Qualia - the vivid hues of subjective experience - emerge from an irreversible neural alchemy. Objective sensory data streams into the brain, where amygdala and hippocampus forge it into private phenomenology through profound process dualism. Brain-computer interfaces capture upstream signals with stunning precision yet hit an »epistemic firewall«: the downstream qualia remain sealed, their essence lost in conversion. Karl Johannes Lierfeld analyzes this physicalist extension that reveals why sentience defies objectification, bridging philosophy of mind and neuroscience without metaphysical escape hatches. Conversionism charts the hard problem's structural limits.