In my last blog I objected to a statement made by physicist David Tong in the December 2012 Scientific American who said it is a "lie" that the building blocks of nature are discrete particles such as the electron or quark. Rather, Tong asserted, the building blocks of our theories are quantum fields.
Here I want to explain why this is not just a pedagogical issue, a trivial dispute between two eggheads. It has real consequences on how scholars outside of physics, as well as the reading public, interpret the dramatic developments in fundamental physics, both experimental and theoretical, that began early in the twentieth century and continue today. Believe it or not, the particle-field debate affects heavy discussions on theology, spirituality and the interaction of religion and science.
Those who read the popular literature on science and religion, such as Tong's article, may receive the impression that modern physics has refuted the picture of atoms and the void proposed by Democritus and other Greek philosophers millennia ago. For example, in The New Sciences of Religion: Exploring Spirituality From the Outside in and Bottom Up, Christian apologist William Grassie says, "The concept of materialism deconstructed itself with the advent of quantum mechanics and particle physics."
To be ecumenical, Grassie quotes the Hindu physicist Varadaraja V. Raman: "Physics has penetrated into the substratum of perceived reality and discovered a whole new realm of entities there, beyond the imagination of the most creative minds of the past."
Now, maybe Democritus did not imagine quarks. But he did imagine material particles, and the quarks, at least in the current model, are material particles. The "new realm of entities" uncovered in modern physics is hardly beyond imagination. They are imagined in the quantum theory of fields, although just imagining something does not make it real -- despite what some theologians claim and what some physicists seem to believe.
The claim that quantum mechanics has revealed a reality beyond matter is based on the notion that two separate realities exist: discrete, particulate matter and a plenum that is reminiscent of the long-discredited aether. However, at least the electromagnetic aether was material. The new aether is more abstract, more in tune with the duality of mind and body that is embedded in all religious thought. Unsurprisingly, theologians and spiritualists delight in this new dualism -- handed to them on a platter by theoretical physicists.
The idea that abstract, holistic quantum fields are the deeper reality while particles are simply the excitations of the fields did not begin with David Tong. Indeed, it has almost become a mantra. For example, in The Atom in the History of Human Thought, historian Bernard Pullman writes,
To the extent that a Democritean influence has shaped our conception of the world, there has been a tendency to stress the corpuscular aspect of the standard model and to introduce a certain formal distinction between particles of matter and intermediary particles associated with force fields. As a result, we may have given the impression that that this corpuscular aspect provides the most exact description of physical reality. Such a view would be unfortunate, as it might obscure what is considered today as the most plausible picture of reality, which not only unifies the concepts of particles and fields, but even considers fields preeminent over particles ... The fundamental and underlying reality of the world is embodied in the existence of a slew of fields and in their interactions.
Pullman is applying the Platonic view of reality, which, as I have discussed previously, is the working assumption of most theoretical physicists and mathematicians. In order to test their models, physicists assume that the elements of these models correspond in some way to reality. But they are compared against the data that flow from our so-called "particle detectors" on the floor of an accelerator lab. It is the data that form the concrete foundation of our knowledge. What is fundamental in our model is not necessarily fundamental to our knowledge. Models are squiggles on the whiteboards in the theory section of the physics building. Those squiggles are easily erased; the data aren't.
Indeed, unpublished results are beginning to trickle in that the whiteboard squiggles of a generation of theorists describing their speculations on a theory called supersymmetry may soon be erased by data from the LHC. Although we need to wait and see, such a result would provide dose of humility to those who think they can infer reality by their thoughts alone, as well as an impetus to explore more unorthodox approaches.
The application of Platonic reality to physics is fraught with problems. First, theories are notoriously temporary. We can never know if quantum field theory will someday be replaced with another more powerful theory that makes no mention of fields (or particles, for that matter). Second, as with all physical theories, quantum field theory is a model -- a human invention. We test our models to find out if they work; but we can never be sure they correspond to "reality." That's metaphysics. If there were an empirical way to determine ultimate reality, it would be physics, not metaphysics. Third, quantum fields all have quanta that we associate with the so-called elementary particles.
In relativistic quantum field theory, which is the fundamental mathematical theory of particle physics and the basis of the standard model, each quantum field has an associated particle called the quantum of the field. These are the elementary particles of the highly successful standard model developed in the 1970s. The recent confirmation of the Higgs boson was a great triumph of the theory. The photon is the quantum of the electromagnetic field. The electron is the quantum of the Dirac field. The Higgs boson is the quantum of the Higgs field. I know of no empirically verified example where a quantum field exists without its quantum. Particles are just as much building blocks of our theories as fields. In fact, they are the same building blocks.
There are no exceptions. For every field, we have a particle; for every particle, we have a field. So, it is incorrect to think that field and particle exist as separate realities. We do not have a field-particle duality. We have, as Pullman says, a field-particle unity.
Please note that the elementary particles of the standard model are not to be thought of as classical objects like billiard balls; they obey all the rules of quantum mechanics. For example, as Feynman showed back in 1948, electrons can zigzag back and forth in space-time and thereby appear many places at the same time. This is usually called "nonlocality" but a better term is "multilocality." Note that, in this picture, the electron never moves faster than the speed of light. No superluminal connections of any kind are required when you recognize that time is reversible in physics. I'll expand on that at another time.
How does all this relate to the so-called wave-particle duality that you read about in books on quantum mechanics (textbooks as well as popular books)? The authors often write, "An object is either a particle or a wave, depending on what you decide to measure." This is very misleading and has led to the widespread misconception that quantum mechanics shows that human consciousness has the ability to control reality, namely, to decide whether an object is a particle or a wave. That object could be a pulse of light from galaxy 13 billion light-years away. So, the implication is that if we can control the nature of reality with our minds, this must occur not just here and now but throughout the universe and for every moment in time, past and future. Do you believe this? This is exactly what the quantum spiritualists, who hear that particles (which cannot travel faster than light) are a lie, are saying.
For those who have not moved beyond non-relativistic Schrödinger wave mechanics, the wave picture provides a perfectly good model to compute quantum effects, without having to think about what mysterious aether is doing the waving. To nuclear and particle physicists who must deal with higher energy phenomena, relativistic quantum mechanics and quantum field theory provide the tools for their calculations, without having to think about which is more real--fields or particles. Both theories are fully materialistic and constitute triumphs for Democritean atomism.
In short, quantum physics has not done away with matter. Matter can be defined as stuff that kicks back when you kick it. When you kick a rock, it kicks back. And when you kick an electron, it kicks back. And that's no lie.
William Grassie, The New Sciences of Religion: Exploring Spirituality From the Outside in and Bottom Up, (New York: Palgrave Macmillan, 2010), p. 169.
Varadaraja V. Raman, Truth and Tension in Science and Religion, (Center Ossipee, NH: Beech River Books, 2009), p. 115.
Bernard Pullman, The Atom in the History of Human Thought; a Panoramic Intellectual History of a Quest That Has Engaged Scientists and Philosophers for 2,500 Years, (Oxford and New York: Oxford University Press, 1998), pp. 346-47.