If you prefer to listen rather than read, this blog is available as a podcast here. Or if you want to listen to just this post:

Or download the MP3


Having explored at some length in our last post the idea that Fermi’s Paradox may offer strong support for the existence of God.  As well as the idea that assumptions made about extraterrestrial communication line up better than might be expected with the process of prayer. I want to flip the coin and look at what the conventional wisdom is as far as the Paradox. For my examination I will be mostly drawing from If the Universe Is Teeming with Aliens … WHERE IS EVERYBODY?: Fifty Solutions to the Fermi Paradox and the Problem of Extraterrestrial Life, by Stephen Webb. There has obviously been quite a bit written about the paradox, but this appears to be one of the only (if not the only) book length treatments. My discussion will use the first edition of the book, which has 50 potential explanations for the Paradox. The second edition, which I have yet to acquire has 75 potential explanations. I cannot speak definitively about the second edition, but of the 50 potential explanations in the first none resemble the explanation I offered in my last post. But otherwise it is admirably comprehensive.

Webb breaks extraterrestrials into three broad categories:

  1. They are here.
  2. They exist but have not communicated with us.
  3. They don’t exist.

The first possibility is broader than the initial title would suggest. It essentially encompasses all scenarios under which aliens exist, and are aware of us. These explanations range from the humorous (They are here and they call themselves Hungarians) to explanations for why, if they exist, they might choose to hide from us. The classic example of this thinking is the Prime Directive from Star Trek, the principle that the federation will not interfere with any less advanced civilizations.

Interestingly enough the final explanation in the “They are Here” section is titled “God Exists”. From the title, at least, it sounded like it must be very similar to my own thinking. It wasn’t. Webb spends a couple of paragraphs talking about some vague theological issues, but then spends the rest of the section (four more pages) examining the idea that there seems to be no good reason for the constants of the Universe to have the values they do (for example the strength of the weak nuclear force or the mass of an electron.) From there he goes on to discuss a theory of universe evolution under which new universes might be created by black holes so universes would “evolve” to maximize black hole production. If the physical constants which lead to the creation of black holes are similar to the constants necessary for the emergence of life you might end up with the second condition being a byproduct of the first.

The second possibility, that they exist but have not communicated with us, generally boils down to the idea that on top of the enormous number of stars and the enormous amount of time that has passed, which argue in favor of alien life, that there are other enormous numbers: the distance between habitable planets (less now than a couple of weeks ago); the number of ways language and communication could develop; the different types of intelligent life; and so forth, which argue against alien communication. This could mean that it’s just too far, or that they are communicating with us and we don’t understand, or in one of the more off-beat explanations, perhaps most worlds have skies perpetually shrouded in clouds. In which case, would they ever even develop astronomy, or even a full Newtonian understanding of the Universe?  

The final possibility is that there is some kind of filter which works against intelligent extraterrestrial life. Some process which keeps life from starting at all, from reaching sufficient complexity, from developing consciousness, from lasting long enough to spread, or from accomplishing any of the thousands of steps required to have a truly interstellar civilization. As you can imagine, such a filter might be behind us, or it might be in front of us. Examples which have been offered for filters we have already passed, have included: the difficulty of moving from prokaryotes to eukaryotes, galactic catastrophes like supernovas, getting life started in the first place, and even plate tectonics.  

Examples which have been offered for filters yet to come include: blowing ourselves up with nukes, losing ourselves in virtual reality, civilizational collapse, or of course galactic or solar catastrophes yet to come. Another explanation is that aliens do exist, but they’re aggressive and warlike and no one wants to risk initiating communication (or what’s termed Active SETI) because they’re all afraid they’ll be discovered and destroyed.

This is of course one of the things that makes Fermi’s Paradox so fascinating, the number of possible explanations is huge and those explanations can tie into anything (from the Runaway Consumerism to having a particularly large Moon.)

I said that Webb’s book offered up 50 explanations for the paradox. That’s not entirely true. He actually offers up 49 explanations and then for the 50th he offers his own explanation. He mentions in one of the introductory sections that the 50th explanation will be his explanation for the paradox, and while reading the book I was intensely curious about what his explanation would be. And if, for whatever reason you were thinking of reading the book (which I recommend only if you are REALLY interested in the paradox) and you don’t want to be spoiled you should stop reading now…

Webb’s final solution titled “The Fermi Paradox Resolved…” is not unique, it’s not some new take on things or an explanation that hasn’t been offered already, it’s the combination several explanations. Having gone through 49 possible explanations for the paradox Webb’s answer is that we are alone. This is an interesting conclusion. And I think he reaches it somewhat reluctantly, but it carries an enormous number of consequences, not all of which he’s willing to grapple with. But before we get to that let’s examine how he arrives at his conclusion.

In a similar fashion to how Fermi and Drake arrived at their numbers, Webb comes up with is own filter for determining how many intelligent civilizations there should be. All of his filters come from the previous 49 explanations of the paradox already laid out in his book. And in a fashion similar to Drake, he starts with the number of stars in the galaxy. He then multiplies that by the average number of planets per star. This gives him a number of 10^12 or one trillion potential planets. Starting from there he begins to filter planets out. His filtering process is somewhat involved and scholarly, but it’s interesting enough that I’d like to walk through it. He goes through seven steps (actually 8, but one of his steps doesn’t actually filter anything, so we’ll skip it.)

Step 1- Eliminate any planets not in the galactic habitable zone. Most people are familiar with the solar habitable zone, (discussed more in step 3). This is the same thing on the galactic scale, and mostly has to do with the frequency of large scale galactic catastrophes. If you’re too close to the center of the galaxy, then the density of stars is such that galactic catastrophes would be frequent, potentially too frequent for life to ever establish a foothold. Consequently only stars out on the rim of the galaxy would accident free enough for life to develop, and this region is the galactic habitable zone. Webb uses an estimate of 20% of stars being in this zone so that takes us down to 200 billion planets.

Step 2- Eliminate any planets which don’t orbit sun-like stars. Bigger stars burn too fast and smaller stars don’t give off enough energy. Only 5% of stars are sun-like (G-Type) which leaves us with 10 billion planets.

Step 3- Eliminate any planets which aren’t in the continuously habitable zone (CHZ) of the star. This means, not only do they currently have to be at a distance from the star where water is liquid, but they have to have always been at that distance. He puts this number at 0.1% of planets. Which frankly seems extremely conservative particularly in light of the data we’re getting from Kepler which is biased against Earth-sized planets. To be fair to Webb part of the low estimate comes from the idea that the Sun was much fainter in the past. That filter takes us to 10 million planets.

Step 4- Eliminate any planet in the CHZ on which life doesn’t actually emerge. After saying that he considers life to be a probable occurrence for planets in the CHZ he, somewhat unexpectedly, goes on to say that it would happen on only 5% of them. Which takes us to half a million.

Step 5- Eliminate any planet where life gets wiped out by a supernova or some similar solar or galactic catastrophe. Here he’s fairly optimistic and thinks that only about 20% of life would be eliminated in this fashion. I think on this step, contrary to all the other steps he is too optimistic, that possibly far more than 20% could be wiped out by something like a supernova or some giant collision. Though we have also eliminated the planets most prone to this in Step 1. In any event this takes him to 400,000.

Step 6- Eliminate any planet where life doesn’t ever get to be multicellular. Conveniently he places the odds at life making the jump from single celled to multi celled at 1 in 40 which works out nicely to give us 10,000 planets with multicellular life.

Step 7- Eliminate any planets where life doesn’t produce an intelligent, tool-using, mathematical species capable of developing technology. He thinks the odds of this happening are least 1 in 10,000 (0.01%) and possibly much greater which means that there is only one of those civilizations, us. We are alone.

At first glance the whole process seems scientific, but similar to the Drake equation Webb has very little evidence for any of his estimates. The late Michael Crichton of Jurassic Park and Andromeda Strain fame once gave a talk about the Drake Equation at Caltech. His purpose was to take a shot at global warming, and perhaps you’ll dismiss it on that grounds, but his point was nevertheless valid:

This serious-looking equation gave SETI a serious footing as a legitimate intellectual inquiry. The problem, of course, is that none of the terms can be known, and most cannot even be estimated. The only way to work the equation is to fill in with guesses. And guesses-just so we’re clear-are merely expressions of prejudice.

Nor can there be “informed guesses.” If you need to state how many planets with life choose to communicate, there is simply no way to make an informed guess. It’s simply prejudice.

As a result, the Drake equation can have any value from “billions and billions” to zero. An expression that can mean anything means nothing. Speaking precisely, the Drake equation is literally meaningless, and has nothing to do with science. I take the hard view that science involves the creation of testable hypotheses. The Drake equation cannot be tested and therefore SETI is not science. SETI is unquestionably a religion.

His point about SETI being a religion is particularly telling for the purposes of this blog and our discussion. As is his point that the guesses are an expression of prejudice. In the case above it’s obvious that Webb already has a final answer in mind before he started plugging in his guesses, it didn’t just happen to come out with one to his amazement and surprise, he arranged his guesses so that it would come out as one.

Think about that for a second, you start off with one trillion, and in the end you’ve created a filter that leaves just one planet left out of the one trillion you started with?  Not zero, not a million? Imagine that you were going to create a set of seven filters which when applied to 7+ billion humans left you with one and only one person, and that you could only use natural criteria, like weight and height, not artificial filters like a social security number or the name of the town they were born in. It would be impossible, and recall that Webb starts with one trillion planets, not seven billion, so he’s already dealing with potential set over 100 times as large.

But let us for the moment assume that he’s correct. That in all the galaxy we are the only intelligent, technological life. As I already mentioned, the consequences of that are far-reaching and extreme.

First it reverses one of the major trends in science. The trend towards de-emphasizing humanity’s place in the universe.

In the beginning if you were the ruler of a vast empire you must have thought that you were the center of creation. Alexander the Great is said to have conquered the known world. I’m sure Julius Caesar couldn’t have imagined an empire greater than Rome, but I think Emperor Yuan of Han would have disagreed.

But surely, had they know each other, they could agreed that between the two of them they more or less ruled the whole world? I’m sure the people of Americas, who were entirely unknown to them, would have argued with that. But surely all of them could agree that the planet on which they all lived was at the center of the universe. But then Copernicus comes along, and says, “Not so fast.” (And yes I know about Aristarchus of Samos.)

“Okay, we get it. The Earth revolves around the Sun, not the other way around. But at least we can take comfort in the fact that man is clearly different and better than the animals.”

“About that…” says Darwin.

“Well at least our galaxy is unique…”

“I hate to keep bursting your bubble, but that’s not the case either,” chimes in Edwin Hubble.

At every step in the process when someone has thought that humanity was special in anyway someone comes along and shows that they’re not. It happened often enough that now they have a name for it, The Copernican Principle (after one of the biggest bubble poppers). Which, for our purposes, is interchangeable with the Mediocrity Principle. Together they say that there is nothing special about our place in the cosmos, or us, or the development of life. Stephen Hawking put it as follows:

The human race is just a chemical scum on a moderate-sized planet, orbiting around a very average star in the outer suburb of one among a hundred billion galaxies.

This is what scientist have believed, but if we are truly the only intelligent, technology using life form in the galaxy, then suddenly we are very special indeed. Which, as you’ll recall, is what religion has been arguing all along, and it is primarily against religion that these various attacks at uniqueness have been leveled.

Now obviously it’s not impossible for the Copernican principle to be wrong, but you can still imagine that it presents a problem for scientists to explain. Particularly for scientists who would rather not give any ammunition to the unbelievers. In other words, for militant atheists, the idea that we might be unique and special, that the universe and the galaxy and the solar system might have been designed for us, is deeply troubling. And if you talk to any of them who are knowledgeable about this issue, they have a response ready, the Anthropic Principle.

The Anthropic Principle is complicated enough that it almost certainly deserves it’s own post, particularly as we are already 2500+ words into this post, but in short what it says is that there’s nothing remarkable about our uniqueness, because only our uniqueness allows it to be remarked upon.

To expand on that a little bit. Conscious life will only be found in places where conditions allow it to exist, therefore when we look around and find that things are set up in just the right way for us to exist, it couldn’t be any other way because if they weren’t set up in just the right way no one would be around to do the looking.

As I said the subject is deep enough that it will probably eventually get it’s own post (though not next week I’m feeling a hankering for something different.) But I will end with four points about the anthropic principle to chew on:

1- It’s logically true, but logically true in the sense that a tautology is logically true. It basically amounts to saying I’m here because I’m here, or if things were different, they’d be different. Which is fine as far as it goes, but it discourages further exploration and a deeper understanding rather than encouraging it.

2- It’s generally used as an answer to the question of why all the physical constants seemed fine tuned for life. To which people reply there could be an infinite number of universes, so we just happen to be in the one fine tuned for life. Okay fine, but is there any evidence that the physical constants we experience don’t apply to the rest of the galaxy? Because that’s what we’re talking about when we talk about Fermi’s Paradox. In fact we don’t even have any evidence that they are different anywhere in the visible universe of the 100 billion additional galaxies. In other words if the Earth is fine-tuned for life as far as physical constants, so is the rest of the galaxy, at a minimum.

3- It’s an argument from lack of imagination. Or in other words Webb asserts that we are alone because there has not been any evidence to the contrary. It is entirely possible that we have just not looked hard enough. Webb admits this possibility of course, but it is not his preferred explanation, which is that we’re alone, because of the factors which I mentioned above, but all of those factors could just be a lack of imagination. Imagining how life could develop in the center of the galaxy, how life could develop outside of the CHZ (say Europa) or, especially, imagining how we might already be in contact with extraterrestrials and just call it prayer.

4- It’s not science. Just as Crichton (and others) argue that SETI is a religion, so is the anthropic principle. In this particular religion it’s easier to believe that we’re alone and use the anthropic principle as justification then to think that we’re not alone and that God exists. It’s the religion of, humanism, especially the belief that there is nothing beyond the limits of rationality and science.

When I said the consequences are far-reaching and extreme, this is what I meant. If we are truly alone, if we are the lone intelligence in the entire observable universe then that puts us in a position of awful responsibility, and takes us back to the premise of the blog. My assertion is that the harvest is past, the summer is ended, and we are not saved. If you assert that humanity is alone, that we are all there is, then what you’re saying is:

The harvest is past, the summer is ended, and we HAVE to be saved.