Algorithms
Equivalence
Emergence
Math
The Anthropic Principle
Substrate-Independence
Significance
Today’s topic is something I’ve long struggled to wrap my head around. In fact, I’ve gotten it wrong in previous blog posts, and only recently have I come to really understand it. This topic is called the Anthropic Principle, and it’s a method for inferring knowledge about our surroundings by observing that we are there.
Suppose you wake up in a locked room. There is a note on the ground, telling you that you are in an experiment. There are a thousand rooms just like this one. Nine hundred ninety-nine of them have their doors painted red, and one has its door painted blue. You look up, and notice your door is blue.
Before the experiment began, the researchers flipped a coin. If it landed heads, a thousand people would be drugged and each put into one of the rooms. Nine hundred ninety nine would find themselves in rooms with red doors, and one in a room with a blue door. If the landed tails, only one person would be drugged and wake up in the room with the blue door.
The note says you must guess whether the coin landed heads or tails. If you get the answer right, you get a hundred dollars. Which do you bet, heads or tails?
On the surface, it seems like the odds are equal, 1:1. After all, a coin can either land heads or tails, and each possibility has one person behind a blue door. However, we’re ignoring part of the story, so let’s look at the probabilities of each possibility.
If the coin landed heads, you would only have a probability of 1/1000 of landing in the room with the blue door, and a 999/1000 chance of landing with a red door. If the coin landed tails, you would be in the room with a blue door, and have 0 chance of a red door.
Let’s put these together. The chances of you getting a red door, written as heads:tails, is .999:0. The chance of you landing at a blue door is .001:1. This means, if you wake up in a room with a blue door, it is a thousand times more likely the coin landed tails than it landed heads!
Wait a minute, you say. If the coin landed heads, someone would have to be with the blue door. How do you know that’s not you? The answer is, we don’t have absolute certainty. However, the fact remains we have a thousand to one odds against it, so the reasonable bet by far is to choose tails.
Now that we’ve gone through that example, let’s take a step back and remember the big picture of what we did. We were given a little bit of information, and based on the fact that we were there, deduced more information. That is the Anthropic Principle.
There are many applications of the Anthropic Principle, and we will talk about some of them in future posts. For now, let’s apply it to the situations most people turn to first: life on Earth and in the universe.
The history of science has shown us that we are not nearly as significant in the grand scheme of the universe as we might like to think. The sun and planets do not go around the Earth, the Earth goes around the sun. Neither the sun nor the Earth is a special feature of the cosmos; there are trillions of stars in each galaxy, and trillions of galaxies in the universe. A significant fraction of the stars are sun-like, and a significant fraction of stars have Earth-like planets. There is nothing special about the sun or the Earth.
This idea, that we aren’t special in the universe, is called the Mediocrity Principle (also known as the Copernican Principle). Because the Mediocrity Principle applies to so many things we know about, it is easy to assume it applies to things we don’t know about too. Perhaps, for instance, life like us exists all over the universe.
But in the realm of the unknown, the Anthropic Principle steps in and says, “not so fast.” We don’t live on a random planet, we live on a planet where the conditions were right for life to emerge, and continued to be right for life to evolve, until intelligent life appeared. Regardless of whether life is common or rare in the universe, this observation would be the same; we are in a place where the conditions are right and have been right for intelligent life. Thus, even if it turns out Earth is the only planet in the entire universe where intelligent life exists, we should not be surprised.
Just like there are people who want us to occupy a special place in the universe, there are people who want everything about us to be commonplace. Both of these beliefs are fallacious. We know our planet and our star are not special, but we don’t have nearly enough evidence to determine how common life is. Given only the information we have, there is roughly the same probability that there are a billion trillion civilizations in the universe as there is that we are the only one.
On a larger scale, the Anthropic Principle can be applied to the universe as a whole. The laws of physics, as we currently understand them, have a bunch of parameters that don’t seem to follow any pattern. However, it seems as though if any of them were slightly different, life could not exist at all.
Let’s apply the Anthropic Principle to this question. Assume we don’t know whether life exists or not. If the physical constants must be what they are, and every other combination is impossible, we would bet against life existing without hesitation. After all, the number of permutations that allow life are vastly dwarfed by the number of permutations where life is impossible. So if there is only one combination, it would be vastly more likely to be one where life is impossible.
However, if the physical constants could have been different, we have another story. It would mean they could be tuned to allow for life to exist, making a universe that allows life vastly more likely.
The fact that we are here, that we observe ourselves to exist, is evidence via the Anthropic Principle that the physical parameters of the universe could have been different. And we know this without even knowing how they were set!
So then, what are the possible explanations for why the parameters of the universe allow life to exist? It could be that there are many universes, each with their own physical constants, most of which don’t have life. It could be that the universe was created for life, either intentionally or unconsciously. See the Multiverses post for more discussion on these. And finally, it may be that if something is unobservable, it is the same as not existing. If this is true, then even if there is a multiverse, all universes have life, because if a universe cannot be observed, then it doesn’t exist. We’ll talk more about that in the next installment of the Consciousness series.
If the Anthropic Principle still confuses you, that’s okay. I’ve been thinking about science and philosophy for years, and I’ve only come to understand it a few months ago. Still, it’s worth spending the time to understand, because it opens up new paths by which to explore deep and interesting questions.
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