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Transhumanist philosopher (and IEET Chair) Nick Bostrom desperately hopes that we never find signs of extraterrestrial life—advanced or otherwise. Why? Because he understands the Fermi Paradox.
Because the Galaxy appears uncolonized and unperturbed by intelligent life, and because there has been ample time and motive for this to happen, we have to conclude that some kind of filter is in place that prevents life from arriving at this advanced phase. In his recent article for Technology Review, Bostrom writes:
...the evolutionary path to life-forms capable of space colonization leads through a “Great Filter,” which can be thought of as a probability barrier…The filter consists of one or more evolutionary transitions or steps that must be traversed at great odds in order for an Earth-like planet to produce a civilization capable of exploring distant solar systems. You start with billions and billions of potential germination points for life, and you end up with a sum total of zero extraterrestrial civilizations that we can observe. The Great Filter must therefore be sufficiently powerful—which is to say, passing the critical points must be sufficiently improbable—that even with many billions of rolls of the dice, one ends up with nothing: no aliens, no spacecraft, no signals. At least, none that we can detect in our neck of the woods.
Now, just where might this Great Filter be located? There are two possibilities: It might be behind us, somewhere in our distant past. Or it might be ahead of us, somewhere in the decades, centuries, or millennia to come.
We are hoping that the filter resides in our past, that we have already overcome highly improbable odds.
More disturbingly, however, it’s likely that the Great Filter still awaits us in the future. There’s some kind of technologically instigated event that exists out there—and no species can avoid it.
Again, Bostrom writes:
Throughout history, great civilizations on Earth have imploded—the Roman Empire, the Mayan civilization that once flourished in Central America, and many others. However, the kind of societal collapse that merely delays the eventual emergence of a space-colonizing civilization by a few hundred or a few thousand years would not explain why no such civilization has visited us from another planet. A thousand years may seem a long time to an individual, but in this context it’s a sneeze. There are probably planets that are billions of years older than Earth. Any intelligent species on those planets would have had ample time to recover from repeated social or ecological collapses. Even if they failed a thousand times before they succeeded, they still could have arrived here hundreds of millions of years ago.
The Great Filter, then, would have to be something more dramatic than run-of-the mill societal collapse: it would have to be a terminal global cataclysm, an existential catastrophe. An existential risk is one that threatens to annihilate intelligent life or permanently and drastically curtail its potential for future development. In our own case, we can identify a number of potential existential risks: a nuclear war fought with arms stockpiles much larger than today’s (perhaps resulting from future arms races); a genetically engineered superbug; environmental disaster; an asteroid impact; wars or terrorist acts committed with powerful future weapons; superintelligent general artificial intelligence with destructive goals; or high-energy physics experiments. These are just some of the existential risks that have been discussed in the literature, and considering that many of these have been proposed only in recent decades, it is plausible to assume that there are further existential risks we have not yet thought of.
Bostrom, who is the director of the Future of Humanity Institute at the University of Oxford, concludes his article by making a case for increased foresight and vigorous inquiry into potential risks.
But even so, Bostrom asks, what makes us think we’d be immune to such a powerful filter?
Which is why, when he looks up at the stars, he is thankful that we have yet to see any signs of extraterrestrial life. Read the entire article, “Where are They?”
seems worryingly like Alistair reynold's "inhibitors". Then again an equally probably arguement may be that any life form that becomes truely space faring will only leave minimal evidence of its existance: perhaps some galactic law on the non-interference with sub interstellar civilisations?
It is also entirely possible that the sorts of signals we are looking for are no longer out there; for example we may argue that any advanced civilisation will use electromagnetic signaling in some form but it is equally likely that they will progress past this to more advanced methods such as quantum entanglement or some other wierd and as yet unknown system.
As to the great filter i think that the major one for all civilisations is - why? It may be that most civilisations can travel between stars they just dont either it costs too much - takes too long or they have become so emersed in their own virtual realities that it holds no interest for them.
I like your introduction of the Great Filter but I do not share your conclusion that finding life on Mars (or elsewhere) would in any way change our prospects of our own future. Like Niels Bohr once said "Predictions are hard to make, especially when pertaining to the future".
We do not know where the bottlenecks are were in the Great Filter in the past, and we know virtually nothing about the filter in the future.
But if the current view of the evolution of life on Earth is any indication, and the timing of the various evolutionary steps, the
we can speculate at least with some knowledge.
First off, let me note that it is surprising how quickly life originated on planet Earth. Single cell organisms like cyanobacteria filled the oceans almost as soon as these formed from the cooling planet. These microorganisms were already pretty complex : they contain simple forms of chlorophyl that engage in photosynthesis. Talking about making progress !
This early rise of life should be a strong indication that either it is very easy to create life from anorganic sources, or (more likely in my opinion) hardy microorganisms are abundant in the galaxy, traveling with comets and/or by themselves, seeding life wherever there is water. A concept called "panspermia"
Another indication that primitive microbal originated long ago in the galaxy is that the second step took a long time :
It took 2-3 billion years to get to from single-cell to multi-cell organisms. If life originated on Earth very quickly, why did it take so long for it to get to the next level. Apparently, the step to multi-cell organisms is a very narrow bottleneck in the Great Filter. If it had taken another 2 billion years, we would not have been here (yet).
Second, it seems that after that complexity problem was solved, life exploded in diversity, but apparently it took the remainer of
time to develop intelligence for tool-making and eventually a technological civilisation. Why did tool-making and technological
intelligence not develop earlier, say during the 200 million years that the dinosaurs ruled ? If even one of the sub-species of
dinosaurs would have been smarter than the others, it could have made tools, eradicate it's predators, and build a technological civilisation.. Why did that not happen ? Maybe the step from complex life to (tool-making) intelligence is again one with very low probability. Maybe that is because intelligence (or a big brain) is not so 'smart' for most species' survival ?
So then here we are. Survivers of the Great Filter of the past. We do not know how many others there were (or are) in the Galaxy
that got to the point where we are. But what we DO know is that we are not even close to expanding through the Galaxy. Technological civilisation in progress for a bit over 150 years. 150 years out of 4.5 billion years, and we already face the first major problems : depleting fossil fuels, overpopulation, cimate change etc etc. If the past 150 years is any indication, I see no reason why we would ever make it to become a true interstellar space-faring civilisation. Unless we find dirt-cheap super-fast interstellar spacecraft technology very quickly and expand through the galaxy fairly soon, we would need to find a way to live in 'harmony' with planet. Stabilize our population and recycle all resources. Else we will run out of something very quickly. If we do, then the ones that depend on these resources the most will be the ones parishing.
The point that I am making is that technological civilisation is not necessarily a 'smart' thing for the survival of the species. It might be good for a while, but when the resources run out, or wars break out over resources, then we cannot invest in the 'progress'
path to interstellar colonisation. And the winner of the wars might not be the smartest one. It might simply be the strongest of our
own species. If that happens, there does not need to be a 'cataclismic' event, we could simply slowly parish, and use less
technology along the way. It's survival of the fittest. Not survival of the smartest that rules evolution. You cannot eat a computer, so to say.
Even if we manage to stabilize our existence on Earth, and start with space colonisation of our own solar system, and even venture out to colonize other solar systems, there is still no guarantee that we will colonize the Galaxy. Unless there is something as 'warp drive', Colonists will be pretty much on their own in their new solar system. So they each will again face the same challenges that we face here today : Expand too fast, and you will deplete your resources and perish before you can move on. Expand too slow and colonisation stops because of flukes of Nature that will set-back civilisations to the point that they will parish.
Here is the bottomline : If colonists don't multiply then there is no expansion through the Galaxy. If they do multiply too fast
then they deplete their resources, endangering their civilisation. If they multiply just right, then their may be a window of
opportunity for interstellar expansion, but we do not know how big this window is or can be.
If the probability of successfull interstellar expansion (the window) is lower than the multiplication factor for a successful
expansion, then the colonisation effort will cease after a few successfull 'hops'.
To succesfully colonize the Galaxy, any civilisation (and it's subsequent species) need consistently executing the correct expansion rate over millions of hubs and millions of years.
That effort is not done before, or we would have noticed it very clearly. There would be massive astro projects in the Galaxy like
Dyson-sphers blocking most starlight from most stars, and surely we would have have been not just visited, but there would have been some astro-projects in our own solar system. Why leave such a beautiful star with so many resources alone for crawling creatures on the third planet ?
So, it looks like all ET civilisations (if there) have a limited 'lifetime'. They come and go, some may venture out of their star system, only to decline in numbers a few million years later. If that is true, then there can still be massive amounts of intelligent civilizations out there at this time. We could use SETI and other scientific means to determine upper and lower bounds for this lifetime.
That said, we need to work on facing our own challenges towards our own lifetime as a technology civilisation, if we ever want to fly to the stars...
We have our future in our own hands, and it does not depend on us finding remnants of life on Mars or anywhere else for that matter.
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The IEET is a 501(c)3 non-profit, tax-exempt organization registered in the State of Connecticut in the United States.
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