Scientists of all worldviews agree that the physical constants of our universe and the conditions of the early universe are exquisitely fine-tuned for life. Multiple theories in physics predict that our universe may be one of very many, an idea known as the multiverse. Some Christians argue that fine-tuning is proof of God’s existence, while some atheists argue that the multiverse replaces God. Neither conclusion can be reached on the basis of science alone, because the existence of God is not a scientific question. Yet our fruitful cosmos resonates with the Christian understanding of God as the creator of a world fit for life. When viewed through the eyes of faith, we see a personal God crafting an abundant, complex universe that includes our life-giving home, the Earth. Even if multiverse theories eventually explain scientifically how our universe began, the multiverse itself would still be God’s creation. Scientific explanations cannot replace God but rather increase our wonder and praise of the Creator God.
Fine-tuning refers to the surprising precision of nature’s physical constants and the early conditions of the universe. To explain how a habitable planet like Earth could even exist, these fundamental constants have to be set to just the right values (like tuning a dial to find just the right radio station). If the universe had physical constants with even slightly different values, the universe simply could not support life: it would expand too quickly, or never form carbon atoms, or never make complex molecules like DNA.
The multiverse is the idea that our universe is one of possibly infinitely many universes. Out of the many possible universes that may exist, each with different strengths of forces and properties of particles, our universe is one of very few which is capable of hosting life as we know it. How do people respond to fine-tuning and the multiverse? What do they imply for our understanding of God?
Fine-tuning refers to “just right” properties
Our universe has several properties that are set to precise values, and slight changes to those values would prevent life as we know it. Here are three examples.
The strength of gravity
When the Big Bang occurred billions of years ago, the matter in the universe was uniformly distributed. There were no stars, planets or galaxies—just particles floating about in the dark void of space. As the universe expanded outwards from the Big Bang, gravity pulled ever-so-gently on the matter, gathering it into clumps that eventually became stars and galaxies. But gravity had to have just the right force—if it was a bit stronger, it would have pulled all the atoms together into one big ball. The Big Bang—and our prospects—would have ended quickly in a Big Crunch. And if gravity was a bit weaker, the expanding universe would have distributed the atoms so widely that they would never have been gathered into stars and galaxies.
The strength of gravity has to be exactly right for stars to form. But what do we mean by “exactly”? Well, it turns out that if we change gravity by even a tiny fraction of a percent—enough so that you would be, say, one billionth of a gram heavier or lighter—the universe becomes so different that there are no stars, galaxies, or planets. And with no planets, there would be no life. Change the value slightly, and the universe moves along a very different path. And remarkably, every one of these different paths leads to a universe without life in it. Our universe is friendly to life, but only because the past 13.8 billion years have unfolded in a particular way that led to a habitable planet with liquid water and rich chemistry.
The formation of carbon
Carbon is the element upon which all known life is based. Carbon atoms form in the cores of stars by fusion reactions. In these reactions, three helium atoms collide and fuse together to make a carbon atom. However, in order for that fusion reaction to work, the energy levels must match up in just the right way, or the three helium atoms would bounce off of each other before they could fuse.
To create this unusual match-up of energies, two physical forces (the strong and electromagnetic forces) must cooperate in just the right way. The slightest change to either the strong or electromagnetic forces would alter the energy levels, resulting in greatly reduced production of carbon. The values are tuned so that carbon is produced efficiently, leading to abundant amounts of an element we need for life.
The stability of DNA
Every atom has a nucleus of protons and neutrons and a cloud of electrons swirling around it. When an atom binds with another atom to make a molecule, the charged protons and electrons interact to hold them together. The mass of a proton is nearly 2,000 times the mass of the electron (1,836.15267389 times, to be precise). But if this ratio changed by only a small amount, the stability of many common chemicals would be compromised. In the end, this would prevent the formation of many molecules, including DNA, the building blocks of life. As theologian and scientist Alister McGrath has pointed out,1
[The entire biological] evolutionary process depends upon the unusual chemistry of carbon, which allows it to bond to itself, as well as other elements, creating highly complex molecules that are stable over prevailing terrestrial temperatures, and are capable of conveying genetic information (especially DNA).
These are just a few examples.
Evidence for fine-tuning is recognized by physicists and astronomers of all religions and worldviews, and has been for decades. As agnostic Steven Weinberg, a Nobel Laureate in Physics, wrote,
…how surprising it is that the laws of nature and the initial conditions of the universe should allow for the existence of beings who could observe it. Life as we know it would be impossible if any one of several physical quantities had slightly different values.
Implications of fine-tuning
Some agnostics and atheists see fine-tuning simply as a lucky accident. For some, this is a nonchalant shrugging of the shoulders; fine-tuning “is what it is” without any further implications. Some make a more specific argument: because humans exist, the laws of nature clearly must be the ones compatible with life, otherwise, we simply wouldn’t be here to notice the fact. (This is called the “anthropic principle;” see this good introduction by leading Christian physicist John Polkinghorne.) To argue against this line of reasoning, philosopher John Leslie makes the analogy of surviving an execution at a firing squad completely unharmed,2 summarized here by astronomer and BioLogos President Deborah Haarsma:
Of course the survivor would look for an explanation for why such an unlikely event occurred! In the same way, most people are curious to figure out why the universe is the way it is, both scientifically and theologically. As astronomer Fred Hoyle wrote, “A commonsense interpretation of the facts suggests that a super-intellect has monkeyed with physics, as well as with chemistry and biology.” Physicist Freeman Dyson wrote, “The more I examine the universe, and the details of its architecture, the more evidence I find that the Universe in some sense must have known we were coming.”3
In recent years, several theories for a multiverse have been put forth. In a multiverse model, there are many other universes in addition to our own. Each of these universes has different properties and different values of the basic constants of physics, such that some of these universes would have gravity set just right to form stars, but many universes would not. Only a few universes would be suitable for life, and of course we would be living in one of those (because we couldn’t survive in the others). If the number of these universes is extremely large, it would be less surprising that one of them would happen to provide the specific conditions for life. Would a multiverse explain away fine-tuning and point away from God?
Science of the multiverse
The term “multiverse” is actually used for several different scientific models, not just one. The different multiverse models arise out of theoretical physics and cosmology and the leading ones have a rich mathematical basis. One version of the multiverse arises from string theory. String theory is the best theory developed so far to unify the four fundamental forces of physics, by picturing each particle as a tiny vibrating string operating in 11-dimensional space. String theory was not invented to explain fine-tuning or multiple universes; the multiverse prediction arose out of the math of the theory. String theory hasn’t been confirmed experimentally yet; testing it will be challenging and requires large, high energy experiments like the Large Hadron Collider and more.
Another version of the multiverse arises from inflation theory, which was developed to answer questions about the properties of the universe, such as its nearly uniform temperature and the imbalance of matter and antimatter. In inflation, the universe expands at an incredibly rapid rate in its first moments (by a factor of 1026 in about 10-33 seconds). In those moments, tiny fluctuations in the early universe expand nearly to the size of galaxies, leading to the structures we see in the universe today. Inflation made specific predictions for properties of the Cosmic Microwave Background, the heat radiation leftover from the early universe, and those predictions have been fully confirmed: inflation theory has been thoroughly tested and confirmed. Intriguingly, most versions of inflation theory also predict a multiverse. New universes form by a phase transition, analogous to a pot of water just beginning to boil, leading to many “bubbles,” each bubble a universe with different properties.
Perhaps the biggest question for the multiverse is, “Is this science?” It is highly improbable that we could ever do any measurements of another universe; it is inaccessible to us. Cosmologists themselves debate whether the multiverse is in the realm of science. Some argue that using the multiverse as an explanation would weaken the very nature of scientific reasoning, since it cannot be tested directly. Others argue that a physical theory (like inflation) can be confirmed if some of its predictions are confirmed (as they have with the Cosmic Microwave Background) even if not all predictions can be tested.
Scientists also have found that, even if the multiverse models are right, the multiverse would not eliminate fine-tuning. For example, in order to produce such an enormous inflationary rate of expansion, inflation theories require certain parameters to take on particularly precise values. While inflation explains some properties in our universe that previously appeared fine-tuned, the fine-tuning is not eliminated—it is pushed a step back into the origin of the multiverse itself.
Whether universe or multiverse, God is the Creator
When some atheists argue that the multiverse weakens the case for God’s existence, they overstep what science itself can claim. The multiverse models are fascinating and address scientific questions in this universe, but at a scientific level the predictions for other universes are virtually impossible to verify. But even if a multiverse model were well-established on a scientific level, it would not and could not replace God. No scientific theory can. From the perspective of biblical faith, science merely investigates the physical world that God created and sustains.
The physicists who are investigating the multiverse include Christians who ponder the multiverse as God’s creation. The multiverse raises theological questions that need consideration (see for example physicist Robert Mann’s discussion). And yet, as physicist Gerald Cleaver writes, if multiverse theories are shown to be correct, it would be “the next step in understanding the beauty, splendor, complexity, and vastness of God’s creation.”
Last updated on July 20, 2021