“I’d like to give you a taste of some of this evidence. Specifically, I want to show you how the masses of three fundamental particles of the universe are set for life. If they were changed by the slightest amount, there could be no life anywhere in the universe.”

The fine-tuning of the universe for the existence of life is fascinating to me. That’s why I was so excited to find A Fortunate Universe: Life in a Finely Tuned Cosmos, co-authored by astrophysicists Geraint Lewis and Luke Barnes, under my Christmas tree. This book provides the most up-to-date scientific evidence for the fine-tuning of the universe for life. But what is truly unique about this book is that it presents the data at a popular level so that the material is accessible to anyone interested in this topic.

As I read the book, I was awestruck by the finely-tuned constants and conditions that had to be just right to get a universe that would permit life. I’d like to give you a taste of some of this evidence. Specifically, I want to show you how the masses of three fundamental particles of the universe are set for life. If they were changed by the slightest amount, there could be no life anywhere in the universe. Unfortunately (at least for some), this requires you to understand a little particle physics.

Now stay with me. The reward at the end is worth it. Trust me. Here we go.

Particle Physics 101

Underlying all of the complexity of this universe—bees, computers, people, stars, and planets—is the simplicity of a few particles. At the most basic level, the world is built from a handful of building blocks. At one time, we believed that the smallest building blocks were atoms. However, today we know that atoms are made up of subatomic particles: neutrons, protons, and electrons. Protons, which are positively charged, and neutrons, which have no charge, compose the nucleus of the atom. Negatively charged electrons orbit the nucleus.

Are you starting to remember your high school chemistry class yet? Some of you are probably still trying to forget it.

These three particles are responsible for building the 92 naturally occurring elements, as well as the unstable elements that have been created in the laboratory. Think periodic table. For example, a stable carbon atom is made of six protons, six neutrons, and six electrons.

But this isn’t the end of the story. While electrons seem to be fundamental, neutrons and protons can be broken into smaller bits. Particle accelerators are used to smash atoms apart. In the process, scientists have discovered that protons and neutrons are made of quarks. Specifically, they are made of a combination of up quarks and down quarks. Protons are composed of two up quarks and one down quark. Neutrons are composed of two down quarks and one up quark.

These three particles—the up quark, the down quark, and the electron—make up everything we see—molecules, mice, maple trees, and the Milky Way galaxy. And each of these particles has a distinct mass. The mass of an electron is approximately 9.1 x 10^-31 kg. That is extremely small. Likewise, the mass of the up quark and the down quark are approximately 4.1 x 10^-30 kg and 8.5 x 10^-30 kg, respectively. (Physicists prefer to use the unit MeV/c²—Mega electron volts per speed of light squared—but let’s stick with units we are all familiar with).

Changing the Masses

These numbers may not look very special, but, as Lewis and Barnes demonstrate, they are finely tuned for the existence of life. Consider how the universe would be different if the masses of the up quark and down quark were slightly different. Barnes and Lewis write, “In fact, it is rather easy to arrange for a universe to have no chemistry at all. Grab a hold of the particle mass dials and let’s create a few universes.”^[1]

So what happens if we change the masses of the three fundamental particles—the down quark, the up quark, and the electron? Let’s see.

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