When I was young, time seemed to stretch endlessly. Waiting—whether for school to end, for playtime to begin, or simply to grow older—felt like an eternity. Every moment was vivid, filled with anticipation and curiosity. And yet, when immersed in play or joy, time felt boundless, as though those moments could last forever.

Now, at the late age decades of my life feel like the blink of an eye, a fleeting flash in the vast expanse of existence. Days, months, and years pass with astonishing speed, slipping through my grasp before I fully register them. This stark contrast in how I have experienced time across my life has led me to reflect deeply on its nature.

Drawing from philosophy and clinical psychology training and professional practice as a psychologist, and my life experiences with recent explorations into popular science, particularly quantum physics, I have come to accept that time is profoundly relative. Einstein’s theories of relativity revolutionized our understanding of time, demonstrating that it is not an absolute, fixed entity but instead depends on movement and perspective. His famous thought experiment involving identical twins offers a compelling illustration: if one twin travels through space at near-light speed while the other remains on Earth, the traveling twin would return younger, having experienced time more slowly relative to the twin on Earth. This phenomenon is not just theoretical; it is a measurable aspect of our universe.

Beyond the grand scale of relativity, I have also considered how biology shapes our perception of time. When we are young, our metabolic rate is faster. This heightened internal rhythm correlates with a slower perception of time—each moment feels rich and expansive. As we age and our metabolism slows, our perception of time accelerates; days feel shorter, years slip by faster, and life, in retrospect, compresses into a series of fleeting memories.

This interplay between biology and perception raises a profound question: Could all living organisms, regardless of their lifespan, experience time similarly? A fruit fly, for example, may live for mere days, while humans typically live for decades. Yet, due to its accelerated metabolic rate, a fruit fly’s perception of those days might feel as lengthy and meaningful as a human’s perception of 80 years. If we frame time as something experienced rather than objectively measured, then the brevity of a fly’s life and the longevity of a human’s might, in some sense, be equivalent in subjective experience.

In this way, time is not just a physical dimension governed by relativity; it is also a deeply personal, biological, and psychological construct. The perception of time arises from a confluence of factors: the external, such as movement and the passage of events, and the internal, such as our biological rhythms and mental states.

As I reflect on my eighty-five plus years of life, I see it not just as a journey through a timeline but as a mosaic of experiences shaped by this dynamic interplay of physics and biology. The young perceive time as expansive because their world is new, their curiosity boundless, and their internal rhythms quickened. The old perceive time as fleeting because their world has grown familiar, their moments are cherished in hindsight, and their internal clocks tick slower. Time is both a universal and deeply personal paradox that binds us all, regardless of how long we live or how we perceive the passing days. It is a reminder to treasure the fleeting moments we have, knowing that in some profound way, they may be infinite in their significance.

Acknowledgments: This writing is inspired by a lifetime of learning and reflection, enriched by my professional experiences in psychology, and early graduate training in philosophy, and influenced by the insights of great thinkers in philosophy and science as well as recent reading of popular science books. I was aided in the editorial process with AI.

Copyright: © [ 2025] [Mohiuddin Ahmed, Ph.D.]. All rights reserved. This document or any portion thereof may not be reproduced or used in any manner whatsoever without the express written permission of the author, except for the use of brief quotations in critical reviews or scholarly work.