“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?,” asks Adrian Bejan, the J.A. Jones Professor of Mechanical Engineering at Duke University, in a paper out on 18 March in the journal European Review.
According to Bejan, the well-nigh universal change in the subjective perception of time as people age can be explained by the reduction of the speed at which our brains form and process mental imagery.
“People are often amazed at how much they remember from days that seemed to last forever in their youth,” said Bejan. “It’s not that their experiences were much deeper or more meaningful, it’s just that they were being processed in rapid fire.”
Considering purely mechanistic explanations of conscious phenomena may often be tinged with a dose of disbelief, yet Bejan’s theory is quite elegant and simple – as our brains get older, they form an ever-greater number of connections, thereby increasing the amount of time required for electrical signals to get through.
To make matters worse, once established those neural connections become less stable and more time-worn as the brain continues to age, which, in turn, further reduces the speed at which mental imagery is generated.
As a related piece of evidence, Bejan also brings up how fast infants tend to dart their eyes around the room – simpler and more information-hungry brains both process and integrate new data more efficiently than more seasoned ones.
Given that older people form less images in the same amount of time, it follows that they also undergo a smaller amount of conscious experience, which leads to the seemingly faster passage of time.
“The human mind senses time changing when the perceived images change,” explained Bejan. “The present is different from the past because the mental viewing has changed, not because somebody’s clock rings. Days seemed to last longer in your youth because the young mind receives more images during one day than the same mind in old age.”