[Originally posted August 29, 2007]
In a New York Times article published on December 27, 2005, Dennis Overbye describes the role of quantum theory in the search for ultimate reality this way:
“Niels Bohr, the Danish philosopher king of quantum theory, dismissed any attempts to lift the quantum veil as meaningless, saying that science was about the results of experiments, not ultimate reality.” (Dennis Overbye, Quantum Trickery: Testing Einstein’s Strangest Theory, The New York Times, December 27, 2005.)
Bohr probably never used the phrase ‘quantum veil,’ but I find it an appropriate title for this series as I think you will see. What Bohr actually said was something like this:
“There is no quantum world. There is only an abstract physical description. It is wrong to think that the task of physics is to find out how nature is. Physics concerns what we can say about nature.” (Aage Petersen, Bohr’s assistant, paraphrasing Niels Bohr as quoted by Nick Herbert in Quantum Reality.)
Bohr, we remember, was the originator of the Copenhagen Interpretation of quantum theory, though he never called it that. The Copenhagen Interpretation developed from dialogs between Niels Bohr and Werner Heisenberg around 1927 when Heisenberg was employed as a lecturer at Bohr’s Institute for Theoretical Physics at the University of Copenhagen. Heisenberg was the creator of the uncertainty principle that bears his name. Heisenberg’s view favored the particle nature of matter with discontinuities during which the wave formulation affected the path of a particle. Bohr’s view was that it takes both the wave interpretation and the particle interpretation to understand the science at the quantum level. Bohr gave equal weight to both interpretations and called this concept ‘complementarity.’ Bohr’s view won out because quantum theory could not precisely address the crucial question of when the wave nature prevailed and when the particle nature prevailed. The most that could be said about this critical point is that the wave nature prevailed until a measurement was made or could in principle be made. This is known as the ‘measurement problem’ because the theory could not say precisely when a measurement might take place.
But, the really interesting thing about Bohr’s statement is that he had to say it at all. Was physics really about discovering ultimate reality? And what was there about quantum physics that made such a quest untenable? We have to recall that before quantum physics, the universe was completely deterministic. For every result, there was a cause. By chaining cause and effect together, and tracing the chain back to the first cause, one could, perhaps, discover the mind of God. This is not such a farfetched claim. Stephen Hawking made such a claim in A Brief History of Time:
“However, if we do discover a complete theory, it should in time be understandable in broad principle by everyone, not just a few scientists. Then we shall all, philosophers, scientists, and just ordinary people, be able to take part in the discussion of the question of why it is that we and the universe exist. If we find the answer to that, it would be the ultimate triumph of human reason – for then we would know the mind of God.” (p. 175, Bantam Books, 1988).
We can debate what a physicist means when he or she uses the word ‘God.’ Few would think that they mean a traditional personal God familiar to most people of faith. I think the G-word tells us more about a physicist’s motivation than anything about a personal belief. I think they are talking about religion in Paul Tillich’s sense of ultimate concern. When someone speaks about religion or god in this sense, they usually mean whatever motivates or drives a person to excel.
Another physicist, Richard Wolfson, put it less dramatically, but no less forcefully:
“I happen to believe, and most of my fellow physicists believe, that the laws of physics as we describe them are either a fairly accurate reflection or a very good approximation of an underling objective physical reality. We happen to believe that. I think it would be difficult to motivate doing physics if we didn’t believe that.” (Einstein’s Relativity and the Quantum Revolution, Lecture 1, The Teaching Company, 2nd Edition, 2000).
Albert Einstein also spoke of God, and he was deeply troubled by quantum theory. In particular he was troubled by the fact that quantum theory could only predict the statistical probability of the results of experiments and could not predict the actions of individual particles. He wrote to Max Born in 1926:
“Quantum mechanics is certainly imposing. But an inner voice tells me that it is not yet the real thing. The theory says a lot but does not really bring us closer to the secret of the ‘Old One.’ I, at any rate, am convinced that He is not playing at dice.”
This is usually paraphrased, “God does not play dice.” Nor was Einstein’s God a personal God. When asked by a Rabbi if he believed in God, Einstein replied, “I believe in Spinoza’s God who reveals himself in the orderly harmony of what exists, not in a God who concerns himself with fates and actions of human beings.” (New York Times, April 25, 1929). Spinoza, a pantheist, rejected dualism and believed that God and The Universe were one and the same. So another way to look at what a physicist means when he or she uses the word ‘god’ is the natural order of the universe as revealed by reason. The discovery and understanding of this natural order is what motivates the physicist to do physics.
This brings us back to the heart of the upheaval that took place in physics in the early twentieth century. At the end of the nineteenth century, physical science seemed to be on the verge of a complete description of the universe. Newton’s laws of motion and gravity had accurately described physical matter and Maxwell’s laws of electromagnetism had described the non-physical forms of energy. These two pillars of physics were the proud accomplishment of two centuries of post-enlightenment scientific thought.
Isaac Newton, working in the late seventeenth century, did not think his theories were contrary to the existence of God, but nevertheless they gave momentum to the Deist movement that promoted a god that did not intervene in the affairs of the world. Deists sought to strip traditional religion of its supernatural mysteries and proclaim a religion in concert with the natural universe. For Deists, the mind of God was revealed by reason and was synonymous with the natural order of the universe.
James Clerk Maxwell, working in the late nineteenth century and extending the work of Michael Faraday, created a set of mathematical equations that described the interaction of the electric and magnetic fields to produce all electromagnetic phenomenon. The most common form of electromagnetism that we encounter in everyday life is light. Maxwell’s laws formulated light as a wave that progressed through space much like an ocean wave traverses the ocean.
By the end of the nineteenth century the essence of the entire known phenomenon of the universe was explained by Newton and Maxwell. There were just two small problems that stood in the way of a complete understanding of ultimate reality. On April 27th, 1900, Lord Kelvin (Sir William Thompson) gave a lecture to the Royal Institution of Great Britain saying “two clouds” overshadowed “the beauty and clearness of theory”. These two clouds were the unexpected results from two experiments. One experiment measured the energy given off from a perfectly radiating object, called ‘blackbody radiation’ and the measured spectrum of energy was not in agreement with expectations. The second experiment was the Michelson-Morley experiment, and it attempted to measure the speed of the earth through the ether by measuring the velocity of light as the earth orbited the sun. Lord Kelvin had proposed the ether as the medium through which light waves traversed empty space. The Michelson-Morley experiment could detect no change in the velocity of light as the earth orbited the sun, another unexpected result.
The answer to these two problems required the development of Einstein’s relativity to solve the problem concerning the velocity of light and quantum theory to solve the problem of blackbody radiation. But these two theories radically changed our understanding of the universe. With relativity, measurements of distance and time could no longer be thought of as an abstract, universal overlay to the physical universe. Measurements of distance and time were part of the underlying reality of the universe. With quantum theory, the underlying reality of the universe was statistical and not deterministic. Quantum theory had a second devastating effect: light could not be thought of as exclusively a wave phenomenon. Energy was transferred in packets of energy called photons, and the energy depended on the frequency of the underlying wave. In other words, each photon transferred energy to a specific location. The transferred energy was not spread out as would be suggested by a wave model.
The revelation that the universe was non deterministic was so devastating to the ideals of physics that Einstein was never reconciled to it. The reason this is such a problem for physics is that it changes forever what we can know about ultimate reality. How can light be both a particle and a wave? How can electrons and other sub-atomic particles be both a particle and a wave? When energy is transferred from one point to another at the quantum level, how does the universe choose the particular outcome from the many theoretical possibilities? Physicists would love to describe in detail how the quantum world works, but are forever prevented from knowing for sure. From the outside, the best answer looks like little more than statistical modeling so that the results of experiments agree in aggregate with theory. The theory says nothing about how the universe actually works behind the quantum veil. That is why Bohr had to declare that the quantum world does not exist.
Therefore, any discussion about what is behind the quantum veil is speculation. But speculation can run the gamut from reasoned conjecture to uninformed surmise. And the question I would like to address in the next segment is this: Are the laws of physics, as we now know them, compatible with a personal God, a God who cares about the fate of individuals and intervenes in human history? Or is belief in a personal God necessarily delusion as some have proclaimed? And, how do we discuss such an issue without getting lost in idle speculation? Is there a way to use reason as a guide?