Update: also see my follow-on post about Sagan Syndrome
I wrote an earlier post supporting the view that Earth is a unique planet. It’s likely the only planet in our galaxy supporting complex life. I wanted to do an update after coming across an excellent post by Stephen Ashworth, who categorizes views on alien life into either “steady state” or “expansionist”.
Ashworth starts by noting that early attempts to estimate the amount of intelligent life in the galaxy were based on steady state models. His illustration is below:
In the steady state model, once the universe gets started the number of civilizations quickly plateaus. This is depicted as time “A” above. The steady state comes from assuming civilizations are born and die at a constant rate, and so over time the number stabilizes. This is the basis of the 1961 Drake Equation and also the model behind a lot of discussion of the Fermi Paradox. I love all the work and thought that went into this, but this approach is showing its 1960 roots. We should respectfully trash it.
Contrast this with what Ashworth characterizes as an expansionist model:
In this model, life is an invasive species. Once it reaches a point where it can cross star systems, it rapaciously expands to fill the galaxy. Now we’re talking. Darwinian life filling empty ecosystems to capacity. A nuance here is the expansionist model doesn’t require every civilization to be expansionist, though Darwinian logic makes this plausible. The real key is the very first expansionist civilization that comes along fills the galaxy. Game over. So why did Drake even consider the steady state model back in 1960? Well, back then it was not clear you could build a starship. And even if you could, how would people survive centuries of travel through radiation filled space? With the constraint that civilizations were restricted to their home sun, the steady state model made sense. Alien civilizations were born alone, trapped around their sun, and eventually died alone.
It was not until the invention of computers and robotics that sending self-replicating probes became conceivable. Now you have a technology that can survive in space for the centuries, replicating to fill the galaxy. Once you accept interstellar travel is possible, and understand robotics, the expansionist view becomes impossible to avoid. Likewise the steady state model becomes archaic and ridiculous, given it’s foundational premise is interstellar travel is impossible. Here’s a quote from Frank Tipler’s paper from 1981:
The basic idea of my argument is straightforward and indeed has led other authors such as Fermi (10), Dyson (11), Hart (12), Simpson(6), and Kuper & Morris (13), to conclude that extraterrestrial intelligent beings do not exist: if they did exist and possessed the technology for interstellar communication they would also have developed interstellar travel and thus would be present in our solar system. Since they are not here (14,15), it follows that they do not exist. Although this argument has been expressed before, its force does not seem to have been appreciated.
Exactly. It’s force was not appreciated in 1981. And is still not completely appreciated now, over 30 years later. The search for extraterrestrial life (SETI) muddles along stuck in the 1960’s, unable to get out. People are still publishing brand new books based on the Fermi paradox and the Drake equation. Please make it stop.
Of course the main reason the public believes simultaneously in interstellar travel and aliens is it makes for awesome popcorn movies. Well enough. I love good alien movies too. But even people who are aware of the argument above can struggle. I think the reason is the relative timescales involved. Let’s start with the age of the universe. It’s 13.8 billion years old as depicted below.
Our Sun and the Earth formed about 4.5 billion years ago. Microbial life evolved shortly after. Intelligent life evolved 3 billion years after the start of life. Repeat: billions of years to evolve intelligent life. In fact, life will end on Earth due to the expanding Sun in only another two billion years. So in some sense we barely evolved in time.
Now compare the billions of years for intelligent life to evolve to the time it takes to expand into the galaxy with self replicating probes. That’s only 20 million years. In the picture above on the far right is a green vertical line showing 20 million years. You may have to squint to find it. It’s an eyeblink.
Now step out even further in time. It turns out the universe will produce stars into the future for 100’s of billions of years. A typical figure is 10’s of trillions. Let’s just use 1 trillion for the scale below. On the far left in red is the 13 billion year age of the universe, which on the new scale looks pretty short. Each block is 100 billion years wide. We still have stars forming at 1 trillion years, and beyond. It’s still daybreak from the universe’s point of view.
We have three disparate time scales: millions, billions and trillions. For simplicity let’s round the numbers to 20, 20, 20:
- Time for intelligent life to fill galaxy: super short 20 million years
- Time for intelligent life to evolve: moderate 20 billion years
- Time of universe to keep having stars: long 20 trillion years
The first timescale is the expansionist view of populating the galaxy. It’s easy to reject emotionally but hard to reject logically. That’s because the expansionist view merely assumes interstellar travel is possible and Darwinian evolved life fills ecosystems. Some math here. The second number is based on the observation that aliens haven’t flooded the galaxy yet. Plus supporting data that intelligent life evolved very late in Earth’s history after billions of years. The last number is current astrophysics and seems very solid. Overall we have a spare, powerful and persuasive model for why there are no aliens. Life has barely had time to get started.
Unfortunately this model shows the chances of us meeting a second form of intelligent life are nil. It takes billions of years to evolve, and millions of years to flood the galaxy. First one gets it all. Also note there’s plenty more time for intelligent life to evolve elsewhere before the universe gets old. So if humans self-destruct before expanding, then other intelligent aliens will do it later. In say, another 10 billion years.
Praxtime by Nathan Taylor 
your logic doesn’t go far enough, the local virgo supercluster is a mere 110 million light years around and contains millions of galaxies like the milky way. This is a fairly close distance for nanotech to travel. Conclusion, there is no other intelligent life in the local supercluster. And if there is none here, given the preponderance of worlds like earth, if the drake equation is true and life arose through some probabilistic mechanism, if we are the only ones in the local supercluster it also seems likely that we are the only intelligent life in the entire universe, because the event must be so rare.
Sagan tried to bring the aliens closer by making expansion super slow. So agree the flip side is that if it’s easy to expand super fast, say .99c, then closest aliens must be very far away. Say 10 billion light years to give time for life to get started. Where this logic might have trouble is speculating how fast ETs can expand, plus in particular the max hop they can take. I think longer trips, say 10 or 50 million light years in the gaps between clusters might require a more massive and hence much slower probe to survive the trip. So I just went out as far as 110 million light years because back of the envelope it works out with a max .1c expansion with no trip lasting more than say 100k years in radiation of space. Agree if you take nanoparticles that can self replicate which can travel .99c and hop a billion years at a time, well, you are exactly right. It makes intelligent life much more rare and the “empty zone” around us much larger.
I am confused as to why you would call sending robots “expansion”. What exactly would they do to prevent the emergence of intelligent life somewhere else and why?
I can see how and why human colonists could prevent the emergence of competing intelligent species. It’s the exact opposite for automatons.
Sending a bunch of probes doesn’t prevent others from expanding. You’re right. But if 1000 years from now we start sending probes out to explore and replicate across millions/billions of stars. We’d have detectable radio traffic and other signs that SETI would pick up. Since SETI has not, that’s means the most likely conclusion is no one’s done this yet. It’s just first out the gate blankets the galaxy. Others could come later, but since it takes billions of years to evolve those late comers would find probes already in their system.
I find this kind of discussion fascinating, but somewhat pointless.
We do not have anywhere near enough information to make a reliable estimate of the time it would take for a civilization to expand beyond its star system.
From an engineering standpoint, the assumption that a planet could be brought to the point of re-expansion in 500 years seems extremely unlikely. Even self replicating machines would need a great deal of time to find and harvest all of the materials needed to replicate themselves. Landing in one location is not going to provide this machine with ready access to the materials needed to build even simple computers.
If the expansion is to be carried out by life forms, it would also take a great amount of time to make the new planet habitable before they could even begin the process of expansion. Keep in mind the fact that we aren’t even capable of expanding throughout the biosphere of our own planet (yet).
These self replicating machines are not such a simple thing either. A very complex machine capable of surviving in pristine condition throughout a very long journey through an extremely harsh environment is not a minor jump from our current technological level.
I think it is entirely possible that the act of expansion to another star system would require such a herculean effort that very few civilizations could pull it off. Consider the difficulty we’ve had in maintaining an expansion of our rudimentary space program.
To draw a biological analogy, many species of life have to spend so much on the act of reproduction that the parents die in the process.
The geometric math is fairly straightforward on expansion. No matter what reasonable (to me) number you plug in for replicating probes, 100 years, 1000 years or even 10,000 years, you still blanket the galaxy in order of magnitude millions of years. Of course if you say 1 million years to replicate at each star, then you can stop the argument in its tracks as you point out. But you need to make replication time surprisingly large to make galactic expansion push into the billions of years timeframe which we know is what it takes for life to evolve.
http://www.open.edu/openlearn/science-maths-technology/science/physics-and-astronomy/how-long-would-it-take-colonise-the-galaxy
Or if you want to dive deep here’s a paper
http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=8949306&fulltextType=RA&fileId=S1473550413000244
Plus Tipler’s original 1980 paper mentioned above does the math as well. This geometric math is really the essence of the Fermi Paradox argument that no one’s out there.
Not sure how the 100 trillion years figure is significant to this argument. If a super-intelligent civilization destroys the entire universe a million years from now, or finds a way to avert universal heat death in the next 50 trillion years, that does not at all affect the probability of intelligent life appearing up to this point.
In the above, replace 100 and 50 trillion years with 1 trillion and, say, 500 billion, respectively.
Also, how do you justify completely discounting the idea of a Great Filter accounting for the apparent lack of intelligent life in the galaxy?
Consider across the muiltiverse all the civilizations at our level of tech that face a Fermi paradox. For some imagine that the true answer is that life is rare in their universe whereas for others the true answer is that life is common but the great filter gets civilizations such as ours before we can colonize the universe. If we are uncertain concerning our place in the multiverse shouldn’t we give high weight to being in the latter group because it probably has more members?
That depends on the relative probability of each universe.
Agreed, but you still need to give greater anthroptic weight to a universe the more observers such as us are in it.
Yes, but you don’t know if that offsets the possible likelihood of non-Great Filter universes. So there’s no reason to “give high weight to being in the latter group”. We have no idea what kind of weight to give to each scenario, at least not until we understand much more about how a Great Filter universe may come about.
I always had this question in my mind: Why would intelligent life be interested in expanding in a galaxy? It is does not seem useful to have an intergalactic empire. The government gets a report, makes a decision, sends an order, receives an evaluation, acts on it. That’s 4 x 100,000 years. Unless physics really surprises us or biology finds a cure for death!
Also, has anyone calculated the cost of intergalactic commerce (after of course one solves the problem of buying something that has been in stock for 100,000 years and receiving it after 200,000 years)?
Or a research agency that will fund an expedition which, if successful, will give results in 200,000 years?
It only takes one person who has access to advanced nanotech to colonize a galaxy.
Konstantin, the purposes of colonizing the galaxy don’t include building and empire or expanding trade routes. As you point out, such exercises would be silly. The purposes do include the quests for knowledge (for its own sake) and adventure (for its own sake). The purposes also include maximizing the survival potential of the colonizing race. It’s difficult for an astronomical catastrophe to wipe out a civilization that is spread across the galaxy.
I think you are laboring under the handicap of applying earthly economics to galactic expansion. Galactic expansion won’t be considerate of anything approaching current (or past) earthly economics. In order to get to the stars, the energy problem has to be solved. Once the energy problem is solved, economics as we know it is going to become an anachronism.
If and when we expand we may well find any other independent occurrence of life sufficiently interesting that we choose to observe it without interference. Others may well have felt the same way, and certainly whatever methods they use for communication within their own culture are likely to be more efficient than randomly directed broadcast. So why do you expect that their presence around (and between) other stars would be apparent to us at this stage in our observational capacity?
What if there’s a more interesting or easier to explore place to go than “out”? I propose two such places:
Used to be that as kids we’d play outside, tinker inside, explore our environment, physically interact with other kids, etc. Today, many kids are happy to stay immobile while they explore cyberspace, virtually interact with each other, or create digitally. Could ETCs all graduate to the point where they are happy to stay put and just explore virtual realities? Or create simulated universes (which we may be in one of) and enter them? This does assume that population pressure allows them the luxury of staying put. (There’s also cataclysm pressure which forces you to move or expand, lest a cataclysm makes you extinct, so even if you can manage your population and resources, a civilization would have to be careless not to expand out.)
My second proposal is that, just as we’ve come to know the moon or Mars better than we know our ocean depths, and how the exploration of space is capturing more of our imagination than the exploration of our planet, maybe there’s yet another place for us to go than out to space.
Coud ETCs, in the process of trying to device schemes to exceed the speed of light, have all stumbled onto inter-dimensional travel and discovered a much more fascinating and less energy-consuming frontier? Why bother with slow, dangerous and expensive travel to space, when stepping into another dimension is considerably easier and equally rewarding?
Reblogged this on CriticalMusings and commented:
What if there’s a more interesting or easier to explore place to go than “out”? I propose two such places:
Used to be that as kids we’d play outside, tinker inside, explore our environment, physically interact with other kids, etc. Today, many kids are happy to stay immobile while they explore cyberspace, virtually interact with each other, or create digitally. Could ETCs all graduate to the point where they are happy to stay put and just explore virtual realities? Or create simulated universes (which we may be in one of) and enter them? This does assume that population pressure allows them the luxury of staying put. (There’s also cataclysm pressure which forces you to move or expand, lest a cataclysm makes you extinct, so even if you can manage your population and resources, a civilization would have to be careless not to expand out.)
My second proposal is that, just as we’ve come to know the moon or Mars better than we know our ocean depths, and how the exploration of space is capturing more of our imagination than the exploration of our planet, maybe there’s yet another place for us to go than out to space.
Coud ETCs, in the process of trying to device schemes to exceed the speed of light, have all stumbled onto inter-dimensional travel and discovered a much more fascinating and less energy-consuming frontier? Why bother with slow, dangerous and expensive travel to space, when stepping into another dimension is considerably easier and equally rewarding?