I have been fascinated by the Anthropic principle for a very long time. It also took me a while to understand it, and while I can’t claim to grasp its implications fully, I have reached a point where I see this principle around me all the time and it’s giving me a warm feeling of appreciation for the world that surrounds me.

The Anthropic Principle is also the ultimate weapon against the obscurantism pushed forth by proponents of creationism or intelligent design.

I’ve been thinking of an easy way to explain the Anthropic Principle so I thought I’d start by offering it here. I’m not quite sure where this story came from, if I read it somewhere (probably) and even if somebody ever connected it to the Anthropic Principle, so feel free to comment at will.

Story time.

One day, someone called Steve sends you an email in which he predicts that tomorrow, team A will win against team B. You don’t think much of that email and you delete it. The next day, you learn that indeed, team A won. A few days later, you receive another email from Steve which, again, makes a prediction for the result of an upcoming game. And again, the prediction turns out to be correct.

After a while, you have received ten emails from Steve, each of which accurately predicted a game outcome. You start being quite shocked and excited. What are the odds that this person would randomly guess correctly ten matches? 1 over 2^10 (1024), about 0.1%. That’s quite remarkable.

In his next email, Steve says “I hope that by now, I convinced you that I can guess the future. Here is the deal: send me $10,000, I’ll bet them on the next match and we’ll split the profits”.

Do you send the money?

Surprisingly, a lot of people fall for this kind of scam on a daily basis. If you think about this a little bit, you can probably see how the scammer did it: he started by sending a prediction that A will win to 512 recipients and one where B will win to the other 512. After the game is finished, he repeats the process with the 512 that received the right result. Every time a new match result comes in, the number of recipients is divided by two, but the remaining recipients have all received 100% accurate predictions so far.

By the time we reach the 10th match, there is only one recipient left — you. And to you, the sender of this email has proven that he has an uncanny ability to guess the future while all he did is walk through an entire solution space until he had reached a point where he can carry out his scam.

How does this short story relate to the Anthropic Principle?

Proponents of creationism and intelligent design usually make claims along the lines of observing the amazing complexity that lies around us and ascribe these observations to the existence of a god. This is very similar to yourself learning about this person who seems to be able to guess the future. Surely, only the existence of a supreme being can explain for such amazing feats, right?

Here are other similar claims:

  • “The eye is such a complex organ that it couldn’t have evolved to become what it is, it must have been created by someone”.
  • “If the atmosphere mix of the Earth had been off by just a few percents, human life would not be possible”.
  • “Our cosmos would not exist if the constants that underlie it were off by just a tiny fraction of a decimal”.

Are all these numbers so remarkable that the only way to explain them is by the existence of a supreme being?

Of course not. There are millions of universes that are similar to ours, and which have all these microscopic variations in their constants. And if you’re not convinced, it’s easy: just go ask the people who live in these universes. Except that… you can’t, of course. Because life never emerged in these universes.

What happened is that you got lucky: you were born in one of these few universes where life was possible. Unlucky people never realized that they were unlucky since they were never born, and as such, they were never able to ponder these questions.

This realization is the very definition of the anthropic principle: all these magic values that surround us and that make life possible are actually unremarkable, because they, and you, are the product of a statistical event. There is nothing so magical about our eyes that can only be explained by the existence of a supreme being. The simple truth is that if the eye was not the complex organ that it is today, you wouldn’t be around to ask questions about it.

Interestingly, the Anthropic Principle is not mutually exclusive with the existence of a deity (actually, nothing really is, which is part of the problem). You can still believe that some god decided that you would be part of the lucky experiment, but the Anthropic Principle is certainly very strong supporting evidence for the mechanism of evolution and also the proof that a lot of the seemingly magical properties that permeate the world around us can be very simply explained by high school level probability concepts.