How Much Different Could Our Universe Be?

I've frequently referred on VP to the phenomenon of cosmic fine-tuning as a powerful argument in support of the claim that the universe was intelligently engineered by a transcendent mind, but have often felt the difficulty of conveying how amazing this phenomenon is.

However, back in 2015 Australian cosmologist Luke Barnes wrote an article for the New Atlantis in which he gives an excellent explanation of what scientists mean when they talk about fine-tuning and what the implications and possible explanations for it are.

His column is a little long, but it does a wonderful job of making the ideas comprehensible to readers with a modest understanding of physics. If this is a topic that interests you I urge you to read Barnes' entire column, since I can only give you a slight taste of it here.

He talks about how the universe consists of numerous physical constants which are numbers which must be plugged into equations in order for the equations to accurately describe phenomena. For example, the gravitational attraction between the earth and the moon can only be calculated if we insert into the equation which describes this attraction a number called the gravitational constant.

There are dozens of such constants that comprise the fabric of the universe. Barnes writes:

Since physicists have not discovered a deep underlying reason for why these constants are what they are, we might well ask the seemingly simple question: What if they were different? What would happen in a hypothetical universe in which the fundamental constants of nature had other values?

There is nothing mathematically wrong with these hypothetical universes. But there is one thing that they almost always lack — life. Or, indeed, anything remotely resembling life. Or even the complexity upon which life relies to store information, gather nutrients, and reproduce.

A universe that has just small tweaks in the fundamental constants might not have any of the chemical bonds that give us molecules, so say farewell to DNA, and also to rocks, water, and planets.

Other tweaks could make the formation of stars or even atoms impossible. And with some values for the physical constants, the universe would have flickered out of existence in a fraction of a second.

That the constants are all arranged in what is, mathematically speaking, the very improbable combination that makes our grand, complex, life-bearing universe possible is what physicists mean when they talk about the “fine-tuning” of the universe for life.

He goes on to give us some examples:

Let’s consider a few examples of the many and varied consequences of messing with the fundamental constants of nature, the initial conditions of the universe, and the mathematical form of the laws themselves.

You are made of cells; cells are made of molecules; molecules of atoms; and atoms of protons, neutrons, and electrons. Protons and neutrons, in turn, are made of quarks. We have not seen any evidence that electrons and quarks are made of anything more fundamental.

The results of all our investigations into the fundamental building blocks of matter and energy are summarized in the Standard Model of particle physics, which is essentially one long, imposing equation. Within this equation, there are twenty-six constants, describing the masses of the fifteen fundamental particles, along with values needed for calculating the forces between them, and a few others.

We have measured the mass of an electron to be about 9.1 x 10-28 grams, which is really very small — if each electron in an apple weighed as much as a grain of sand, the apple would weigh more than Mount Everest. The other two fundamental constituents of atoms, the up and down quarks, are a bit bigger, coming in at 4.1 x 10-27 and 8.6 x 10-27 grams, respectively.

These numbers, relative to each other and to the other constants of the Standard Model, are a mystery to physics....we don’t know why they are what they are.

However, we can calculate all the ways the universe could be disastrously ill-suited for life if the masses of these particles were different. For example, if the down quark’s mass were 2.6 x 10-26 grams or more, then adios, periodic table! There would be just one chemical element and no chemical compounds, in stark contrast to the approximately 60 million known chemical compounds in our universe.

With even smaller adjustments to these masses, we can make universes in which the only stable element is hydrogen-like. Once again, kiss your chemistry textbook goodbye, as we would be left with one type of atom and one chemical reaction. If the up quark weighed 2.4 x 10-26 grams, things would be even worse — a universe of only neutrons, with no elements, no atoms, and no chemistry whatsoever.

Considering that we know of no reason why the masses of these particles couldn't have had a broad range of values these are incomprehensibly tiny differences - on the order of a decimal point followed by 25 zeroes and a 1. To give us an idea of how narrow the range of masses these particles must reside in if they're to build a universe that would have chemistry, Barnes invites us to,

Imagine a huge chalkboard, with each point on the board representing a possible value for the up and down quark masses. If we wanted to color the parts of the board that support the chemistry that underpins life, and have our handiwork visible to the human eye, the chalkboard would have to be about ten light years (a hundred trillion kilometers) high.

And that's for the masses of just two fundamental particles. Add a third parameter and the life-permitting zone becomes vanishingly small:

There are also the fundamental forces that account for the interactions between the particles. The strong nuclear force, for example, is the glue that holds protons and neutrons together in the nuclei of atoms. If, in a hypothetical universe, this force is too weak, then nuclei are not stable and the periodic table disappears again.

If it is too strong, then the intense heat of the early universe could convert all hydrogen into helium — meaning that there could be no water, and that 99.97 percent of the 24 million carbon compounds we have discovered would be impossible, too.

And... these forces, like the masses, must be in the right balance. If the electromagnetic force, which is responsible for the attraction and repulsion of charged particles, is too strong or too weak compared to the strong nuclear force, anything from stars to chemical compounds would be impossible.

Stars are particularly finicky when it comes to fundamental constants. If the masses of the fundamental particles are not extremely small, then stars burn out very quickly. Stars in our universe also have the remarkable ability to produce both carbon and oxygen, two of the most important elements to biology. But, a change of just a few percent in the up and down quarks’ masses, or in the forces that hold atoms together, is enough to upset this ability — stars would make either carbon or oxygen, but not both.

Here's a chart that shows the delicate balance that must exist between just two fundamental forces in order for carbon-based life to exist.

Barnes is himself persuaded that cosmic fine-tuning points to the conclusion that our universe has been designed by an intelligent agent, although many other physicists resist that conclusion. They hold out hope that some other explanation for this amazingly precise calibration of constants and forces will emerge.

Maybe so, but what we know right now about the universe does not engender optimism that their hope will ever be justified.