The Anthropic Principle: Was the Universe Made for Us?

Diagram on the dimensionality of spacetime, by Max Tegmark

Posted by Keith Tidman

‘It is clear that the Earth does not move, and that it does not lie elsewhere than at the center [of the universe]’ 

— Aristotle (4th century BCE)

Almost two millennia after Aristotle, in the 16th century, Nicolas Copernicus dared to differ from the revered ‘father of Western philosophy’. Copernicus rattled the world by arguing that the Earth is not at the center of the universe — in a move that to many at the time seemed to knock humankind off its pedestal, and reduce it from exceptionalism to mediocrity. The so-called ‘Copernican principle’ survived, of course, along with the profound disturbance it had evoked for the theologically minded.

Five centuries later, in the early 1970s, an American astrophysicist called Brandon Carter came up with a different model — the ‘anthropic principle’ — that has kept philosophers and scientists debating its significance cosmologically and metaphysically. With some irony, Carter proposed the principle at a symposium to mark Copernicus’s 500th birthday. The anthropic principle points to what has been referred to as the ‘fine-tuning’ of the universe: a list of cosmological qualities (physical constants) whose extraordinarily precise values were essential to making intelligent life possible.

Yet, as Thomas Nagel, the contemporary American philosopher, suggested, even the physical constants known to be required for our universe and an intelligent carbon-based life form need to be properly understood, especially in context of the larger-scaled universe:

‘One doesn’t show that something doesn’t require explanation by pointing out that it is a condition of one’s existence.’

The anthropic principle — its adherence to simplicity, consistency, and elegance notwithstanding — did not of course place Earth back at the center of the universe. As Carter put it, ‘Although our situation is not necessarily central, it is inevitably privileged’. To widen the preceding idea, let’s pose two questions: Did the anthropic principle reestablish humankind’s special place? Was the universe made for us?

First, some definitions. There are several variants of the anthropic principle, as well as differences among definitions, with Carter originally proposing two: the ‘weak anthropic principle’ and the ‘strong anthropic principle’. Of the weak anthropic principle, Carter says:

‘… our location in the universe [he was referring to the age of the universe at which humankind entered the world stage, as well as to location within space] is necessarily privileged to the extent of being compatible with our existence as observers.’

Of the strong anthropic principle, he explained,

‘The universe (and hence the fundamental parameters on which it depends) must be such as to admit the creation of observers within it at some stage’.

Although Carter is credited with coining the term ‘anthropic principle’, others had turned to the subject earlier than him. One in particular among them was the 19th-century German philosopher Arthur Schopenhauer, who presented a model of the world intriguingly similar to the weak anthropic principle. He argued that the world’s existence depended on numerous variables, like temperature and atmosphere, remaining within a very narrow range — presaging Carter’s fuller explanation. Here’s a snapshot of Schopenhauer’s thinking on the matter:

‘If any one of the actually appearing perturbations of [the planets’ course], instead of being gradually balanced by others, continued to increase, the world would soon reach its end’.

That said, some philosophers and scientists have criticized the weak variant as a logical tautology; however, that has not stopped others from discounting the criticism and favoring the weak variant. At the same time, the strong variant is considered problematic in its own way, as it’s difficult to substantiate this variant either philosophically or scientifically. It may be neither provable nor disprovable. However, at their core, both variants (weak and strong) say that our universe is wired to permit an intelligent observer — whether carbon-based or of a different substrate — to appear.

So, what kinds of physical constants — also referred to as ‘cosmic coincidences’ or ‘initial conditions’ — does the anthropic principle point to as ‘fine-tuned’ for a universe like ours, and an intelligent species like ours, to exist? There are many; however, let’s first take just one, to demonstrate significance. If the force of gravitation were slightly weaker, then following the Big Bang matter would have been distributed too fast for galaxies to form. If gravitation were slightly stronger — with the universe expanding even one millionth slower — then the universe would have expanded to its maximum and collapsed in a big crunch before intelligent life would have entered the scene.

Other examples of constants balanced on a razor’s edge have applied to the universe as a whole, to our galaxy, to our solar system, and to our planet. Examples of fine-tuning include the amount of dark matter and dark energy (minimally understood at this time) relative to all the observable lumpy things like galaxies; the ratio of matter and antimatter; mass density and space-energy density; speed of light; galaxy size and shape; our distance from the Milky Way’s center; the sun’s mass and metal content; atmospheric transparency . . . and so forth. These are measured, not just modeled, phenomena.

The theoretical physicist Freeman Dyson poignantly pondered these and the many other ‘coincidences’ and ‘initial conditions’, hinting at an omnipresent cosmic consciousness:

‘As we look out into the universe and identify the many accidents of physics and astronomy that have worked together to our benefit, it is almost as if the universe must in some sense have known we were coming.’

Perhaps as interestingly, humankind is indeed embedded in the universe, able to contemplate itself as an intelligent species; reveal the features and evolution of the universe in which humankind resides as an observer; and ponder our species’ place and purpose in the universe, including our alternative futures.

The metaphysical implications of the anthropic principle are many. One points to agency and design by a supreme being. Some philosophers, like St. Thomas Aquinas (13th century) and later William Paley (18th century), have argued this case. However, some critics of this explanation have called it a ‘God of the gaps’ fallacy — pointing out what’s not yet explained and filling the holes in our knowledge with a supernatural being.

Alternatively, there is the hypothetical multiverse model. Here, there are a multitude of universes each assumed to have its own unique initial conditions and physical laws. And even though not all universes within this model may be amenable to the evolution of advanced intelligent life, it’s assumed that a universe like ours had to be included among the infinite number. Which at least begins to speak to the German philosopher Martin Heidegger's question, ‘Why are there beings at all, instead of nothing?’