This book is about the Fermi Paradox, which is also related to the Drake Equation, both of which are named for famous scientists.
The Drake Equation is intended to estimate the number of intelligent species in the universe by taking the total number of stars, multiplying it by how many planets each one has on average, multiplying that by the fraction of planets that have all the necessary conditions for life to start, etc., etc. Of course there’s a huge amount of guesswork involved in almost every number you plug into the equation, but most scientists who’ve speculated in this area have ended up with a very large number as their estimate of how many intelligent alien civilizations there are, mostly because when you start off with a number that’s so large as to almost be infinite, then even after you multiple it by several tiny fractions, the result is still a very big number.
The Fermi Paradox is based on Enrico Fermi’s famous question “Where is Everybody?,” which in the context of the conversation in which he uttered it meant: If there are so damn many aliens running around the universe, why haven’t we ever encountered any?
The author identifies and summarizes fifty answers people have put forth over the years to Fermi’s question. There’s nothing precise about the fact that he discusses fifty. Some are closely enough related that they could just as well have counted as one, some could have been divided into more than one, at least one is intended humorously, and the final one is the author’s own preferred solution that combines elements from multiple of the others. So if someone else had written the book it could have been twenty or it could have been seventy-five.
Thankfully the book is written from a rational, scientific perspective, so the author gives short shrift to the idea that UFOs in fact have already been shown to be alien craft, and even shorter shrift to the Von Däniken “ancient astronauts” malarkey (which I confess I bought into when I was about 14). He doesn’t even bother addressing the notion that the universe was created by the Judeo-Christian God for just us and is only intended to last a few thousand years. He treats evolution by natural selection as settled science; he doesn’t pretend that it’s in doubt, or that some religious hypothesis constitutes a viable competitor theory. So that’s all to the good.
The mystery isn’t just why no one’s visited, but why we haven’t seen any evidence of anyone’s existence, such as attempted communication or some other identifiably artificial activity even hugely far away.
It’s a lot easier to come up with plausible explanations for why we aren’t being visited. Interstellar travel could simply be a lot harder than we think. So many of us assume–maybe under the influence of science fiction–that it’s “just around the corner for us,” that we’ll make whatever scientific breakthroughs we need to make for it to happen. But that may simply be wrong. Perhaps even if mankind exists for thousands or millions more years, it’ll never be practical for manned spacecraft to go very far beyond our own solar system. Maybe there’s even some unknown factor–that we have no clue about at our present level of understanding of physics–that makes it physically impossible for anything to successfully transport a living being the distance necessary for interstellar travel.
It’s a little tougher to explain the complete lack of communication or other evidence discernible from a distance, however.
I think this stuff is interesting, so I was pretty engrossed in the book the whole way.
I don’t want to just list some or all of the suggested solutions and respond to them, so I’ll instead make some more general comments.
A lot of the proposed solutions, as the author points out, plausibly lower the estimate of the number of extraterrestrial civilizations, but don’t lower it enough.
For instance, one possibility is that aliens choose not to signal, because it is technologically more difficult to send a signal anyone is likely to ever pick up than it is to point antennae at the sky and listen, and/or because it happens to be something they’re not interested in (the way many people on Earth have zero interest in such matters). But while such considerations might justify reducing our estimate of the number of intelligent extraterrestrial civilizations that are discoverable, it’s really not plausible that zero such civilizations could conquer the technological issues and/or that somehow every single one of them would be psychologically disinclined to want to let other planets know they exist. That requires too much uniformity across species that presumably vary enormously after evolving in enormously varied environments.
My thought while reading the book though, is that even if each such suggestion is insufficient by itself to be a solution, if you combine them then maybe collectively they reduce the justified estimate of alien civilizations enough to make it understandable why we haven’t run into any of them yet.
Indeed, when the author finally gives his preferred solution, that’s pretty much what he says. He contends that once you chip away at the number so many times in so many ways, the upshot is that there may in fact be extremely few species intelligent enough and technologically advanced enough for things like sending radio signals or spaceships across space. Perhaps there’s only one in our particular galaxy–us.
I have a possibility that I thought of that I don’t think matches up all that well with any of his fifty solutions.
Perhaps there is something that’s an inevitable step in technological development that always, unpredictably obliterates intelligent civilizations.
Think about that supercollider thing that some people say could create a black hole that swallows up the planet and everything around it. The author happens to mention that one, and notes that the fears are completely groundless and something like that can’t happen.
OK, let’s grant that relative to the evidence available to us at present, and our understanding of how the universe works, there’s a one in a billion chance that that will destroy us. In reality, it’s either going to happen or it isn’t, so the true probability is 1 or 0. Relative to the level of our knowledge the probability is extremely close to zero, but drop that qualifying clause and the probability is 1 or it’s 0.
There only has to be one thing like that that would come as a total surprise to civilizations early in their exploration of advanced technology to do the trick. Maybe there’s something you can do with gravity or antimatter that would provide basically unlimited power if it worked, it absolutely looks like it should work, and it is easily discovered once you have gotten slightly beyond where we are technologically, but in fact it creates some weird quantum Escher drawing-type fold in the universe that instantly wipes out your planet.
It’s the kind of mistake you can’t learn from. There won’t be anyone left to say, “Ah, now we need to make a slight adjustment in our theories. Just as Newtonian physics works in almost all circumstance, but there were a few weird things at the margins that required relativity and quantum theory that Newton could have never imagined, now we see there’s something at the margins of the margins that requires this still more sophisticated theory.” And if it’s the kind of thing that’s easy to discover shortly after radio and primitive rockets to the moon and such, then maybe every intelligent civilization eventually slips on this particular banana peel before they quite get to the stage where they would have achieved interstellar travel or at least communication.
Precisely when a civilization hits that surprise doomsday will no doubt depend on many factors. For us, perhaps depending on the various relevant contingent factors, it could be 2020 or 2150 or any time in between that we figure out that firing neutrinos into Pop Rocks should generate an incredibly useful laser-type phenomenon, but sooner or later we will, and it’ll unexpectedly turn every molecule of water on the planet into ice-nine and we’ll all be dead.
This idea has a clear advantage over the sociological solutions that the author says can only plausibly account for why some intelligent civilizations don’t last, like the notion that they destroy their planet with pollution, or that they develop nuclear weapons and can’t stop themselves from warring with them until they’re all dead.
As noted, it’s highly unlikely that every alien civilization will have the same psychological or sociological flaws like that. (Though I’m pessimistic enough to think that self-destruction through stupidity may indeed be depressingly common.) But the laws of physics don’t differ from place to place. And if there’s some really bizarre unexpected one that obliterates scientifically advanced civilizations in their early stages, then they’ll all fall into the same trap.
Anyway, there are all kinds of things like that that one can speculate about after reading this book.