Adrian Bejan PhD ( MIT 1971, 1972, 1975 )J.A. Jones Distinguished Professor Duke University

Where Did the Day Go? Why Time Flies As We Age Interview with:

Adrian Bejan PhD ( MIT 1971, 1972, 1975 )J.A. Jones Distinguished Professor Duke University

Dr. Bejan

Adrian Bejan PhD ( MIT 1971, 1972, 1975 )
J.A. Jones Distinguished Professor
Duke University What is the background for this study? What are the main findings?

Response: Among the most common human perceptions is that time passes faster as an individual becomes older. The days become shorter, and so do the years. We all have stories of this kind, from the long days of childhood and the never-ending class hours in elementary school, to days, months and years that now pass in a blur.

Why does it feel that the time passes faster as we get older? What is the physical basis for the impression that some days are slower than others? Why do we tend to focus on the unusual (the surprise), not on the ever present?

This new article unveils the physics basis for these common observations. The reason is that the measurable ‘clock time’ is not the same as the time perceived by the human mind. The ‘mind time’ is a sequence of images, i.e. reflections of nature that are fed by stimuli from sensory organs.

The rate at which changes in mental images are perceived decreases with age, because of several physical features that change with age: saccades frequency, body size, pathways degradation, etc.

The misalignment between mental-image time and clock time serves to unite the voluminous observations of this phenomenon in the literature with the constructal law of evolution everywhere, as physics. What should clinicians and patients take away from your report?

Response: More subtle, and worth questioning is the impression that some days appear to pass more slowly than others. The ‘ slower’  days are full of productivity, events, and memories of what happened.

Productive days happen when the body and mind are rested, after periods of regular sleep, when in the morning you look in the mirror and you see a younger you, not a tired you.

Athletes learn the hard way the correlation between good rest and the speed of the passing time. Lack of rest makes you miss plays, unable to anticipate, unable to see the ball before it arrives. While sleep walking, the game is over before you know it.

Young students learn the same physical truth while taking exams during a fixed time interval. The rested mind has more time to go through the problems, to find mistakes, to go back to the beginning, and try again. Lack of sleep, due to cramming the night before the exam, makes the time pass faster during the exam period.

Cramming does not pay, but rest does, which is why the good coach rests the team before the big game.

Here is why this is important to you, the reader:

  • Today, many young people experience time distortion because they spend too much time on social media. This has serious consequences, ranging from sleep deprivation to mood changes and mental disorder. This is why an understanding of the physics basis of how humans perceive the passing of time is essential. Is there anything else you would like to add?

This work is the latest  discovery in the new field of life and evolution as ‘physics’.

Response: Recommended reading are the books The Physics of Life (2016) and
Design in Nature (2012) Thank you for your contribution to the community.


Bejan, A. (n.d.). Why the Days Seem Shorter as We Get Older. European Review, 1-8. doi:10.1017/S1062798718000741

Note: Content is Not intended as medical advice. Please consult your health care provider regarding your specific medical condition and questions.

Last Updated on March 21, 2019 by Marie Benz MD FAAD