Sabrina (Beishi) Hao

In this paper, I explore the relation between actual scientific practice and conceptual interpretation of scientific theories by investigating the particle concept in non-relativistic quantum mechanics (NRQM). On one hand, philosophers have raised various objections against the particle concept within the context of NRQM and proposed alternative ontologies such as wave function realism, Bohmian particles, mass density field, and flashes based on different realist solutions to the measurement problem. On the other hand, scientists continue to communicate, reason, and explain experimental phenomena using particle terms in the relevant regimes.

It has been explicitly argued and, for most of the time, implicitly assumed in the philosophical literature that we do not need to take scientists’ particle talk seriously, and recovering position measurement of particles in our ontological accounts is sufficient to make contact with scientific practice. In this paper, I argue that although scientific discourse does not postulate a uniform and coherent ontology, it nevertheless postulates real properties. Our ontological accounts thus need to recover the various properties associated with the NRQM particle concept in scientific discourse. I show that recovering these particle properties is not trivially achievable by pointing out some particular challenges these revisionary ontologies face in the process.

The consensus among philosophers of physics is that quantum field theory is not fundamentally about particles, yet whether we should admit particles as emergent entities into our ontology remains unsettled. In this paper, I defend the existence of particles from a bottom-up approach by examining the causal structure in experimental setups and what scientists prepare, manipulate, detect, and measure in experimental details. I argue that particles need to be postulated to explain experimental phenomena and that the existence of particles is epistemically independent of the fields. Therefore, particles should be considered independent, distinct elements in our ontology.

Our theoretical understanding of particles has changed from classical to quantum mechanical and relativistic, but particle terms continue to refer. In this paper, I defend the causal theory of reference for natural kind terms in scientific theories by providing a fine-grained account on how to understand the reference fixing event for a natural kind term. I argue that the event that fixes the reference for a natural-kind term occurs during the confirmation stage instead of the hypothesis stage of a scientific theory. 

Consider the phlogiston theory that was once widely accepted but later abandoned by scientists: scientists first discovered some phenomena that demanded an explanation—combustion. They postulated different hypotheses including the phlogiston theory. At this time, the term “phlogiston” was already introduced, but it did not yet refer to anything because there was little evidence for the term users to believe in the referent’s existence. Then scientists designed and performed new experiments to test the hypotheses. This is when the process of reference fixing started, but it never succeeded for phlogiston because its existence was never confirmed. 

The case for electrons is different: through the successful detection of electrons in cloud chambers and other detectors, the reference for the term is fixed by the descriptions of these experimental setups. Although descriptions of electrons’ theoretical properties were later revised due to theory changes, the term continues to refer to the entities detected by the early detectors.

1. A paper on the difference between theoretical evidence and experimental evidence for an entity's existence. Theoretical evidence for an entity’s existence is that the entity is postulated in the theoretical explanation of an experimental phenomenon; experimental evidence for an entity’s existence is that the entity is postulated in the direct causal explanation of an experimental phenomenon. I maintain that there is an epistemic distinction between committing to quarks because they are postulated in the theoretical explanation of proton mass and committing to electrons because they are postulated in the causal explanation of a cloud chamber (i.e., an electron detector). 

2. A paper on how an unobservable natural kind term's reference gets fixed when scientists come to the consensus that its existence is confirmed. Confirmation is achieved if the set of evidence is strong enough to rule out all other possible theoretical hypotheses and only one scientific explanation of the observed phenomena is confirmed. The reference is thus fixed through some crucial causal properties postulated in that explanation.

3. A paper proposing a novel definition for emergent entities based on the ontological distinction between state-independent and state-dependent properties. State-independent properties are the properties that are carried by the bearers all the time regardless of what state the bearers are in. In contrast, state-dependent properties are the ones that are carried by the bearers only when the bearers are in some specific states. Following this, I define emergent entities as the ones that 1) can be seen as specific states of some other entities and 2) carry a set of state-independent properties crucial to scientific explanation that are not state-independent for other entities. 

4. A paper proposing a revised version of structural realism reconciling with traditional scientific realism. For non-fundamental levels, even if we grant that we should only commit ourselves to the structural content of our theories, this structural content already instantiates emergent entities (just like the structure of the fields instantiates particles). 

In Dao De Jing, the most important work of Daoism, Lao Zi considers the common-sensical intuition of carving nature in a binary way: if there is a concept of beauty then there is a concept of ugliness (non-beauty); if there is a concept of goodness then there is a concept of badness (non-goodness). This phenomenon also occurs in Western logic and can be related to the set-theoretic representation of properties: naively, for every property P, there exists a set whose members are all and only the objects that satisfy P and a set whose members are all and only the objects that do not satisfy P. This binary nature in Western logic leads to famous paradoxes, including Russell’s paradox in set theory.

Lao Zi suggests that we should see the opposite beings and properties as co-existent and complementary to each other. All beings in the binary world that we observe are derived from Oneness, and Oneness is derived from Nonbeing—Dao. If we consider the concept of Oneness in a set-theoretic framework, it should be represented by the universal set which includes itself. Most importantly, Oneness is not subjected to paradoxes because the concepts of truth, negation, and contradiction are all derived concepts and cannot be attributed to the descriptions of Oneness. Oneness is metaphysically prior to all binary and negatable concepts. In this way, I offer a new perspective on some key ideas in Dao De Jing by situating them in the framework of Western logic. 

In 1922, Fung Yu-lan published a famous paper titled "Why China Has No Science", in which he argued that "what keeps China back is that she has no science", but that "China has no science, because according to her own standard of value she does not need any." In this paper, I compare the verdicts on values of science in Daoism and Western analytic tradition by tracing the source of the difference to their different metaphysical pictures.