The older we get, the more time accelerate

Abstract: 3 biological clocks and a perceptual theory to explain the acceleration of the passage of time experienced with age. Enough to satisfy both the materialist and phenomenological viewpoints. But these two approaches still need to be coordinated for a complete explanation.

The mind begins on a tricycle, ends on a high-speed train

We all experience time passing ever faster with age. Car journeys and the time between school vacations seemed interminable in childhood, but as adults, the years fly by. One day you turn 50, but far from feeling jubilant, you’re left with a vague sense of dread, of being on board a high-speed train from which it’s impossible to get off. Is it because work and a multitude of routines are clogging up your day? That’s one reason, no doubt, but retirement doesn’t slow the train down. On the contrary, it speeds up even more, and the last 20 years fade away in a flash far removed from the impression of eternity left by the first 20.

Whatever age we’re asked, the answer is the same: time passed more slowly when we were younger. Teenagers say it was their childhood, young adults say it was their adolescence, and so on. The sensation of acceleration doesn’t wait for years to become clear; it’s present very early on. This indicates that the speed is not linear —it would be imperceptible over a few years— but logarithmic: much higher at the beginning, then progressively dampened. This is in line with our experience: the years pass quickly after 60, but not much faster than each other; whereas between 5 and 10 years of age, the earliest period of our memories, the changes are breathtaking. Christian Yates, a specialist in bio-mathematical models, considers this period to be equivalent to the 40-80 age bracket.

What explanations have been proposed?

The oldest is the proportional theory, proposed by Paul Janet in 1877: as we age, each year of our life becomes a smaller part of its total duration. A 10-year-old child experiences one year as 1/10th of his or her total life, while a 50-year-old adult experiences it as only 1/50th. Taking this principle back to its origins, this would mean that for a 1-month-old infant, 1 week is equivalent to a quarter of its life. And at birth, that personal Big Bang, we’d be in such a slowed-down subjective time that we’d simply feel eternal!

This may seem a far-fetched conclusion, but we don’t yet know much about the origin of psychological time. It’s worth noting that such seemingly preposterous conclusions also apply to objective physical time. The advantage of this theory is that it accounts for the logarithmic scale of acceleration. But it assumes that psychological time is a permanent comparison between the interval considered as the ‘present’ (short-term memory) and the total duration experienced (episodic memory). However, the mind functions rather sequentially: hours pass, then days… Memories punctuate this sequence, but are not permanently present.

Metabolism becomes lazy

The flow of our thoughts doesn’t seem to contain the acceleration. But this is only the conscious process. Psychological time is probably an unconscious construct. We don’t calculate it, we don’t think about it; we experience it intrinsically.

A more biological hypothesis attributes acceleration to slower physiology: heart and respiratory rates are higher in children; they react and move faster; the metabolism becomes lazier with age. In the 1930s, psychologist Hudson Hoagland linked subjective time to body temperature, noting that time slows down during a fever. Basal body temperature is slightly higher in children and gradually decreases with age. But all this is observation, not theory.

Perceptual gridlock

The perceptual theory is more solid. It assumes that psychological time is linked to the amount of information absorbed and processed by the brain. Robert Ornstein verified this in the 60s: he had students listen to audio tapes with varying amounts of noise, and asked them at the end how much time they thought had elapsed. The more signals the tape contained, and the more complex they were, the longer the estimated duration. As children are immersed in a world of largely unknown sensory stimuli, the novelty and complexity of these signals considerably slows down their psychological time. This is corroborated by the attention children pay to details —insect movements, mist on windows, lighting effects, people and buildings passed in the street— that adults hardly notice any more. The world is much more familiar to them.

But then again, it’s all about observations. How do novelty and the sheer quantity of information slow down psychological time, intimately? Could it be that attention is the metronome of this time, with each remarkable event representing a beat? Too simple an explanation, and one that doesn’t correspond to our experience: the passage of time is a fusional, continuous impression, different from the discontinuity of events.

Three clocks

Biological explanations have been enriched by the contribution of neuroscience. In the ’90s, Warren Meck suspected that one neural center, the striatum, set the pace for the brain by gathering information on the timing of other networks, thanks to its rich connectivity. An internal neural clock stimulated by dopamine, disrupted in many diseases (Parkison, Alzheimer’s, dyslexia, hyperactivity syndrome) or by the effect of drugs (cocaine and amphetamine producing a sensation of temporal acceleration).

This neural synchronicity clock is in addition to the metabolic circadian clock, which also varies body heat —this could be the influence of temperature noted by Hoagland. A third, spatial clock was discovered by May-Britt and Moser in 2018 in the lateral entorhinal cortex. This area chronologically encodes events based on our movements in space recorded by the neighboring medial entorhinal area. These two areas would send their information to the hippocampus (the memory engraver) to make an “episodic time”.

On the road to a global theory

But if these internal clocks account for the sensation of time passing at any given moment, they don’t explain why we perceive a logarithmic slowdown with age. Admittedly, the 3rd clock is connected to long-term memory, but all periods of life are rich in memories. Where is the evaluation of their succession externalized? It’s like asking an old clock if it’s as punctual as when it was first made! Who is the independent observer who becomes aware of the slowdown?

There is no overall theory that integrates the previous ones and provides a complete explanation. Familiar now with UniPhiM, you have classified the various hypotheses as belonging either to the downward look (the logarithmic scale of experienced time, the perceptual theory) or to upward look (slowing down of physiology, synchronization registered by the striatum, spatial clock). What remains to be done is to make these two views coincide, in other words, to bring neuroscience into line with the phenomenon – and not replace one by the other.

You’ve guessed, dear reader, that this succession of articles on time is the prelude to a new book, Temporium, which will offer a solution to past and future enigmas…

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