Why do some philosophers think consciousness is difficult to explain using only physical descriptions of the brain?

In the philosophy of mind, many thinkers argue that consciousness is difficult to explain through physical descriptions of the brain because of an "explanatory gap" between material processes and subjective experience.12

While modern science can explain non-mental phenomena—such as why water expands when it freezes—by detailing the physical properties and forces of particles, this "upward necessitation" does not seem to apply to consciousness. Key challenges include:2

• The Nature of Experience: It appears impossible to provide an account of conscious experience that simultaneously captures what it is "really like" for a human being while remaining consistent with the strictly physical vocabulary of scientific theories.1
• The Inverted Spectrum: It is difficult to determine if two people have identical color experiences based solely on physical facts about their brains, as one could theoretically behave normally while having entirely different internal experiences.2
• The Problem of "Absent Qualia": Philosophers often note that it is coherent to imagine "zombies"—beings that function like humans but lack any conscious mental states—suggesting that physical facts alone do not compel the conclusion that a creature has a mental life.2

Because of these difficulties, some philosophers, known as "mysterians," argue that understanding how the brain gives rise to consciousness may be beyond human conceptual capacity. Others, like John Searle, suggest that consciousness is a biological phenomenon that, while complex, should be explainable in scientific terms once we move past outdated dualism.1