How Things Work: Anthropic principle explores the universe's coincidences

Credit: Lauro Roger McAllister via Flickr Credit: Lauro Roger McAllister via Flickr

Have you ever wondered why the mathematical constant pi is approximately equal to 3.14159? Why the gravitational constant is of the order 10-11? Why stardust gathered in such a precise way as to create Earth as a habitable planet? These constants constitute formulas and mathematical equations that dominate our lives: The sun in our sky, the vehicles we use, and even the water that we drink. The coincidental way in which all these values fit together to create a world compatible for sapient life is explored through the concept of the anthropic principle.

Before we delve into the anthropic principle, it is worthwhile to look at some of the coincidences which inspired it. The first is that the electromagnetic force is about 39 orders of magnitude stronger than the gravitational force. Had they been closer in magnitude, the stars would have collapsed long before the existence of life in the universe.
The second coincidence is the temperature of the sun. If the sun happened to be a little hotter or a little cooler, photosynthesis would not be able to occur, putting an end to the natural biochemical processes necessary for life on Earth.

A third coincidence is the value of pi. If pi were larger or smaller than it is, then all that we perceive as circular, such as orbits, or spherical objects, such as planets, would be completely reshaped. This would, in turn, lead to different planetary motion and life might not have appeared on Earth.

The anthropic principle seeks to summarize what we can learn from these incredible coincidences. In 1973, a meeting was held in Cracow, Poland in commemoration of the 500th anniversary of Copernicus’ birth. It was at this conference that theoretical astrophysicist Brandon Carter first brought up the idea of the anthropic principle. In 1974, Carter gave the first official presentation of the principle to the world, hypothesizing that the anthropic coincidences are not purely the result of chance, but are actually built into the structure of the universe that we know.

Carter proposed two versions of the anthropic principle. Carter’s weak anthropic principle says that our location in the universe is privileged. In other words, the coincidental way in which all the parameters of the universe fell into the narrow range which resulted in life on Earth is purely the result of being in the right place at the right time. This grand coincidence does not necessarily mean that the world was created for humans; rather, because our universe happens to be able to sustain human beings, human beings are capable of questioning these coincidences.

On the other hand, Carter’s strong anthropic principle is much more theological, and states that the universe was created specifically so that life capable of observation and reflection would one day emerge from it.

Most scientists today believe that the weak anthropic principle is a tautology — that it is always true — because if our location and environment had not been privileged or suitable, humans would not exist to observe it in the first place. But what also makes the anthropic principle truly valuable is its strong version, which we can interpret in the following way: The universe is compelled, or designed, to have certain properties such that one day conscious life would emerge from it and, consequently, observe this universe. This implies that there may also be an infinite number of other lifeless universes in which at least one factor or property failed to fall within the specific range required for life. But our universe, just as the strong anthropic principle states, is the one in which the nature gets all its properties correct — and our very existence testifies this argument.

The anthropic principle tells us that everything in this universe was predetermined, because if the values of constants are not set correctly for life (as could be the case in another hypothetical universe), then no life would emerge to discover these constants. On the contrary, the constants and coincidences known by us are proof that the right combination must eventually occur. Nevertheless, critics to this principle argue that the anthropic principle is a non-scientific concept and that it is instead more of an induction process — something that we assume to be true because of past experiences. Moreover, even the tautology of the weak anthropic principle is questioned, because we have concluded that the anthropic principle is valid by using humans’ axiomatic system, but even this axiomatic logical system is a tool that we developed to understand this universe, which follows from the anthropic principle. This is just like using the outcome of a theorem to prove a theorem, which may be subject to the problem of circular explanation.
This brings us back to our initial position — the unbelievable coincidences.

The physical constants of our universe are balanced in such a way that it seems they have been fine-tuned and carefully made for our existence. Why?