Everything you experience is experienced from your personal perspective. That seems like a rather obvious statement, but it also applies to humanity as a whole. Everything we experience in the universe is from our point of view. Cosmologically that view is a very narrow window. Humanity has only been around for a moment of cosmic time. We see the heavens from the vantage point of a small rock orbiting a medium star. Our comprehension of the universe is framed by the biases of our primate minds.
It is this idea that is encapsulated by a philosophical idea known as the anthropic principle. Of all the ideas in astronomy and cosmology, the anthropic principle is perhaps the most controversial. Despite its name, there are in fact several variations of the anthropic principle.
The Weak Anthropic Principle states basically what I summarized in the first paragraph. Our view of the universe is not random. It is biased by the fact that we are observing it. For example, we observe a universe that is billions of years old because it takes billions of years for planets to form and life to evolve.
The Weak Anthropic Principle is simply a reminder that we shouldn’t read too much into observations that seem special. I live in the United States, so a random sampling of people around me finds that most speak English as their first language. I can’t presume however that humans speak English as their first language, because my sample is biased by my location. Someone living in Japan would find that most people speak Japanese.
The Strong Anthropic Principle is more controversial. It states that the universe as a whole must have conditions necessary for life such as ours to exist. For example, gravity in three spatial dimensions allows for stable planetary orbits, but gravity in four-space doesn’t. If the universe had expanded more quickly than it did, then stars and galaxies wouldn’t have formed. Too slowly and it would have collapsed back on itself.
On the one hand the strong principle is rather obvious. If the universe was too different from the way it is (gravity too strong, speed of light too small, etc.) then we wouldn’t be here. But this fact is sometimes used to argue a stronger version of the principle. Specifically, the fact of our existence means the universe must be fine tuned to a set of conditions that allows us (or a similar sentient species) to exist. This idea was first proposed by Brandon Carter in 1974, and it has stirred controversy ever since.
But that’s a story for another day.