When I was a lad, the duration of time between December 1st and Christmas Day bordered on the infinite. The duration of time measured by normal standards (Sun, moon, chronometers, etc) remains the same, but the experience has been altered. What was once near infinite is now trending towards no time at all. In some sense, each of us has our own “inner time” unrelated to the passing of hours, days, and years on clocks and calendars. I had often thought it was related to some latent ratio of the duration and the time lived.  For example, the 25 days until Christmas is a significant percentage of the entire life of a six-year old child; not so much for a septuagenarian. What lasts forever for the six-year old is the blink of an eye to grandfather. While that may be true at some level, there are more technical explanations being offered these days.

Duke University mechanical engineering professor Adrian Bejan. He believes physics flow principles can explain everything. He has written extensively about how the principles of flow in physics dictate and explain the movement of abstract concepts, like economics – for which he was awarded the Franklin Institute’s Benjamin Franklin Medal for “his pioneering interdisciplinary contributions…and for constructal theory, which predicts natural design and its evolution in engineering, scientific, and social systems.” His interdisciplinary thinking is fascinating to say the least. And now he turned his attention to time – or rather the flow of time.

In a recent paper, he examines the mechanics of the human mind and how these relate to our understanding of time, providing a physical explanation for our changing mental perception as we grow older. According to Bejanm, time as we experience it represents perceived changes in mental stimuli. It’s related to what we see. As physical mental-image processing time and the rapidity of images we take in changes, so does our perception of time. All the while “external time” is its own constant.

It is related to the number of mental images the brain encounters and organizes and the state of our brains as we age. When we get older, the rate at which changes in mental images are perceived decreases because of several transforming physical features, including vision, brain complexity, and later in life, degradation of the pathways that transmit information. And this shift in image processing leads to the sense of time speeding up.

It is as though the six-year old has an intuitive sense of the flow of images and the duration of external time involved in processing the flow of stimuli. As we age the same sample of images takes longer but our expectation of the passage of external time no longer matches up to the time it takes – and it is as though “time flies.”

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