Hyun Cheng

Contemporary thermodynamic research has discovered that our universe is filled with "Boltzmann Brains"—disembodied minds arising from random particle collisions. Moreover, the number of Boltzmann Brains is virtually infinite compared to human brains. From a probabilistic standpoint, this suggests that we are far more likely to be Boltzmann Brains rather than human beings—an unsettling skeptical scenario that we are reluctant to accept. In response, various approaches have been proposed to refute Boltzmann Brain skepticism. For instance, Dogramaci and Schoenfield (2025) argue from the perspective of “Bayesian Belief Updating”, while Mozersky (2025) explores the implications of “Infinite Sets”. This paper formalizes and reconstructs these recent approaches, revealing that each contains significant logical flaws. Consequently, contemporary attempts to counter Boltzmann Brain skepticism remain unsuccessful. In contrast, this paper challenges the “Probabilistic Typicality” assumption that underlies Boltzmann Brain arguments, asserting that human brains and Boltzmann Brains differ not only in external conditions but also in the fundamental nature of conscious experience. Ultimately, this paper adopts an approach akin to that of G.E. Moore, defending an anti-skeptical position through an analysis of daily phenomenological experience.

The Predictive Processing (PP) model outlines a "top-down" picture of mental operations, proposing the existence of bidirectional neural information flows that converge and match to generate prediction errors, with the brain consistently aiming to minimize these errors. While the predictive processing paradigm is comprehensive, this article focuses specifically on a counterintuitive proposition within PP—"perception as controlled hallucination." In contemporary discussions, the predictive processing model has developed into two main approaches: the neurocentric approach, led by Hohwy, and the action-perception coupling approach, championed by Clark. This paper aims to examine the justifications of the "perception as controlled hallucination" proposition within these two distinct PP theoretical approaches, discuss their divergences, and further compare their strengths and weaknesses. The study finds that the neurocentric justification, due to its internalist tendencies, faces skeptical challenges and issues of insufficient justification. In contrast, the action-perception coupling approach to predictive processing, which emphasizes embodiment, adopts an externalist stance that can uphold the everyday justificatory status of perception. Moreover, when perceptual experience serves as a channel coupling the mind and the world, the process reliability it entails is absent in hallucinatory experiences. Thus, while acknowledging the similarity between perception and hallucination, this approach successfully substantiates the argument that perception is "controlled hallucination."