God of Many Worlds (Extended Cut)

(This long version is meant only for nerds and others really interested. Everyone else should just read the shorter version.)

Quantum physics has always been shocking. Contrary to classical physics intuition, every single microscopic particle can actually exist in a state of contradiction, such as being in two different positions at once or simultaneously having undergone a chemical reaction and not. Strange as it may be, quantum mechanics has been verified for very small things to a spectacular level. For instance, a single atom has been made to simultaneously travel different paths separated from each other by a full meter.

Does quantum mechanics also provide the correct description for larger objects, such as humans? If so, then the shock of quantum mechanics would be taken to an entirely new level. History would be described not as a single narrative, but as a sort of tree branching constantly into parallel realities that are often very different from one another. This is the so-called Many Worlds interpretation of quantum mechanics. (Since some of these ideas have made their way into popular culture, a note on vocabulary might be helpful. The term Multiverse is often used denote a Many Worlds interpretation, but it can mean very different things as well.) Far from being a science-fiction fancy added onto a more basic quantum theory, a Many-Worlds Multiverse emerges naturally from the verified quantum equations. Although it is still a controversial issue among physicists, my perspective is that the overwhelming success of quantum theory strongly suggests that the Many Worlds picture is true.

Perhaps surprisingly, shifting to a Many Worlds perception of reality does not have practical or ethical implications for day to day living. But it seems that there are profound implications for how we think about God and our place in the universe, and that can shape how we go about our lives and how we interact with others. I will discuss the question of personal destiny, including lessons from a terminal illness that I face. And I will discuss implications for how Christians view Jesus.

From the Laboratory Into the World

Since I lead an experimental quantum physics laboratory at Northwestern University, we can illustrate a Many Worlds reality by applying quantum mechanics to a real macroscopic object, namely myself. We are here discussing a real-world implementation of the Schrodinger’s cat thought experiment.

Students in my group routinely use lasers to manipulate the quantum states of single barium atoms held in place by electromagnetic fields. Quantum mechanics allows us to orient the atom’s magnetism to be in a seemingly contradictory state, simultaneously pointing two directions at once. A measurement of the orientation will yield either “up” or “down”, and we cannot predict beforehand which it will be. The situation is very different from one of ignorance, where one might imagine the atom to have one or the other definite orientation but we don’t know which. Instead, we easily verify that before we measure the orientation, the atom is actually pointing both directions at once.

On X date, I put myself into the experiment. My student prepared a barium atom in the contradictory state described above, and I agreed to take one of two actions depending on the outcome of his subsequent measurement. If he measured “up”, then I would immediately walk toward my favorite coffee shop to the North, and I would give $100 to someone I encountered along the way. If he measured “down”, then I would do similarly but walking toward a coffee shop to the South.

The description I have given so far is undisputed. But how to interpret reality ensuing from the quantum measurement is not currently agreed upon by physicists. The Many Worlds interpretation says we should apply the simple equations of quantum mechanics not just to the atom, but to me as well. This very reasonable approach results in a picture of reality getting split into different “worlds”. (“World” in this context refers not to the planet on which we live, but rather the description of reality.) One world has a version of me walking North, and the other world has a version of me walking South. Each version of me is convinced that I am real and only walking one direction or the other. Both versions of me actually exist, but neither can directly verify the existence of the other.

In the world I am writing from, the outcome of my student’s measurement was X, so I walked Y. While on my way I gave the money to a person doing Z. He told me that he would do Q with the cash. The Many World interpretation asserts that the other version of me also exists, but we can only speculate about what he encountered. Perhaps he gave the money to someone in need of a little extra to pay their rent. A ripple effect in each reality ensues, because many subsequent people will in turn be affected by these seed events.

A Guiding Principle in Science: Simpler is Better

A few years ago, a theoretical physicist with a Nobel prize gave a series of lectures at Northwestern. I was not yet very familiar with the Many Worlds picture, and I asked his opinion of it during lunch. He replied, “Many Worlds? That’s just plain quantum mechanics, isn’t it? But I think it’s probably wrong.” That is a reasonable position to take. I appreciate his acknowledgement that the most basic theory leads to Many Worlds, but nonetheless he was betting on a yet-unknown alternative. Although I respect his honest position, I will briefly justify why many physicists’ bets differ.

In the 16th century, Copernicus used mathematics to address the question of which picture of the universe was more correct — one with the Sun or Earth at the center. Although the data available at the time did not support one over the other, it was argued by Copernicus that a heliocentric universe was the more elegant model and therefore more likely to be correct. The heliocentric picture offended sensibilities of his contemporaries, because it conflicted with their philosophical and religious convictions. Their objections also resonated with a naïve interpretation of common experience — it certainly doesn’t feel to us like the earth is moving or rotating. However, Galileo’s observations and then Newton’s gravitational theory eventually made clear that holding to a geocentric picture would require laughably more complex laws of physics. The principle that the simpler model is more likely correct, as long as it can correctly explain all observations, continues to be an important guiding principle for science.

Many Worlds quantum mechanics presents a situation with parallels to the heliocentric revolution. Although it took decades to appreciate, we now understand that a simple application of the quantum equations developed in the early 20th century, to both small and large things, yields correct predictions for all current observations. There is a price to be paid for this simplicity. The resulting Many Worlds picture of reality offends our philosophical and perhaps religious sensibilities. And there is a naïve objection from common experience as well, as I never get to experience the feeling of walking both North and South at the same time. However, just as in the time of Copernicus, the simpler model is more likely correct — even if it forces us to change some cherished perceptions of reality and requires us to do a bit of honest thinking about consistency with our felt experience.

Many Worlds Emerge from the Simplest Theory

The framers of quantum mechanics had lively arguments as they struggled to describe the reality being thrust upon them by experimental discoveries. They soon found that microscopic objects such as atoms must obey the Schrodinger equation, which allows them to be in two contradictory states at once. Such a state is called a “superposition”. But we don’t observe large things like humans or macroscopic detectors in superpositions. This microscopic/macroscopic split required an explanation. The so-called Copenhagen interpretation of quantum mechanics became the consensus view, and it is still taught in standard textbooks today. The Copenhagen interpretation posits that only microscopic things obey Schrodinger’s equation. In contrast, large things cannot be in superpositions. Whenever something macroscopic interacts with something microscopic, any superposition of the latter “collapses” into one state or the other. Which way it collapses is random and cannot be predicted.

The Copenhagen interpretation never passed the smell test for physicists. We have never before encountered a fundamental theory that had some unexplainable cutoff for when it could be applied and when it couldn’t. But it is hard to argue with success, and Schrodinger’s equation, with the Copenhagen interpretation tacked on, has had a flawless track record for predicting results of experiments.

But things are changing. Schrodinger’s equation still is unassailable, even under the scrutiny of modern experiments. And therein lies the problem. For instance, the lab of Austrian physicist Markus Arndt recently succeeded in sending a 2000-atom molecule along contradictory paths. If such a large molecule still obeys Schrodinger’s equation, then how much larger must we go before we find the Copenhagen threshold separating microscopic from macroscopic? The Copenhagen interpretation, at least as a fundamental part of quantum theory, smells worse than it ever did.

Meanwhile, in the last half-century something interesting was also happening on the theory side. The story began with the bold doctoral thesis of Hugh Everett in the late 1950s. Everett argued that Schrodinger’s equation, applied consistently to both small and large things, correctly predicts all observations. Everett’s early work was bolstered by the later development of decoherence theory, and we now have a natural explanation for the apparent microscopic/macroscopic split. The answer has to do with irreversibility of large systems. The underlying laws of physics are time-reversible, so we cannot tell whether a movie showing two atoms bouncing off one another is being played forward or in reverse. However, when it comes to processes with more particles involved such as the breaking of an egg, we know very well if we are watching the movie in reverse. In classical physics, the microscopic/macroscopic split is not put into the theory by hand; rather an arrow of time only emerges once we start describing irreversible dynamics of large systems. As in classical physics, the underlying laws of quantum mechanics do not treat forwards and backwards in time differently, nor do they treat microscopic systems differently from macroscopic ones. Nonetheless, an arrow of time and a microscopic/macroscopic split also emerges in quantum mechanics, as they did in classical physics. But in quantum mechanics, the implications are even more profound. We can verify when small systems are put into superposition states. But because of their emergent irreversibility, when macroscopic objects end up in superposition states (which they often do and which we call Many Worlds) we can never verify this fact. This prediction agrees with observations. So, the Copenhagen interpretation’s clumsy approach of inserting into the theory by hand a microscopic/macroscopic split not only lacks self-consistency, it turns out to be completely unnecessary. And we are left with a Many Worlds reality.

Many physicists now accept a Many Worlds picture of reality. Some physicists remain faithful to the single-world Copenhagen interpretation as originally formulated, without acknowledging its internal contradiction. Some others acknowledge its inconsistency, but they suspect that the true underlying theory, yet to be discovered, will bring us once again to a single-world picture of reality. This last group is certainly operating within bounds as scientists to ask such questions, and some testable alternatives to plain (Many Worlds) quantum mechanics have been proposed.

How Different Are the Other Worlds? (Spoiler: Most of Them Do Not Contain You)

If the Many Worlds picture of reality is true, then how different are the other worlds? There is not an alternate Earth with a moon made of swiss cheese, because in all worlds the laws of physics are followed. But there might be an Earth which has two moons. And there are certainly worlds in which the Earth does not exist at all. Sorting out what variations the other worlds might contain is a bit of a delicate business. For reality to branch into different worlds, there must be an amplification of a quantum phenomenon. There are two general ways for this to occur: chaos and quantum measurement.

Chaotic systems behave wildly, in that miniscule changes in initial conditions lead to vastly different outcomes. A classic example is the weather, where for instance a tornado might take a different course or not even form at all, depending on tiny details of initial air currents. In classical mechanics, chaos means unpredictability. In Many Worlds quantum mechanics, chaos implies something more fundamental. The uncertainty principle means that each air molecule has an unavoidable spread of speeds and positions. If this spread of initial conditions leads to wildly different outcomes, then not only is there unpredictability as in classical physics, but each outcome is actually realized in a different world. And ripple effects ensue in the subsequent reality. Chaos being what it is, these systems are notoriously difficult to analyze. There are divergent worlds where a tornado strikes different houses, but it is difficult to say how often such divergences occurs.

The second type of amplification is from a quantum measurement, and here we can make some concrete statements about how often worlds diverge. An admittedly contrived, albeit still real, example discussed earlier is my walk to a coffee shop directed by quantum measurement of an atom’s orientation. But nature turns out to be full of quantum measurements.

For example, quantum fluctuations in the early universe resulted in slight irregularities in the early distribution of matter. Over vast timescales the clumping was amplified by gravitational attraction, eventually forming galaxy clusters, galaxies, solar systems, and planets. Each of the worlds branching from the Big Bang has clustered masses, but there are worlds in which slightly differing initial conditions led to no Milky Way galaxy, no Sun, no Earth, and no humans. Intelligent life can still be expected to occur in these other worlds, but it would be different than anything we know.

Divergent histories of Earth also developed. For instance, radioactive decay of radon gas atoms is a type of quantum event that can be amplified in humans. Radon concentrations are higher indoors than outdoors, but breathing typical outdoor air your lungs experience around 3 million radon decays per year, which deposit radioactive polonium biproducts into your lung tissue. Each radon decay ejects the polonium with a quantum superposition of different angles, times, and energies. We can think of your lung tissue as being a collection of a huge number of detector sites recording the details of each radon decay. Different sites have different sensitivities; for instance, polonium decay on sites near an important part of a DNA molecule will more often lead to cell mutation. (Although downstream quantum processes would not significantly affect the story, for simplicity we will assume that deterministic classical physics governs the effects after a polonium decay at each site.) In Many Worlds quantum mechanics, all possible outcomes from each radon decay occur in parallel, with the disconnected worlds corresponding to the polonium landing on different sites. In the vast majority of these worlds, no lasting harm is done, in part due to your body’s defenses. In a very few of these worlds, a cell mutation occurs which eventually leads to lung cancer and death. If microscopic details of that offending radon decay had been slightly different, as they are in other worlds, then death would not have occurred. The odds of dying of radon-induced cancer are quite low. For nonsmokers they are about 1 in 70,000 per year, which translates to less than 1 in 500 billion radon decays being deadly. There are worlds in which any given radon decay leads to your death, but they are exceedingly rare. Even accumulating risk over the course of decades, the number of worlds in which you survive far exceeds the number in which you die from lung cancer.

However, the same cannot be said for the long line of your ancestors. Consider lineage going back 300,000 years to the first Homo Sapiens. In order for any modern person to have received their unique genetic material, a certain female and a certain male must have survived each of those years. Accounting for the fact that our ancestors were most often breathing outdoor air and that smaller lungs during childhood reduces exposure, an estimate yields that each otherwise viable ancestry tree has only around a 1 in 3 chance of surviving to the present day. And radon is only one of the many quantum hazards your ancestors faced. It can safely be said that in well over half the present-day worlds where Earth does exist, you do not.

Other interesting questions are beyond our capability to answer at present. For instance, are there worlds in which you made different decisions in your past? If brain processes are governed by non-chaotic biochemistry of neurons, then the large number of molecules involved would cause small quantum deviations to be smoothed over rather than amplified. In that case, none to very few worlds exist in which you made different decisions. However, there is some evidence for the role of chaos in individual neurons and in networks of neurons. If chaos turns out to be an important feature in decision-making, then quantum differences could be amplified, resulting in parallel versions of you having behaved differently.

God, the Constant Pruner?

In this section I describe a possibility which I find intriguing, but not convincing. God could collapse the wave function and create a single-world reality indistinguishable from the Copenhagen picture. God would have to be judicious and allow the Schrodinger equation to play out on small scales where it is known to work, and then collapse the wave function when the system got large enough to be irreversible. Thus, God could opt for a single-world reality by constantly pruning what would otherwise be a Many Worlds reality tree.

Faith traditions which view God as external to the universe, but reaching in from time to time to tweak an outcome, face some challenging but perhaps not insurmountable questions. Curiously, a picture of a constantly acting God might be more self-consistent than an infrequently acting God, and in that sense quantum mechanics provides a theological opportunity. While I find the idea interesting to consider, it is not my best guess for a mechanism of how God works in the world. The picture of God as constant pruner would be uncomfortably reminiscent of many other times that believers have not given God enough credit. We have too often mistakenly thought that mechanisms of the universe required active divine intervention — for instance to keep the sun rising and setting each day or for evolution to achieve human life. Another objection is that this picture of God is motivated not by how we find the world to be, but rather how we think the world should be — always a questionable path for religious thinking to take.

Implications for Living

A Many Worlds picture is such a departure from our previous classical conception of reality that we might expect implications for how we should behave. Interestingly, physicists and ethicists who have thought about this question are largely in agreement that there are few to no immediately pragmatic implications.

The present world which you and I are experiencing together is very real, notwithstanding the existence of other worlds which are equally real. These different worlds are necessarily disconnected from one another, disallowing any interaction. The existence of those disconnected worlds does not somehow add to our responsibility list for mindful living, and neither does it alleviate responsibilities in this real world of our experience.

As far as the future goes, just as in classical physics, in Many Worlds quantum mechanics we are mostly unable to predict what our future experience of life will be. Many of us have a value system intended to optimize the future wellbeing for some combination of other people, ourselves, and our entire world. Multiple real futures will emerge from this point in time. But just as in a classically uncertain world, trying to act in a way consistent with your values is the best you can do to shape all futures.

One exception, where being persuaded of a Many Worlds reality will make a difference for living, is for people who’s actions are shaped by their beliefs about God. If our theology shifts, then aspects of how we live could shift as well. A few theologians have written about various types of Multiverses, considering whether or not these scenarios are consistent with certain convictions. I will take a somewhat different approach. I have argued that Many Worlds has good odds of being the correct picture of reality. I will take that as the starting point, and begin to ask what beliefs about God and ourselves seem to follow.

God, “Yes to You in This World”

As a personal example, at age 46 I was diagnosed with a slowly progressing type of brain cancer. What does quantum mechanics have to say about this? Some ancient philosophies, which still persist today, see our fate as being written in the stars. It is interesting to note that this picture of reality is almost literally true in classical physics. Classical physics is completely deterministic, such that the given positions and velocities of all particles shortly after the Big Bang leaves possibility for only a single future. Of course, as illustrated by the intuition of the Greek tragedies, even if that were true it would be of little use to humans. Because of our lack of information and computing resources, even if the future were pre-determined we would not be much good at predicting most of its details.

However, in quantum physics, it is not true that our experience of life is written in the stars. Single-world versions of quantum mechanics hold that the future is fundamentally unpredictable because of randomness in wave function collapse. The Many Worlds picture is subtly different. The overall fate of the universe does not include random collapses, but the tree of reality constantly splits into parallel and disconnected futures. As careful with your decisions as you might be, you cannot guide your future self down a chosen set of branches to a desired destiny. In fact, you do not have a single destiny. Branching from this moment, there will be many future versions of you each experiencing different realities.

A Many Worlds reality encourages us to internalize some spiritual truths already familiar from our old single-world picture. Consider how we hold any sense of personal destiny. The book of James says: “Come now, you who say, ‘Today or tomorrow we will go into such and such a town and spend a year there and trade and make a profit’ — yet you do not know what tomorrow will bring. What is your life? For you are a mist that appears for a little time and then vanishes. Instead you ought to say, ‘If the Lord wills, we will live and do this or that.’” Similarly, Kant cautioned against our tendency to treat people as a means to an end, and a person with a strongly developed sense of personal destiny is often tempted to do just that. A Many Worlds view of the universe underlines these truths. I do not even exist in most other worlds. And in this world where my existence is very real, I have divergent futures from this moment. If I am inclined to believe God has plans for my life, what I mean by that conviction must be modulated. I do not have a single future, which I might naively imagine to be God’s destiny for me. Instead I have many futures, each with different details. James, Kant, and quantum mechanics all suggest that we hold any sense of personal destiny with great humility.

Along with plans for our future comes questions about missed opportunities in the past. The familiar question: “Could things have been different?” takes on a different flavor in a Many Worlds reality. Yes, things often could have been different. And in fact, they were for different versions of you. Clearly, we must interpret our narratives leading to this point with grace made by ourselves and others, and with humility regarding our perceived successes.

I now return to the subject of my cancer. Occasionally it is tempting to lose faith and ask, “God, could you not have planned a better future for me?”. A Many Worlds reality makes asking those types of questions less compelling, since there are after all worlds in which I don’t even exist. Instead, I find myself thankful for my existence in this world of my experience, knowing that although it is real, it does not contain the totality of God’s reality. And I choose to trust that God’s presence will go with me (or more precisely all versions of me) into all future worlds branching from this moment. It is also occasionally tempting to ask whether different past lifestyle choices might have given my body a better chance of preventing the cancer. For all I know, there could be parallel versions of me which are still completely healthy. Be that as it may, this world is real, and my response to God needs to be, “Yes to you in this world”.

Jesus and Christ

In a Many Worlds reality, there are Earths in which Jesus of Nazareth was never born. What are the implications for Christian theology? In the development of Christian orthodoxy, Jesus was never synonymous with God nor with Christ. The title Christ, literally meaning “anointed one”, usually is taken to also imply Incarnation — that is to say a material host for God’s presence. Another bit of orthodox theology is that God’s intention is to invite all people to participate in the Christ mystery. By what means can this invitation be heard and accepted?

Whatever the Divine invitation looks like in different worlds, in a vast number of them it appears with differences from the world of our experience. Christians can at the same time embrace the creeds as a window into God’s narrative, and also the reality that they must describe at most a piece of the overall story. Helpful here is the theology of the universal or “cosmic” Christ, which describes a picture of God being Incarnate in all of the universe. There is no bit of matter which is not imbued with God’s presence. Against that backdrop, the idea of Christ in Many Worlds becomes magnificent. God’s invitation into conscious participation in the Christ mystery takes on an infinite set of permutations and infinite creativity.

However, we experience only one world. Besides cultivating a sense of awe, does an appreciation for Christ in Many Worlds have implications for how we interact with our own? I think it does. Even in the single world of our experience, Christians already have to deal with a multiplicity of historic and cultural “worlds”. From the millennia before Jesus to the present day, there have always been cultures which know nothing about Jesus, or at least nothing compelling. Does an authentic invitation into the Christ mystery exist for these people? The infinite creativity of God who offers Christ in a Many Worlds reality makes a compelling case that the answer is “yes”. If God demonstrates flexibility rather than rigidity in the Many Worlds universe he created, why would we expect him to otherwise in any single world? We just need to remember that these invitations, both in Many Worlds and in our single one, come in many forms. Correspondingly, acceptance of the invitation takes many forms as well.

Thus, a Many Worlds reality encourages us to shift the question from form to substance. Details of belief become less important than the experience of the Incarnation. Dogma about God becomes less important than relationship with God.

Conclusion

Physicists still debate, sometimes rationally and sometimes with religious fervor, whether the correct version of quantum mechanics involves Many Worlds. A significant number of us think that it probably does, because this is the simplest and most elegant version able to make correct predictions. Among these predictions is that there are parallel realities where we don’t exist and others where we exist under different circumstances. But we only experience one reality, and it is disconnected from the others.

People of faith have a spotty history when it comes to being receptive to science. Looking back, early Christian insistence that Earth must be at the center of the universe now looks silly. But we can say that in hindsight only because we learned from science an alternate interpretation of our faith, one which is open to a bigger reality. Given that the Physics community has not yet agreed on the correct interpretation of quantum mechanics, it would be unbecoming for people of faith to declare their loyalty to a Many Worlds viewpoint. But wouldn’t it be interesting for people of faith to be ahead of the game, cultivating an openness to this uncomfortable picture of reality?

A Many Worlds reality does not require an entirely new theology. But it does require a shift to a more expansive view, where we as a species and as individuals once again acknowledge that we are less central to overall reality than we had previously thought. It requires us to attribute to God more creativity and flexibility than was required in a single-world theology. When thinking about how all creation might participate in the Incarnation, Christians already needed to consider largely disconnected cultures on Earth and the strong likelihood of intelligent life elsewhere in the universe. In a Many Worlds reality, the need for an expansive view of Christ is writ in technicolor.

Likewise, single-world wisdom already suggested that we hold any sense of personal destiny with humility and grace. John Wimber, who attracted much attention as the leader of the Vineyard church movement, was fond of saying, “God, I’m just change in your pocket.” The wisdom of Wimber’s humble posture in a Many Worlds reality is even more profound. On the other hand, at the end of his life Saint Francis expressed a sense of having lived a personal calling, saying to his followers, “I have done what was mine to do. May Christ teach you what is yours.” Our task is to hold both views at the same time. We are quite small and not at the center of the story. And yet, this world of our experience is very real, and God invites us to willingly participate in the shaping of all its futures.

Further Reading

MIT physicist Max Tegmark published an introductory article Many Lives in Many Worlds in Nature; a free version of the article can be found here. Caltech physicist Sean Carroll wrote an excellent and accessible book Something Deeply Hidden, a good read for both non-experts and physicists. The Emergent Multiverse by David Wallace is a thorough book for physicists. And Observing a Quantum Measurement by Jay Lawrence is a physics journal article, which nicely illustrates how plain quantum mechanics makes correct predictions once the irreversibility of large systems is taken into account.

Brian Odom is a Professor of Physics and member of the Center for Fundamental Physics Northwestern University, and a member of Saint Chrysostom’s Episcopal Church in Chicago.