Why does time fly when you're having fun?

Because when you're absorbed, your attention isn't on the clock. Psychologists call the state of total absorption "flow", and it comes with a transformation in your sense of time: all your attention goes to the task, so you lose awareness of everything else, time included. People in flow describe hours that seem to pass by the minute. More generally, motivation can make a task feel shorter, while interruptions stretch it. Boredom works the other way: the German word for it, Langeweile, literally means "long while".

There's a twist, though. Your brain judges time twice: while it happens, and later from memory. Intervals packed with changes tend to be perceived as longer, and one leading idea is that remembered duration depends on how many new memories were formed. That may be why routine weeks blur together, while a trip full of new things feels long when you look back on it.

Neuroscientist David Eagleman tested the famous feeling that time slows down in danger by dropping volunteers, and himself, from a 150-foot tower. In free-fall tests like this, people's ability to perceive fast flickers did not improve during the fall. Time seemed to have stretched only in retrospect, possibly because memories were packed more densely.

The same memory logic may explain why years seem to speed up as we age. Subjective time tends to accelerate with age, and if adults form fewer new memories in their routines, long stretches shrink when they look back.