When we were children, the summer holidays seemed to last forever, and waiting for Christmas felt like an eternity. So why is it that when we get older, the time just seems to zip by, with weeks, months and entire seasons disappearing from a blurred calendar at dizzying speed?

This apparently accelerated time travel is not a result of us filling our adult lives with grown-up responsibilities and worries. Research shows that perceived time in fact seem to move more quickly for older people.

There are several theories which attempt to explain why our perception of time speeds up as we get older. One idea is a gradual alteration of our internal biological clocks. The slowing of our metabolism as we get older matches the slowing of our heartbeat and our breathing. Children’s biological pacemakers beat more quickly, meaning that they experience more biological markers (heartbeats, breaths) in a fixed period of time, making it feel like more time has passed.

When we’re young the summers feel endless.

Another theory suggests that the passage of time we perceive is related to the amount of new perceptual information we absorb. With lots of new stimuli our brains take longer to process the information so that the period of time feels longer. This would help to explain the “slow motion perception” often reported in the moments before an accident. The unfamiliar circumstances mean there is so much new information to take in.

It may be that when faced with new situations our brains record more richly detailed memories, so that in our recollection the event seems longer.

But how does this explain the continued shortening of perceived time as we age? The theory goes that the older we get, the more familiar we become with our surroundings. We don’t notice the detailed environments of our homes and workplaces. For children, however, the world is an often unfamiliar place filled with new experiences to engage with. This means children must dedicate significantly more brain power shaping their mental ideas of the outside world. The theory suggests that this appears to make time run more slowly for children than for adults stuck in a routine.

So the more familiar we become with the day-to-day experiences of life, the faster time seems to run, and generally, this familiarity increases with age.

No time like the present

There’s also the idea that we perceive a period of time as the proportion of time we have already lived through. To a two-year-old, a year is half of their life, which is why it seems such an incredibly long period of time to wait between birthdays when you are young.

To a ten-year-old, a year is only 10% of their life, (making for a slightly more tolerable wait), and to a 20-year-old it is only 5%. Using this scale, for a 20-year-old to experience the same proportional increase in age that a two-year-old experiences between birthdays, they would have to wait until they turned 30. Given this view point it’s not surprising that time appears to accelerate as we grow older.

If you want to slow the pace of time try experiencing new things!

We commonly think of our lives in terms of decades – our 20s, our 30s and so on – which suggests an equal weight to each period. However, on a proportional scale, we perceive different amounts of time as the being the same length. The following differences in age would be feel the same under this theory: 5 to 10, 10 to 20, 20 to 40 and 40 to 80.

I don’t wish to end on a depressing note, but the five-year period you experienced between the ages of five and ten could feel just as long as the period between the ages of 40 and 80.

So get busy. Time flies, whether you’re having fun or not. And it’s flying faster and faster every day.

Written by Christian Yates, Lecturer in Mathematical Biology, University of Bath. This article is republished from The Conversation.