Music: Dreamline - Rush
Recently, I was reading Nick Bostrom's (Director, Future of Humanity Institute; Professor of Philosophy, University of Oxford) article: Where are They? Why I Hope the Search for Extraterrestrials Life Finds Nothing and I found myself questioning some of the assumptions. What better place to voice my own views than in my blog. So, here we go.
Dr. Bostrom's reasoning behind the title essentially breaks down into a discussion of what's referred to as 'the Great Filter' and it's affect on our future. A Great Filter, is a concept that describes an incredibly difficult stage in in a process that is effectively a roadblock to the vast majority of species passing through it. For example, a stage in the development of a galactic civilization--a highly improbably developmental stage, a natural disaster, or autogenocide--that has a very high probability of ending the existence of most species that pass through it (by majority, it's meant >99.9999% -- not precisely, but you get the idea).
Why do we need the idea of a Great Filter? Well, if there is no Great Filter then, with the vast number of planetary systems in the galaxy (not to mention the universe), and the long expanse of time, alien species--including the highly advanced--should be everywhere. But they're not. So why not? (This is known as the Fermi Paradox).
Dr. Bostrom offers several possible candidates for a Great Filter, most of which I agree with. He also catagorises them into Early Filters (in our past) and Late Filters (in our future).
Early Filters
1) development of life (early self-replicators) from inorganic material
2) evolution of eukaryotes from prokaryotes
3) evolution of multicellular life
4) evolution of sexual reproduction (I'm not sure this is a large evolutionary leap, even bacteria have sex)
Late Filters
1) natural disasters
2) technology-induced autogenocide (an existential catastrophe)
The relationship to alien bacteria comes when you think of the consequences of the Early vs. Late Great Filters in respect to finding life in the universe.
If the Great Filter is an early one, then we would expect there to be relatively little life in the universe. In fact, we would be a rare, or possibly the only, species lucky enough to have survived. In this case, our chance of finding other life 'out there' would be almost non-existent. However, our species should then have a future devoid of any extinction-level surprises.
If, however, the Great Filter is a late one, that is, still in our future, then we should expect to find simple life, and even up to our own tech-level, on other planets. In fact, on a great many planets. For astrobiologists this is a great scenario, but for our species, not so much. It would mean that we still have to face the Great Filter. Probably in our near future. And the odds of our survival as a species would be exceedingly low.
It's scary, but well-reasoned stuff and I'm not here to detract from the general idea. I did, however, want to offer a tempered alternative.
My own view of the development of life in general, and especially intelligent life (from the 1 data point we have) is that it proceeds through what I call an annealing process.
For clarification, to anneal is (the free dictionary):So I envision the road to intelligent life as a series of catastrophic shake-ups of the biosphere (heating=add energy) that allows the biosphere to 'cool' in a new direction, with the development of new species.
1) to subject to a process of heating and slow cooling in order to toughen and reduce brittleness
2) to strengthen or harden
For example, normal evolutionary processes take care of the small details. Speciation occurs in conjunction with the basic geographical evolution of the planet, and the biosphere can, and will, bubble away happily for a eons as the species evolve down one path to fit the environment, eventually reaching a dynamic equilibrium with each other and the world. But in a single interation such as this, in a relatively unchanging system, the results are likely to tend to a local minimum (there will be many more local minima than the few global minima). Which is to say that life could get 'stuck' under certain conditions, and wouldn't evolve past a particular stage. Without a geological catastrophe, very little significant evolution would occur in that system.
But introduce a global ice age (snowball Earth? - 650 million years ago), or an asteroid collision (65 million years ago) and the existing species suddenly have dramatically new conditions to influence their evolution. They will evolve in new directions until another minimum is reached and another catastrophe necessary.
Each of these stages I consider to be a new annealling process. The original system is heated up, grossly disturbed, and will change until is settles down into a new minimum. So each time the annealing happens, there are massive changes to the remaining biosphere. Species die out, giving other species, like humans, a chance to evolve that they never would have otherwise had.
Maybe I'm just being pedantic but, to me, the idea of a single Great Filter seems to over simply the development of intelligence. It seems to suggest a fairly simple, straight path with probability roadblocks in the way:
prokaryote-->[%P]-->eukaryote-->[%P]-->multicellular-->[%P]-->animal-->[%P]-->human
But my own thoughts are that the process is more akin to a multidimensional evolutionary landscape where the system could very easily find itself 'stuck' in a local minima, unable to proceed further until a random, catastrophic variable is introduced.
(a) would represent the relatively straight path of each stage in the Great Filter idea, with the filter being either at the top or bottom of the developmental stage. Presumably there would be some kind of blockage at the bottom (b) is akin to an evolutionary landscape with many local minima. If the biosphere is represented as a ball rolling down the landscape, it could easily get stuck before reaching the bottom, requiring the system to be 'heated up' to get it moving again. This image is used only as an example of a process with multiple energy minima, and is from Protein aggregation in disease: a role for folding intermediates forming specific multimeric interations, Arthur Horwich, J Clin Invest. 2002; 110(9):1211-1232. Incidentally, the complexity of protein folding mimics the evolutionary landscape I'm intending to describe, even to the point where unfolded proteins require help to navigate the landscape and reach their folded states at the bottom.
With this in mind, a Great Filter need not take the form described by Bostrom, as an extinction-level road block, reducing the number of intelligent lifeforms by killing them all off. Instead, the entire process itself could be viewed as a Great Filter with many long stops along the way, where only those reaching the bottom achieve intelligence and then move out of their gravity well to bring civilization to the universe.
So, I think my real issue with Dr. Bostrom's reasoning is that he suggests finding life, even ancient, dead, single-celled life on Mars, means that intelligent life would necessarily fourish in the galaxy (and therefore the Great Filter is ahead of us). I don't believe these can be equated. Getting from self-replicators to humans is not just a straight march of low probably steps, but a series of evolutionary minima that an ecosystem can get permanently stuck in without efficacious, sometimes catastrophic, factors acting on it. This also suggests that catastrophes are not life-ending, but only life rearranging, and are a necessary part of biophere evolution (and a way for getting through the filter). It could perhaps also suggest that, given enough time and catastrophes, most ecosystems should evolve intelligence. But clearly many, if not most, ecosystems would require vast time frames (it would, however, be interesting to know whether our own pattern of global extinctions would mimic that of another intelligent species).
Thus, without a snowball Earth (or some similar catastrophy) Earth may only be covered in bacteria or simply multicellular organisms. Without the asteriod 65 million years ago, dinosaurs might still rule the Earth. In both cases the great filter would be an 'Early' one, but the Earth would still be teeming with life. But none of it would be able to travel to the stars.
This could very well be the state of a great many planets. So, I for one, welcome any discovery of extraterrestrial life and I'm very hopeful of the future.
Insight and longevity
[stayed tuned for discussions of ways through a possible future filter]
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