Parallel Universes

Getting to Parallel Universes via the Copenhagen Interpretation

Why do some physicists believe there may be parallel universes? The usual path to this is through quantum mechanics. Developed a century ago, quantum mechanics is the physics of very small particles, such as electrons. Starting in the late 19th century, a series of experiments demonstrated that classical mechanics developed by Sir Isaac Newton in the late 17th century failed to accurately describe the motion of subatomic particles. This was quite a shock since classical mechanics had described the macroscopic world so accurately for two centuries. It took a few decades to develop the foundation of quantum mechanics. Perhaps the greatest difference between classical mechanics and quantum mechanics is how well we can know things. In classical mechanics, our ability to know the position and velocity of a particle is limited only by how precisely we can measure them. If we could measure with infinite precision the position and motion of a particle at some time and if we precisely knew the forces acting on the particle, then we could predict the future position and velocity of the particle with infinite precision. However, in quantum mechanics our ability to measure such things is limited because the microscopic world is fuzzy.

Fuzzy and Wavy

Why is the microscopic world fuzzy? Subatomic particles behave as if they are waves. A particle can be localized in that we can express its position as the location of its center of mass. But by its very nature, a wave is spread out, so what is its location? One could argue that a wave’s location is the position of the wave’s maximum height, but one could just as well claim the wave is located at the wave’s minimum height—or the location could be somewhere in between. Physicists express this fundamental fuzziness with the Heisenberg uncertainty principle. This uncertainty is not a matter of not having enough information or lacking precision. The uncertainty of quantum mechanics is fundamental in that there is a limit of how precisely we can know things about subatomic particles, such as their position or energy, regardless of how precisely we think we ought to be able to measure such things.

One key part of quantum mechanics is the Schrödinger wave equation. Physicists solve this equation to describe the behavior of subatomic particles. A famous example of this is firing a collimated beam of electrons at two slits located close to one another. When waves approach two closely spaced slits, the waves pass through both slits simultaneously so that the two transmitted waves produce an interference pattern on the other side. This is a well-understood behavior of waves. When many electrons are substituted for the waves, they too exhibit an interference pattern on the other side, indicating that the electrons passed through both slits simultaneously, much as waves do. That is even though electrons often exhibit behavior in other experiments that indicate they are particles and not waves. Nevertheless, the appropriate solution to the Schrödinger equation in this situation accurately predicts the distribution of the electrons that have passed through the slits. But the story gets weirder. It is possible to redo the double-slit experiment so that instead of monitoring many electrons, we measure individual electrons to see if they pass through both slits of just one of the slits. When we do this experiment, we find that rather than passing through both slits, the electrons pass through one slit or the other. How can this be?

This agreement between theory and reality is the gold standard in testing ideas in science.

This perplexing question consumed physicists nearly a century ago. Physicists quickly realized that the wave solution of the Schrödinger equation for a system of identical particles was a probability function. A wave is positive over half of its domain and negative over the other half. Squaring the wave eliminates all negative values. This squared wave accurately predicts the distribution of a large sample of quantum mechanical particles, such as electrons. Where the probability is high, there are many particles, and where the probability is low (near zero), there are few particles. Hence, the wave equation of an experiment must be treated as a probability distribution of a large sample of experiments. The observed distribution of particles in experiments always matches the distribution function predicted by the wave equation for the experiment. This agreement between theory and reality is the gold standard in testing ideas in science. Still, when we consider individual particles, they assume a single value, such as going through one slit or the other rather than going through both slits as when considering a large sample. How can we resolve this apparent discrepancy?

A Resolution?

Around 1930, Niels Bohr proposed his Copenhagen interpretation to resolve this question. Named for where Bohr lived and worked at the time, the Copenhagen interpretation posits that all particles subject to quantum mechanical experiments exist in all probability states simultaneously. The particles exist in this odd state until we perform the experiment of observing the behavior of individual particles. The act of observing a particle causes its wave equation to collapse, and only then does the particle assume a particular state. As weird as this understanding is, it has been the dominant belief among physicists since its inception. It has deep, metaphysical implications. For instance, the universe could be viewed as the sum of many quantum mechanical experiments making the universe the ultimate quantum mechanical experiment. If so, then how can the universe assume a definite state of existence unless there is someone to observe the universe, causing the wave function of the universe to collapse into a state of definite existence? Some physicists reason that the answer to that question may explain our existence. If the universe did not contain any sentient life to observe that the universe exists, then the universe’s wave function would not collapse, and the universe would exist only in the never-never world of a probability function. That is, the existence of the universe depends upon our presence to observe the universe and hence collapse its wave function so that the universe could exist.

If there is only one universe, then that universe is extremely improbable.

This approach has been invoked to explain the highly improbable characteristics of the universe that seem to make our existence possible. Many physicists and cosmologists have marveled over the fine-tuning that our universe seems to display. In 1973, Brandon Carter coined the term anthropic principle to refer to the fact that the universe appears designed for man. If even one of many properties of the universe were changed only slightly, then the universe would not be conducive to our existence. In their 1986 book, The Anthropic Principle, John Barrow and Frank Tipler argued that the universe only appears to be designed. They reasoned that if the universe were any different, then we wouldn’t be here to have this discussion, so it shouldn’t be any surprise that the universe appears to favor our existence. But this avoids the question entirely. If there is only one universe, then that universe is extremely improbable. If there is a very large number (infinite?) of ways that the universe could have existed, but most are inhospitable for life, why is that the universe just happened to have the right properties that make life possible?

One way out of this dilemma is to assume that our universe is not the only universe. The multiverse, as this idea has come to be called, is the belief that there are many, perhaps an infinity of, universes. Most universes are sterile, lacking any life at all, but a very tiny minority of universes are conducive for life. Since we cannot exist in most universes, there is a selection effect so that living beings exist only in the relatively rare universes where life is possible. What if we apply the Copenhagen interpretation to the multiverse? Assuming that the Copenhagen interpretation is applicable to all universes, only those universes having sentient beings undergo wave function collapse to assume very physical existence. All other universes where sentient life does not exist remain in a condition of simultaneously existing and not existing. Therefore, only universes that exist are those where sentient life is present. Therefore, the selection effect works in the opposite direction that Barrow and Tipler proposed: we don’t exist because the universe exists in a certain state, but the universe exists in a certain state because we exist.

The Many-World Interpretation

One can reach this conclusion about other universes in other ways. Here is one. While the Copenhagen interpretation is the dominant understanding of quantum mechanics, it is not the only interpretation of quantum mechanics. In 1957, Hugh Everett offered his many-worlds interpretation. Rather than relying upon a collapsed wave function, the many-worlds interpretation is that the wave function is objectively real. Therefore, all possible outcomes of a quantum mechanical experiment are played out physically in proportion to the probabilities. Since in our universe only one possibility is manifest, then the other possibilities must play out in other worlds, or other universes. Consequently, each quantum mechanical experiment results in the creation of alternate universes branching off from our universe. When multiplied over all possible events over all time, there must be a staggering number of alternate universes, with new ones with identical histories being created all the time. When first proposed, Everett’s idea was largely panned, but it has received increasing support, particularly in recent years.

Assuming that the whole is the sum of the parts, even macroscopic possibilities must be subject to this interpretation. Whenever a macroscopic choice is presented, new universes are spawned, where each possibility plays out in separate universes. For instance, I usually wear to work whatever my wife lays out for me the night before. Last night, she laid out black slacks and an olive polo shirt for me to wear today, so that is what I am wearing while I type this. But she could have picked any number of other ensembles for me to wear. So, there must be several other universes where I am typing away on this blog while wearing entirely different clothes. Or perhaps there is a universe where I am wearing what I am wearing right now but I’ve decided to take a break and watch a cat video on the internet. I hope that my boss in that alternate universe, Andrew Snelling, doesn’t find out! Or maybe in that alternate universe someone else is my boss, or maybe I’m the boss. The possibilities are endless. This is how people arrive at the thinking upon which the Twilight Zone episode I mentioned at the beginning of this blog.

Conclusion

There are other ways to reach the same conclusion about the existence of a multiverse. Many of them are tied to quantum mechanics, but many are tied to general relativity. Quantum mechanics and general relativity are the twin pillars of modern physics, but they ultimately are incompatible theories. For instance, there is no theory of quantum gravity. Most physicists believe that unification of these two theories into a single one is possible, but that new, more encompassing theory probably lies far into the future. It is this pursuit of unification that has led many physicists to think that there is a multiverse. Not many years ago the notion of a multiverse was a far-out idea, but now it has become mainstream.

How should the Bible-believing Christian respond to these musings? Some Christians might conjecture that God is the Observer responsible for collapsing the wave function(s). However, this would seem to limit God, forcing him to abide by some principle that is out of his control. Of course, some people who have suggested that God is the supreme Observer have a decidedly nonbiblical view of a very limited Creator. Notice that much of this thinking about the multiverse was prompted by a desire to avoid the design implications of the universe. If there is no Designer, then design cannot exist, so when one sees what appears to be design, it must be explained away. But to the Christian, we expect to see design in the world because God designed the world for us. We have a purpose, and so the world has a purpose too. Since there is design in the world, then there is no reason to invoke parallel universes. Therefore, the multiverse and other ideas about parallel universes are antithetical to biblical thinking.

I began this blog by saying I had developed an elegant, irrefutable proof that there are no parallel universes. If parallel universes exist with all possible outcomes playing out in those universes, then there must exist at least one universe where the Captain and Tennille recording of “Muskrat Love” was the number one song of the 1970s. Everyone knows that is impossible. Hence, there is no universe where “Muskrat Love” was the number one song of the 1970s. Therefore, there are no parallel universes where all possible outcomes play out.

Q.E.D.