…the particle interpretation of quantum physics, as well as the field interpretation, stretches our conventional notions of “particle” and “field” to such an extent that ever more people think the world might be made of something else entirely.
Kuhlmann is currently a philosophy professor at Bielefeld University in Germany and has dual degrees in physics and philosophy. I was happy to see that he is firmly committed to the idea that the task of understanding the physical world requires both disciplines.
The two disciplines are complementary. Metaphysics supplies various competing frameworks for the ontology of the material world, although beyond questions of internal consistency, it cannot decide among them. Physics, for its part, lacks a coherent account of fundamental issues, such as the definition of objects, the role of individuality, the status of properties, the relation of things and properties, and the significance of space and time.
Kuhlman takes the time to describe, in fairly simple terms, the content of the Standard Model which consists of groups of elementary particles and the forces that mediate their interaction. He describes how the particles blur into fields while, at the same time, the fields are quantized rather than continuous. His discussion of how the particles are not really particles and the fields are not really fields leads him to his point:
If the mental images conjured up by the words “particle” and “field” do not match what the theory says, physicists and philosophers must figure out what to put in their place.
Kuhlman then takes his article in two interesting directions. The first is to focus on the notion of structure.
A growing number of people think that what really matters are not things but the relations in which those things stand…We may never know the real nature of things but only how they are related to one another…New theories may overturn our conception of the basic building blocks of the world, but they tend to preserve the structures. That is how scientists can make progress.
I was immediately reminded of a passage in the Courant/Robbins classic What is Mathematics? When I first read the book, I was impressed with implications of this observation which appears early in the text.
The “ether” was invented as a hypothetical medium capable of not entirely explained mechanical motions that appear to us as light or electricity. Slowly it was realized that the ether is of necessity unobservable; that it belongs to metaphysics and not to physics. With sorrow in some quarters, with relief in others, the mechanical explanations of light and electricity, and with them the ether, were finally abandoned.
A similar situation, even more accentuated, exists in mathematics. Throughout the ages mathematicians have considered their objects, such as numbers, points, etc., as substantial things in themselves. Since these entities had always defied attempts at an adequate description, it slowly dawned on the mathematicians of the nineteenth century that the question of the meaning of these objects as substantial things does not make sense within mathematics, if at all. The only relevant assertions concerning them do not refer to substantial reality; they state only the interrelations between mathematically “undefined objects” and the rules governing operations with them. What points, lines, numbers “actually” are cannot and need not be discussed in mathematical science. What matters and what corresponds to “verifiable” fact is structure and relationship, that two points determine a line, that numbers combine according to certain rules to form other numbers, etc. A clear insight into the necessity of a dissubstantiation of elementary mathematical concepts has been one of the most important and fruitful results of the modern postulational development.
Fortunately, creative minds forget dogmatic philosophical beliefs whenever adherence to them would impede constructive achievement.
In the context of the Courant book, this is an important observation about the development of mathematics. But I have always thought that it can be seen as an important observation of a more general intellectual maturity. And this, I think, leads to Kuhlmann’s second alternative for interpreting the meaning of quantum physics which chooses ‘properties’ rather than ‘objects’ as having an existence.
What we commonly call a thing may be just a bundle of properties: color, shape, consistency, and so on.
This idea is consistent not only with current theories in cognition, but also has roots in 19th century philosophy and science (in the work of Hermann von Helmholtz and Johann Friedrich Herbart, for example). Kuhlmann rightly argues that our first experiences are of properties.
As infants, when we see and experience a ball for the first time, we do not actually perceive a ball, strictly speaking. What we perceive is a round shape, some shade of red, with a certain elastic touch. Only later we do associate this bundle of perceptions with a coherent object of a certain kind – namely, a ball. Next time we see a ball, we essentially say, “Look, a ball,” and forget how much conceptual apparatus is involved in this seemingly immediate perception.
With respect to physics,Kuhlmann explains
theory predicts that elementary particles can pop in and out of existence quickly. The behavior of the vacuum in quantum field theory is particularly mind-boggling: the average value of the number of particles is zero, yet the vacuum seethes with activity…A particle is what you get when those properties bundle themselves together in a certain way.
The forgetting of ‘conceptual apparatus’ to which Kuhlmann refers is the very thing that I always hope (and expect) that mathematics will remind us of – in one way or another.