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How Weird Is the World?

Quantum mechanics has a reputation for “weirdness,” which has become almost a technical term in popular discussions. Many of its implications are not only contrary to everyday experience but seem absurd to the uninitiated. However, quantum theory isn’t just speculation about strange phenomena. It is supported by many high-precision experiments and has not yet failed any observational test. Because some writers have drawn far-reaching philosophical and theological conclusions from the theory, it is important for us to have some idea of what it’s about.

The older physics was very successful with its assumption that the energy of a system could vary by arbitrarily small amounts: “Nature does not make jumps.” But this gave the absurd result that a heated body would radiate energy at an infinite rate. In 1900 Max Planck showed that correct results could be obtained if energy could be radiated or absorbed only in discrete amounts, or quanta. Albert Einstein suggested that light actually traveled as particles, though it was known to have wavelike properties, and Niels Bohr used the idea of “quantum jumps” to explain the hydrogen atom’s structure.

Toward an Adequate Theory
These provocative ideas explained puzzling phenomena and demanded a revision of the traditional picture of the physical world but did not constitute an adequate theory. One suggestion toward such a theory was provided by Louis de Broglie’s suggestion that not only light but everything else had a dual character, so that waves were associated with all types of matter. In 1925 Erwin Schrödinger developed an equation to describe how these waves would behave in various situations, making it possible to describe the properties of atoms and molecules, their interactions with light, and particle collisions.

Werner Heisenberg had already found another version of quantum mechanics. He wrote equations for the motion of a particle that look like those of classical physics but in which position and velocity are represented by matrices — square arrays of numbers that don’t obey all the laws of elementary algebra. These equations also gave correct descriptions of atomic phenomena. “Wave mechanics” and “matrix mechanics” are different mathematical representations of the same underlying theory.

Particles or waves? Bohr argued that these are complementary aspects of the world. In an experiment designed to measure particle properties, the wave aspect will not appear, and vice versa, but both descriptions are needed to deal with the totality of phenomena. There have been attempts to extend the concept of complementarity to other pairs of descriptions outside the atomic realm, and some have suggested that the human and divine aspects of Christ can be understood as complementary. This works better for a Reformed Christology than for traditional Lutheran Christology, in which there is a closer communication between divine and human natures.

How is this theory to be interpreted? The waves that Schrödinger’s theory describes are waves of probability, telling us the relative likelihood of finding a particle at different points. Heisenberg’s analysis of position and velocity measurements resulted in his uncertainty principle, which says that they cannot be known simultaneously with complete precision. This is a radical departure from the common-sense view of classical physics that we can, in principle, know both quantities exactly.

This shatters the old mechanical picture of the world in which the future state (positions and velocities) of any physical system is determined by its initial state and the forces that are acting. The elimination of complete determinism was greeted eagerly by some as a way to understand how people could have free will, and even as an explanation of how God might have some freedom to act within the limits of the laws of physics. Quantum uncertainty in mutations of the DNA molecule might provide a way for God to give direction to the evolutionary process.

But we should not overstate matters: Quantum physics freed the will only if classical physics enslaved it.

Doubts
Einstein was a major contributor to the development of quantum theory, but he was never able to accept its fundamental uncertainty and what he saw as its lack of realism. He thought it was correct as far as it went but incomplete. In 1935 Einstein, with coworkers Podolsky and Rosen (hence the abbreviation EPR), described a hypothetical experiment that he thought showed this incompleteness. The EPR argument assumed that there could be no instantaneous interaction between two separated particles — what Einstein called “spooky action at a distance.”

Most physicists were not convinced by this argument, but some had an uneasy feeling about it. In the 1970s it became possible actually to do the type of experiment proposed by EPR, and it was found that there is “spooky action at a distance,” known more formally as quantum nonlocality. Once two particles have interacted, their waves remain entangled even when they have separated to a great distance. Thus the quantum world has a more holistic appearance than that of classical physics. In many problems we can focus on a small part of the world, but in principle everything is interconnected. This nonlocality provides at least an analogy for speaking about the omnipresence of Christ’s humanity, which Luther and the Formula of Concord insist on.

Few physicists have any doubt that quantum mechanics is correct in the sense that it gives the correct numerical results for the results of experiments. But there is a puzzle that has provoked a great deal of debate and a number of radical proposals for solutions: the measurement problem.

The wave that tells us the probabilities of finding an electron in different places spreads through space in the course of time in a way described by Schrödinger’s equation. Until we actually measure its position we know only these probabilities. But once we measure the position we find that it is 100 percent at one place and nowhere else. Somehow the wave has “collapsed” to a single point. But why? Many textbooks say that the physical interaction involved in the measurement is responsible, but this is too simple an answer. There are situations in which the wave will collapse because the measuring apparatus fails to observe the electron.

“Wild” Explanations
One wild-sounding explanation that is nevertheless serious science and not just fantasy is the many-worlds interpretation (MWI). For an experiment in which an electron could be at A or B, this explanation says that a measurement will not collapse the wave but instead will split the universe in two! In one branch universe the electron is at A, and in the other it’s at B. Because of all the observations that can be made, our world is then just one of a vast number making up a “multiverse.” For theologians this raises challenging questions about divine sovereignty and eschatology.

Another proposal is that the collapse of the wave occurs only when the results of a measurement reach the level of consciousness. This suggests that intelligent life plays a fundamental role in the existence of a real world. But many physicists are content with more prosaic solutions of the measurement problem.

A good introduction is John C. Polkinghorne, The Quantum World (Princeton, 1989). Einstein’s coworker Banesh Hoffmann explained the theory and its history in The Strange Story of the Quantum, second edition (Dover, 1959). Some recent developments are described in Amir D. Aczel, Entanglement (Plume, 2001).

George L. Murphy, an ELCA pastor and physicist living in Tallmadge, Ohio, is an adjunct faculty member at Trinity Lutheran Seminary in Columbus and a pastoral associate at St. Paul’s Episcopal Church in Akron. His e-mail address is gmurphy@raex.com.