Shan Gao

Hardy’s $$\psi$$ -ontology theorem proves the reality of the wave function under the assumption of restricted ontic indifference. It has been conjectured that restricted ontic indifference, which is a very strong assumption from the $$\psi$$ -epistemic view, can be derived from two weaker sub-assumptions: an ontic state assumption and a locality assumption. However, Leifer argued that this derivation cannot go through when considering the existence of the vacuum state in the second-quantized description of quantum states. In this paper, I present a new analysis of Hardy’s theorem. First, I argue that the ontic state assumption is valid in the second-quantized description of quantum states. Second, I argue that the locality assumption is a locality assumption for product states and it is weaker than the preparation independence assumption of the PBR theorem. Third, I argue that Leifer’s objection to the derivation of restricted ontic indifference is invalid. Finally, I argue that although the vacuum state is irrelevant, the existence of the tails of the wave function will block the derivation of restricted ontic indifference from the ontic state assumption and the locality assumption.

It is argued that in Bohmian mechanics the effective wave function of a subsystem of the universe does not encode the influences of other particles on the subsystem. This suggests that the ontology of Bohmian mechanics does not consist only in Bohmian particles and their positions. It is nonetheless pointed out that since the wave function in configuration space may represent the state of ergodic motion of non-Bohmian particles in three-dimensional space, the ontology of Bohmian mechanics may still consist only in particles.

It has been argued that the existence of a minimum observable interval of space and time is a model-independent result of the combination of quantum field theory and general relativity. In this paper, I promote this result to a fundamental postulate, called the MOIST postulate. It is argued that the postulate leads to the existence of a maximum signal speed and its invariance. This new result may have two interesting implications. On the one hand, it suggests that the MOIST postulate can explain the invariance of the speed of light, and thus it might provide a deeper logical foundation for special relativity. Moreover, it suggests that the speed constant c in modern physics is not the actual speed of light in vacuum, but the ratio of the minimum observable length to the minimum observable time interval. On the other hand, the result also suggests that the existing experiments confirming the invariance of the speed of light already provide observational evidence to support the MOIST postulate.

According to Penrose, the fundamental conflict between the superposition principle of quantum mechanics and the principle of general covariance of general relativity entails the existence of wavefunction collapse, e.g. a quantum superposition of two different space–time geometries will collapse to one of them due to the ill-definedness of the time-translation operator for the superposition. In this paper, we argue that Penrose's conjecture on gravity's role in wavefunction collapse is debatable. First of all, it is still a controversial issue what the exact nature of the conflict is and how to resolve it. Secondly, Penrose's argument by analogy is too weak to establish a necessary connection between wavefunction collapse and the conflict as understood by him. Thirdly, the conflict does not necessarily lead to wavefunction collapse. The reason is that the conflict or the problem of ill-definedness for a superposition of different space–time geometries also needs to be solved before the collapse of the superposition finishes, and once the conflict has been resolved, the wavefunction collapse will lose its physical basis relating to the conflict. In addition, we argue that Penrose's suggestions for the collapse time formula and the preferred basis are also problematic

We investigate the meaning of the wave function by analyzing the mass and charge density distributions of a quantum system. According to protective measurement, a charged quantum system has effective mass and charge density distributing in space, proportional to the square of the absolute value of its wave function. In a realistic interpretation, the wave function of a quantum system can be taken as a description of either a physical field or the ergodic motion of a particle. The essential difference between a field and the ergodic motion of a particle lies in the property of simultaneity; a field exists throughout space simultaneously, whereas the ergodic motion of a particle exists throughout space in a time-divided way. If the wave function is a physical field, then the mass and charge density will be distributed in space simultaneously for a charged quantum system, and thus there will exist gravitational and electrostatic self-interactions of its wave function. This not only violates the superposition principle of quantum mechanics but also contradicts experimental observations. Thus the wave function cannot be a description of a physical field but a description of the ergodic motion of a particle. For the later there is only a localized particle with mass and charge at every instant, and thus there will not exist any self-interaction for the wave function. Which kind of ergodic motion of particles then? It is argued that the classical ergodic models, which assume continuous motion of particles, cannot be consistent with quantum mechanics. Based on the negative result, we suggest that the wave function is a description of the quantum motion of particles, which is random and discontinuous in nature. On this interpretation, the square of the absolute value of the wave function not only gives the probability of the particle being found in certain locations, but also gives the probability of the particle being there. We show that this new interpretation of the wave function provides a natural realistic alternative to the orthodox interpretation, and its implications for other realistic interpretations of quantum mechanics are also briefly discussed.

Recently Lewis et al. [Phys. Rev. Lett. 109, 150404 ] demonstrated that additional assumptions such as preparation independence are always necessary to rule out a psi-epistemic model, in which the quantum state is not uniquely determined by the underlying physical state. Their conclusion is based on an analysis of conventional projective measurements. Here we demonstrate that protective measurements, which are distinct from projective measurements, already shows that distinct quantum states cannot be compatible with a single state of reality. This improves the interesting result obtained by Pusey, Barrett and Rudolph [Nature Phys. 8, 475 ].

It has been widely thought that consciousness has no causal efficacy in the physical world. However, this may be not the case. In this paper, we show that a conscious being can distinguish definite perceptions and their quantum superpositions, while a physical measuring system without consciousness cannot distinguish such nonorthogonal quantum states. The possible existence of this distinct quantum physical effect of consciousness may have interesting implications for the science of consciousness. In particular, it suggests that consciousness is not emergent but a fundamental feature of the universe. This may provide a possible quantum basis for panpsychism.

The physical origin of holographic dark energy is investigated. The main existing explanations, namely the UV/IR connection argument of Cohen et al, Thomas' bulk holography argument, and Ng's spacetime foam argument, are shown to be not satisfactory. A new explanation of the HDE model is then proposed based on the ideas of Thomas and Ng. It is suggested that the dark energy might originate from the quantum fluctuations of spacetime limited by the event horizon of the universe. Several potential problems of the explanation are also discussed.

The ontological status of the wave function in quantum mechanics has been analyzed in the context of conventional projective measurements. These analyses are usually based on some nontrivial assumptions, e.g. a preparation independence assumption is needed to prove the PBR theorem. In this paper, we give a PBR-like argument for psi-ontology in terms of protective measurements, by which one can directly measure the expectation values of observables on a single quantum system. The proof does not resort to nontrivial assumptions such as preparation independence assumption.

In this paper, we propose an ontological interpretation of the wave function in terms of random discontinuous motion of particles. According to this interpretation, the wave function of an N-body quantum system describes the state of random discontinuous motion of N particles, and in particular, the modulus squared of the wave function gives the probability density that the particles appear in every possible group of positions in space. We present three arguments supporting this new interpretation of the wave function. These arguments are mainly based on an analysis of the mass and charge properties of a quantum system. It is realized that the Schroedinger equation, which governs the evolution of a quantum system, contains more information about the system than the wave function of the system, such as the mass and charge properties of the system, which might help understand the ontological meaning of the wave function. Finally, we briefly analyze possible implications of the suggested ontological interpretation of the wave function for the solutions to the measurement problem.

Since environmental ethics research started in China in the 1980s, it has been deeply influenced by environmental ethics theory in the United States. Some Chinese environmental philosophers have adopted the key concept of intrinsic value to construct Chinese environmental ethics. However, in recent decades, the concept of intrinsic value has been criticized by scholars in both the United States and China. Many Chinese have found that environmental ethics in the United States that is founded on the concept of intrinsic value is incompatible with Chinese philosophy and culture. They have begun a new effort that is aimed at developing a localized environmental ethics based on traditional Chinese philosophy. However, the Chinese scholars’ theoretical effort neglects the important concept of wilderness that is emerging from preservation and conservation practices in China. In this context, the emotion of wonder and its interrelationship with intrinsic value is the new paradigm for constructing a Chinese environmental ethics.

Because of rapid industrialization and urbanization, many natural resources in China have increasingly been degraded. In response to this situation, China haslearned from the United States about one of its best ideas, national parks. This idea triggers many philosophical questions. How is wilderness interpreted in theUnited States? What are the philosophical foundations for the concept of intrinsic value in wilderness? Can Chinese philosophy accept wilderness? To answer these questions, the idea of intrinsic value in wilderness and the Western philosophical foundations for this idea need to be examined as well as the concept of topophilia which may better represent the Chinese people’s attitude toward nature, but which currently influences the Chinese people’s negative attitude toward wilderness. It may be possible to improve Chinese affection for wilderness in terms of topophilia by following two principles: the principle of emotion and theprinciple of practice.

According to the laws of physics, the state of a physical system can only be measured by another system (usually a particular measuring device) via a physical interaction. However, when our brain is in a conscious mental state, it can in principle output the information about its physical state based on the psycho-physical correspondance between the mental state and the physical state. It is argued that this suggests that the conscious mind violates physical laws and it is not physical as physicalism claims.

It has been realized that in order to solve the measurement problem, the physical state representing the measurement result is required to be also the physical state on which the mental state of an observer supervenes. This introduces an additional restriction on the solutions to the measurement problem. In this paper, I give a new formulation of the measurement problem which lays more stress on psychophysical connection, and analyze whether Everett's theory, Bohm's theory and dynamical collapse theories can satisfy the restriction of psychophysical supervenience and thus can indeed solve the measurement problem. My analysis of the potential problems of the forms of psychophysical supervenience required by Everett's and Bohm's theories suggests that dynamical collapse theories might provide a promising solution to the measurement problem. Finally, by further analyzing how the mental state of an observer supervenes on her wave function, I also propose a possible solution to the structured tails problem of dynamical collapse theories.

A possible mechanism of nonlinear quantum evolution is introduced and its implications for quantum communication are investigated. First, it is demonstrated that an appropriate combination of wavefunction collapse and the consciousness of observer may permit the observer to distinguish nonorthogonal quantum states in principle, and thus consciousness will introduce certain nonlinearity into quantum dynamics. Next, it is shown that the distinguishability of nonorthogonal states can be used to achieve quantum superluminal communication, by which information can be transmitted nonlocally and faster than the speed of light. Finally, the issue of apparent incompatibility between superluminal communication and special relativity is briefly addressed.

According to Penrose, the fundamental conflict between the superposition principle of quantum mechanics and the general covariance principle of general relativity entails the existence of wavefunction collapse, e.g. a quantum superposition of two different space-time geometries will collapse to one of them due to the ill-definedness of the time-translation operator for the superposition. In this paper, we argue that Penrose's conjecture on gravity's role in wavefunction collapse is debatable. First of all, it is still a controversial issue what the exact nature of the conflict is and how to resolve it. Secondly, Penrose's argument by analogy is too weak to establish a necessary connection between wavefunction collapse and the conflict as understood by him. Thirdly, the conflict does not necessarily lead to wavefunction collapse. For the conflict or the problem of ill-definedness for a superposition of different space-time geometries also needs to be solved before the collapse of the superposition finishes, and once the conflict has been resolved, the wavefunction collapse will lose its physical basis relating to the conflict. In addition, we argue that Penrose's suggestions for the collapse time formula and collapse states are also problematic.

We investigate the implications of protective measurement for de Broglie-Bohm theory, mainly focusing on the interpretation of the wave function. It has been argued that the de Broglie-Bohm theory gives the same predictions as quantum mechanics by means of quantum equilibrium hypothesis. However, this equivalence is based on the premise that the wave function, regarded as a Ψ-field, has no mass and charge density distributions. But this premise turns out to be wrong according to protective measurement; a charged quantum system has effective mass and charge density distributing in space, proportional to the square of the absolute value of its wave function. Then in the de Broglie-Bohm theory both Ψ-field and Bohmian particle will have charge density distribution for a charged quantum system. This will result in the existence of an electrostatic self-interaction of the field and an electromagnetic interaction between the field and Bohmian particle, which not only violates the superposition principle of quantum mechanics but also contradicts experimental observations. Therefore, the de Broglie-Bohm theory as a realistic interpretation of quantum mechanics is problematic according to protective measurement. Lastly, we briefly discuss the possibility that the wave function is not a physical field but a description of some sort of ergodic motion (e.g. random discontinuous motion) of particles.