Theorizing that Energetic Constraints in Aging Make Time Appear to Have Passed More Rapidly
Our perception of the passage of past time appears to change with age. Studies suggest that when looking back at recent personal history in later life time appears to have passed more rapidly than it did in youth. One potential explanation for this is that people recall less of what happened in later life than they do in earlier life, or that the storage or retrieval of experiential memory becomes otherwise more compressed. Studies of recall suggest that we remember something like 2% of our experience; we're all ghosts of ourselves in that sense. Does this tiny fraction become even smaller with advancing age, and if so, why does this occur? The author of this paper offers a testable hypothesis connected to age-related declines in energy metabolism in the brain.
A year of chronological time is typically assumed to represent comparable experiential encoding across individuals and age groups. This assumption is rarely examined. Yet subjective reports across adulthood consistently suggest that extended periods - months and years - are often remembered as having "passed quickly," particularly in later life. Importantly, this phenomenon does not imply a change in objective time but reflects differences in how time is encoded and reconstructed. Time-perception research distinguishes moment-to-moment passage-of-time judgments from retrospective duration judgments, and evidence indicates that long-interval judgments rely heavily on memory structure rather than internal clock mechanisms.
I introduce the concept of experienced longevity, defined as the amount of lived time subjectively contained within a fixed chronological interval. Within the present framework, this construct is operationalized through experiential density, defined as the number and distinctiveness of event units segmented, encoded, and later retrievable per unit of chronological time. I propose that age-related biological changes - particularly declines in mitochondrial efficiency, increased vascular stiffness, and reduced nitric oxide-mediated neurovascular coupling - may constrain the brain's capacity for high-fidelity updating during ongoing experience. By limiting event segmentation and episodic distinctiveness, these neuroenergetic constraints may increase the probability of retrospective temporal compression.
I term this framework the Neuroenergetic Constraint Model of experienced longevity. In this framework, experienced longevity is the broader aging-related construct, experiential density is the proximate memory-level property through which it is expressed, and retrospective temporal compression is the downstream subjective outcome expected when that density is reduced.