Because the brain is a localised aperture that performs dimensional reduction.
Processing an entire worldline simultaneously would cause immediate computational overload. The biological brain therefore takes sequential cross-sections of spacetime, rendering each as a three-dimensional scene and discarding the rest. The sequence of scenes is experienced as motion and as the passage of time.
The film projector is the exact analogy. A projector flashes static two-dimensional frames in sequence and the viewer experiences a moving three-dimensional world. The aperture flashes static cross-sections of a four-dimensional worldline in sequence and the organism experiences time passing. In neither case is the motion in the material; it is generated by the mechanism of presentation.
What the aperture is for
The aperture is not a defect or a veil to be removed. It is the mechanism that makes action possible. An organism that perceived its whole worldline at once, together with the full high-dimensional field, could not compute where to step next. Compression is what lets the organism act (this constraint is developed fully in §3.1).
Two properties to hold onto
- It is selective. The aperture prunes the overwhelming majority of available field data. What reaches experience is a tightly filtered projection tuned for survival and locomotion in three dimensions.
- It is adjustable. Its width, meaning how much raw data it admits before compression, is not fixed. Part III is concerned with operating that adjustment deliberately.
- Aperture
- The localised biological mechanism (brain and sensory apparatus) that slices the four-dimensional worldline and the high-dimensional field into sequential, compressed three-dimensional renderings, so that the organism can act.
- Dimensional reduction
- The compression performed by the aperture: a high-dimensional input projected onto a lower-dimensional interface.
- Interface
- The rendered three-dimensional scene, including the sense of a located self within it. Also called the ego interface when the self-model is the point of reference.