Related articles

• Brain tells time by morphing
• High-fat diet can mess with body clock
• Babies' internal clock development hindered by artificial lights
• Manic depression may be a rhythm thing
• Einstein is still right on time

BUT WE ALL KNOW there are safer and more natural ways to experience a time warp. Which brings us to why time flies when we're having fun. It turns out our perception of time also depends on how much attention we pay to our internal clock. "When we're having fun our attention is diverted elsewhere," explains Meck. "It's as if we're missing ticks, so time seems to fly." On the other hand, when we pay close attention, we count every monotonous tick. Hence a watched pot never seems to boil.

This makes intuitive sense, but how can we account for the paradoxical complaint of some elderly and unemployed people – that days seems to drag on forever while the years flash by? Wearden thinks the answer might be that our perception of time depends on whether we're thinking about time 'in the moment' or after an event.

Wearden tested this idea in his well-known Armageddon experiment. In the study, one group of volunteers watched nine minutes of the movie Armageddon – an action-packed science fiction thriller involving a menacing asteroid on a collision course with Earth. Another group sat for the same length of time in a waiting room.

As expected, the Armageddon group reported that "in the moment", time seemed to pass more quickly than usual, while the group from the waiting room felt as if time dragged. But when both groups made a retrospective judgement of how much time had passed, the results were surprising: despite feeling that time had flown, the movie-watchers judged the period as about 10 per cent longer than the group in the waiting room.

The explanation, says Wearden, is that "in the moment" judgements depend on attention to the clock, while retrospective judgements depend on how much information we process in a period. So while the waiting room group paid attention to the clock and felt as if time dragged, not much happened, so in retrospect the period seemed short. By contrast, the movie-watchers were distracted from the clock "in the moment", but processed lots of information, so the period seemed long.

Since we learn and encode less information as we age, the years seem to pass quickly, says Wearden. But if we're bored we watch the clock, so days drag. David Eagleman of the Baylor College of Medicine in Houston, Texas, thinks novel events may also play a part.

"When you're a child, you lay down rich memories for all your experiences; when you're older, you've seen it all before and lay down fewer memories," he says. "Therefore, when a child looks back at the end of a summer, it seems to have lasted forever; adults think it zoomed by."

EAGLEMAN HAS LONG BEEN fascinated by another type of time warp – the feeling that time slows down during a traumatic event. As a child he fell off a roof in what felt like a slow-motion sequence; as a researcher he collected similar anecdotes from car crash and other trauma victims. And over the years he began to wonder whether people really experience the world in slow motion, or whether it only seems to have happened that way in retrospect.

To answer the question, Eagleman designed an unconventional experiment. One by one, he had 20 subjects jump backwards off a 50-metre tower, so they experienced free fall before landing in a net below. Strapped to each person's wrist was an LED screen alternately flashing a number and its negative image, at a rate slightly faster than would normally allow them to distinguish the number from a uniformly coloured screen. Eagleman wanted to know whether his subjects' ability to see the number improved during the fall – evidence of a slow-mo experience.

For those with fantasies of one day strolling round bullets like Neo in The Matrix, the results were disappointing: no one could read the number flashing on the screen. They did, however, experience a retrospective time distortion: after taking the plunge, on average they estimated that the fall took 36 per cent longer than estimates they made based on watching other people fall.

According to Eagleman, this time distortion after the fact is a result of a brain region called the amygdala kicking into gear to lay down extra memories. "Frightening events are associated with richer and denser memories.

And the more memory you have of an event, the longer you believe it took." This makes sense from an evolutionary perspective, since we use memory for forward planning. "Dangerous events are the ones you really need to remember – and avoid," he says.

So how do we account for elite athletes who report that the ball or an opponent seems to move in slow motion when they get into "the zone"? The amygdala lays down richer memories during any emotional event, so it could be partly responsible, says Eagleman. So might a surge of adrenalin that modulates dopamine levels and speeds up the inner clock.

But Wearden offers an alternative explanation: "With training, many of their reactions become automatic, so they have more time to think about other things."

Readers' comments