1. What is time in aging?

In physics, a growing view is that time is not a fundamental ingredient of reality but an emergent bookkeeping of irreversible change, an arrow created because interactions leave records that cannot be perfectly reversed. In the same way, in organisms, aging is not something that merely unfolds in time; it is how time becomes written into the body. Every metabolic reaction, replication event, immune response, mechanical stress, and exposure leaves traces (some as by-products/errors, some adaptive) that accumulate as distributed records across DNA, epigenome, proteome, extracellular matrix, tissue architecture, etc. Because the organism cannot erase the total downstream consequences of these records, aging acquires directionality: the past is physically embedded in the present state, while the future is not. In this framing, aging clocks work because they read different subsets of these records, and interventions extend lifespan by slowing record-writing, improving error correction/turnover, or resetting specific registries of state.