I've seen a bunch of people linking approvingly to this piece about the "Fermi paradox," (the question of why we haven't seen any evidence of other advanced civilizations) and I can't quite understand why. The author expends a good deal of snark taking astronomers and physicists to task for constructing elaborate solutions to Fermi paradox on the basis of shoddy and unjustified assumptions. And then proceeds to offer a different solution for the Fermi paradox based on shoddy and unjustified assumptions. Whee!
I mean, there is an element of this that's useful, namely the reminder that "We haven't seen aliens because there are no aliens to be seen" is a perfectly valid solution and at least as likely as anything else anyone has come up with. But really, the entire business is so data-poor and bullshit-rich that I have a hard time taking it seriously.
The paradox comes down to a question of time scales, as the galaxy has existed for (in round numbers) ten billion years, while life on Earth took only four billion years to get from nothing to us. Surely, given the vast number of stars in our galaxy, some other species must've done the same before us, probably long enough before us to reach greater heights of technology, including interstellar travel. And as many people with half-assed network models will happily tell you via preprints on any number of web sites, if you can travel at 0.1c, you can colonize the entire galaxy in just a few tens of millions of years. So, there ought to be alien colonies all over the place.
But there's all sorts of weird stuff behind those estimates, even leaving aside the "physicists don't understand biology"/"biologists don't understand math" sniping that goes on. The biggest neglected issues for me are the "why" questions. If you look at those estimates of time to cover the galaxy, a lot of them are talking about self-replicating robot probes. And while I'll admit that it's a lot more plausible to send a small robot off to another star at relativistic speed, I've never really understood what it is that the launching species is supposed to get out of that gigantic investment of energy resources. Some sort of abstract intellectual satisfaction, I guess. Even a single non-replicating probe to a neighboring system would be a huge undertaking, and require an astonishingly patient community of alien scientists willing to wait a few hundred years for pictures of the neighbors.
And even if robot probes were buzzing into the solar system, self-replicating, and leaving again, I'm not sure why anyone thinks that would be obvious. Space is vastly, mind-bogglingly huge, and that goes for space within the solar system. I mean, if some alien equivalent of Voyager or Cassini zipped past us snapping pictures, I'm not convinced we'd even notice. The only real hope is that whatever they use for a drive system is big and noisy and makes a lot of extra light at a time when we happen to be facing in the right direction.
Even the self-replicating part doesn't need to leave obvious traces. There's no reason at all why the self-replicating part of things would need to happen here, with our relatively dense atmosphere and strong gravity. There are huge numbers of floating space rocks and balls of ice out there in the Kuiper belt and Oort cloud that alien robots could mine to their heart's content, and we'd never even notice.
And the problems are equally puzzling for anybody who could get here in person. Even at a peak speed of 0.1c, you're talking decades to centuries to get from star to star. But if you have the resources and technology to maintain a livable environment in interstellar space over that span of time, I'm not sure why you'd need to visit Earth in the first place. Nostalgia? Some sort of alien-hipster retro affectation for the lifestyle of a dozen generations back? Again, you could park dozens of space arks in the asteroid belt and happily live there basically indefinitely without humans being any the wiser. If you need raw materials, it's still easier to snag the occasional comet than to get on and off a rock ball like Earth.
The use case for alien visitation of Earth is ridiculously narrow-- it's basically limited to civilizations with some sort of hibernation technology that can preserve live specimens for decades or centuries, but only in some sort of suspended state that requires thawing out on a planet at the other end of the trip. And also some means of re-creating enough of their biosphere and technological base to make a viable colony there, but not enough of that technology to make habitats in space, or on asteroids or moons. So, assuming the aliens fall into that really narrow range of parameters, yeah, I guess we should've seen them by now.
Which comes around to the problem of communications, namely that we haven't detected any signs of alien communications. But the electromagnetic spectrum is so huge, and our effort to find them has been so short and half-assed that it's ludicrous to think we've actually ruled anything out.
So, I do agree with the Praxtime post in one very limited sense, namely that it's ridiculously arrogant to think that the kind of calculation Enrico Fermi could dash off on a napkin says anything about the likelihood of alien civilizations. But at the same time, it's equally ridiculous to think that the make claims in the opposite direction, based on the after-dinner napkins of biologists. We know so little about any of the parameters that go into any of this that it's impossible to have a meaningful discussion about the idea.
I have wondered the same things. What they may be thinking is Star Trek is not far off and we will be cruising to Alpha Centuri for lunch and I would agree that if it weren't far off, it would require explaining, but I see that incredibly difficult if not impossible.
On the point about electromagnetic communications: even we are now using lasers to target communications with space, because it's simply more efficient and reliable.
It's also basically impossible to intercept, since you literally have to interrupt the beam to do so.
It's not quite true that you'd need to block the beam to intercept it-- over interstellar distances, even a laser would expand rather dramatically, and probably cover a good chunk of the solar system. That's probably a good topic for a full blog post, though...
Back when I was in high school, I played around with Drake's equation a bit. Using optimistic estimates I thought that 1 in 5 solar systems would have intelligent life. Using pessimistic estimates I got that 1 in 5 galaxies would have intelligent life.
This gave me a pretty obvious hint at how Fermi's paradox would be resolved.
Now that I'm older and know more about biology and statistics I'm tempted to replace my previous optimistic estimate by my pessimistic estimate, and replace the pessimistic estimate by: about a dozen in the visible universe.
Here's a reason to send out those self-replicating probes that blanket the galaxy:
At the point the probes can be sent out, you are still probably a long way from being able to even send a seed colony, (much less start shipping large numbers of people). However, you don't want to wait until you can send out those seeds to send out the probes looking for a place to go.
Thus, you send out the probes with the aim of finding any suitable planets/systems that are near by. You use self-replicators both to reduce the distances you need to loft probes and to set up a system that replaces any that fail on a more reasonable time frame. You then let the probes continue expanding their coverage, it's not like it's costing you any more to continue on across the galaxy.
I think the only thing we can safely conclude from all of this is that most people's ideas about extraterrestrial life are shaped more by science fiction than by rigorous thinking. People dream of colonising other planets because that's a common sci-fi trope, not because it makes any actual sense, and then assume that ET must share the same dreams.
Here’s a reason to send out those self-replicating probes that blanket the galaxy:
At the point the probes can be sent out, you are still probably a long way from being able to even send a seed colony, (much less start shipping large numbers of people). However, you don’t want to wait until you can send out those seeds to send out the probes looking for a place to go.
You don't need to find a place to go. By the time you're able to get there, you can live in space indefinitely anyway. Why would you want to colonise planets?
I'm with Dunc:
"People dream of colonising other planets because that’s a common sci-fi trope, not because it makes any actual sense, and then assume that ET must share the same dreams."
Plus it's not like we have any shortage of problems to solve back on Earth, the only habitable planet we know of.
Chad - I think makeinu's more general point is that the beam would still have to be aimed very carefully at our tiny target, and for no apparent reason. Still the laser post would be cool and offers an opportunity to refernece "The Mote in God's Eye".
Nuts. Didn't see today's post before I wrote that - nevermind!
You don’t need to find a place to go. By the time you’re able to get there, you can live in space indefinitely anyway. Why would you want to colonise planets?
To begin with, note that I included the possibility of wanting to find a suitable _system_. Somehow I think you would rather go to one that has plenty of resources rather than one that had all its small rocks stripped away by an incident a billion years ago. You might also have rules about taking systems that are already 'claimed', (e.g. any signs of native intelligent life means that the system gets left for them).
As for why you might want a planet: Even if you can live indefinitely in space, planetary life is easier in a number of ways. Besides, you might know that 12% of your population is never going to really like being spaceborne and thus you want systems where they can move planetside.
But what about the inner life of after-dinner napkins. :) :) :)
Good post Chad! Thank you. Finding life in the universe is like all good contract work and depends on Time and Distance. I do like the idea of sending out self-replicating probes, but again it has to do with the vast size of the universe. It's a very very big place.
I used to speculate about a possible Kuiper Belp civilization. If a civilization has enough technologiacl capability they might be able to live on these objects -obtaining energy from fusion. Then if they can occasionally seed other nearby objects, they will eventually diffuse throughout the galaxy. One analogy might be Polynesians populating Pacific islands. Of course the diffusion time is a lot longer than any realistic time over which we would expect a species to remain recognizable, i.e. there would presumable be huge diversity, even if only one civilization started the whole thing.
But, I suspect there would be evidence if this happened on a large scale.
That was more my point, which today's post does explain quite well.
There's also the point that omnidirectional RF communications decay drastically over long distances, and we'd have to be able to demodulate the intelligence from the carrier on a very weak signal, and then interpret that intelligence, which is also true of targeted communications, and neither thing might be something we are even technically capable of.
The universe could very well be swarming with signs of intelligent life that we're just not up to the task of recognizing yet. Heck, we're barely at the point where we're recognizing other intelligences on our own planet. If you want to meet an alien intelligence today, go to an aquarium and spend some time with the octopus tank.
Why should intelligent life seek to go interstellar?
To preserve its lineage of life and knowledge longer than the usable life of its local home star. Why not send bacteria to seed other planets and leave it at that? Because you also seek to preserve and extend your culture and knowledge.
Why not send self-replicating probes?
Because of the risk of a software malfunction leading to exponential growth, thereby unleashing a cosmic plague that might eventually behave in ways hostile to your own culture's self-interest. Alternately, because you've already discovered, by reading signals from other intelligent civs, that unleashing any such thing is considered a hostile act that will be punished severely.
Much simpler & more achievable to develop a standardized type of non-replicating probe that can be built relatively cheaply. Send out large quantities of these to areas of interest, using mesh technologies for robust and redundant communication back to the home world.
Why seek out planets to live on, rather than only living in space colonies?
Because planets have advantages such as gravity to hold down an atmosphere, and electromagnetic fields to shield or divert harmful radiation, and more usable area than you're likely to get on any artificial device of size smaller than a planet.
How to get from here to there?
Interstellar migration is the single largest engineering project any civilization will face up to that point in its history. The prerequisites are a planetary civilization that has overcome its sustainability and war issues in order to free up the resources for the required span of time. Having done that, they will have the resources to plan long-term and carry out their plans.
First, send out robotic probes to survey likely destinations. Assuming 0.01 C, which is reasonable, this is a multi-thousand-year project. At the same time, develop the tech to house and transport sufficient qualities of people & other life from your home planet to the new planets. Goal: a "space liner" or "ark ship" that can support a genetically diverse population over a period of thousands of years between launch and destination. Design & testing will also be multi-thousand-year projects.
The project timelines converge to give you: the means to go there, and a place to go. Then do it, and repeat as often as you find new potential destinations.
Why haven't we found "them" yet?
They're using lasers or other communications we can't easily intercept. And because they're too busy discovering and building, and possibly interacting with others at equivalent stages of development.
Realism, pessimistic and otherwise:
We are not alone or unique, with all the "self-importance" that such a conclusion would warrant.
We are merely of little interest to others in our galaxy at this point in time, with all the "self-unimportance" that this conclusion warrants.
If and when we become an interstellar civilization ourselves, we will most likely discover that that's the stage at which others in our galaxy find it worthwhile to talk with us.
The choice we face is between darwinizing ourselves via ecological catastrophe or other means, or overcoming our atavisms and becoming a cosmic civilization.
"We are not alone or unique, with all the “self-importance” that such a conclusion would warrant.", was unclear and suggests the opposite of the intended meaning.
The following is what I was trying to say:
"The idea that we are alone or unique tends to foster an excessive sense of our own self-importance. In all probability we are not alone or unique, and we should overcome our attachment to cosmic uniqueness as a component of our collective self-worth."
My father - Herb York - was at that famous lunch. Fermi was a good friend, along with Segre.
Teller, not so much.