What Is The Fine-Tuned Universe? The Hypothesis That Can Invoke Either Parallel Dimensions Or God

The idea is simple. Life as we know it cannot exist if the constants of nature were different, ergo the universe must be tuned for life (as we know it). I wrote as we know it in brackets again to emphasize how this hypothesis hinges on the fact that we have one example of life in the universe, and it's life on Earth. The assumptions that life must require water, carbon molecules, and energy are all extremely sensible, but they are still based on this singular example.

From here to infinity

In fact, the first idea of this fine-tuning doesn’t look at the universe as a whole. It looks at Earth. The elements of the theory come from the book The Fitness of the Environment by chemist Lawrence Joseph Henderson. Written in 1913, it highlights the fact that Earth has very specific conditions that made it suitable for life.

One particular focus is water. Water has incredible properties that make it crucial to life on Earth. There are peculiarities too: its existence as three distinct states of matter over a relatively small range of temperatures, as well as the unusual ability of ice to be less dense than water, making it float. Water on Earth cycles, something that would help spread molecules that might eventually become life.

But we could extend the discussion even more, beyond the properties of a particular molecule. Changes to the fundamental constants of the universe would make things dramatically different. It has been claimed that if the fine structure constant, a value that underpins the strength of electromagnetic interactions, were just 4 percent different, stars would not be able to make enough carbon. Definitely goodbye life in that case.

There are other arguments and calculations that suggest that a small variation of several constants would be catastrophic. Not everyone agrees that the constants' values are balanced on a knife-edge. Most of the variations between a universe we’d recognize and one completely different are relatively small, but some claims seem absurd.

The internet has an abundance of claims that, for example, gravity is so perfectly fine-tuned that even a variation of 1 part in billions of billions to its strength would destroy the universe. Despite searching, however, we couldn’t find the actual calculation to back such claims up.

 A cosmological fix

The problem of fine-tuning can have both physical and philosophical solutions. There is an example in cosmology, the study of the universe as a whole, with what’s known as the flatness problem. Data suggests that the universe is three-dimensionally flat, or at least is very close to being three-dimensionally flat. We do not have to bog ourselves down with what that means geometrically, but to provide one example, it means that parallel lines in the universe always stay parallel.

For the universe to be flat, it needs to be very close to a very specific density known as the critical density. As the universe expands, the value will slightly change. But measurements suggest that the universe’s density today is very close to that critical density. This means that if you shrink the universe backwards, removing all those changes, the density needs to be so much closer to the critical one that it requires incredible fine-tuning to start with it in the first place.

A physical solution to that problem is the idea of cosmic inflation, a process by which the universe expanded exponentially in the very first instants after the Big Bang. Inflation doesn’t just solve this problem, but others too, making it a very attractive hypothesis.

A more philosophical idea is the anthropic principle. If two versions of the universe are equally likely, but one allows us to exist and one doesn’t, then it is no surprise that we are in the one that allows us to exist. There’s nobody else in the other version.

Beyond the limits of the universe

The idea of an anthropic principle can push us to consider explanations that go beyond our physics, whose remit is our known universe. There could be a multiverse with constants of all values, but only when those values are suitable for life, there are beings to observe such universes. Or maybe there’s a cosmic natural selection, where a universe like ours can give birth to other universes via black holes, so universes that can make black holes are more common, and universes like ours that can do both black holes and life would end up being numerous.

The other common thread when it comes to the fine-tuned universe idea is that it is a natural justification for the existence of God, or a general creating deity or being. This theistic explanation has many supporters, though they do not seem to like the fact that such an explanation can be equally applied to the idea that the universe is a simulation. 

Writer Douglas Adams satirized this very idea in 2002, in his book The Salmon of Doubt: “Imagine a puddle waking up one morning and thinking, 'This is an interesting world I find myself in, an interesting hole I find myself in, fits me rather neatly, doesn't it? In fact, it fits me staggeringly well, must have been made to have me in it!'”

The universe hates clean floors

It is impossible to avoid the human element when it comes to understanding the universe. The way we comprehend it, how we relate to it, and wonder why it is like this and not different, all pass through our knowledge and our views. To stress that, let me provide you with a wonderfully bizarre claim: the universe hates clean floors!

You might be familiar with the idea that buttered toast always falls on the buttered side. This is not true; it doesn’t always fall on the buttered side, but a large experiment has demonstrated that statistically, it is more likely to fall on the buttered side than the other side. Researchers were then able to link that statistical difference to the fine structure constant we encountered above. Basically, you are saying that the universe, at its very fundamentals, prefers buttered toast to fall on the buttered side. In other words, the universe hates clean floors.

But if you look at the details of the paper, the connection between the fall on the buttered side and the fine structure constant appears after several steps. Toast falls as it does because it only has a certain amount of time to spin around. The reason why it only has a certain amount of rotation in it is that it only falls from a small range of heights. 

The reason why there is a small range of heights in tables, counters, and standing humans is that evolution has favored a particular range of heights for our bodies. That range was favored because it meant that falling down doesn’t result in a death sentence for us all. It’s from the calcium in our bones that the connection to the fundamental constant can be found.

So does the universe really hate clean floors? Are the constants of the universe really fine-tuned? Maybe yes to one, maybe even to both, but let’s not forget how our nature plays a role in posing and interpreting those questions.