Point a decent-sized radio antenna at any part of the sky, or just look up at it all on a cloudless night: not a trace of aliens - doesn't that strike you as odd?
   It struck physicist Enrico Fermi as very odd: if the laws of nature are universal, working in the same way all over the galaxy, and have produced the Earth, life (and us) here, then they should have produced Earths (and 'us') everywhere. Worse, our solar system may be more than four billion years old, but the Universe itself is more than thirteen billion - so there should have been Earths out there with their versions of us for aeons already. Yet here we are, apparently alone. This has become known as the Fermi Paradox - in Fermi's own words, 'Where is everybody?' - and the more we learn, the more mystifying it becomes: the Search for ExtraTerrestrial Intelligence programme has been running for decades now, without detecting even a single stray signal, while at the same time the latest space probes are discovering new planets by the truck-load.
   In fact, this isn't a full-blown paradox at all, just a flat contradiction between what, on the one hand, we believe to be the way the Universe works (its laws of nature, science as a rationale, reason itself for that matter) and, on the other, the Universe we seem to be living in. One of these must be incomplete or even wrong in some way. Perhaps the former; to give just one example, perhaps there are unknown phenomena at work, vast cataclysms which periodically sterilize the entire cosmos and set the clock of life back to zero each time - if that were the case then we would, in a sense, be the first. Or maybe it's the latter: Fermi's 'everybody' are all out there, but for some reason don't want us to know that.
   This book is a compendium of fifty possible explanations of that sort, from the stolidly scientific to the wildly speculative - and flawed: many contain assumptions about alien psychology for instance (just one alien civilization behaving differently from the rest would flood the galaxy with radio transmissions or speeding spaceships). It's a thorough round-up which also reminded me just how odd all this is; any way you look at it, that silent sky may be the single most important fact our civilization has. ( )

In the (COVID-19 free!) summer of 1950, physicist Enrico Fermi was discussing the possibility of extraterrestrial intelligence over lunch. He asked "where is everybody?" In a universe so old and large, other intelligences than ours should have arisen long ago, and they should be here now, on our planet and in our skies, starting from before we evolved. We see no fundamental physical reason why we humans could not expand into and settle our galaxy in 1-100 million years. That's a long time by human standards, but only 1% or so the age of the universe. If we could do it, why haven't others done it already? They've had plenty of time. At least, their radio communications should be everywhere we look.

Author Webb starts with brief introductions to Enrico Fermi, to the idea of paradox, and to the Fermi Paradox itself. Fermi is probably the most distinguished of those 20th century physicists whom most people haven't heard of, known for cutting to the heart of an issue.

Seven decades on, there's still no resolution to the paradox. Webb presents fifty possible solutions drawn from the literature people have produced since then, sorted into three categories.

First, "They Are Here" - or were here on Earth in the past. He starts with Leo Szilard's joke answer, "they are here and they call themselves Hungarians," referring to the many brilliant emigres from Hungary in the US at mid-century, including Edward Teller and John von Neumann. Webb disposes of flying-saucer theories, and considers that we might be in some sort of zoo or planetarium. Some of these ideas are more testable than you might guess.

The second general category is "They Exist But Have Not Yet Communicated." They're out there, but we haven't found their signal yet. Here he discusses interstellar probes, radio/optical communication, and possible reasons why they might not try to communicate, or travel, or carry out engineering on a scale visible over light years. The problem here is that any explanation along these lines must apply to all of the millions of intelligent species we like to think share our galaxy. If just one species develops technology and decides to spread out, they should have been here long ago.

Science fiction writers have mostly been aware of the paradox since the 1980s at the latest. Most of the proposed solutions in these first two categories can be matched with one or another SF story. In particular, solution number 28, "They Hit the Singularity" has been popular. Maybe we will make our selves smarter by genetic engineering or by building intelligent computers, and then sublime in some unknown sense, leaving the world behind. Webb points out that this solution has the same flaw as many of the others - if it doesn't apply in every single instance, we're still left with the paradox.

Also popular is solution number 27, that intelligent species inevitably self-destruct. Check today's news and make your own estimate here, but remember that the solution has to apply to presumably millions of species. Will they all be selfishly stupid?

The third category is "They Do Not Exist." Webb discusses all the scientific reasons why Earth, Earthly life, or humans might be unique, at least out to great distances in the universe. Maybe we needed rare features of the Earth-Moon system, or the solar system. We seem to have come along when most of the Earth's era of habitability has passed, and we may be the only one of 50 billion species in Earth's history with the right sort of intelligence - the ability to build radio telescopes.

Here, the book, published in 2002, is sometimes out of date. Webb wonders whether rocky planets like ours might be rare. Progress in finding extrasolar planets means we now know that they are fairly common. Webb also dismisses the cognitive abilities of other animals; would be interesting to see what Peter Watts would think about that.

Webb's last solution is his own. He goes through the various inputs into estimates of the prevalence of intelligence, and decides that we are indeed alone. If we come to an end then intelligence, at least technologically-capable intelligence, ends everywhere.

For me, that's maybe not a bad idea to keep in mind amid political unrest and pandemics. The stakes are higher than we may think. ( )

What an interesting book! Not only did I learn a great deal about the landscape of theories regarding the Fermi paradox, but I also learned a lot about a variety of related topics, including astrobiology, evolution, probabilities, maths, quantum mechanics, and general/special relativity! While I don't 100% agree with the author's final conclusion that we are likely alone in the Galaxy, if not the Universe as a whole, I was able to clearly follow and understand his reasoning in support of it.

Another important perk is that I was able to speed through it in only two days of dedicated reading, which is a big deal for me. The last few books I've read have taken a month or more each, which has got me feeling pretty badly about my reading speed. But now that I've seen how fast I can read, I feel hopeful that maybe it won't always be such a slog. Maybe I should just be reading more nonfiction. ( )

This is an outstanding presentation of the author's evaluation of fifty possible explanations for Fermi's paradox, i.e., why we have never contacted an alien civilization when the logic and the math seem to indicate that they ought to be out there. I particularly loved the neo-Aquinas layout of placing each explanation is a discrete chapter and working through it. I also agree with his conclusion. ( )

I was totally unimpressed by this book. If I could have given it a zero, I would have. As it is 1/2 star is the least I can give it. In some calculations I believe the basic math is wrong by factors for 10 or 100 due to misplaced decimal points. ( )