The Anthropic Principle

The anthropic principle: where science, philosophy and theology meet

POSTED JANUARY 9, 2020

Our universe is a very fine-tuned place.  The constants of nature - those quantities that always have the same value throughout the universe - are so precisely fixed that a miniscule change in any one of them would result in a world very different from what we have now or even no universe at all.  

For example, if the strong nuclear force were not exactly what it is, elements would not be able to form. Or, if protons were not exactly 1836 times the size of an electron, elements would not be able to combine into molecules. Two other important examples are the ratio of the electromagnetic force to the gravitational force (this keeps stars from immediately collapsing) and the excited energy level of the carbon atom (without this exact level of 7.65 million electron-volts, insufficient carbon would be formed in stars to form the basis for life).  

Ethan Segal, writing in Forbes, adds another consideration - the rate of expansion of the universe.  

A Universe with too much matter-and-energy for its expansion rate will recollapse in short order; a Universe with too little will expand into oblivion before it's possible to even form atoms. Yet not only has our Universe neither recollapsed nor failed to yield atoms, but even today, some 13.8 billion years after the Big Bang, those two sides of the equation appear to be perfectly in balance.  If we extrapolate this back to a very early time — say, one nanosecond after the hot Big Bang — we find that not only do these two sides have to balance, but they have to balance to an extraordinary precision. The Universe's initial expansion rate and the sum total of all the different forms of matter and energy in the Universe not only need to balance, but they need to balance to more than 20 significant digits. 

How amazing is that?  Segal explains:

It's like guessing the same 1-to-1,000,000 number as me three times in a row, and then predicting the outcome of 16 consecutive coin-flips immediately afterwards.

The problem that scientists face is that no one has been able to develop any of these constants from theory.  The constants of nature just are what they are, and what they are is exactly what is needed for the universe to exist and for intelligent life - us - to evolve.  From the late 1800's on, as physicists and cosmologists tried to explain these observations, some began to consider extra-scientific (i.e. philosophical and religious) reasoning.  In a lecture in Venice in June 2004, Mariano Artigas, author of "The Mind of the Universe," describes these efforts which include work by Dirac, Eddington, Einstein, Dicke, and Hawking.  

Building on these speculations, astrophysicist Brandon Carter coined the term "anthropic principle" at a 1973 symposium in Krakow, marking the 500th anniversary of Copernicus' birth. Copernicus was the Renaissance astronomer who first formulated a cosmology wherein the earth was not at the center of the universe but rather revolved around the Sun. Carter created the phrase in reaction to a recent extension and generalization of Copernican Principle - i.e., not only is the Earth not at the center of the universe but humans are not even privileged observers of the universe. Carter, examining the remarkable coincidences similar to those noted above, disagreed: “Although our situation is not necessarily central, it is inevitably privileged to some extent.” 

The anthropic principle comes in several flavors. The most basic distinction is between the “Weak” and “Strong” anthropic principles. Beyond these two versions, there are the more scientifically speculative “Participatory” and “Final” Anthropic Principles. Here is a short description of each for your consideration. 

Let's start with the Weak Anthropic Principle and work our way up. The Weak Anthropic Principle (WAP) basically states that all the possible values for the physical and cosmological constants are not equally probable. Some are more probable than others. Specifically the values of these constants are restricted to what is compatible with the observable facts: namely, that there are sites where carbon-based life can evolve and that the Universe has existed long enough for carbon-based life to have done so.  

Now let's up the ante a bit and consider the Strong Anthropic Principle (SAP). Simply stated: the Universe must have those properties which allow life to develop at some stage in its history. 

One interpretation of the SAP is that the Universe requires observers and is designed with the goal of generating and sustaining these observers.  Humanity (or some other intelligent, information-gathering life form) is thus necessary to the Universe's existence.  This is sometimes referred to as the Participatory Anthropic Principle.  It is derived from the concepts of quantum mechanics - i.e., it takes an intelligent observer to collapse the Universe's probability waves into relatively concrete reality.

Last and most speculative is the Final Anthropic Principle. In this version, intelligent information-processing must come into existence in the Universe, and, once it comes into existence, it will never die out.