These are just some additional things I noted which don’t fit into the main review:
The first is that it was funny reading about all the 70s doomsday scenarios. The population bomb. The limits to growth. Runaway environmental collapse. Mass starvation and wars fought over water and crops in the 2000s. None of that happened and all the hysteria was, in retrospect, completely unfounded, despite appearing very convincing then.The world population is now 7 billion, but mass starvation has not yet appeared and indeed in most developed countries the problem is one of underpopulation and low fertility. The only real place where fertility rates remain high and overpopulation is a possible problem is sub-saharan africa, and hopefully rates will lower there soon. Neither have the limits to growth or “peak oil” ever shown themselves to be real issues thus far. We are still growing, albeit slowly, but this slownss is probably due to aging demographics and technological stagnation/slowdowns in all technology except the computer sector rather than a shortage or raw materials and/or petrochemicals. This has made me slightly update in favour of civilisations social stability and against today’s crop of doomsayers.
The second is that I was surprised at the amount of opposition there was to NASA and the Apollo missions. Today they are an exemplar of American Greatness, as well as an inspiring monument to humanity’s technological prowess. Back then they were seen as a ridiculously expensive vanity project attacked from the right for its extravagance and from the left because it wasn’t money spent on their pet projects such as the inner cities (and also probably because it could have (and did!) embarrass the Soviets.). NASA and Kennedy were definitely correct on this one. In terms of benefit for dollar spent the space race and the Apollo program definitely returned rewards higher than the vast majority of other government spending. And the inner cities are a black hole into which untold billions have vanished since the sixties with nothing to show for it.
The third is how much O’Neill underestimates the progress in automation and computing technology. His ideas for a 2010s computer is about as powerful as a 1970 mainframe, but can fit on a desktop, and costs just a bit less than an automobile(!). His idea of space requires a huge amount of people working in the habitats on heavy industry and to pilot all spacecraft. This probably would have been accurate had his predictions come to pass, and Island One was constructed by 2000,but it just seems silly now. Space exploitation will be a highly automated affair, with few humans enjoying life in space. His idea of a lone family going off and homesteading among the asteroid belt seems positively antediluvian. With self-replicating probes, telecontrolled from earth (to say nothing of more general AI) we should be able to reach extremely rapid growth rates in our space industial capacity given a relatively small starting “seed”.
My final speculations are about what this means for the Fermi paradox. He makes a strong case that spacefaring civilisations will not be planet based, but will instead use habitats strewn throughout the solar system. This is good, because it makes “aggressive” and “dark forest” scenarios much less likely. The principle behind a dark forest scenario is that attack is lethal, undetactable, and unstoppable. This is true of relavistic kill vehicles, or RKVs. These are just chunks of rock that have been accelerated to a significant fraction of the speed of light and set on a trajectory intercepting the enemy planets. And it is true; they are largely undetecable until it is too late. But this only applies to a planetary civilisation. Once most of the economy and population is based off of habitats then the civilisation becomes immune to such destruction. It simply isn’t possible to detect habitats from that range, let alone send an RKV on a trajectory to intercept one, and space is so large that the chance of hitting a habitat by randomly firing at the system is practically zero. The only way to truly exterminate a civilisation will be the old fashioned way, by sending a fleet to their system and painstakingly hunting them down (unless there is a long distance way to trigger their star to nova or something). This makes interstellar war a much more expensive and involved undertaking so civilisations will ahve much less of an incentive to destroy other civilisations they detect, just in case they become a threat later.
This shifts the balance of probability much closer to what I believe is the true answer - an early filter. The lack of our ability to simulate or recreate the beginning of life is suspicious as we know a lot about the composition of the ancient ocean. If life begins easily in such circumstances we should have demonstrated that already. Most likely, spontaneously assembling enough proteins together with cell walls to create the “minimal replicating unit” necessary for life requires an incredibly unlikely confluence of elements. The evidence against this, of course, is that it appears life began relatively shortly (within a billion years) after our planet became suitable for it. But this seeming luck could be countermanded somewhat by anthropic considerations. On the other hand it is hard to find plausible candidates for a late filter. Astronomical events like nearby supernovas and gamma ray bursts are just too unlikely to wipe out enough species. As well our specific self-destruction possibilities like nuclear war, runaway global warming, and so on. I simply can’t image these destroying a high enough fraction of species to matter. UFAI is not a possibility, because we should see an UFAI eating the universe and converting it into paperclips or whatever. So, if not an early filter, then the Fermi paradox remains confusing.
My ideal solution would be a utopian one - that all civilisations quickly discover some relatively easy source of infinite and eternal energy that they can harness from within their system, and so have no incentive to expand and colonise the rest of the universe, and they spend all their days in an eternal simulated paradise.
I think this is pretty unlikely though. Most likely is a combination of an early filter, a selection of mini-filters which together combine to render technological life extremely unlikely, or simply that we don’t have the technology to see them yet. Our capabilities in this regard are actually fairly pathetic. We have analysed in detail only a tiny percentage of our galaxy’s stars, and that with pretty small telescopes compared to what is feasible when we imagine a telescope array covering hundreds of thousands or millions of kilometers, located at the gravitational lensing focal radius of our sun which, if our space industries took off, would be feasible remarkably soon. If they are out there,however, then the apocalyptic singularitarian predictions cannot be true, as we can be pretty sure that nobody is currently converting a sizable fraction of our galaxy into computronium.
Overall, I think the silence is a good thing. A late filter is unlikely in my opinion, so the silence either means that we are alone, and the whole universe is ours to explore, or that there are aliens, but the kind of exponential expansion of the singularity and a UFAI cannot occur. Both of which are promising conclusions for the maintenance of our current type of civilisation.