionary hiccup that just turned out well.

As these are just the basic reasons. There are a lot more out there that I'm unaware of, I'm quite sure.

I have no doubt that there are other life-bearing planets out there, but I suspect that intelligent, tool-using life is quite a bit rarer than we'd like.

[phanatic.livejournal.com]

just think about everything required for humanity to have reached the stage it has:

Yeah, but that's humanity, not sentient life in general. Many of your hurdles are not limitations at all on tool-using sentient life, let alone sentient life.

You're right, we don't know how likely it is. But that's the entire point of the Fermi Paradox: either there's something flawed in our understanding that leads us astray in its formulation (like, maybe the creation of self-replicating machines is a great deal more difficult than anticipate, or even impossible for some reason, or physical laws operate differently in different regions of the galaxy, like in a Vinge book), or even the most conservative values we can input as coefficients in the Drake equation are in reality wildly optimistic.

[lordshell.livejournal.com]

But we have a pretty good knowledge of biochemistry, and know that the development of life as we know it requires a certain range of enviromental conditions. Unless physical laws alter when one travels the universe, life will most likely be based on carbon and need water and light/heat. This gives us a rough idea of the needed conditions.

Radically different life is, of course, possible, but evolution tends to take the path of least resistance.

[zaimoni.livejournal.com]

Precisely...we don't have an intuition for alternate implementations. Lack of imagination is no basis for "it's impossible". That's where "no man can survive riding in a train at 30mph" came from, in the 1800's.

For instance, it's not at all clear that a six-nucleic acid DNA/RNA system is physically uncompetitive [simply use both thymine and uracil, and add inosine (which is the common metabolite of the purine breakdown path].

A generation I star (pre-heavy elements) would still have primordial boron to work with, for instance; it's not clear that "trivalent DNA backbone" is impossible, rather than inconceivable. If hydrogen bonding is important, liquid ammonia is an alternative solvent; such a civilization would have much easier access to superconductivity. If temperature isn't important but tetravalence is, silicon becomes an option.

[patrissimo.livejournal.com]

I think 4 is the big one. I think your 1/million is ridiculously high. I don't think we can derive much from the fact that we exist. It demonstrates that sentient life is probable, but demonstrats *almost nothing* about how probable it is.

Even if its so improbable that only one planet in the universe develops intelligence, *someone* will still exist and ask the question of how likely it is, and have themselves as evidence. Its just like winning the lottery - someone wins, and all that proves is that someone could win. The winner can't say "well, I feel about 1000 times luckier than the average person, so they should win the lottery about 1 in 1000 times" - that's just wrong.

Hell, for all we know, there are tons of universes out there with different physical constant - it may take lots of universes to produce intelligence, not just lots of planets.

Also note that if there is no FTL travel, we don't have to be "first", just "first in the neighborhood".

[fishsupreme]

Remember that I wasn't saying 1 in a million had sapient life, merely that one in a million was habitable to a race with sufficiently advanced technology to colonize other worlds.

It only takes one other race in the galaxy 100 million years ahead of us to fill all those up. It's this that makes me wonder why they're not full.

With exponential growth, the neighborhood gets really big, really fast (in geologic time -- it's still mind-bogglingly slow by human time standards.)

[ilcylic.livejournal.com]

#6 doesn't seem all that unlikely. We certainly haven't gotten to the colony spreading level quite yet, and we may not.

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

[whip-lash.livejournal.com]

There was an article on something like #1 not too long ago, I forget where, essentially discussing it in terms of Earth, saying that anyone listening for us will probably have a window of no more than a hundred years or so, because of the rapidity with which landlines and extremely low-power (cellular) sources are replacing our big transmitters.

Combine #1 with Phanatic's #7 - people who leak don't leak long, and people who shout don't live long, plus 'people who have the technology to explore also have the technology to build biodomes and maybe terraform if they're lucky enough to have a sister planet like Mars' - and we may have a winner.

[whip-lash.livejournal.com]

Oh, yeah, #8 - the Galactic Confederation abides by the Prime Directive and we're not advanced enough to join the club yet.

[whip-lash.livejournal.com]

I see you addressed this. Difficult to say how advanced the Galactic Confederation's enforcement mechanisms are. The chip in the brain that gives you an electric shock whenever you think about contacting the primitives seems distressingly possible.

[2percentright.livejournal.com]

Not to bother you on your home LJ, but how in blazes do people post on the Libertarianism Lj? I'm stumped.

[2percentright.livejournal.com]

Nevermind. Figured out my problem five seconds after annoying you with my question.

[lucky-eddie.livejournal.com]

I think it's likely that the Martians find interstellar colonization uncompelling, for the following reasons:

- Governments might discourage it: you can't govern (or collect taxes) over such distances. The colonies would have to be self-governing. Why would a government want to start another government?

- As for private enterprise: little or no ROI on an extremely long-term investment? Why?

- If they can colonize their own solar system to the point of virtually guaranteeing their survival 'til the death of their sun, then what's the point, anyway?

- It takes many thousands of years to colonize a neighboring star, during which evolution is causing divergence already. Why colonize another star with a different species?

So, my theory is that they're out there, probably sending occasional small robotic probes that we haven't noticed, but otherwise sitting tight and enjoying really advanced forms of entertainment.

Simply impossible

[redslime.livejournal.com]

I look at it a little differently. I think all of your points, and the points of others, are valid. Taken together we can say that we are simply impossible. It is a mystery that we are not likely to solve. Also, I don’t think that supposing that there is a god involved would make it any less mysterious. What kind of god makes a whole universe and then only populates one planet in some obscure corner of the galaxy?

In any case, here is another possibility. Perhaps the desire to announce oneself is not very common among intelligent species. If it also turns out that super than light travel is not possible, then the lack of contact may mean much less then we would have it mean. I think we make much to big an issue of the idea that there will be artifacts of our communication visible by other civilizations. If you look at how we are going, it seems evident that high-powered broadcast will be a short story in the history of communications. Communication will be primarily through narrowly focused networks, with little or no high-powered-wide-area broadcast that will leak into space. That is, in a few years, less then 50, we will become essentially invisible again. Only if you were within less then say 200 light years of us could you have a likelihood of ever seeing our short lived signals, and then only if you cared a great deal about finding us.